Application of dispersed and immobilized hydrolases for membrane fouling mitigation in anaerobic membrane bioreactors

Enhancing the hydrolysis of microbial macromolecules by supplementing exogenous hydrolases may improve membrane performance via structural disruptions of fouling layers and alterations to sludge characteristics. This was investigated by short batch filtration (< 1 h) and 30-day extended filtration experiments using laboratory-scale anaerobic membrane bioreactors. Crude hydrolases were either dispersed directly into the reactor, or immobilized onto microfiltration membranes. Under constant flux operation, dispersed enzymes consistently moderated increases in transmembrane pressures (TMPs) compared to the control setup. Immobilized hydrolases appeared effective in the short filtration test, but in the extended experiment, the pseudo-stable TMP was not significantly lower compared to the control TMP. With dispersed enzymes, the average TMP was almost 30% lower than the control value. This was associated with a 33% reduction in the protein content of the bulk extracellular polymeric substances, and a 45% reduction in the membrane cake density. Immobilized enzymes limited cake formation to a similar extent through hydrolysis at the base of the cake, but this was negated by the increase in gel resistance attributed to the hydrophobic attraction between the immobilization layer and proteinaceous hydrolysis products. Even as the dispersed hytholases exhibited greater effectiveness under the conditions studied, there is scope for further enhancement in both approaches. (C) 2015 Elsevier B.V. All rights reserved.