Abstract
Tanneries reusing wastewater by combination of conventional and advanced Reverse Osmosis (RO) treatment technologies were assessed for technical and economic viabilities. Conventional treatment methods such as neutralization, clari-flocculation and biological processes are followed to clean the effluents before feeding to RO membrane modules. The characteristics of untreated composite effluents such as pH, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), total dissolved solids (TDS), and total chromium were in the range of 4.00-4.60, 680-3600 mg/L, 1698-7546 mg/L, 980-1480 mg/L, 4200-14500 mg/L, and 26.4-190 mg/L, respectively. Inorganic ions like Ca2+, Na+, Cl– and SO42– were found more in the wastewaters. Conventional treatments significantly removed the organic pollutants however failed to remove dissolved inorganic salts. Membrane technology removed the salts as well as remaining organic pollutants and the product water is reused in the process. The studied tanneries (5 numbers) have achieved 93-98%, 92-99% and 91-96% removal of TDS, sodium and chloride, respectively. Seventy to eighty five percentage of wastewater was recovered and recycled in the industrial processes. The rejects are subject to either solar evaporation system or Multiple Effect Evaporation (MEE) technology. The resulting salts are collected in polythene bags and disposed into scientifically managed secured land fill (SLF) site. The cost of wastewater treatment for operation and maintenances of RO including the pre-treatments (conventional methods) is INR 100-110 m-3.
Highlights
Processing of hides and skins of animals are carried out in tanneries for making durable and flexible leather material which is used for manufacturing of shoes, overwear goods, bags etc
The wastewater streams are segregated to three types such as highly toxic chromium containing wastewater, high biochemical oxygen demand (BOD) and chemical oxygen demand (COD) containing wastewater and high inorganic salts containing waste water
The effluents of tanneries are segregated as high total dissolved solids (TDS) soaking wastewater, toxic chromium wastewater and other wastewaters channels
Summary
Processing of hides and skins of animals are carried out in tanneries for making durable and flexible leather material which is used for manufacturing of shoes, overwear goods, bags etc. During the tanning processes about 300 kg of chemicals are added per ton of hides and they generate large volume of effluents generally in the range of 34-56 m3 per ton of hides with high total dissolved solids, organic pollutants and toxic chemicals. In India there are about 3,000 tanneries with a total processing capacity of 700 k Tons of hides and skins per annum. They are categorized as large, medium and small tanneries depending on their production capacity. The tanning activities have been carried out in that area for more than 100 years with out any pollution control equipments and the treatment concept has emerged only after 1980’s
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