Characterization and control of membrane fouling during dewatering of activated sludge using a thin film composite forward osmosis membrane.

This study investigated the feasibility of applying a thin film composite (TFC) forward osmosis (FO) membrane in the dewatering of activated sludge (AS). Membrane fouling was investigated and controlled to enhance the system's performance. Investigations showed that the TFC FO membrane provided a water flux that was 120 % higher and a concentration factor that was three times higher compared to a cellulose tri-acetate (CTA) membrane. The foulant layer on the TFC membrane surface was mostly irreversible when 1.44 mg-C/cm and 0.13 mg-C/cm dissolved organic carbon (DOC) were extracted in sodium hydroxide (NaOH) and deionized (DI) water, respectively. The results of principle component analysis (PCA) revealed that among the operating conditions, the amount of aromatic organic compounds (indicated by UV values) followed by their hydrophilicity (specific ultraviolet absorbance (SUVA) indices) were the dominant factors controlling the different fouling potentials. SUVA value indices ranged from 0.4 to 0.6 L/m-mg DOC, illustrating that hydrophilic compounds were more responsible for membrane fouling than hydrophobic components. These results implied that aromatic and hydrophilic substances, in particular protein and polysaccharides were key components of the fouling layers, which need to be considered to enable a reduction of membrane fouling. We thus employed several novel fouling control methods, in which the combination of mono-chloramine pre-treatment and membrane cleaning by NaOH resulted in the recovery up to 86 % of the water from raw AS.