Impact of electrocoagulation of soluble microbial products on membrane fouling at different volatile suspended solids' concentrations.

This research had two objectives: (1) to study the combined effect of volatile suspended solids (VSS) and soluble microbial product (SMP) on membrane fouling in an attempt to explain the discrepancies of previous studies and (2) to investigate the feasibility of reducing SMP impact on membrane fouling rate by electrocoagulation. Electrocoagulation successfully removed up to 55% and 90% of protein and polysaccharides, respectively, which resulted in a substantial reduction of membrane fouling rate (four times less). The results showed that at a comparable VSS concentration, membrane fouling increased with an increase in SMP. For example, for the same magnitude of VSS, membrane fouling rate was four times higher as the concentration of SMP tripled. Higher VSS concentrations were not directly responsible for higher fouling rates unless there was an increase in the SMP concentration. It was concluded that the correlation of membrane fouling with VSS alone is misleading unless accompanied with SMP concentration. Statistical analysis demonstrated that VSS impact on membrane fouling was not significant when it was considered as a single independent variable. The most accurate prediction of the membrane fouling was built by multiple regression model based on a quadratic VSS and linear SMP as independent variables.

Novel electrokinetic approach reduces membrane fouling.

An innovative submerged membrane electro-bioreactor (SMEBR) was built to reduce membrane fouling through a combination of various electrokinetic processes. The objective of this research was to assess the capability of SMEBR to reduce fouling under different process conditions. At the bench scale level, using synthetic wastewater, membrane fouling of the SMEBR was compared to the fouling of a membrane bioreactor (MBR) in five runs. Different protein concentrations in the influent synthetic wastewater were selected to develop different membrane fouling potentials: high (240 mg/l), low (80 mg/l) and zero protein addition. The MBR and SMEBR were operated at a flux equal to the membrane critical flux in order to create high fouling rate conditions. Membrane fouling rate, expressed as the change in the trans-membrane pressure per day (kPa/d), decreased in the SMEBR 5.8 times (standard deviation (SD) = 2.4) for high protein wastewater, 5.1 times (SD = 2.4) for low protein content, and 1.3 times (SD = 0.7) for zero protein, when compared to the MBR. The supernatant concentrations of the soluble microbial products (SMP) were 195-210, 65-135 and less than 65 mg/l in respective experimental series. Following the bench scale study, membrane fouling was assessed in a pilot scale SMEBR, fed with raw un-clarified municipal wastewater, and operated under real-sewage variable quality conditions. The pilot SMEBR exhibited three times smaller membrane fouling rate than the MBR. It was concluded that electrokinetic processes generated by SMEBR led to a reduction of membrane fouling through: i) removal of soluble microbial products (mainly protein and polysaccharides) and colloidal organic materials; ii) change of the structure and morphology of the suspended solids due their conditioning by DC field.