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PREDICTING THE FORMATION OF CHLORINATED AND BROMINATED BY-PRODUCTS.
Citation:
Clark*, R M., R C. Thurnau*, M. Sivaganesan*, AND P. Ringhand. PREDICTING THE FORMATION OF CHLORINATED AND BROMINATED BY-PRODUCTS. Arnold, R.G. (ed.), JOURNAL OF ENVIRONMENTAL ENGINEERING. American Society of Civil Engineers (ASCE), Reston, VA, 127(6):493-501, (2001).
Description:
Although disinfection has been and continues to be one of the major public health advances in the 20th century, the disinfectants themselves may react with naturally-occurring materials in treated water to form unintended by-products which may themselves pose risks. This is of particular concern with regard to the use of chlorine.
In 1974 chloroform, a product of the reaction of chlorine and naturally occurring organic matter, was identified in disinfected drinking water. Since that time a number of other chlorinated by-products (DBPs) have been identified including trihalomethanes (THMs), by-products other than chloroform (e.g., bromodichloromethane), haloacetic acids (HAAs), haloacetonitiles, haloketones, and haloaldehydes. Generation of DBPs has been shown to be a function of various factors including total organic carbon (TOC) concentration, the type of organic precursor, chlorination level, pH, temperature, bromide level, reaction time, and UV-254 absorbance.
To control chlorination disinfection by-products, requires an understanding of the factors that influence their formation including pH, time, temperature, chlorine concentration and the concentration of organic and inorganic matter. Another factor affecting disinfection by-product formation is the presence and concentration of the bromide ion in the raw or finished water. The absence or presence and concentration of some organic by-products of chlorination depend on the bromide ion concentration in the water because bromide substitutes for chlorine to produce bromine-containing homologues of the more familiar chlorine species.
Once bromide ion is present in source waters, it is difficult to remove it. The current list of by-products targeted for regulation contains brominated and mixed bromine-chlorine species of TTHMs and haloacetic acids (HAAs). These are known to form in bromide-containing waters when chlorinated.
This paper presents a model that can be used to predict the formation of chlorinated, brominated and mixed compounds based on initial chlorine concentration, chlorine consumption, bromide concentration, and pH. The model clearly shows that the higher the level of bromide in the water the lower the level of the chlorinated compounds. Bromide compounds form faster then chlorinated compounds.