The latest PrIEST lecture entitled "Minimization of Solid Waste Generation in the Tannery" was held at ILPA-Freya auditorium in Kolkata. Delivered by Dr J Kanagaraj, principal scientist at the leather processing division of CSIR-CLRI, the talk was targeted at the tanners in CLC. It reached the target very successfully, as was evident from the questions asked by the participants at the end of the lecture.

The programme started with the Presidential address by Shri Arnab Kumar Jha of the Indian Leather Technologists’ Association. Shri Jha highlighted the serious problem facing the industry concerning the safe disposal of tannery solid waste. He pointed out that research is going on all over the world to find better and cleaner solutions to this problem. He emphasised the principle that prevention would be better than cure and urged the industry to take effective steps to reduce the generation of solid waste as much as possible. With regard to the PrIEST, he said that the programme would go a long way to assist tanners in solving their various technology related problems including those concerning the tannery solid waste.

Calls for improvement

Dr Dipankar Chaudhuri, who is currently heading the Regional Centre for Extension and Development of CSIR-CLRI in Kolkata, also addressed the meeting. He reminded the participants of the various technologies discussed and demonstrated under the PrIEST and wondered why the Kolkata region could not do what Chennai had already done in the area of cleaner technology practice. He expressed apprehension about the future of the tanning industry for not practicing cleaner processing techniques and urged the CLC tanners to work as an industry to take effective measures to improve upon its environmental performance. Dr Chaudhuri drew the attention of the participants to a four-page document, which CSIR-CLRI had developed for the CLC tanners for efficient operation of their pre-treatment plants, and appealed to them to try the given procedure and seek CSIRCLRI assistance for smooth implementation of the same.

Dr J Kanagaraj in his presentation covered a review of various solid wastes generated in leather industry and stressed the need for minimising such waste in leather processing. He classified the tannery solid waste into various groups and also gave a detailed estimate of their corresponding volumes. Dr Kanagaraj identified the unit operations from which the tannery wastes emanate and proposed a strategy for minimising their generation in leather processing. Speaking about the implementation of waste reduction initiative, he emphasised that the practice of cleaner leather processing techniques was an important part of the strategy. He also stressed the need for recycling and reuse of some potential solid wastes and possible consideration of some other tannery wastes as a raw material for making value added products. Dr Kanagraj cited a number of new technologies developed at CSIR-CLRI to illustrate the proposed strategy. For instance, he talked about three alternative systems based on silica gel, boric acid and sodium metabisulfite that could be used to replace the conventional salt based curing system to reduce solid waste and keep the environment clean. Likewise, a variety of chrome exhaust aids developed at CSIR-CLRI from tannery solid waste that could be used to reduce chromium in sludge were discussed in the lecture. Dr Kanagraj concluded his lecture by highlighting the key role played by clean and green chemistry in the reduction of solid waste in the tannery.

The presentation was followed by an interaction session. Shri Misbahul Haque, a veteran leather manufacturer in CLC, thanked the organisers for arranging the lecture. Shri Haque appealed to ILTA and CSIR-CLRI to invite the technicians working at CLC and train them well to make them acquainted with the new technologies discussed in the lecture. He appealed to all the CLC tanners to check the quality of the lime used in their respective tanneries. He felt that the CLC tanners should ensure a minimum of 70% available lime in their lime to reduce the volume of lime sludge, which is augmented by the presence of a significant quantity of calcium carbonate. He expressed his interest in the saltless and less salt preservation systems of rawhide and skins. On the possible reduction of the environmental impact of salt used in conventional curing, he highlighted the initiative taken by CLC tanners for removing the salt adhered to the leather by physical means. Shri Haque opined that adopting this technique would not only reduce the water consumption but also minimise the total dissolved solid in the wastewater.

Essential education

Shri Arup Mitra expressed satisfaction over the saltless and less salt alternative cleaner curing systems developed at CSIR-CLRI. However, he felt that it would be difficult for the tanners to convince those engaged in curing to change over to cleaner curing systems as tanners have no control over them. Shri Haque responded to this by saying that it might be a bit difficult but each tannery should take proactive steps to encourage their rawhide suppliers to adopt cleaner curing process for the benefit of the industry. He recalled the recent constitution of an expert committee by the Government of West Bengal to look after the environmental issues in CLC. Shri Haque warned the tanners that negligence on their part in curbing the pollution in CLC might lead to heavy penalty or even cancellation of their licenses by the regulatory authority.
Shri Tarak Saha felt that apart from tanners and technicians the students of leather technology should also be made familiar with the clean technologies for the benefit of the industry. So, he made a suggestion to revise the syllabus of B Tech (Leather Technology) to include the cleaner technology options. Dr Dipankar Chaudhuri pointed out that the PrIEST organisers could not help it. However, it might be possible for outside institutions, such as the Institute of Creative Leather Technologies in the UK, to offer such training and courses.


In late April the next lecture titled ‘Processing Animal and Tannery Byproducts’ was held with an attendance of 63 people from various sections of the industry .

