Ultrafiltration significantly increased the scaling potential of municipal secondary effluent on reverse osmosis membranes

Xin Tong; Zi-Wei Zhang; Yin-Hu Wu; Yuan Bai; Nozomu Ikuno; Kazuki Ishii; Hong-Ying Hu

doi:10.1016/j.watres.2022.118672

Ultrafiltration significantly increased the scaling potential of municipal secondary effluent on reverse osmosis membranes

Water Res. 2022 Jul 15:220:118672. doi: 10.1016/j.watres.2022.118672. Epub 2022 May 26.

Authors

Xin Tong¹, Zi-Wei Zhang¹, Yin-Hu Wu², Yuan Bai¹, Nozomu Ikuno³, Kazuki Ishii³, Hong-Ying Hu⁴

Affiliations

¹ Environmental Simulation and Pollution Control State Key Joint Laboratory, State Environmental Protection Key Laboratory of Microorganism Application and Risk Control (SMARC), School of Environment, Tsinghua University, Room 524, Beijing 100084, PR China.
² Environmental Simulation and Pollution Control State Key Joint Laboratory, State Environmental Protection Key Laboratory of Microorganism Application and Risk Control (SMARC), School of Environment, Tsinghua University, Room 524, Beijing 100084, PR China; Beijing Laboratory for Environmental Frontier Technologies, Beijing 100084, PR China. Electronic address: wuyinhu@mail.tsinghua.edu.cn.
³ Kurita Water Industries Ltd., Nakano-ku, Tokyo 164-0001, Japan.
⁴ Environmental Simulation and Pollution Control State Key Joint Laboratory, State Environmental Protection Key Laboratory of Microorganism Application and Risk Control (SMARC), School of Environment, Tsinghua University, Room 524, Beijing 100084, PR China; Research Institute for Environmental Innovation (Suzhou), Tsinghua, Suzhou, Jiangsu 215163, PR China.

PMID: 35635920
DOI: 10.1016/j.watres.2022.118672

Abstract

Ultrafiltration (UF) was often used as pretreatment in front of reverse osmosis (RO) unit because of its high rejection efficiency of microbes and particles. However, in some cases UF pretreatment might show adverse effects on the RO membrane flux. In this study, the effects of UF pretreatment on secondary effluent water quality and its RO membrane fouling characteristics were explored. There was almost no change of water quality after UF with different molecular weight cut-off (MWCO) membranes (100, 30 and 10 kDa), including total dissolved solid (TDS), alkalinity, conductivity, ion concentrations, etc., while pH increased a little and dissolved organic carbon (DOC) declined by about 1 mg/L. On the contrary, the RO membrane flux of UF permeates presented clear decline in comparison to the secondary effluent. The membrane fouling velocity and steady-state flux of secondary effluent was 0.052 and 0.656, while fouling velocity increased (0.077, 0.071, 0.067) and steady-state flux decreased significantly (0.397, 0.416, 0.448) after 100, 30, 10 kDa UF membrane pretreatment. Scanning electron microscope (SEM) images showed many crystals on the fouled membrane surfaces, which turned out to be CaCO₃ by Energy dispersive spectrometer (EDS) analysis and precipitation calculation. After the addition of UF retentates to UF permeates, scaling was prevented and crystals on the RO membrane almost disappeared, which implied the anti-scaling effect of the UF retentates with low concentration. According to anti-scaling performance experiments, the anti-scaling performance of 100 k, 30 k, 10 k retentates was 2.7%, 4.0% and 7.3%, respectively. Excitation emission matrix (EEM) and fourier transform infra-red (FTIR) results showed that these retentates retained by different MWCO membranes were similar and composed of protein-like substances and soluble microbial products. The effect of key minority components in RO system deserved further exploration.

Keywords: Antiscaling effect; Reverse osmosis membrane fouling; Scaling; Ultrafiltration pretreatment.

MeSH terms

Filtration
Membranes, Artificial
Osmosis
Ultrafiltration* / methods
Water Purification* / methods

Substances

Membranes, Artificial