Water footprint assessment of viscose staple fiber garments

According to data from the China Statistical Yearbook, in 2017, China's per capita water supply was only approximately 25% of the world's average supply, highlighting severe water shortages in the country. In the same year, the proportion of industrial water consumption to China's total water consumption (including agricultural, industrial, domestic, and ecological water usage) measured 23%–24%, and the proportion of industrial wastewater discharge to the total national wastewater discharge (including industrial and domestic wastewater discharge) was 27%–47% (NBS 2017a, 2017b, 2017c). China's environmental situation in terms of water resources is a cause for concern, with water consumption and wastewater discharge from industry being one of the main reasons. The textile and garment industry is a traditional pillar industry in China, and viscose, including both viscose staple fiber and viscose filament yarn, has become an important raw material for the production of textiles and garments. In 2017 and 2018, China's viscose production was 3.70 and 3.97 million tons, respectively, with viscose staple fiber production accounting for approximately 95% thereof (Ji 2019). The market share of viscose staple fiber is larger than that of viscose filament, and China is the world's largest consumer of viscose staple fiber, with the domestic consumption of viscose staple fiber increasing from 2.8 million tons in 2011 to 3.4 million tons in 2018 (CBG 2019). Viscose staple fiber is mainly used for the manufacturing of textiles and garments due to advantages in comfort and moisture absorption, and its proportion in the mid-to-high-end fabric market continues to increase. It is often used in two major garment categories, namely shirts and suits. According to statistics, approximately 65 tons of fresh water is used for the production of one ton of viscose staple fiber, and approximately 110 tons of fresh water is used for the dyeing and finishing of one ton of textiles. Alkali, carbon disulfide, sulfuric acid, and other chemicals used in the production process, in total approximately 3.3 tons/ton viscose staple fiber, remain in the wastewater and are discharged together with the wastewater (Yang 1989). Therefore, the viscose staple fiber industry and its associated textile and garment industries consume a large amount of water and are responsible for serious wastewater pollution, which has multiple environmental impacts on water resources.

Water footprint assessment (WFA) is an effective tool for analyzing the correlation between human activities or manufacturing of specific products and water shortages and pollution problems. It aims to quantify the water footprint of production processes, products, producers, or consumers and also evaluates the sustainability of water resources and the environment. The water footprint network (WFN) defines water footprint as a comprehensive evaluation indicator to measure the level of water resource utilization, including the blue, green, and gray water footprints (Hoekstra et al. 2011). The International Standard (ISO) 14046:2014 ‘Environmental management – water footprint – principles, requirements and guidelines’ classifies water footprints by various environmental impact categories, such as water scarcity and degradation footprints. Results from water footprint analyses according to ISO 14046 focus on identifying water environmental impact categories and quantifying the potential environmental impact on water resources. The water scarcity footprint accounts for regional differences in water shortage based on the blue water footprint, whereas the water degradation footprint quantifies the environmental impact of pollutants on water resources using pollutant types and emissions. The WFA method, developed by the WFN and International Standards Organization (ISO), is centered on water volume and potential environmental impact. Furthermore, Zonderland-Thomassen & Ledgard (2012) and Berger & Finkbeiner (2013) considered the impact-oriented WFA method more suitable for decision-making than the volume-oriented WFA method, as it better reflects the supply capacity of the water resources as well as the wastewater pollution tolerance capacity of the water environment (Huang et al. 2015).

