Pilot Scale Comparison of Enhanced Coagulation with Magnetic Resin Plus Coagulation Systems

Abstract

Previous work has shown that magnetic ion-exchange treatment before coagulation gives high natural organic matter (NOM) removal and reduced levels of disinfection byproduct when compared to conventional enhanced coagulation. The impact of the resin process on the downstream floc formation process after coagulation and the subsequent effect on clarification has not previously been shown. Water containing high concentrations of NOM were treated at pilot scale using (1) conventional enhanced coagulation and compared with (2) treatment using magnetic resin followed by coagulation at reduced doses of 50–70%. Bench scale testing was also carried out to determine floc properties for systems with and without resin pretreatment. It was demonstrated that pretreatment using magnetic resin was able to significantly reduce the turbidity load onto filters as a result of the formation of a large and more robust floc. Resin pretreatment also improved NOM removal and reduced disinfection byproduct formation when compared with conventional coagulation. The turbidity load on to the filters following resin pretreatment was 1.5 ± 0.7 NTU, whereas this value was 2.9 ± 0.3 NTU for conventional coagulation. Flocs produced with resin pretreatment were larger than those produced by conventional coagulation, with a median floc size of 1000 µm compared to 600 µm. The improvement in floc properties following magnetic resin pretreatment was proposed to be due to the removal of NOM that was characteristic of carboxylic acids before the coagulation stage.