Research On The Denitrfication And Phosphorus Removal Of The Improved A~2/O Process

Many problems exist in the traditional A2/O process that can remove phosphorus and nitrogen simultaneously by biological method, for instance: the conflict of SRT between PAO and nitrobacteria, and the competition for limited carbon source between PAO and denitrifying bacteria, which results in that high removal for phosphorus and nitrogen simultaneously hardly is realized in the process. As for the above mentioned problems, we bring forward to improved A2/O process, which uses the technology of cultivating the microbe heterotrophic bacteria and autotroph bacteria separately and shortening the aeration time in the activated sludge system to enhance the nutriment removal. The HRT of this process is equal to the traditional A2/O process so that it suit to the reconstruction and upgrade of existing city wastewater treatment plant.This research studied the startup of the improved A2/O process, the influencing ingredients in the operation of improved A2/O process, the choice of effluent, analysis of the nutriment removal mechanism, analysis of the circs of microbe cultivated separately. It demonstrates that:The improved A2/O reactor can be started up normally in the room temperature of 18～25℃, and it holds a large capability for the organic load and NH4-N load. When the inner circumfluence rate is 200%, SRT is 5d, and the influent COD concentration is 450 mg/L, the capacity of denitrification and phosphorus removal in the system is the best, and the operation expense is economic. At this time, COD removal rate is 89%, NH4-N removal rate is 97%, TN removal rate is 73.8%, TP removal rate is 64.8%. The TP removal rate is not so high, so we advise using much shorter SRT in the experiment in the future. The distributing of sludge is sometimes badly influenced by the border effect in the reactor which reduces the removal rate of nutriment.Through comparing the quality of the effluent from the two sedimentation ponds, the quality of effluent from the last sedimentation pond is slightly better than the quality of effluent from the middle sedimentation pond. In order to achieve the discharged standard of NH4-N, effluent from the last sedimentation pond should be chosen in the system.From mechanism analysis through the change of contamination concentration along the the improved A2/O reactor, the organic load is largely reduced after the activated sludge phase, biology contact pond is running in the state of the low organic load. The removal of nitrogen is through the nitration and denitrification. The removal of TP is through anaerobic phosphate release and aerobic phosphate excess absorbing.Through the analyzing the biology of the system, the A2/O process has cultivated the microbe heterotrophic bacteria and autotroph bacteria separately successfully: the sludge grain in the activated sludge phase has big size, thick colloid, and compact structure, and it forms the zoogloea which is mainly dominated by heterotrophic bacteria. The Protozoa and metazoan are few in the activated sludge phase. There are mostly heterotrophic bacteria in the bio-film system, such as nitrobacteria and subnitrobacteria. There are also plenty of Protozoa and metazoan in the bio-film system.Selecting high organic load is better for the cultivating the microbe heterotrophic bacteria and autotroph bacteria separately from the analyzing the NOx- in the flow from the middle sedimentation pond, SRT is a key factor for the cultivating the microbe heterotrophic bacteria and autotroph bacteria separately. When SRT is shorter than 10d, we can cultivate the microbe heterotrophic bacteria and autotroph bacteria in the system separately successfully.