Control of Membrane Fouling by Coagulant and Coagulant Aid Addition in Membrane Bioreactor Systems

Abstract

The mixture of polysilicate and Fe(III), and commercial polysilicato-iron (PSI) were employed to control membrane fouling risk. Batch experiments and long-term membrane bioreactor (MBR) experiments were conducted with the addition of 1) polysilicate, 2) mixtures of polysilicate and Fe(III) with various ratios, and 3) sole Fe(III) and commercial PSI with two available molar ratios, Fe/Si = 1:1 (PSI-100) and Fe/Si = 1:0.25 (PSI-025). Sole polysilicate addition in MBR showed no effect on controlling membrane fouling risk, while the mixture of polysilicate and Fe(III) could yield some advantages at a specific combination, 90 mg/L Fe(III) with 5 mg/L Si for batch experiment, and 45 mg/L Fe(III) with 20 mg/L Si for long-term MBR experiment. On the other hand, the higher efficiency of biopolymer removal was attained by the addition of PSI in batch experiments. Furthermore, the membrane fouling frequencies were reduced and the concentrations of protein and carbohydrate in soluble microbial products (SMP less than 1μm) were largely diminished by the addition of PSI in long-term MBR experiments. These results suggested that PSI would be useful to control membrane fouling problem and enhance the performance of membrane filtration.