Tannery and Chrome Chemicals Manufacturing Sector
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Cleaner Technology Development Near zero chromium discharge tanning methodology The need to manage chromium better in leather industry is widely recognised. Generally, chromium(III) salts are employed in tanning. In India, more than 90 per cent of hides and skin processed annually receive chromium in one form or the other. The annual use of BCS salts has been estimated at 50000 t. The discharge of chromium containing tannery wastes is of great environmental concern because of the bio toxicity of certain Cr(III) salts. Several end-of-pipe treatment methods for tannery wastes have been explored and some have been adopted commercially, but these result in generation of large quantity chrome bearing hazardous sludge . The in-plant control methods generally result in saving of water and material, thereby reducing the pollution load. Some of the technological measures for better management of chromium include:
Use of enzymes instead of sodium sulphide for dehairing Various dehairing methods have been developed based on proteolytic enzymes and lactobacilus based enzyme applications. The range of dehairing methods developed includes sulphide free and low sulphide applications. Enzyme assisted lime-sulphide dehairing is used in some parts of the world. Many commercially available enzymatic unhairing agents offer a possibility of reducing the amount of sulphide used in liming. Enzymes work by attacking the proteoglycon, that holds the hair and helps in its removal with the root. Pickle less tanning methodology Pickle less chrome tanning with commercial basic chromium sulfate has been attempted with a view to design an appropriate process with optimal conditions. The primary objective is to decrease TDS and chlorides using pickle less chrome tanning and thereby avoiding the use of salt in the pickling process. Pollution is significant from the pre-tanning process compared to the tanning and post tanning process. About 65% of total pollution load is generated from pre tanning operations. Copious volume of water is used in beam house (pretanning) operations. About 14 m3 of water is required per ton of raw hide in this segment. The waste streams are contaminated with skin proteins, fat, dirt and unabsorbed chemicals. Waste streams from soaking and pickling are saline in nature. In the scheme for zero waste water discharge for pretanning processes the waste streams from soaking, liming, deliming and pickling are separated and treated electrochemically. |
