This project determined disinfection by product contribution from chlorination of algae.

Honours/PhD Thesis completed by Adam John Tomlinson in July 2018.

Source waters contain a class of chemical compounds collectively known as ‘bromides’. Standard water treatment includes chlorination; a process designed to kill harmful microorganisms in source and recycled waters. The problem is that chlorination agents react chemically with bromides to form ‘brominated Disinfection ByProducts’. These bDPBs can contribute to the development of cancer and this led the Australian Drinking Water Guidelines to recommend very low concentrations of bromides in source waters, less than 0.1 parts per million (0.1mg/L). At this level, if any bDBPs subsequently formed during chlorination, their occurrence will be too low to pose a public health risk. Some Australian source waters have higher bromide concentrations, but existing removal methods are expensive and/or do not work very well. The scientists in this team have already synthesised a new bismuth substance (see image) that removed 86% of an experimental bromide from artificial groundwater.

This project will aim to combine the modified bismuth with alum, which is currently used to treat water. If researchers succeed in creating a composite that incorporates bromide removal into existing tried-and-tested water treatment processes they will deliver a cost-effective improvement to water quality and safety. However, it will require clever and careful chemical design to create the new bismuth-alum composite, and to run experiments that will test its ability to remove bromides from source waters. As if that isn’t challenging enough, they also propose to develop a software programme that will predict bDBP formation. If they are able to eventually build a validated model it will be an extremely useful addition to the suite of tools currently used to produce safe, high-quality drinking water.

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.

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.

Disinfection is essential for removing harmful microbial pathogens and making safe drinking water but can also cause formation of disinfection by-products (DBPs), some of which pose a health risk. Thirty years of research have amassed a wealth of knowledge about the identification, formation, treatment and control, toxicology and epidemiology of DBPs in Australia. This project compiled, assessed and presented an overview of DBP-related research in Australia.

Microscopic pathogens in drinking water pose a risk to public health. In Australia, chlorine or chloramine are used to inactivate these pathogens, to disinfect drinking water and prevent widespread outbreaks of debilitating illness in large populations. Although largely successful, problems arise when drinking water is contaminated by pathogens after being disinfected in the treatment plant but before reaching the customer. A variety of situations cause this, one being small pipe leaks which become a route for soil micro-organisms to get into drinking water. To prevent pathogen contamination in pipe networks, higher levels of disinfectants can be added at the treatment plant, or secondary disinfection can be administered in the pipe network. This research project produced a guidance manual which explains how to maintain and monitor effective disinfection levels in post-treatment pipelines, and the major challenges to maintaining effective disinfection.

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 in surface waters are a source of cells, taste and odour compounds, and a range of toxins. This research optimised treatment processes for the removal and control of cyanobacteria and their metabolites from a range of source waters. It was concluded that pre-chlorination is not advisable when cyanobacteria are present, but that in some situation’s potassium permanganate is a viable alternative. Although all three tested coagulants; ferric chloride, aluminium chlorohydrate and aluminium sulphate (alum) removed 90 to 95% of cells, alum at pH 6.3 was the most cost-effective. Maintaining pH > 6 reduced cell lysis and metabolite release. Since cyanobacteria in sludge remained viable for 2-3 weeks it was recommended that sludge detention in the clarifiers should be minimised.

Chlorine removes harmful pathogens from water but has the disadvantage of forming disinfection by-products (DBPs) by reacting with organic matter sometimes found in water. Chloramine also disinfects, is less likely to form DBPs and is more stable, so remains active in for longer in the pipelines which distribute drinking water from the plant to the tap. The problem is that it is difficult to predict exactly how much chloramine to add; it needs to be enough to maintain disinfecting activity in the pipeline distribution system, but not so much that customers find the smell of chlorine in tap water unpleasant. Traditionally, the chemical reaction rate has been used to predict the gradual ‘decay’ of chloramine in pipelines, but this is inaccurate. This research developed a computer software statistical programme that uses ‘artificial neural network’ concepts and operations to predict the longevity of chloramine residuals in water distribution systems. This is more accurate than traditional methods.