New insights into membrane fouling during direct membrane filtration of municipal wastewater and fouling control with mechanical strategies

• Published in: The Science of the total environment 2023-04, Vol.869, p.161775, Article 161775
• Main Authors: Men, Yu, Li, Zifu, Zhu, Lixin, Wang, Xuemei, Cheng, Shikun, Lyu, Yaping
• Format: Article
• Language: English
• Subjects: Biofouling; Bioreactors; Direct membrane filtration; Filtration - methods; Flat-sheet ceramic membrane; Intermittent aeration; Membrane fouling mechanism; Membranes, Artificial; Periodic backwash; Wastewater; Water Purification - methods
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2023.161775

Direct membrane filtration (DMF) technology achieves energy self-sufficiency through carbon recovery and utilization from municipal wastewater. To control its severe membrane fouling and improve DMF technology, targeted research on fouling behaviour and mechanisms is essential. In this study, a DMF reactor equipped with a flat-sheet ceramic membrane was conducted under three scenarios: without control, with intermittent aeration, and with periodic backwash. This system achieved efficient carbon concentration with chemical oxygen demand below 50 mg/L in permeate. Membrane fouling was dominated by intermediate blocking and cake filtration. And reversible external resistance accounted for over 85 % of total resistance. Predominant membrane foulants were free proteins, whose deposition underlies the attachment of cells and biopolymers. Backwash decreased the fouling rate and increased fouling layer porosity by indiscriminately detaching foulants from the membrane surface. While aeration enhanced the back transport of large particles and microbial activity, causing a relatively thin and dense fouling layer containing more microorganisms and β-d-glucopyranose polysaccharides, which implies a higher biofouling potential during long-term operation. In addition, aeration combined with backwash enhanced fouling control fivefold over either one alone. Therefore, simultaneous operation of backwash and other mechanical methods that can provide shear without stimulating aerobic microbial activity is a preferred strategy for minimizing membrane fouling during DMF of municipal wastewater. [Display omitted] •External organic foulants are mainly responsible for membrane fouling.•Foulants accumulated on the membrane surface originally are free proteins.•Intermittent aeration and periodic backwash effectively controlled membrane fouling.•Higher porosity in fouling layer decreased COD rejection with periodic backwash.•Aeration increased β-d-glucopyranose polysaccharides attached to membrane surface.