Polyethersulfone membrane fouling mitigation during ultrafiltration of wastewaters from car washes

Abstract

The car wash wastewater was separated by ultrafiltration. The commercial ultrafiltration (UF) polyethersulfone (PES) membranes (10 and 100 kDa) were applied. The FTIR analysis indicated that membrane matrix beside PES also contained poly(vinyl pyrrolidone) (PVP). These membranes were used for the wastewater separation, achieving over 50 % rejection of most contaminants and the permeate with a turbidity of <0.2 NTU. It has been shown that a severe membrane fouling was caused not only by the pollutants removed from the cars but also by the detergents used for car washing. As a result, the permeate flux disappeared after 5–10 h of filtration. The Hermia's models analysis indicated that raw wastewater (841 NTU) caused both complete blocking and intermediate fouling mechanism. Wastewater turbidity was reduced by sedimentation (29 NTU), and consequently, cake formation was dominant fouling mechanism in this case. Fouling was reduced by washing the membranes with alkaline agents (pH = 11–12), commonly used in car washes, to clean wheels and remove insects. By washing the membranes every 5–7 h for 30 min with solutions (0.3–0.5 %) of these agents a stable permeate flux at a level of 80 % of the initial flux was obtained during 100 h wastewater filtration tests.