Environmental management in tanneries—Waste minimisation opportunities

306

Waste Materials in Construction G.R. Woolley,J.J.J.M. Goumansand P.J. Wainwright(Editors) 9 2000 Elsevier Science Ltd. All rights reserved.

E n v i r o n m e n t a l M a n a g e m e n t in T a n n e r i e s - Waste M i n i m i s a t i o n O p p o r t u n i t i e s E. A. M. E. Archeti and N. N. B. Salvador Civil Engineering Department, Federal University of S~.o Carlos, Rodovia Washington Luiz, km 235 - CEP 13.565-905, Sgo Carlos - SP, Brazil

This article is based on a survey, carried out in Franca, S~o Paulo State, Brazil, of the opportunities for waste minimisation in thirteen tanneries in that city, and the potential benefits for environmental management. Waste minimisation opportunities mean the feasibility of implementing practices or measures of waste reduction, pollution prevention and cleaner production, in relation to this industrial activity. This opportunity was delined in terms of waste minimisation indicators found in a bibliographical survey and in data obtained from field research done in those tanneries. Using this information, an "opportunity matrix" was created in order to identify and evaluate alternatives and possibilities for waste minimisation. Potential benefits for industry and the environment are also evaluated, on the basis of this matrix. A discussion about the development and application of the matrix is also presented.

1. INTRODUCTION Industry is now facing environmental issues that go beyond the traditional concem with restricting liquid, solid and gaseous emissions, according to legal standards. Problems such as waste of resources, raw material and energy, dangerous waste disposal, workers' satiety and health, waste minimisation, pollution prevention, cleaner production and environmental management, are generally major concerns nowadays. Moreover, corrective actions, or endof-pipe practices, involve higher costs and have been demonstrated to be less effective. As environmental issues become more and more complex, strategies for waste control and management also become more systematic and integrated. The importance of incorporating practices for pollution prevention and waste minimisation in the productive cycle is globally recognised. The main aim is to make products with better quality, while reducing the input of resources (raw materials, energy, etc.) and costs and generating fewer and lower impacts on the environment. The tannery industry is one of the Brazilian industrial sectors where more efforts have been made to develop and implement pollution prevention and waste minimisation practices. In Brazil, there are nowadays about 700 tanneries, employing direct and indirectly about 48,000 workers, with an annual revenue of US$1.5 billion (1). Tanneries, like many other industrial activities, have impacts on the environment, such as: harmful effects on surface water and aquatic life, soil and groundwater contamination, deterioration of air quality, and risk to human health, among others (2, 3). These environmental impacts are mainly related to wastes that are generated in the tanning process.

307 Such wastes can be liquid effluents from spent floats, solid wastes (organic, from animal source, and Jinorganic, composed of residuals of chemical inputs) and atmospheric emissions from chemical reactions, treatment of liquid wastes and from the activity of boilers. The pollution potential of those wastes varies, according to their quantity and degree of toxicity. The field survey for this study was conducted in the town of Franca, located in S~o Paulo State, Brazil:, which has the second largest leather-shoe industrial complex in the country. The town has an area of about 603 square kilometres and a population of 267,235 inhabitants (4). The monthly average production of leather is 650,000 square meters, with over 2,500 persons being employed directly. All the leather production is concentrated in sixteen tanneries, thirteen of which are located in the tannery industrial district of the town. The other three are dispersed around the town. Regarding environmental issues, Franca has been facing problems about the disposal of tannery wastes, including those containing chromium. The monthly average generation of tannery solid[ waste in 1998 was 300 tons, this being disposed in the municipal landfill. The volume of liquid wastes is also high, resulting in costs up to US$ 0.50 per square meter of produced leather. Atmospheric emissions are not quantified. To evaluate the potential of minimisation of industrial tannery wastes in Franca, a field survey took place on the thirteen tanneries located in the industrial district. The data and information obtained made possible the construction of an "Opportunity Minimisation Matrix". This matrix was used as a tool for analysis and evaluation of which tanneries are more suitable for the implementation of waste minimisation measures and which practices are more feasible. Therefore, the aim of this article is to present criteria used in the analysis of the potential minimisation of tannery wastes, based on the concepts of cleaner production, pollution prevention, and the reduction, reuse and recycling of wastes.

