The environmental conditions which cause blue-green algae (cyanobacteria) blooms vary according to location, the climate, and other attributes of aquatic ecosystems. This variety has made it difficult to develop one broadly applicable predictive model for cyanobacterial blooms. Water utilities monitor source waters to implement cyanobacterial risk management programmes but there are no standard protocols while limited information transfer between utilities has prevented the identification of management strategies that do or do not work. This research reviewed literature about early warning systems (Almuhtaram et al., 2021) and source control strategies, conducted a survey of 35 utilities in America and Canada (74%) and Australia (Kibuye et al., 2021) and evaluated selected control strategies. These different types of information were synthesised into decision trees within an overarching guidance document. It was concluded that a 3-tier framework to detect algal blooms which monitored biological activity, then confirmed the identification of cyanobacterial genes and associated metabolites gave sufficient early warning, while multi-barrier control strategies gave field-scale efficacy and enabled timely responses.

N-nitrosodiumdimethylamine (NDMA) in drinking water is one of many factors – such as a persons’ genes – that cause cancer. Although NDMA is not a sole cause of cancer, the water industry aims to minimise its contribution to illness and disease. This research measured levels of NDMA in drinking and recycled waters and found the majority well below the Australian Drinking Water Guideline values that are considered safe for public consumption. Different sources of NDMA were identified and water monitoring and treatment strategies to optimise NDMA removal from source waters were recommended.

Compliance with the Australian Guidelines for Water Recycling ensures that recycled wastewater does not present a health risk due to infectious pathogens or disease-causing chemicals. Many pathogens in wastewater are inactivated by disinfection treatments such as chlorination, but this causes a problem when disinfectants react with nitrogen compounds in wastewater and form Disinfection By-Products (DBPs), some of which pose a health risk. This research collected samples from four wastewater treatment plants (WWTPs) with different treatment methods and climate zones. A comprehensive and innovative analysis of the types of pathogens, various chemical forms of nitrogen and DBPs, and removal of these components during the recycling process, was related to season, climate and the four different treatment trains. It was concluded that the WWTP using a combined anaerobic/aerobic pond system was best at removing nitrogens and minimising DBP formation, but the best overall treatment performance was delivered by an activated sludge, oxidation ditch and infiltration pond WWTP in a temperate climate. Pathogens were found in influents but not treated effluents, and so were other nitrogen-removing micro-organisms. Treatment was better in summer, and the wastewater quality in these four WWTPs posed a low health and environmental risk to non-potable reuse.

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.

Source waters are disinfected to remove harmful pathogens, but chlorine reacts with organic matter and bromides to form disinfection by-products (DBPs) which can affect health. Water treatment reduces DBPs to safe levels by using alum to remove organic matter before disinfection but some water sources, particularly those with high bromine levels, are still difficult to treat. This research aimed to compile the best protocols for alum coagulation and disinfection when source waters contain different levels of organic matter and bromides, and to relate these to health risks. When organic matter was removed with 125 mg/L alum, and this treated source water was disinfected twice, and the first dose was calculated to generate chlorine levels of 0.5 mg / L for two days before administering the second dose, then DBP levels in drinking water were minimised. Neither alum-treated nor disinfected water caused toxicity in two laboratory tests used to examine risks to health.

Components of dissolved organic matter (DOM) and dissolved organic nitrogen (DON) in source waters can react with disinfecting chlorine or chloramine to form nitrogenous disinfection byproducts (n-DBPs) which might be toxic and hazardous to health. In this research, water samples were collected from nine water treatment plants and found to contain 28 n-DBPs. Total n-DBP formation, and particularly brominated n-DBP formation, was affected more by the levels of bromine in raw water than the different forms of nitrogen, and this led to the recommendation that it could be beneficial to monitor raw waters with high bromine concentrations. Although chloramination caused formation of more n-DBPs than chlorination, coagulation treatment decreased total DBP levels. Further research was recommended to characterise the toxicity of n-DBPs and to optimise the removal of DOM, DON and other n-DBP precursors by using GAC Acticarb in the treatment train.

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.