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Co-Composting with Biochar

Co-Composting with Biochar to Turbocharge Microbial Metabolism and Mitigate Greenhouse Gas Emissions

By Michael Cohen, Organic Materials Management and Agri-Food Systems Advisor

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Photo: Sanjai Parikh


     Remember learning in school that mitochondria are the powerhouses of the cell? Well, compost piles have their own powerhouses - bacteria that are relatives of mitochondria. These hardworking bacteria help break down organic material, a process that requires oxygen. Just as our circulatory system supplies oxygen to our mitochondria, compost operators strive to supercharge aeration through frequent turning or infusing air into compost piles.

     Recent studies have demonstrated that adding a small amount of biochar, the blackened remnants of slowly combusted organic materials, enhances aeration and accelerates metabolic processes at a micro-scale within composts. Biochar's presence in composts boosts gas diffusion into small clumps, ensuring oxygen reaches the internal bacteria more efficiently. Interestingly, biochar particles also aid in channeling energy (as electrons) from the "food" in the pile to oxygen-consuming bacteria, further expediting metabolic transformations in the compost. An added bonus is that these biochar-enabled processes override other metabolic pathways that release greenhouse gases.

     One of the most notable demonstrations of the benefits of using biochar in large-scale composting comes from the research group led by Dr. Rebecca Ryals at UC Merced. Their studies, which focused on composting dairy manure with plant-derived biochar, revealed significant reductions in greenhouse gases as well as a substantial drop in stable flies attracted to gases emanating from the compost.

     The diversity of biochar forms, as depicted in the photo above, is influenced by factors such as feedstock variety and production temperature. How these different biochars compare in lowering gaseous compost emissions is an open question.

     Drawing insights from their previous studies, Dr. Ryals and collaborators in the UC Climate Action research group are exploring a potential investigation into co-composting municipal food waste with biochar at the GreenWaste Z-Best Composting Facility in Gilroy. UCCE Santa Clara County is actively working to facilitate this collaboration and other regional studies, paving the way for the widespread adoption of biochar-composting as a pivotal strategy in the global fight against climate change and the improvement of air quality.

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Research group members visiting the GreenWaste Z-Best Composting Facility, January 18, 2024. Host, Beto Ocha (fourth from the right).