Leather Industry Waste Management for Architectural Design

Abstract

The leather and footwear cluster in Tungurahua state has a main role in the country’s production chain, supplying 76% of the country’s tanned hides for the textile, footwear, and furniture industries, among others. The processes involved in leather tanning generate liquid, gaseous, and solid waste, the latter including the shavings from the leather trimming process, which, due to their composition and volume, are compressed and disposed of in sanitary landfills. Through Strategic Design and circular processes, as axes of change in production, new processes and strategies are established for the creation of products derived from the reuse of tannery waste; as a result, a decorative block is obtained for the design of architectural spaces with dimensions of 150 × 75 × 355 mm, 300 g in weight, and a compressive strength of 15.72 MPa. This is subjected to physicochemical tests for its validation.

1. Introduction

Goods and services generation has been based on a linear economy, dominant in the world context, where raw material is used to produce goods and services. Once these products fulfill their life cycles, they are discarded, resulting in an inefficient process. However, the circular economy goes beyond considering the recovery phase [1], giving new opportunities by recovering components and materials or intervening in the recycling of the production processes. In this sense, some industries are currently implementing these processes.

The Ecuadorian manufacturing sector, formed by 24 subsectors according to International Standard Industrial Classification (ISIC), comprises 13% of the GDP. The C15 subsector (leather and related products manufacture) has its principal activity in Tungurahua [2], with economic activities including the production of footwear, boots, and associated articles; tanning skins, the manufacture of artificial leathers, chamois and parchment leathers, patent, and metalized leathers; and the manufacture of suitcases, backpacks, handbags, and other similar articles. In this sense, the Ecuadorian government, through its Ministry of Production, Foreign Trade, Investment and Fisheries [3], presents a clear vision of policies aligned with a circular economy, where manufacturing is the main strategic axis to be intervened along.

Participation in the leather production chain is an important axis in the production of tanned skins at the national level with a 76% contribution [4], a necessary input for the manufacture of footwear that comes to cover 80% of the country’s domestic consumption, in addition to other derivative products. According to Ministerio de Producción, Comercio Exterior, Inversiones y Pesca de Ecuador, the intermediate and final industries (IIF) of textile and leather generate a greater contribution to this industry, with a rate of participation in Tungurahua of 75.6% in artisanal, tanning, leather, and footwear activities [2].

The Tungurahua tanning companies do not currently consider integrating processes that allow the use of the residue obtained in the leather trimming process; therefore, its destination is the sanitary landfill. In addition, since this is a sector that does not handle a finished product, it applies a design approach. Around 50% to 55% of collagen ends up as finished leather, generating substantial amounts of solid waste in tanneries. The reuse and/or disposal of this solid waste is one of the most difficult challenges at present [5].

For this reason, a strategic change in the sector should be proposed to integrate circular processes based on design to transform waste into new functional products, described by [4] as the “application of new materials or recycled materials to obtain new products”. In addition, this will allow us to establish the possibilities of use for other sectors of the economy and the viability of these processes for use and commercialization.

Relevance to Design Practice: The proposed methodology based on Strategic Design allowed us to devise ideas from tanneries’ waste, analyze the feasibility of use in the generation of new products that do not exist on the market, and ensure compliance with design and manufacturing standards for future extrapolation to other residues.

2. Leather Sector

Considering the key areas in leather production, such as resources (hides/skins, chemicals, water, energy), emissions generated during the production process (solid, liquid, and gaseous waste), quality and attractiveness of the final product (durability), and use of the product after its useful life, the production processes in tanneries generate a negative environmental impact. They affect natural water sources by discharging liquid waste containing chemicals into streams and rivers, generating unpleasant odors, gases, and polluting solid waste [5].

In Ecuador, more than 350 thousand hides are processed per year, and estimates suggest that more than 1500 t of waste shavings are produced from the process of leather trimming [6], waste which is finally destined for city landfills. For this reason, tanneries seek to reduce their water consumption, improve the absorption of chemicals, and reduce levels of banned or hazardous substances (substances of very high concern, SVHC), both for health and the ecosystem, with the impact of specific pollutants, such as heavy metals and electrolytes contained in them for their processes, being important; they also seek to improve the quality of alternatives for the reuse of solid waste [5].

