Drinking water quality management progress in Ontario, two decades after Walkerton.

Following the waterborne disease outbreak in Walkerton, Ontario, the province made significant efforts to implement recommendations of the public inquiry that resulted. As Ontario reformed its drinking water sector, other jurisdictions were advancing risk-based quality management frameworks for drinking water, including the World Health Organization (WHO) through its water safety plan (WSP) framework. Two decades after the Walkerton tragedy, this paper seeks to: (i) evaluate alignment of Ontario's Drinking Water Quality Management Standard (DWQMS) with the WSP framework (ii) review readily available data for evidence that Ontario's DWQMS implementation has improved drinking water safety and promoted a preventive approach through risk-based quality management. Our study found strong alignment between the Ontario DWQMS and WSP frameworks, with supporting programmes and risk assessment procedures present. Analysis of available regulatory data revealed abundant reporting of water quality and adverse incidents in municipal water systems. However, performance data were publicly available, the use of percentage scores for water quality testing obscures the details of system performance and water safety. Reports describing the DWQMS plan and audit results were difficult to obtain and not standardized. There is a need to develop mechanisms to ensure continual improvement of the DWQMS.

Influence of chloride on the 185 nm advanced oxidation process.

The use of 185 nm radiation from a conventional low pressure mercury lamp generates the hydroxyl radical (OH) from the photolysis of water and offers an advanced oxidation process (AOP) for water treatment that does not require chemical addition. However, the influence of the water matrix on the process differs substantially from that of other ultraviolet and ozone based processes. In particular chloride (Cl-), and not water, absorbs the majority of 185 nm photons when [Cl-]>20mgL-1 and generates the chlorine atom radical (Cl) as a reactive species. Evidence suggests that when Cl- is present, Cl and OH both contribute to contaminant degradation to varying extents. Using nonselective (carbamazepine) and selective (nitrobenzene) radical probes, as well as nonselective (t-butanol), and selective (acetone and acetate) radical scavengers, the influence of Cl-, and therefore 185 nm AOP treatment efficiency, is observed to strongly depend on four independent second-order radical rate constants. Furthermore, ionic strength effects support the assumption that Cl is in equilibrium with the relatively nonreactive dichlorine radical anion ().

Inuence of major anions on the 185 nm advanced oxidation process - Sulphate, bicarbonate, and chloride.

The 185 nm wavelength radiation generated by the conventional low pressure mercury lamp forms the basis of an advanced oxidation process (AOP) that does not require chemical addition. The photolysis of water by 185 nm photons generates the hydroxyl radical (OH) used to degrade trace organic contaminants. While AOPs in general suffer decreased efficiency in direct proportion to the concentrations of dissolved organic matter (DOM) and alkalinity (HCO3-/CO32-), acting as OH scavengers, such solutes impose an additional parasitic effect on the 185 nm AOP as absorbers of photons. Furthermore, the major inorganic anions sulphate () and chloride (Cl-) also absorb at 185 nm to generate the highly reactive sulphate () and chlorine (Cl) radicals. Like OH, and Cl. are also scavenged by DOM and HCO3-/CO32-. Using carbamazepine as a radical probe, and t-butanol or Suwannee River isolate as model DOM, the relative reactivity of these radicals with both DOM and HCO3- was found consistent with the order . Experimental evidence suggests some interconversion between these radicals. The 185 nm AOP treatment efficiency thus depends strongly on the anionic composition of the water matrix, as well as on the relative reactivities of the target contaminant, DOM, and HCO3- with the three radicals OH, Cl., and . Changes in any of these parameters may result in substantial differences in treatment efficiency.