| With the social development and the speeding up of urbanization, there are more and more industrial and domestic sewage. However, there is no significant improvement in sewage treatment. There are many sewage treatment plants can’t meet the emissions standards along the Ashihe River. Many of these sewage treatment plants employ the plug-flow A-AAO process which increases nitrate denitrifying zone of reflux sludge and multipoint distribution. However, A-AAO process has long aerobic retention time, causing the waste of energy and has negative effects on nitrogen and phosphorus removal. In addition, some nearby industrial wastewater, especially some yeast production wastewater containing high concentration of colored organic matter, which can’t be effectively removed by these A-AAO process, flow into sewage treatment plants, which causes these sewage treatment plants can’t meet the emissions standards with the high colored and fluctuant effluent. So it’s extremely urgent to improving the sewage treatment plant capacity, optimizing of process parameters and meeting the emissions standards. This study put forward to extend the retention time of anoxia zone while the total HRT of anoxia and aerobic zones did not change on the purpose of promoting the efficiency of nitrogen and phosphorus removal. Further, this study came up with changing the plug flow anoxic zone into the oxidation ditch anoxic zone which is completely mixed, aiming for promoting nitrogen and phosphorus removal.This study operated two lab-scale plug-flow A-AAO processes, aiming for discussing the influences of extension of residence time of anoxic phase on pollutants removal. The results showed that under the same condition of total residence time(18.25h), the denitrification of the two A-AAO reactors strengthened when residence time of anoxic phase extended, which lead the average removal rate of total nitrogen of the 1# reactor reaching 61.36% higher than 57.08% of the 2# reactor. Meanwhile, with the less aerobic reaction time, the nitrate nitrogen of return flow reduced which lead to the average removal rate of total phosphorus of the 1# reactor higher than the 2# reactor. According to the 3DEEM of reactors’ influent and effluent, it could be seen that the plug flow A-AAO could removal protein with aromatic ring, soluble metabolites and tryptophan protein effectively. However, the concentration of humic acid in effluent increased significantly as a result of microbial metabolism. The experiments indicated that in some AAO process wastewater treatment plants, it was proper to close some aerobic zones and transform them into anoxic zones, which was contributed to decreasing the concentration of nitrogen and phosphorus so that the effluent quality could meet the emissions stabilized.Intending to discuss the shape of anoxic zone on pollutants removal further, two lab-scale oxidation ditch A-AAO processes were operated. The results showed that under the same condition of total residence time(17.1h), the denitrification of the 3# reactor strengthened when residence time of anoxic phase extended,leading the average removal rate of total nitrogen of the 3# reactor reaching 64.88% higher than 58.08% of the 4# reactor. Compared with the plug flow A-AAO processes, the oxidation ditch A-AAO processes with the anoxic zones designed into oxidation ditch, had strengthened the hydrolysis of particulate carbon source with higher efficiency of utilizing carbon source. Meanwhile, the denitrifications and phosphorous removal strengthened significantly with the anoxic zones mixed completely.Combined with field test results, the process of the second phase in the Acheng sewage treatment plant and the process of the first phase in the Chenggaozi sewage treatment plant were operated to optimize debugging, intending to meet the emission standard for the whole year. |
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