9.2.1 Circular Economy and Sustainable Development

Sustainability has started to gain more attention due to “wicked” environmental threats like global warming, soil acidification, biodiversity loss, and pollution (Duckett et al. 2016). The need for sustainable development and the impact of urbanization has been discussed in a variety of industries (Opoku 2019) involving the three pillars of sustainability: society, economics, and environment. Global sustainability can be achieved only by transforming the widely accepted and used linear economy model to a CE, which is restorative and regenerative by design. The CE aims to close the loops to regain resources back to the economy (Baydar et al. 2015). In order to do so, a new relationship between businesses and resources needs to be formed. Along with reduction of waste and efficient resource consumption, industries have to improve the safety of workers and customers, develop innovative products rather than conventional ones, and at the same time make a profit (Rugani et al. 2014). The main challenge while creating this new relationship is the lack of tools that support decision‐making from a sustainability perspective (Traverso 2018). Environmental, social, and cost assessment methods that are easily applied commercially need to be developed to help in such decision‐making processes, to facilitate economic growth while minimizing negative impacts on the environment and society.

9.2.2 Textile Industry – Sustainability Issues and Recycling

The textile industry is considered highly unsustainable due to the sheer volume of textiles that is produced and wasted, and concerns about disposal and management of textile waste are increasing (Pensupa et al. 2013). The fast‐changing fashion trends and the increase in demand has resulted in an increase in the rate of textile production as well as the subsequent waste generation. As a consequence, more than 1.2 billion tonnes of carbon emissions are created every year through textile manufacturing processes, and most textile waste ends up in landfills (Zamani et al. 2015). The increasing amounts of textile waste, accompanied by decreasing landfill space in cities, has further prompted investigation into novel reuse and recycling methods (Sandin et al. 2011). Ideally, reuse of products is a more environmentally beneficial route as compare to recycling; however, the fast‐changing fashion industry limits the reuse of clothing and encourages the development of recycling as the main solution to the textile waste problem.

9.3.1 Description of Environmental Assessment

Environmental Life Cycle Assessment (ELCA) is considered to be one of the best‐established systems analysis tools to measure the environmental impacts of products/processes/services across the entire lifecycle, encompassing different stages from raw material extraction, through production, distribution, use, and disposal. It is widely used by researchers and policymakers for a holistic evaluation of the environmental dimensions of sustainability (Chopra et al. 2019; Chopra and Theis 2017; Falinski et al. 2018; Subramanian and Yung 2017; Yeo et al. 2019; Zaimes et al. 2015). As already mentioned, numerous studies have applied ELCA to analyze environmental aspects of various textile products, supply chain and recycling techniques following the ISO 14040 (2006) guidelines. Additionally, a few researchers have explored the applicability of ELCA to evaluate the environmental dimension of biorefineries (Moussa et al. 2016; Neupane et al. 2013; Smidt et al. 2016; Gilani and Stuart 2015). Hence, the applicability of ELCA for assessing environmental impacts of textile biorecycling is justified.

ELCA is conducted in four main phases based on ISO 2006 (Song et al. 2013): (i) goal and scope, (ii) Life Cycle Inventory (LCI), (iii) Life Cycle Impact Assessment (LCIA) and (iv) interpretation. The aim of the study, process flow, system boundaries, geographical limitations, functional unit used, and any other assumptions made, are included when defining the goal and scope in the first step. Collection of data regarding the inputs and outputs of the analyzed process needed to conduct an LCA study are discussed in the LCI step. Data can be collected from primary (site‐specific) and secondary sources (literature sources, previous studies). In the third step of impact assessment, inventory data are used and the results are characterized into impact categories. It includes four main steps: classification, characterization, normalization, and weighting. Only classification and characterisation are included here – the optional steps of normalization and weighting are excluded. The characterization factors reported by the ReCiPe (H) method are considered in this analysis. The ReCiPe method was chosen for impact assessment as it can provide results at midpoint and endpoint level (Muthu et al. 2012). There are 18 midpoint categories into which the inventory results can be translated. The characterization factors are applied to the inventory results, and results are obtained in the corresponding indicator units. For example, results are obtained in kg CO₂ for the impact category of global warming potential (GWP). The midpoint results are represented as contribution percentages, the impact category that contributes the maximum environmental implications is represented as 100%, and the rest of the impact categories are calculated as relative percentages. The 18 midpoints are further grouped into three endpoints: human health, ecosystem quality, and resource depletion. Endpoint results are easily interpretable even by non‐LCA experts, as they are represented using points. The following four basic and important midpoint impact categories are chosen for this study: global warming potential (GWP), human health, terrestrial acidification (TA), freshwater eutrophication (FE), and fossil resource scarcity (FRS). In the final interpretation step, the impact categories, the processes and materials that contribute to these impact categories can be identified and analyzed. Results help decision‐makers to identify critical or key problematic processes in the analyzed system, and derive recommendations to mitigate the environmental impacts. SimaPro 8.5 software with the inbuilt Ecoinvent v3.5 database is used to implement LCA and derive results (Goedkoop et al. 2014).