Alternatives have already been proposed for the treatment of leather shavings, among which the most used are adsorbents of other chemical waste such as dyes, motor oils, chromium, and arsenic present in wastewater; they are also used in the reinforcement of composite materials made with polymeric matrices of rubber, polyvinyl chloride, polyvinyl pyrrolidone and polyvinyl alcohol (PVA) [6].

Within environmental management, waste management is becoming the most challenging task [5], and the established method is becoming unfeasible for reuse or disposal due to regulations or commercial reasons in some cases. On the other hand, waste management does become a relevant factor in a tannery as it relates to ethical aspects such as the environmental social responsibility it should have. Therefore, in the province of Tungurahua, it is gaining greater interest by being part of the leather and footwear cluster and contributing to the economy of the province; the environmental footprint derived from the tanning process generates large volumes of solid and liquid waste, especially by-products such as rawhide trimmings, fleshings, keratin waste, polishing powders, and post-tannage leather shavings [6].

There is no denying that the leather tanning process is important for obtaining raw materials for the manufacture of a wide variety of products and that consumers perceive leather as a natural and resistant material. But it is also necessary to associate it with sustainability and the responsibility of the sector for the qualitative improvement of the product for the benefit of the community and the environment. Therefore, the leather industry must adopt sustainable criteria by implementing circular processes, an orange economy, and other practices in its industries [5].

A sustainable strategy seeks, as much as possible, the non-production of waste and, if it exists, to convert it into an efficient and valuable product. Therefore, it is important that the waste does not contain chemicals of concern, as they would only limit its further use. New products or services can be obtained that minimize the waste generated, reuse it, and avoid the negative impact as much as possible, providing benefits for the economic, social, and environmental sectors, and enabling the extraction of the maximum value from raw materials and waste to promote energy savings and reduce greenhouse gas emissions [1].

3. Strategies from a Design Point of View

The implementation of the Strategic Design approach and methodologies focused on the user and user welfare allows us to discover problems and opportunities for the generation of new products. The need to propose development strategies from design is a principal issue in developed countries’ economies, which understand the real value of design [7]. The purpose of design and design disciplines is to seek the good of the individual, in its context, that is, in the sociocultural whole, in addition to boosting consumption; therefore, solutions cannot come from isolated facts, but from a broad vision of complex problems and practical solutions, i.e., “systemic solutions, not individual” [8].

The transition from production models that do not set objectives aligned with a circular production philosophy, and which use their waste in order to reincorporate it into the production chain, is a complex path that requires multidisciplinary cross-cutting work that also understands the need to integrate academia and design for its development [3] and which is committed to building a production ecosystem guided by clear policies and government support. At the company level, a change of philosophy is also necessary in order to accept and adapt these new processes, adopt them as a company’s own, and support them with clear functions and objectives within the company. For this, Finizio [9] establishes dual thinking in the company, emphasizing, on the one hand, the solidity and organization of the company, and on the other hand, a cycle of continuous transformation from the design culture. He is also interested in actions that allow the development of innovation in the company. For Best [10] and Borja de Mozota [11], design strategies arise from the management of the design activity, control of its stages and planning, as well as its interaction with the functions of the company that participate in decisions about conceptualization, development, and production.

A strategic model based on an approach to the application of design methodologies should focus on the investigation of user needs, understanding the effects and impacts that may result from the use of a product, in addition to analyzing how to improve it. As a complex activity, design considers a continuous action of strategic renewal, a situation that if not considered entails costs in terms of time, as well as human and economic resources, for the company.

It is also necessary to consider the factors that particularly enhance or constrain a strategic action and relate to the research activity, these being innovation, type of knowledge, competitive strength, quality of the work environment, and respect towards the environment, moderating factors between strategic orientation and performance [12]. Therefore, efforts to address how design strategically impacts complicated problems can be seen from Papanek’s approach, with a key aspect being social problems, and with emphasis on research and social innovation from the industrial context or culture [13,14,15].

The strategic value of design becomes widely evident for a public not accustomed to or that develops outside the design sector; through the trends followed by the masses, design is positioned with products that communicate with people, reaching directly to the ideologies and new customs that are in prominent position. Identifying and sizing trends from new raw materials, environmental awareness, and technologies is the challenge that companies must take into account in view of their economic, social, and political relevance, factors which also affect consumption.

