The acid wastewater mainly comes the processes of acid erosion, neutralization, oxidation, oil removal by spraying pre-disposal, pickling in the oxidation workshop. The acid mass fraction is the same big, the low is less than l%, the high is greater than l%. The alkaline wastewater mainly comes alkali erosion in the oxidation workshop alkaline washing after pre-treatment by spraying. The mass fraction of alkali can be higher than 5% lower than l%. Spraying dyeing also produce waste water. Wastewater, in addition to rich in acid alkali, often rich in oil, paint, fluoride other inorganic organic matter.
Acid alkali wastewater is highly corrosive can be discharged only after proper management. The general guidelines for the management of acid alkali wastewater is: high concentration of acid alkali wastewater, should give priority to the recovery of use, according to the water quality, water volume different technical requirements, as far as possible repeated use: such as repeated use is difficult, low concentration, water volume, can choose to concentrate the way to recover acid alkali. Low concentration of acid alkali wastewater such as pickling tank clean water, alkaline washing tank rinse water, should be neutralized treatment.
As for neutralization, we should first consider the criterion of waste to waste. For example, acid alkali wastewater neutralize each other use waste alkali (slag) to neutralize acid wastewater, use waste acid to neutralize alkaline wastewater. In the absence of these conditions, can choose neutralizer disposal.
According to the national standard gb8978-1996, the discharge requirements of water pollutant discharge limit are: COD level 1 ≤60mg/L, level 2 ≤120mg/L, suspended substance ≤100mg/L, fluorine ion f-≤ 10mg/L, pH value 6-9.
Modern wastewater treatment methods are mainly divided into three types: physical treatment, chemical treatment biological treatment.
1) physical treatment: wastewater treatment method in which insoluble suspended pollutants (including oil film oil bead) are separated recovered after physical effects. Generally, methods such as deposition, filtration, centrifugal separation, air flotation, transpiration crystallization reverse infiltration are selected. The suspended solids, colloids, oils other pollutants in the wastewater are separated, so that the wastewater is purified.
2) chemical disposal method: through chemical reaction mass transfer effect to separate remove the dissolved colloidal pollutants in the wastewater transform it into harmless waste water disposal method. General selection methods are: neutralization, coagulation, oxidation recovery, extraction, stripping, stripping, adsorption, ion exchange electric immersion methods.
3) biological disposal method through the metabolic effect of microorganisms, waste water solution, colloids, micro-suspended organic matter, toxic substances other pollutants, into a stable, harmless waste water disposal method. The biological disposal method is divided into aerobic disposal anaerobic disposal. At present, activated sludge process, biological filter oxidation pond are commonly used in aerobic treatment. Anaerobic treatment, also known as biological recovery treatment, primarily used to treat high concentration of organic wastewater sludge, the use of disposal equipment, primarily for digester.
The purpose of sludge disposal is: (1) reduce the sludge moisture content, for the disposal, use transport of sludge to create conditions. Eliminate harmful substances that pollute the environment. Recover power capital, to achieve harm into profit. Sludge disposal methods include sludge concentration, sludge digestion, sludge dehydration, sludge boring methods. The purpose of sludge concentration is to dehydrate the sludge reduce the sludge volume to provide conditions for subsequent disposal. The intention of sludge dehydration is to further dehydrate the sludge to reduce the moisture content to less than 80%. Its method has mechanical dehydration natural dehydration two kinds. Mechanical dewatering is divided into vacuum filtration, pressure filtration centrifugation. Its advantage is dehydration rate is high, cover an area to be little, but capital contribution is more expensive. The cost of natural drying method foundation construction operation is very low, but the dehydration power is low, the land area is large, the sanitation environment is poor. The dull intention of sludge is to heat the dehydrated sludge to further reduce water content volume. Boring disposal method is often used rotary drum boring machine. Its advantages are stable function, reliable operation, but covers a large area.