Ultraviolet Light Oxidation of Free-Chlorine in Water
Chlorine is the most frequently used chemical for water disinfection. Many industrial and commercial manufacturing facilities cannot tolerate the introduction of chlorine into the process because of contamination and unwanted chemical reactions. Chlorine affects the flavour and odour of drinks and fluids, accelerates corrosion on process vessels and piping, and can also damage delicate process equipment. Process equipment such as reverse osmosis (RO) membranes and deionization (DI) resin can be damaged by continual exposure to chlorine. Granular activated carbon (GAC) filters or the addition of chemicals, such as sodium metabisulphite, are the most commonly used methods of removing both free chlorine and chloramines (combined chlorine) within a water treatment system. Sodium Sulphite or Sodium Metabisulphite This is purchased in a premixed solution or as a dry powder and then mixed on site. It is commonly injected in front of RO membranes so that the sodium combines with the chlorine to make harmless salt and is frequently used in the pharmaceutical and semiconductor industries. One common problem with this approach is the solution itself becomes an incubator of bacteria, causing bio fouling of the membranes. The bisulpite only adds to the complex chemistry of the incoming water, which must be removed during the water purification process. Also this is another chemical which must be documented in use, handling and storage for Health and Safety regulators. In addition to these factors is human error, which allows over and under mixing of the chemical. Granular Activated Carbon (GAC) This method is frequently used for industrial applications such as the beverage and pharmaceutical industries. It is also used in point of use units for residential and commercial applications. GAC has an imperfect structure, which has a high degree of porosity. Intermolecular attractions in the smallest pores result in adsorption forces, which enable GAC to remove volatile organic compounds, trihalomethanes, and otherhalocarbons from process streams. Because of the porous structure and the nutrient rich environment, GAC beds become prime incubators for microorganisms. Long ago, it was discovered that natural sunlight oxidises free chlorine in water. This natural phenomena forces owners of outdoor pools to routinely add chlorine to their pools in order to maintain a disinfection residual. Municipal water districts using surf chlorinating. This phenomenon can be duplicated on a commercial level using a concentrated UV light emitting specific wavelengths. This article reviews different field trials conducted to evaluate the effectiveness if UV oxidation of free chlorine.