It started with the opening address by the President of Indian Leather Technologists’ Association, Shri Arnab Kumar Jha. Shri Jha welcomed the gathering and emphasised the need for zero waste leather processing technology to keep the environment clean and green. He pointed out that in conventional leather processing 80-85% of the hide/skin would eventually turn into waste. Therefore, making value added products from such waste would be like turning waste into wealth. He felt that this would be possible and if carried out, it would be a great advantage for the industry.

Dr Dipankar Chaudhuri, Head, Regional Centre for Extension and Development (CSIR-CLRI), Kolkata, reminded the participants that the PrIEST had completed a full year and attributed the sustenance of this programme to the strength derived from the association of CSIR-CLRI with organisations like ILTA, CLCTA and ILPA. Speaking about the outcomes of the PrIEST, Dr Chaudhuri highlighted the virtual relocation of CSIR-CLRI, Chennai, to Kolkata as one of the most important achievements though he noted the limited progress made in the area of implementation of various sustainable technologies talked about in this programme. Dr Chaudhuri expressed hope that the young people attending PrIEST would take the lead in implementing sustainable technologies in the Kolkata leather industry to make fast progress.

Dr T P Sastry, Head, Bio-products Division, CSIR-CLRI, Chennai, made a detailed presentation on various avenues available for making value added products from solid tannery wastes. His presentation covered the slaughterhouse byproducts, such as the use of bone and carcase. As regards solid tannery wastes, he briefly described processing of four major tannery wastes, namely skin trimmings, fleshings, chrome shavings and finished leather cuttings for deriving useful products from them. Dr Sastry proposed making glue/gelatin and dog chews from skin or rawhide trimmings and pointed out that the technology for making dog chews was available with CSIR-CLRI. On the utilisation of fleshings, he said fleshing meal could be prepared using dry rendering techniques. The fleshing meal in turn could be utilised as an ingredient in poultry feed formulation. About the value added products that can be made from chrome shaving, which is causing a major disposal problem in CLC, Dr Sastry indicated a number of products, namely leather board, dog chews, collagen sheets for wound healing, poultry feed and parchment-like production. He pointed out that developed technologies are available for commercial manufacture of all these products. Dr Sastry also spoke about a new product, which he called Regenerated Leather (RGL). He mentioned that about 20- 30% of the leather procured for fabrication of footwear and leather goods finds its way into waste as waste leather trimmings and cuttings and CSIR-CLRI has developed a process for making RGL from such waste. Dr Sastry commented that the process for making RGL was simple and cost effective. He felt that RGL could be used for making chappal upper, children’s footwear and light leather products as the regenerated material exhibits good physico-chemical properties.

Colour Matching and Quality Control in Leather Dyeing

Ms Malathy Jawahar from the Leather Processing Division of CSIR-CLRI delivered a lecture entitled ‘colour matching and quality control in leather dyeing’. The programme opened with the welcome address by ILTA President Shri Arnab Kumar Jha. He stressed the importance of colour matching in leather manufacture and shared his own experience in this area. He said it was indeed very challenging at times to match the grain colour with that of the flesh. Speaking about the quality control in dyeing he said that it was a very critical area as dyeing has a great impact on defect hiding, which in turn is reflected in the grade of the final leather.

The speaker, Ms Malathy Jawahar began her presentation with an explanation of how human beings perceive colour. She emphasised the importance of knowledge and experience of the behaviour of various substrates as well as dyes and their interaction in colour matching. She spoke about the selection of multiple dyes for combination in colour matching and highlighted the roles played by several factors like dye class, their compatibility, exhaustion characteristics, depth of shade, and fastness characteristics. She also recommended a careful consideration of these contributing factors before arriving at the final choice. Touching upon the metamarism phenomenon, Ms Malathy Jawahar introduced various terms such as primary, secondary, tertiary, complementary and achromatic colours that are used in dyers’ parlance and explained briefly the practical approach to manual colour matching.

She then elaborated on the various steps to be followed in colour matching and pointed out the need for identification of the dominant hue, selection of a suitable dyestuff of required penetration, exhaustion and fastness characteristics to get the desired hue, picking the minor shading dye for the combination, and prior knowledge of the behaviour of the substrate before proceeding for colour. However, all these require considerable skill and experience, which comes after a lot of time and, of course, at the expense of material resources like leather and dyestuffs. Moreover, manual colour matching is a slow process with a lot of subjective elements involved in it. Ms Jawahar suggested using computer-aided colour matching system for eliminating a large part of these limitations.

About computer-aided colour matching, Ms Jawahar told the audience that it was based on reflectance measurement. A spectrophotometer interfaced with a computer takes all the measurements using leather samples for making an objective assessment of matching, which could be used for in-house colour matching as well as quality control in production. While this system could be used for generating various possible combinations of dyes for colour matching for tannery using a database made available beforehand, the same equipment could prove useful for taking the colour measurement of dye samples in solution form for assuring input quality as well. She declared that CSIR-CLRI was in possession of a database for a group of dyestuffs and that the institute could generate a tailor made one to suit the requirement of any individual tannery, if it so desires.