Acid pickling and phosphating treatment is a chemical reprocessing process applied to the surface of metal materials and their components. The surface of metal materials and their products treated with phosphating forms an immersive phosphate film layer, which has good bonding ability, wear resistance, and adhesion to coatings with the metal substrate. Therefore, industries such as machinery and steel use phosphating treatment technology to produce protective layers for mechanical parts. The phosphating treatment process generally includes several steps such as alkaline washing to remove oil, hot water rinsing, cold water rinsing, acid washing to remove rust, secondary cold water rinsing, and phosphating. During the process, various types of wastewater are mainly generated, including alkaline washing emulsion wastewater, rinsing wastewater, acid washing waste liquid, and phosphating waste liquid.

In addition to a large amount of phosphate, zinc ions, acidic and alkaline substances, and organic matter, acid pickling and phosphating wastewater sometimes contains a certain amount of heavy metals such as nickel ions, copper ions, or lead ions, as well as surface active agents and other pollutants depending on the production process. The composition is complex and the treatment difficulty is relatively high. Phosphate emissions are high, mainly in the form of inorganic salts such as zinc dihydrogen phosphate, as well as pollutants such as COD, petroleum, and suspended solids.

A process for treating acid pickling and phosphating wastewater, comprising the following steps:

1) Filter the acid pickling and phosphating wastewater through a grid to remove impurities from the wastewater;

2) The acid pickling and phosphating wastewater after preliminary filtration is sent to the homogenization regulating tank to homogenize the acid pickling and phosphating wastewater;

3) By lifting the pump, the homogenized acid pickling and phosphating wastewater is sent to a mixed reaction clarifier, and a coagulant is added to the mixed reaction clarifier through a dosing pump, so that the acid pickling and phosphating wastewater undergoes solid-liquid separation in the mixed reaction clarifier, and alkali aluminum and polypropylene amide are added to remove phosphate ions, heavy metal ions, and COD;

4) The wastewater separated by the mixed reaction clarifier is pumped to the hydrolysis acidification reactor for acidification treatment;

5) Send the acidified wastewater into an anaerobic tank, where denitrifying bacteria treat the wastewater for phosphorus removal;

6) Transfer the wastewater treated in the anaerobic tank to the aerobic tank, where the organic matter in the wastewater is degraded by the action of organic matter degrading bacteria;

7) The wastewater treated in the aerobic tank enters the air flotation tank to remove oil and reduce COD in the wastewater;

8) The wastewater treated by the air flotation tank is sent to a mechanical filtration device to remove suspended solids in the water and then sent to a clean water storage tank.

Furthermore, in step 2), the residence time of acid pickling and phosphating wastewater in the homogenization regulating tank is 2-3 hours.

In addition, the coagulant mentioned in step 3) is selected from one of aluminum sulfate, aluminum trichloride, ferrous sulfate, calcium hydroxide, and magnesium carbonate.

Additionally, the coagulant mentioned in step 3) is calcium hydroxide.

Furthermore, the residence time of the acid pickling and phosphating wastewater in the mixed reaction clarifier described in step 3) is 0.5-1 hour.

Furthermore, in step 3), the pH value is between 10 and 11.

Moreover, in step 6), the residence time of domestic sewage in the aerobic tank is 0.3~0.5 hours.

In addition, the DO in the aerobic tank mentioned in step 6) is 2-4mg/L.

Furthermore, in step 6), the aerobic tank is equipped with YDT type elastic three-dimensional packing, on which microorganisms adhere to form a layer of microbial film.

The beneficial effects of the present invention are:

The process adopts the A/O method for treatment, which combines the advantages of anaerobic and aerobic treatment. It can effectively remove phosphorus and organic matter from acid pickling and phosphating wastewater. The pH value of the treated effluent is 6-8, which meets the national discharge standard. The CODcr content in the effluent is ≤ 35mg/L, significantly lower than the national standard of 100mg/L. The phosphorus content in the effluent is 0.4-0.5mg/L, with good treatment effect, low cost, and environmental friendliness.