The WFA method has been widely applied across various organizational, regional, service, and product levels, especially for agricultural products, such as cotton (Chico et al. 2013; Xuan et al. 2014), wheat (Ababaei & Etedali 2014; Xuan et al. 2014), corn (Ababaei & Etedali 2014; Xuan et al. 2014; Duan et al. 2016), rice (Cao et al. 2018), coffee, tea (Chapagain et al. 2006), tomatoes (Chapagain & Hoekstra 2007), sugarcane (Barbosa et al. 2017), mangos (Ridoutt et al. 2010), citrus (Munro et al. 2016), poultry (Gerbens-Leenes et al. 2013), pork (Gerbens-Leenes et al. 2013; Bai et al. 2018a), and beef (Gerbens-Leenes et al. 2013; Harding et al. 2017). The WFA method is also used for industrial products, such as sugar-rich carbonated beverages (Ercin et al. 2011), dairy products (Bai et al. 2018b), coal (Ding et al. 2016), building materials (Gerbens-Leenes et al. 2018), cables (Bai et al. 2016), and chemical products (You et al. 2014). In the textile and garment industry, the WFA method has been used to evaluate viscose staple fiber (Zhu et al. 2019), cashmere knitwear (Sun et al. 2018), polyester dyed cloth (Zhong et al. 2016), polyester knitted coral fleece (Xu et al. 2015), cotton textile products (Yan et al. 2014), and jeans (Chico et al. 2013). In particular, Chico et al. (2013) calculated the water footprint of various fabrics, with results indicating cotton denim fabric to have a greater blue and gray water footprint, but a smaller green water footprint than that of lyocell denim fabric. Wang et al. (2013) calculated the direct blue and gray water footprint of China's textile industry from 2001 to 2010, with results indicating a rise in the direct blue water footprint and showing both the direct blue and grey water footprint of the textile industry to be larger than that of the clothing, footwear, and chemical fiber industries. Wang et al. (2012) conducted an industrial water footprint analysis on seven types of knitted cotton dyeing fabrics from yarn to finished fabric and found the dyeing stage to have the largest industrial water footprint. Results from a study by Yan et al. (2014) on the industrial water footprint of four different shades of cotton textiles indicate that the darker the color, the greater the industrial water footprint. Furthermore, He et al. (2017, 2018) analyzed and discussed the water degradation footprint of various textiles and garments and calculated the baseline water degradation footprint of functional units of silk products based on the silk industry's water intake quota and wastewater pollutant discharge limits. Results from this study showed nitrogen and ammonia nitrogen to be responsible for water eutrophication with sulfide and total antimony to be responsible for water ecotoxicity (He et al. 2017, 2018). Recently, Linhares & Amorim (2017) evaluated the environmental impact caused by two dyed cotton fabrics (natural direct dyed and synthetic reactive dyed) with results showing the use of natural direct dyes to have less of an environmental impact than synthetic reactive dyes.

Water scarcity and degradation footprints are used as indicators to quantify water use in terms of total water resource supply capacity and wastewater discharge pollution in terms of the total pollution capacity of the water environment, respectively. Although the WFA is already used in the textile and clothing industry, it is not yet possible to fully quantify all the environmental impacts caused by the production of textiles and garments. In particular, there is no report on the environmental impacts of alkaline wastewater from viscose fiber production. In addition, water scarcity and degradation footprints can be quantified and evaluated from either a water consumption (volume) or a water pollution perspective (environmental impacts). Notably, the different evaluation methods for volume and quality do not reflect the overall environmental load in terms of water resources, making it difficult to horizontally compare and evaluate across products and processes.

Within this context, our study aims to (a) calculate the water footprints of typical viscose garment products from fiber production through to clothing consumption, and (b) conduct a comprehensive assessment and comparison of products and processes using the life cycle assessment (LCA) polygon method.

For our study, the WFA method was used based on the ISO 14046 standard and the comprehensive LCA polygon evaluation method. The water alkaline footprint was used to quantify the water alkalization impact caused by pollutants in wastewater discharge, thereby improving the WFA method. Furthermore, we quantified the environmental impact of viscose staple fiber blouses and blended men's suits on water resources; specifications of the blouses (size: 160/84A for the national garment size series standard in China) and men's suits (size: 170/92A for the national garment size series standard in China) are presented in Table 1. The functional unit of the water footprint calculations was set to 1,000 pieces of viscose staple fiber garments and the calculation of all related inputs (e.g., water and chemicals) as well as outputs (e.g., wastewater discharge) was based on this unit.

The total life cycle of the viscose staple fiber blouses and blended men's suits included the following seven parts: cotton linters, viscose production, fabric production, dyeing and finishing, garment production, consumer care, and recycling (Figure 1).

In this study, the system boundary of viscose staple fiber apparel included water usage and wastewater discharge from the production and processing of fibers, fabrics, and linings, as well as from the production and use of apparel products, but excluded consumption and emissions related to employees, transportation, as well as the maintenance and cleaning of machinery and equipment. As the amount of auxiliary materials (non-woven lining, buttons, etc.) was negligible, the processes related to their production were not included in our calculations. A summary of the system boundary is shown in Figure 2.

The WFA framework of the ISO 14046 standard includes the following guidelines: (a) determine the objectives and scope of the assessment, which should be consistent; (b) analyze the water footprint list, which should include the input and output of each process unit in the research system; (c) assess the impact of the water footprint, taking into account any potential environmental impacts caused by changes in water quantity and quality in the system, such as the water scarcity footprint and water degradation footprint; and (d) interpret the results in terms of the water footprint list and environmental sustainability (Bai et al. 2015).

The water degradation footprint (WF_DE) is used as an indicator to evaluate the potential impact of wastewater pollutant discharge on the water environment and includes sub-indicators such as water eutrophication, acidification, and ecotoxicity footprints (Heijungs et al. 1992; Goedkoop et al. 2009).

The weight of 1,000 blouses and men's suits were calculated according to specifications, fabric, and linings. Following this, the consumption of raw materials was estimated from the end to the start of the production process according to the loss rate. The conversion processes and results are shown in Figures 3–5.

