Effect of Membrane Fouling with Different Backwash Mode for Ultrafiltration Process in Municipal Wastewater: Hydraulic Backwash and Backwash with Sodium Hypochlorite

Abstract

Abstract Ultrafiltration process is widely used in the municipal wastewater treatment. However, membrane fouling is posing a critical obstacle limiting the further application which lead to membrane performance decline and operating costs increase. In this study, the raw water was the denitrifying biological filter from Beijing municipal wastewater treatment. The performance and membrane fouling under different backwash modes was investigated. One mode was the traditional hydraulic backwash and the other was the addition of sodium hypochlorite (NaClO) into the backwash water. The results showed that the trans-membrane pressure (TMP) increased from 33.2 kPa to 48.2 kPa under the hydraulic backwash in 80 filtration cycles, but increased from 33.3 kPa to 39.3 kPa under the addition with NaClO. It also can be noticed that the hydraulic-irreversible fouling index decreased from 5.58×10− 3 m2/L to 3.58×10− 3 m2/L under the introduction of NaClO to backwash. Moreover, the membrane fouling mechanism under different backwash modes was expored. According to EEM, the response value of protein-like was increased from 11.9–15.2% under the addition of NaClO. The protein-like was identified as the main component contributed to the membranes fouling by blocking the membrane pores. The fouling layer can be stripped by the backwash with the adding of NaClO. In addition, the consumption of NaClO was decreased from 675 g to 670 g after the addition of NaClO in backwash during 2.5 chemically enhanced backwash cycle. Moreover, backwash with the addition of NaClO was an easy and better control method for membrane fouling in real application.