Macrotrends within the Sustainable Development Goals [16], especially goal 12: responsible production and consumption, challenge companies to efficiently manage natural resources, in addition to reducing waste, which also encompasses joint actions mitigating the responsibility of traders and consumers as a goal by 2030. This is feasible with the active intervention of academia and research centers that, through R&D&I (research, development, and innovation), connect with design and sustainability in a harmonious way without compromising future generations, but which consider the needs of the present ones, even moving towards a personalized and coherent design with ethical and reasonable production adapted to the non-indiscriminate use of resources.

4. Material and Methods

Based on design management criteria with a strategic approach [10,11], which guarantees a vision towards the current issues that design must look at such as new technologies, the environment, and sustainability at all levels in the processes of the company, a process must be sought that maintains bearable levels, suitable for use by and close to the human being. We must also develop the appropriate techniques and controls necessary to achieve a viable product [5], finally pursuing a reduction in waste and the consequent impact on the ecosystem.

The key factors for the reuse of leather shavings produced in the lowering process are analyzed, as well as the possible negative effects that may limit the viability of the use of the product. Through the design, a related methodology is proposed that allows the development of a functional product that integrates solid residues from the leather production into its composition. This is according to the new design trends focused on the user and sustainability [17]; these are the prioritized aspects to be considered in the conceptualization and subsequent evaluation of the product [18]. These criteria are defined from the prefiguration as supports for the solution proposal and the consequent validation of the prototype. The Double Diamond methodology schematic diagram shows the developed process’s schematization (Figure 1).

The Discover stage, which refers to divergence, involves the investigation of the context in which the tannery sector develops, understanding its dynamics within the economic and productive system, the internal processes of raw material transformation, and its thinking in terms of sustainability and design. The possibilities within companies to manage waste and perform its treatment up to being sent to sanitary landfills were investigated. The waste generated in the tanneries was analyzed to identify the problem and the opportunity; its possibilities were detected in terms of factors such as composition, malleability, and chip compression.

For the Define stage, through convergent thinking, alternatives for waste management were proposed. From the context analyzed, related and representative sectors were identified as the most dynamic in the local and national economy; of these, the construction sector was selected, which at a national level has constant growth, needs new materials for the development of its projects, and offers approaches, as well as designs, for the integration of sustainable processes for the projects they develop. Thus, the use of leather shavings becomes an input for the generation of new products for construction, taking into account that it is not considered toxic as long as the chromium contained does not decay into hexavalent chromium.

In the Development stage, ideation is carried out through the application of divergent thinking, where the precepts of Strategic Design and product development allow connection with circular processes to obtain the product. Combining waste with stabilizing materials resulted in cobblestones, bricks, agglomerates, and prefabricated plates as alternatives for use based on creative proposals for the definition of shapes. This proposal also analyzed the consensus with companies in the tanning and construction sector as a feasibility factor, considering the awareness of the raw material processed, differences in the tanning process, and substantial variations in the water content of the waste. The commitment of the tannery management is a prerequisite for good environmental performance, considering the awareness of the inputs and outputs of the process with respect to the characteristics of the materials, their quantities, and their potential environmental impacts.

According to figures from the Central Bank of Ecuador in May 2023, the construction industry’s share of the national GDP will remain at 6.1%; this industry continues to be the fifth most important sector of the Ecuadorian economy and is seeking to generate synergies between environmental, social, and economic aspects in order to consolidate sustainability criteria. At present, traditional materials continue to be used in the construction sector, and it is expected that public policies will encourage the use of alternative materials [19].

In the Delivery stage, the proposal of ornamental bricks for interior spaces was implemented, thus obtaining a neutral material that guaranteed the confinement of the waste. Its use was certified through the validation of physical–chemical tests of the prototype and subsequent validation by experts in the areas of construction, design, tanners, and the general public. In addition, in relation to comparable products, it is competitive in the market and can be adapted to user requirements in terms of form, function, and color.

5. Results and Discussion

In the first stage, the need for physical spaces for chip processing and dispatching was identified, in addition to the necessary budget; in this regard, there were no public policies or projects dealing with waste recovery. There were many companies that continued with linear processes and environmental impacts.

With regard to the solid waste from the leather trimming process, the characteristics that delimited the development of the product were determined, and are shown in

Table 1. Characteristics of leather waste.

Criteria	Description
Structure	Highly organized in the form of fibers ∅ = 100 nm, which are in parallel and close together.
Protein	A significant percentage of 78.64–78.00%
Trivalent chromium	3–3.3%

Note: Data from Lakrafi et al. [20].

