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Biochar-amended biofilters for removal of trace organic contaminants from stormwater
Ulrich, Bridget A.
Ulrich, Bridget A.
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2016
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2017-07-12
Abstract
Urban runoff has degraded water quality by transporting harmful contaminants to receiving waters. Low Impact Development (LID) systems have emerged as a popular approach to protect water quality, but are less effective for removal of polar trace organic contaminants (TOrCs). Amendment of LID systems with biochar could enhance the sorptive removal of TOrCs, but system lifetime may be limited if TOrCs leach from exhausted media. TOrC accumulation could potentially be prevented by stimulating biodegradation in biochar-amended biofilters: these systems could contain an upper layer of vegetation and bioretention media to stimulate biodegradation, and a lower layer of biochar-amended sand to enhance sorption. The objective of this dissertation was to assess the effectiveness of biochar-amended biofilters for removal of TOrCs from stormwater. Three research efforts were undertaken to evaluate (Chapter 2) abiotic TOrC removal processes, (Chapter 3) biological TOrC removal processes, and (Chapter 4) overall TOrC removal in vegetated biofilter columns under intermittent flow. Chapter 2 revealed that biochar-amended infiltration systems may retain TOrCs by sorption for multiple years (indicated by conservative forward predictions from a calibrated and verified transport model); but that additional biological removal processes may be necessary to achieve a desired system lifetime of 10-15 years. Microcosm experiments in Chapter 3 revealed that the presence of dissolved organic carbon (DOC) from biodegradable carbon sources enhanced the TOrC-degrading activity of a representative runoff microbial consortium. Further, greater TOrC removal was observed for biologically active, biochar-amended columns than for biologically inhibited controls; indicating the potential for biological processes to prevent TOrC accumulation in larger-scale systems. Finally, vegetated biofilter column experiments in Chapter 4 revealed improved TOrC removal in biochar-amended columns relative to conventional configurations: remarkably, biochar-amended biofilter columns maintained >99% TOrC removal throughout treatment of the equivalent of greater than a year’s worth of runoff volume. The results of this dissertation motivate further efforts for long-term evaluation of larger-scale systems. These efforts may lead to significant improvements in urban water quality; potentially by providing performance data and design guidelines for practitioners, and informing efforts to establish TOrC discharge regulations.
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