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Characterizing biochar nitrogen and phosphorus sorption properties to close the loop in the circular nutrient economy
Conference presentation

Characterizing biochar nitrogen and phosphorus sorption properties to close the loop in the circular nutrient economy

Evanna McGuinness, Maja Arsic and Diogenes L. Antille
2023 ASABE Annual International Meeting
American Society of Agricultural and Biological Engineers
2023 ASABE Annual International Meeting (Omaha, Nebraska, 09/07/2023–12/07/2023)
2023
DOI: https://doi.org/10.13031/aim.202300783

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Abstract

Agricultural recycling Aquaculture Circular bioeconomy Pyrolysis Resource recovery and re-use Waste management hierarchy Wastewater
Nutrient recovery from wastewaters for re-use in agriculture is a key opportunity for a circular nutrient economy. The rapid consumption of rock phosphate and rising costs of ammonium production, alongside the environmental impacts of the discharge of nutrient-loaded wastewaters, highlight the necessity to recover and re-use nutrients, which otherwise may be lost to the environment. Nitrogen (N) and phosphorus (P) are essential plant nutrients predominantly applied via manufactured fertilizers, where concerns around environmental impacts of production and use are increasing. Amid these concerns, there is a growing interest in “closing resource loops” by capturing and re-utilizing nutrients from wastewaters and waste-derived products. Biochar, a carbon-rich product produced through the pyrolysis or gasification of organic materials, has attracted attention due to its ability to adsorb nutrients from aqueous solutions, in addition to retaining some nutrients from parent feedstocks. Together, biochar sorption properties provide opportunities to capture nutrients from wastewaters for application back onto farms; thus, improving nutrient and carbon circularity while maintaining soil fertility. The work reported in this study characterized the ammonium and phosphate sorption capacities of biochars from four waste feedstocks, in pure solutions and in a real freshwater aquaculture wastewater. Results showed that the ammonium and phosphate adsorption capacities for all the biochar samples were similar to those reported in the literature for unfunctionalized biochars, demonstrating potential for their use in commercial settings. Biochars produced from walnut shell waste (WB) and eucalyptus green waste (GMC) had higher respective phosphate sorption capacities, while biochars produced from a composite nutshell and pine-pallet waste (TB) had higher ammonium sorption capacities. Biosolids biochar (BB) released phosphorus into ultrapure KH2PO4 solutions, but this was not observed when BB was added to a real freshwater aquaculture wastewater sample. Further research is needed to identify the specific mechanisms responsible for ion sorption and to investigate subsequent nutrient leaching from biochars in solution. Biochar production should focus on applicability for specific end use cases, and industry research should focus on developing biochar products which are uniform and consistent for use in a growing circular economy.

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