Ferrous sulphate is a strong reducing agent, which can reduce hexavalent chromium from chromium wastewater containing water to trivalent chromium, instead of expensive sodium sulfite, sodium bisulfite, sulfur dioxide, etc. the advantage is that it does not produce toxic and carcinogenic sulfur dihydrogen, and the price is low. In addition, ferrous sulphate has the following functions:

1. As flocculant: ferrous sulphate is the most widely used as flocculant. It has the following advantages as flocculant: fast settling speed, large sludge particles, small and dense sludge volume, good color removal (very suitable for dyeing, washing and other textile wastewater treatment), non-toxic and beneficial to biological growth (very suitable for wastewater treatment with biochemical treatment process) As a flocculant, ferrous sulphate can replace polyaluminum chloride, basic aluminum chloride, polyaluminum ferric chloride, aluminum sulphate, ferric chloride, etc.

2. As biological nutrient: mainly used as iron nutrient of microorganism in biochemical system to strengthen the activity of microorganism in the system.

3. As precipitant: it can form precipitate with sulfide, phosphate, and then remove sulfide, phosphate, etc., for example, ferrous sulphate is used to treat sulfur-containing wastewater from printing and dyeing plants.