Removal of micropollutants from treated domestic wastewater by addition of powdered activated carbon to rapid filtration

Abstract

Advanced treatment of wastewater is currently being discussed throughout Europe in an effort to reduce emissions to surface waters and protect drinking water resources. In this study the combination of adsorption onto powdered activated carbon (PAC) and coagulation/filtration was investigated as a single advanced treatment step for simultaneous removal of organic micropollutants (OMPs) and phosphorus from domestic secondary effluent. Two pilot-scale dual-media filters were operated in parallel for a period of 4 months to investigate the influence of PAC addition on filtration parameters and determine removal of 14 selected OMPs. OMP abatement in the PAC filter was compared to batch tests and correlated with relative removal of UV254 absorption (UVA254). Stable operation with an average PAC dose of 8 mg/L and a removal >90% of total suspended solids was possible for filtration cycles of 24 h. The results show that PAC dosing does not negatively affect either filtration resistance or removal of phosphorus by precipitation. Concentrations of benzotriazole and carbamazepine were reduced by >70%, while sulfamethoxazole and diclofenac were removed to the extent of 40–60% (median values). Relative OMP removal showed only minor fluctuations despite occasionally strong changes of influent concentrations. Moreover, the results indicate that contact times were not sufficient for complete PAC exhaustion before separation and that further adsorption onto embedded PAC in the filter significantly contributes to overall OMP removal.