Reuse of carwash water with a cellulose acetate ultrafiltration membrane aided by flocculation and activated carbon treatments

A reuse system for carwash water with a cellulose acetate (CA), hollow-fiber-type ultrafiltration membrane with the aid of flocculation and activated carbon treatments was proposed. The multi-blended flocculating agent containing bentonite, Al₂(SO₄)₃, sodium alginic acid and a cationic polyacrylamide showed higher removals of COD and turbidity for carwash wastewater compared with Al₂(SO₄)₃ or a water-soluble polymer individually. The effect of pure water permeability of the membrane on permeation flux in pretreated carwash wastewater by this agent was examined using three kinds of CA membranes whose molecular weight cut-offs were 150,000 Dalton. Permeation flux showed a higher value in the case of the membrane with higher pure water permeability. Practical scale experiments with a membrane area of 32 m² and 48 m² were conducted under a membrane pressure of 20 kPa. When carwash wastewater was pretreated with 50 mg/L of this multi-blended flocculating agent, permeation flux through the CA membrane with pure water permeability of 0.78 m³/(m²/h) at 100 kPa showed 1.0 m³/(m²/d) for more than 6 months. The COD, BOD and extract by n-hexane values of reuse water were 3.7-15.7 mg/L, 2.5-14.0 mg/L and below 0.5 mg/L, respectively.