Research And Application Of Step-feed Multistage A/O Biological Nitrogen Removal Process

Nitrogen is one of the predominant pollutions in the water body and can lead to water eutrophication. To protect water environment quality and strengthen the control of pollutants discharge of municipal wastewater treatment plants, based on "comprehension discharge standard for wastewater (GB8978-1996 ) , total nitrogen of influents in wastewater treatment plants was included in "discharge standard of pollutants in municipal wastewater treatment plant (GB18918-2002 ) , while A level of first class standard was put forward for the first time. In the subsequent years , the application scope of A level of first class standard was enlarged in many cities, province and the whole nation, for example, the municipal wastewater treatment plant built after January of 2008 must comply with the A level of first class standard strictly in Taihu valley.According to research results of realizing technology of A level of first standard in Taihu valley, key factor to reach this standard stability is how to reach the standard of total nitrogen stability. The research on advanced nitrogen removal in china is still at the beginning stage, and the processes used are mainly A²O process and its modified processes, however, these processes have some problems, such as, nitrogen removal efficiency is low, total nitrogen concentration discharged could not meet the standard, energy consumption is expensive, etc.Based on the analyses of the features of the nitrogen removal process, experiences of advanced design and operation on nitrogen removal and construction and operation status of the municipal wastewater treatment plants, construction of step-feed multistage A/O biological nitrogen removal process which contains the technology of step-feed, multistage A/O strategy and internal circulation utilizing the different water level by aeration is put forward. The technology and economic parameter for its first engineering application are discussed. Results shows that:(1)The application of step-feed and multistage A/O strategy in step-feed multistage A/O biological nitrogen removal process provided sufficient carbon and appropriate environment for nitrogen removal process. Treatment performance is excellence, such as, total nitrogen removal ratio can reach 75%-85%, the total nitrogen concentration discharged is very low, which can be under 10 mg/L, etc.(2) In the design of engineering application of the process in china, many advanced technologies, such as, optimum of pretreatment, integration arrangement of sediment tank and biochemical tank, internal circulation strategy of nitration liquor and introduction of novel process equipment are adopted, which can reduce the energy consumption a lot. Taking the biochemical tank of it for example, it can save energy cost 2,154.8 Yuan every day, and 787,000Yuan annual, compared with A²O process. In addition, the application of these technologies will provide strong technology support to main operation stability and guarantee good discharge water quality.(3) The wastewater treatment plant of Linghai city applied the step-feed multistage A/O biological nitrogen removal process, and the recent built scale of it is 20,000 m³/d, the construction cost of it is 42,909,000.0 Yuan, the operation costs of it is 0.61 Yuan per ton. Otherwise, the project is under construction. Taking similar projects abroad as reference, the water quality discharged can reach the A level of first class stand or a little better, for example BOD₅≤10 mg/L, CODcr≤10 mg/L, TN≤15 mg/L, TP≤0.5 mg/L, SS≤10 mg/L.(4) The building and operation of wastewater treatment plant of Linghai city will terminate the history of no wastewater treatment in Linghai city,and it will the reduction the pollutants discharge amount as follows, CODcr = 2190 t/a, BOD₅ = 1241 t/a, SS = 1387 t/a, TN= 146 t/a, TP= 25.55 t/a. It is believed that the infrastructure level, water environment quality and ecological environment quality of Linghai city will be improved greatly.