# Degradation of Trace Organic Contaminants by a Membrane Distillation--Enzymatic Bioreactor
## 1 Introduction  
Lacase (EC 1.10.3.2), a copper-containing oxidoreductase enzyme, has been studied extensively for the degradation of recalcitrant compounds such as phenols and aromatic hydrocarbons [1; 2; 3; 4; 5]. In recent years, lacase-catalyzed degradation of trace organic contaminants (TrOCs) such as pharmaceuticals, pesticides, personal care products, industrial chemicals and steroid hormones has gained significant attention [6; 7]. These TrOCs occur ubiquitously in municipal wastewater and have the potential to adversely affect aquatic ecosystems and human health [8; 9; 10]. TrOC degradation by lacase depends on a number of factors including pH, temperature, chemical structure of TrOCs and lacase properties [11; 12; 13]. In general, effective lacase-catalyzed degradation of TrOCs containing electron donating functional groups (EDGs) such as amine (-NH\({}_{2}\)), alkoxy (-OR) or hydroxyl (-OH) was observed. On the other hand, degradation of TrOCs containing electron withdrawing functional groups (EWGs) such as halogen (-X), amide (-CONR\({}_{2}\)) or nitro(-NO\({}_{2}\)) has been reported to be poor or unstable [11; 14]. Degradation of TrOCs can be improved by adding different natural and synthetic redox-mediators that are low molecular weight compounds capable of exchanging electrons between increase and TrOCs [15; 16; 17]. Initial studies have assessed the performance of lacase-catalyzed Troc degradation in batch enzymatic bioreactors due to the concern of enzyme washout in a continuous flow system. In an attempt to prevent enzyme washout, an enzymatic membrane bioreactor (EMBR) was developed by coupling an ultrafiltration (UF) membrane to an enzymatic bioreactor [18; 19]. Interestingly, during the operation of the EMBR, adsorption of some hydrophobic TrOCs (e.g., amitriptyline, oxbenzene and octocylene) onto the enzyme gel layer over the membrane surface resulted in enhanced degradation of the adsorbed compounds [18]. In another study, removal of four non-phenolic TrOCs, namely atrazine, sulfamethoxazole, diclofenac and carbamazepine was improved by 15-25% following the addition of granular activated carbon (GAC) in EMBR. This was probably because simultaneous adsorption of lacase and TrOCs on GAC promoted the interaction of TrOCs with the active sites of lacase [20]. Results from previous studies indicate the complementarity of simultaneous lacase and TrOC retention within EMBR in contrast to only lacase retention by UF membranes utilized in the previously developed EMBRs. Hence, in this study, it is postulated that the integration of an enzymatic bioreactor with a high retention membrane could facilitate the degradation of resistant TrOCs by retaining both lacase and TrOCs. Different configurations of conventional activated sludge-based high retention membrane bioreactors (HR-MBR), employing membrane distillation (MD), forward osmosis (FO) or nanofiltration (NF) membranes, have been investigated for advanced wastewater treatment [21; 22; 23; 24]. Complete TrOC retention in HR-MBR improved the membrane permeate quality, but the poor removal of certain groups of TrOCs such as those containing EWGs led to their accumulation in the bioreactor. This indicates the necessity of formulating means to enhance biodegradation of TrOCs. In this context, it is noteworthy that recent reports confirm enhanced lacase-catalyzed degradation of selected TrOCs that are not amenable to degradation by conventional activated sludge [25; 26]. However, the performance of a high retention--enzymatic membrane bioreactor for the removal of a wide range of TrOCs remains to be elucidated. Among the high retention membrane systems, in MD, a vapor-liquid interface is developed around a hydrophobic micro-porous membrane that allows the water to pass through the membrane via diffusion due to vapor pressure gradient. Compared to conventional distillation processes such as fractional distillation, the MD process requires low temperature and could be operated by using low grade heat or solar energy [27; 28].