Optimization of chlorination process and analysis of THMs to mitigate ill effects of sewage irrigation

Chlorination has been employed extensively for sewage disinfection so that it can be reused, but the health issues related to its disinfection byproducts (DBPs) have forced to search for safer options. The present study focuses on the efficiency of chlorine disinfection on five dominant coliform bacterial species present in the secondary treated effluent. Resistance to low doses of chlorine was observed by few coliform species, such as Serratia/Hafnia which in turn required much higher doses of chlorine to achieve Total Coliform Count (TCC) within standards. This consequently increased formation of DBPs. A quadratic model of design of experiments (DOE) softaware was opted as an optimization strategy for chlorination, which was attempted to achieve counts for rest of the species to be brought within standard except for resistant ones so that the initial disinfection with chlorine could be terminated at this dose. This would then be followed by another disinfectant (UV/Ozone) against which such resistance among those species was not observed. The optimized results of chlorination (2.5 ppm of CD at 14.83 min/42 mg-min/L) would be useful in designing a hybrid disifection strategy which may help reduce the CD substantially and thereby its byproducts. Analysis of four Trihalomethanes (THMs) was carried out with the help of Gas chromatography-mass spectrometry and gas chromatography/tandem mass spectrometry (GC-MS/MS) to assess their concentrations due to chlorination of sewage. The effect of chlorine on physiology of bacterial cells was also examined through scanned electron microscopy (SEM) analysis to get a clue to inactivation mechanism.