Filter presses are also widely used in steel pipe factories. Before the steel pipes are galvanized, they all need phosphating and saponification treatment, and then pickling. In this process, the commonly used pickling agents are sulfuric acid, phosphoric acid and so on. After pickling, the waste acid is recycled, and the final wastewater is treated for sewage sludge dewatering.
For this kind of washing wastewater, because of its strong acidity, one of the main treatment steps is neutralization. After the sewage passes through the buffer tank for water volume adjustment, the neutralizer is added. Sodium hydroxide is generally used as the neutralizer here. Eventually, iron hydroxide, zinc hydroxide and other precipitates are formed. In this step, if you want to save costs, you can use lime instead of caustic soda. However, the output of sludge will increase after lime is used (lime residue), so the selection of filter press will increase accordingly. If phosphoric acid is used, iron phosphate precipitates will be formed. In addition, in order to ensure the stability of iron ions, aeration can be used before neutralization to convert ferrous iron particles into trivalent iron. Then it is mixed and stirred with the coagulant, and finally flows into the sedimentation tank.
For this kind of pickling wastewater from the steel pipe factory, due to its corrosiveness and harder impurities, it is said that corrosion-resistant and wear-resistant slurry pumps are generally used when pumps are selected. However, since it does not contain organic ingredients, after flocculation, it is generally dehydrated by using a chamber filter press. The dehydration effect can meet the expected requirements, and it is also convenient for subsequent transportation and stacking. The final water quality meets the first level discharge standard of GB8978-1996 "Integrated Wastewater Discharge Standard".