• field test and validate DIY UV and fluorescence spectrometers for water quality and biochar water treatment analysis

• develop a column test method utilizing one or more suitable “unicorn” fluorophore surrogate adsorbates

• train members of the local team in updated biochar adsorbent analysis methods

Here’s how we fared…

Excellent performance by DIY spectrometers

Left-to-right: Lil Woody AKA El Spectro Casero (UVA₂₅₄), RealTech commercial field spec (UVA₂₅₄), modified ioRodeo Open Colorimeter (fluorometer), Turner AquaFluor commercial spec (fluorometer).

The biggest W of the trip award goes to our radically inexpensive DIY spectrometers. In the final validation tests using local high DOM surface water spiked with a “unicorn” fluorophore, the DIY spectrometers did an excellent job perfomance-matching their commercial counterparts:

I’m beyond pleased; this really exceeded my expectations. Especially in the case of the El Casero UV spec. Mid-week it looked to be the biggest L of the trip by far. What a comeback story!

Next Steps

• El Casero earned his spot with the Ecuador team. I left him with them to use for their ongoing water quality and biochar adsorbent analysis.

• Meanwhile, me and the boys back home are already designing Gen 2.0 of the field UVA₂₅₄ spec. Improvements will likely include:

  • a 3D printed plastic enclosure (instead of wood)

  • a compartment for adding dessicant packs to help keep the electronics dry

  • a larger output screen

  • gasket seals, more heavy-duty componentry, and other ruggedizing enhancements

  • a rechargeable battery pack and wireless operation

• I brought the Open Colorimeter based fluorometer home with me for further modification in collaboration with ioRodeo. This will likely involve:

  • expanding capabilities with different configurations of optical filters, light sources, and detectors to quantify additional fluorescence parameters

  • development of a calibration procedure and associated firmware code to output similar fluorometry units reported by commercial instruments (as opposed to raw intensity units such as uW/cm² shown above)

  • ruggedizing of 3D printed instrument housing

Thinking ahead, we may start producing UVA₂₅₄ and fluorometry spectrometers for purchase. If you are interested in product testing please reach out.

Challenges and lessons in “unicorn" adsorbate biochar testing

Our current top three “unicorn” fluorophore adsorbate contenders, in order, are:

1. 7-amino-4-methyl coumarin

2. 7-amino-4-trifluoromethyl coumarin

3. acridone

They all exhibit strong fluorescence signals and good stability over a typical period needed for biochar adsorption tests. They are benign from human health and environmental standpoints. And they’re inexpensive to purchase. Their ranking is based on their predicted adsorbabilities. (The ranking is from lower to higher predicted adsorption strength. Choosing the weakest adsorbing “unicorn” speeds up testing and provides a more conservative indicator for biochar bed life.)

A practical challenge we faced with method development this week came from the very high DOM water we selected for testing. Even with (1 micron) prefiltration to remove particles and the addition of a glass wool guard column in front of the biochar column we still had repeated issues with column overpressure due to fine colloids clogging the biochar. So we weren’t able to obtain a “unicorn” breakthrough curve. This was the biggest L of the trip.

In reality, water reaching a biochar adsorber would be unlikely to contain the excessive levels of DOM, particulates, and colloids of our test water this week. Upstream treatment steps such as gravel roughing filtration and biological slow sand filtration reduce these factors substantially so that a biochar adsorber “sees” much cleaner input water.

With only just over a week to conduct field R&D we wanted to issue a maximum challenge to our system. Although we didn’t generate a “unicorn” breakthrough curve we know what we need to change to bring this goal within reach

Next Steps

• Back home I will implement additional measures to screen out biochar-column-blocking particles and colloids, and use more representative DOM levels. I can also put other techniques into play, including:

  • a redesigned RSSCT method optimized to hasten unicorn breakthrough

  • batch equilibrium capacity testing to provide additional quantitative insights into “unicorn” adsorbabilities and how they compare with micropollutants of concern

Biochar water treatment analysis teambuilding

We had several intense but fun hands-on days familiarizing with RSSCT methods and collecting data with the commercial and prototype DIY spectrometers.

Tech team members Andres and Pablo (Lexi and Luis not shown.) The training was held at Amisacho but the biochar water testing setup will live at the nearby Clinica Ambiental (Environmental Clinic).

And I got to meet the newest recruit to the decentralized water treatment committee of Lago Agrio, miss Estelita! (Congrats to Lexi and Luis!)

The biggest W of all!

Share A Field Guide to Biochar Water Treatment

To this end, we’re trying to replace a ~$3,500 commercial UVA₂₅₄ field spectrometer with a ~$250 DIY unit. Both are shown here relaxing in the comfortable climate controlled space of my home lab in North Carolina:

Prelude to Spectrometer UFC: Lil Woody stares down Macho Man UV at weigh-in.

Arriving in the Amazonian northeast corner of Ecuador several days ago things got real heated, real fast. The Amazon is humid, y’all. Not North Carolina humid - Amazon humid. The air here is moist on a whole ‘nother level.

And electronics no me gusta Amazon humid.

If where you are looks like this your electronic devices are probably not happy.

[By the way, this is the jungle pond where we get high DOM water for our biochar and water quality tests…]

Round one of Spectrometer UFC hurt Lil Woody bad. His eco-groovy exterior made of all natural material became a humidity-sponge. The flux leftover from soldering his electrical circuit innards soaked up the ample ambient moisture. This scrambled Lil Woody’s brains real bad. He could barely see, and couldn’t hold a stable reading to save his life. Our wobbly fighter was on the ropes!

Mercifully the round one bell rang and Lil Woody retreated to his corner for a pep talk and some smelling salts. And by smelling salts, I mean I literally stuffed a couple small silica gel dessicant packs into his case.

This worked, sort of, and Lil Woody limped through round two against Macho Man UV. Macho Man seemed unphased by the humidity of the Amazonian away arena, far from his home field advantage in arid Canada.

That’s probably because Macho Man is an old school fighter relying on raw horsepower. His light source is a big honkin mercury lamp bulb. That sucker gets so hot during operation even Amazon humidity get pushed aside.

Where Macho Man UV keeps his power (and also his vulnerability): an old school mercury bulb that costs more to replace than Lil Woody’s whole getup.

The coaches and trainers got together and decided that there was one hope left for Lil Woody, though it was a longshot. Lil Woody needed surgical intervention to remove some of the cancerous flux that plagued his resistors like metastasizing tumors - scrambling their voltages and turning Woody’s own neural impulses against him in epileptic seizures.

Lil Woody’s detector board all goopy with humidity-swilling solder flux…

In a rudimentary operating theater in the jungle we opened Woody up and gave his innards a good scrubbin with disinfecting alcohol using an old toothbrush. Then we stiched him back up and prayed for a miracle.

It was not good. Woody zirped to life but measured a fat goose egg transmittance while flatlining zero voltage through his circuits. For a moment a few millivolts zapped through his circuits, then his screen went blank. Woody was gone.

We opened his case and pecked at wires and tugged at connections. We higgled, and jiggled, and even piggled his circuit boards. We prodded his inner bits without any clue what we were doing. Still, nothing.

Woody was dead. Graveyard dead, apparently.

Fighting Macho Man UV in the Amazon Octagon was just too much for his delicate build.

We were all but ready to bury his biodegradable natural body when a flicker of life flashed across his screen. Woody was still in there, fighting for life!

The EMTs went to work performing life-saving measures. What I mean is that I literally just dumped a bunch of silica dessicant beads all over his circuit boards and clamped the lid shut. Real high-precision stuff we’re doin here.

When in doubt just fill the damn thing full of dessicant beads and hope for the best.

We then transferred Woody to the ICU, AKA a lidded tupperware container full of even more silica dessicant beads, to recover.

After couple hours’ time Woody was on his feet and ready to get back in the ring! Go get ‘em champ!

DING went the bell to signal the start of round three with Lil Woody and Macho Man UV facing off over a novel DOM breakthrough curve.

Lil Woody pounced back into the fight, this time (appropriately) under his Latin American Lucha Libre moniker, “El Spectro Casero”!

Woody...I mean, El Casero…was finally punching above his weight, trading blow-for-blow with El Macho:

The saga continues…

Ready or not, time to field test all this!

I might even have room for a change of clothes!

I’m off to Amazonian Ecuador to reunite with colleagues for the next phase of setting up our biochar and water testing field laboratory and water treatment consulting service!

I’ll be posting near-real-time updates of our work so watch this space.

I’ve just added the latest experimental results to the sections on

• Discovering ideal surrogate adsorbates

  • including identification of two new candidate “unicorn” fluorophores and their stability in natural water

• Prototyping DIY UV and fluorescence spectrometers

  • including some impressive results with our radically inexpensive DIY UVA₂₅₄ unit!

We’ll be continuing with RSSCT method development and spectrometer testing and optimization under real life field conditions in the Amazon jungle over the next couple of weeks.

Looking forward to an exciting trip!

Last week I published an overview of these two projects.

Now they each have their own section. As we hit milestones in these projects I will post updates so you can follow along with the work. As always, we love to get your feedback and questions in the comments!

Left-to-right: the AquaFluor made by Turner Designs, the SP-380 made by Pyxis, and the P200 UV₂₅₄ meter made by RealTech (RealTech was bought by ABB and now similar meters are sold as UviTech).

The three portable spectrometers shown here are excellent instruments. They have long been essential pieces of kit in our field labs and biochar water treatment system monitoring program. I’ve owned and distributed to colleagues several of the RealTech UVA₂₅₄ “lunchbox” spectrometers (on the right in the photo). I’ve been using these units since 2011 if not earlier. Our study published in 2014 contained a year of monitoring data collected in Thailand over 2011-2012:

More recent studies have further developed the potential of UVA254 and fluorescence monitoring for evaluation of biochar water treatment system performance:

There are, however, two main drawbacks to using commercial spectrometers in our field lab R&D and monitoring programs:

• They’re configured to measure specific parameters (which they do very well), but don’t offer the possibility of adjusting or tuning the parameters to optimize for different applications.

• Cost. The instruments shown above cost roughly between $2,000-$4,000 each. All three together will set you back $9,000-$10,000. The rest of the field lab hardware costs only $2,000-$3,000. So the analytical instrumentation represents the lion’s share of the total cost of setting up a field lab.

If we can find a way to greatly reduce instrument costs (say, by a factor of ten), it will massively lower the barrier to establishing biochar and water quality field labs wherever they’re needed in low resource settings around the world.

Project objectives

Develop one or more radically inexpensive UV absorbance and/or fluorescence portable spectrometers.

Design the spectrometer(s) to be tunable for optimally quantifying water quality parameters of interest in evaluating biochar adsorbents, source waters, and treatment units. This will include quantifying background DOM (dissovled organic matter) as well as surrogate adsorbates.

Utilize open-access hardware and software platforms, and offer our design schematics, computer code, and associated products open-access and for free.

DIY UVA₂₅₄ spectrometer

A couple of colleagues have been working this summer on a from-scratch design for a UVA₂₅₄ meter. They’ve been iteratively prototyping the hardware (light source and sensor), firmware, enclosure, and cuvette holder.

The most recent version sports a really nice looking wooden enclosure! Can’t wait to get this unit and run it through my gauntlet of water tests!

UPDATE! - It’s here!!!

The showdown is on! Let’s see how this made from scratch DIY UV₂₅₄ absorbance spectrometer does going toe-to-toe with the OG RealTech field meter.

Thanks to the mystery Renegade Science Bros who designed and built this prototype! Let the games begin!!!…….

UPDATE (August 18, 2026)

We have been doing lots of rounds of iteration to calibrate the DIY UVA₂₅₄ spectrometer.

Right out of the box its performance was impressive! We have been making tweaks to the firmware to try to get it to reproduce the performance of the RealTech, note-for-note.

How it started…and how it’s going…

A hodgepodge of UV₂₅₄ absorbing solutions on the left; fluorescein standard solutions on the right.

The chart on the left above compares UVA₂₅₄ absorbance between the RealTech and DIY units for a mishmash of lake water and fluorophore solutions - just to get some readings as a starting point for a basis of comparison.

The chart on the right shows an early trial with a calibration method we’re developing using solutions of fluorescein. A slope of 1.0 on this chart would mean perfect 1:1 correspondence between the DIY and RealTech units measuring fluorescein solutions over this concentration range.

Why fluorescein? Fluorescein is a relatively stable (if kept in the dark) compound with a strong UV absorbance and fluorescence “fingerprint.” It’s often used to calibrate commercial fluorometers such as the Turner and Pyxis models we have. Since we have fluorescein on hand anyway to calibrate fluorometers, why not have it do double-duty as a way of calibrating our UVA₂₅₄ spectrometers as well?

Fluorescein absorbance and emission spectra. Note the absorbance peak near 254 nm - this is what we can use to calibrate our DIY UV spectrometer against commercial units like the RealTech.

I was also able to capture lake water DOM (partial) breakthrough curves from a couple of RSSCTs using the RealTech and DIY UVA₂₅₄ spectrometers.

