Study On The Wastewater Treatment Of Carrousel Oxidation Ditch

Because of the serious valley water environment status in china, some provinces and cities have established valley integrated discharge standards to protect the local water environment quality, which is more rigid than national standards.In 2007, the EPA of Shandong Province and the Quality and Technical supervision Agency of Shandong province jointly issued the "valley water pollutant integrated discharge standards of Xiaoqing river in Shandong province" and the "valley water pollutant integrated discharge standards of peninsulas in Shandong province", which focus on improving the water environment quality of the peninsulas and the Xiaoqing river valley. Their basic requirements are that all the urban and town sewage treatment plants execute the first class B standard of the "pollutant discharge standards of urban and town sewage treatment plants" (GB18918-2002), that is, the wastewater drained to the third type valley executing the first A standard and the drainage concentration of COD, TN, NH₃-N and TP separately being 50mg/L,15mg/L,5mg/L and 0.5mg/L. This will bring forward more advanced requirements for the process design and operating of removing nitrogen and phosphorus.The Carrousel oxidation ditch wastewater treatment process has been widely used in china especially in Shandong province. It adopted the simultaneous nitrification and reverse-nitrification technology to remove nitrogen, which was an economical and high-efficient biological treatment process of removing nitrogen, and became one of the study hotspots of the current sewage treatment technology. We selected domestic wastewater as the study object and adopted Carrousel oxidation ditch test model as the treatment technology. After the middle test study, on the basis of a detailed study on the technology operating conditions and parameters, the simultaneous nitrification and reverse-nitrification factors were reviewed and the control conditions were intensified. By the theoretical analysis, the inherent rules of the simultaneous nitrification and reverse-nitrification occurrence of the Carrousel oxidation ditch were revealed and its operating and control parameters for good effluent quality and the best operating effects were got.The factors such as HRT, DO concentration and sludge age were studied, which affected the removal of COD, NH₄⁺-N and TN in Carrousel oxidation ditch. The research results included: (1) after the Carrousel Oxidation Ditch test device was rebuilt, it owned the full-mixed and pushed dual-hydraulic characteristics, which ensured the sludge not to deposit. Its model has the similarity to the hydraulics, oxidation and anoxic conditions and biology; (2) HRT had little influence on the removal of COD and NH₄⁺-N. Under different operating conditions, the removal of COD and NH₄⁺-N were above 80% and its effluent concentration is up to the first class B standard-"the pollutant drainage standard of urban and town sewage treatment plant"(GB18918-2002). But HRT had a great influence on the removal rate of TN and at 4 hours and 8 hours, its removal is only 50% and at 12 hours, the removal rate of TN reached to the optimal value of 62.8%;(3) In the Aerobic District, the dissolved oxygen concentration is the key parameter to control the technology operating. It not only affected various physiological activities of aerobe in the Carrousel oxidation ditch, but also affected the effective volume of the A/O district. The experiments showed that if DO concentration was controlled in the range of 1.5～2.5mg/L in aerobic district, the effect of reverse nitrification was better and the average TN removal rate reached to 68.4%. But excessive aeration cannot raise the effect of reverse nitrification, which showed the appropriate choice of limited oxygen aeration. This not only maintained higher pollutant removal efficiency, but also reduced the energy consumption; (4) the sludge age has a great impact on the removal of TN, while less impact on the removal of COD and NH₄⁺-N. Therefore, in order to have higher and steadier effects on nitrogen removal, about 16 days SRT of operating conditions should adopted and its average removal rate of TN reached to 63.6%.Aiming at the water flow complex characteristics of the crooked oxidation ditch, a plane two-dimensional mathematical model of crooked oxidation ditch under a certain depth was set up and the velocity distribution of crooked channel was simulated. By analyzing the water flow velocity changes fore-and-after setup guiding flow wall, the mechanism of reducing sludge deposition was discussed when oxidation ditch was set up offset guiding flow wall.