2. METHODOLOGY The present study was developed using, among other methods, two current methods of Environmental Impact Assessment (EIA): Checklist and Impact Matrix. These two methods were adapted in order to identify and analyse the opportunity for implementing of waste minimisation practices in tanneries. All the methods used are presented next: a) Bibliographical survey of tannery processes, environmental aspects, practices and intemational experience in waste minimisation. This survey was done in research centres, sectoral institutions, environmental organisations and Internet. b) Questionnaire with the aim of producing a broad profile of the tanneries, including the productive processes and environmental aspects, such as pollution and waste minimisation data (5). This questionnaire was directed to managers and process technicians. c) Checklist containing the minimisation practices that arose in the survey (item a) and identifying environmental benefits of such practices. d) Matrix of waste minimisation opportunities and environmental benefits, based on the LEOPOLD Matrix (6). The matrix was used to identify both the opportunity of implementation of waste minimisation practices and also their benefits. The matrix also assesses which tanneries are more suitable for the development of such practices, using a scale of valuation.

308 3. P R O C E D U R E S

From the bibliographical survey and existing experience, possible actions for waste minimisation were identified, as well as their benefits. Next, the questionnaire was elaborated, covering a range of information, as follows: o General data- address, number of employees, industrial activity, revenue, etc.; o Inputs - type, quantity and usage of energy, water and raw material; o Type of products and industrial production; o Description of industrial processes and manufacturing operations; o Current practices for cleaner production, pollution prevention and waste minimisation; o Solid waste, wastewater and atmospheric emissions; o Waste treatment and emission control; o Information on environmental aspects: legal requirements, environmental impacts of industrial activities, expenditure related to environmental protection, etc. Then, visits to the tanneries of Franca were made, to become acquainted with the industrial plants and processes, to apply the questionnaire to the managers and process technicians, and to gather data. A typical flow-chart of the tannery process could thus be drawn, with the industrial operations and their respective wastes (see Figure 1). From the bibliographical survey, experience and information collected, and questionnaire answers, a checklist was elaborated, containing 47 possible waste minimisation practices in tanneries. This checklist is presented next, being the practices identified within each industrial process stage.

Checklist- Waste Minimisation Practices Beamhouse Stage: o Short-term preservation of hides, by antiseptic treatment (7); o Freeze preservation of hides (7); o Preservation of hides by electron-beam sterilisation (8); o Preservation of hides with sodium chlorite (9); o Recovery and valorisation of residual sodium chloride (7, 10, 11); o Classification of hides according to the final product (leather) (12); o Adoption of pre-soaking and pre-fleshing operations (12); o Direct recycling of liming floats (7, 10, 13); o Recovery and valorisation of hair (7, 10, 11, 14); o Replacement of sodium sulphide by enzymatic and amine treatment (7, 10, 15, 16); o Sulphide oxidation during the unhairing and liming operations (16, 17); o Flesh valorisation (7, 18, 19); Tanning Stage: o Carbon dioxide deliming (7, 10, 12); o Sulphide oxidation during the deliming operation (16); o Deliming without ammonia products (7, 10); o Recycling of pickling floats (7, 20); o Use of non-tumefying acids together with formic and sulphuric acids in the pickling

(15,21); o o o

Use of oxidants in the pickling (1 O, 15, 16); Splitting operation before tanning (7, 1O, 21); Shaving and trimming operations before tanning (7, 12, 21);

309 n High exhaustion tanning (10, 20, 22, 23); a Direct recycling of chrome tanning floats (7, 10, 20, 23); o Recovery and reuse of residual chrome, through precipitation (7, 20, 22, 23); Replacement of chrome, where possible, by other tanning agents (7, 23);

Figure 1. Tannery Process Operations and Respective Wastes.

310

Post-tanning (finishing) Stage. o o o o o o o o o o [] [] [] c~

Valorisation of shavings (18, 19); Thermo-chemical destruction of shavings to recover chrome (24, 25); Use of acrylic polymers to fix the re-tanning chrome during the neutralization operation (10); Accomplishment of a single treatment by mixing re-tanning agents and fatliquoring products (12, 26); High exhaustion re-tanning (10); Recovery and reuse of residual chrome from the re-tanning operation, by precipitation (10); Replacement of chrome, where possible, by other re-tanning agents (26); High exhaustion dyeing (10); Continuous immersion dyeing (26); Infra-red drying, in a tunnel (27); Valorisation of buffing dust (18, 19, 28); Replacement of lacquer in a solvent base by urethane polymers in an aqueous emulsion (15); Using roller or cylinder for finishing coat, instead of spray application (7, 15,261i; Use of finishing products in aqueous base (7, 10, 26, 28);

