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.

Some wastewater treatment plants (WWTPs) use membrane bioreactors (MBR). These contain a microporous membrane which clarifies treated wastewater by removing microbial organisms. Wastewater must also be treated to remove nitrogen and phosphorus, which can act like uncontrolled fertilisers if they are released to the environment. Iron or aluminium salts added to the wastewater react with phosphorus and make solid particles which can be ‘caught’ and separated in the MBR. The problem is that the amounts of iron salts commonly added to some WWTPs foul the membrane and reduce its performance. This research used a laboratory-scale MBR to discover that lower amounts of specific iron salts effectively reduce phosphorus to levels that are safe to discharge while also reducing fouling and increasing the operating life of the membrane. Another conclusion was that ascorbic acid (vitamin C) cleaned iron-associated foulants from membranes more effectively than the conventional cleaning agent, citric acid.

Blue-green algae (cyanobacteria) reduce water quality especially when they bloom and form high numbers of cells which produce toxins, and taste and odour compounds. Most cyanobacteria photosynthesise and tend to grow and float at depths which optimise their exposure to sunlight, but an increase in unexplained occurrences of taste and odour compounds in reservoirs, and a bloom of benthic (bottom-living) cyanobacteria, forced the closure of a water supply. This research examined the role that bottom-living benthic cyanobacteria play in the production of toxins or taste and odour compounds. Seven DNA-based PCR tests were developed to identify benthic species of cyanobacteria and their capacity for producing toxins. A taste and odour compound, and two toxins were found in winter and spring in an SA reservoir, whereas a different taste and odour compound and toxin assemblage were found in summer and autumn in a reservoir in NSW. These results will help water suppliers to anticipate and manage future aesthetic or toxin issues related to benthic cyanobacteria.

Cyanobacterial blooms are a major problem for reservoir managers because of the large numbers of cells and the toxins they contain. These blue-green algae blooms have traditionally been treated with the algaecide copper sulphate, but this was expensive and unsustainable because it killed non-target species and left residual contaminants. This research examined and rejected alternatives: other copper-based algaecides, hydrogen peroxide, substances that trap cyanobacterial-growth supporting nutrients on the floor of the reservoir, and mechanical surface mixers. Laboratory experiments that tested the ability of ultrasound to prevent the photosynthetic cyanobacteria from floating at the depth that optimises light absorption were initially promising because the ultrasound reduced photosynthesis and metabolism and the blue-green algae died. Unfortunately, when an ultrasound system was deployed in a reservoir, the much larger volume of water attenuated and ‘absorbed’ the low-power ultrasound and led to the conclusion that sustainable, environmentally friendly levels of ultrasound do not provide effective control of blue-green algae. This rigorously conducted scientific study has generated useful information about methods which do not work, and resources can now be directed to promising new innovations.

This research has provided the most comprehensive account of the geographical distribution of blue-green algae (cyanobacteria), and the toxins they produce, in Australia. The blue-green algae cells were collected and stored. This collection now forms a valuable national asset which is particularly valuable for managing the complex array of factors that affect the accurate assessment of risk posed by any one algal bloom. Not all cyanobacteria produce toxins, and the identification of species and the presence of toxin is an important step in the decision-making process necessary to produce high quality, safe water. This research led to some notable conclusions; one being that a traditional method that uses cell-shape to identify algal species is unreliable, and also that the number of cyanobacterial cells does not necessarily correlate to the amount of toxin in source waters. Five laboratory tests were reviewed and it was found that tests for cylindrospermopsin were reliable, but tests for microcystin and saxitoxins differed as to the amount they measured, although they reliably identified the presence or absence of toxin. Problem cyanobacteria species are ubiquitous in Australia and if climatic events create favourable conditions, blooms can occur in unexpected locations.