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

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 m(2), 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(-2)h(-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(-2)h(-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.