Overpressure issues shut down my column tests early, but for at least initial DOM breakthrough the correspondence between DIY and RealTech spectrometers is really good! A few more round of optimization and we should have ‘er licked!

A fantastic coincidence?

Above I was lamenting about the costs of commercial spectrometers. I noted that:

Well - and I am not making this up - my collaborators sent me the parts list and itemized cost of building the prototype DIY UVA₂₅₄ spectrometer:

$234.35

No kidding! nearly within $1 of the price of the replacement bulb of the commerical unit!

How cool is that?

With a few more tweaks of the calibration method and firmware code I’m going to go ahead and call this a major WIN for Renegade-Science-On-A-Budget.

DIY Fluorometer

Rather than start from scratch to build a fluorometer I’ve been adapting the Open Colorimeter platform produced by the brilliant folks at ioRodeo.

I’ve been trying different configurations of light sources, detectors, and optical filters. A combination that seems to be working so far, at least as a starting point, is:

• light source: 378 nm radial LED board from ioRodeo

• detector: Adafruit TSL2591 High Dynamic Range Digital Light Sensor

• optical filter: Edmund Optics 400 nm longpass filter

With this configuration I’m trying to approximate the specifications of the Turner fluorometer.

Light source and optical sensor specifications for the Turner fluorometer (purple) and my gen-1 prototype fluorometer using the ioRodeo Open Colorimeter platform.

Turner specifies that their “cDOM” (“chromophoric dissolved organic matter”) parameter uses a light source centered on 375 nm and ranging from 270-430 nm. To replicate this as closely (and easily) as I could, I selected and installed a 378 nm radial LED board. I did not install any optical filters on the light source - I wanted to let as much light as possible impinge on water samples since the spectrum of the 378 nm LED falls completely within the range specified by Turner.

The Turner fluorometer (presumably) utilizes a longpass optical filter which blocks all light below 420 nm and transmits everything larger then 420 nm. For my gen-1 prototype I selected a 400 nm longpass filter, which I installed in front of the detector.

This setup recreates the Turner fluorometer “cDOM” specifications, more or less, without having to make significant modifications to the Open Colorimeter physical design or source specialized light sources, detectors, or optical filters.

Performance testing and iterative optimization

As a first-round performance test, I made solutions of two candidate surrogate adsorbates (potential “unicorn molecules”) 7-amino-4-trifluoromethyl coumarin and acridone in DI water:

• 7-amino-4-trifluoromethyl coumarin: 4, 8, 13, 6, and 40 ppb

• acridone: 8, 16, 26, 52, 80 ppb

I measured these solutions using the Turner and ioRodeo fluorometers (note the two meters report in different units):

Comparing fluorescence signal responses for DI water solutions of 7-amino-4-trifluoromethyl coumarin (top) and acridone (bottom) using the Turner (purple) and ioRodeo (orange) fluorometers.

Really great results, especially for a first try! I am impressed with the linearity of these curves. And it appears that we can get to low-ppb levels with these fluorophores and still be above detection limits with the commercial and DIY fluorometers!

Next steps

• Repeat this test in natural water containing background DOM. This will challenge our fluorometers to distinguish between fluorescence signals coming from DOM versus from fluorophore surrogate adsorbates like the two compounds shown above.

• Try different combinations of light sources and optical filters. This could help to minimize interference between DOM and surrogate adsorbate fluorescence signals.

• Discuss results with staff at ioRodeo and get their suggestions and input. Perhaps some adjustments to the firmware could further optimize performance? Perhaps an updated design file for the Open Colorimeter Plus body to allow for additional optical filters?

UPDATE - More performance testing

The graphs above compare fluorescence signal responses by the Turner (cDOM channel) and ioRodeo modified Open Colorimeter for acridone and 7-amino-4-trifluoromethyl coumarin in DI water. Here are the corresponding plots for natural (lake) water:

A very happy result! Very linear over this concentration range, great correspondence between commercial and DIY units.

Check this out: if I plot fluorescence response on the ioRodeo against that of the Turner…Wow! I could not have asked for a tighter correspondence!

This is fantastic!

If the open access DIY ioRodeo can stand in for the Turner fluorometer for our biochar and water quality analyses…that results in an order-of-magnitude reduction in cost - from around $4,000 to only $400!

Root for us to make this work! That’s what I call WINNING!!!!

Next Steps

• Review these observations with the developers at ioRodeo and solicit their feedback and suggestions, including but not limited to

  • Exploring more options for tuning and optimizing the spectrometer, e.g. using different or additional optical filters, different light source and/or sensor specifications or configurations, modifications to firmware to optimize for parameter specific measurements, etc.

• Test drive the ioRodeo analyzing samples from biochar RSSCTs with acridone and 7-amino-4-trifluoromethyl coumarin in natural (lake) water.

• Build scenarios and strategies for how to distinguish surrogate adsorbate spectroscopic signals from background DOM spectroscopic signals.

  • For example, pair ioRodeo analysis with the DIY UVA₂₅₄ spectrometer to dis-aggregate and quantify DOM and target fluorophore signals.

• In the field-lab setting and when monitoring decentralized biochar water treatment systems “in the wild” we generally cannot measure specific pollutants of concern (e.g., herbicides, PFAS, flame retardants, etc.) due to analytical, logistical, and cost limitations.

• Instead we rely on proxy measurements of DOM (dissolved organic matter), since DOM fouls biochar adsorbent and reduces it’s useful life for removing pollutants of concern. And DOM can be measured in the field/field-lab using UV and fluorescence spectrometry. Monitoring DOM this way provides a conservative indicator of bicohar adsorption efficacy.

This approach has worked well for us over the years. But what if we could improve on it?

Enter the search for a “Miracle Molecule.” What if we could find a compound that

• behaves like a (micro)pollutant of concern (e.g., PFAS) from an adsorption standpoint,

• but is itself benign from an ecological and human health standpoint,

• and is also detectable down to low-parts-per-billion (ppb) levels using inexpensive field instruments,

• and can be readily obtained at low or modest cost?

Such a compound could be spiked into water samples and used in a field lab to evaluate different source water / biochar adsorbent combinations. It wouldn’t pose a health risk to staff or the local environment or generate a waste stream that’s difficult or impossible to dispose of. But it would give us additional quantitative information guiding the design, implementation, and monitoring of biochar water treatment systems.

With this in mind we began a “unicorn hunt” to identify candidate molecules that could meet the stringent criteria laid out in the preamble to this project. The first round of selection turned up 14 compounds that might do the job.

But before I get to those, a word on the analytics we’re using to interrogate our putative unicorn molecules…

Commercial portable spectrometers

Two commercial portable fluorometers (left) and a portable UV₂₅₄ meter (right).

The data discussed in this project section is collected using these three commercial instruments. They are

• the AquaFluor, made by Turner Designs

• the SP-380, made by Pyxis

• the P200 UV₂₅₄ meter, made by RealTech (RealTech was bought by ABB and now similar meters are sold as UviTech)

First I want to say - I love all of these meters. I have gotten a lot of mileage out of them and they have provided enormous benefit to our field projects and R&D program over the years. My interactions with staff at Turner, Pyxis, and RealTech (I haven’t had any interactions so far with ABB) have always been very helpful and pleasant.

The main (only, really) downside is the cost. That’s $9,000-$10,000 worth of field gadgets sitting on my lab bench. (Hence the companion project to try to build our own field spectrometers on the cheap…)

Ideally, our field labs will be equipped with some combination of UV absorbance and fluorescence instruments that are sensitive to both (1) background DOM in source waters of interest, and (2) surrogate adsorbate(s) that we spike in to simulate the removal of (micro)pollutants of concern. We need to be able to measure the background DOM, and simultaneously exclude it or minimize it as “noise” in the measurement of our surrogate adsorbate(s).

When we’re interrogating potential unicorn molecules we’re mainly concerned with fluorescence - this measurement has the potential sensitivity to detect compounds down to low-ppb levels. All along I measure UVA₂₅₄ as well - ideally, unicorn molecules will have a weak or effectively zero UVA₂₅₄ signal. One of the challenges of this project will be to minimize any cross-interference in UV absorbance and fluorescence measurements between DOM and target adsorbates.

Commercial fluorometers: same-same, but different

The work detailed below utilizes the Turner AquaFluor and Pyxis SP-380 instruments. I’ll cover all the details of how they are similar and different in the companion section on spectrometers. For our purposes here seeking unicorn molecules, all you need to know is:

• The Turner instrument utilizes wide wavelength ranges. The light source centers on a wavelength of 375 nm, and ranges from 270 nm to 430 nm. The detector is sensitive to light at and above 420 nm.

• The Pyxis instrument uses narrow wavelength ranges. The light source centers on 365 nm, and the detector on 410 nm. I’ve requested the exact bandwidth ranges from Pyxis and will post when they respond. Regardless, they are much narrower than the Turner instrument.

Since the Turner fluorometer uses such wide wavelength ranges more light reaches the detector and so it is inherently a more sensitive instrument than the Pyxis fluorometer. But, picking off narrow wavelength bands could be an advantage if they match well to the absorbance and fluorescence spectra of unicorn candidates while excluding background “noise.” So neither instrument is better; they’re similar tools that have different niches of applicability.

Understanding what the units mean

Both Turner and Pyxis instruments report fluorescence in units of “ppb (as PTSA)”. PTSA (pyrenetetrasulfonic acid) is a fluorescent compound that is used to calibrate the instruments. Water samples don’t typically contain PTSA. What the units signify is that a given water sample fluoresces as if it were a solution of PTSA of X-concentration. So if the meter reads 100 ppb, that means the fluorescence signature of the water sample is like that of a 100 ppb solution of PTSA. Hence “ppb (as PTSA)”.

One more important detail: the Turner has a working range of approximately 1-1,000 ppb (as PTSA), and the Pyxis has a working range of approximately 1-300 ppb (as PTSA).

So what’s the plan?

Roughly, this…

1. Identify and obtain unicorn molecule candidates that meet our criteria in batches of 10-20 compounds.

2. Put them through a rapid screening procedure by determining their fluorescence response with the Turner and Pyxis instruments at a nominal concentration of 100 ppb in DI water.

3. For compounds with a significant fluorescence response, determine the stability of response over a ~48 hour period in DI water.

4. For compounds with a significant and stable fluorescence response in DI water, quantify the intensity and stability of their fluorescence response in natural water (i.e., water containing DOM).

5. For compounds exhibiting a strong and stable fluorescence response in natural water, determine their adsorption behavior with biochar in RSSCTs (Rapid Small Scale Column Tests) and compare with (micro)pollutants of interest.

6. Repeat for the next group of unicorn molecule candidates.

7. Select one or a few of the top performers and build methods around them for our field lab biochar water testing program.

Interrogating the first herd of unicorn molecule candidates

Using our search criteria I rounded up the first batch of 14 test subjects, representing five compound classes:

Here are the fluorescence responses of each compound at a nominal concentration of 100 ppb in DI water (note that the y-axis is a log scale):

Key observations:

• 7-amino-4-trifluoromethyl coumarin and acridone exhibit very strong fluorescence signals with the Turner fluorometer. Immediately it’s recognizable that these are strong candidates for unicorn molecules from a fluorescence perspective.

• All compounds except for acridone exhibit a low or BDL (below detection levels) response with the Pyxis fluorometer. Acridone exhibits a modest fluorescence signal with the Pyxis instrument.

• Compounds displaying a modest fluorescence signal (Turner) - umbelliferone, quinizarin, 4-methyl umbelliferone, and purpurin - can be filed under the “maybe unicorn” category. In the companion DIY spectrometers project it could be possible to adjust wavelength ranges of light sources and detectors in ways that derive stronger fluorescence signals from these compounds.

It’s fascinating that both 7-amino-4-trifluoromethyl coumarin and acridone exhibit very strong fluorescence signals with the Turner, but only acridone exhibits a signficant response with the Pyxis. Let’s look at most likely why this is the case:

Shown here are absorbance and emission (fluorescence) spectra for 7-amino-4-trifluoromethyl coumarin (left) and acridone (right). Overlaid on the plots are the light source and detector wavelengths of the Turner (top) and Pyxis (bottom) instruments.

The absorbance and emission peaks for 7-amino-4-trifluoromethyl coumarin overlap very well with the light source and detector wavelength windows of the Turner fluorometer, accounting for the strong response. The acridone emission peak has partial but still good overlap with the Turner’s detection window.

Although the Pyxis light source wavelength aligns well with the 7-amino-4-trifluoromethyl coumarin absorbance peak, the Pyxis detector wavelength does not overlay the 7-amino-4-trifluoromethyl coumarin emission peak. In contrast, good alignment is evident for both the Pyxis light source and detector wavelengths and the acridone absorbance and emission (fluorescence) spectra. This accounts for the difference in responsiveness of the Pyxis fluorometer to 7-amino-4-trifluoromethyl coumarin compared with acridone.

