Ocorrência de cloro residual combinado no sistema de distribuição de água de Campina Grande (PB).

Abstract

The aim of this study was to describe the occurrence of combined residual chlorine (CRC) in the water distribution system of Campina Grande City (7°13'50" South, 35°52'52" West), Paraiba state, Northeast Brazil, as a contribution for the maintenance schedule of the system, particularly distribution reservoirs and other strategic points. Monochloramine (NH2CI), resulting from the reaction of hypochlorous acid and ammonium salts, dichloramine (NHCI2 ) and trichloramine (NCI3 ) formed respectively by the oxidation of monochloramine and dichloramine by hypochlorous acid, constitute the combined residual chlorine (CRC) which may coexist with free residual chlorine in water supply systems, particularly in reservoirs and extremities of water distribution network which favor the accumulation of organic nitrogen, mineralizable through reactions of ammonification. Such an accumulation is commonly favored by inefficient maintenance schedules of water distribution network especially those applied for distribution reservoirs and other parts of the system that are more capable of exposing water to deterioration. Water quality indicators measured at different times along the daily cycle were statistically analyzed in order to demonstrate the existence of significant differences between groups of indicators at different monitoring points of the system. Differences were related to operational, environmental, anthropogenic and maintenance factors associated with these sites. Significant concentrations of combined residual chlorine, which have not important disinfection capacity, were determined in the water distribution system of Campina Grande, being its occurrence attributed to a number of factors associated with the degradation of water quality as well as aspects related to operation and maintenance.