The Thai Journal of Veterinary Medicine


The investigation of the relative roles of Soluble Microbial Products (SMP) in membrane fouling was studied in submerged membrane bioreactors (SMBRs). Three lab-scale SMBRs were operated at a constant permeate flux (12.5 l/m2 h) with a flat sheet microfiltration membrane (hydrophilic polyolefin, pore size of 0.25 μm) using different sludge retention times (SRTs of 8, 20 and 80 days, respectively). The concentrations of SMP in terms of dissolved organic carbon (DOC) and protein at the steady-state period were compared. The results showed that as SRT increased, the organic carbon content of SMP tended to be independent of SRT while the protein content in the SMP tended to decrease with increasing SRT. Batch filtration tests were conducted to determine the specific cake resistances of the fouling layer, using both the raw sludge and the twice-washed sludge with a buffer solution. The difference in specific cake resistances in both sludges indicated that the specific cake resistance of SMP contributed approximately half the total specific cake resistance. Furthermore, SMP were found in major portions in both the biofilm and the mixed liquor. It follows that SMP played a relatively significant role in membrane fouling.

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