Influence of various operating conditions on cleaning efficiency in sequencing batch reactor (SBR) activated sludge process. Part II: Backwash and water rinsing introduced membrane filtration process

In this paper, the influences of backwashing conditions on the washing efficiency (P) were systematically investigated by a combination of orthogonal table and multivariate linear regression methods. The experiments were performed with the feed suspension from SBR and deionized water in laboratory-scale dead-end microfiltration test unit with 0.1 μm PES microfiltration membrane. The impact of shearing stress on the backwashing recovery (ri), and mass-transfer coefficient on washing efficiency (P) were studied respectively. The results showed that backwash and water rinsing introduced membrane filtration process could restore the declined flux close to 100%. However, the ability of backwashing was gradually reducing with the increase of backwashing cycle, which was associated with the increasing accumulation of irreversible fouling onto and into the membrane pores. ri and P increased with the increase of transmembrane pressure (TMP), and decreased with the increase of operating temperature. Since the foulants are more susceptible to be washed away from the membrane pores during a longer backwash, the ri got a high value, on the contrary, the productivity decreased with an increase of backwash duration due to the back pumping of more detergent. The average contribution of backwashing conditions on P were detergent temperature (50.49%) > transmembrane pressure (39.84%) > backwashing times (7.27%) > backwashing time (2.39%). The backwashing conditions were optimized and the relationship between backwashing conditions and washing efficiency (P) was analyzed and defined quantitatively.

Research Highlights
► The membrane flux increased significantly after the backwashing process.
► The shearing stress can efficiently remove foulants during a backwashing process.
► With the increase of TMP and T, k and P showed the same tendency.
► The optimum condition and the sequence of the influence factors were obtained.
► The regression equations for the backwashing efficiency were obtained.