Study On SBR To Removal Nitrogen And Phosphorus Added Ozonation Sludge Reduction

The treatment and disposal of excess sludge has become a serious issue of wastewater treatment plant because of the large amount of excess sludge, high treatment cost and secondary pollution. Therefore, the technique of sludge reduction attracts more attention in the field of environment protection. Moreover, as entrophication becomes serious year by year, the removal of nutriment, such as nitrogen and phosphorous, has become a most important mission for municipal sewage treatment plant. In practical operation, it was found that the nitrogen and phosphorous removal efficiency was hard to be improved because of the low COD concentration of wastewater. By making use of ozonation, as a low energy cost treatment with high efficiency and few secondary pollution, this study tried to achieve two objectives: the fist was to realize sludge reduction, and the second was to improve the nitrogen and phosphorous removal efficiency, using the organic obtained from cell breaking as a carbon source for nitrogen and phosphorous removal. In another word, this study aims at the harmony of sludge reduction and the nitrogen and phosphorous removal.Using a ozonation-SBR process, this thesis studied the effects of ozonation on sludge reduction process and on nitrogen and phosphorous removal efficiency. Results were described as follows:As for sludge oxidization, a portion of ozone was used to break cells with protein release, a portion of ozone was used to degrade compounds such as protein and ammonium. A parameter of the observed broken-rate was proposed. The lowest concentration was selected in different conditions with same observed broken-rate, and the optimal ozone supply was found to be 0.16gO₃/gSS。After ozonation, DO concentration of the liquor declined fast. And it took less than 30min to fall to 0.3mg/L even when the ozone supply was as high as 0.2gO₃/gSS. However, the oxidizing capability could maintain for 2h in this condition. Combining the nitrogen and phosphorous removal process of SBR, which was controlled at 1.5h, 3.5h, 1.5h, 0.5h and 1h for anaerobic stage, aerobic stage, anoxic stage, latter aerobic stage and water exchange stage respectively, the author proposed that the sludge should be slowly recirculated to initial anaerobic stage when it settled down after ozonation.Four recirculation rates of ozonation sludge were chosen for the nitrogen and phosphorous removal process of SBR. It was showed that a comparatively lower recirculation rate of ozonation sludge had few effect on effluent quality and a comparatively higher recirculation rate of ozonation sludge had a great effect on effluent quality.During a long-term operation, the sludge activity in OSBR-0.1 system and OSBR-0.2 system were close to the SBR system, which prevented sludge bulking effectively. The sludge activity in OSBR-0.3 system and OSBR-0.4 dropped a lot in initial stage and after that, maintained stable at about 70% and 60% of the SBR system respectively. The accumulation of the inorganic didn't occur in all ozonation systems.The observed sludge yield were 0.366gMLSS/gCOD,0.231 gMLSS/gCOD,0.146 gMLSS/gCOD,0.081 gMLSS/gCOD and 0.037 gMLSS/gCOD for SBR, OSBR-0.1, OSBR-0.2, OSBR-0.3 and OSBR-0.4 systems respectively. Through analyzing the effluent quality and sludge activity, the ozonation sludge recirculation rate of 0.2 L/L?d was found to be the optimal. Under this condition, a sludge reduction rate of 60% with good effluent quality and sludge activity could be achieved, which also kept the long-term good quality of effluent.In a word, it was showed that the combination of ozonation sludge reduction with the nitrogen and phosphorous removal process of SBR would not affect the quality of effluent and could achieve some sludge reduction efficiency, when the system was controlled at a suitable sludge recirculation rate. The obtained results were practically valuable.