9.3.2 Description of Social Assessment

Social Life Cycle Assessment (SLCA) is used to quantify social aspects of products/processes/systems through their entire lifecycle (Petti et al. 2018). SLCA is a new variant of LCA that analyses processes from a lifecycle perspective, hence it includes processing of raw materials, manufacturing, transportation, use, and disposal. Though human health is measured as an endpoint in ELCA, still SLCA varies from ELCA slightly due to its nature and objectives. The effect of production processes on the environment and consequently on human health is measured in ELCA, whereas effects of business activities and how they affect the human wellbeing of stakeholders are analyzed in SLCA (Subramanian and Yung 2018). Hence, SLCA can be used along with ELCA and LCC to assess social dimensions in sustainability assessments. Environmental consequences (impact categories) of the analyzed process are included in the inventory. Social consequences like forced labor, child labor, workers' rights, and discrimination in business activities are measured using social indicators in SLCA (Weidema 2018).

The social indicators need not necessarily be quantitative – they can be qualitative or semi‐quantitative in nature. For instance, quantitative social indicators can be salary, number of working hours, percentage of child labor in an organization, women:men ratio in a business; qualitative indicators and representative data can be descriptions about cultural heritage in a region, or community engagement activities being conducted; while semi‐quantitative indicators can be presence or absence of a child labor/technology development strategy in an organization. Overall, the social consequence or issue is represented by numbers or percentages for quantitative social indicators; yes/no answers for semi‐quantitative indicators; and described in words for qualitative indicators. Due to the qualitative nature of the social data in most cases, measuring social aspects and deriving meaningful results can be complicated. UNEP/SETAC (2009) came up with guidelines based on the ISO 14040 framework, including the four main phases given in Section 9.3.1. In SLCA, human wellbeing is the main endpoint, and the effects of social pressures on this endpoint are measured using social indicators (Arcese et al. 2016). Organization and societal wellbeing are also considered as additional endpoints in this work to broaden the range of social aspects that possibly affect the involved stakeholders.

The measure of social aspects within sustainability assessment is emerging and is relatively very new at a technology level (Subramanian et al. 2018). Hence, the measurement of social impacts through the lifecycle of products from emerging technologies like biorefineries needs special attention. Human wellbeing directly measures social indicators like health and safety, working hours, discrimination; organizational wellbeing measures aspects like supplier relationships, fair competition; and societal wellbeing measures aspects like safe and healthy living conditions and access to resources.

There are many social indicators to measure a varied set of social aspects or issues proposed by the UNEP methodological sheets (Benoît‐Norris et al. 2011). From these, social indicators that are relevant to the studied concept of biorefineries are selected and included here. The selected indicators linked to the corresponding endpoint can be found in Figure 9.1. These social indicators are linked to different social endpoints based on their potential contribution to the social issues that affect the involved stakeholders like workers, the local community, and society. Finally, a social sustainability index can be derived by taking into account all three endpoints equally, with a set of indicators detailed below, that describe aspects like working hours, health, safety, transparency, and access to resources by the people involved in the bioproduct manufacture.

The following indicators are selected under each social endpoint to measure the wellbeing of stakeholders in biorefinery production and the effects on the local community and society where biorefineries are situated: workers, local community, society, and value‐chain actors.

