Municipal Drinking Water Treatment

Municipal Drinking Water Treatment: Access to safe drinking water is considered to be a basic human right. However, more than one-sixth of the world’s population, predominantly in developing countries, lack reliable access to such water. Customers complain to drinking water companies regarding incidents like taste, odour, colour, slime, low pressure and no supply of water. In the UK, it is estimated that one-third of all customer complaints concerning drinking water are related to water discolouration (Cook et al., 2005). These complaints greatly undermine customers’ confidence in water companies.

Iron and Manganese contamination of water have long been considered to only lead to aesthetic problems, in that they are secondary contaminants that have little or no adverse health effects. However, research conducted by Wasserman et al. (2006) indicated a relationship between increased Mn concentrations in drinking water and reduced intellectual functions of children. Increased levels of Iron and Manganese concentrations have been found to be the main cause of drinking water discolouration (Slaats, 2002). Furthermore, discoloured water could also lead to coloured stains on laundries and sinks, increased treatment costs, reduced treatment capacity and increased pumping costs. Water with high concentrations of Iron and Manganese has been found to give water an unpleasant metallic taste and vegetables cooked with it become dark and look unappetizing (Herman, 1996).

High Iron and Manganese levels can lead to non-compliance with drinking water regulations. The drinking water standard for most jurisdictions for iron is 0.3 milligrams per liter (mg/l), and the standard for manganese is 0.05 mg/l respectively. The quality of water changes as it travels from source to consumers in Water Distribution Networks (‘WDNs’). Although water companies generally set post-treatment targets of Fe and Mn to about 3% of their respective MCLs, low concentrations of Fe and Mn still enter the network and gradually accumulate on pipe walls within WDNs. Given the wrong conditions, such as high flows created by a water main burst or high diurnal consumption of drinking water, these accumulated particles may subsequently lead to water discolouration and end up in customers’ taps.

In order to begin the process of oxidation of the iron (and manganese) in solution DMI-65® is designed to operate in the presence of chlorine or other oxidants. In this process the oxidant removes electrons and is consumed in

the process. The operator needs to ensure that there is a 0.1 – 0.3 ppm free chlorine residual in the effluent water. Chlorine, fed as sodium hypochlorite or bleach (12.5% NaOCl), is the preferred oxidant since it is relatively inexpensive, readily available around the world and it is effective. It also performs the vast majority of any disinfectant process.

Unlike ion exchange resins where higher regenerant dosages will increase the ion exchange capacity, NaOCl residuals or concentrations higher than required to oxidize the Iron and Manganese do not increase the oxidative properties of the media. Additionally, since the media is often used to pretreat waters prior to an RO system a higher free chlorine residual would require more extensive post treatment to reduce the residual and protect the membranes from chlorine attack.

DMI-65® has been certified to the US Standard of NSF/ANSI 61 for Drinking Water System Components and for use in England and Wales Under Regulation 31(4)(a) of the water supply (Water Quality) regulations 2010 and has also been tested by many other water treatment authorities and laboratories.