1 Project Overview

　　A mechanical processing plant is a processing enterprise that produces automobile transmissions. The designed water volume of the sewage treatment station is 600 m3/d, including 200 m3/d of industrial wastewater and 400 m3/d of domestic wastewater. Oily industrial wastewater mainly comes from cutting fluid wastewater generated by CNC lathes in machining workshops, release agent wastewater generated in forging workshops, emulsion wastewater generated in shell processing, etc. Domestic sewage includes canteen wastewater, bathing wastewater in employee dormitories, offices and workshops Waste water from toilets, etc.

　　2 treatment process

　　2.1 Selection of treatment process

　　According to the water quality characteristics of the mechanical processing wastewater and the effluent quality requirements, a comprehensive analysis and selection of the treatment process of "oil separation + demulsification reaction + air flotation + hydrolysis acidification + mixing + biological contact oxidation + MBR"

　　2.2 Process description

　　2.2.1 Sewage treatment process description

　　Grease trap. Since the sewage discharged from the production workshop contains a large amount of grease, the effective removal of floating oil in the water has become an important part of the treatment station. The removal of slick oil can reduce the total oil concentration in the sewage, thereby reducing the pressure on the subsequent treatment structures. The grease trap is a structure that removes the grease contained in the sewage. It uses the principle of different oil and water densities to gather oil droplets with low density. The surface of the pool is then collected into the oil sump.

　　Air floatation integrated machine. The effluent from the grease trap is sent to the integrated reaction box through a transfer pump, which integrates a demulsification box, a flocculation box, a pH adjustment box and a coagulation box. The appropriate amount of H2SO4, CaCl2, NaOH, flocculant PAC, And after the coagulant PAM reacts with the wastewater, the emulsion and some flocculating pollutants in the water form larger particle flocs. At the same time, due to the air flotation equipment generating tiny bubbles, a large number of tiny bubbles are adsorbed on the surface of the floes. In the process of continuously rushing to the water surface, the floccules that have undergone flocculation reaction float on the water surface and are collected and discharged by the scraper.

　　Hydrolysis and acidification tank. The wastewater in the air flotation tank enters the hydrolysis acidification tank through a water pump. The hydrolysis acidification tank is equipped with a water distributor to play the role of hydraulic stirring. A large number of facultative bacteria grow in the tank, which can change the long-chain organic matter of the aerobic bacteria that is not easily degraded For short-chain small molecular organics, improve the biodegradability of wastewater, create good conditions for subsequent aerobic treatment, and at the same time denitrify nitrate in water and reduce nitrate nitrogen to gaseous nitrogen. It can effectively prevent the eutrophication of the water body and has the function of improving the properties of aerobic sludge in the membrane biological reaction tank.

　　Regulation pool. The adjustment tank collects industrial waste water and domestic waste water, mainly plays the role of water volume adjustment and water quality balance, and is equipped with a pre-aeration device to help homogenize the water quality while preventing waste water corruption, effectively preventing the odorous air pollution caused by sewage corruption from disturbing the people The phenomenon.

　　Contact the oxidation reaction tank. Due to the high concentration of pollutants in the sewage influent, the large amount of water, and a certain impact load on microorganisms, a contact oxidation tank with resistance to impact loads is used to provide a good carrier for the growth of microorganisms and ensure the quality of the effluent. Sewage decomposes organic matter through aerobic microorganisms (activated sludge) in the aeration tank. A sufficient number of non-blocking air aerators are evenly installed at the bottom of the contact oxidation tank. The air continuously supplies oxygen to the sewage through the air aerator to ensure the amount of oxygen required for the biological oxidation reaction in the sewage. Each group of air diffusers is equipped with a regulating valve before it.

　　Membrane biological reaction tank. A membrane module and aeration system are arranged in the membrane biological reaction tank. The membrane module is composed of hollow fiber membranes. The membrane pore size is 0.2~0.4 μm, which is smaller than the diameter of bacteria. It belongs to the range of microfiltration membranes and can effectively intercept bacteria in the water. It is regarded as a means of isolation and sterilization, which reduces the dose of disinfectant added subsequently. The mass concentration of high-concentration activated sludge intercepted by the microfiltration membrane in the reaction tank reaches 8 000~10 000 mg/L, and the activated sludge BOD loading rate is low, generally 0.1~0.2 kg/(kg˙d). The late stage of decelerating growth and the early stage of endogenous respiration. The organic matter in the sewage is thoroughly and effectively degraded. The treated water is filtered through the membrane module and reused after being disinfected by sodium hypochlorite.

　　2.2.2 Sludge treatment process description

　　The scum produced by the air flotation machine, the remaining sludge produced by the contact oxidation tank and the MBR reactor are mixed into the sludge thickening tank for concentration, and then dewatered by the stack screw dehydrator. The moisture content of the sludge after dehydration is less than 75%, and finally The sludge is transported to the hazardous solid waste treatment plant for incineration and harmless treatment.