Assessment of a chlorine dioxide proprietary product for water and wastewater disinfection

Chlorine on its own is adequate for many, if not most, potable water pre-oxidation and disinfection systems at plants where the application is straightforward. Similarly, most wastewater plants can be disinfected by chlorine in one of its commercially available forms. However, when more intense pre-oxidation is required or significant iron or manganese is present in a potable supply, the use of alternative disinfectants is often preferable. Similarly, when secondary problems are present in wastewater effluent, such as high ammonia, a stronger oxidant may be preferable. Hitherto, the use of stronger oxidants has been limited to large works due to the complexity of the operational processes required. Recently, the use of ozone has spread to smaller works as new developments in equipment have become available. However, chlorine dioxide has not been used in small works until now. This paper provides details regarding a product which is simply dissolved in water in tablet or granular form and generates chlorine dioxide on solution in water. The solution is stable over weeks or even months and can be used for disinfection and or pre-oxidation purposes. The chemical was assessed in a series of tests. The performance of the chlorine dioxide product was compared against sodium hypochlorite, for different water types. The reduction in microbial counts was monitored in a secondary effluent sample and a high-ammonia secondary effluent sample. The oxidation ability in a high iron and manganese water was also assessed. A cost assessment was carried out and compared to the use of sodium hypochlorite. Other factors such as safety ease of use, and storage requirements are discussed.Keywords: chlorine, chlorine dioxide, oxidant, iron, manganes

Chlorine: Is it really so bad and what are the alternatives?

Chlorine disinfection has been practised for over a century and has been credited with saving a significant number of lives worldwide on a daily basis, but it has received a great deal of negative publicity over the past few decades. The discovery in the 1970\'s that chlorination of water could result in the formation of potentially harmful trihalomethanes (THMs) caused concern amongst the water treatment fraternity and resulted in authorities reviewing chlorination practices in order to minimise THM formation and the United States Environmental Protection Agency (USEPA) setting maximum concentration limits for THMs in potable water. Many of the manufacturers and suppliers of water “purifiers” and alternative disinfectants exploit this information to their own advantage, misinforming the public regarding the dangers of chlorine, but even in the water treatment industry, chlorine is often misunderstood. Based on their experience in both water and wastewater disinfection and on the findings of a Water Research Commission (WRC) sponsored project into alternative disinfectants, the authors discuss the benefits and disadvantages of chlorine disinfection and compare this to the more promising alternative disinfectants. One of the main perceived advantages is the property of chlorine to maintain a residual and although THM formation can occur under these conditions, the compounds produced are perceptibly less toxic than those produced by some of the alternatives. A number of alternatives, including ozone, UV, peracetic acid, bromine and advanced oxidation are compared to chlorine in terms of their disinfectant abilities, residual effect, by-product formation, cost and ease of use. Water SA Vol. 30 (5) 2002: pp.18-2