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UBC Theses and Dissertations

System dynamics analysis of impacts of biosolids and biosolids-derived biochar land application on agricultural soil quality Robinson, Connor


Modern sewage treatment results in the production of biosolids (treated sewage sludge), and more biosolids are produced as populations grow and minimum treatment standards increase. This leads to the question of what to do with the biosolids we create. For decision-makers determining a biosolids use strategy, choosing an appropriate use for their context is not a straightforward decision, as it involves weighing pros and cons and making trade-offs. One jurisdiction currently engaged in biosolids management decision-making is the Capital Regional District (CRD) in British Columbia, Canada. The CRD is constructing a new sewage treatment system which will be producing dried Class A biosolids by the end of 2020 and must determine a long-term use for these biosolids. Two biosolids use options that may be considered are (1) direct agricultural land application and (2) conversion to biochar for subsequent agricultural land application. This thesis applied a systems approach to comparing the impact of these two management options (land-applying either dried Class A biosolids or biochar derived from those biosolids) on agricultural soil quality. This was done by using system dynamics (SD) modelling. Biosolids land application led to a greater amount of plant available nitrogen and both stable and labile carbon in the soil, as well as greater crop yields, but also led to more nitrogen leaching and an increased presence of endocrine disrupting compounds. Biochar land application surprisingly did not lead to a greater amount of stable carbon, but did result in a lower amount of nitrogen leaching and no risk due to endocrine disrupting compounds, however also led to a minimal crop yield and meant nitrogen needed to be added to the soil. Reducing the application frequency of biochar did not have a significant influence on soil quality and crop growth, whereas adding mineral fertilizer had a substantial positive effect, and this second strategy should be investigated further. This study contributes to biosolids management decision-making by providing a comparative analysis of the use of biosolids or biosolids-derived biochar on agricultural land as a biosolids reuse option, from the perspective of soil quality.

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