This project investigated the impact of hazardous events (i.e. high organic, high salinity, high toxic shock loads in influent, aeration lost or membrane damage) on decentralised membrane bioreactor performance. This investigation demonstrated validation of membrane bioreactors to fully comply with the requirements of current Australian water recycling guidelines and to provide necessary risk-based information for health and environmental regulators.

PhD Thesis completed by Thi Thanh Trang Trinh in November 2013.

The proposed project will evaluate new methods for synthesising novel fluorescent biopolymer nanoparticles (BNPs) in quantities that are suitable to facilitate challenge testing at full-scale and investigate techniques for stabilising the BPNs for distribution. The prepared BNPs will then be used to demonstrate a full-scale challenge test at a South East Water membrane treatment plant. The BNP test will be performed at the same time as a scheduled MS2 bacteriophage challenge test or pressure-based test in order to compare the two methods.

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.

The Australian Guidelines for Water Recycling (AGWR) encompass acceptable health, safety and environmental targets for different types of recycled water. This research begins development of a series of processes that utilities can apply to achieve compliance with the AGWR. This Stage 1 of the project describes six systems for recycling water (natural, managed aquifer recharge, membrane treatment, chemical and photooxidation, biological and adsorptive treatments); six aspects of recycling validation systems which included regulator, utility and technology provider perspectives in different States and jurisdictions, as well as micropollutant risk assessment, instrumentation performance and knowledge transfer, training and capacity building. Current and emerging techniques for scheme validation, and relevant guidelines and case studies were reviewed, and knowledge gaps and core issues were identified. Altogether these were used to develop a ‘National Validation Framework’ and were the basis of a plan for completing Stage 2 (WaterRA project 3018).

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.

Membranes are used to remove viruses from treated wastewater to make it safe for discharge or recycling. It is important to monitor the integrity of membranes and check that viruses cannot break through. This creates a need for surrogates that are cheaper, safer and easier to use than the non-hazardous indicator virus currently applied to test membrane integrity. This research synthesised a series of fluorescent nanoparticles with similar dimensions to viruses, with the idea that the fluorescence would support continuous in situ monitoring in real time, but unfortunately the nanoparticles did not emit enough fluorescence and could not be detected in the product water.

The steam produced by boiling a kettle of salty water can be collected, condensed and drunk. Membrane distillation is an analogous process to this, but in this study the salty feedwater forms a salt-free vapour at a lower temperature; 30 – 40°C. The warm feedwater and vapour are pumped past a thin, porous membrane which repels liquid water but allows vapour to pass through the pores into a cold stream of freshwater on the other side. The vapour condenses and increases the volume of fresh, salt-free water. In this project an operational pilot plant was built and installed at an electricity generating station which produces waste heat and a stream of salty effluent that is normally discarded. The pilot plant was equipped with a 0.67m2 membrane, ran continuously for 3 months, and produced an average of 2.2L freshwater per hour. This equates to 3.4L/h/m2. The membrane area can be scaled up to increase production. It was concluded that this is a viable treatment technology for industrial wastewater that emits minimal greenhouse gasses.

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.