An idea to reduce leather industry pollution
“By simply changing the chemicals used in tanning, you can bring down the amount of unused chromium released to a bare minimum,” says Dr J Kanagaraj, senior principle scientist at the CLRI. It’s chromium (III), found in the effluent released by the leather industries, which causes most of the damage to the environment.
Kanagaraj and his team published their results in a paper with the Royal Society of Chemistry explaining how the quantum of chromium in the effluents can be reduced.
Tanning is a process that makes leather non-perishable. The most popular method is chrome-tanning, which uses chromium for treatment. “The use of chromium (III) is indispensable for tanning. So we just have to find an efficient and cost effective way to cut down on the amount of chromium released,” said Kanagaraj.
There are two way of controlling the heavy metal content in the effluent: increasing exhaustion of chromium from the effluent sent out by treating it or increasing the adsorption on the material, so that most of the heavy metal sticks to the product, leaving very little unused.
To achieve optimal adsorption by the leather, he and his team devised a bio-based copolymer (an organic chemical chain) matrix that efficiently spreads chromium (III) through the pores of the material and fixes it at the active sites in the leather in an aqueous (water-soluble) environment.
“Over 90 per cent of all leather tanneries globallyuse chromium for tanning. Managing its pollution will have a large impact on the environment,” said Kanagaraj. Technological limitations allow only for 70 per cent of the chromium containing chemicals to be adsorbed during treatment, leaving 30 per cent unused.
Leather tanning industries use protein based syntans for tanning. “More responsible industries use additives like Aspartic acid to exhaust the chromium from the effluent.” There are several polymers and biopolymers that are in practice for effective adsorption of chromiumfrom an aqueous environment. In fact, 99.5 per cent can be removed from the effluent by using the bacteria, Bacillus pumilus.
Kanagaraj said his method will leave only a small residue as most chromium (III) would be taken up in the tanning stage itself. This minimal residue can be treated with bacteria, thus making heavy metal traces negligible. “In addition, the raw materials needed to manufacture the adsorbent can be obtained from the by-products of other steps used in the industry. Along with reducing chromium in the waste, this process can be applied in other areas such as de-fleshing, trimming and pre-tanning. This also reduces solid waste from the leather industry,” he said.
“This compound is not only environment friendly, it also produces finer quality of leather. The colour properties of the leather become richer and more uniform, the softness increases, the thickness of the leather is increased and the product is more physically and thermally stable,” he added.
While chemicals used by the industry cost about `150 a kg, his compound can be manufactured at about `90 a kg. The only limitation he sees is that the adsorbent that is also obtained from animal product, may increase the degradability after a year of manufacture.