:

The critical factor is that, according to several toxicity manuals, they do not represent a potential risk when inhaled or ingested; however, it is necessary to mention that this waste has a possibility of oxidation from CrIII (chromium 3) to CrVI (chromium 6), according to Lakrafi [20], under the following conditions:

• Acid rain can leach CrIII waste from landfills causing possible oxidation.
• Air over a wide pH range has the potential to generate oxidation.
• According to Gibbs’ free energy law, spontaneous oxidation can occur in an acidic or alkaline medium.

The authors mention the possibility of oxidation of CrIII to CrVI, but they did not perform experimental tests to confirm this hypothesis. According to Altadill Colominas [21], in the thermal field, for there to be oxidation of Cr III to Cr VI, the temperature must be greater than or equal to 850 °C, a fact that must be considered when considering thermal tests.

The second stage established a strong and viable connection with the construction sector, where a direct pathway was generated between obtaining waste, the elaboration of the product, and a dynamic consumer market. In Ecuador, by 2019 the construction sector was the fifth most represented sector, accounting for 8.17% of the country’s GDP. Additionally, foreign investment was over 69 M USD, and employment was generated for more than 480,000 people, [22].

In Bangladesh, the shavings from the regrinding process with clay stabilization processes are used in the production of bricks. This product ensures sustainable production by being energy-efficient and it has mechanical properties suitable for use in construction [23]. The materials have a neutral pH and can be used for these processes.

The bricks were manufactured with different percentages of chip composition, these being 10%, 20%, 30% and 40% in dry weight, in controlled laboratories and in the field, complying with all the properties required by a material for construction, such as resistance, water absorption, shrinkage, weight loss by ignition, and apparent density. The bricks with incorporated chips obtained a compressive strength ranging from 10.98 MPa to 29.61 MPa, with a water absorption ranging from 7.2% to 20.9%, and they met the established ASTM standards for construction materials.

The leaching behavior of several heavy metals (Cr, As, Cu, Ni, Cd, Pb and Zn) from the chip-modified bricks was found to be negligible and well below Dutch regulations and the United States Environmental Protection Agency (USEPA)’s regulatory limits. The results of this study indicate that wastes from the leather trimming process of tanneries can be sustainably stabilized into clay bricks and large-scale application of this technique can be envisaged in the context of Bangladesh, where brick remains a dominant building material [23].

An additional study proposed the generation of bricks made from wet blue shaving, mixed with sand–cement ratio of 1:5 in various proportions 1%, 2% and 4% by total dry weight, to prepare a total of 48 building blocks of dimensions 254 mm × 127 mm × 76 mm; the blocks with 1% and 2% wet blue showed a compressive strength of 17.65 MPa and 13.87 MPa, respectively, being viable and environmentally friendly alternatives [24].

In 2021 in India in the state of Tamil Nadu, around 900 tanneries were identified because the animal skin tanning industry is one of the most polluting industries and causes an unfavorable impact on the environment. Here, approximately 3 MLD of wastewater from tanneries is treated and the resulting sludge weighs about 1.5 tons. This is disposed of in landfills.

Having identified this problem, an Eco Brick was developed based on sludge and bagasse ashes, which acted as substitutes for traditional brick-making materials. Experiments were carried out with different compositions of sludge such as 5%, 10%, and 15% and bagasse ash proportions of 15%, 10%, and 5% for the manufacture of bricks. It was shown that working in the proportion of 15% ash and 5% sludge resulted in Eco Bricks with higher water absorption and increased their compressive strength and hardness when the bricks were burned [25].

In the third phase, the product design was proposed. Specifically, this was a block built with stabilizing material. This material allows its interior to confine the chip from the leather deburring process so that superficially the residue does not come out (Figure 2). This was produced under a process of mixing of the materials, compaction in a mold, and subsequent drying.

Tests were carried out under ASTM 785 standard [26] conditions to measure the compressive strength, which resulted in 15.72 MPa for the ceramic matrix composite material with a composition of 35% chips and 65% ceramic material (Figure 3).

A simple but volumetric shape was defined, with practical dimensions for its handling (Figure 4), establishing the most important characteristics. The concept of the prototype involves adding value to specific characteristics such as the reuse of waste from the leather trimming process in tanneries, being environmentally friendly, stimulating the local economy, meeting technical characteristics, functionality, and being aesthetically attractive to the consumer. These attributes define the product and add value, enabling a product to become an integral product (insight), and harmonizing each need through the proposed design methodology.

