Effect of coagulation pretreatment on membrane filtration performance

The addition of a coagulant as a pretreatment before membrane filtration is becoming a common practice among utilities. However, little is known about the effects of coagulation pretreatment on membrane filtration performance.The objective of the study presented in this article is to improve the understanding of the effects of coagulants on membrane performance. The primary variables used in the study included source water, type of coagulant, coagulant dose, coagulation application conditions, and membrane material. Fouling was evaluated using flat-sheet membranes in an unstirred filtration cell. Prefiltration was used to separate the effect of coagulation on particulate matter and dissolved organic carbon. To provide more widespread applicability, five natural surface waters and three membrane materials were included. The research found that coagulant dose was an important factor in determining whether performance was better or worse. A positive linear relationship was found between the ability of coagulation to remove dissolved organic carbon and to improve membrane performance. No single coagulant was consistently better than the others; rather, whichever coagulant tended to be most effective at removing dissolved organic carbon in a particular source was also most effective at improving membrane performance.