Ferrous sulfate is often used as a decolorizing agent in wastewater. In the decolorization of printing and dyeing wastewater, ferrous sulfate is basically used for decolorization. However, it is well known that the addition of ferrous sulfate will cause a large amount of iron sludge to be treated after wastewater coagulation, resulting in increased pressure of sludge treatment. Why does ferrous sulfate produce so much sludge?

The amount of sludge produced in wastewater treatment, in addition to the factors of adding chemicals, will also be affected by the position of sludge, drainage process, sludge age and other states, and as long as it is treated by chemical coagulation and sedimentation, it will inevitably produce sludge. The function of ferrous sulfate is to flocculate the suspended solids in sewage, so it is normal to produce sludge precipitation.

The amount of sludge produced by one ton of ferrous sulfate is about 4 tons. Ferrous sulfate is an acidic coagulant, which will inevitably reduce the pH value of wastewater after dosing. The optimal pH value of ferrous sulfate coagulation reaction is about 8.5. In order to ensure the coagulation effect of ferrous sulfate, calcium hydroxide or sodium hydroxide alkaline agent should be added to adjust the pH value. In this process, the sulfate radical of ferrous sulfate will react with calcium ion in lime to produce calcium sulfate, and iron ion will react with hydroxyl to produce iron hydroxide. Iron hydroxide + calcium sulfate + wastewater coagulation alum precipitation will jointly produce a large amount of sludge.