A Study on the Effect of Gamma Rays on Reducing the Burden of Some Pathogens in Sewage Sludge

The reuse of sludge in agriculture leads to the transfer of some pollutants into food chain, thus hazarding the public health. The pathogens, heavy metals and nutrients in the sewage sludge from two wastewater treatment plants in Tehran-Iran, Shahid Mahallati and Ekbatan, were investigated in three independent samplings. Moreover, the reduction of pathogens after irradiation by 10kGy gamma ray from 60Co was studied. The obtained results indicated that the heavy metals and nutrients in both of the wastewater treatment plants comply with Environmental Pollution Agency Standards and the pathogens counts reduced to the extent of the permitted level after irradiation. Viable Ascaris eggs in Ekbatan sludge was more than permitted level even after irradiation. According to the obtained data, just the sewage sludge of Shahid Mahallati treatment plant produced class A biosolids by irradiation which means that it can be applied to the agricultural lands, public contact sites and even home gardens. The odor of irradiated samples reduced as compared with the control ones. Vector attraction reduction processes must be conducted before use. The capability of the mentioned dose of gamma ray in converting the municipal sewage sludge into a sanitary fertilizer, depends on the microbial contamination level, specially the numbers of viable Ascaris eggs.