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Parallel experimental tests to measure mixed liquor filterability for submerged membrane bioreactors were conducted over a six month period using three ZW-500 pilot plants and a ZW-10 lab-scale filterability apparatus. Non-air sparged conditions during the tests yielded operation behaviour that was equivalent to dead-end filtration. The fouling resistance increased linearly with the intercepted mass until a critical point was reached at which point significant cake compression was induced and the resistance began to increase exponentially. Although the point of cake compression appears to be dependent on the membrane module design, similar resistance per unit solid mass intercepted per unit area (R(mass)) values were observed when the same mixed liquor was filtered. Coupled with the established correlation between the R(mass) and the critical flux, it is suggested that the filterability test results from a side-stream, lab-scale module may be used to predict fouling potential in a full scale MBR wastewater treatment system without interrupting the full-scale MBR operation.

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Membrane fouling was studied using three pilot-scale submerged membrane bioreactors operated at a series of permeation and aeration conditions to treat municipal wastewater. The transmembrane pressure increases were used to calculate the fouling ratios to compare the relative fouling rates. The results showed that the trends of fouling resistances differed greatly, depending on the permeate flux and mixed liquor characteristics. A stable fouling resistance can result when the filtration is operated at sustainable permeate flux conditions. At the unsustainable permeate flux conditions, the fouling resistance increased exponentially as the filtration progresses. In all the cases, the fouling ratios increased with permeate flux and decreased with aeration intensity. Furthermore, the effects of aeration intensity on fouling ratio is independent of the permeate flux and vice versa. Finally, the variation of fouling ratios at different operating conditions strongly depends on the sludge characteristics of mixed liquor and it appears that more than one parameter of mixed liquor is needed to define their relationship.

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