Many people will encounter such a situation in printing and dyeing wastewater treatment. At the beginning, when ferrous sulfate is added as flocculant, the transparency of effluent water is very good, but when it comes to anaerobic tank, it turns black, and when other agents are added as coagulant, it will not. And this kind of situation only appears after anaerobic. What's going on? Is it caused by ferrous sulfate?

When ferrous sulfate is used for coagulation treatment of printing and dyeing wastewater, the residual iron ions enter the anaerobic tank and react with the sulfide dyes in the wastewater to produce light ferrous sulfide suspended in the wastewater. The ferrous sulfide itself is black, the particle size is very small, and it is not easy to settle. In the aerobic aeration process, due to the biochemical effect of aeration, the water body turns black after the formation of iron oxide. This is the principle that ferrous sulfate makes printing and dyeing wastewater black. In view of this situation, Gongyi Filter Industry Co.,Ltd tells you that you can deal with it in the following ways:

1. As ferrous sulfide is relatively light, it is difficult to precipitate by standing, so the flocculation effect can be improved by increasing the amount of ferrous sulfate.

2. PAM was added to accelerate the precipitation of ferrous sulfide and reduce its utilization in biochemical tank.

3. It is difficult for ferrous sulfate to oxidize to trivalent iron by stirring instead of aeration.

In the treatment of printing and dyeing wastewater, a small amount of black sediment after adding ferrous sulfate has little effect on the anaerobic treatment effect, so there is no need to worry about it.