Biochar application
Soil fertilisation
Most of the nutrients (apart from nitrogen) in the feedstock will remain in the biochar during pyrolysis. The concentration of nutrients even increases due to the volatilisation of some of the organic matter in the feedstock and hence enrichment of the nutrient fraction.
Nutrient-rich biochars produced from waste materials are a great way of safe and sustainable recycling of nutrients.
(Buss et al., 2016a, 2016b; Jeffery et al., 2017; Pandit et al., 2018)
Soil liming
Most biochars have a high pH in the range of 7.5-11 and have a high CaCO3-equivalence. Applied to soil, they increase soil pH which can render heavy metals unavailable and increase the availability of nutrients. Soil pH is a very important soil characteristic and therefore, biochar shows its greatest effects when applied to acidic soils.
(Biederman and Harpole, 2013; Jeffery et al., 2017)
Soil improvement
Depending on process conditions and feedstock, biochar can have a high cation exchange capacity which improves the nutrient retention and nutrient exchange in soil. Furthermore, some biochars can sorb and retain high amounts of water which can increase the drought tolerance in plants. Biochar can also have a positive influence on microbial growth in soil which is very important for soil fertility. Higher microbial activity improves many soil functions, such as the turnover of organic matter in soil, providing nutrients for plant growth.
(Beesley and Dickinson, 2011; Glaser et al., 2002, 2001; Liang et al., 2006; Rondon et al., 2007; Warnock et al., 2007)
Composting and anaerobic digestion
Since biochar stimulates microbial growth, it also enhances the composting and anaerobic digestion processes.
Co-composting biochar with biomass results in reduced emissions of greenhouse gases, less odour and an overall improvement of the composting process. The resulting biochar-compost material is a great soil improver and nutrient provider that shows superior effects on plant growth compared to the application of the individual materials.
Biochar also helps to increase the biogas yields during anaerobic digestion, in particular in stressed digesters, e.g. with high concentrations of ammonia.
(Hagemann et al., 2017a, 2017b; Kaudal and Weatherley, 2018; Mumme et al., 2014)
Carbon sequestration
The conversion of biomass into biochar increases the recalcitrance of the carbon structure in the material. Biochar comprises of a highly condensed, aromatic framework of carbon atoms which makes it difficult for microorganisms to degrade it. Consequently, when biochar is applied to soil, it remains in soil much longer than its feedstock.
Therefore, biochar is an ideal, low-cost tool for sequestering carbon in the soil. It is one of the only negative-carbon technology that can currently be implemented on large-scale.
(Kuzyakov et al., 2014; Lehmann, 2007)
Soil remediation
Biochar has been successfully used in remediating contaminated soil in many circumstances. It can sorb heavy metals (e.g. copper, zinc, lead) and organic contaminants (e.g. PAHs).
(Beesley et al., 2011; Buss et al., 2012)
Water filtration
Biochar can also sorb nutrients (phosphate), organic contaminants and metals from wastewater and hence purify the water. This can be used as a strategy in wastewater treatment plants.
(Shepherd et al., 2017, 2016)
Literature
Here you can find the references that have been cited above.
Beesley, L., Dickinson, N., 2011. Carbon and trace element fluxes in the pore water of an urban soil following greenwaste compost, woody and biochar amendments, inoculated with the earthworm Lumbricus terrestris. Soil Biol. Biochem. 43, 188–196. https://doi.org/10.1016/j.soilbio.2010.09.035
Beesley, L., Moreno-Jiménez, E., Gomez-Eyles, J.L., Harris, E., Robinson, B., Sizmur, T., 2011. A review of biochars’ potential role in the remediation, revegetation and restoration of contaminated soils. Environ. Pollut. 159, 3269–3282. https://doi.org/10.1016/j.envpol.2011.07.023
