Effect of gamma irradiation on activities and physicochemical characteristics of sewage sludge

In this paper, the response mechanism of sewage sludge exposed to (60)Co gamma irradiation at a dose of 0-25 kGy was investigated. Results showed that gamma irradiation could disintegrate sludge flocs and release proteins, polysaccharides and extracellular enzymes into the bulk solution. The maximum oxygen uptake rate decreased by 58%, and 99% of the culturable bacteria were inactivated at 25 kGy. However, the tested protease, superoxide dismutase and catalase showed slight inactivation during irradiation treatment. The efficiency of sludge solubilization reached around 6.5% with a dose of 25 kGy. Nitrate in the supernatant decreased rapidly to nearly zero after gamma irradiation which may have been due to the conversion of nitrate into N(2) or N(2)O gases through reductive reactions by hydrated electrons. Ammonium was the main inorganic nitrogen product. (C) 2011 Elsevier B.V. All rights reserved.