The fourth stage focused on validating the product and proposing alternatives for its use. Chromium content tests (

Table 2. Final product characteristics.

Criteria	Description
Dimensions	150 mm (width) 75 mm (height) 35 mm (depth)
Weight	300 g
Density	2.14 g/cm3
Composition	65% material 35% chips
Quantity of crill	0.74 mg/kg
Cost per m2	43.29 USD

Note: Data from physical–mechanical evaluations.

) were conducted on the final product in the first validation. The Cr values obtained for the long chip samples were 0.74 mg/kg. The maximum permissible limit for extraction of heavy metals on a dry basis (acid digestion) for total chromium was 3000 mg/kg. Product stacking tests were also conducted to identify if the product was resistant and could withstand activities such as transport, exhibition, or storage; the result was the possibility of stacking up to 50 blocks without any perception of damage to or deformation of the product.

There are two possible uses for the blocks in the areas of architecture and interior design; the first option is its application in commercial showcases and the second is in applications for living or waiting rooms. Due to its physical–chemical characteristics, it can be proposed for use in interior and exterior spaces. The proposal emphasizes its application as a modular set for the creation of a decorative block.

The product can be finished with textures or colors to enhance its commercial possibilities (Figure 5).

As for the manufacturing cost, it should be considered that it will be performed manually through the use of molds and will depend on the shape and design to be considered. For the commercialization, it will have a value of 43.29 USD per m², which makes it competitive in the market; the cost of decorative pavers can range between 35 USD and 75 USD dollars for each m². As for the manufacturing cost, it should be considered that it will be produced manually through the use of molds and will depend on the shape and design to be considered. For commercialization, the value of each m² will be 43.29 USD, making it competitive in the market; the cost of decorative pavers can range from 35 to 75 USD per m².

6. Conclusions

The waste generation (solid, liquid, and gaseous) in tanneries generates environmental impacts that have not been mitigated, allowing researchers to analyze and propose novel circular processes within tanneries to obtain new products from this waste.

Strategic Design relates concepts and languages between designers and industries to achieve through interactive action the realization of projects, where they define priority objectives and available resources to respond to new contexts and problems. Furthermore, Sustainable Design harmonizes the social, economic, and environmental sectors by solving difficulties such as health, jobs, and current local business models in these areas.

The Strategic Design model developed is a contribution to the macro trend of achieving the SDGs, especially goal 12, in which, through the convergent and divergent phases, we have identified a problem, defined the solution, developed, and delivered a new product that responds to the management of waste (shavings) generated in the tanning industry to mitigate effects on the environment.

The application of the Double Diamond methodology allows the interaction of actors that form a network between academia (researchers), decentralized autonomous governments, industry, and the construction sector, who are the appropriate actors to jointly develop research projects that contribute positively to society with respect to social responsibility.

A new product has been developed with functional, technical, and aesthetic attributes that can be used in the construction sector due to its constant growth and the innovation in designs and materials. A product was obtained that confined the chip inside to a chromium content of 0.74 mg/kg, had a weight of 300 g, and was modular and aesthetically attractive to the user.

The weighted cost is 43.29 USD, which makes it competitive in the market concerning the price offered for 3D panels used for space design, the price of which range from 30 to 60 USD/m². The product fulfills its function and generates value by giving a second chance to process waste. It is taken into account that the product derived from waste has a medium-to-long lifetime. Subsequently, the necessary actions must be generated for its treatment when its life cycle is finished.

It is estimated that 120 t per year of shavings from leather trimming processes in a single tannery can be avoided, with a total of 1500 t of this waste being saved at the national level. Waste could be prevented from reaching city dumps and landfills, which cause leachates that cause environmental damage.

It is recommended to test the mechanical strength and water absorption of the new product to determine if the confinement of the chips inside the product does not allow chromium to leach under aqueous conditions. In addition, it can add a hydrolysis process for the chip, which will allow the total elimination of Cr III.

Further research is suggested to determine if the block can contribute as an acoustic or thermal insulator in its final use. At the governmental level, incentives can be developed through public policies for companies that reuse their waste to obtain new products, a practice in other countries. The low industrial development of the peripheral regions can be taken as an opportunity to develop control policies for environmental pollution, but on the other hand, the globalization of companies, production, and commercialization is inexorably transferring the interests of the central countries to the peripheral ones.

It is necessary to continue the project in its intellectual property registration phase and to trademark registration for commercial purposes.