| Summary: | Direct membrane filtration (DMF) of municipal wastewater offers an alternative solution for centralized and decentralized wastewater treatment in Iceland. The efficiency of biological-based wastewater treatment is restricted in Iceland, due to low temperatures and high wastewater inflow rates with extremely low concentration of organics. This study aims to investigate membrane fouling mechanisms and mitigation approaches during DMF of municipal wastewater. The DMF experiments were performed using a crossflow flat sheet membrane filtration cell integrated with an optical coherence tomography (OCT) imaging system. The effects of membrane material, operation conditions and cleaning protocol on DMF performance and foulant composition were examined. The threshold flux testing results indicated that a PVDF membrane (0.08 μm) was suitable for DMF of wastewater. Increasing crossflow velocity, physical flushing frequency and flushing water temperature contributed greatly to mitigate fouling. During a continuous DMF process, reversible fouling was predominant, while during intermittent DMF with periodical physical cleaning, irreversible/ irremovable fouling was dominant. A possible shift of tightly attached cake layer to irreversible/ irremovable fouling was revealed by the direct observation of fouling via OCT. The foulants autopsy indicated that a combination of organic and inorganic foulants was attributed to membrane fouling, instead of biological fouling. Under the optimized filtration condition, sustainable long-term DMF operation (~230 h) was achieved by employing a combination of periodical physical flushing with chemical-enhanced flushing. The water quality analysis showed that the DMF process could efficiently remove solids and greater-sized soluble organics, allowing the treated water to meet wastewater discharge standards. University of Iceland Research Fund
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