Heterogeneous TiO2 photocatalysis coupled with membrane technology for persistent contaminant degradation: a critical review

A huge amount of untreated or partially treated wastewater (come from industrial, agricultural and human activities) is released into the water bodies with dangerous impacts on aquatic life, human health and environment. Traces of organic contaminants (called persistent organic pollutants) were also found in water bodies, and they cause adverse ecological and human health effects. In addition, several of these contaminants have not been regulated by national or international legislation, hence posing a enormous risk for the entire world. The removal of these pollutants is not easy because traditional wastewater treatment systems are not designed to handle them. Photocatalytic membrane reactors (PMRs), which coupled photocatalysis with the membrane separation process, have gained enormous interest in the purification of water and wastewater treatments. Titanium dioxide (TiO2) is the most commonly photocatalyst used for the preparation of photocatalytic membrane reactors due to its low cost, high chemical stability and as high surface to volume ratio. In this review, a description on heterogeneous photocatalysis and configuration designs are deeply discussed. The disadvantages that hinder the application of this process at a large scale were also given. Afterward, the recent progress on the application on PMRs-TiO2 based on the degradation of recalcitrant pollutants is presented in detail. The influence of various operating parameters on photocatalytic activity and membrane separation performance is also analyzed. In addition, the fouling control strategies in PMRs are also reviewed. Finally, the research gaps and the outlook for future research on PMRs were deeply discussed.