Pilot-scale study on the performance of high-rate DAF based on removal of organic precursors and formation characteristics of disinfection by-products

Abstract

In recent years, there has been an increased focus on the design and development of dissolved air flotation (DAF) with a high surface loading rate (SLR), but little research has been conducted using advanced natural organic matter characterization techniques. This research thus investigates the performance of pilot-scale DAF (10–30 m h–1) and compares them with those for a full-scale coagulation–flocculation–sedimentation (CFS) system based on the reduction of organic precursors, different molecular weight (MW) fractions characterized by liquid chromatography with organic carbon detection, and disinfection by-products. The removal of dissolved organic carbon (DOC) decreased with increasing SLR, ranging from 29 % to 38 %. This may be because of the short flocculation retention time for high SLR. Thus, achieving a similar removal of DOC by high SLR required higher coagulant doses. Furthermore, the organic precursors were measured lower in the high-rate DAF effluent than the CFS, maybe because of the high coagulation pH of the CFS effluent (7.5–8). Similarly, the concentration of different MW fractions, especially biopolymers and building blocks, was lower in the high-rate DAF effluent than in the CFS. The removal of biopolymers was 74.64 % and 87.20 % for the CFS and high-rate DAF, respectively. Likewise, 2.78 % and 27.09 % for the CFS and high-rate DAF, respectively, for building blocks. The normalized trihalomethanes/DOC and chloralhydrate/DOC were higher for the CFS than the high-rate DAF. Coagulation chemistry (pH, coagulant doses, and retention time) strongly influences the DAF and CFS unit performance and should not be neglected.