Effects of gamma irradiation on physicochemical and biological characteristics of wastewater effluent and sludge

The effluent and sludge samples collected at the Municipal Wastewater Treatment Plant of Southern Tehran were irradiated with doses of 5, 10 and 20 kGy using a 60 Co gamma source and without irradiation (control) in a completely randomized design with three replications. In the term of total and fecal coliforms load, the gamma ray was more effective in the effluent disinfection than in the sludge. Approximately, three logs reduction in total and fecal coliforms were observed at the dose of 20 kGy in the sludge. The complete inactivation of the coliforms load in the effluent was achieved by 10 kGy gamma ray, whereas for sludge, it was not achieved even at 20 kGy. The improvement in the irradiated effluent quality was demonstrated by the significant reductions in chemical oxygen demand, biochemical oxygen demand, turbidity, pH, EC and concentrations of nitrate and phosphate. The other characteristics of the effluent and sludge did not change and/or changes did not show any trend as a result of treatments except concentrations of nitrogen and copper in the sludge and calcium and potassium in the effluent. The results proved that gamma ray can be applied as an effective technique for the reuse of effluent and sludge in agricultural soils.