Reverse osmosis (RO) is used to desalinate seawater and brackish groundwater, and to remove microscopic pathogens from treated wastewater. The salty water is pressurised on one side of the RO membrane and this is part of the process that results in water molecules passing (diffusing) through the membrane to the lower pressure solution on the other side. Salts such as sodium chloride (table salt) and calcium sulphate and calcium carbonate (scale) do not diffuse easily across the RO membrane and build up on the high-pressure side. Eventually scale deposition on the membrane prevents the diffusion of water molecules and the production of freshwater declines. This research tested four commercial and three in-house antiscalent chemicals, and additionally developed a technique to monitor scale formation and RO membrane performance in real-time. It was concluded that the antiscalent ‘PC-191T’ was best and that adding an ‘Electrical Impedance Spectroscope’ to RO systems has the potential to deliver a sensitive in-situ, real-time monitoring method capable of detecting very early scale formation, well before membrane performance declines. This will enable optimisation of membrane scale removal and improve the efficiency of freshwater production.

Water treatment plant operators remove cyanobacteria and the toxins they produce from source waters but calculating the amount of treatment needed for effective removal is difficult, particularly in bloom conditions when cyanobacterial cell numbers and toxins change quickly. Current cell counting and toxin measurement can take hours or days to complete, and the results are not available quickly enough to help treatment plant operators respond to changing conditions. There is a need for a real-time method that gives instant results. This research examined the utility of fluorometers; probes that emit light that is ‘reflected’ back at different wavelengths by living cells and other matter in the water and is detected by the fluorometer. It was found that when only one species of cyanobacteria was present, there was a good correlation between the fluorescent signal and cell number, particularly when source waters were clear and not cloudy. Cell numbers did not relate well to levels of toxins or taste and odour compounds. When fluorometers were installed in 13 water treatment plants the correlation between cyanobacteria cell numbers and fluorometer signals was validated, and this led to the conclusion that fluorometers can give early warning of blue-green algae blooms.