How does temperature affect wastewater advanced treatment membrane contamination?

Tao Chen, a young teacher from the School of Earth and Environment of Anhui University of Science and Technology, and Wayne Parker, professor of the School of Engineering, University of Waterloo, and Pierre Berube, professor of the University of British Columbia, cooperated with the research group of Professor Pierre Berube of the University of British Columbia to conduct early historical data analysis and experimental research on the problem of intensified pollution in the winter advanced treatment of Keswick Sewage Reuse Center in Toronto, Ontario, and clarified the influence mechanism of secondary biological treatment operating temperature and advanced treatment ultrafiltration operating temperature on membrane pollution. The results were published in the Journal of Separation and Purification.

Schematic diagram of the influence mechanism of secondary and advanced treatment operating temperature on membrane fouling Courtesy of Anhui University of Science and Technology

Advanced sewage treatment refers to the further water treatment process in which urban sewage is reused as water resources for production or life in order to meet certain water reuse standards after primary and secondary treatment. Ultrafiltration is considered to be a very promising method for wastewater reuse, but the problem of membrane fouling has always been a bottleneck that limits its long-term stable operation and operating cost control.

“Because membrane fouling can cause transmembrane pressure differentials to rise, the frequency of membrane cleaning and replacement needs to be increased while maintaining the target treatment efficiency, thereby increasing operating costs and energy consumption. Generally speaking, the cost of membrane fouling control accounts for 20%-30% of the operating cost; Among them, the cost of membrane cleaning and membrane replacement accounted for 9%-30% and 40%-65% of the total cost of membrane pollution control, respectively. For the operation scenario of advanced wastewater treatment, these data will further increase as the temperature decreases in winter. Tao Chen introduced to China Science News.

In recent years, scholars from various countries have carried out relevant studies on the influence of temperature on membrane fouling, but most of the research objects are membrane bioreactor (MBR) processes. On the one hand, in advanced treatment, because the membrane does not directly contact with the sludge mixture, the membrane fouling mechanism is very different from MBR; On the other hand, the membrane filtration process in advanced treatment is carried out separately from the secondary biological process, and the degree of influence of temperature on the two is different and cross-influenced, which is worth discussing separately.

In this study, Tao Chen et al. proposed a method of combining activated sludge model and experiment, and evaluated the influence mechanism of temperature affecting secondary biological processes and their metabolites, as well as the influence mechanism of temperature affecting the intrinsic properties of membranes on advanced treatment membrane pollution through novel experimental design.

“Our study found that when the operating temperature of secondary biological treatment is reduced from 20°C to 8°C, and the ultrafiltration operating temperature is unchanged at 20°C, the total membrane resistance increases significantly. This is mainly due to the large increase in soluble microbial products produced at low temperatures by secondary biological processes, of which organic matter (BAP) associated with biomass decay is the most important membrane contaminating substance. Tao Chen said.

Further, when the operating temperature of ultrafiltration is reduced, the total membrane resistance increases by 122%, and the increase in this part of the membrane resistance is due to the decrease in membrane pore size and the increase in liquid viscosity. It is found that the increase in total membrane resistance is not a simple superposition of the effects of various parts, but a complex interaction effect.

Tao Chen said that this work comprehensively discusses the influence of operating temperature on membrane fouling, provides a theoretical basis for designing membrane fouling mitigation measures under different temperature operating conditions, and also provides a method reference for exploring the relationship between secondary biological processes and membrane fouling under other extreme operating conditions. ”

The reviewer believes that the author studies the influence mechanism of the actual sewage treatment plant operating temperature on the deep treatment membrane pollution, distinguishes the different reasons for the increase of total membrane resistance under low temperature conditions, which is an interesting research work, which provides a theoretical reference for alleviating membrane fouling and reducing operating costs, which has practical significance. (Source: Wang Min, China Science News)

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