Wastewater discharge from world tannery sector is about 600 million m3/annum. The tanneries in Asia discharge more than 350 million m3 of wastewater per annum from the process of 8 to 10 million tons of hides and skins. The ground and surface water resources in many locations in and around tannery cluster contain high Total Dissolved Solids (TDS) and not fit for domestic and industrial use. The conventional treatment systems implemented all over the world reduce Biochemical Oxygen Demand, Chemical Oxygen Demand, Suspended Solids, Heavy Metals etc. and not TDS and salinity which are mainly contributed by chlorides, hardness and sulphates. The treatment plants are unable to meet the standards in terms of TDS, chlorides and salinity which are being enforced in India and many other countries. The pollution control authorities also insist on water recovery integrated with Zero Liquid Discharge (ZLD) system. Naval treatment systems such as special Micro Filter, Ultra Filtration, Membrane Bio-Reactor, Nano Filtration, Reverse Osmosis, etc. have been developed for recovery of water from domestic and tannery wastewater. The achievement of ZLD concept has got many technical challenges. Management of the concentrated saline stream treatment by adopting energy intensive evaporation system is one of the major sustainable issues. The innovative treatment technologies developed and adopted for water recovery, saline stream management, etc. are dealt in this paper.
Environmental laws define the scarcity of environmental resources as they affect the factor endowment of a country and therefore its position in the international division of labour. There is now also a general agreement that applying the "polluter pays" principle should solve environmental problems. As the burden of abatement increases, as measured by the ratio of abatement expenditure to sales, there is definitely an incentive for firms to either invest in cleaner technology or more efficient abatement technology. There is also evidence that taxes and charges, designed to internalise externalities, can actually affect trade. It is interesting to know if the developing countries face particular market access problems in the face of stringent environmental standards and regulations. While it is true that stringent measures impose market access restrictions and cause limitations on competitiveness, this is much more widely felt by the developing countries because of lack of infrastructure and monitoring facilities, limited technology choices, inadequate access to environment-friendly raw materials, lack of complete information, presence of small-scale exporters and emergence of environmental standards in sectors of export interest to developing countries. The small and medium enterprises often divert sales either to the domestic market or to external markets where environmental requirements are less stringent, in order to save on their costs. In developing countries, 80% of the tanning industry is comprised of small and medium enterprises (SMEs) processing raw to semi-finished leather, usually less than 2 tons per day. In Europe and other developed countries the SMEs in the leather sector have vanished due to strict environmental legislation and this will likely occur in developing countries also. The environmental legislation has not always been practical, either because the laws are too ambitious or unrealistic in certain parameters, or because they have lacked effective instrumentation and institutional support. Some environmental regulations have not succeeded as they do not match the technical requirements and economic reality of the country or region, or because they do not take the institutional capabilities of the society that has to implement them into consideration. For the survival and sustenance of the SMEs in the leather industry, it may be a viable alternative to carry out the tanning process in a decentralized fashion such that the raw to semi-finished process is carried out in the large scale sector while the semi-finished to finished process could either be reserved or open to competition as per the countries' requirements. But the issue of concern is whether it is fair that the raw to semi-finished tanning process, containing 70% of the pollution discharge should be undertaken by developing countries alone, especially if it is at the cost of their survival! However, the game analysed in the paper reveals that tanning units in developing countries would prefer to comply with the regulations and st...
Ecological friendly processes with recovery of salt, chemicals and water for reuse in the tanning process as well as from liquid and solid waste are necessary for the promotion of circular economy.Recent developments in cleaner production and treatment process by reducing volume of effluent and pollution discharges, recovery of quality salt in the segregated streams such as saline soak liquor, spent chrome liquor and adoption of advanced aerobic oxidation process in the treatment system resulted in the recovery of purified salt, quality chromium and water for reuse. The achievements of innovative cleaner production and effluent treatment for promotion of circular economy are: Reduction in water usage in soaking process from 6000-8000 liters to less than 3000 liters/ ton of hides, Separate treatment of saline streams and recovery of quality salt, chromium in the form of cake / powder and Replacement of physiochemical treatment into biological treatment reduction in chemical usage and sludge generation by more than 60%. Viable cleaner production and sustainable treatment technologies had been engineered and are being implemented in many major leather clusters and Common Effluent Treatment Plants.
The effluent discharged from conventional process in textile dyeing and tanneries are unable to meet some of the discharge parameters such as Total Dissolved Solids (TDS) in the existing physiochemical & biological treatment units. In addition to TDS management the control of volatile solids in hazardous category sludge is also becoming a necessity. To overcome these challenges faced by tanneries in the world leather, improved cleaner production, segregation of saline soak liquor and separate treatment, modified chrome recovery system and recovery of chromium & sodium chloride salt in the form of powder and quality water with TDS less than 500mg/l for reuse by tanneries have been developed for field application. Physiochemical treatment is converted into total biological treatment with sulphide oxidation using enzyme and biomass which resulted in 50% reduction in sludge generation. The secondary treated effluent and supernatant from chrome recovery system are processed with membrane units for recovery of high saline stream and quality salt for reuse in pickling process and other industrial requirement. These developments are being implemented at field level for cluster of nearly 400 tanneries in India which is first of its kind in the world.
Conventional process and treatment system adopted by Indian and Global Tanneries consist of Segregation of Spent Chrome Stream and discharge of supernatant for combined treatment along with effluent from all sectional operations starting from soaking to finishing, Conventional physiochemical and biological treatment for reduction of Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), etc., Ultra-filtration and Reverse Osmosis (RO) system for recovery of water and Multiple Effect Evaporator (MEE) for the evaporation of RO reject stream and generation of mixed salt in case of Zero Liquid Discharge (ZLD) system and Storage of mixed salt recovered from the MEE system for which no viable disposal system is found. Establishment of treatment system for the mixed stream results in poor performance of biological treatment units, increases the Operation & Maintenance (O&M) cost and accumulation of recovered mixed salt in case of ZLD system. It is estimated that, more than 8-10 tones of mixed salt is generated during the treatment of 1.0 MLD effluent under ZLD system. To address this serious environmental problem, an innovative approach of segregation of saline streams such as soak liquor and chrome liquor are planned to be collected separately with the feasibility of recovering reusable quality salt and chromium in the form cake for regeneration and use in the form of Basic Chromium Sulphate (BCS) by the tanneries. This innovative treatment concept has been developed and is being implemented in many Common Effluent Treatment Plants (CETPs) in India. This will become the first of its kind in Global Leather World. This developmental scheme is in accordance with the guidelines and recommendations of UNIDO in terms of sustainability of ZLD system for leather sector. The technological developments on cleaner productions, centralized chrome recovery reuse system, segregation of saline soak water for separate treatment with recovery of water and quality salt are dealt in this technical paper.
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