Ozone disinfection of primary effluent using a stirred tank reactor

A pilot-scale stirred tank reactor was used to evaluate the efficiency of ozone for disinfecting primary effluent. Total and fecal coliform numbers before and after disinfection were evaluated concomitant with several common wastewater characteristics. A disinfection model was built using the method of linear least squares. The model enables the designer to choose the transferred ozone dose to achieve a given number of indicator bacteria in the effluent when the BOD5 is known. The model was found to be useful for the primary effluent studied but should not be used in other applications without pilot plant investigations. Examination of similar models reported in the literature suggests that weak wastewaters (COD < 25 mg/L) may be described by a regression model using COD and transferred ozone as variables but extrapolation to moderate and strong wastewaters, as was done in this study, introduced gross errors. Further research into the fundamental kinetics of ozone disinfection of wastewater is necessary before a reliable design model is available. Key words: ozone, disinfection, primary eflluent, model, coliforms.