Optimizing chemically enhanced primary treatment processes for simultaneous carbon redirection and phosphorus removal

Abstract

There has been increased interest towards maximizing wastewater energy recovery by enhancing the carbon captured through the primary treatment process such as chemically enhanced primary treatment (CEPT). This research was conducted to optimize the CEPT performance in terms of redirection of carbon and nutrients in both bench- and full-scale operations. In order to improve the CEPT process, the performance of ferric chloride and seven types of polymers were evaluated through jar testing. The optimal coagulant (15 mg/L ferric chloride) and flocculant (0.5 mg/L poly aluminum chloride (PACl)) combination achieved total COD, soluble COD, total suspended solids (TSS), and total phosphorus (TP) removal efficiencies of 76, 58, 89, and 84, respectively, in a full-scale primary clarifier operation. In doing so the organic matter and phosphorus were concentrated in CEPT sludge, making them available for recovery. Furthermore, the relationship between influent characteristics and removal rates under varying operating conditions was investigated. It was found that soluble COD removal appeared to be season-dependent, and TSS removals were independent of influent TSS concentrations in all scenarios. The removal of tCOD, sCOD, and TP had a positive relationship with their corresponding concentrations when the polymer Alcomer® 120L was used, whereas no correlation between removal and concentration was observed with PACl.