Human wellbeing

• Fair salary
• Working hours
• Discrimination
• Health and safety
• Social benefits/security

Organizational wellbeing

• Fair competition
• Promoting social responsibility
• Supplier relationships
• Respect for intellectual property rights
• Feedback mechanism
• Transparency

Societal wellbeing

• Safe and healthy living conditions
• Local employment opportunities
• Access to material resources
• Public commitment to sustainable issues
• Contribution to economic development
• Prevention and mitigation of conflicts
• Technology development

9.4.1 Recovery of PET Fiber from Cotton–Polyester Blended Textile Waste

The textile waste biorecycling method analyzed in this work converts cotton–polyester blended textile waste into polyester and produces glucose as a byproduct. The polyester recovered is respun to produce polyethylene terephthalate (PET) fibers. The proposed biorecycling method can be considered as a circular economy initiative that brings resources back to the textile industry as a raw material. Environmental impacts of the biorecycling method are analyzed based on the LCA approach. Briefly, in the developed biorecycling method, cotton–polyester textile waste is crushed, then the crushed fabric is pretreated, and subjected to enzymatic hydrolysis to separate polyester and cotton. The recovered polyester is re‐spun to PET fiber. In addition, the hydrolysate is purified to obtain glucose syrup as a value‐added byproduct. Results demonstrate (i) the most impactful processes and subprocesses in the biorecycling method; (ii) the most detrimental materials and energy used in the impactful unit processes, (iii) the most affected impact category among the four major categories assessed (global warming potential (GWP), freshwater eutrophication (FE), terrestrial acidification (TA), fossil resource scarcity (FRS)).

All the related inputs and outputs of the studied recycling method are referred to the functional unit (FU), which is chosen as 1 kg of recovered PET fiber. Input is the 50:50 cotton–polyester blend waste textile fabric. The system boundary includes all unit processes like crushing, pretreatment, enzymatic hydrolysis, hydrolysate purification, and respinning (Figure 9.2). The use and end‐of‐life of the produced PET fiber, such as clothing, washing, and disposal of used clothes are not considered. The first life of the textile waste is not considered – a cutoff approach is used. Since the waste that enters as input into recycling is in any case considered waste, a burden‐free approach is assumed.

9.4.2 System Description of the Biorecycling Method

A system description of the biorecycling method used to convert 50% cotton and 50% polyester waste fabric into polyester and glucose is given below, with brief explanations of each step (Figure 9.3). A much more detailed description can be found in Li et al. (2018).

Crushing: Insufficient surface area availability obstructs the abrasion of the biological components, which is needed to separate the biodegradable components from non‐biodegradable ones. Therefore, a double shaft shredder was used to crush the input waste in order to increase the surface area, to enhance the effectiveness of the chemicals in pretreatment, and the efficiency of the enzymes used in the enzymatic hydrolysis step.

Pretreatment: In order to decrease the crystallinity of the cellulosic fibers, the crushed fabric was exposed to chemicals that are reusable. The crushed waste fabric was mixed with a solution of 12 w/v% urea and 7 w/v% NaOH and was stored in a freezer at −20°C for 6 h. The mixture was then taken out of the freezer and neutralized with HCl. Then, the sample was washed under tap water and dried in an oven at 40°C for 48 h.

Enzymatic hydrolysis: In order to separate polyester from cotton, the biodegradable component of the textile waste is hydrolyzed. The pretreated textile waste was mixed with sodium citrate buffer (50 mM, pH 5) at a solid loading of 3 w/v%. Cellulose from cotton, which is biodegradable, is hydrolyzed in a bioreactor with an enzyme solution made of 20 FPU/g cellulase and 10 U/g β‐glucosidase at 50°C and pH 5.

PET recovery/purification of hydrolysate: The nonbiodegradable component of the textile waste was separated in a solid form by filtration and the recovered PET residue proceeds to the next step for re‐spinning. Purification of glucose‐rich hydrolysate solution was achieved by the addition of activated carbon at a loading of 15 w/w%. After the hydrolysate is purified from chemicals such as dye, activated carbon is removed by paper filtration. Then, for removal of ions, the filtered solution is passed through ion exchange columns. The columns were cleaned and regenerated with deionized waster, H₂SO₄ (50 w/w%) and NaOH (7 w/v%) for reusability purposes. Cleaning of resins resulted in a decrease in the efficiency of the glucose recovery method due to the glucose amount lost during washing. Finally, glucose syrup is obtained by placing the hydrolysate solution in an evaporator. This glucose‐rich syrup is a value‐added byproduct and can be used in industries for production of bioplastics, biosurfactants (cleaning agents), and biochemicals.

Re‐spinning: In the final step of the biorecycling method, the recovered PET residue is re‐spun into PET fibers. Re‐spinning the recovered PET into a fiber is needed for further weaving and knitting purposes, which can only be achieved if the fiber has a suitable tenacity. Therefore, the recovered PET residue is processed in three steps: granulation, solid‐state polymerization (SSP), and melt spinning. In the granulating step, the filtered residue was washed and dried before granulation. The dried residue was then passed through the melting stages of granulation and cut into PET pellets. To increase the molecular weight of the pellets, the SSP process was applied. The recovered PET chips were heated at 230°C for 1800 min and mixed with PET bottle chips for the final step. The mixture was spun into PET fibers by the melt spinning process. The whole biorecycling method is designed to ensure the further processability of the final product. Therefore, the proposed method can be considered as a novel solution to the textile waste challenge.

