High efficiency capture of COD and phosphate in real domestic wastewater by Fe(VI)/PAC combined with high-rate contact stabilization process: Performance and mechanism.

This study proposed the integration of potassium ferrate (Fe(VI)) in combination with poly-aluminum chloride (PAC) into a high-rate contact stabilization (HRCS) process for simultaneous carbon and phosphorus removal from real domestic wastewater. Results showed that by adding 15 mg/L Fe(VI) (as Fe) for pre-oxidation followed by 20 mg/L PAC (as Al) for coagulation before the HRCS system, the removal efficiency of the whole system for COD and PO43--P reached 89.74 % and 100 %, respectively, and the concentrations of COD and PO43--P in the effluent reached the Chinese Class 1A wastewater discharge standard. More importantly, the pathway of COD and phosphorus elimination was extremely different from that of conventional activated sludge process, mainly through adsorption, with adsorption accounting for 86.11 % and 100 %, respectively. This enhanced adsorption capacity derived from the enhanced flocculation of Fe(VI), the promoted formation of inorganic particles (e.g., FeOOH, Fe2O3) and mineral precipitates (e.g., Fe2PO4(OH) and Al2PO4(OH)3), the increased secretion of extracellular polymeric substances by the sludge (an increase of 33.20 %), and the enrichment of bacterial genera with biosorption function (unclassified_f_Comamonadaceae and Zoogloea) upon exposure to Fe(VI) and PAC. Furthermore, microbial toxicity analyses indicated that applying Fe(VI) and PAC promoted the overproduction of reactive oxygen species (ROS) and the disruption of cell membrane integrity, which reduced microbial activity and made it difficult for microbial degradation of pollutants to facilitate the adsorption of carbon and phosphorus. This study provides theoretical guidance for the application of Fe(VI) to the low-carbon treatment of real domestic wastewater.