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Evaluation of Biochar to Enhance Green Infrastructure for Removal of Heavy Metals in Stormwater
Citation:
Wallace, R., C. Su, AND W. Sun. Evaluation of Biochar to Enhance Green Infrastructure for Removal of Heavy Metals in Stormwater. Oklahoma University International Water Conference, Norman, OK, September 18, 2017.
Impact/Purpose:
Submitting poster at the Oklahoma University International Water Conference, September 18, 2017, Norman, OK.
Description:
The changes in the natural North American drainage system over the centuries have given rise to significant modern ecological impacts during high precipitation events. Contaminated stormwater runoff is of particular concern during these events. Urban development increases impermeable surfaces which can raise stormwater runoff by as much as 45 percent. Controlling excess stormwater runoff poses some challenging issues as stormwater runoff has not been established as a pollutant nor is the source of the runoff well defined. Studies have revealed that at least 78 metals and other inorganic elements and 385 xenobiotic organic compounds have been observed/quantified in stormwater. Heavy metals are a significant contaminant from urban runoff due to their prevalence, toxicity, and persistence in the environment. Innovative stormwater mitigation designs (green infrastructure (GI)) capture runoff through a variety of catchment methods for the purpose of localized water use. Remediation of this water is necessary and may be achieved by adding sorptive material to GI matrices. Biochar is one material that has substantial practical application for implementation in GI. Little work has been done on the deployment of this material in GI for heavy metal removal. Thus, six unique kinds of biochar were evaluated to provide a basis for understanding metal/biochar physiochemical properties for application in GI. This was accomplished through FITR, specific surface area (SSA), column and isotherm studies. FTIR results show that there is little to no difference between the three unique Douglas Fir (DF) biochars. There are distinct peaks in the 2500 to 2700 aldehyde range, and the 1300 to 1500 fingerprint range of the DF biochars. For the diary manure (DM) biochar, the peaks are shifted about 100 wavenumbers higher compared to the DF. There are also some weak peaks at 2300 in the DM biochar. Results for SSA show that biochar surface areas were highly variable between DF biochar and DM biochar. For the three unique DM biochar, there was a large variance in the SSA. Highest and lowest SSA was 493.6 and 3.9 m2/g for DF biochar 5 and DM biochar 3 respectively. Column results show that time to break through (minutes) was 86 for zinc, 53 for cadmium, cobalt and nickel. Copper and lead did not break through. The results for the cadmium isotherm show that as pH increases, sorption increases, reaching a plateau around a pH of 9.5-10. Comparison of the Langmuir and Freundlich isotherm models show that the sorption of biochar follows a Freundlich isotherm. The isotherms were modeled at several different pH values to observe the impacts of pH on the sorptive capacity of the biochar. The surface functional groups identified using FITR, and the high surface area of DF biochar 5, may influence the efficacy of metal sorption in column and isotherm studies. Based on Freundlich modeling, DF biochar 5 has a high sorptive capacity for Cd (R2>0.90) at wide pH range (pH 5.6 to 8). This indicates that DF biochar 5 may perform well under variable pH conditions.