Intermittent operation of low pressure UF membranes for sewage reuse at household level

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A household-scale wastewater treatment system was operated with domestic sewage. The system could recover gardening/irrigation water from raw sewage or secondary effluent by low pressure ultrafiltration (UF). The UF membranes (surface area = 3.5 m2, pore size = 0.04 μm) were operated at constant transmembrane pressure (0.13 bar). The proposed technology was examined for approximately 2 months without membrane cleaning. Membrane operation was performed periodically (one or two times per week), simulating water usage for gardening irrigation. During raw sewage filtration (chemical oxygen demand (COD) total = 242 ± 71 mg L–1, COD soluble = 105 ± 51 mg L−1, suspended solids = 188 ± 58 mg L−1), low permeate COD was achieved (52 ± 25 mg L−1), whereas nitrogen and phosphorus were recovered in the permeate. The water recovered during 1 h of operation displayed a gradual decrease from 42 to 22 L m−2h−1 during the 50-d time period. For the secondary effluent filtration, the UF module achieved consistently a recovery rate of 39.6 ± 8.0 L m−2h−1, with an average permeate COD of 37 mg L−1. In this case, the fouling layer (cake layer) was completely reversible after the relaxation period, rendering the process suitable for unattended household applications.

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