This provides a good example of how spectrometers can be tuned through the use of optical filters - lenses that selectively block and transmit different wavelengths of light. We’re exploiting this in the companion project to develop tunable spectrometers for measuring background DOM as well as target adsorbates.

How strong of a fluorescence signature is “strong enough” for our purposes?

The screening test was done on each of the 14 candidate compounds at a concentration of 100 ppb (100 ug/L). That’s at the upper end of our working range for micro(pollutants). In our biochar testing method we want to observe the removal of the micro(pollutant) surrogate compound. So we need to be able to quantify the compound over at least one, and much better two, orders-of-magnitude below this. An ideal surrogate adsorbate would be detectable by fluorescence over a working range of 1-100 ppb.

Thus we need a fluorescence signature that’s strong enough at 100 pbb such that at 100x lower concentration (~1 ppb) the fluorescence signal is still strong enough to be detected reliably above the detection levels of our fluorometer(s). The (Turner) fluorescence signals with 7-amino-4-trifluoromethyl coumarin and acridone are clearly strong enough to be able to resolve two-plus orders-of-magnitude lower concentration. With umbelliferone, quinizarin, and 4-methyl umbelliferone we could probably resolve over one order-of-magnitude (10-100 ppb). Likewise, the Pyxis fluorometer could resolve acridone over one order-of-magnitude. These responses could perhaps be increased with spectrometer optimization.

Next steps

Based on this screening, 7-amino-4-trifluoromethyl coumarin and acridone are graduating to the next level of testing. This will include:

• Quantifying fluorometer responses over a range of concentrations down to low-ppb levels and estimation of detection limits (in DI water)

• Quantifying over ~48 hours (in DI water) to determine if compounds are stable enough for the duration of biochar and water testing experiments

• Determining detection levels, stability, and signal-to-noise ratios for quantifying the compounds in natural water containing DOM

• RSSCTs with biochars to determine compounds’ adsorbabilities along with our analytical capabilities for resolving and distinguishing measurements of compounds and background DOM

Stability in DI water and natural water

One important criteria for a unicorn molecule is that it be conserved during the course of adsorption testing. In other words, it needs to be stable - i.e., not reacting or breaking down by physical, chemical, or biological processes - while we’re performing an RSSCT, batch tests, or other tests with biochar or other adsorbents.

To determine compound stability over about a two-day period (a typical timeframe for many adsorption tests) I prepared solutions of acridone and 7-amino-4-trifluoromethyl coumarin in DI water and natural (lake) water at the following concentrations:

• acridone: 0, 8, 16, 26, 52, 80 ppb

• 7-amino-4-trifluoromethyl coumarin: 0, 4, 8, 13, 26, 40 ppb

I placed the solutions on a shaker table and periodically sampled them over ~ 48 hours for analysis with our commercial spectrometers (Turner, Pyxis, and RealTech)

The sample of natural (i.e., containing DOM) water was obtained from lake and diluted using DI water to the following characteristics:

• Turner, cDOM parameter: 28 ppb (as PTSA)

• Pyxis (PTSA channel): BDL (around or less than 1 ppb as PTSA)

• RealTech UVA₂₅₄: 0.041 cm^-1

Here is a comparison of the stability of acridone (8-80 ppb) and 7-amino-4-trifluoromethyl coumarin (4-40 ppb) in DI water and lake water over about two days (quantified using the Turner cDOM parameter):

Key Observations

• Both compounds are stable over two days in DI water.

• Acridone appears stable over two days in lake water.

• 7-amino-4-trifluoromethyl coumarin concentration declines over two days, and the decline appears to be proportional to concentration.

  • This could possibly indicate biodegradation taking place. The lake water sample was filtered to remove particulates (which cause light scattering and interfere with spectrometer measurements) but was not sterilized so biological activity is possibly if not likely. I plan to repeat the experiment with an additive that stops microbial activity.

  • The decline in concentration over the first 24 hours is fairly small. Many adsorption tests (e.g., RSSCTs) can complete within one day, so the effects removal of 7-amino-4-trifluoromethyl coumarin by reaction and/or biodegradation might be negligible compared with adsorption process over short experiments (e.g., RSSCTs).

Here are the fluorescence (left-hand scale, purple) and UV absorbance at 254 nm (right-hand scale, orange) measurements for DI water (left) and lake water (right) solutions of acridone (triangles) and 7-amino-4-trifluormethyl coumarin (circles):

Key Observations

• 7-amino-4-trifluoromethyl coumarin does not appear to contribute fluorescence measurable by the Pyxis fluorometer (PTSA channel) or UVA₂₅₄ in either DI water or lake water.

• acridone appears to contribute to both the Pyxis-quantifiable fluorescence as well as UVA₂₅₄ in both DI water and lake water.

  • Acridone fluorescence detectable by the Pyxis fluorometer is explained above. Acridone’s UVA₂₅₄ signature (and the absence of a 7-amino-4-trifluoromethyl coumarin UVA₂₅₄ signature) can be explained by comparing their respective absorbance spectra:

Acridone has a giant absorbance peak very near 254 nm. Comparatively, 7-amino-4-trifluoromethyl coumarin is insensitive to light at 254 nm.

Observations such as these inform our strategic choices in method development - since an important goal is to be able to distinguish between spectroscopic signals from DOM versus target surrogate adsorbates.

Next Steps

• Repeat 7-amino-4-trifluoromethyl coumarin stability test in natural water, with sodium azide added to arrest microbial activity.

• Repeat test solution preparation protocol, substituting ethanol for methanol as the initial solute.1

• Conduct RSSCTs using natural (lake) water, biochar, and our two (so far) candidate unicorn fluorophores. Compare the results to our database of column studies using biochar and target pollutants of concern such as PFAS and herbicides.

UPDATES (Aug 18, 2026)

From above…

• Repeat 7-amino-4-trifluoromethyl coumarin stability test in natural water, with sodium azide added to arrest microbial activity.

My sodium azide supplier fell through so I have not been able to do this yet. However, I thought of a work around that’s possibly or probably better.

Since 7-amino-4-trifluoromethyl coumarin seems to be “stable enough” over a period of up to 12-16 hours, fresh solutions could be prepared during experiments to offset the apparent degradation.

Also, sodium azide is fairly hazardous. I’ve often used it in the lab but would most likely want to avoid its use in field lab protocols if at all possible.

• Repeat test solution preparation protocol, substituting ethanol for methanol as the initial solute.

I did a quick check on this, and yes, ethanol will work. The initial dissolution to form a concentrated solution of 7-amino-4-trifluoromethyl coumarin in ethanol seemed to have more undissolved solid material than in methanol. So methanol is the better choice, but ethanol will work if that’s what is available.

• Conduct RSSCTs using natural (lake) water, biochar, and our two (so far) candidate unicorn fluorophores. Compare the results to our database of column studies using biochar and target pollutants of concern such as PFAS and herbicides.

I started this with 7-amino-4-trifluoromethyl coumarin in lake water (twice), but had column overpressure issues that forced me to shut down before completing the tests. No worries, I have a fix for this problem and will repeat in Ecuador in a few days’ time. (Gearing up to travel now…)

Two new candidate fluorescent adsorbates

I tested two new promising “unicorn” molecules for their fluorescence signal strength and stability in natural water. One is a close cousin of the fluorophore described above, 7-amino-4-methyl coumarin. The other is a laser dye used in peptide analysis called coumarin 7.

Top four candidate unicorn fluorophore adsorbates, so far.

The two new compounds show good stability in natural water over two days.

Candidate fluorophores at 70 ppb in lake water (UVA₂₅₄ 0.040 cm^-1).

Interestingly, 7-amino-4-methyl coumarin is picked up with a moderately strong fluorescence signal by the Pyxis (narrow bandwidth) fluorometer. That might turn out to be a useful feature…

Neither fluorophore contributed UVA₂₅₄ at these concentrations. That could help to distinguish them spectroscopically from the DOM background.

Next Steps

If travel goes OK I will be on the ground in Ecuador soon. We will get up and running right away running RSSCTs with these fluorophores in local surface waters. I will report out our findings here. Also, check in on our DIY spectrometers project as we will also be doing head-to-head performance tests between commercial and DIY units.

Note to readers: This post gives an overview of two new interrelated R&D projects. We’re going full-gas this summer in the development phase and plan to pilot the results in the field in Ecuador beginning late August.

Since so much is happening so fast I plan to post near-real-time updates for these projects on the fly. Everything is open access, so each project will have it’s own page under the “Open Access Materials” section, all free. As new data, observations, ideas and experiences come in I will update the relevant sections.

I hope you will find these new tools interesting and useful! The income we get from paid subscribers provides an R&D budget for building tools and methods like these. Thank you to all our readers and supporters!

Colleagues at Amisacho in Ecuador recently received funding for the next phase of our project so things have shifted into high gear.

In T-minus one month I’ll be on the ground with them helping to implement some new-and-improved biochar and water testing methods. I’m working feverishly now to get those new methods and associated equipment spun up. Everything we’re developing will be open access and I’ll be highlighting milestones here in near-real time.

FYI you can find previous installments about the work in Ecuador (and more in the Field Notebook archive):

This summer we’re aiming to make two big leaps forward in biochar and water quality testing:

• Objective #1 is to drastically reduce the costs associated with setting up a biochar and water quality testing field laboratory.

• Objective #2 is to increase the resolution and quantitative value of biochar adsorbent testing by discovering one or more “unicorn” surrogate adsorbates.

I’m in a race to make major headway on these goals before my fast-approaching visit to Amisacho mid-to-late August. When I’m there we’ll hold a training for water team staff and pilot these new methods in the field. Exciting times!

Objective #1 - reduce analytical costs using DIY spectrometers

During a previous visit we established the biochar and water quality testing field lab at Amisacho. In short, this involves running Rapid Small Scale Column Tests (RSSCTs) using different biochar adsorbent and source water combinations to obtain quantitative input to guide the design, implementation, and monitoring of biochar water treatment systems.

The kit includes common laboratory implements - volumetric flasks and graduated cylinders, pipettes, a pump and associated tubing and fittings, supplies such as gloves, wipes, pipette tips, etc. - and can fit readily into carry-on and checked luggage.

Biochar and water quality testing field lab kit ready for transport.

The biggest cost factor in the field-lab kit is the analytics. We use portable UV and fluorescence spectrometers to quantify different components of DOM (dissolved organic matter) as the method for establishing the efficacy of a particular biochar to treat a particular source water.

We rely on measuring DOM removal by biochar because this is something that can be measured under field conditions (as opposed to in a full-featured university or commercial laboratory) and relatively inexpensively.

DOM fouls biochar surfaces, blocks pores, and competes with target adsorbates - pollutants such as pesticides, PFAS, and pharmaceutical residues - for adsorption sites in biochar pores. Quantifying individual herbicide or PFAS compounds is typically cost prohibitive and logistically infeasible in low resource settings like Amazonian villages. So rather than directly measuring specific pollutant molecules of interest we measure DOM surrogates - fractions of DOM that are detectable by UV and fluorescence spectrometry and, that correlate with fouling of biochar and reduction in the lifecycle efficacy of biochar water treatment systems.

(For a more in-depth discussion of DOM fouling of biochars and related UV/fluorescence spectroscopy metric see here and references therein.)

Though A LOT cheaper than top-of-the-line mass spectrometers, portable UV and fluorescence spectrometers are not exactly cheap. Commercially available portable (“lunchbox”) UV and fluorescence spectrometers typically

• measure one thing (or sometimes two or a few related parameters),

• do it really well, and

• cost a few to several thousand (US) dollars apiece.

With the state-of-the-science now, ideally a biochar and water quality testing field lab would be able to measure two or three different parameters - one UV absorbance parameter and one or two fluorescence parameters. In later posts I’ll go into more detail about these. For now, just understand that would require two or three different instruments at a total cost around US$9,000-$10,000.

By comparison, the rest of the hardware for setting up the field lab can be had for a couple thousand dollars (US). So the bulk of the cost to establish a field lab (other than the building) comes from the analytics.

A while back in conversation with folks at Amisacho I was running my mouth (as usual):

And so of course Lexie and Luis dared me to do it.

Luckily in recent years there have been great advancements in open-source maker hardware, devices, code, 3D printing, pre-fab circuit boards, inexpensive light sources, optical filters and sensors, and so on.

And luckily I have been able to enlist the help of some people who are way smarter than me on this stuff. The result so far is we have working (but not yet optimized) prototypes of DIY UV and fluorescence spectrometers!

A couple of ingenious collaborators (not sure if they want to be named here, but they get the credit…) have been working on a UV absorbance spectrometer completely from scratch! As we learned, it turns out the cuvette holder is a critical piece of kit for getting consistent replicates. Fun with 3D printing prototypes!

The first-gen of the UV absorbance spec has passed coarse optimization so they’re sending it to me to break it test it later this week.

For a multi-parameter fluorescence spectrometer I’m adapting the Open Colorimeter platform produced by the brilliant folks at ioRodeo.

