The acid wastewater from aluminum plate production mainly comes from the acid etching process, neutralization, oxidation process, spray pretreatment, oil removal, acid washing and other processes, which are rich in various harmful substances or heavy
metal salts. The mass fraction of acid is very different, the low content is less than 1%, and the high content is more than 10%. Alkaline wastewater mainly comes from oxidation workshop alkali corrosion, spraying pretreatment, alkali washing and
other processes. The mass fraction of alkali is higher than 5% and lower than 1%. Spraying and dyeing also produce waste water. In addition to rich acid and alkali, wastewater is often rich in oil, paint, fluoride and other inorganic and organic substances.
The acid-base wastewater has strong corrosivity and can be discharged only after proper management. The general principles for the management of acid-base wastewater are as follows: 1) high concentration acid-base wastewater should be given priority to
recovery and utilization, and should be reused as much as possible according to the water quality, water quantity and different technical requirements. If the reuse is difficult, or the concentration is low and the water volume is large, the concentration
method can be selected to recover the acid and alkali. ② Low concentration acid-base wastewater, such as cleaning water of pickling tank and rinsing water of alkali washing tank, should be neutralized.
In terms of neutralization treatment, we should
first consider the criterion of treating waste with waste. For example, acid and alkali wastewater neutralize each other, or use waste alkali (slag) to neutralize acid wastewater, and use waste acid to neutralize alkaline wastewater. In the absence of
these conditions, neutralizer can be used for disposal.
According to the national standard GB8978-1996 discharge limits of water pollutants, the discharge requirements are as follows: cod class I ≤ 60mg / L, grade II ≤ 120mg / L, suspended solids
≤ 100mg / L, fluorine ion F - ≤ 10mg / L, pH value 6-9.
Modern wastewater treatment methods are mainly divided into physical treatment, chemical treatment and biological treatment.
1) The physical treatment method is a waste water treatment
method in which the physical effects are separated and the insoluble suspended pollutants (including oil film and oil droplets) are recovered. Generally, sedimentation, filtration, centrifugal separation, air flotation, transpiration crystallization,
reverse osmosis and other methods are selected. The pollutants such as suspended solids, colloids and oil are separated from the wastewater, so that the wastewater can be purified.
2) Chemical treatment is a wastewater treatment method that separates
and removes dissolved and colloidal pollutants 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 electric penetration.
3) Biological treatment is a kind of wastewater treatment method which can transform wastewater solution, colloid, organics, toxic substances and other pollutants into stable and harmless substances
through the metabolic effect of microorganisms. Biological treatment is divided into aerobic treatment and anaerobic treatment. At present, the commonly used aerobic treatment methods are activated sludge process, biological filter and oxidation pond.
Anaerobic treatment method, also known as biological recovery treatment method, is mainly used for the treatment of high concentration organic wastewater and sludge, the use of treatment equipment, mainly for digestion tank.