Abstract
Nanofiltration membrane technology is an effective method for secondary treated sewage purification. However, membrane fouling, which is inevitable in the membrane-separation process, can reduce membrane performance and shorten membrane life. Installing a turbulence promoter is a promising means of improving the hydraulic conditions inside the membrane chamber. In this study, the effect of turbulence promoter on prolonging membrane life was studied for the first time. Flat-sheet polyethersulfone nanofiltration membrane was used to filter humic acid solution, used for simulating secondary treated sewage. By comparing photographs and SEM images of the membrane before and after the simulated secondary treated sewage filtration, it was found that humic acid tended to be deposited on the low-velocity region, which was reflected by COMSOL simulation. After incorporating a turbulence promoter, the reduction of the humic acid deposition area and membrane fouling resistance indicated that the turbulence promoter could reduce membrane fouling due to the improved hydraulic conditions. Additionally, the turbulence promoter also increased the flux and reduced the flux decay rate. The turbulence promoter was then place in the crossflow flat-sheet membrane filtration module, and the variation of flux with time was tested in simulated secondary treated sewage with different concentrations. The results showed that the membrane life for the filtration of simulated secondary treated sewage comprising 50, 250, and 500 ppm humic acid increased by 23.1%, 80.4%, and 85.7%, respectively. The results of this article can serve as a reference for the prediction of membrane life and the performance enhancement mechanism of membranes containing a turbulence promoter.
Highlights
Water shortage and water pollution significantly hinder sustainable development, which is one of the greatest challenges facing humanity in the 21st century
By comparing the photographs and the SEM images of the membrane before and after 2 h of fouling by simulated secondary treated sewage (SSTS) (200 ppm HA, pH = 7) (Figure 6), it can be seen that HA deposited unevenly on the membrane surface
The level of membrane fouling followed the order Zone c > Zone b > Zone a, where extensive fouling was deposited in Zone c, consid
Summary
Water shortage and water pollution significantly hinder sustainable development, which is one of the greatest challenges facing humanity in the 21st century. Nanofiltration is a typical pressure-driven membrane-separation process that can treat secondary treated sewage, drinking water, and leachate [1,2,3,4]. Due to the significant improvement of nanofiltration membrane-separation performance and the reduction of operational costs, nanofiltration is widely used to meet the increasing demand of fresh water and strict standards of sewage discharge [5,6]. If membrane fouling causes permeate flux to drop to a certain level, the membrane needs to be rinsed or potentially replaced, which increases the operational cost, but causes the interruption of the membrane process, limiting the application of membrane technology. Researchers are devoted to mitigating the membrane fouling rate as much as possible, thereby prolonging the membrane life [10]
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