9.4.3 Life Cycle Inventory

A reliable environmental assessment needs valid data. In this study, primary data specific to the analyzed biorecycling method are used for calculating the environmental impacts. All data are collected and converted according to the functional unit considered. Data related to all the inputs and outputs of the unit processes correspond to a lab‐scale textile waste biorecycling process. Information from the lab is used to model the unit processes. An itemized cost report (ICR) and a materials and streams report (MSR) of the TEA, carried out by our research group previously, were used as the basis for creating the inventory. The original TEA report was generated based on textile biorecycling conducted at the laboratory scale for processing 10 MT of 50:50 cotton–polyester waste to produce PET fiber and glucose. Energy requirements of all the subprocesses involved in the unit processes, like heating, cooling, drying, and freezing, were all calculated from the TEA report according to the functional unit of this study. Machine specification, power consumption details, hours of usage, and so on, were also calculated from laboratory information.

Solid‐to‐liquid ratios and weight‐to‐volume ratios of the solutions used in the laboratory were used to determine stoichiometrically (based on molar mass) the mass of materials and chemicals (sodium hydroxide, urea, citric acid, and hydrochloric acid) used in the pretreatment and enzymatic hydrolysis steps. Beta‐glucosidase was not found in the Ecoinvent database, hence only cellulase was used while modeling the enzymatic hydrolysis. Commercially, beta‐glucosidase is used only when the cellulase enzyme does not contain enough beta‐glucosidase; such a scenario was not assumed, and hence beta‐glucosidase was excluded and replaced with cellulase while modeling. The TEA report was also used to determine the amount of activated carbon used in the hydrolysis purification step. Production processes associated with steam, tap water, electricity mix, activated carbon, sulfuric acid, cationic and anionic resins were all taken from Ecoinvent v3.5.

Polyester recovered in the enzymatic hydrolysis step was sent to Taiwan for melt re‐spinning. Recovered polyester is mixed with 80% w/w PET bottle chips in the melt spinning process (80:20 ratio of PET bottle chips to recovered polyester sent for re‐spinning) to produce PET fiber. The PET fiber production process takes place in Taiwan and it includes three main processes: pellet production, melt spinning, and drawing processes. The TEA report was used to determine the electricity, water, and steam needed for re‐spinning, again using the database Ecoinvent v3.5 for data related to production processes. Table 9.1 provides a summary of LCI for the biorecycling method used to produce 1 kg of PET fiber.

9.5.1 Environmental Sustainability of Bio‐based PET Fiber

The characterization results per kg of valorized 50:50 cotton–polyester textile waste for the four selected midpoints is displayed in Figure 9.4. The relative contribution (%) for each step in the biorecycling towards the impact categories can be found in Figure 9.4. Alkaline pretreatment and melt spinning are identified as the main processes responsible for creating potential environmental impacts in the bio‐based PET fiber recovery. Enzymatic hydrolysis is the third main step responsible for creating impacts. Among all the unit processes, pretreatment is the environmental hotspot, as it is responsible for the maximum contributions (100%) in all four selected impact categories. The rationale behind this huge environmental burden can be attributed to the electricity production (coal‐powered generation) required in the freezing and drying for crystallinity reduction in the pretreatment step, together with the production of urea, a chemical required in alkaline pretreatment. Impacts can be traced back to ammonia liquid, commonly used in urea production. “Hard coal mine operation” (coal‐powered electricity generation) and ammonia production also increase the contribution to GWP. Also, fossil resource scarcity is mainly impacted by coal and natural gas used for electricity generation.

Melt spinning makes the second‐highest contribution to all the four selected impacted categories. Production of electricity (oil and gas fired generation within electricity production) required in the granulation, SSP and re‐spinning are considered as the main contributors to environmental impacts. Also, fossil resource scarcity is mainly affected by the melt spinning step with a contribution ratio higher than 80%, and pellet production with a contribution ratio of 36%. Impacts can be traced back to xylene production, a subprocess in the PET granulate, used in the production of PET bottles. Enzymatic hydrolysis makes the maximum contribution in affecting eutrophication potential. Impacts can be traced back to the production of citric acid in China, a chemical used in hydrolysis using the submerged fermentation process.

