Tannery Wastewater Treatment With Application Of The Gacs Method Of Zeologic S.A.
Process of skins in tanneries contains various stages such as:
Soaking: Skins are hydrated and foreign bodies (such as: impurities, salts etc) are removed. Large amounts of sodium chloride are produced (which is used for preserving the raw skins).
Lashing: hairs, fats, part of the subcutaneous tissue, elastin, and other hard proteins are removed. Limewater and sodium bisulfite are used.
Flesh removal: The removal of fatty subcutaneous tissue (by mechanical means which produces solid waste) is completed.
Bating: The complex of collagen fibers is returned to its deflated initial state. Ammonium sulphate, ammonium chloride, hydrochloric acid, sodium metabisulphite (for oxidizing the sulphides) and enzymatic products rich in ammonium salts are used.Pickling: Skins acidification with addition of sulfuric and formic acid, and completion of decalcification as well.
Tanning: The skin acquires a range of desirable qualities and durability. Powdered chromium sulphate and sodium bicarbonate are used.
Wetblue and crust: With these procedures, skins acquire tenderness, softness, crack resistance, water resistance and desired colour. Also pigments, lubricants and other auxiliary substances are fixed, defects are covered, and the skin acquires its final shade, the required durability and attractiveness in appearance and touch. Many substances are used such as paints, alkalis, plant extracts, formaldehyde, resins, waxes and oils.
Wastewater produced from the production procedure of tanneries are of high pollutant load, since with the technology available to date, mainly due to their particular physicochemical properties and morphology of the skin itself, it is still impossible to avoid the utilization of significant excesses of auxiliary materials through all production stages.
Many of the auxiliaries contained in that wastewater type, are difficult to degrade. Some of them actually, are inhibiting biological activity in a wastewater treatment plant operating with a biological based method, as they contain cobalt and trivalent chromium, and in some cases copper, nickel and iron which derives from painting substances used.
The GACS Solution (Geochemical Active Clay Sediment)
The Geochemical Method GACS consists an innovative solution on an international level on the subject of treatment and disposal of tannery wastewater. The key characteristic of the Geochemical Method GACS is the usage of geopolymer materials, which have the ability to adapt on the characteristics and particularity of any type of waste. Under this manner, process optimization and performance maximization are achieved.
Benefits of the GACS Method, on treatment of tannery wastewater against the conventional existing methods can be summarized in the following:
- Competitive investment cost
- Significantly reduced operational cost
- Reduced maintenance cost
- Reduced sludge production
- Reduced operational time
- Heavy metals removal even on high concentrations
- Effluent complying with legislation
- Production of inert sludge
- Use of natural materials
- Elimination of odors