| Because of intensification of the nitrogen pollution, the waste water biological nitrogen removal technology has aroused the universal interest of many countries. Single stage autotrophic nitrogen removal process refers to the whole process of autotrophic bacteria in a single system from NH4+ to N2, the whole process does not consume the organic carbon source and consume oxygen less, it’s especially suitable for wastewater with high concentration of ammonia nitrogen, low carbon and nitrogen ratio, so it becomes a novel promising biological nitrogen removal process with high efficiency and low energy consumption. The nitrogen removal pathways in the single stage autotrophic nitrogen removal process were complex, they may involve in many denitrification pathways such as nitrification, denitrification and anaerobic ammonium oxidation and so on. The present study is still controversial on its main nitrogen removal pathways; at the same time, the nitrogen removal pathway may occur dynamic succession in the starting and running period of the single-stage autotrophic nitrogen removal process, which are not conductive to the precise control and performance optimization of the process, thus limiting its application in practical engineering. To solve the above problems, the main research conclusions are as follows:(1)This research inoculated with activated sludge from a city sewage treatment plant sludge nitrification oxidation ditch system and high ammonia nitrogen wastewater as influent manual configuration in the SBR reactor, with the temperature of 30±2℃ and pH of 8±0.2. It took 284 days to start up the single-stage autotrophic nitrogen removal process after three stges—the aerobic granular sludge, the nitrification stage and the single-stage autotrophic nitrogen removal stage. When the influent ammonia concentration was 200 mg·L-1, the ammonia conversion rate was 96.5% and the nitrogen removal rate was 89.1%, its nitrogen removal performance was good.(2)The pathways of nitrogen transformation were studied by the way of the combination of the material balance and batch experiments during the start process of the single-stage autotrophic nitrogen removal system. The results are as follows: ①the most important nitrogen removal way is nitrification and denitrification at the aerobic granular sludge and nitrosation stage. The nitrogen balance percentage is 91.27% in the aerobic granular sluge cultivation stage. It included the nitrogen took away by the effluent(6%), the nitrogen consumed in denitrification(72%), the nitrogen took away by the remaining sludge discharged(6%), and the nitrogen loss(9%). ②In the nitrification stage, the amount of nitrogen removal by nitrification and denitrification decreased and the nitrification effect is getting better and better with the influent ammonia concentration increased and COD concentration decreased. In the 82 d to the 110 d, the rate of nitrogen removal by nitrification and denitrification was more than 70%, which was the largest nitrogen removal pathway; it decreased significantly after the 114 d, eventually fell to 14.57%. At the same time, the rate of nitrogen removal with the effluent draining away increased from 4.47% to 82.66% finally. ③ There were many nitrogen removal pathways at the single stage autotrophic nitrogen removal stage. They were the nitrogen conversion(7.32%), smmonia stripping(5%), nitrification and anaerobic ammonia oxidation(57.88%). There were two nitrogen conversion ways of anaerobic ammonia oxidation: one way was that at first NO2- was reduced to NH2 OH, NH2 OH reacted with NH4+ to form N2H4, which was further converted to N2 subsequently, realizing the nitrogen removal; another way was thatafter part of NH4+ was oxidized to NH2 OH under aerobic conditions, NH2 OH and NO2- were converted to N2 O under anaerobic conditions, at last N2 O was further converted to N2 which realized the nitrogen removal. The former accounted for a larger proportion. The former accounted for a larger proportion, rate is 32.17%, and the latter accounted for 25.16%.(3)By using qPCR quantitative fluorescence techniques, the functional bacteria of the nitrogen removal system—ammonia oxidizing bacteria(AOB), nitrite oxidizing bacteria(NOB),anaerobic ammonia oxidation bacteria(AAOB) and denitrifying bacteria(DNF) were quantitative analyzed. The results are as follows: the AAOB gene copies were 645 pieces·μL-1、 6790 pieces·μL-1 and 74800 pieces·μL-1 respectively in the inoculation sludge, nitrification sludge and single autotrophic nitrogen sludge. It increased moderately in the nitrification stage and had a lot of enrichment in the single stage autotrophic nitrogen removal stage. The AOB gene copies were 10600 pieces·μL-1、28000 pieces·μL-1 and 22000 pieces·μL-1 respectively in the inoculation sludge, nitrification sludge and single autotrophic nitrogen sludge. It got a big enrichment in the nitrification stage, then decreased slightly due to the competition with AAOB in the single stage autotrophic nitrogen removal stage. The NOB gene copies were 17610 pieces·μL-1 in the inoculation sludge, which was the most in the three sludges. It decreased sharply in the nitrification stage because of the competition of AOB and NOB’ growth was eliminated. It was further eliminated to 669 pieces·μL-1 in the single stage autotrophic nitrogen removal stage. The DNF gene copies changed as same as NOB. The results also verified the research on the main nitrogen removal pathways of the single stage autotrophic ammonia system. |
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