Chemically enhanced primary treatment processes for wastewater resource redirection and its impact on downstream processes

There is a recent focus within the global wastewater industry on the steps being taken by treatment facilities to move towards net zero, or in some cases, energy positive operation. As part of maximizing energy recovery from the incoming wastewater, there has been increased attention upon the energy contained in the wastewater, and maximizing the redirection of more carbon captured through the primary treatment process rather than conventional removal through carbon oxidation. The chemically enhanced primary treatment (CEPT) process is a promising method for carbon redirection and improving the performance and efficiency of wastewater treatment processes. This research was conducted to optimize the CEPT performance regarding simultaneous carbon and nutrients redirection in both bench-scale and full-scale operations. In order to improve the CEPT process, the performance of ferric chloride and seven types of polymers were evaluated by jar tests. Results indicated that 15 mg/L ferric chloride and 0.5 mg/L poly aluminum chloride (PACL) showed the best performance which was determined by a simplified comparison matrix regarding removal efficiencies. The best coagulant and flocculant combination determined by this study achieved total chemical oxygen demand (tCOD), soluble chemical oxygen demand (sCOD), total suspended solids (TSS) and total phosphorus (TP) removal efficiencies of 76%, 58%, 89%, and 84%, respectively, in a full-scale primary clarifier operation. Furthermore, the relationship between influent characteristics and removal rates under varying operating conditions were investigated. The impact of CEPT on the downstream liquid and solid train processes were also investigated. The study on the impact of CEPT on the downstream liquid train processes showed that PACl addition has improved the SVI in the activated sludge process, and lowered TSS and TP concentrations in secondary clarifier effluent. Furthermore, the addition of PACl did not affect the BOD5 and the ammonia concentration of the effluent from the secondary clarifier. However, the sludge produced from CEPT dosed with ferric chloride and PACl (test clarifier sludge) showed a lesser methane production rate compared to the sludge produced from CEPT dosed with ferric chloride (control clarifier sludge)