Biochar benefits composting in 10+ ways
Biochar is an ideal input into composting systems because of many benefits to the system itself. An outline of a number of positive benefits that enhance the efficiency and product yield, as well as mitigating some of the negative environmental effects that arise in commercial composting operations follows shortly. The addition of biochar at rates from 2%-10% w-w can lead to improvements in the following areas:
1. Water retention Biochar’s sponge-like structure can hold considerable quantities of water. Typical ranges for softwood biochar range from 3-4 times by weight to achieve saturation. This characteristic not only helps to maintain moisture levels in the compost, but can also help buffer excess water infiltration during rainfall events and prevent leaching and runoff and is also a moderating agent helping maintain optimum moisture levels for microbial activity1.
2. Aeration Biochar does not decay under microbial activity and the porosity and high internal surface area (as much as one hectare per 25 g biochar) provides air exchange at the microscale2. This quality helps maintain better aerobic conditions during the composting process, potentially reducing the number of passes required to aerate windrows.
3. Nutrient adsorption The cation exchange capacity of biochar means that nutrient ions in solution are attracted and held by it. This means losing substantially less gaseous nitrogen during composting, thus improving the C:N ratio of the finished product3.
4. pH regulation Biochar is typically alkaline (often around 9) and so its addition reduces the acidity in composting processes. The presence of calcium, potassium and other metallic elements makes biochar an effective liming agent4.
5. Microbial habitat The combination of better aeration, nutrient adsorption, water retention, and pH moderation leads to an environment that is highly beneficial to the microbiology required to create an effective composting process. The carbon matrix of biochar in compost is rapidly colonised by bacteria and fungi and this home and reservoir keep the decomposition process going better than if they were not there and for the whole compost process5.
6. Leachate control The nutrient holding ability and water holding functionality of biochar mean that nutrient leaching from the compost pile (or windrow) is reduced significantly6 7 . However, for times of high rainfall, the deployment of biochar in sediment traps as a filter will catch nutrients from the runoff that can then be returned to another compost batch once the sorption limit is reached8.
7. GHG emissions reduction Nitrous oxide and methane have heating potential of about 300 times and 30 times that of carbon dioxide, respectively, and under certain conditions both are formed during composting. When biochar has been added, it also favours facultative bacteria that prevent or reduce the formation of anerobic pockets within a compost pile/windrow and thus the formation of methane and nitrous oxide9.
8. Carbon credits & carbon sequestration Producers of biochar are able to claim carbon credits on the international voluntary markets because biochar is recognised as an effective means of storing carbon safely for long time scales (100+ or 1000+ years). These markets offer accreditation based on criteria that include feedstock sourcing, life cycle assessment of the production and application methods, and quality assurance testing of the biochar itself. The income from these carbon offset and removal credits improve the business case for making biochar as a compost input. The long term non-decay of carbon in biochar has also led to its designation by the IPCC as one of only a handful of viable and scalable carbon drawdown and removal (CDR) technologies. Estimates of its potential to reduce atmospheric carbon are by as much as 15% percent of annual emissions worldwide10. Every application of biochar containing compost to the soil thus benefits the climate in taking carbon out of the carbon cycle.
9. Market differentiation Biochar enhanced compost sets it apart from competitors and can be promoted on the basis of its increased benefits to soil and plant life as well as the environmental benefits accrued during the compost making process itself.
10. Air Quality Strong smelling ammonia and hydrogen sulfide are significantly reduced when biochar is an input to the composting process11 These objectionable odours and potential health hazards are often an issue for neighbouring land use and make gaining or keeping consent more difficult.
The Future?
The benefits of biochar as a co-composting addition to compost inputs are numerous and compelling. Imagine a future when a pyrolysis kiln or machine is a standard part of any commercial composting operation. Compost creation is more environmentally friendly with the carbon sequestered in the end users soil application leaving it permanently improved for future generations as well as being a positive action mitigating climate change.
COMBI (co-composting biochar) flowchart highlighting the benefits12
References
1 Sanchez-Monedero, M.A., Cayuela, M.L., Roig, A., Jindo, K., Mondini, C., Bolan, N., Role of biochar as an additive in organic waste composting, Bioresource Technology (2017), https://doi.org/10.1016/j.biortech.2017.09.193
2 Ibid
3 Ibid
4 Lehmann and Joseph, p 148-150
5 Sanchez-Monedero et al
6 Kammann, C. I.; Schmidt, H-P.; Messerschmidt, N.; Linsel, S.; Steffens, D.; Müller, C.; Koyro, H.-W.; Conte, P.; Joseph, S., Plant growth improvement mediated by nitrate capture in co-composted biochar. Scientific. Reports, 2015. https://doi.org/10.1038/srep11080
7 El Hanandeh, A., Bhuvaneswaran, A., de Rozari, P. (2017), Removal of nitrate, ammonia and phosphate from aqueous solutions in packed bed filter using biochar augmented sand media, MATEC Web Conf. Volume 120, 2017 International Conference on Advances in Sustainable Construction Materials & Civil Engineering Systems (ASCMCES-17), https://doi.org/10.1051/matecconf/201712005004
8 Kuoppamäki, K., Hagner, M., Valtanen, M., & Setälä, H. (2019). Using biochar to purify runoff in road verges of urbanised watersheds: A large-scale field lysimeter study. Watershed Ecology and the Environment, 1, 15–25. https://doi.org/10.1016/j.wsee.2019.05.001
9 Yin, Y., Yang, C., Li, M., Zheng, Y., Ge, C., Gu, J., Li, H., Duan, M., Wang, X., & Chen, R. (2021). Research progress and prospects for using biochar to mitigate greenhouse gas emissions during composting: A review. Science of The Total Environment, 798, 149294. https://doi.org/10.1016/j.scitotenv.2021.149294
10 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories Appendix 4: Method for Estimating the Change in Mineral Soil Organic Carbon Stocks from Biochar Amendments: Basis for Future Methodological Development https://www.ipcc-nggip.iges.or.jp/public/2019rf/pdf/4_Volume4/19R_V4_Ch02_Ap4_Biochar.pdf
11 Sanchez-Monedero et al
12 Antonangelo, J. A., Sun, X., & Zhang, H. (2021). The roles of co-composted biochar (COMBI) in improving soil quality, crop productivity, and toxic metal amelioration. Journal of Environmental Management, 277, 111443. https://doi.org/10.1016/j.jenvman.2020.111443
Further Information
Here are some great supporting resources we have found. Let us know if you have further ones to add:
USBI brochure on composting with biochar (pdf)
Video featuring biochar made at a composting facility in Spain: https://youtu.be/oHbdtJxb6ZE?si=ckop5L8FBJg0OURr (4.5 mins)
Thorough and referenced blog post: https://www.compostmagazine.com/biochar-in-compost
Extremely well referenced white paper by Pacific Biochar: https://pacificbiochar.com/wp-content/uploads/Pacific-Biochar_Biochar-Compost_white-paper.pdf
Credits
This informational document was created by Biochar Network New Zealand.
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