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Fate of NaClO and membrane foulants during in-situ cleaning of membrane bioreactors: Combined effect on thermodynamic properties of sludge

Zhang, Haifeng, Sun, Ming, Song, Lianfa, Guo, Jingbo, Zhang, Lanhe
Biochemical engineering journal 2019 v.147 pp. 146-152
cleaning, filtration, fouling, hydrophobicity, membrane bioreactors, polymers, sludge, sodium hypochlorite, thermodynamics
In this study, the fate of sodium hypochlorite (NaClO) and detached membrane foulants and their impacts on the thermodynamic properties of raw sludge were investigated in a membrane bioreactor (MBR). It was found that about 20.3% of the total NaClO was potentially released into the bulk sludge, which significantly altered the raw sludge surface properties, such as a reduction in the number of surface electron donor components (γ−) and an increase in surface hydrophobicity. After exposure to NaClO, the treated sludge had a higher adhesive and cohesive propensity compared to the raw sludge. Based on the extended Derjaguin-Landau-Verwey- Overbeek (XDLVO) theory and the batch filtration test results, the detached foulants potentially aggregated with the treated sludge and form the reconstructed sludge. The reconstructed sludge had a high protein (PN) level in the extracellular polymeric substances (EPS), with a higher membrane fouling potential compared with the raw sludge.