Complete Digestion of Sewage Sludge Using Wet-Oxidation and Subsequently Simultaneous Removal of Residual NH4+ and Volatile Fatty Acids by Biological Treatment

Abstract

Thickened sewage sludge consisting of primary and surplus sludges with a total solids of 4% was treated by wet-oxidation without catalysts. The digestion efficiency of VSS was 94 to 96% at 80 kgf (cm2G) -1 and 250°C for holding times ranging from 30 to 120min. However, TOC and NH4+ in the liquid generated by the wet-oxidation pmcess was as high as 3, 845 mg l-1 and 1, 410 mg l-1, respectively, even at a holding time of 120 min.The organic matter containing in the wet-oxidized wastewater could be removed in the biological denitrification with the supplement of NaNO3.The TOC and VFA removal efficiencies in the biological denitrification were 65% and 100%, respectively, at a TOC loading rate of 5.0g l-1 d-1.The NH4+ remained in the denitrified wastewater was treated in the biological nitrification after two-times dilution and the NH4+ was oxidized to NO3- completely, at the same time the TOC removal efficiency was 36 to 50%.On the basis of these results, NH4+ and organic matter in the two-times diluted wet-oxidized wastewater could be removed simultaneously in a biological denitrification and nitrification process with a recirculation, resulted in reduction of the supplementation amount of NO3- and HCO3- necessary for denitrification and nitrification, respectively. Moreover, the supplementation of NO3- and HCO3- could be reduced to zero by an improved process, namely, installing an activated sludge tank between the denitrification and the nitrification reactors.