Evaluation of biochar for reduction of nitrogen compounds in stormwater remediation systems

Beneski, Valentina
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University of Delaware
As stormwater travels over impervious surfaces it collects a variety of contaminants, including nitrogenous compounds that can contribute to eutrophication if they reach water bodies. Engineering systems, such as bioretention facilities, can treat stormwater; however, these structures typically have inadequate removal of nitrogen compounds like ammonium (NH4+ ) and nitrate (NO3-). The objective of this study was to evaluate the potential for poultry litter (PL) or wood derived (WD) biochar to remove NH4+ and NO3- from artificial stormwater (ASW) and to evaluate any affects biochar may have on the microbial nitrogen cycle. Both PL and WD biochar removed more than 90% of the NH4+ from ASW solutions, while NO3- removal was negligible. WD biochar removed more NH4+ from ASW than PL biochar, and its NH4+ sorption capacity was not significantly affected by the presence of other cations in solution. Particle size of the biochar influenced adsorption. Smaller WD biochar had increased NH4+ adsorption, whereas smaller PL particle size increased NH4+ leaching into solution. In addition, PL biochar produced at 400̊C had significantly higher leaching of NH4+ than PL biochar produced at 500̊C. In column experiments, WD biochar slightly decreased the pH of the effluent, while PL biochar caused increase in effluent pH. Using the measured adsorption isotherms, the NH4+ sorption capacities of both PL and WD biochars were calculated for field conditions. At application rates of 2% by weight, calculated PL and WD biochar removal of NH4+ was quickly depleted. However, for WD biochar at 10% application, removal efficiencies of over 50% can be achieved for inflows over 200,000 L. This equates to effectiveness for multiple storm events. The microbial results of the experiments were inconclusive, needing a much larger scale of research to get a better representation of the soil communities. These results suggest that biochar can be a useful amendment to bioretention facilities for the removal of NH4+. However, source of the biochar and preparation techniques will influence sorption capacity and may induce different changes to the soil environment of the system.