1. The characteristics of wastewater. The production process of aluminum profiles
mainly includes degreasing, alkali etching, pickling, oxidation, sealing and coloring of the formed aluminum profiles. The profiles after the above-mentioned processes need to be cleaned with water. The overflow form is discharged from the cleaning tank, which is the main source of wastewater from the aluminum profile factory. In addition to a large amount of aluminum ions, the wastewater from aluminum profile manufacturers also contains some metal ions such as zinc, nickel, and copper. The pH of the wastewater varies depending on the production requirements, but most of it is acidic. 2, wastewater treatment process Because the aluminum profile wastewater mainly contains various metal ions and suspended solids, it needs to use neutralization adjustment and coagulation sedimentation process. The aluminum profile production wastewater is discharged from the workshop and flows into the neutralization adjustment tank, which is equipped with air agitation to balance the water quality. After the wastewater is balanced in the water quality and volume of the adjustment tank, alkali is added to adjust the pH value to 6-9, and then pumped into the sedimentation tank, and the flocculant (PAM) is added at the same time during the pumping process. After the metal ions in the wastewater react with alkali to form hydroxides, under the action of the flocculant, they form larger particles of alum, which settle quickly under the action of gravity. The upper half of the sedimentation tank can be directly discharged to the outside. The quality of the effluent It has reached the second-class regional emission standard of DB4426-89, the local emission standard of Guangdong Province. The sludge in the sedimentation tank is concentrated in the sludge tank and pumped into the plate and frame filter press for dewatering and then used for sanitary landfill or comprehensive utilization. 3, process principle 3.1 adjustment tank In the aluminum profile wastewater treatment, the tank type of the adjustment tank is divided into two types: intermittent and continuous. During manual adjustment, the adjustment tank needs to be divided into two compartments. The residence time of each compartment is 1～2h, which is used in turn and intermittently to facilitate manual adjustment; 3.2 The reaction tank The main function of the reaction tank is to make Al3+ in the aluminum profile wastewater. Fully react with OH- to produce insoluble Al(OH)3 precipitation. Usually vertical flow sedimentation tanks use vortex flow reactors, and advection sedimentation tanks use baffled flow reactors. 3.3 After the metal ions in the wastewater of the coagulation sedimentation tank react with the alkali, insoluble hydroxides are formed. However, because the formed particles are small and are not easy to settle under the action of water flow, flocculants must be added to make These particles adhere to each other and aggregate into larger particles, which are removed by solid-liquid separation in the sedimentation tank. The sedimentation tank adopts advection or vertical flow, especially the latter is the most widely used. Vertical flow sedimentation tank is particularly suitable for floc settlement, and is simple to operate, easy to manage, and the supernatant can be drained directly. The retention time of the sedimentation tank is 2h, and the surface load is 1m3/(m2?h). 3.4 sludge treatment The moisture content of the aluminum profile sludge discharged through the sedimentation tank reaches more than 90%, and it needs to be dehydrated. According to the factory's production capacity and scale of sewage disposal, two methods of natural drying and mechanical dewatering are selected to treat sludge. Natural drying is to use a drying tank to hold the sludge and use the sun to dry it. The advantages of this method are labor-saving and economical, but it is only suitable for enterprises with a small amount of sludge, and it is very troublesome in rainy weather; mechanical dewatering includes the use of centrifuges, belt filter presses, and plate and frame filter presses. However, due to the loose structure and corrosiveness of the aluminum sludge, only the plate and frame filter press has the best effect. Therefore, in the engineering design, the sludge is discharged from the sedimentation tank to the sludge thickening tank by static pressure, and then pumped to the plate and frame filter press after being concentrated. After treatment, the moisture content of the sludge can be reduced to about 70%, and the sludge cake can be transported or comprehensively utilized. 4. Summary ① Engineering practice shows that the process is reasonable and feasible. ② Due to the amphoteric state of aluminum in the solution, aluminum ions also play a role as a water purifier in wastewater. At the same time, various flocculants and coagulants added also contain a large amount of aluminum, so in the water quality project after treatment There is no requirement for the concentration of aluminum. ③The aluminum profile wastewater treatment process is simple in principle, easy to operate and manage, and it is also suitable for the treatment of other metal wastewater and acid-base wastewater. The current problem is the treatment of waste residue. The aluminum sludge still contains more hydroxides after being dehydrated by the filter press, and random disposal will cause secondary pollution. In fact, the sediment of aluminum wastewater contains a large amount of aluminum hydroxide. If it is developed and utilized, very pure aluminum hydroxide can be extracted as a chemical raw material, which has a wide range of uses.
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