Through the small and medium sized city sewage treatment plant process selection, design, training students majoring in environmental engineering to use learned of the water pollution control theory, master sewage treatment scheme comparison and optimization. The main structures structure design and parameter calculation, main equipment modeling package comprises a grille, lifting pump, a blower, an aerator, sludge dewatering machine, sand water separator, scraping mud machine, water agitator and dosing equipment, disinfection equipment, such as, and layout and elevation calculation. According to the determined process and calculation results, draw the general layout of the sewage treatment plant, process flow chart and the main structures.

This graduation design to a municipal wastewater as treatment object, mainly for sewage organic matter content is relatively high, relatively high content of nitrogen and phosphorus, we finally decided to choose the Carrousel 2000 oxidation ditch process. The main task is to complete the preliminary design of the sewage treatment plant and the construction drawing design of monomer treatment structure. The preliminary design to complete the design specification, a sewage treatment plant, a total plan of a sewage treatment plant process flow chart and the main process of building a process map.

The total size of the sewage treatment plant is 55400m3/d. We design the sewage process: from the pumping station to grit chamber and into a clarifier oxidation ditch and the second again into the pool disinfection, PAP metering tank, and finally to the water; and the sludge treatment process is: excess sludge from the secondary sedimentation tank of into concentrated pool again into the digester to reach the final dewatering room. After dehydration and transported to the outside for processing.

We pass several technological after comparison, from covers an area of angle of view, oxidation ditch covers an area smaller than the A2 / O reactor; from the perspective of energy consumption, A2 / O process due to the sludge return flow, so that the energy consumption is to is higher than that of the oxidation ditch; due to the design of small and medium sized sewage treatment plant, from the perspective of cost, and also for small and medium-sized sewage treatment plant, oxidation ditch cost low, so this design choice oxidation ditch process. As the design of nitrogen and phosphorus removal rate is not high, so in the oxidation ditch before the need to set anaerobic pool, oxidation ditch selection Carrousel oxidation ditch.

Oxidation ditch process features are: (1) to simplify the pretreatment. Oxidation ditch hydraulic residence time and sludge age than general biological treatment method and suspended organic matter can be with dissolved organic matter and get a thorough removal and discharge of excess sludge has been highly stable, therefore the oxidation ditch can not set up early sedimentation tank, the sludge does not need to carry on the anaerobic digestion.

(2) less land occupation. Because in the process, the primary settling tank and sludge digestion tank are omitted, so that the total area of the sewage plant is reduced.

(3) the characteristics of the flow regime. The oxidation ditch has the characteristics of push flow, which makes the concentration of dissolved oxygen in the long direction along the pond to form a concentration gradient, which forms the aerobic, anoxic and anaerobic conditions. Through the reasonable design and control of the system, it can get a better effect of nitrogen and phosphorus removal.

(4) simplify the process. The oxidation ditch and the second sedimentation tank jointly built for the integrated oxidation ditch, and in recent years the development of alternating oxidation ditch, without secondary sedimentation tank, so that the processing process is simplified.

After treatment, we have to deal with the final effluent requirements to achieve the "urban sewage treatment plant pollutant discharge standards" (GB18918-2002) in the provisions of the standard B standard. The oxidation ditch process is selected in the process, which has the function of removing nitrogen and phosphorus, so as to reach the requirement of design. Then determine the process flow and elevation layout, and then calculate the relevant hydraulic calculation,