Hybrid UV-C/microfiltration process in membrane photoreactor for wastewater disinfection

Abstract

A novel hybrid UV-C/microfiltration process for water disinfection is presented, and its application in continuous mode operation to the removal of different pathogen germs (Escherichia coli, Enterococcus faecalis, and Candida albicans) present in urban wastewater. The membrane photoreactor is based on porous stainless steel membranes coated with a TiO₂ layer and illuminated by a UV-C lamp (254 nm). A valve actuator in the outlet of the UV-C stream allows operation of the system under conditions of constant transmembrane pressure (TMP) keeping the UV-C contact time in few seconds, significantly lower than the typical irradiation time employed in TiO₂ photocatalytic processes. An E. coli removal of up to 4-log in the permeate stream and up to 2-log in the UV-C outlet was achieved with a 0.2 μm membrane operating with a TMP of 0.5 bar and a UV-C contact time as low as 8 s. The microbial balance data from the cells recovered from the membrane confirmed that 96–98% of the removed microorganisms died due to the UV-C action over the membrane surface. Modification of the membrane with a TiO₂ layer has been also shown to be a suitable way to improve both the UV-C inactivation and the filtration efficiency. The results reported in this work constitute a proof of concept of the synergy between UV-C and filtration that can be achieved in a hybrid UV-C/microfiltration system, being a good example of process intensification where two products of different quality can be simultaneously obtained.