The acidic wastewater produced by aluminum profiles is mainly derived from the oxidation workshop, acid neutralization process, oxidation process, spray pre-treatment, oil removal, pickling and other processes, which are rich in various harmful substances or heavy metal salts. The mass fraction of acid is not the same, low is less than 1%, and high is greater than 10%. Alkaline wastewater mainly comes from the process of alkali etching in the oxidation workshop and pre-treatment alkali washing. The mass fraction of the base is higher than 5%, and some are lower than 1%. Waste water is also generated by spraying and dyeing. Waste water, in addition to rich in acid and alkali, is often rich in oils, paints, fluoride salts and other inorganic and organic matter.
Acid-base wastewater is highly corrosive and needs to be properly managed before it can be discharged. The general guidelines for the management of acid-base wastewater are: 1 high-concentration acid-base wastewater, priority should be given to reclaiming the application, according to water quality, water quantity and different technical needs, as much as possible: if repeated use is difficult, or the concentration is low, the water volume is large, Concentration can be used to recover acid and alkali. 2 Low-concentration acid-base wastewater such as clean water in the acid washing tank and rinsing water in the alkali washing tank should be neutralized.
Regarding neutral disposal, we should first consider the criteria for waste treatment. For example, acid and alkali wastewater are neutralized with each other or waste alkali (slag) is used to neutralize acidic wastewater, and waste acid is used to neutralize alkaline wastewater. In the absence of these conditions, a neutralizer may be used.
According to the national standard GB8978-1996 "Water Pollutant Emission Limit", the emission demand is: COD level ≤ 60mg / L, level ≤ 120mg / L, suspended matter ≤ 100mg / L, fluoride ion F - ≤ 10mg / L, pH 6-9.
The modern wastewater disposal methods are mainly divided into three categories: physical disposal method, chemical disposal method and biological disposal method.
1) Physical Disposal Method The wastewater treatment method that removes the undissolved pollutants (including oil film and oil beads) in the wastewater after physical effects. Generally, sedimentation, filtration, centrifugation, air flotation, transpiration crystallization, and reverse soaking are selected. The waste water, colloids and oils in the waste water are separated, so that the waste water can be purified.
2) Chemical treatment method The wastewater treatment method that separates and removes the dissolved or colloidal pollutants in the wastewater or converts them into harmless substances through chemical reaction and mass transfer effect. The general selection methods are: neutralization, coagulation, oxidation recovery, extraction, stripping, stripping, adsorption, ion exchange and electro-osmosis.
3) The biological treatment method converts the waste water solution, the colloid, and the organic matter and toxic substances in the fine suspension state into a waste water disposal method of the stable and harmless substance through the metabolic effect of the microorganism. The biological disposal method is divided into two methods: aerobic treatment and anaerobic treatment. The aerobic treatment method currently used is activated sludge method, biological filter and oxidation pond. The anaerobic treatment method, also known as the biological recovery treatment method, is mainly used to dispose of high-concentration organic wastewater and sludge, and uses disposal equipment, firstly for the digester.
The intention of disposing of sludge is to: 1 reduce the moisture content of the sludge and create conditions for the disposal, application and transport of the sludge. 2 Eliminate harmful substances that pollute the environment. 3 Recover power and capital to achieve profitability. Sludge disposal methods include sludge concentration, sludge digestion, sludge dewatering, and sludge drying. The purpose of sludge concentration is to start the dewatering of the sludge and reduce the volume of the sludge to provide conditions for subsequent disposal. The purpose of sludge dewatering is to further dewater the sludge to a moisture content of less than 80%. The methods are mechanical dehydration and natural dehydration. The mechanical dehydration method is further divided into a vacuum suction filtration method, a pressure filtration method, and a centrifugal method. Its strength is high dehydration rate and small floor space, but it is more expensive. The natural drying method has low infrastructure and operation costs, but the dehydration power is low, the floor space is large, and the sanitary environment is poor. The intention of sludge drying is to heat the dewatered sludge to further reduce the water content and reduce the volume. The dry treatment method is commonly used in rotary drum type boring machine. Its strength is stable function and reliable operation, but the floor space is large.
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