In this study, cotton linters were used as the raw material for viscose staple fibers using caustic soda pulping and the Wuhe machine method (Zhang 1984). Data relating to water consumption and wastewater discharge from the production process were mainly obtained from monitoring data of chemical fiber plants with an annual output of approximately 125,000 tons and accessed through an environmental data platform (www.ipe.org.cn), as well as from relevant literature (Ke 1987; Yang 1989; Han 1998; Zhang 2005; Xiao 2015). Water usage and wastewater discharge data for the nylon and polyester production processes were obtained from the First National Pollutant Source Census Industrial Pollution Source Discharge Coefficient Handbook (FNPSCIPSDCH 2010).

Water consumption and wastewater pollutant discharge related to the cleaning of equipment used for textile processes were not included in our calculations. Blouse fabric was pre-treated before scouring, and reactive dyes were subsequently used for one-step dyeing in overflow dyeing machines; finally, the post-processing was softened. Data for water consumption and wastewater pollutant discharge related to the dyeing and finishing of blouse fabric was obtained from the monitoring data of chemical fiber printing and dyeing enterprises and accessed through an environmental data platform (www.ipe.org.cn). Men's suit fabric and lining was pre-treated according to fiber composition (e.g., degreased), followed by the reactive dye/acid dye or reactive dye/direct dye one-bath one-step method for neutral color dyeing using overflow dyeing machines; finally, the post-processing was shaped or softened. Data related to water consumption and wastewater pollutant discharge for the processes related to men's suit fabric, including the lining dyeing and finishing stages, were obtained from statistical data found in related studies (Zhu 2002; Fan & Wang 2004; Wu 2015) and from both monitoring and measurement data of chemical fiber printing and dyeing plants, which were accessed from an environmental data platform (www.ipe.org.cn).

In general, machine washing is used by consumers to wash blouses. In this study the washing of blouses by consumers was set to 50 machine washes, with washing machines having a capacity of 10 kg and a water consumption standard of 125 L. In contrast, men's suits are generally dry cleaned, which uses considerably limited water; therefore, it was considered negligible. The environmental impact categories and characteristic factors used in this study are shown in Table 2 (Heijungs et al. 1992).

The WF_SC and the WF_DE related to three types of typical viscose staple fiber garments were calculated using Equations (1)–(5), and LCA polygons were drawn based on the results obtained from water footprint analyses. The area of each LCA polygon was calculated based on Equation (6) to obtain a single integrated value for multiple indicator results.

The WF_SC of three types of viscose staple fiber apparel as well as viscose staple fiber production is shown in Figure 6.

Results presented in Figure 6 show the WF_SC of blouses to be larger than that of men's suits, with the washing of blouses by consumers having the highest WF_SC value of 225.57 m³ H₂O eq/1,000 pieces in terms of production processes, and accounting for 92% of the total WF_SC related to blouses. The total WF_SC of (a) men's suits made of 100% viscose staple fiber and (b) blended men's suits made of 55% viscose staple fiber and 45% nylon was 89.59 and 63.81 m³ H₂O eq/1,000 pieces, respectively. The WF_SC for suit (a) and suit (b) was mainly influenced by the viscose staple fiber production process with a value of 65.95 and 38.87 m³ H₂O eq/ton relatively. In the fiber production process, the presoaking process had the highest WF_SC of 31.76 m³ H₂O eq/ton, representing 34% of the total viscose staple fiber production stage WF_SC, followed by the scouring process with a value of 22.23 m³ H₂O eq/ton, which are the main steps that consumed considerable amounts of fresh water for dissolving into pulp in an alkaline environment and reducing the amount of impurity on the viscose fiber, and thus the whiteness index and oil rate can be improved for the scouring process (Shen & Patel 2010). The difference between the WF_SC of blouses and men's suits was mainly due to differences in viscose staple fiber production and different washing processes by consumers. In total, 154.90 kg of viscose staple fiber was used for the production of 1,000 blouses, while 709.90 and 418.40 kg was used for the production of 100% viscose staple fiber and 55% viscose staple fiber blended men's suits, respectively. The main reason for the difference is that a large amount of water (225.57 m³, based on water usage for 50 machine washes of 1,000 blouses) was used by the washing of blouses by consumers, while for men's suits treated with dry cleaning, little water was consumed.

The water degradation footprint (WF_EU, WF_AC, WF_AL and WF_AET) of three types of viscose staple fiber apparel as well as viscose staple fiber production is shown in Figures 7–10.

