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UVChlorine AOP in Potable Reuse

Project Number # 3046

UV/Chlorine AOP in Potable Reuse: Assessment of Applicability, Operational Issues, and Potential By-Products

Background:

Potable water reuse is increasingly recognised as an important water management strategy for future Australian and international cities. In order to produce the highest quality drinking water from municipal wastewater sources, advanced treatment by ultraviolet radiation advanced oxidation processes (UV-AOPs) is a prominent feature of some of the most sophisticated potable reuse projects. Validation and monitoring of the UV aspects of UV-AOPs are well established and effective. However, validation of the AOP aspects (i.e., the production of oxidative radical species) is poorly developed and ongoing performance monitoring methods are currently impractical for most projects. This is a significant gap in advanced water treatment process reliability for chemical contaminant degradation.

In terms of full-scale operational potable reuse projects, high intensity UV and UV-peroxide are the only fully established processes. However, there is rapidly growing interest in an alternative catalytical process, UV-chlorine. There is one full-scale operational UV-chlorine AOP plant in California, but there is currently no experience with this technology in Australia.

With this project, we will develop a framework for the validation and ongoing performance monitoring of the advanced oxidation aspects of UV-chlorine employed for potable water reuse. We will systematically explore relationships between monitorable UV-chlorine operational conditions and treatment performance outcomes. The development of this framework will allow for ongoing practical and cost-effective real-time performance monitoring, thus satisfying a key requirement of Australian water quality public health regulators when assessing and licencing proposed potable water reuse projects.

Objectives:

(1)   Review current knowledge regarding the performance (including advantages and disadvantages) of UV-chlorine for advanced oxidation treatment of water.

(2)   Assess the effectiveness of UV/Cl for the elimination of a range of indicator chemical contaminants.

(3)   Assess the production of byproducts from UV/Cl advanced oxidation of real water samples.

Approach:

Task 1: Literature Review

A literature review will be prepared and submitted for publication on the topic of “Comparison of UV/Cl and UV/H2O2 Advanced Oxidation Processes in the removal of contaminants from water and wastewater”.

Task 2: Experimental Testing

How effectively does UV/Cl perform to eliminate a range of indicator chemicals? How well do experimental observations support model validation? These questions will be addressed by testing a wide range of indicator chemicals for photolytic and oxidative degradation during a range of test reactor conditions. At UNSW Water Research Centre, we have a series of “wastewater indicator” chemicals, which we routinely use for assessing performance of experimental and advanced water treatment processes. This suite contains over 30 trace chemicals and has been used to assess the performance of a wide range of pilot scale treatment processes (Phan et al., 2016; Phan et al., 2018; Song et al., 2018; Zheng et al., 2019). The target chemicals include a wide range of pharmaceuticals, hormones, industrial chemicals and ‘trace organics’.  Treatment performance will be assessed for each of these ‘indicator chemicals’ under a variety of AOP operational conditions. These include in the absence of any AOP catalyst, with variable dosings/concentrations of H2O2, with variable dosings/concentrations of HOCl, and in the presence of variable scavenger components in the matrix (NOM, bicarbonate, etc). Trace chemical analysis will be undertaken by high performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) in the analytical laboratories of the UNSW Water Research Centre.

These experiments will facilitate the distinction of which chemicals are removed by photolytic processes, relative to those which are removed by radical-mediated oxidative processes. They will also provide a direct comparison between the performance of the two catalysts. Experiments will be undertaken in ultrapure (lab-grade) water, as well as a series of ‘real’ water samples, including RO permeates.

This work will build on previous studies, which have begun to assemble databases of reaction rate constants for the oxidation of a range of trace organic chemical substances. It will then be used to be used to provide validation of a predictive model for trace contaminant oxidation.

UV/Cl AOP byproduct formation. Using the pilot-scale LP AOP rig, a range of experiments will be undertaken to assess the production of byproducts produced during UV/Cl treatment of a various water types/compositions and at various doses.  This work will be undertaken at the St Marys Advanced Water Recycling Plant (Sydney Water) with pretreatment including ultrafiltration and reverse osmosis.  Amendments to water quality will then be made, including various adjustments to pH, bromide and organic matter composition.

The (potential) byproducts targeted for analysis will be focused on DBPs known to be produced during chlorine disinfection of drinking water, including bromate, chlorate, perchlorate, as well as suite of N-nitrosamines (including NDMA), trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and chlorophenols. Each of these methods is currently operational in the UNSW Water Research Centre, the method for N-Nitrosamines has been published (McDonald et al., 2012).

Task 3: Guidelines and Tools

Stuart Khan will provide guidance to ensure that the approach taken for the Guidelines and the way in which they are presented are consistent with contemporary practice and regulatory expectations in Australia. Khan has considerable experience with the development of major water quality guidelines through his longterm appointment to the Water Quality Advisory Committee (WQAC) to the Australian National Health and Medical Research Council (NHMRC). In this role, he has contributed to a number important guideline documents, including the Australian Drinking Water Guidelines, the Australian Guidelines for Water Recycling (Phases 1 and 2) and the World Health Organization (WHO) Guidelines for Potable Reuse.

A key aspect of the Guidelines will be a focus on the identification and use of critical control points (CCPs) for monitoring and ensuring continuous effective treatment performance.

Industry relevance:

Interest in applications of purified recycled water are rapidly growing in Australia. The use of treated municipal effluents to provide source waters for high water quality applications requires high standards of treatment. Advanced water treatment processes are well developed in terms of their capability for producing high purity water. However, many processes are expensive to install, manage and operate. Development such as the replacement of UV-peroxide with UV-chlorine offer the potential to reduce these costs while maintaining effective and reliable advanced water treatment. However, assessment and process validation is required before these potential benefits can be delivered.

References:

McDonald, J. A., Harden, N. B., Nghiem, L. D. and Khan, S. J. (2012) Analysis of N-nitrosamines in water by isotope dilution gas chromatography-electron ionisation tandem mass spectrometry. Talanta, 99, 146-154.

Phan, H. V., McDonald, J. A., Hai, F. I., Price, W. E., Khan, S. J., Fujioka, T. and Nghiem, L. D. (2016) Biological performance and trace organic contaminant removal by a side-stream ceramic nanofiltration membrane bioreactor. Int. Biodeterior. Biodegrad., 113, 49-56.

Phan, H. V., Wickham, R., Xie, S., McDonald, J. A., Khan, S. J., Ngo, H. H., Guo, W. and Nghiem, L. D. (2018) The fate of trace organic contaminants during anaerobic digestion of primary sludge: A pilot scale study. Bioresource Technol., 256, 384-390.

Song, X., Luo, W., McDonald, J., Khan, S. J., Hai, F. I., Price, W. E. and Nghiem, L. D. (2018) An anaerobic membrane bioreactor – membrane distillation hybrid system for energy recovery and water reuse: Removal performance of organic carbon, nutrients, and trace organic contaminants. Sci. Total Environ., 628-629, 358-365.

Zheng, L., Price, W. E., McDonald, J., Khan, S. J., Fujioka, T. and Nghiem, L. D. (2019) New insights into the relationship between draw solution chemistry and trace organic rejection by forward osmosis. J. Membr. Sci., 587.

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