Radiation treatment of sewage effluent

The water demand of the past several years increased rapidly. Recycling of municipal wastewater is the effective means of coping with water shortage in Tokyo. We studied the radiation treatment method of further purification of the effluent from sewage treatment plant. By gamma irradiation the refractory organic substances in effluent were decomposed. The COD values decreased and the light brown color faded with increasing dose. The high molecular weight components in effluent were degraded to lower molecular weight substances and were decomposed finally to carbon dioxide. Recent attention has been given to the disadvantages of using chlorine as a disinfectant of municipal wastewater effluents. It has been shown that the chlorination of organic substances in water may produce chlorinated hydrocarbons with carcinogenic properties. So a development of the effective sterilization method for the effluent has been needed instead of chlorine. The radiation sterilization of coliforms and total bacteria in primary effluent, secondary effluent and rapid sand filtered effluent were studied. Coliforms were very sensitive to radiation treatment in comparison with total bacteria. Especially, coliforms in secondary and rapid sand filtered effluents were disinfected to 10 % of initial at 0.1 kGy. (author)