Advanced water treatment technologies to minimise the formation of emerging disinfection by-products in potable water

Abstract

As the international standards for drinking water become more stringent and the health guideline values for currently regulated disinfection by-products (DBPs) decrease, the challenge increases for water utilities to produce water which conforms to the guidelines. In Australia, expanding populations, and drought in some areas, particularly Western Australia, have already resulted in scarcity of water in many urban and regional centres. As a result, water of more marginal quality must be utilised for potable purposes, and the variable and more concentrated natural organic matter (NOM) in these water sources makes the treatment, distribution, and disinfection processes increasingly difficult.While NOM itself does not appear to be harmful, when it reacts with disinfectants, some of the resulting DBPs have been found to be potentially harmful to human health. Due to concerns about these potential health effects, other disinfection methods aimed at reducing the major DBPs from chlorination, such as the trihalomethanes (THMs), have been investigated. Chloramination is increasingly being used as an alternative disinfection method to chlorination, because it has the advantage of producing only trace amounts of THMs and haloacetic acids (HAAs). However, chloramination can result in the formation of other DBPs, some of them newly identified and termed ‘emerging DBPs’, such as the N-nitrosamines, with many of the emerging DBPs being reported to be carcinogenic, mutagenic, and/or teratogenic. For the purpose of this Thesis, ‘emerging DBPs’ refers to DBPs which have little or no regulations or guideline values assigned to them.An effective approach to reducing the formation of potentially harmful DBPs is to remove the DBP precursors prior to the disinfection stage. For removal of dissolved organic carbon (DOC) as a DBP precursor, it is becoming increasingly common for ozone to be used as a pre-oxidant or intermediate oxidant during drinking water treatment. Ozone followed by biological activated carbon (BAC) filtration has been shown to improve water quality by removing a portion of the DOC, depending on the content of ozone-reactive DOC within the water source. However, in bromide-containing waters, ozonation can result in the formation of bromate, a potent carcinogen. Advanced oxidation processes (AOPs), which usually involve the addition of a combination of chemical oxidants and/or a source of UV light, are also attracting increasing interest as DOC removal techniques.