Water Journal : Water Journal September 2011
refereed paper water treatment water SEPTEMBER 2011 89 Abstract Filtered waters, prior to chlorine disinfection, were obtained from three wastewater treatment plants (WTPs), one in regional South Australia and two in Sydney. Samples were spiked with known concentrations of various cyanotoxins and treated with various doses of chlorine. The order of ease of cyanotoxin oxidation followed the trend, CYN > STX-eq > m-RR ≈ m-LR > m-LA. Under the conditions of this study the oxidation of microcystins was dependent on the chlorine dose in waters from plants in Sydney, with increased removal seen at a dose of 3.0 mg L-1. Increasing the dose from 1.5 to 4.0 mg L-1 did not have an impact on the oxidation of microcystins in the South Australian water. Introduction Cyanobacteria (blue-green algae) are ancient organisms that have adapted and thrived in many environments, including drinking water sources. While they are thought to be one of the first organisms to produce oxygen and, hence, were possibly instrumental in creating the Earth's atmosphere, their presence in drinking water sources has negative connotations for drinking water quality. This is predominantly due to their ability to produce secondary metabolites, in particular toxins that can affect human health. A majority of these cyanobacterial toxins (cyanotoxins) are not well removed by conventional water treatment (Mouchet and Bonnélye, 1998; Newcombe and Nicholson, 2004) and require either new and costly treatment technologies (eg, activated carbon, ozonation, membrane filtration) or optimisation of existing conventional treatment options. Of major concern in Australia are the cyanotoxins, cylindrospermopsin, microcystins and saxitoxins. Chlorination is considered a major treatment barrier for these toxins; however, little information has been gathered with respect to the effectiveness of this treatment for the oxidation of a range of cyanotoxins under conditions that would be experienced in Australian WTPs. While Merel et al. (2010) recently provided a review on the chlorination of a range of cyanotoxins, little has been published with respect to the chlorination of a range of cyanotoxins under equivalent conditions. This is particularly relevant since multiple classes of cyanotoxins are now being simultaneously detected in water bodies (Graham et al., 2010; Paerl et al., 2011). The efficiency of the chlorine oxidation process is dependent on a range of factors that are not limited to the chemical structure of the target compound, the water quality (in particular, pH and the presence of organics), the dose of chlorine and the reaction time. The main objective of this study was to identify the CT (the amount of chlorine exposed at a specific contact time) required to oxidise the cyanotoxins to levels equal to or below the Australian Drinking Water Guidelines (ADWG) and/or World Health Organisation (WHO) limits in three filtered waters, sourced from two WTPs in the Sydney area and one from a WTP in regional South Australia. This information will enable water authorities to identify and implement operational actions, such as optimising chlorine dosing and contact times, required to effectively oxidise these cyanotoxins. The CT values in this study were calculated by determining the area under a graph of chlorine concentration vs. time, different from the USEPA method of calculation which is essentially the residual chlorine concentration at a specific time (C, in mg L-1) multiplied by the specific detention time (T, in min) (USEPA, 2003). Current State of Play in Cyanotoxin Chlorination Some information on the cyanotoxins studied, including their documented reactions with chlorine, is given below. Cylindrospermopsin Cylindrospermopsin (CYN) is produced in Australia predominantly by the cyanobacterium Cylindrospermopsis raciborskii, and has been associated with serious tissue damage and cell necrosis in the liver, kidney and other organs (Falconer, 2005). In addition, studies have suggested that this cyanotoxin is carcinogenic, genotoxic and involved in the inhibition of protein synthesis (Froscio et al., 2001, 2003; Falconer, 2005). While no official guideline value exists for CYN, the WHO is in the midst of proposing a 1 μg L-1 level, due to concerns regarding the potential effect of CYN on human health (Rodriguez et al., 2007a). Figure 1 shows the structure of CYN. L Ho, J Dreyfus, P Lambling, H Bustamante, T Meli, G Newcombe Chlorination can be an effective final treatment barrier for a range of cyanotoxins APPLICATION OF CHLORINATION FOR CYANOBACTERIAL TOXIN CONTROL O O H H H NH OH NH HN -O3SO H3C NH N+ Figure 1. Structure of cylindrospermopsin.
Water Journal November 2011
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