Cleaning and regeneration of irreversibly fouled and discarded reverse osmosis membranes: Method and mechanism

Abstract

The regeneration and recycling of discarded membranes are of great importance for extending the membrane lifespan, and thus, they are crucial to achieve the economic feasibility of the industrial scale membrane process. In this research, an end-of-life reverse osmosis (RO) membrane was analyzed, and a cleaning protocol and mechanism were investigated. Several chemical agents were optimized, including acid (H 2 SO 4 ), base (NaOH), metal-chelating agents (Na 2 -EDTA), surfactants (SDS), oxidizing agents (KMnO 4 ), and their combinations. The results showed that good regeneration of the membrane can be achieved after the membrane was cleaned by a KMnO 4 + NaOH solution, followed by NaHSO 3 . To achieve a high cleaning efficiency, the effects of oxidant concentration, cleaning time, and solution pH were studied. The optimum cleaning protocol was a 0.5% (w/v) KMnO 4 + 0.2% (w/v) NaOH solution, followed by NaHSO 3 ; and the optimum cleaning time was 60 min, allowing for a cleaning efficiency of 5.87. The experimental results showed that the cleaning procedure could be divided into three stages and that both the KMnO 4 concentration and pH can control the cleaning stage. Based on economic feasibility, controlling the solution pH with low KMnO 4 concentrations could lead to the transformation of membranes into target recycled membranes (such as reverse osmosis, nanofiltration, and ultrafiltration).