Evaluation of a recirculating hydroponic bed bioreactor for removal of contaminants of emerging concern from tertiary-treated wastewater effluent

Abstract

Tertiary-treated effluent from a municipal wastewater treatment plant in Tucson, AZ, was added to recirculating hydroponic bed bioreactors filled with light expanded clay aggregate (LECA) and recirculated for 10 days. Bioreactors were planted with high and low densities of sorghum (Sorghum bicolor), switchgrass (Panicum virgatum) and Bacillus thuringiensis cotton (Gossypium sp.). The experiment also included a non-planted bioreactor treatment and a control bioreactor with neither plants nor substrate medium. Of 46 contaminants of emerging conern assayed with liquid chromatography tandem mass spectrometry (LC-MS/MS), 16 were initially identified at detectable levels in the effluent. After one day, concentrations of Ibuprofen and Diphenhydramine fell below detection limits in all treatments as well as the control. After five days, initial concentrations of atenolol, benzotriazole, carbamazepine, hydrochlorothiazide, iohexol, iopamidol iopromide, primidone, sulfamethoxazole and tris TCPP were reduced by greater than 80% in all treatments, while the control exhibited little to no removal. Diclofenac, simazine and sucralose exhibited variable removal rates among treatments ranging from 44 to 84% after five days. After 10 days, concentrations of DEET, diclofenac, iopromide, primidone and simazine were all below detection levels, while there was near zero removal in the control. Bioreactors planted with cotton had significantly more removal of sulfamethoxazole than unplanted bioreactors by 16–19% after five days and by an additional 18–20% removal after 10 days. The percentage uptake of benzotriazole by every planted treatment was significantly higher than the non-planted treatment after five and 10 days. Significant contaminant removal occurred in the media substrate, likely through adsorption to LECA or microbial degradation. More research is needed to examine specific pathways of degradation and removal by various microbials and plants.