This research has investigated the effects of varying mixed liquor pH (i.e. 5.5, 6.5, 7.5, 8.5) on the landfill leachate biodegradability and fouling behavior in two submerged membrane bioreactors (MBR) for a 150-day period. In the experiments, variations in organic removal and dissolved organic matters (DOM) transformation, microbial community and mixed liquor properties as well as the fouling behavior were monitored and systematically analyzed. The findings indicated that the organic removal in both MBRs was insignificantly different for the entire experimental pH range and that the pH levels influenced the DOM transformation. In the analysis of microbial community, PCR-DGGE revealed considerable structural changes, pointing to an effect of pH on the dynamic shift in bacterial species. In addition, clone library analysis showed that Proteobacteria was the dominant phylum in the MBRs and that the dominant bacterial community belonged to the classes Betaproteobacteria and Gammaproteobacteria, both of which were more abundant at pH 8.5 than at pH 5.5. The experiment also showed that the mixed liquor properties were affected by the pH variations. The extracellular polymeric substance (EPS) formation in the mixed liquor at pH 5.5 significantly contributed to membrane fouling while hindering the inorganic and humic substances fouling. Nevertheless, the organic fouling under the low pH condition could be effectively removed by membrane chemical cleaning. It is expected that the experimental results could be applied to enhance the biodegradability and mitigate the fouling in the MBR process.

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This research investigated the membrane fouling and micro-pollutant removals in treatment of municipal landfill leachate at various pH levels (i.e. 5.5, 6.5, 7.5, and 8.5) using membrane bioreactors. The findings revealed that membrane fouling was influenced by the pH level of mixed liquor, with pH 5.5 exhibiting the most severe membrane fouling. At pH 5.5, proteins and carbohydrates were predominant in the membrane foulants, while at pH 8.5 humic-like and inorganic substances constituted the largest proportion of the foulants on the membrane surface. The removal efficiencies of micro-pollutants (bisphenol-A; 2,6-di-tert-butylphenol and 2,6-di-tert-butyl-4-methylbutylphenol) were nevertheless insignificantly influenced by the pH levels of mixed liquor. In addition, the removal rates of the compounds at pH 5.5 were slightly lower vis-à-vis at the higher pH levels. The micro-pollutant retention on the fouled membranes was also significant and highest under the mixed liquor pH of 8.5. Furthermore, the experiments demonstrated that the varying degrees of rejection by the fouled membranes could be attributed to the alteration of foulant characteristics as a result of the pH variations.

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