Assessment of a hybrid membrane distillation-LED-UV process: focus on fouling mitigation

Abstract

The main objective of this study was to evaluate the performance of a hybrid module of membrane distillation and LED-UV (MD-LED-UV) focusing on fouling control. The newly built module has a quartz plate in the feed compartment, allowing the irradiation of the concentrate and the fouling layer. First, the module's performance in the treatment of secondary wastewater from anaerobic treatment was evaluated. There was an outstanding contribution of fouling in permeate flux decrease. The hybrid system's performance was similar to the MD's. Analysis of the membrane surfaces revealed a smaller extension of fouling in the MD-LED UV system. The fouling layer was much less adhered to the membrane surface, being easily removed mechanically. It was attributed to the higher hydrophilic character of the layer formed in the hybrid system, resulting in a weaker bond with the hydrophobic membrane. A lower concentration of SMP/EPS in the biofilm formed in the hybrid system was observed, suggesting an inactivation action of microorganisms. Then, the effect of the hybrid system on the removal of 17 α-Ethinylstadiol (EE2) was evaluated. The hybrid module and MD had very similar performances. The permeate flux in MD-LED-UV was higher than in MD, although MD-LED UV had a higher vapor pressure polarization effect. There was no significant difference between the increment in the feed and the permeate conductivities in both tests. However, the hormone removal efficiencies (97.7 and 97.9% for MD and MD-LED-UV, respectively) and the estrogenic effect removals (99.2 and 99.0% for MD and MD-LED-UV, respectively) were not impaired. Thus, when applying the MD-LED-UV module to mitigate fouling in real wastewater and seawater treatment, radiation is unlikely to lead to performance decline regarding micropollutants removal. Finally, a careful literature review on biofilm formation in MD, its consequences, and possible mitigation methods was carried out. It was concluded that the biofilm in MD leads to several damages and MD performance decay, and there should be efforts to mitigate it.