Starting to test different configurations of LED light sources, sensors, and optical filters for obtaining the fluorescence parameters we need to evaluate biochar water treatment systems.

(FYI our team at Caminos de Agua and associates has been working with ioRodeo for several years now using the ioRodeo open access potentiostat platform to develop an electrochemical method for quantifying arsenic in drinking water. Read more about that work here...)

The DIY spectrometry project is currently in high gear - I will post developments here as they come in in a dedicated section. Hopefully more WINS than FAILS!

Objective #2 - unicorn hunt for a “Miracle Molecule”

I’ve written above and elsewhere about why we focus on background water chemistry - specifically DOM (Dissolved Organic Matter) - as a fieldable proxy measurement for quantifying the efficacy of a particular biochar to treat a particular source water.

Such a compound would indeed have to be very special - hence a kind of “unicorn molecule.” It would necessarily meet several tough criteria:

• It would have to be benign from a human health and environmental standpoint. We need to be able to spike it into source waters we want to evaluate with biochar adsorbent in a field lab setting - and so doing cannot present a hazard to tech staff or anyone who might come into contact with the water. Further, it can’t result in negative environmental or ecological effects or present an expensive, laborious (and often impossible) hazardous waste disposal problem. Our unicorn molecule must be low-risk to HH+EH (human health and environmental health).

• It would need to exhibit adsorption behavior similar to the target pollutants we care about removing in biochar water treatment. Recall from our discussion of Sentinel Chemicals - representatives of broad pollutant classes that are weakly-adsorbing, so as to provide a challenge to biochar adsorbent and conservative design and operational specifications of treatment units. Our unicorn molecule should display weak adsorption behavior, so that it can be an effective surrogate for weakly adsorbing chemical pollutants. (Refer to our modeling tool for predicting and comparing adsorption behavior.)

• It would need to be detectable in water down to low ppb (parts-per-billion) levels in source waters. (I won’t go into detail here, but you can read about the importance of operating below the adsorbate concentration threshold effect for micropollutants, and this threshold is typically in the 50-100 pbb range.) Our unicorn molecule must have strong UV absorbance and fluorescence signatures within the wavelength range capabilities of inexpensive field instruments.

• It must be stable in natural water for at least 24-48 hours. All sorts of processes can act to break molecules down in natural water sources - photolysis, hydrolysis, oxidation, and biodegradation to name a few. We need to be able to spike our unicorn molecule into natural source water and carry out adsorption testing over a one two day period. We can’t have our special molecule breaking apart or being gobbled up by naturally present microbes mid-experiment.

• It can’t cost an arm and a leg. A molecule that’s stable in water, adsorbs just like an herbicide, flame retardant, or short-chain PFAS, and is detectable down to 1 pbb with a lunchbox spectrometer is no good to us if it costs $1,000 per milligram. Our unicorn molecule must be cheap and readily obtainable.

As you can see, this is a tall order. That’s why I’m calling it a “unicorn hunt.” I had this idea three or four years ago, and I’ve been hunting unicorns in the background off-and-on since.

(To be honest, this project has been shoved onto the back burner more times than I can count over the past few years. The new round of funding for the Ecuador project has provided the kickstart to bring it front-and-center and make real progress. Finally!)

Where to start hunting unicorns?

Unicorn molecules are optically active - that is, they interact with light, absorbing some wavelengths, transmitting some wavelengths. Kind of like…dyes!

Henna is a natural (plant-derived) dye many women use on their hair and skin:

Henna hair dye sold on Amazon; henna tattoo featured at healinghenna.com.

The main photo-active ingredient in henna dye is lawsone (2-hydroxy-1,4,-naphthoquinone).

Lawsone is naturally occurring in the leaves of the henna plant, and has been used as a hair and skin dye for thousands of years. So it might be benign from a human health and environmental standpoint (???).

We can look lawsone (2-hydroxy-1,4,-naphthoquinone) up at PubChem and find:

OK, interesting, some HH (human health) hazard warnings there. “Harmful if swallowed” (don’t eat it). “Causes skin irritation” (interesting since it’s used for skin tattoos…). “Suspected of causing genetic defects” - this one is troubling.

Here’s how I break down the HH+EH hazard status of lawsone:

• The “irritant” hazards apply to almost any compound you can to look up. I tend to regard a candidate unicorn compound as HH-benign if it only lists a few mild warnings in the hazards column.

• The warning “acute toxicity, oral” gets a compound DQ’d. Even though it would just be used in biochar water testing experiments (not for consumption) I don’t want to run the risk of someone imbibing something with “acute toxicity.”

• Anything like suspicion of causing “genetic defects,” “mutagenicity,” “cancer,” “carcinogenicity,” and similar - DQ’d.

• There are no “Danger” classifications that appear for lawsone, but this elevated risk results in a candidate compound being DQ’d.

• Likewise, any EH warnings that indicate the compound poses a serious threat to aquatic life, DQ’d.

With these two initial criteria - optically active, low risk from an HH+EH standpoint - we can begin our unicorn hunt.

Lawsone might be nixxed, but that doesn’t mean there aren’t other quinones out there that could quality as potential unicorn molecules. Coumarins, it turns out, are another class of synthetic and natural dye compounds that could contain unicorn molecules. And acridines as well…

The basic molecular building blocks that make up quinones, coumarins, and acridines.

There are many chemical classes that could be hiding unicorns - such as polycyclic aromatic hydrocarbons (PAHs), flavonoids, xanthenes, azo dyes, and others.

I’ve been unicorn hunting through these compound classes using the research literature and in particular a couple of extremely helpful online databases:

• PhotoChemCAD - online database, affiliated research paper

• Deep4Chem - online database, affiliated research paper

Using these and other online tools, I’ve built my own database of candidate unicorn molecules. I used the following criteria to winnow a list of thousands and thousands of possible candidates down to a manageable number of substances I can actually acquire and test in my lab:

1. Using empirical (experiment-obtained) or computational (predictive) data - does the compound have UV absorbance and fluorescence emission spectra in the capable light source and sensor ranges of field spectrometers?

2. Are the molecules small, i.e., have molecular weights below about 350 g/mol? (This is a first-cut criteria for weakly-adsorbing molecules. Many dye compounds are large, sprawling molecules. They’re unlikely to exhibit adsorption behavior similar to small herbicide or PFAS molecules.)

3. Predicted adsorbability. I use the tool we developed using adsorption models derived from data to predict compounds adsorbability and compare with known target pollutants.

4. Level of HH+EH risk. (In my post on the Puerto Rico project I detail how we developed an HH+EH risk index, which can be compiled easily for long lists of compounds using my colleague Matthieu’s skillful Python script!)

5. Can I buy the compound, from where, and how much does it cost? (This step turned out to be trickier and take longer than expected…)

And with that, I started the unicorn hunt this month with the first batch of 14 compounds. I detail what we learned and where we go from here in a dedicated section.

The north-central region of Puerto Rico, where the workshop took place, is a fascinating and tragic case study in environmental geology and chemical water pollution.

See the end of this article for a bibliography of geology, water, and public health studies conducted in the region, from which the following summary is drawn.

A vast karst aquifer system underlies 19% of the island’s land area, in a region that is home to over 10% of the population. Karst is comprised of highly fractured and weathered rock – typically limestone and dolomite. Karst subsurface topography has very high porosity and permeability, allowing karst aquifers to capture, store, and transmit enormous quantities of water. While hydraulic conductivities in most subsurface systems and porous media (e.g., sand filters) are 1 m/day, karst systems exhibit conductivities of tens to hundreds of m/day. Karst aquifer systems readily interact with overlying surface water systems through recharge zones, springs that emerge from the subsurface, streams that disappear underground and re-emerge downgradient, and sinkholes. Groundwater from karst aquifer systems provides 20-25% of water use globally and over 40% of the drinking water in the US.

The high porosity and permeability that make karst aquifer systems so productive and valuable also make them highly vulnerable to contamination, allowing pollutants to be stored and transported over large distances with potential for exposure to humans, wildlife, and ecosystems.

The abundant freshwater resource of Puerto Rico’s north coast karst aquifer system is a factor that propelled the development of pharmaceutical, chemical, agricultural, and manufacturing industries in the region along with associated urban development and the proliferation of landfills and waste disposal sites. Accidental spills, clandestine disposal, and even intentional injections of wastes into the aquifer (a practice discontinued after the 1970s) has led to widespread contamination of northern Puerto Rico’s water supply. Sinkholes were often used as informal/clandestine dump sites, leading to direct and heavy contamination of the underlying aquifer.

Accordingly, Puerto Rico and the north coast karst aquifer region in particular has the highest density of Superfund and RCRA (Resource Conservation and Recovery Act) Corrective Action sites in the US and its territories. As of 2025 Puerto Rico hosts a total of 25 Superfund sites, with 12 of those Superfund Sites along with 15 RCRA Corrective Action sites located within the north coast karst aquifer region.

The US EPA estimated that pharmaceutical manufacturers associated with just one of the north coast Superfund sites discharged approximately 60 metric tons of waste material during the 1980s. At another Superfund site US EPA documented releases of 5,000 kg per year of just one compound – trichloroethylene (TCE) – during the 1980s, and 1,600 kg per year during the 1990s.

A multitude of deleterious health effects can arise from exposure to this environmental and groundwater pollution. For example, rates of preterm birth, infant mortality, spontaneous abortion, and premature thelarche (breast development) in Puerto Rico are also the highest or among the highest in the US and its territories.

Two classes of widely detected contaminants in the north coast karst aquifer system are chlorinated volatile organic compounds (CVOCs) and phthalates. Exposure to CVOCs and phthalates has been associated with endocrine disruption, developmental impairment, reproductive dysfunction, neurological damage, cancer, organ damage (e.g., liver, heart, kidneys), and immunological effects.

Phthalate contamination of the north coast karst aquifer system

Phthalates are widely used as plasticizers to impart flexibility and durability to plastics, and as solvents and manufacturing additives in a wide array of pharmaceuticals and personal care products and in disposable food packaging. Because of their toxicity, prevalence in the environment, wide- spread use, and potential human exposure, phthalates are of particular concern. The US EPA includes six phthalates as priority pollutants:

• DEHP – di-(2-ethyl hexyl) phthalate

• BBP – butyl benzyl phthalate

• DBP – di-n-butyl phthalate

• DnOP – di-n-octyl phthalate

• DEP – diethyl phthalate

• DMP – dimethyl phthalate

A water quality survey (Torres et al. 2018) found extensive contamination of the north coast karst aquifer by DEHP, DNOP, DBP, and DEP. In 197 sampling sites at least one phthalate was detected in 92% of sites. The most detected phthalate was DEHP in 89% of sites. The least detected was DEP, in 29% of sites. Total phthalate concentrations averaged around 5 ug/L and ranged up to 58 ug/L. These are among the highest phthalate concentrations reported even for sites impacted by landfills and urban development.

A study of urinary phthalate biomarkers (Cantonwine et al. 2014) found evidence for widespread exposure to phthalates among pregnant women living on the Northern coast of Puerto Rico. Phthalate metabolites were detected in nearly 100% of the urine samples, and at higher concentrations (in some cases up to twice as high) compared to women in the mainland US population.

CVOC contamination of the north coast karst aquifer system

CVOCs are used in large quantities as industrial solvents and degreasers, as well as in an array of consumer products and textile cleaning (e.g., dry cleaning). In the north coast karst aquifer region, CVOC contamination has been associated with pharmaceutical and electronics manufacturing companies as well as landfills and informal disposal sites. CVOCs are volatile, sparingly soluble in water, and are resistant to degradation in the environment. Therefore, CVOCs typically are projected to have long residence times in aquifers of hundreds to thousands of years.

A water quality survey (Torres et al. 2019) found extensive contamination of the north coast karst aquifer by CVOCs with at least one type of CVOC present in 64% of groundwater samples collected from throughout the region. 53% of samples contained two or more CVOC compounds. CVOCs are present in half of the Superfund designated sites in the north coast karst aquifer region. The seven most frequently detected CVOCs in the region are:

• CCl₄ – carbon tetrachloride

• TCM – trichloromethane

• DCM – dichloromethane

• PCE – perchloroethylene

• TCE – trichloroethylene

• 1,1-DCE – 1,1-dichloroethylene

• cis-1,2-DCE – cis-1,2-dichloroethylene

CVOCs were detected at very high concentrations in many water samples – total (sum of) CVOCs averaged 54 ug/L (ppb), and ranged as high as 16.4 mg/L (ppm…!!!). An earlier survey (Yu et al. 2015) had found lower average levels (ppt to ppb range) of 17 CVOCs present in sampling sites throughout the region. Another study (River et al. 2018) revealed CVOCs in 62% of groundwater samples and 58% of tap water samples in the north coast aquifer region, including CCl₄, PCE, TCE, and TCM frequently detected.

