The conventional leather tanning
technology is highly polluting as it produces large amounts of organic and
chemical pollutants. Wastes generated by the leather
processing industries pose a major challenge to the environment. According to
conservative estimates, about 600,000 tons per year of solid waste are
generated worldwide by leather industry and approximately 40–50% of the hides
are lost to shavings and trimmings. Everyday a huge quantity of solid waste, including
trimmings of finished leather, shaving dusts, hair, fleshing, trimming of raw
hides and skins, are being produced from the industries. Chromium, sulphur,
oils and noxious gas (methane, ammonia, and hydrogen sulphide) are the elements
of liquid, gas and solid waste of tannery industries.
Biomethanation (or anaerobic digestion) systems
are mature and proven processes that have the potential to convert tannery
wastes into energy efficiently, and achieve the goals of pollution
prevention/reduction, elimination of uncontrolled methane emissions and odour,
recovery of bio-energy potential as biogas, production of stabilized residue
for use as low grade fertilizer.
Anaerobic digestion is a favorable technologic solution which degrades a
substantial part of the organic matter contained in the sludge and tannery
solid wastes, generating valuable biogas, contributing to alleviate the
environmental problem, giving time to set-up more sustainable treatment and
disposal routes. Digested solid waste is biologically stabilized and can be
reused in agriculture.
The implementation of gasification has the
potential to provide significant cost benefits in terms of power generation and
waste disposal, and increase sustainability within the leather industry. The
gasification process converts any carbon-containing material into a combustible
gas comprised primarily of carbon monoxide, hydrogen and methane, which can be
used as a fuel to generate electricity and heat.
A wide range of tannery wastes can be macerated,
flash dried, densified and gasified to generate a clean syngas for reuse in
boilers or other Combined Heat and Power systems. As a result up to 70% of the
intrinsic energy value of the waste can be recovered as syngas, with up to 60%
of this being surplus to process drying requirements so can be recovered for
on-site boiler or thermal energy recovery uses.
The energy generated by anaerobic digestion or gasification of tannery wastes can be put to beneficial use, in both drying the wastes and as an energy source for the tannery’s own requirements, CHP or electricity export from the site. A large amount of the energy recovered is surplus to the energy conversion process requirements and can be reused by the tannery directly. Infact, implementation of waste-to-energy systems have the potential to make the industry self-sufficient in terms of thermal energy requirements. Tanneries are major energy users, and requires up to 30 kW of energy to produce a single finished hide. Thus, waste-to-energy plant in a tannery promotes the production of electricity from decentralized renewable energy sources, apart from resolving serious environmental issues posed by leather industry wastes.
