Long-term operation of a full-scale membrane bioreactor for industrial wastewater treatment using polyvinyl fluoride hollow fiber membranes: A systematic evaluation during 18-year operation

•A full-scale membrane bioreactor for treating industrial wastewater was operated for 18+ years.•In-depth inspection of the membrane surface revealed marginal biocake formation.•A stable treated water quality and transmembrane pressure (TMP) were achieved.•Membrane fouling was prevented by chemical cleaning at a threshold TMP. A membrane bioreactor (MBR) is a robust, high-performance technology for wastewater treatment that has been commercialized and disseminated worldwide since 1990. Despite broad implementation of this technology in the wastewater sector, ultralong operation beyond the membrane lifetime has rarely been reported. Therefore, the objectives of this study were to investigate (1) the effectiveness of a manually-operated feedback strategy to prevent membrane biofouling by dosing with sodium hypochlorite and oxalic acid and (2) the organic carbon removal of industrial wastewater treated by a full-scale MBR system in a chemical plant. The manually-operated feedback strategy consisted of monitoring the transmembrane pressure (TMP) by a test module in a bench-scale MBR to detect an inflection point, that is, the point (15 kPa) at which the TMP switched from growing gradually to exponentially in time. Biocake formation became noticeable at the inflection point, suggesting the TMP at which the membrane should be chemically washed to prevent severe biofouling. A full-scale MBR system was installed with a polyvinylidene fluoride (PVDF) membrane for organic carbon removal. The membrane was washed with 3000 mg/L of sodium hypochlorite and 1 wt% oxalic acid when the TMP reached 15 kPa during operation. The MBR was successfully operated for over 18 years without the PVDF membrane being damaged or compromised by biofouling. Characterization of the foulants on the membrane surface revealed that membrane washing removed inorganic (calcium and iron) and organic (acid amides and polysaccharides) foulants, plausibly by the action of oxalic acid and sodium hypochlorite, respectively. Installing a robust PVDF membrane and performing chemical washing at an inflection point in the TMP dynamics enabled ultralong MBR operation beyond the regular membrane lifetime. The implementation of the advocated strategy paves the way for the low CO2 footprint operation of a PVDF MBR, which does not require frequent membrane replacement and laborious membrane ex-situ cleaning.