The acidic wastewater from aluminium profile production mainly comes from the acid etching process, neutralization, oxidation process, spraying pretreatment, degreasing, pickling and other processes in the oxidation workshop, which is rich in various harmful substances or heavy metal salts. The mass fraction of acid is very different, the lower is less than l%, the higher is more than l 0%. Alkaline wastewater mainly comes from alkali corrosion in oxidation workshop and alkali washing in spraying pretreatment. The mass fraction of alkali is higher than 5% and lower than l%. Wastewater also occurs in spraying and dyeing. Wastewater, in addition to acid and alkali, is often rich in grease, paint, fluoride salts and other inorganic and organic matter.
acid and alkali wastewater has strong corrosiveness and can be discharged only after proper management.
The general criteria for the management of acid and alkali wastewater are as follows:
As for neutralization disposal, we should first consider the criterion of abandonment. For example, acid and alkali wastewater neutralize each other or waste alkali (slag) is used to neutralize acid wastewater, and waste acid is used to neutralize alkaline wastewater. In the absence of these conditions, neutralizers can be selected for disposal.
According to the national standard GB8978-1996 "Water Pollutant Discharge Limit Value", the discharge requirements are as follows: COD level 1 < 60 mg/L, Level 2 < 120 mg/L, suspended matter < 100 mg/L, fluoride ion F - < 10 mg/L, and pH value 6-9.
Chinese style
Modern wastewater disposal methods are mainly divided into physical disposal method, chemical disposal method and biological disposal method.
1) Physical disposal method is a waste water disposal method which separates physical effects and recovers insoluble suspended pollutants (including oil film and oil beads) in wastewater. Deposition, filtration, centrifugal separation, air flotation, transpiration crystallization and reverse immersion are commonly used. The pollutants such as suspended matter, colloid and oil in wastewater are separated, so that the wastewater can be purified.
2) Chemical treatment is a waste water treatment method which separates, removes or converts the dissolved and colloidal pollutants into harmless substances through chemical reaction and mass transfer. The general selection methods are neutralization, coagulation, oxidation recovery, extraction, stripping, stripping, adsorption, ion exchange and electro-soaking.
3) Biological disposal method, through the metabolic effect of microorganisms, transforms the wastewater solution, colloid, micro-suspended organic substances, toxic substances and other pollutants into stable and harmless wastewater disposal methods. Biological disposal can be divided into aerobic disposal and anaerobic disposal. At present, the commonly used aerobic disposal methods are activated sludge process, biological filter and oxidation pond. Anaerobic treatment method, also known as biological recovery treatment method, is mainly used to treat high concentration organic wastewater and sludge, use disposal equipment, digestion tank and so on.
The intention of sludge disposal is:
Eliminate harmful substances that pollute the environment.
Sludge disposal methods include sludge concentration, sludge digestion, sludge dewatering and sludge dryness. The intention of sludge concentration is to dehydrate sludge and reduce sludge volume to provide conditions for subsequent disposal. The purpose of sludge dewatering is to further dewatering, so that the water content of sludge can be reduced to less than 80%. The method includes mechanical dehydration and natural dehydration. Mechanical dewatering method is divided into vacuum suction filtration method, pressure filtration method and centrifugal method. Its advantages are high dehydration rate, less land occupation, but more expensive investment. The capital construction and operation cost of natural drying method are very low, but the dehydration power is low, the area is large, and the sanitary environment is poor. The purpose of sludge dryness is to heat the dewatered sludge to further reduce water content and volume. Rotary drum dryer is commonly used for drying treatment. Its advantages are stable function and reliable operation, but it covers a large area.