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1、 Chromium-containing wastewater treatment scheme一、 Basis and Target of the PlanBasis:The average daily treatment capacity shall be 140 Mt and the design capacity 200 Mt per day.It is required to treat the waste water constantly, and the operation must be convenient. Equipment life time 15 yearsTarge
2、t:It is required that in the treated waste waterOverall chrome content 1.5mg/LHexavalent chrome content 0.5mg/LPH value: 6-9Phosphate (P) 0.5mg/LChemical oxygen demand 150 mg/LCopper content 0.5mg/LZinc content 5mg/L二、 Plan DesignGeneral:We adopted the method of oxidation reduction to treat the hexa
3、valent chrome, transform it to trivalent chrome, and remove the heavy metal ions by means of chemical precipitation method. This process features in its stable performance, high efficiency, simple operation and low operative costs. In the DongFeng Auto Corporation there are quite a few surface treat
4、ment workshops where this method has been put into production for years and its practical effect has been proven to be good.This project has also been awarded as a Class-3 Advanced Industrial Technology of China Auto.Principle: Add reducer when the waste water in the reaction tank is controlled as P
5、H 6, transform the hexavalent chrome into trivalent chrome。 Regulate the PH value to 8-8.5; transform the trivalent chrome, copper, zinc, manganese and iron ions into hydroxid to let them settle. After that add flocculating agent to make the small grain flocculation become large grain flocculation,M
6、eanwhile ,settle other substances which are forbidden to discharge.Separate the mud and water in the settling basin, the mud is transferred to the mud condensing pool through the pipes, and then pressed into blocks by the pressing and filtering machine. Finally the secondary pollution of the mud is
7、removed after burning it into brick. Design of Water-storing TankThe size of tank is determined according to the water runoff in the workshops, the treatment time in the reaction tank, and any possible interruption and disturbance. As required by the Project Entrusting Documents, the average daily w
8、aste water output is 120 Mt. In our design the tank capacity is 80Mt, in addition to the two reaction tanks; the overall water storage capacity reaches 120Mt. That means under normal production conditions the waste water system may have a One-day maintenance time.The tank design must be suitable for
9、 the fully mixing of waste water. Taking account of the separation of large suspended matter blocking the pipes, we have designed an oil-separation plate. Except the function of storing the water from the workshops, the tank may also play a regulating role to enable the waste water thickness keep a
10、relatively balanced level that will avoid large thickness difference of the waste water in the reaction tank. For the location of tank, we have taken advantage of the altitude difference in the plant area to form automatic flow and therefore save power. Also for the purpose of the landscaping, we ha
11、ve designed the tank below the ground and covered by lawn. The tank structure is as follows:Design of Reaction TankThe reaction tank is formed of two tanks, each has a 15 Mt storing capacity and they are utilized alternatively. When one is performing oxidation reduction treatment, the other may rece
12、ive the waste water from the water-storing tank so as to keep a constant waste water treatment. The tank is designed below the ground and enables the water automatically flows to the tank, saving either power consumption or pump maintenance costs, and material feeding becomes simpler also.In order t
13、o enable quick and balanced chemical reaction and shorten the treatment time, there is air mixer installed in the tank. Material feeding and PH regulating are controlled manually.Once the reaction is finished, the waste water pump transfers the treated and qualified waster water to the settling resi
14、n to separate it. Design of Settling BesinThis is a key point, because if the settling substances resulted from the reaction is not separated immediately, then the discharge will not meet the standard and the treatment efficiency will be restricted also. Based on the daily treatment volume, we have
15、designed a 160m3 settling resin. In order to increase the settling efficiency we have installed an oblique pipe settling device in the tank to ensure the outlet water quality. In the tank bottom the mud is transferred to the mud condensing pool by the mud pump or automatic flow. Meanwhile, for the p
16、urpose of watching the effect we have designed walkway above the settling resin.The resin bottom is a funnel shape which allows the mud comes to bottom and therefore is convenient to be transferred out. The overflow port of the resin is a triangle weir to avoid watermark flow that means the mud on the oblique pipe will not be taken out and the water will remain clean. The depth of the resin is determined according to the four areas of settling: Clean water area
