Abstract
A comprehensive assessment of the effects of temperature on hydraulically irreversible membrane permeability in tertiary ultrafiltration of municipal wastewater was conducted through bench scale testing. The influence of temperature was differentiated into impacts on SBR effluent characteristics, water rheological properties, and intrinsic membrane properties, which all subsequently affected the development of hydraulically irreversible permeability. When filtration tests were conducted at 20 °C with the effluents from sequencing batch reactors (SBRs) that were operated at 8, 14 and 20 °C, hydraulically irreversible permeability declined by 38%, 22% and 17%, respectively, during the steady period. The greater decline was attributed to higher generation of effluent organic matter (EfOM) at low SBR operating temperatures. When filtration tests were conducted at the corresponding SBR operating temperature, the hydraulically irreversible permeability with the effluents from SBRs operated at 14 and 8 °C further decreased. The water viscosity and intrinsic membrane resistance were observed to be responsible for 20–29% of the total decrease in hydraulically irreversible permeability. These declines established the upper limit to which fouling mitigation strategies could enhance hydraulically irreversible permeabilities at low temperature. The hydraulically irreversible permeability decline with low filtration temperature beyond that associated with changes in viscosity and intrinsic membrane resistance was attributed to narrowed membrane pores that retained additional EfOM fractions and modified membrane-foulant interactions. The novel approach in differentiating the effects of temperature on secondary treatment and filtration processes developed in the present study provides insights into hydraulically irreversible fouling development and the results from the present study can be employed to understand the limits of tertiary fouling control under challenging conditions.
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