Carbon source recovery from excess activated sludge by alkaline treatment and oxidation

In the biological denitrification processes a carbon source is required for the cell synthesis of bacteria. The use of an external carbon source such as methanol and ethanol results in not only the extra cost of chemical but also the extra sludge production. Chemical (alkaline, acid) and thermal treatment have been extensively studied for the production of internal carbon source from the excess activated sludge. In this study, the gamma ray irradiation was applied to produce an internal carbon source from the excess activated sludge for the biological denitrificaition. Alkaline pre-treatment and ozone oxidation were combined with gamma ray irradiation to enhance the efficiency of carbon source recovery and sludge reduction. The effects of initial pH, radiation dose and ozone dose on the efficiency of carbon source recovery and sludge reduction were studied, and the reaction conditions were optimized. SCOD/TCOD ratio, BOD5/COD, SS, T-N, NO2--N, NO3--N, NH4+-N, T-P variations were monitored. From the results, the alkaline treatment was more effective than the gamma ray irradiation or ozone oxidation for the carbon source. However, the ozone oxidation was most effective for the sludge reduction. The efficiency of sludge solubilization for the carbon source recovery as well as that of sludge reduction could be simultaneously enhanced by alkaline pre-treatment and ozone oxidation combined with a gamma ray irradiation. The results confirmed that the radiation technology combined with an alkaline pre-treatment and an additional advanced oxidation process can be used to achieve the efficient production of carbon source and the sludge reduction from the excess activated sludge. (authors)