Effect of Biochar on Metals and Nutrient Removal in Bioretention Systems

This study investigated whether amending the bioretention soil mix with biochar improves the reduction of copper, zinc, nitrate, ammonia, and phosphate from stormwater. Four vegetated test planters were setup for this experiment: one control with the bioretention soil mix, one control with the components of the bioretention soil mix (compost and loamy sand) in layers, one with biochar mixed with the bioretention soil mix, and one with layers of compost, biochar, and loamy sand. Five tests were conducted with stormwater collected from a nearby industrial site, and influent and effluent were analyzed for copper, zinc, total nitrogen, nitrate, ammonia, total phosphorus, and phosphate. The results show that copper and zinc removal was inconsistent in the mixed and layered setups. Removal varied significantly between tests and did not appear to be impacted by biochar. Nutrient removal was also inconsistent, with varying removal rates between tests for the control and biochar planters. Layering of bioretention soil components appeared to slightly improve removal during some of the tests, but differences were not statistically significant over all 5 tests. This study showed that removal of stormwater contaminants in bioretention systems did not significantly improve with the addition of biochar.