Persistent presence of CVOCs in the karst aquifer system, even after contaminated sites have been subjected to remediation efforts, is attributed the high capacity of the aquifer to store, transport, and slowly release contaminants over long periods of time.

Evaluating the potential of biochar water treatment

There is an extensive literature on removal of phthalates and CVOCs from drinking water using activated carbon. We don’t have empirical laboratory or field data on treatment of phthalates or CVOCs using biochar within our research consortium. There are a couple of tools we can use, however, to explore the potential applicability of biochar adsorbent for removing these pollutants.

Adsorbate comparison tool

One tool described here previous, is the adsorbate comparison tool. This tool uses a modeling approach to compare the adsorbability of a compound of interest to dozens of other water pollutants belonging to several chemical classes (e.g., agrichemicals, PFAS, pharmaceuticals and personal care products, industrial compounds, etc.).

The adsorbate comparison tool includes references to the adsorbability of Sentinel Chemicals – selected common water pollutants for which we have the largest datasets and that we rely on most heavily in the design and operation of biochar water treatment systems.

A first step is to run the phthalate and CVOC compounds identified in the research summarized above through our adsorbate comparison model to get a sense of how difficult to remove by adsorption they are compared with Sentinel Chemicals and other water contaminants of concern.

Remember: “All models are wrong; some models are useful.” Whenever you run a model you will always get an answer. However, the relationship between that answer and the on-the-ground reality is often tenuous and uncertain. Validation of model predictions, whenever possible, is critical! As a first step in design and decision support, we find it helpful to have a sense of the predicted adsorbability of contaminants for which we don’t have hard data.

Human health / environmental health risk index tool

Another decision support tool that can help us prioritize and focus our efforts is to gauge the severity of environmental/ecological and human health impacts of different contaminants of concern. It might well be the case that in our treatment system design we want to prioritize the removal of compounds associated with the more negatively consequential ecological and human health effects.

Described here is an admittedly rough approach to comparing the risk of negative ecological and human health effects of compounds. Though the method is a little crude, it can serve as a first-cut, “quick-and-dirty” decision support tool for prioritizing treatment objectives.

Our human health / environmental health (HH EH) risk index ranks chemical compounds by the number of human health and environmental health warnings listed in the US NIH’s PubChem database. As an example of how we tabulate the HH EH risk index, we’ll use the CVOC perchloroethylene identified in the research summarized above.

Put “perchloroethylene” into the search bar and inspect the best match result.

It will list other compound names, formula, molecular weight, SMILES code, etc. (For example, “tetrachloroethylene” is a synonym for “perchloroethylene.) FYI, this is the same process used to obtain inputs for the adsorbate comparison tool. Make sure these identifiers match the compound you’re looking up.

The entry will list primary hazards as well as “Safety and Hazards” section on the menu bar to the right – click on this.

The Safety and Hazards section will typically provide one entry of several. Click “View All.” This will list several “Safety and Hazards” entries from different databases.

For our example compound perchloroethylene, we see six reports from different Safety and Hazards databases. The “GHS Hazard Statements” list one or more ecological and/or human health warnings. Our “quick-and-dirty” HH EH risk index method is to total up the number of GHS hazard listings and divide by the number of databases. So it’s just a kind-of average HH EH risk based on how many times a warning is listed for the compound.

In the case of perchloroethylene, the GHS hazard listing counts are 2, 6, 10, 9, 2, and 7, for a total of 36 listings across six databases and an average of 6 HH EH warnings across all the databases returned in the PubChem search. So perchloroethylene has an HH EH risk index of 6, according to our crude method. The idea is simply that the more times a compound is listed in these hazard databases, the greater the HH and/or EH risk it represents.

Visualizing health risk and treatability for water contaminants of concern

Using this method we tabulated HH EH risk indices for the phthalate and CVOCs identified in the research summary above, as well as the chemicals used in our contextualized analysis of comparative adsorbability. A two-dimensional plot of health risk versus biochar treatability looks like this:

The further up you go on the plot, the higher the HH EH risk index. The further right you go on the plot, the more difficult to adsorb by biochar (according to the model prediction, with all the necessary caveats, disclaimers, etc…).

This rough analysis suggests that, of the two main classes of north coast karst aquifer water pollutants identified by environmental health researchers in Puerto Rico, CVOCs tend to represent the great health hazard as well as the more difficult treatment challenge compared with phthalates. The CVOCs are small, polar molecules, and are very environmentally persistent due to their strong carbon-chlorine bonds. So it’s not entirely surprising they are more difficult to adsorb and represent a somewhat greater HH EH risk than phthalates as a chemical class.

The model predicts that the CVOCs are similar to or even slightly more difficult to remove by biochar adsorption than many of our Sentinel Chemicals. So one way we might use this information is to design biochar treatment systems on a very conservative basis – in other words, to a high level of confidence that even the most difficult-to-adsorb compounds would be expected to be substantially removed. Qualitatively, that probably would translate to larger biochar contactor units and more frequent adsorbent refurbishment.

Of course, when implementing treatment systems we will need to put quantitative specifics on that. But for now this analysis provides a “good enough” starting place to deepen our conversation with local partners about the potential for decentralized water treatment with biochar in Puerto Rico!

As this project develops I will post updates here. And as always, thank you for your enthusiasm and support for our work!

References

Cantonwine, D. E., J. F. Cordero, L. O. Rivera-González, L. V. Anzalota Del Toro, K. K. Ferguson, B. Mukherjee, A. M. Calafat, N. Crespo, B. Jiménez-Vélez, I. Y. Padilla, A. N. Alshawabkeh and J. D. Meeker (2014). “Urinary phthalate metabolite concentrations among pregnant women in Northern Puerto Rico: Distribution, temporal variability, and predictors.” Environment International 62: 1-11.

Cordero José, F., D. Meeker John, T. Sheahan, I. Padilla, R. Giese, B. Silevitch Michael, R. Loch-Caruso, D. Kaeli and N. Alshawabkeh Akram (2012). Case Study?Puerto Rico Test Site for Exploring Contamination Threats. GeoCongress 2012: 3553-3562.

Padilla, I., C. Irizarry and K. Steele (2011). “HISTORICAL CONTAMINATION OF GROUNDWATER RESOURCES IN THE NORTH COAST KARST AQUIFERS OF PUERTO RICO.” Rev Dimens 3: 7-12.

Rivera, V. L., I. Y. Padilla and N. I. Torres (2018). Spatiotemporal Assessment of CVOC Contamination in Karst Groundwater Sources and Exposure at Tap Water Point of Use. Karst Groundwater Contamination and Public Health, Cham, Springer International Publishing.

Torres, N. I., V. L. Rivera, I. Y. Padilla, R. E. Macchiavelli, D. Kaeli and A. N. Alshawabkeh (2019). “Effect of hydrogeological and anthropogenic factors on the spatial and temporal distribution of CVOCs in the karst system of northern Puerto Rico.” Environ Earth Sci 78(20).

Torres, N. I., X. Yu, I. Y. Padilla, R. E. Macchiavelli, R. Ghasemizadeh, D. Kaeli, J. F. Cordero, J. D. Meeker and A. N. Alshawabkeh (2018). “The influence of hydrogeological and anthropogenic variables on phthalate contamination in eogenetic karst groundwater systems.” Environmental Pollution 237: 298-307.

Yu, X., R. Ghasemizadeh, I. Padilla, C. Irizarry, D. Kaeli and A. Alshawabkeh (2015). “Spatiotemporal changes of CVOC concentrations in karst aquifers: Analysis of three decades of data from Puerto Rico.” Science of The Total Environment 511: 1-10.

Caribbean Agroforestry Institute, Camuy Puerto Rico, Feb 28 - Mar 1

link for registration

Organic Growers School Conference, March Hill NC, Mar 7-8

link for registration

Thanks to the diligent tech team of Caminos de Agua and members of the San Elias community for making this project happen!

The Purificadora (treatment plant) is designed to produce 1,650 L per day. The village’s groundwater source contains elevated arsenic (30-40 ug/L) and fluoride (1.3-1.8 mg/L) and is at risk for contamination by biological pathogens. The treatment system is designed to keep arsenic below 5 ug/L and fluoride below 0.7 mg/L.

Water moved from left to right on the diagram above. Raw well water passes through a coarse sediment filter (130 um) and is stored in a tank on the roof of the treatment plant. It flows by gravity into the treatment plant and through a fine sediment filter (5 um, granular iron oxide sorbent for arsenic removal, granular bone char for fluoride removal, carbon adsorbent (biochar or GAC) for color/taste/odor control, and through another fine sediment filter (1 um) to capture any small ad/sorbent particles.

It’s then exposed to ceramic impregnated with colloidal silver for disinfection. A pump and pressure tank provide the pressure needed for carboy cleaning and filling. The water passes through an additional disinfection stamp using UV light and on to the carboy washing and disinfection station, and then to the station for filling clean carboys.

Caminos de Agua tech team member Jaime working on the install.

The treatment plant looks so clean and professional!

On inauguration day the Purificadora was blessed by the local priest!

The project was led by a group of nine people from the local San Elias community, with technical assistant (treatment plant design and installation) by the Caminos de Agua tech team.

The San Elias water committee generated a set of agreements for the operation and maintenance of the system including a long term sustainability plan.

They designated two operators - Maria Jesus and her assistant Fatima - to cover day-to-day operations and oversee hygiene practices.

In contrast with previous projects, such as the treatment system in Alonso Yáñez - the San Elias team elected to forego in-home point-of-use (POU) treatment for greater simplicity. However, this necessitates higher hygiene requirements on the treatment plant side and during transport and in-home practices. This was accomplished by an expanded and more ambitious training curriculum - about 20 hours in total covering not only water hygiene practices but also communication, logistics, problem solving, leadership, conflict resolution, and financial details.

With the liaison assistance of Caminos De Agua, the San Elias water committee obtained approval for their system by the State of Guanajuato Water Authortity and has been added to the list of authorized water providers.

The inaugural festivities even included a fantastically decorated cake!

To my knowledge this might be the first water treatment themed cake! Very cool!

Variation 2.0 was developed after several months of heavy use of the previous version (Version 1.4). It represents advancements in performance and reliability compared with previous designs, and is simpler to construct.

More updates coming soon, including some photos and reporting on a new Groundwater Treatment System that just came online serving the community of San Elias in Guanajuato state, Mexico, courtesy of Caminos de Agua.

Solar Biochar Oven Version 2.0

Based on several months of heavy usage of the Solar Biochar Oven we have made upgrades to the design.

It’s now simpler to construct, has a 25% larger batch volume, and vulnerabilities of the electrical components to moisture, smoke, oils, and other deleterious substances have been mitigated.

I’m working on an updated graphical manual. The changes made in this iteration are substantive enough to jump from Version 1.4 to Version 2.0 (instead of Version 1.5). The updated manual will be posted soon and we’ll commence stress-testing Version 2.0 of the oven and report back results.

Water Guardians game

The Ecuador team has finished creating the Guardianes del Agua (Water Guardians) game and it looks fabulous!

The team printed off big copies of the game board to take to schools and parks in order to train teachers and docents how to use the game to teach children about ecology and conservation of water resources!

They are finishing up the English translation as well. We’re working on how to get game packs printed and shipped. Proceeds from sales are going to support the Ecuador teams’ water projects.

Upcoming Workshops

There are two workshops on Decentralized Water Treatment with Biochar coming up soon - one confirmed and one waiting to be confirmed.

• The confirmed workshop will be March 7-8, 2026, at the Organic Growers School Conference in Mars Hill, NC. Besides biochar water treatment there are a ton of cool practical topics presented at the Conference so check out the full schedule.

• The tentative, not-yet-confirmed workshop will be late February - early March at the Caribbean Agroforestry Institute in Puerto Rico. As soon as I have those details locked in I will post a notification here.

There will be more workshops to come this year but I wanted to post these since the timelines are fairly short.

Thanks to everyone for supporting our work! In 2026 I pledge to do a better job keeping this site up-to-date.

2025 was a rough and tumble year for us. In particular there were some significant family health challenges, financial stresses/shortfalls, and the demands (and joys!) associated with raising a wild 2-to-3-year-old!

We’re also scaling up our regenerative farm project and the panoply of activities associated with that have taken a ton of my time and energy in recent months. Water projects are set to come back strong in 2026 and I will be sure to highlight progress and milestones here.

Thank you! Be well and keep in touch…

This version includes some troubleshooting tips as well as a simple design for an emissions control system that can be added on to the oven.

If you try it out we’d love to hear your feedback. Especially if you have problems and/or make interesting adaptations!

Very busy lately but many more interesting project updates to come as soon as I can get write-ups done…

Current Version 2.0

January 2026

Design variation 2.0 of the Solar Biochar Oven presents a few advantages over the 1._ series. The reactor sits on top of the heating element. This eliminates drilling/cutting the bottom of the reactor which saves time and labor and reduces complexity of the build. It also eliminates the vulnerability of moisture and fluids/melted substances leaking through the bottom of the reactor onto electrical connections.

