Tannery industry production generally includes degreasing, liming and hair removal, softening, tanning, dyeing, drying, finishing and other procedures. Many chemicals (such as sodium hydrosulfide) need to be added in the processing process, so that the wastewater contains grease, collagen, animal and plant fibers, dyes and other pollutants and toxic substances.
Tannery wastewater is characterized by complex composition, deep chroma, high suspended solids, high oxygen consumption and large amount of water, so it is quite difficult to treat. Generally, first of all, the wastewater is treated with physicochemical treatment to remove the fur, oil residue, meat residue and other components in the wastewater. Suitable chemicals are then added to complex the heavy metals in the wastewater, such as chromium. Then add anionic polyacrylamide and polyaluminium chloride to flocculate and precipitate the sewage, concentrate to sludge, and finally add cationic polyacrylamide to dewater the sludge.
In this way, the sewage treated step by step greatly reduces the content of COD, total phosphorus, total nitrogen and heavy metals, and reaches the standard of sewage discharge.