Simultaneous removal of nutrients and pharmaceuticals and personal care products using two-stage woodchip bioreactor-biochar treatment systems

The co-occurrence of nutrients and pharmaceuticals and personal care products (PPCPs) in sewage effluent can degrade water quality of the receiving watersheds. This study investigated the simultaneous removal of excess nutrients and PPCP contaminants by developing a novel woodchip bioreactor and biochar (B²) treatment system. The result revealed that woodchip bioreactors could effectively remove nitrate via a denitrification process and adsorb some PPCPs. Biochar as a secondary treatment system significantly reduced the concentrations of PPCPs and dissolved reactive phosphorus (DRP) (p < 0.05), compared to the woodchip bioreactor. The removal efficiencies of all targeted contaminants by the B² system were evaluated using various hydraulic retention times (HRTs) and biochar types (pelletized versus granular biochar). Longer HRTs and smaller biochar particles (granular biochar) could enhance the removal efficiencies of targeted contaminants. Average contaminant removals were 77.25 % for nitrate-N, 99.03 % for DRP, 69.51 % for ibuprofen, 73.65 % for naproxen, 91.09 % for sitagliptin, and 96.96 % for estrone, with woodchip bioreactor HRTs of 12 ± 1.4 h and granular biochar HRTs of 2.1 ± 0.1 h. Notably, the second-stage biochar systems effectively mitigated by-products leaching from woodchip bioreactors. The presence of PPCPs in the woodchip bioreactors enriched certain species, such as Methylophilus (69.6 %), while inhibiting other microorganisms and reducing microbial community diversity. Furthermore, a scaled-up B² system was analyzed and assessed, indicating that the proposed engineering treatment system could provide decades of service in real-world applications. Overall, this study suggests that the B² system has promising applications for addressing emerging and conventional contaminants.