Wastewater recycling uses reverse osmosis (RO) membranes to produce freshwater but this process also generates a waste stream – the reverse osmosis concentrate (ROC) – which contains almost all the contaminants present in the original wastewater. The disposal of untreated ROC poses a health and environmental risk. This research used 18 samples of ROC to test various treatment combinations and concluded that coagulation with ferric chloride followed by filtration with biological activated carbon reduced dissolved organic carbon, phosphorus and nitrogen compounds, and disinfection by-products, to safe and acceptable levels.

Recycling wastewater by using reverse osmosis (RO) and ultrafiltration appears to be associated with the formation of some groups of micropollutants but there is not much information about these processes. This research selected iodinated disinfection by-products (DBPs) and N-nitrosamines (NDMA), and benzotriazoles and benzothiazoles, which are compounds in dishwasher detergents, for further investigation. It was concluded that minimising the formation of dichloramine (a precursor molecule to NDMA formation) by reducing pH and maximising activated sludge ammonia production, reduced the formation of N-nitrosamines in RO-treated wastewater. Iodinated DBPs and benzotriazoles were detected in RO treated wastewater in this study but at lower concentrations than those thought to pose a risk to human health.

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.

The Australian water industry uses a variety of membrane processes to remove unwanted pathogens or compounds, such as salt, from source waters. As membranes age their ability to fulfil these removal and filtering functions declines. The problem is that although there are recognised and validated tests for membrane integrity, they are usually performed only on new membranes, and information about the effect of membrane aging on pathogen removal is limited. This project reviewed published literature and identified four methods suitable for future development as Membrane Integrity Tests that may prove applicable to evaluate aging membranes during ongoing and long-term plant operation.

Wastewater must be treated to remove harmful pathogens and chemicals before it can be released to the environment, but the cost of proving that all pollutants have been removed is prohibitive because potentially thousands of separate chemicals would have to be measured. Another problem is that classical chemistry measurement tests are sometimes not sensitive enough to be able to detect the very low levels of chemicals which still harm animals and plants. This research developed a suite of extremely sensitive in vitro cell culture tests and an in-situ laboratory test in which mosquitofish were observed when swimming in recycled treated water. These bioassays measured the effects of mixtures of contaminants and were compared with traditional chemical measurements of separate contaminants. The in vitro cell culture, in situ mosquitofish and classical chemical analyses of selected contaminants generated equivalent results and led to the conclusion that combining multiple lines of evidence into a toolbox approach for the assessment of water quality provides data which is more informative and relevant when assessing potential impacts on the environment than traditional chemical measurements alone.

Wastewater (WW) contains harmful chemicals, including pesticides, that can disrupt normal gene function or hormone activity. The cost of measuring each separate contaminant at the frequency needed to demonstrate the safety of recycled WW is prohibitive. This research reviewed the risk assessment and regulation of chemicals in Australian water, with a focus on ‘thresholds of toxicological concern’. Laboratory techniques were developed to extract and concentrate WW contaminants into solutions suitable for analysis using both new in vitro cell culture assays and analysis in expensive, established chemical tests. WW and treated samples were collected from nine Australian water reclamation plants. The total effect of each sample (which contained a mixture of contaminants) on cell death, gene integrity and aspects of liver, hormone, nerve and immune system activity, was determined using in vitro cell culture bioassays, and compared with the classical chemical measurement of each separate contaminant. The cheaper cell-culture tests correlated well to the levels of groups of chemicals and could be used to find thresholds of toxicological concern. Both testing regimens also demonstrated that reverse osmosis is a highly effective method that removes harmful chemicals to levels much lower than those designated safe by regulatory authorities.