Contribution of proteins to ceramic membrane fouling at the early stage of membrane filtration

Membrane-based filtration is widely applied for water and wastewater treatment, while membrane fouling caused by contaminants such as proteins is an inevitable problem. Protein-containing mixtures or intact model proteins (e.g., bovine serum albumin, BSA) have been conventionally adopted and recognized as important membrane foulants. However, due to the complex composition of the protein-containing mixture or the inappropriate concentrations of model substances adopted, the real contribution of protein-like fractions toward ceramic membrane fouling remains unknown yet. In this work, the fouling behaviors of BSA and tryptones, representing the intact protein and the mixture of peptides, respectively, in a ceramic membrane microfiltration system were investigated. Both of them exhibited a negligible flux decrease and membrane fouling. For comparison, the fouling behaviors of the environmental protein-like substances (EP) extracted from different sludge sources were also examined. In addition, the experimental and simulation results demonstrate that all the EP samples were easier to aggregate and be adsorbed on the membrane surface than the two model proteins because the environmental protein-like substances had more unsaturated groups. However, those properties were insufficient to cause rapid membrane pore blockage or biocake formation compared with the previous studies. Both the model and actual protein fractions led to light membrane fouling, implying that proteins were not mainly responsible for membrane fouling at the early stage of ceramic membrane microfiltration.