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Attenuation of stormwater micropollutants in biochar-amended biofilters and engineered streambed hyporheic zones
Portmann, Andrea C.
Portmann, Andrea C.
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2023
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2024-10-18
Abstract
Urbanization is an important factor in driving water shortages through the increase in impermeable surface areas, which creates greater runoff volumes and less groundwater infiltration. This disruption of the natural water cycle is accompanied by a growing pollution of urban waters – stemming from diffuse anthropogenic sources, i.e., stormwater, and leading to water quality degradation. The use of black carbon adsorbents such as biochar in stormwater control measures (SCMs) has been shown to enhance removal of trace organic contaminants (TOrCs). Though often considered “black box” passive treatment systems, knowledge of the dominant treatment processes impacting long-term system performance can ultimately inform design, maintenance, and lifetime of SCMs. The overall objective of this dissertation was to evaluate the role of biodegradation and biochar in the long-term removal of TOrCs in novel biochar-amended SCMs.
Exhaustive column studies sought to advance our understanding of the impact of a biofilm on TOrC removal and biofilter lifetime (Chapter 2), whereas flume experiments provided insight on the attenuation of TOrCs in engineered hyporheic zones (i.e., streambed biofilters known as Biohydrochemical Enhancements for Streamwater Treatment; BEST) and evaluated the removal of the highly polar diabetes medication metformin in full-scale modules (Chapter 3) and a range of different TOrCs in a pilot-scale flume system (Chapter 4). Findings from Chapter 2 indicated that the presence of an active biofilm prolonged filter lifetime by 2-fold and that biological processes (i.e., biodegradation and biologically enhanced sorption) contributed 20-36% to overall TOrC removal. Chapter 3 revealed that BEST engineered streambeds led to enhanced hyporheic exchange and attenuation of metformin compared to non-engineered sediment. Chapter 4 revealed that 14 consecutive 1-m long modules featuring BEST streambeds amended with 7% biochar (by volume) and sand (8-mesh Unimin) resulted in surface peak concentration reductions of >50% for all TOrCs studied except for one. The research conducted in this dissertation provides critical performance data and design recommendations for biochar-amended SCMs. Resulting water quality improvements in urban areas lead to greater human and ecosystem health. Furthermore, a better understanding of TOrC removal in these novel SCMs may facilitate their regulatory approval and acceptance by stormwater practitioners.
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