Variation 2.0 also uses a larger reactor for increased batch sizes – a 100 qt (94.6 L) stock pot instead of an 84 qt (79.5 L).

Design Variation 2.0 (“Ver 2 0”) is found in an Appendix in the last two pages of the document linked just below. The 1._ series instructional info is preserved from the previous “Ver 1 4” file for reference of the evolution of this project.

Solar Biochar Oven Ver 2 0

27.3MB ∙ PDF file

Download

Download

Previous Versions

Version 1.4 (September 2025)

Solar Biochar Oven Ver 1 4

24.9MB ∙ PDF file

Download

Download

Version 1.3 (July 2025)

Solar Biochar Oven Ver 1 3

23.9MB ∙ PDF file

Download

Download

FYI we are offering this work open-access under Creative Commons terms:

Upgrading to paid subscription helps us to continue to offer the fruits of our R&D programs. If money is a problem we’re happy share our materials for free with enthusiastic creators.

Thank you for your support and engagement with our work.

For now here are snapshots of a few things we’re working on, as previews for coming articles.

Solar biochar/bone char

A while back I wrote about new R&D using solar (PV) power to make biochar and bone char:

Despite proximity to the winter solstice, on clear sunny days the system was able to attain and hold excellent thermal conditions for making bone char sorbent. For example:

kLux is a measure of sunlight intensity falling on the PV panels. The bottom plot shows temperature within the pyrolysis reactor. A control system (thermostat) was used to keep the temperature just below 500 C. On the day these data were collected the average ambient temperature was 33 F (0.6 C) with a high of 49 F (9.4 C) and a low of 17 F (-8.3 C).

Even on a December day at temperate latitude the system was able to maintain 500 C for about 4 hours. These are excellent pyrolysis conditions for making bone char sorbent for fluoride removal.

Preliminary data indicate our solar bone char substantially outperforms two commercially available bone chars for fluoride removal from groundwater:

In summary…

• Process uses sunlight falling on PV panels to provide the energy to drive pyrolysis - and thus does not require wood or other biomass fuel, propane, etc.

• High precision temperature control is achieved. A suitably sized PV array can provide ample power even when skies are partly cloudy or overcast.

• Labor inputs are simplified and reduced. Feedstock is added to the reactor, the thermostat is set, and the reactor is switched on. The reactor can be shut off at any time, or allowed to cool naturally after sunset.

UPDATES

The bone char results were so promising we built a second unit for Caminos de Agua to use in their in-house bone char production.

I recently completed and shipped out a third solar biochar oven for a client in Austin, Texas who operates a food waste and organic matter composting and up-cycling business.

With the second and third iterations we have incorporated a variety of design improvements based on experience operating the ovens.

Solar-powered biochar oven and control system. With this version the temperature controller is powered by a solar-PV rechargeable battery pack, so the system functions 100% off-grid.

In the previous article I mentioned some ongoing R&D items, including:

• Scale up for larger batch sizes (prototype batch reactor size is 20 gallons (75 liters).

• Possible to make pseudo-activated biochar for adsorption of organic chemical contaminants akin to high temperature gasifier biochar?

• Simple emission controls for offgassing pyrolysis vapors.

• Production of commercial units for sale to biochar enthusiasts? Inquire if interested…

I’m currently working on the emission control system - essentially an afterburner for combusting pyrolysis gases as they exit the chimney.

I also got some very promising preliminary results using feedstock pretreatments to achieve pseudo-activation conditions at modest pyrolysis temperatures:

Organics adsorption assay on chars made from hardwood sawdust pretreated with high pH solutions of wood ash, calcium hydroxide, or sodium hydroxide. Also, biochar made from hardwood sawdust pretreated with distilled/de-ionized (DI) water (control), and DI-water-pretreated biochar treated with sodium hydroxide and re-pyrolyzed. For comparison, the high temperature semi-aerobic gasification biochar (“GSB,” or “Gold Standard Biochar” as it is the most-studied bochar in the world for organics adsorption). Here, all feedstocks were pyrolyzed at 600 C.

In short, the data above indicate that pretreating feedstock with sodium hydroxide solution prior to pyrolysis at 600 C can generate an adsorbent with similar organics uptake as a semi-aerobic gasification biohcar produced at much higher temperature (900-1,000 C). Other base pretreatments of feedstock, e.g. calcium hydroxide, ash water, don’t work as well for facilitating pseudo-activation conditions during pyrolysis of hardwood sawdust, apparently. (For more info about base and metal cation pretreatments, see here, and our publications page.)

This is potentially a big breakthrough since the temperatures needed for thermal-air activation of biochar adsobents (>850 C) is really hard on equipment. For a simple, inexpensive drum oven thermal stresses wearing out equipment can be an acceptable cost, and in really low resource situations the high temperature gasifier method might be all that is feasible.

But if biochar adsorbent effective for uptake of organic chemical contaminants can be generated at 600 C, or even below 600 C, that is a really important result because oven components can withstand those comparatively modest temperatures much better than 900 or 1,000 C.

The results above also indicate biochars with moderate or poor organics adsorption (e.g. the “DI water” pretreated biochar above) can be upgraded by base treatment and re-pryolysis.

I demonstrated this dramatically as shown by the data below using a biochar made from recycled tires. The raw tire biochar had poor organics adsorption performance, and even leached color and odor into the water. But tire biochar treated with base and repyrolyzed (at 600 C) had some of the most impressive organics adsorption performance.

Tire biochar upgraded to better adsorption performance by treatment with base and repyrolyzed at 600 C.

SUMMARY

In summary, the solar/electric biochar oven is versatile in the range of materials and material properties it can produce. It can be run fully off-grid, or on-grid (Caminos intends to run theirs on-grid out of fear of theft of PV panels in their area).

N.B.: I have glossed over a bunch of details here intentionally. For a while I thought I might patent this design and classify it under intellectual property restrictions. I’ve thought about it and talked it through with some “experts,” and decided to release the design open-access under Creative Commons license.

I omitted details here because all that will be supplied in a forthcoming post illustrating the design, fabrication, and use of the solar biochar oven.

Fun with constructed wetlands

We often get asked:

“Will your (e.g., blue barrel) system work for gray water or wastewater/septage, or water sources impacted by gray water or wastewater?”

The answer to this question is:

“Probably not without pretreatment.”

The reason is that gray water, wastewater, sewage, and water sources impacted by these, contain a lot of solids, dissolved organic matter, and harmful pathogens such as E. coli.

If you pipe that water right into a gravel filter→sand filter→biochar adsorber treatment system, the whole system goes anaerobic (stinky and gross) and nasty microbes take over. It quickly becomes a messy failure.

Therefore alternative source water(s) should be sought. However, if your only choice is a water body impacted by sewage, gray water, livestock manure, etc., one option could be to use a constructed wetland to provide natural biological pretreatment to improve water quality to the point that it could be further treated in the gravel→sand→biochar system and then safely consumed.

Constructed wetlands use plants and aquatic organisms along with other natural physical and chemical processes such as hydrolysis, photolysis, and solar-UV inactivation to improve water quality.

At some point I will do a deep-dive summary of constructed wetlands for water quality improvement here. But for now, since I am always tinkering I’ll provide a thumbnail sketch of a mini constructed wetland approach I have been developing for treatment of duck wastewater.

Anybody who has raised ducks knows that they are messy. They poop everywhere! A lot! Especially in the water.

I’m actually grateful that they poop so much in their water tub, since I use the poopy duckwater to “fertigate” fruit trees and berry bushes and grape vines. The ducks are for fertilizer - the eggs are a bonus.

But I am always trying to find clever ways to get more out of our agroecosystems, and I can’t resist a try-it-and-see water project.

Here I have rigged up a 12 volt DC wastewater macerator pump (commonly used in RVs and marine applications) to suck up the poopy duckwater and pump it into a mini constructed wetland.

The pump is powered by the two PV panels shown in the photo above, and is controlled by a programmable DC controller unit wired up through the box on the wall.

I put a couple water hyacinth and water lettuce plants in the wetland tub a few weeks ago and they have started to multiply bigtime! (Note that these are invasive plants and so shouldn’t be used if there is a risk to a nearby water body).

The water hyacinth and water lettuce take up nutrients from the poopy duckwater. This partially cleans it before it flows by gravity back into the ducks’ water tub. Make-up water is supplied by gravity flow from rainwater tanks.

Ducks love to eat water hyacinth and water lettuce so I am using their wastewater nutrients to grow a portion of their food, thus cutting our feed costs.

I’m still working kinks out of the system to get it operating seamlessly. Once things are optimized and in steady-state I will do a water quality study to quantify how much actual improvement is happening.

Once I’m happy with everything I will do a detailed how-to write up and post it here in case people want to replicate or adapt the system.

It’s possible something like this could be used to pretreat poor quality source waters to get enough improvement to put through a gravel→sand→biochar system for producing potable water.

New installations and retrofits in Ecuador

The Ecuador team has been busy installing new water treatment systems. Here are a few photos from a recent (May 2025) installation in a Cofan (indigenous group) community:

The water source is the local Aguarico river.

This project is being carried out by the local women’s association, with funding from The Nature Conservancy and technical support from the Aqueous Solutions/Amisacho team based in Lago Agrio, northeastern Ecuador.

The treament system provides water to a central kitchen and bathhouse that serves the local Cofan community as well as an ecotourism guesthouse.

Tanks 1, 2, and 3 are gravel roughing filter, biological slow sand filter, and carbon adsorber, respectively.

Tanks 4,5 and 6 store treated water. Tank 4 stores water that has passed through all three filters. This water is used for direct consumption: drinking, cooking, washing vegetables, etc.

Tanks 5 and 6 store water that has passed through the gravel and sand filters but bypassed the carbon adsorber. This water is used in showers, baths, handwashing sinks, and other domestic uses.

The Ecuador team has made very good use of this “tiered treatment” approach in our projects there - i.e., treating water to an appropriate level for its intended use. Whether locally made biochar or imported activated carbon is used in the carbon filter-adsorber, this unit process is often the most costly on a per-liter basis. The carbon adsorber can be made much smaller - and therefore less costly and labor-intensive - if it’s just used for directly consumed water.

Or, put another way, treated water of adequate quality for non-consumptive domestic uses can be provided at modest additional cost to providing drinking water.

LEFT: constructing the concrete foundation for the treatment system. RIGHT: water tanks and other project materials were transported to the village by canoe.

LEFT: Washing sink installed in central kitchen with taps (water not treated by carbon adsorption) and gray water drain. RIGHT: Kitchen taps for water treated by carbon adsorption for drinking and cooking.

LEFT: Gray water from kitchen piped away for “fertigation” of fruit trees. RIGHT: Drinking water tap installed in common area.

LEFT: Plumbing connected for showers and handwashing sinks. RIGHT: Clothes washing station.

May 24, 2025: Carlos, the local technician elected by the women’ association, explains the function and maintenance of the treatment system.

RETROFITS OF DISUSED INFRASTRUCTURE

Over the years, many thousands of water systems have been installed in communities throughout the Ecuadorian Amazon. Unfortunately, many of these systems are poorly designed. They often fail, and are abandoned by locals.

A well built but poorly designed water system, sitting unused by the local community.

A new direction our work is taking us is the redesign and retrofit of disused and abandoned water infrastructure. What’s great about this is that a lot of the expensive stuff is already done - the nice towers shown in the photo above for example. The water tanks, piping, etc. are usually fine, just not configured properly, or not configured optimally.

So for a fraction of the time, labor, and cost of building a new system from scratch we can reconfigure existing infrastructure to make it work well, and add features - such as biochar adsorption for control of chemical contaminants - that existing systems lack.

Thank you again for your interest in our work. Detailed write-ups on these and other topics coming soon.

Ecuador

In this short video he describes their experience of the earthquake (no damage or injuries at their location), and the work he and others are doing at a self-reliance center near Bangkok to prepare for crises. He highlights projects in water security - water collection and storage in swales, ponds, and in cisterns made from bamboo reinforced concrete, and water treatment using charcoal/biochar and other techniques. He also highlights the team’s efforts in food security.

We’re using our contacts in the region to help get aid into affected areas. More to come…

The answer, generally, is “Yes, biochar can probably be made to work…” There are several questions that have to be answered, though, such as:

• What kind of biochar (how was it made and from what material)?

• What background water characteristics influence removal of the target pollutant(s) such as pH and the type and concentration of dissolved organic matter (DOM)?

• How much biochar is needed (i.e., how large of a biochar contactor), and how often does the biochar need to be refurbished? How do these factors figure into the feasibility and economics of biochar water treatment?

• In a relative sense, how difficult is biochar adsorption of the specific pollutant(s) of interest relative to select chemical pollutants that we have extensively studied and used as the basis for treatment systems design and operation?

The new open-access tool described in this article addresses the last question. In other words:

“How can we know if biochar adsorption is expected to be a good option for removing your chemical(s) of concern from water?”

