Exploring the influence of gypsum coating on polyethersulfone membrane for ammonia removal in aquaculture water treatment

Dissolved ammonia is a persistent contaminant in aquaculture water systems, endangering aquatic species if not adequately eliminated. Although ultrafiltration (UF) is the most commonly used worldwide, its limited application in ammonia removal must be enhanced. Here, the performance of UF membrane for the ammonia removal were increased by coating modification. Coating was conducted by spraying gypsum solution over the membrane surface. To achieve an optimum ammonia removal, the filtration conditions were optimized using response surface methodology (RSM) and experimentally validated in laboratory. RSM was used to determine optimal filtering conditions, elucidating the relationships among various variables. The significance of the influence value between optimization condition and ammonia rejection was determined by the hierarchical multiple regression method. The modified membrane demonstrated a higher hydrophilicity, with a contact angle of 72.9° and a water uptake of 137%. Under the optimal conditions of 1 bar pressure filtration and 4 ppm feed concentration, the permeate flux and ammonia rejection were 145.6 L/m².h and 68.1%, respectively. When tested for stability and reusability, the modified membrane demonstrated a negligible decline in permeate flux and rejection for four-cycles ammonia separation. Hierarchical multiple regression analysis revealed that both filtration pressure (r = 0.227) and feed concentration (r = 0.118) significantly affected ammonia rejection (p < 0.05). This study suggests that the gypsum-coated UF membranes have potential practical applications for ammonia removal from aquaculture water system.