Chlorination of secondary treated wastewater with sodium hypochlorite (NaOCl): An effective single alternate to other disinfectants

The present study provides details about the usefulness of chlorination in the recovery effluents of sewage, and to make it useable for irrigation purposes. Chlorination is one of the effective simplified, and cost-effective traditional methods for disinfection. The study was done for the period of March, 2019 to February, 2020. The disinfection process was optimized by adding sodium hypochlorite to the secondary treated effluents with the help of jar apparatus at a mixing speed of 100 rpm. To optimize the various process variables such as dose, and contact time, several concentrations of NaOCl (0.5, 1, 1.5, 2, 2.5, 3.0) ppm were carefully chosen at different time intervals of 15, 30, and 60 min respectively, which were centered on the foregoing studies. The factors like seasonal variation on MPN index of total coliforms (TCs), CR * T concept, and effect of pH on log elimination of TCs, outcome of pH with rate constant (k), and results of pH against dilution coefficient (n) was also studied. The Chick-Watson, Rennecker-Marinas, Collin-Selleck, and modified Selleck models have shown good reliability to the experimental data of chlorine disinfection to be fit into these kinetic models for the treatment of sewage wastewater. The upgraded CR * T values were attained by using disinfection models. Among these four models, the kinetic modeling by Collin-Selleck, and Selleck-White was investigated as the best modeling to be fitted more finely to the chlorination experimental data to count for the effectiveness of NaOCl. The selected indicator organism in the optimization process of chlorine was Total coliforms (TCs). The residual chlorine and most probable number per log unit (Log) for TCs were measured before the start and after the termination of the disinfection process. The World Health Organization (WHO) standard for pathogenic removal from wastewater, and to irrigate the crops is 3-to 4-log and the chlorine residual under 1 mg/l limit was accomplished.

Automated summary

This study provides detailed information on the usefulness of chlorination in treating sewage for irrigation purposes. Chlorination is a cost-effective method for disinfection. The study optimized the disinfection process using sodium hypochlorite and investigated various process variables. The results showed that certain kinetic models fit well with the experimental data of chlorine disinfection.