Online fluorescence monitoring of RO fouling and integrity: analysis of two contrasting recycled water schemes

A fluorescence-based sensor was used to conduct real-time, online monitoring of reverse osmosis (RO) membranes at two Australian municipal advanced water recycling schemes. Trials monitored real-time changes in fluorescent organics, measured at lambda(Ex/Em) = 350/430 nm (Peak C), in RO permeates as an indicator of water quality and membrane performance. The RO membranes in each plant were operated using contrasting conditions; the Water Reclamation and Management Scheme plant was operated under constant pressure and the Ground Water Replenishment Trials pilot plant under constant flux. The Peak C sensor detected differences between permeates from staged RO systems, changes in water quality due to an underperforming membrane suspected to have an integrity breach, and changes in water quality from increasing transmembrane pressure in fouled membranes. Peak C fluorescence had stronger correlation with transmembrane pressure and may have potential application in detecting the onset of membrane fouling. Interestingly, while RO EC signals indicated improving permeate quality, fluorescence revealed an increase in (Peak C) organics in the RO permeate. This demonstrated that the passage of fluorescent organics and ionic species are dissimilar, and monitoring EC alone is not an accurate surrogate measure to ensure on-going effective removal of organic chemicals.