Removal of trace organic contaminants by enzymatic membrane bioreactors: Role of membrane retention and biodegradation

Performance of an enzymatic membrane bioreactor (EMBR) equipped with either an ultrafiltration (UF) or a nanofiltration (NF) membrane was explored for the degradation of a set of 29 chemically diverse trace organic contaminants (TrOCs). The NF membrane provided effective retention (90-99%) of TrOCs within the NF-EMBR. On the other hand, partial retention of charged and significantly hydrophobic (log >3) TrOCs was achieved by the UF membrane via charge repulsion and adsorption on the enzyme gel-layer formed on the membrane surface during UF-EMBR operation. Laccase achieved TrOC-specific degradation in both EMBRs. The extent of TrOC degradation was significantly (5 to 65%) better by NF-EMBR as compared to that achieved by UF-EMBR. Addition of a redox-mediator (violuric acid) at concentrations ranging from 10-100 μM improved the degradation of non-phenolic TrOCs, but degradation efficiency reached a plateau when its concentration was increased beyond 25 μM. Although the permeate flux of the UF/NF membranes dropped with time due to membrane fouling caused by enzyme gel-layer and/or concentration polarization, membrane flushing with water was effective in recovering the flux by up to 95%.