Biosolids TOPICs: Interesting Ideas Connected to the World
Say YES! to Biosolids Carbon Storage
Mark sat across from me finishing off his lunchtime appetizer of pea soup and main dish of goulash and spaetzle with a dessert of chocolate pecan pie. “I just twitch my elbow and I will burn off this pie, so fast is my metabolism. That’s the thing with me, the more fuel I put in the tank, the faster I burn.” His girlfriend, Laura, visibly annoyed, replied: “Let me have just one bite, but it is going straight to my hips, and I don’t need that.” I mused over the inexplicably different pathways of food in the human body; how can pathways of carbon energy be so different, with one “good” (like Mark’s muscle burn) and one “bad” (like Laura’s belly fat storage)?
I would like to flip this judgment: storage is good and burning is bad. When given the chance, I like to explain that biosolids is well-balanced nutrition for the soil, full of carbon energy and nutrients, containing every trace element necessary for plant and soil microbe health. As biosolids managers, we get to choose the end goals and the pathways to get there. Do we want to blow the biosolids carbon through processes that extract energy and release it as atmospheric carbon? Or, do we instead direct biosolids carbon to storage in the soil?
You would think all soil scientists would jump at the soil storage option. Nevertheless, keeping biosolids carbon away from the soil seemed the message from a recent “biosolids webinar” sponsored by the Pennsylvania Farmers Union. The guest scientist was Cornell’s Murray McBride, who poured through his litany of concerns (see Case for Caution Revisited), including familiar elements like molybdenum and less familiar ones like thallium, including familiar fears of persistent pollutants, and including familiar concerns like excess nutrients. The bottom-line message from McBride was that we should apply the precautionary principle to soil management, in which case farmers would avoid biosolids.
I, of course, hold the entirely opposite view. That is, wise soil management demands use of biosolids. I am compelled by the message of a large group of scientists that the urgent need is to restore soil carbon. I hold that biosolids recycling to soil is a valuable climate change mitigation measure.
You may have noted the cosmic irony that the report of World Scientists’ Warning of a Climate Emergency came literally one day after the media attention to the U.S. submittal of paperwork to withdraw from the Paris climate accord (On the U.S. Withdrawal from the Paris Agreement). The statement, ratified by 11,000 scientists, says “We should leave remaining stocks of fossil fuels in the ground,” while Secretary Pompeo’s press release says the U.S. approach “uses all energy sources and technologies cleanly and efficiently, including fossils fuels.” Importantly, the scientists assert that “an immense increase of scale in endeavors to conserve our biosphere is needed to avoid untold suffering due to the climate crisis.” Efforts, they say, should include “natural climate solutions [NCS].” A recent article on Natural climate solutions says “NCS offer a powerful set of options for nations to deliver on the Paris Climate Agreement while improving soil productivity, cleaning our air and water, and maintaining biodiversity.”
NCS is an opportunity for the wastewater industry. As environmental professionals, we can choose to use biosolids projects that lock ourselves into infrastructure and programs that sequester biosolids carbon in soil and support NCS.
Do we know that the carbon in biosolids can be sequestered? The science of soil organic matter is complicated, and the fate of biosolids-borne carbon is especially so. The study Soil Carbon Sequestration Resulting from Biosolids Application offers this challenge: “there is still limited knowledge on soil sequestration mechanisms of biosolids-borne C or the main factors influencing this capacity.”
Nevertheless, a clear and affirmative answer is emerging. A scan of Google Scholar reveals an impressive record of evidence that biosolids benefits soil carbon. The journal article Relationship Between Mineral Soil Surface Area and Carbon Sequestration Rate for Biosolids Added to Soil concluded “[t]herefore, land application of biosolids is an effective way to enhance carbon sequestration in soils and reduce greenhouse gas (GHG) emissions.”
Biosolids has been shown to sequester carbon in a variety of cropping systems. Biosolids works for dry wheat land soils. In Soil carbon and nitrogen fraction accumulation with long-term biosolids applications researchers concluded “Biosolids markedly elevated total, stable and LF [light fraction] soil C and N pools in semiarid conditions, while maintaining comparable wheat productivity to commercially fertilized wheat-fallow.” It works for Midwest corn. The report Soil carbon sequestration resulting from long-term application of biosolids for land reclamation” found “[o]ur results indicate that biosolids applications can turn Midwest Corn Belt soils from current C-neutral to C-sink.” Biosolids also worked well for the cultivation of a willow bioenergy crops. The report Life cycle assessment of a willow bioenergy cropping system reported that the “[r]esults from the LCA support the assertion that willow biomass crops are sustainable from an energy balance perspective and contribute additional environmental benefits.”
Biosolids of different forms all generally yield increases in soil carbon stores. This was the specific focus of the report The effects of fertilization with anaerobic, composted and pelletized sewage sludge on soil, tree growth, pasture production and biodiversity in a silvopastoral system under ash (Fraxinus excelsior L.). It found “[a]naerobic sludge had a higher initial effect on both tree and pasture productivity. Pelletized sludge sustained better tree and pasture production. Composted sludge was found to be the most appropriate treatment for improving soil characteristics over the long term on sandy soils. It was concluded that pelletized sludge should be promoted because it enhances productivity, allows for better nutrient recovery and is less costly to store and apply compared with anaerobic sludge and composted sludge.”
Is the carbon added to soil by biosolids is transitory? Nutrient-rich biosolids might stimulate microbial decomposition of organic matter, thereby blowing off the carbon might, instead of storing it. This was addressed by Soil Carbon Characterization 10 to 15 Years After Organic Residual Application. This study showed that: “The addition of organic residuals… thus improves long-term soil C stability.”
Biosolids contribution to soil carbon storage is recognized by international experts. The United Nations Climate Change Convention has formally granted carbon credits for such mitigation measures. The biochemistry was worked out for biosolids in the report Degradation rate model [DRM} formulation to estimate soil carbon sequestration from repeated biosolids application: “Based on the 34-yr database, the DRM simulates the process that decomposes SOC [soil organic carbon] produced by biosolids application into C in biosolids that have not been degraded…. and provides an easy quantitative method for evaluating C credits from biosolids added to soil.”
Another question answered affirmatively was that when biosolids is used for carbon sequestration no negative effects are seen in soil health. A study in the U.K., Long-term Effects of Biosolids on Soil Quality and Fertility, concluded “no adverse effects on crop quality were observed.” Soil fauna seems to benefit from biosolids nutrition. In Effect of biosolid amendment on enzyme activities in earthworm (Lumbricus terrestris) casts scientists determined “Enzyme activity… and the contents of organic matter and nutrients N and P in earthworm casts and surrounding soil increased with increasing biosolid application.”
Repeated applications of biosolids are also effective for carbon storage and compatible with soil health. The report Long-Term Effects of Land Application of Class B Biosolids on the Soil Microbial Populations, Pathogens, and Activity concluded “[o]verall, the 20 annual land applications showed no long-term adverse effects, and therefore, this study documents that land application of biosolids at this particular site was sustainable throughout the 20-yr period, with respect to soil microbial properties.”
We have a big “thumbs up” for use of biosolids for carbon storage in soil. Chocolate pecan pie may have its detractors in the healthy-eating arena, but undoubtedly it offers carbon for storage in the human body. Biosolids may have its detractors in the organic farming arena, but undoubtedly it offers carbon for storage in the soil. There is only one sensible step to take when faced with the option: Say Yes to Storage!.
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