Catalytic ceramic nanofiltration for direct surface water treatment and fenton cleaning

Over the past decades, direct nanofiltration (NF) without pre-treatment has been widely recognized as an alternative for conventional membrane technologies in both drinking water and wastewater treatment, owing to its advantages in energy saving, low chemical usage and high permeate purity. As an alternative, ceramic NF has received growing attention in recent years, given its good robustness and stable separation capabilities as compared to polymeric NF membranes. Organic fouling of ceramic NF membranes remains the key problem affecting the performance of the membranes in water treatment. However, conventional forward flush with pure water is not effective for removing the organic fouling due to its sticky nature. Backwash with pure water has to be applied at high pressures, thereby having a risk of damaging the structure of the membranes. Therefore, chemical forward flush with strong acids, bases or chlorine is frequently required as a substitute for backwash and conventional forward flush, leading to more consumption of the chemicals. To apply innovative ceramic NF in direct surface water treatment, an eco-friendly cleaning strategy of using Fenton-based oxidation was studied in relation to the fouling characteristic of the membrane.
A literature study was done to review the present knowledge on using oxidation methods for fouling mitigation of ceramic membranes. It was found that existing studies predominantly were focused on direct oxidation of organic substances in feed water of ceramic membrane filtration. This kind of oxidation strategies could mainly reduce cake layer fouling of the membranes, while in many cases aggravating pore clogging due to an oxidation-induced conversion of large-sized organic molecules into smaller ones. Additionally, there is a risk of secondary pollution by using oxidation in the feed water, since the oxidants and potentially produced oxidation by-products can penetrate the membranes into permeate. However, little knowledge is available on using oxidation for cleaning fouling layers, in particular, on a ceramic NF membrane, in terms of the impact of its fouling characteristics on the efficacy of oxidative cleaning. It was thus recommended that, investigating the efficacy and mechanisms of an oxidative cleaning method for ceramic NF membranes, should be based on an in-depth understanding of fouling of the membranes...