Complete Process. [] Recovery and valorisation of residual sodium sulphide (2, 7); Automation of hide processing (12); [] Planning of water usage (2, 12); Q Planning of chemical products usage (12); [] Recovery of gases and particulates with capture equipment (7); [] Reduction of the stocking time of solid wastes (12); [] Valorisation of chemical product packing, if feasible (12); [] General cleaning and maintenance of machinery, equipment and work environment (2, 12). In possession of the checklist and the preview survey on the tanneries, the opportunity matrix was built. This matrix is composed of a vertical list containing forty-seven possible waste minimisation practices previously defined in the checklist. These practices are classified according to the stage of the industrial process. The matrix is also composed of a horizontal list of the thirteen tanneries in the study. The correlation between each tannery and each practice is made in the related matrix cell, through two attributed values or weights. The value A, in the bottom left-hand comer of the cell, represents the implementation opportunity of the practice. The value B, in the top righthand comer, represents the benefit from this practice (see Figure 2).

Figure 2. Scheme of a Matrix Cell.

311 Both values may vary from 1 to 3, according the degree of correlation between practices and tanneries, as follows.

Opportunity of minimisation practice implementation (A value) o High opportunity: 3 o Medium opportunity: 2 o Low opportunity: 1 In some cases the value A can be considered as follows: o Yet implemented: 3" a Not applicable: na The degree of opportunity of implementation of a practice is defined in terms of: physical structure and industrial lay-out, process operations, types of raw materials and products, waste characteristics, existing equipment, available cleaner technologies, cost of implementation of the practice, culture of the industry regarding environmental issues, intentions of the board of directors of the company to implement minimisation practices and so on.

Benefits of practices (B value) n High benefit: 3 o Medium benefit: 2 o Low benefit: 1 o Undetermined benefit: ub The degree of benefit is defined by taking into account direct financial gains (e.g. reduction of inputs or raw materials), indirect financial gains (e.g. better public image), potential for waste minimisation, environmental gains, decrease or end of non-compliance with legal requirements, etc. To establish a relation between a minimisation opportunity and its benefit, the sums of the products of A and B values are indicated in the last column and last row of the matrix. This procedure results in a total valuation of opportunities plus benefits, indicating the synergetic effect between these variables. The total value, measured on a scale of 1.0 to 9.0, is useful to show the degree of opportunity associated to the importance of its respective benefit. For example, when there is a high opportunity and a high benefit, the sum is 9.0, resulting in a maximum synergetic effect. The total valuation is given by the following expressions:

~AxB 1

n

m

~-] A x B 1

(1)

(2)

m

Expression (1) refers to the last column of the matrix, n being the number of practices identified (forty-seven for this work). Expression (2) refers to the last row and m is the number of tanneries studied (thirteen in this case). Finally, another visit to the tanneries was made, to check data, obtain more information and define opportunities and benefits with the aim of completing the matrix.

312 4. RESULTS AND COMMENTS The first or major result is the Matrix of Waste Minimisation Opportunity shown in Figure 3, for the thirteen tanneries studied in Franca (tanneries A to M). According to the matrix, the most important minimisation practices are six: replacement of sodium sulphide by enzymatic and amine treatment, high exhaustion tanning, high exhaustion re-tanning, chrome replacement by other re-tanning agents, high exhaustion dyeing, and use of water-based finishing products. These practices correspond to total valuations of 9.0 in the last column. Another result is related to the priority tanneries, in other words, the tanneries which have more opportunity for the implementation of waste minimisation practices, taking into account environmental benefits. In the present work, these tanneries correspond to which ones with total valuations of more than 6.0, in the last row (tanneries A, F, H and L)

5. CONCLUSIONS The methodology applied to the present work may be used for any type of industrial activity, not only for tanneries. The methods of Checklist and Impact Matrix, currently used in Environmental Impact Evaluation, can be satisfactorily applied to identify and evaluate waste minimisation opportunities. However, more research on the matter is needed. The matrix affords an overview of the tanneries of Franca, with respect to environmental management and waste minimisation practices. The matrix just shows a general tendency, indicating opportunities, priority practices and priority industries for such practices. It can be used as an interesting and useful environmental management tool, as an auxiliary to decision making. On the other hand, the results have to be considered carefully, not as accurate information, but a trend indicator, as aforementioned. It is recommended that specific and detailed studies be done, for each case.

Acknowledgements The authors are grateful to C N P q - Conselho Nacional de Pesquisa e Desenvolvimento Tecnol6gico, from Brazil, for the financial support to the research that resulted this article.

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