Nanofiltration in pilot scale for wastewater reclamation: Long-term performance and membrane biofouling characteristics

Abstract Nanofiltration (NF) has been recognized as a cost-effective membrane technology for wastewater reclamation, while little information is available about its performance in pilot scale for practical engineering application. In addition, the biofouling issue is always a barrier to membrane process for its long-term stable operation which requires further investigations. In this study, the performance of a pilot-scale two-stage NF system was continually monitored for three months. The membrane autopsy characterization was conducted when the irreversible membrane fouling occurred. The rejections of COD, TOC and TP by NF were 96.5 ± 1.2%, 91.9 ± 1.9% and 97.7 ± 2.1%, respectively. A total of 23 emerging contaminants have been detected in NF influent, including 19 pharmaceuticals and personal care products (PPCPs) and four environmental estrogens (EEs). Except for bisphenol A (57.6%) and ibuprofen (69.9%), the rejections of other 21 emerging contaminants were all higher than 80% by the NF system. Microbial community structure analysis showed that Proteobacteria and Bacteroidetes were the two predominant bacteria on the membrane surface with percentages of 34.1%-41.0% and 23.4%-30.6% at phylum level, respectively. At genus level, Stenotrophomonas and Pseudoxanthomonas were primarily dominant in the first stage, while Cloacibacterium and Methyloversatilis showed higher relative abundances in the second stage. Sphingopyxis was an extremely stubborn genus on the membrane surface. Besides, the biodiversity of microbial communities in the first stage was higher than that in the second stage, possibly showing more severe biofouling in the first stage of the two-stage NF system. This study has provided insights to understand the practical performance of NF technology in pilot scale and could give guideline for biofouling control in NF engineering application.