Creation of this tool was inspired by our correspondent and friend, Mr. Wilfrid from the island of Guadeloupe. From Wilfrid we learned that Guadeloupe has a major contamination issue from the use of chlordecone insecticide, primarily on banana plantations.

Chlordecone is a serious threat to human and environmental health and has been banned in most countries. All those carbon-chlorine bonds make it an environmentally persistent organic pollutant, so there are major ongoing cleanup challenges associated with chlordecone’s legacy of pollution.

Wilfrid wrote to inquire whether biochar adsorbent would work for removing chlordecone from water sources in Guadeloupe. We hadn’t worked specifically with chlordecone in the past, so I needed a way to answer Wilfrid’s question.

That led to the development of the tool described here - to leverage the large datasets we have collected over the years on biochar adsorption of many different compounds and develop a basis for comparison with chlordecone. In other words:

Compared to chemical pollutants we have studied extensively, would we expect chlordecone to be easier or more difficult to remove by biochar adsorption?

And if we develop a method to answer this question for chlordecone, it could in principle be applied to any organic chemical pollutant of interest.

We will return to chlordecone and Mr. Wilfrid’s question at the end of this article. First I will explain how the tool works and provide a link for you to download Version 1.0 and take it for a test drive inputting your own chemical pollutant(s) of concern.

Adsorbate Comparison Tool

[Definition: the adsorbate is the substance that gets adsorbed to the surface of the adsorbent.]

The objective of this tool is to generate a relative ranking based on the degree of difficulty of removing a variety of organic chemical adsorbates from water by biochar.

With this relative ranking established, a particular chemical pollutant of interest can be placed in that ranking to give a first approximation of its difficulty of removal by biochar adsorption, compared with other chemicals of concern in water sources.

For example, if your pollutant of interest is an herbicide, how difficult would we expect it to be to remove from water using biochar compared with other common herbicides? And especially, compared with herbicides for which we have collected extensive biochar adsorption datasets?

The Adsorbate Comparison Tool was developed primarily from a study we published a few years ago:

Kearns JP, Kennedy AM, Shimabuku KK. Models for predicting organic micropollutant breakthrough in carbon adsorbers based on water quality, adsorbate properties, and rapid small-scale column tests. AWWA Water Science, Vol. 4, Is. 2, April 2022.

I wrote a “Cliff’s Notes” version of the article for this Substack if you’d like to read more:

To create the Adsorbate Comparison Tool, I used one of the biochar adsorption models we developed in that paper to make predictions about the difficulty of removing a wide range of organic chemical water pollutants.

The model utilizes physical-chemical characteristics of target pollutants which can be readily obtained for free from online databases. Specifically, the model uses Abraham Solvation Parameters. Without going into detail, Abraham Solvation Parameters describe a variety of solute-solvent or solute-surface interactions. (If you would like more specifics, see the “Cliff’s Notes” article linked above.)

To use the Adsorbate Comparison Tool, you simply cut-and-paste Abraham Solvation Parameters for your compound of interest from an online source into the MS Excel based calculation tool. You can then view how your compound ranks in its degree of difficulty for removal from water by biochar adsorption.

Caveat/Disclaimer

Predictions about the adsorbability of different organic compounds is based on an adsorption model. Remember: all models are wrong; some models are useful. Predictions made using the Adsorbate Comparison Tool are not meant to be the definitive final word on the treatability of pollutant(s) using biochar. Rather, the Tool provides decision support to aid in the design and operation of biochar water treatment units. Ultimately the operator is responsible for water quality/safety. Predictive models such as the one embedded in the Adsorbate Comparison Tool should not be over-relied upon. Monitoring and evaluation of biochar water treatment units is always recommended to verify water quality.

How to use the Adsorbate Comparison Tool

You will need MS Excel to run this tool. Click here to download:

Adsorbate Comparison Tool Ver01

580KB ∙ XLSX file

Download

Download

Note: This is Version 1.0 of the Tool. As we continue to make refinements, and incorporate user feedback, subsequent Versions will be uploaded with a notation log regarding changes.

To illustrate how to use the tool, I have selected the insecticide imidacloprid as an example compound of interest.

Imidacloprid happens to be my favorite pesticide. Not because I am in love with chemical pesticides (quite the opposite). But because while doing pesticide surveys in West Bengal, India, in 2007 I came across this in a rural ag supply shop:

Step 1

Search for your compound in the PubChem database.

Step 2

Highlight and copy the SMILES code for your compound.

Step 3

Paste your SMILES code into the AbraLlama pediction app and click “Predict.”

Step 4

Highlight and copy the calculated Abraham Solvation Parameters.

Step 5

Type or paste the compound name, SMILES code, and Abraham Parameters into this table in the Adsorbate Comparison Tool (located on the right side of the worksheet “INSTRUCTIONS” tab).

Step 6

Click the “RESULTS” tab to view your results.

Interpretation of results

Model prediction results appear as a series of “pinwheel” plots on the “RESULTS” worksheet. For our example compound imidacloprid the following plots are shown:

The green pinwheel plot indicates where your test compound’s predicted adsorbability falls relative to a list of 40 common agrichemicals.

These 40 agrichemicals are compounds for which the US EPA has established regulatory values for drinking water, and/or the World Health Organization (WHO) has established Guideline Values for drinking water.

As you go around the pinwheel from the top in a clockwise direction, compounds are predicted to be more strongly adsorbing to biochar (i.e., in order of decreasing difficulty for removal by adsorption). Conversely, as you go around the pinwheel from the top in a counterclockwise direction, compounds are predicted to be less strongly adsorbing to biochar and therefore more difficult to remove by adsorption.

Compounds indicated by bold text/color are select “Sentinel Chemicals” - compounds of particular focus in our biochar adsorption research, and upon which we base much of our design and operation specifications for biochar water treatment systems. Here, the herbicides 2,4-D and simazine are highlighted as Sentinel Chemicals in the agrichemical compound class.

The model predicts that imidacloprid is slightly easier to adsorb on biochar than simazine, and significantly easier to adsorb than 2,4-D. We can infer, then - with due caution as stressed in the disclaimer above regarding over-reliance on model predictions - that a biochar water treatment system design to provide high levels of removal for 2,4-D and simazine would be expected to also provide high levels of removal of imidacloprid.

Note also that a compound’s difficulty of removal by biochar adsorption is relatively proportional to the area shown on the pinwheel plot. The predicted most difficult-to-adsorb agrichemical on the list is glyphosate (RoundUp). It is predicted to be so weakly adsorbing that it takes up a large proportion of the pinwheel plot, compressing the rest of the plot and making it more difficult to interpret. Therefore glyphosate has been omitted from the plot for clarity. Just bear in mind that glyphosate is predicted by this model to be very difficult to remove by biochar adsorption! Also, I anticipate that many users will be interested to make their own predictions for RoundUp as it is one of the most well known (and notorious) agrichemicals. (Perhaps I should dedicate a future post for another day just to discussing “What to do about RoundUp?”…)

The purple pinwheel plot indicates where your test compound’s predicted adsorbability falls relative to a list of 20 widely studied perfluoroalkyl substances (PFAS).

Sentinel PFAS perfluorobutane sulfonate (PFBS) and GenX are shown in bold type/color.

The model predicts imidacloprid to be slightly more strongly adsorbed on biochar than GenX, and substantially more strongly adsorbed on biochar than PFBS. Thus (with appropriate precautions) a biochar water treatment system designed for high levels of removal of PFBS and GenX would also be predicted to achieve high levels of removal of imidacloprid.

The blue pinwheel plot indicates where your test compound’s predicted adsorbability falls relative to a list of 42 industrial compounds, flame retardants, and plasticizers of concern to drinking water quality. The industrial chemicals on this list are compounds for which EPA and WHO have established regulatory or guideline values.

Sentinel flame retardant/plasticizer tris 2-chloroethyl phosphate (TCEP) is barely visible as a dark blue line near the top of the pinwheel plot. The example adsorbate imidicloprid is indicated by the yellow wedge near the top of the plot.

For this list of industrial compounds, the model predicts that 28 compounds are more difficult to remove by biochar adsorption than imidacloprid, and that imidacloprid is predicted to be more difficult to remove than Sentinel compound TCEP.

Thus a treatment system design to achieve acceptable levels of TCEP removal might not be adequate for controlling imidacloprid, along with many other industrial organic chemical pollutants.

It bears noting that many of these weakly adsorbing industrial compounds are very small molecules - this in part explains why they are difficult to remove by adsorption, as adsorption acts by nonspecific attractive forces between matter (van der Waals forces). A bit larger molecule, such as imidacloprid, simply has more mass to be attracted to the biochar surface.

If small and weakly adsorbing molecules like the ones shown in this list are at issue, then it could be necessary to design a biochar water treatment system specifically with these compounds in mind. It is most likely possible to design a biochar treatment unit that would work for these compounds, however it would be larger in size and require more frequent refurbishment of the adsorbent than in our “base model” treatment system designs. This could incur elevated costs and/or logistical challenges that might preclude feasibility.

The gray pinwheel plot indicates where your test compound’s predicted adsorbability falls relative to a list of 32 compounds that have been designated by the Stockholm Convention on Persistent Organic Pollutants (POPs) - which aims to eliminate or heavily restrict the manufacture and use of such chemicals due to environmental and human health concerns.

If the industrial chemicals pinwheel plot represents “bad news” of many substances being harder to adsorb by biochar than our example compound imidacloprid, then this plot reveals some “good news.” Namely, that compared with the Stockholm list of POPs, imidacloprid is predicted by the model to be more difficult to adsorb on biochar than all of the Stockholm listed POPs.

Thus, a biochar water treatment system designed to achieve high levels of imidacloprid removal is predicted to also achieve high levels of removal of the Stockholm Convention POPs.

The orange pinwheel plot indicates where your test compound’s predicted adsorbability falls relative to a list of 41 common pharmaceuticals and personal care products (PPCPs) of concern to water quality globally. These compounds are often detected in wastewater and water bodies impacted by wastewater (from humans and livestock).

Sentinel pharma compounds sulfamethoxazole and carbamazepine are shown in bold text/color.

The model predicts imidacloprid to be more strongly adsorbing than sulfamethoxazole, but more difficult to adsorb on biochar than carbamazepine. Thus a biochar treatment unit designed to achieve high levels of removal of sulfamethoxazole is predicted to also achieve high levels of removal of imidacloprid (and also carbamazepine).

Identifying compounds of potential concern in drinking water sources

You might already have a list of potential water contaminants you want to run through our predictive Adsorbate Modeling Tool.

On the other hand, if you feel lost about where to start in identifying potential contaminants of concern, one starting place could be in this review paper (and its supplemental information) I published a few years ago:

Kearns JP, 2020. The role of chemical exposures in reducing the effectiveness of water-sanitation-hygiene (WASH) interventions in Bangladesh, Kenya, and Zimbabwe. Wiley Interdisciplinary Reviews – Water, Vol. 7, Is. 5.

In this study I provided lists of compounds belonging to several classes - agrichemicals, PFAS, industrial compounds, flame retardants, plasticizers, pharmaceuticals and personal care products, etc. - demonstrated to impact water sources around the world. I also provided some accompanying information on human and environmental toxicity as a framework for helping implementers in the WASH (water-sanitation-hygiene) sector prioritize possible drinking water contaminant threats.

Chlordecone and Wilfrid’s question

Now we’re ready to answer Wilfrid’s question about whether biochar adsorption could be effective for remediating chlordecone impacted waters in Guadeloupe.

To reiterate: our exercise here uses a predictive model, and “all models are wrong…” The purpose of the Adsorbate Comparison Tool is to provide a first-level insight - a “scientific educated guess” - about whether a particular compound (chlordecone in this case) would be expected to be a more difficult challenge or a less difficult challenge to remove from water using biochar than other chemicals for which we have large datasets and comparatively a lot of experience with.

With that disclaimer in mind, following Steps 1-6 outlined above, we get the following results for chlordecone:

What happened?!!?!?!?

The model predicts that chlordecone is significantly more strongly adsorbing to biochar than most of our comparison compounds shown on the pinwheel plots. On all the plots except for the Stockholm POPs, you really have to squint to make out chlordecone’s tiny wedge at to top of the pinwheels.

Chlordecone’s wedge is more obvious on the Stockholm POPs pinwheel plot - in fact, chlordecone is already listed in the Stockholm Convention (number 21 on the list in the gray box above), so it was already present in that plot (although its wedge was not labeled due to space constraints).

So - with all caveats and disclaimers and precautions in mind - biochar water treatment is predicted to be a viable option for chlordecone removal. Chlordecone is predicted to be less difficult to remove from water than our Sentinel Compounds, upon which most of our treatment system designs are based.

Perhaps Wilfrid will welcome this as good news for the people of Guadeloupe?

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One of the main reasons for this - a reason, not an excuse (and I do commit to doing better in the future) - is a project I have been working on over the past 5-6 months to make biochar using only sunlight as a power source.

