ADVANCES IN BIOCHAR RESEARCH: CARBON SEQUESTRATION, HARMFUL ALGAL BLOOMS, AND URINE DIVERSION
By Ken Carloni
Readers of this newsletter will recall a number of articles I’ve written over the last several years on the subject of biochar. I’d like to update you here on the progress of ongoing testing and experimentation in the production and use of this fascinating substance.
For those unfamiliar with biochar, it is a type of charcoal made by heating biomass to 450 to 550oC (850 to 1025OF) in kilns that maintain a low oxygen environment. In contrast to combustion, this process is known as pyrolysis and is the same thing that happens when you damp your wood stove down too tightly at night – lots of heat with little oxygen yields lump char in the morning. Pyrolysis converts the carbon in woody biomass into a highly stable form that sequesters it for centuries. It becomes biologically active in the soil, promoting plant growth and more carbon capture through increased photosynthesis.
Flame Curtain Kiln Testing: Ryan Thompson of Mt. Air Engineering positions a probe for measuring emissions over the plume of a biochar kiln. Moisture and carbon in the feedstock were measured before each burn, and samples of the resulting char were sent to a lab for testing.
Biochar Bag: This bag full of biochar is undergoing testing before being deployed in a freshwater pond to mitigate harmful algal blooms.
In this article, I will report on:
- Measurements of carbon sequestration and avoided emissions in flame curtain kilns.
- The use of biochar to adsorb nutrients from freshwater bodies to reduce harmful algal blooms (HABs).
- The use of biochar to capture and recycle nutrients from urine and convert urea into harmless nitrogen gas.
Carbon Sequestration: In Oct. 2023 and again in Oct. 2024, a team including an emissions engineer, sawyers, and I traveled to Martha’s Vineyard to test a flame curtain kiln I designed to be modular, highly portable, scalable, and easily assembled and disassembled in rough terrain without tools. We compared 11 kiln burns using fuels with varying moisture content to 4 open burns. We measured the emissions produced and had the feedstock analyzed in a certified lab before each burn and the resulting char afterwards to assess the quantity and quality of carbon.
We found that green feedstock resulted in approximately 30-40% of its carbon sequestered in the char, while char from seasoned feedstock sequestered 40-50% of feedstock carbon. Although the 2024 emissions data are still being analyzed, emissions from our first round of tests showed that converting woody biomass to biochar in a flame curtain kiln cuts emissions roughly in half compared to open burn piles.
This is the first tightly controlled study of flame curtain kiln efficiency conducted anywhere in the world, and we hope to publish these results soon. These data will then be used to access carbon markets to provide the funds necessary to pay for this important ecosystem service.
Mitigating Harmful Algal Blooms (HABs): In April, I will again travel to Martha’s Vineyard (MV) to install biochar bags in a small pond (~1.3 ac.) that is plagued with HABs every summer. Because soils in Cape Cod, Long Island, MV, and Nantucket are composed of deposits from glaciers active during the last ice age (~120,000 to 11,500 years ago), they are extremely porous mixtures of sand and gravel. Groundwater laden with nutrients from farms and septic systems can therefore flow for long distances before entering natural water bodies.
The pond we have chosen is an ideal test site for our project – it has a nearby well where we can test nutrients in the groundwater as they feed into the pond, and just one point of outflow where we will test the water after passing by bags of biochar secured in salvaged lobster traps (of course!). Because biochar has a large surface area (one gram of our char has a surface area nearly the size of a tennis court) and has a strong electrochemical attraction to dissolved nutrients, we hypothesize that our char will act as a “reverse tea bag” to pull those nutrients out of the water. Once we determine the capacity of biochar to remove the nutrients that drive HABs, we will get a better idea of the mass of char necessary to drop nutrient levels in a given volume of water to below HAB thresholds.
Closer to home, I am also working with researchers from the Univ. of Oregon and the Univ. of Nebraska on a National Science Foundation grant proposal to use biochar bags to mitigate the HABs that foul Tenmile Lake on the Oregon coast every summer (if DOGE doesn’t pull the funding). As part of that project, I am currently working with Dr. Mick Davis, a physics professor at Umpqua Community College, to design and test an environmental gas analyzer to measure the activity of denitrifying microorganisms that remove dissolved nitrogen from the water and convert it into harmless nitrogen gas.
Urine Diversion: As noted above, SE Mass. and the Islands have very porous soils, and the best solution to groundwater contamination is to keep nutrients out of the soil in the first place. Since 70-80% of the nitrogen that comes out of humans is in the form of urea, a system to divert urine from the waste stream could greatly decrease groundwater contamination at a relatively small expense. Significant amounts of phosphorus, potassium, and other HAB-promoting nutrients are also produced in urine, and biochar charged with these nutrients can be used to recycle them back into agricultural soils.
U2N2 Bioreactor: Urine is introduced into the funnel at the top and travels to the bottom of the barrel. It then passes up through biochar where nutrients are adsorbed onto the biochar substrate. One guild of bacteria breaks the urea down to ammonium which is then converted to nitrite and then nitrate by two other guilds of bacteria. Denitrifying bacteria then convert the nitrate to harmless nitrogen gas (N2).
On my way to MV in April, I will stop at a lab on Cape Cod (the Massachusetts Alternative Septic Testing Center) to test a bioreactor that will physically remove phosphorus and other HAB-inducing nutrients from human urine by adsorption to biochar while biologically converting urea to nitrogen gas (dubbed “U2N2”). We will use the gas analyzer mentioned above to continuously monitor nitrogen and other gas production as microbes process urea. Once we have proof of concept, we will look to scale up the process in SE Mass and other areas with groundwater contamination issues.
When results from these tests and experiments become available, I will share them with you in the pages of the 100 Valleys – stay tuned!
