ADVANCED TREATMENT OF SAHEBGHARANIEH SECONDARY EFFLUENT BY OZONATION

Abstract

Chemical oxidation is one of the most suitable treatment methods for reducing organic pollutants and the number of pathogens remaining in secondary effluents. Ozone is the most powerful oxidizing agent commonly used because of it's many advantages over chlorination. In this study the efficiency of ozonation in advanced wastewater treatment of Sahebgharanieh Plant has been determined. Ozone generation has been performed by irradiation of compressed air with 4 special UV lamps. The total output of these lamps was determined to be 0.74 mg ozone per minute at established conditions. Considering 3 periods of ozonation of effluent samples (30, 60 and 120 min) and ozone transfer coefficient of 95%, the concentrations of applied ozone for wastewater treatment were specified to be 10.5, 21 and 42 mg/l, respectively. Ozonation of secondary effluents at these periods has resulted in 17, 24 and 30 percent reduction in average COD and about 20, 18 and 32 percent decrease in BOD5. It is believed that the 2 percent increase observed in BOD after 30 minutes is caused by changing some amount of COD to BOD5 by applied ozone. According to the prescribed reduction values it could be concluded that the final effluent of a typical treatment plant would become better qualified for water reuse in irrigation. But it should be declared that the effluent might not be completely disinfected irrespective of about 99.0% decrease determined in MPN of total coliforms. Also it must be noted that this degree of disinfection was accomplished only for 62.5% of samples. Ozonation of effluent samples has caused an increase in pH value which was at least 0.4 of a pH unit.