Daisuke Okamura

Identification of biofoulant of membrane bioreactors in soluble microbial products.

To reveal primary biofoulant in soluble microbial products (SMP) and/or soluble extracellular polymeric substances (EPS), after removal of sludge particles, activated sludge samples were subjected to microfiltration tests in a submerged MBR. Filtration resistance directly correlates with the saccharide concentration. Saccharides in wastewater from several sources contained uronic acids, which increased the filtration resistance. When the microfiltration test liquids contained saccharides over 80mg l(-1), a gelatinous mass remained on the membrane surface after filtration and contained concentrations of saccharides and uronic acids 50 times higher than the original test liquid while only trace amounts of these substances were contained in the filtrate. The gelatinous mass contained high molecular weight substances of 10(6)-10(8)Da, suggesting the presence of polysaccharides. However, molecules of this size were calculated to be much smaller than the pore size of the membrane. Ethylenediaminetetraacetic acid decreased filtration resistance, suggesting that polysaccharides containing uronic acid units could undergo intermolecular or intramolecular ionic cross-linking by polyvalent cations and form the gel, thus clogging the membrane pores as an actual biofoulant.

Effects of microbial degradation of biofoulants on microfiltration membrane performance in a membrane bioreactor.

In membrane bioreactors (MBRs) for wastewater treatment, membrane fouling, particularly biofouling caused by soluble microbial products (SMP), is a nuisance problem causing decreases in permeation flux. In a previous study, we identified primary biofoulants of microfiltration (MF) membranes in SMP as polysaccharides containing uronic acids that undergo inter- and intramolecular ionic cross-linking by polyvalent cations, forming a gelatinous mass that clogs membrane pores. In the present study, we therefore attempted to isolate biofoulant-degrading microorganisms from activated sludge on a polygalacturonic acid-overlaid agar medium and evaluate their efficiency for preventing biofouling of MF membranes. Among the isolates, the fungal strain HO1 identified as Phialemonium curvatum degraded 30% of polysaccharides containing uronic acids into smaller molecules in a SMP solution containing a high concentration of saccharides after 30 days of cultivation. Microfiltration tests using a laboratory-scale submerged MBR indicated that the filtration resistance of this degraded SMP solution was lower than that of the control SMP solution without fungal inoculation. Importantly, accumulation of gelatinous mass on the membrane responsible for biofouling was avoided in the SMP solution augmented with P. curvatum HO1 during the microfiltration test. This is the first report to describe a new method for avoiding biofouling of MBRs by microbial degradation of primary biofoulants.