The sources, fate and behaviour of disinfection by-products in Australian waters

Alexandrou, L 2019, The sources, fate and behaviour of disinfection by-products in Australian waters, Doctor of Philosophy (PhD), Science, RMIT University.


Document type: Thesis
Collection: Theses

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Title The sources, fate and behaviour of disinfection by-products in Australian waters
Author(s) Alexandrou, L
Year 2019
Abstract Disinfection is a major component of water treatment, the final step in a strict treatment regime to convert water to a potable form for consumers worldwide. While drinking water sources are heavily regulated, recycled waters currently have limited use, primarily in agriculture and industry, and are kept away from possible human contact. However, with an ever-increasing global population and concomitant increase in demand for potable water, there is increasing pressure and incentive for recycled water to be used to augment water supplies. This is a potential problem since disinfection of organic rich water, such as recycled water, can lead to the formation of disinfection by-products (DBPs), of which over 600 compounds have currently been identified. Due to limited regulations on recycled waters, there are few occurrence studies on DBPs in recycled waters and fewer optimized methods for DBP analysis in such matrices. The work presented in this thesis explores and develops analytical capabilities for the analysis of DBPs. The focus of the work in this thesis, studies novel extraction techniques and analysis methods using chromatography and mass spectrometry. Emphasising fast and effective analysis with minimal sample preparation prior to analysis.

The work outlined in this thesis was built using DBPs of three classes: trihalomethanes (THMs), haloacetic acids (HAAs) and nitrosamines. Methods were developed on a range of instrumentation and optimised to suit the different compound classes. Analysis of multiple compound classes in a single analytical method was utilised where possible. As there are no enforced regulations for DBPs in Australian treated recycled waters, compounds were selected from those regulated in drinking water so as to be able to compare occurrence data between recycled waters and drinking waters. Previous studies on DBPs in recycled waters in Australia and the rest of the world are scarce, with the only source of occurrence data for recent years in Melbourne being provided by water companies in their annual reports. Such reposts only show the levels of DBPs are below the regulatory limit, they do not report the actual amounts found.

Although not a new technique solid phase extraction (SPE) appears in many methods for the analysis of DBPs. Such methods are often very old usually require filtration of large volumes to allow suitable sample filtration and pre-concentration. A novel SPE cartridge was brought to market in 2014, which reduced the sorbent mass needed and allowed for a sample to be extracted via a cartridge attached to the end of a syringe. Aptly named micro solid phase extraction, this technique allows much smaller sample volumes to be extracted, reducing sample preparation time and sample/solvent waste. Standard solid phase extraction was compared to micro solid phase extraction for the analysis of trihalomethanes in recycled waters. The results showed an increased recovery for these highly volatile compounds along with drastically reduced sample preparation steps, achieving much higher sample throughput and extraction reliability when using micro solid phase extraction cartridges.

Headspace techniques for the analysis of DBPs, often involve the use of specific sorbents, using a technique called solid phase micro-extraction. For this work direct headspace analysis was used to bypass the need for a specific sorbent to extract the DBPs, relying on volatility instead of sorbent affinity. This gave the benefits of solid phase micro-extraction, but with the extra the capability to run samples without any preparation steps. Through the development of this method, I was able to optimise a direct headspace injection to analyse for THMs in samples, with no pre-treatment and minimal preparation. This method was then used to undertake a survey on drinking water from around Melbourne and a selection of recycled waters direct from treatment plants and inner-city fountains. This study provided occurrence data on THMs in Melbourne waters.

Two classes of DBP, the Nitrosamines and HAAs, generally require either large volume extractions for pre-concentration, or derivatization methods that often show poor reproducibility. With advancements in liquid chromatography instrumentation, there was potential seen to improve available methods for these compound classes. For this work, positive-negative switching was used to analyse both of these very different compound classes in a single separation using multi-reaction monitoring to differentiate between overlapping peaks. The method achieved detection of 11 commonly occurring species from the two classes, all of which are DBPs, in only six minutes. The samples analysed were neat water samples, with the only pre-treatment, being a few minutes for sedimentation (to avoid column blockages) and no pre-concentration. The observed detection limits were at parts per trillion levels. This method was able to rapidly complete both qualitative and quantitative analysis on samples that would otherwise have required hours to prepare for typical analysis methods.

This research involved the development of multiple methods for the analysis of DBPs that can, and were, applied to both drinking and recycled waters. With further development, any of the methods displayed in this thesis can be enhanced to include a wider suite of compounds as needed in the event regulations for more DBPs are enforced. With the increasing list of observed DBPs and the increasing need for alternate water sources, DBP occurrence data is a must have moving forward. Faster methods are needed to keep up with demand and thus rapidity and ease of methods were the main criteria when optimizing and developing the analytical methods documented in this thesis.

Overall, this study helps to increase our knowledge in DBP analytical method development and occurrence. The knowledge out of this project is likely to be of benefit to those interested in the environment such as the water industry, government regulators and the general public.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Science
Subjects Instrumental Methods (excl. Immunological and Bioassay Methods)
Environmental Monitoring
Keyword(s) disinfection by-products
recycled water
drinking water
trihalomethanes
gas chromatography
liquid chromatography
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