Increasing water demand due to a growing population and improved lifestyles is exerting greater pressure on existing water resources. The increasing number of contaminants entering the water supplies is further challenging water authorities worldwide. This project investigated using membrane filtration as a physical separation process and as an effective barrier for a wide range of inorganic and organic contaminants, producing excellent quality product water.

PhD Thesis completed by Muhammad Umar in October 2014.

Water treatment by micro- or ultrafiltration, or reverse osmosis is applied to a range of purposes, including recycling wastewater or reducing contamination sufficiently to make it safe for discharge to the environment. The problem is that membranes age, foul, are blocked by compounds in the feedwater and stop working. Ceramic membranes last longer and are more resistant to cleaning and defouling processes than other types of membranes. This research used a 25m2 ceramic microfiltration membrane pilot plant installed downstream of an ozone disinfection process to examine the effect of the integrated combination of these two units on turbid (3-5 NTU), highly fouling secondary effluent from a wastewater treatment plant. Adding coagulation with ‘PAC’ to the process stream more than doubled (flux) flows through the membrane. The pathogen indicators E. coli and MS2 were used to calculate Log Removal Values of >3.2 and 4 for protozoans and viruses respectively. It was concluded that the hybrid ozone-PAC – ceramic membrane treatment process was highly effective for treating and recycling challenging wastewaters.

Treated wastewater may still contain some harmful, infectious pathogens. These are removed and the wastewater recycled by ultrafiltration (UF) through a porous membrane, but over time the membranes age, the pores enlarge and infectious pathogens such as viruses can break through. This makes it important to constantly monitor the integrity of the UF membranes, and is currently done by growing large amounts of a harmless virus, MS2, which is added to treated wastewater and detected in the recycled water if the membrane is damaged. The problem is that this MS2 monitoring system is relatively slow and expensive. This research developed and validated a better alternative using curcumin, an extract from turmeric, which was encapsulated in a biological compound ‘PLA’ by using a method that formed particles the same size as virus. The encapsulated, but not the ‘free’ curcumin, emits fluorescence that can be detected continuously by a specialised spectrophotometer placed on the downstream, recycled side of a UF membrane. The curcumin-PLA particles identified aged and broken UF membranes in small, pilot-scale recycling units, and had the added advantage that they decomposed naturally within a few days.

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.

Ultrafiltration membranes are used to remove viruses from treated wastewater. This makes it safe for release to the environment or for recycling, but it is important to monitor integrity of the membrane to ensure there are no damaged sections that viruses can break through. This research demonstrated that a silver nanoparticle is a valid, safer alternative to using non-infectious bacteriophage viruses that are currently used to test membrane integrity. The silver nanoparticle was tested and validated in a laboratory-scale ultrafiltration membrane unit. It was concluded that work should proceed to full-scale validation and integrity-testing of ultrafiltration membranes in recycled water applications.

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.