I was far from sure that I could get it to work. And I spent a lot of time feeling foolish and banging my head trying to solve various problems, remedy headaches, find and fix failures, etc.

And if I could get it to work, I wasn’t exactly sure what I was going to do with that information. And I’m still not sure.

For going-on-twenty-years-now every discovery I have ever made, every method or technique or tool I have ever developed, I have given away completely for free. If I thought it could be useful to others I gave it away in the form of internet resources, how-to videos, instruction manuals, journal publications. I have given countless lectures by remote and in-person workshops in locations around the world. I’ve answered questions by email and phone and fully described the state-of-the-science to the best of my ability at the time, holding nothing back.

But this time, it might be different. This might be an innovation worth patenting. I’m actually contemplating engaging a concept I have actively run away from all these years - intellectual property. (I still shudder as a I type those words…)

I don’t know yet where all this is going. This is new territory for me and I am figuring it out as I go. But at least for now I’ve decided to cram a lid onto my first impulse to Tell Everyone About This Awesome New Innovation and All About How It Works, Because It Is Just So Cool!

(If we decide to go the I.P./patent route, it’s not to hog all this coolness for ourselves. It’s because that might be the method that makes the most sense for spreading the potential benefits of this innovation far and wide. That’s what we’re trying to resolve right now…)

After several months of trial-and-error, last month I started getting some really promising results. So as not to bury the lede, a duly circumspect overview of my solar biochar prototype is posted just below (in this demonstrative case, for making bone char).

I feel guilty for having to hold back on the details of this invention at least for now. I’m so grateful to the subscribers, readers, and commentors who have shown so much support and enthusiasm for our work here. Since I have to keep some current R&D work under wraps for a bit, which is giving me pangs of guilt, I decided to create a new section of this site as a clearing house for our Open Access Materials.

In the new Open Access Materials section you’ll find graphical how-to manuals for setting up decentralized water treatment systems, a selection of video resources that offer instructionals and insights to some of our field projects, a bibliography of peer-reviewed publications, and other sundry practical materials.

(N.B.: Much of what is currently posted in this section will be familiar to readers who have encountered the website and projects of our non-profit Aqueous Solutions. New open access materials will be publicized here as they are produced, typically tied with project profiles in the Field Noteboook section.)

Also coming soon…

We have updates about new workshops and water system installations in Ecuador as well as the Guardianes del Agua (Water Guardians) game.

We’re just about to break ground on the sorbent regeneration facility Caminos de Agua is building to refurbish exhausted bone char for re-use in fluoride removal systems. The bone char/fluoride system economics are such that without sorbent regeneration this treatment method would not be feasible from a cost perspective. I’ll be posting updates from facility design and construction during the build.

We have also had some recent major advancements in our workshop/laboratory construction project here at biochar water treatment HQ. I might create a whole new section on this site to showcase key elements of our design-and-build. We’re incorporating a bevvy of eco-groovy design elements…

Without further ado…

Solar biochar/bone char

For context and to provide a baseline for comparison, here’s the method we have been using to make bone char for water treatment to remove excessive fluoride:

The bottom drum is operated as a high temperature (>900 C) gasifier for making wood-based biochar for removal of organic chemical contaminants, analogous to activated carbon. The heat from that process carbonizes a retort drum full of bones into bone char.

While the biochar bed in the lower gasifier drum can reach 900-1,000 C (or higher), the temperature the bone char retort is exposed to is wood gas flame temperature, around 600 C, from combustion of the pyrolysis gases given off by the wood in the lower drum. This is important since the optimal pyrolysis temperature for making bone char sorbent is 450-650 C. Overheating bone char results in a rapid destruction of fluoride sorption capacity.

The disadvantages of the above-described system include:

• The fuel source required to provide the heat energy for charring bones (here, wood) is an additional cost in labor and materials (e.g., chopping and drying the wood to prepare for gasification), and may exert undesirable environmental impacts (e.g., in central Mexico where Caminos operates wood is scarce)

• For safety and for proper operation the gasifier must be continuously monitored. After the first gasifier drumload of wood is finished, operators must move the hot bone retort and chimney drum to a second gasifier to continue the burn, which is a safety risk.

• Burn duration, maximum temperature, and temperature variability inside the bone retort during pyrolsyis are somewhat difficult to control. Given a consistent gasifier feedstock source, a skilled artisan can achieve moderate reproducibility in thermal conditions and fluoride sorption properties between batches.

Compare with this:

Solar panels wired to a drum oven.

Because of the potential I.P./patent concerns expressed above I can’t say how this works right now. But I can say that this photo was taken during an early prototype test on a mid-September afternoon at around 36 degrees North latitude. Within 2 hours the temperature in the reactor reached 530 C.

That was a promising start, but there were a number of problems and hangups and fails to resolve with the system (which also included repairing damage done by Hurricane Helene…)

By December I had made significant advancements and had succeeded in resolving a few rounds of troubleshooting.

December, however, brought its own set of challenges for solar biochar/bone char innovation - including shorter days, a lower sun angle, more frequent overcast conditions, lower ambient temperatures, and the occasional need for snow removal.

Despite proximity to the winter solstice, on clear sunny days the system was able to attain and hold excellent thermal conditions for making bone char sorbent. For example:

kLux is a measure of sunlight intensity falling on the PV panels. The bottom plot shows temperature within the pyrolysis reactor. A control system (thermostat) was used to keep the temperature just below 500 C. On the day these data were collected the average ambient temperature was 33 F with a high of 49 F and a low of 17 F.

Even on a December day at temperate latitude the system was able to maintain 500 C for about 4 hours. These are excellent pyrolysis conditions for making bone char sorbent for fluoride removal.

Preliminary data indicate our solar bone char substantially outperforms two commercially available bone chars for fluoride removal from groundwater:

In summary…

• Process uses sunlight falling on PV panels to provide the energy to drive pyrolysis - and thus does not require wood or other biomass fuel, propane, etc.

• High precision temperature control is achieved. A suitably sized PV array can provide ample power even when skies are partly cloudy or overcast.

• Labor inputs are simplified and reduced. Feedstock is added to the reactor, the thermostat is set, and the reactor is switched on. The reactor can be shut off at any time, or allowed to cool naturally after sunset.

Ongoing R&D…

• Scale up for larger batch sizes (prototype batch reactor size is 20 gallons (75 liters).

• Possible to make pseudo-activated biochar for adsorption of organic chemical contaminants akin to high temperature gasifier biochar?

• Simple emission controls for offgassing pyrolysis vapors.

• Production of commercial units for sale to biochar enthusiasts? Inquire if interested…

Thank you again for your ongoing support and enthusiasm for our work! I will do better about providing regular updates here. Your support and encouragement is a major assist to our ongoing R&D and field service projects!

More to come soon…

Webinar hosted by the Centre for Affordable Water and Sanitation Technology (CAWST): “Biochar adsorbent for control of synthetic organic contaminants in affordable decentralized water treatment”

“Make your own water filter and never buy drinking water again” ::: A practical guide to setting up a “blue barrel system” by Jon Jandai of Pun Pun Pun Pun Center for Self-Reliance (northern Thailand).

Self-Reliant Water Treatment in 5 minutes and 12 seconds (Thai language, English subtitles) ::: A humorous short video with narration and animation describing the water treatment system at Pun Pun Center for Self-Reliance (northern Thailand).

Questions about the water system at Pun Pun…Pi Jo answers some FAQ…

Pi Jo’s tutorial on making gasifier charcoal/biochar…

Making gasifier biochar for decentralized water treatment ::: An English language video explaining the theory of biomass gasification and step-by-step instructions for fabricating and operating a 200 L (55-gal) drum gasifier.

Kearns JP, Gropper, A, Muñoz JL, and Yepéz P. 2023. Adaptable community participatory design to provide water that is Estético, Seguro, y Saludable (pleasant, safe, and healthy) in the Ecuadorian Amazon. Water Security 20, 100150.

Kearns JP, Kennedy AM, Shimabuku KK. Models for predicting organic micropollutant breakthrough in carbon adsorbers based on water quality, adsorbate properties, and rapid small-scale column tests. AWWA Water Science, Vol. 4, Is. 2, April 2022.

Aung MT, Shimabuku KK, Soares-Quinete N, Kearns JP. Leveraging DOM UV absorbance and fluorescence to accurately predict and monitor short-chain PFAS removal by fixed-bed carbon adsorbers. Water Research, Vol. 243, April 2022.

Bentley MJ, Kearns JP, Murphy BM, Summers RS. Pre-pyrolysis metal and base addition catalyzes pore development and improves organic micropollutant adsorption to pine biochar. Chemosphere, Vol. 286, Part 3, January 2022.

Thompson MP, Kearns JP. 2021. Modeling and experimental approaches for determining fluoride diffusion kinetics in bone char sorbent and prediction of packed-bed groundwater defluoridator performance. Water Research X, Vol 12., August 2021.

Kearns JP, Mulhern RE. 2021. Achieving safe drinking water and clean cooking for all. The Lancet – Global Health, Vol. 9, Is. 6, e755.

Kearns JP, Dickenson E, Aung MT, Joseph SM, Summers RS, Knappe DRU. 2021. Biochar Water Treatment for Control of Organic Micropollutants with UVA Surrogate Monitoring. Environmental Engineering Science, Vol. 38, No. 5.

Kearns JP, 2020. The role of chemical exposures in reducing the effectiveness of water-sanitation-hygiene (WASH) interventions in Bangladesh, Kenya, and Zimbabwe. Wiley Interdisciplinary Reviews – Water, Vol. 7, Is. 5.

Kearns JP, Dickenson E, Knappe DRU, 2020. Enabling organic micropollutant removal from water by full-scale biochar and activated carbon adsorbers using predictions from bench-scale column data. Environmental Engineering Science, Vol. 37, Is. 6.

Kearns JP. 2019. Moving towards transformational WASH. The Lancet – Global Health, Vol. 7, Is. 11, pp. e1493.

Kearns JP, Bentley MJ, Mokashi P, Redmon JH, Levine K. 2019. Underrepresented groups in WaSH – the overlooked role of chemical toxicants in water and health. Journal of Water, Sanitation and Hygiene for Development, Vol. 9, Is. 4.

Kearns JP, Shimabuku KK, Knappe DRU, Summers RS. 2019. High Temperature Co-pyrolysis Thermal Air Activation Enhances Biochar Adsorption of Herbicides from Surface Water. Environmental Engineering Science, Vol. 36, Is. 6.

Kearns JP, Krupp AS, Hartman S, Szogas K, de Boskey M, Harrington JM. 2019. Evaluation of arsenic field test kits as a learning exercise for engineering students in global water and sanitation class. International Journal for Service Learning in Engineering: Humanitarian Engineering and Social Entrepreneurship. Vol. 14, No. 1, pp. 32-46.

Kearns JP, Krupp A, Diek E, Mitchell S, Dossi S, Hartman S. 2018. Lead-lag series and staged parallel operational strategies improve the performance and cost-effectiveness of bonechar for control of fluoride in groundwater. Journal of Water, Sanitation and Hygiene for Development, Vol. 8, Is. 4, pp. 777-784.

Thompson KA, Shimabuku KK, Kearns JP, Knappe DRU, Summers RS. 2016. Environmental comparison of biochar and activated carbon for tertiary wastewater treatment. Environmental Science & Technology, Vol. 50, 11253-11262.

Shimabuku KK, Kearns JP, Martinez J, Mahoney RB, Moreno-Vasquez L, Summers RS. 2016. Biochar sorbents for sulfamethoxazole removal from surface water, stormwater, and wastewater effluent. Water Research, Vol. 96, pp. 236-245.

Kearns J, Knappe DRU, Summers RS. 2015. Feasibility of using traditional kiln charcoals in low-cost water treatment: The role of pyrolysis conditions on 2,4-D herbicide adsorption. Environmental Engineering Science, Vol 32, No. 11, pp. 912-921.

Kearns J, Shimabuku KK, Mahoney RB, Knappe DRU, Summers RS. 2015. Meeting multiple water quality objectives through treatment using locally generated char: improving organoleptic properties and removing synthetic organic contaminants and disinfection by-products. Journal of Water, Sanitation and Hygiene for Development, Vol. 5, Is. 3, pp. 359-372.

Kearns J, Knappe DRU, Summers RS. 2014. Synthetic organic water contaminants in developing communities: an overlooked challenge addressed by adsorption with locally generated char. Journal of Water, Sanitation and Hygiene for Development, Vol. 4, Is. 3, pp. 422-436.

Kearns J, Wellborn LS, Summers RS, Knappe DRU. 2014. 2,4-D adsorption to biochars: Effect of preparation conditions on equilibrium adsorption capacity and comparison with commercial activated carbon literature data. Water Research, Vol. 62, pp. 20-28.

Huggins T, Wang H, Kearns J, Jenkins P, Ren ZJ. 2014. Biochar as a sustainable electrode material for electricity production in microbial fuel cells. Bioresource Technology, Vol. 157, pp. 114-119.