Biederman, L.A., Harpole, W.S., 2013. Biochar and its effects on plant productivity and nutrient cycling: a meta-analysis. GCB Bioenergy 5, 202–214. https://doi.org/10.1111/gcbb.12037
Buss, W., Graham, M.C., Shepherd, J.G., Mašek, O., 2016a. Suitability of marginal biomass-derived biochars for soil amendment. Sci. Total Environ. 547, 314–322. https://doi.org/doi:10.1016/j.scitotenv.2015.11.148
Buss, W., Graham, M.C., Shepherd, J.G., Mašek, O., 2016b. Risks and benefits of marginal biomass-derived biochars for plant growth. Sci. Total Environ. 569–570, 496–506. https://doi.org/10.1016/j.scitotenv.2016.06.129
Buss, W., Kammann, C., Koyro, H.-W., 2012. Biochar reduces copper toxicity in Chenopodium quinoa Willd. in a sandy soil. J. Environ. Qual. 41, 1157–1165. https://doi.org/10.2134/jeq2011.0022
Glaser, B., Haumaier, L., Guggenberger, G., Zech, W., 2001. The “Terra Preta” phenomenon: a model for sustainable agriculture in the humid tropics. Naturwissenschaften 88, 37–41. https://doi.org/10.1007/s001140000193
Glaser, B., Lehmann, J., Zech, W., 2002. Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – A review. Biol. Fertil. Soils 35, 219–230. https://doi.org/10.1007/s00374-002-0466-4
Hagemann, N., Joseph, S., Schmidt, H.P., Kammann, C.I., Harter, J., Borch, T., Young, R.B., Varga, K., Taherymoosavi, S., Elliott, K.W., McKenna, A., Albu, M., Mayrhofer, C., Obst, M., Conte, P., Dieguez-Alonso, A., Orsetti, S., Subdiaga, E., Behrens, S., Kappler, A., 2017a. Organic coating on biochar explains its nutrient retention and stimulation of soil fertility. Nat. Commun. 8, 1–11. https://doi.org/10.1038/s41467-017-01123-0
Hagemann, N., Kammann, C.I., Schmidt, H.P., Kappler, A., Behrens, S., 2017b. Nitrate capture and slow release in biochar amended compost and soil. PLoS One 12. https://doi.org/10.1371/journal.pone.0171214
Jeffery, S., Abalos, D., Prodana, M., Bastos, A.C., Van Groenigen, J.W., Hungate, B.A., Verheijen, F., 2017. Biochar boosts tropical but not temperate crop yields. Environ. Res. Lett. 12. https://doi.org/10.1088/1748-9326/aa67bd
Kaudal, B.B., Weatherley, A.J., 2018. Agronomic effectiveness of urban biochar aged through co-composting with food waste. Waste Manag. 77, 87–97. https://doi.org/10.1016/j.wasman.2018.04.042
Kuzyakov, Y., Bogomolova, I., Glaser, B., 2014. Biochar stability in soil: Decomposition during eight years and transformation as assessed by compound-specific 14C analysis. Soil Biol. Biochem. 70, 229–236. https://doi.org/10.1016/j.soilbio.2013.12.021
Lehmann, J., 2007. A handful of carbon. Nature 447, 10–11.
Liang, B., Lehmann, J., Solomon, D., Kinyangi, J., Grossman, J., O’Neill, B., Skjemstad, J.O., Thies, J., Luizão, F.J., Petersen, J., Neves, E.G., 2006. Black carbon increases cation exchange capacity in soils. Soil Sci. Soc. Am. J. 70, 1719. https://doi.org/10.2136/sssaj2005.0383
Mumme, J., Srocke, F., Heeg, K., Werner, M., 2014. Use of biochars in anaerobic digestion. Bioresour. Technol. 164, 189–197. https://doi.org/10.1016/j.biortech.2014.05.008
Pandit, N.R., Mulder, J., Hale, S.E., Martinsen, V., Schmidt, H.P., Cornelissen, G., 2018. Biochar improves maize growth by alleviation of nutrient stress in a moderately acidic low-input Nepalese soil. Sci. Total Environ. 625, 1380–1389. https://doi.org/10.1016/j.scitotenv.2018.01.022
Rondon, M.A., Lehmann, J., Ramirez, J., Hurtado, M., 2007. Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with bio-char additions. Biol. Fertil. Soils 43, 699–708. https://doi.org/10.1007/s00374-006-0152-z
Shepherd, J.G., Joseph, S., Sohi, S.P., Heal, K. V., 2017. Biochar and enhanced phosphate capture: Mapping mechanisms to functional properties. Chemosphere 179, 57–74. https://doi.org/10.1016/j.chemosphere.2017.02.123
Shepherd, J.G., Sohi, S.P., Heal, K. V., 2016. Optimising the recovery and re-use of phosphorus from wastewater effluent for sustainable fertiliser development. Water Res. 94, 155–165. https://doi.org/10.1016/j.watres.2016.02.038
Warnock, D.D., Lehmann, J., Kuyper, T.W., Rillig, M.C., 2007. Mycorrhizal responses to biochar in soil – concepts and mechanisms. Plant Soil 300, 9–20. https://doi.org/10.1007/s11104-007-9391-5