Deciphering the spatial fouling characteristics of reverse osmosis membranes for coal chemical wastewater treatment

Reverse osmosis (RO) membranes are widely used in the advanced treatment of coal chemical wastewater. Nevertheless, membrane fouling is an intractable concern which decreases permeate flux, impairs water quality and increases energy consumption. Mapping the spatial distribution of membrane fouling and identifying the key factor for flux decline are of great significance for membrane fouling control. In this study, each membrane sample from first-stage and second-stage RO membrane elements was divided into 12 regions for autopsy. The results showed that membrane fouling at both stages was exacerbated from the feed end to the concentrate end owing to the concentrating effect and concentration polarization. Organic and inorganic foulants mainly deposited at the concentrate end and near the permeate tube, whereas biofouling did not show a regular distribution pattern. Biofouling was the paramount contributor to flux decline, whether at the first stage (40%) or the second stage (27%). However, the effect of inorganic fouling became prominent at the second stage due to the higher concentration of inorganic ions and stronger interactions with other foulants. Suggestions for membrane fouling control strategies include reinforced anti-biofouling countermeasures at the lead element, anti-scaling schemes after the first stage, and customized feed spacer and membrane designs for specific fouling at different locations.