The impact of secondary operating temperature on in-line coagulation/flocculation and fouling of membranes used in tertiary treatment

Abstract

In-line coagulation/flocculation is a promising approach for fouling mitigation for membranes of tertiary treatment of wastewaters. However, the potential to minimize membrane fouling under low temperatures by optimizing coagulant dose during in-line coagulation/flocculation has not been examined. In the present study, the effect of secondary operating temperature on the performance of in-line coagulation/flocculation, and subsequent membrane fouling due to the differing SBR effluent components, was differentiated over a range of alum dosages (0–1.0 mM). The results demonstrated that in-line coagulation/flocculation achieved similar DOC reduction for effluents from SBR operated at 8 and 20 °C, however, the reduction in high and low MW organics by in-line coagulation/flocculation were higher for the effluent from SBR operated at 8 °C than that of 20 °C. Moreover, the reduction in high MW organics by in-line coagulation/flocculation were greater than those of low MW organics. Filtration tests revealed that in-line coagulation/flocculation reduced the development of cake fouling more than intermediate pore blocking and this was more obvious with the effluent from the SBR operated at 8 °C. The preferred alum dosages to control total membrane resistance accumulation were 0.2 and 0.1 mM for the effluents from the SBR operated at 8 and 20 °C, respectively. However, the temperature corrected membrane resistances were two times higher at low filtration temperature than those of 20 °C regardless of coagulant dosages. It was concluded that the potential of in-line coagulation/flocculation with alum for membrane fouling alleviation was limited in cold regions.