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.

Harmful pathogens and compounds must be removed from wastewater before it can be discharged to the environment or used for irrigation, and many source waters need salts removed to make them potable. Microfiltration and ultrafiltration membranes remove pathogens and unwanted chemicals but as they are used, they become fouled and blocked by particulates and compounds from the water being filtered, as well as by the formation of biofilm, and by chemical interactions between solutes and the membrane materials. Although the membranes are cleaned regularly, the cleaning chemicals themselves can cause a problem. This research characterised the damage that various cleaning regimens inflict on membranes made of different materials and examined the effects of progressive and consecutive stages of membrane aging and degradation on performance. It was concluded that the type of cleaning agent affects the mechanism of membrane degradation and the severity of membrane integrity loss. More information is needed regarding the cleaning protocols and agents used in industry. Information from this research can inform a generally applicable model to predict membrane aging and decline in performance.

Remote and regional Australian communities commonly produce potable water by removing salt from brackish groundwater. Existing desalination technologies, such as reverse osmosis (RO) have high electrical energy and technical requirements. Groundwaters often contain high levels of silica (quartz) which, together with the salts, form scale which blocks RO membrane and other components which are expensive to replace. This research examined an alternative desalination process: capacitive deionisation. Laboratory-scale experiments found that single-walled carbon nanotubes were the best material to use for electrodes, that membranes placed before the electrodes increased efficiency of salt removal and decreased energy usage, while silica, which lacks a charge that would bind it to either the positive or negative electrode, did not form scale deposits nor interfere with the desalination process. A full-scale version of this unit was tested onsite in the Northern Territory and described in WaterRA Project 1047.

Some remote and regional areas of Australia rely on groundwater. A problem with this is that naturally occurring salts, such as calcium carbonate, make the water ‘hard’ and cause scale deposition on the elements used to heat water. Scale also blocks taps and showerheads. This research examined different methods for predicting the amount of scale that a groundwater might form and also considered the pro’s and con’s of various treatment technologies which prevent scale formation. The consideration of community size and the chemical characteristics of different groundwaters was incorporated into this assessment and recommendation for scale prevention.