Pretreatment makes the maximum contribution on all four impact categories. Relative contributions from the melt spinning process are 31, 21, 29, and 84% of total GWP, TA, FE, and FRS respectively. Relative contributions from enzymatic hydrolysis are 19, 18, 20, and 21% of total GWP, TA, FE, and FRS. Thus, further optimization of textile biovalorisation techniques should focus on energy‐efficient processes that demand less electricity and use chemicals that do not add to environmental impacts, or identify and use alternative organic chemicals and pretreatment agents that can be recycled. However, such replacement has to be again analyzed to check for a reduction in environmental impacts. The overall quality of the PET fiber recovered from hydrolysis has to be improved, to reduce the amount (%) of PET bottles being added in the melt spinning step, consequently reducing the associated environmental impacts. Though the final product is said to replace virgin PET fiber that can be used in the production cycle of textiles, rebound effects caused due to increased usage and economics have to be considered in the future.

Figure 9.5 presents the endpoint results for the production of 1 kg of PET fiber through the analyzed textile biorecycling method. Like the midpoint results, pretreatment caused the highest impact on all the three endpoints compared with the other steps in biorecycling (human health, ecosystems, and resource depletion respectively). Electricity production and ammonia within urea production are the major process/substance contributors to ecosystem quality and human health impacts. Process energy used includes use of coal and natural gas within electricity production, contributing the most to resources depletion. Enzymatic hydrolysis was the next most dominant step that affected ecosystem quality (70.7%) and human health (52.2%). This step caused comparatively lower impacts on mineral resources and fossil resources scarcity (33%). Melt spinning was the next most impactful step, and it majorly affected the resource depletion category (83.58%), but was comparatively less impactful on ecosystems and human health. Again, process energy used in electricity and steam production, as well as xylene used in PET bottle production, were responsible for the impacts. Like the midpoint characterization results, pellet production, hydrolysate purification, and crushing were found to be less critical in terms of environmental impacts.

9.5.2 Social and Economic Sustainability of Bio‐based PET Fiber

An economic evaluation of PET recovery by the biological method was carried out based on the ICR prepared as a part of the techno‐economic analysis conducted by our research group previously (Kwan 2018). It was done on a large scale. The annual production rate of the proposed plant at a 95% working capacity was approximately 170 000 MT PET fiber/year, manufactured from 83 000 MT 50:50 cotton–polyester textile waste/year. The three main stages of the process that were taken into consideration in the techno‐economic analysis were enzymatic hydrolysis, purification of hydrolysate, and PET re‐spinning. Expenses outside of material and utility costs, such as labor, wastewater treatment, logistics, maintenance, insurance, distribution, and marketing, were also taken into consideration. The enzymatic hydrolysis stage contributed 85% of the total material cost (US$1.08 billion) of the plant, mainly due to the high rate of cellulase enzyme consumption. PET bottle chips contributed 15% of the overall material cost. PET re‐spinning and enzymatic hydrolysis stages generated 46% and 42% of the total labor costs (US$1 million), respectively. For 1 MT PET fiber production, raw materials cost approximately US$6300, 88% of the total cost. For recycling of 83 000 MT textile waste/year, the total generated cost was around US$1.22 million. The economic feasibility of a system can only be demonstrated through its benefits. The revenue generated by the biological method comes from the PET fiber (US$1450/kg) and glucose syrup (US$67/kg) obtained. The overall cost–benefit analysis showed a deficit of US$860 million per year (Kwan 2018). Raw material costs due to the commercial enzyme usage and the PET bottle chips added into the melt spinning affected the economics. Again, the PET bottle chips cannot be removed or reduced, as it firstly affects the final quality of the recovered fiber and secondly increases the environmental impacts. For now, the results from the economics analysis do not favor the textile biorecycling technique. However, future research should focus on reducing these deficits, for example, by optimizing the biorecycling method to recover polyester of improved quality that does not require addition of commercially bought PET bottle chips. Cellulase enzyme production that is economically feasible, hydrolysis reactor design, improvements in the process design to accommodate other kinds of textiles such as silk, nylon and wool, are a few other ways that can possibly reduce the raw material and operational costs.

Social sustainability results cannot be calculated as of now, since the process is currently conducted at the laboratory scale. More meaningful results for social dimensions of the biorefineries can be obtained from industry‐scale biorefineries using the outlined approach. Social information for the selected indicators has to be gathered from the involved stakeholders through questionnaires and interviews. The collected social data has to be processed using social impact assessment methods to derive social sustainability results.