Results from our WF_EU analysis indicated that blouses had the highest WF_EU footprint, followed by 100% viscose staple fiber men's suits (a) and 55% viscose staple fiber blended men's suits (b). In the production chain of the three garment types, the viscose staple fiber production as well as fabric dyeing and finishing processes were partly responsible for the WF_EU of 1.58, 6.42, and 3.94 kg PO₄³⁻ eq/1,000 pieces, respectively, of which viscose staple fiber production accounted for more than 89%. The difference between the WF_EU values of the three types of clothing was due to the washing of blouses by consumers (51.45 kg PO₄³⁻ eq/1,000 pieces), accounting for 77% of the total WF_EU of blouses, and mainly caused by the presence of COD, BOD₅, and NH₃⁻N in the wastewater from washing machines. Although the dry cleaning of men's suits did not influence the overall WF_EU, the lining dyeing and finishing process of 0.40 kg PO₄³⁻ eq/1,000 pieces did affect the overall WF_EU. Furthermore, the WF_EU caused by the production of viscose staple fiber was 8.25 kg PO₄³⁻ eq/ton, of which the presoaking process had the largest WF_EU of 6.78 kg PO₄³⁻ eq/ton, accounting for 82% of the total WF_EU of viscose staple fiber production. The main pollutants were COD, BOD₅, and NH₃⁻N, which are mainly from a large amount of organic impurities such as cellulose in the wastewater (black liquor) from the presoaking process, with COD concentrations of as high as 8,000 mg/L (Zhang 1984; Ke 1987).

Figure 8 shows the WF_AC related to three types of viscose staple fiber garments and the production of viscose staple fibers. Here it can be seen that the WF_AC of the three types of garments was mainly affected by the viscose staple fiber production as well as the dyeing and finishing processes. The WF_AC of men's suits (a) and men's suits (b) were more than four and two times higher than that of blouses, respectively. The dyeing and finishing of men's suits included dyeing and finishing of fabric and lining, with the WF_AC of the lining dyeing and finishing accounting for 10% of their total WF_AC, while blouses only included fabric dyeing and finishing. The WF_AC in the dyeing and finishing stage was mainly derived from chloride. The WF_AC of the production of viscose staple fiber was mainly due to the fact that fibers are spun in an acid salt bath, with H₂SO₄ in the wastewater discharged from the two-bath, acid-station, and scouring processes (Shen & Patel 2010). The WF_AC of viscose staple fiber production was 77.98 kg SO₂ eq/ton, whilst the WF_AC of the scouring process and the two-bath process was 40.94 kg SO₂ eq/ton and 29.64 kg SO₂ eq/ton, respectively, accounting for 91% of the total viscose staple fiber production WF_AC.

As seen in Figure 9, the WF_AL of men's 100% viscose staple fiber suits (a) and men's 55% viscose staple fiber suits (b) were more than four and three times that of blouses, respectively. One reason for this is that men's (a) and (b) suits used approximately five and three times as much viscose staple fibers as blouses, respectively. A second reason is that the dyeing and finishing stages of men's suits included fabric and lining dyeing as well as finishing, while blouses only included fabric dyeing and finishing. The WF_AL of blouses, men's (a) suits, and men's (b) suits was 11.55, 55.90, and 38.33 kg OH⁻ eq/1,000 pieces, respectively. In summary, the WF_AL related to the production of viscose staple fiber was 40.25 kg OH⁻ eq/ton, with wastewater discharge WF_AL from the presoaking process being the highest at 37.54 kg OH⁻ eq/ton and accounting for 93% of the WF_AL of viscose staple fiber production. Water alkalization caused by the main pollutants NaOH and Na₂CO₃ originated mainly from the utilization of caustic soda in the viscose staple fiber production as well as dyeing and finishing process, functioning as a dissolution and dyeing auxiliary (Shen & Patel 2010; Wang 2017).

Figure 10 shows the WF_AET resulting from three types of viscose staple fiber clothing and the production of viscose staple fiber. Results from our analysis indicate that the WF_AET of blouses is caused by viscose staple fiber production, whilst the WF_AET of men's suits is caused by viscose staple fiber production as well as lining dyeing and finishing. The WF_AET of lining dyeing and finishing is mainly due to the presence of Cu in the wastewater, which originated from the use of metal dyes and played a significant role in increasing the dyeing rate from the dyeing process (Zhang et al. 2018). In our study, the WF_AET of the viscose staple fiber production was 3,594,564.4 m³ H₂O eq/t, with the main pollutant Zn²⁺ coming from the input of ZnSO₄ in the spinning stage. Some of the Zn²⁺ was discharged with the acid station wastewater, whilst some remained adhered to the fiber surface thereby entering the scouring stage and resulting in a higher Zn²⁺ content of the scouring wastewater (Shen & Patel 2010). The WF_AET of the scouring process was the largest with 2,876,296 m³ H₂O eq/t, accounting for 80% of the total viscose staple fiber production WF_AET.

The LCA polygons related to blouses, as well as men's suits (a) and (b), are shown in Figure 11, with areas of 9,187.29, 23,999.93, and 9,977.91, respectively. From these results, it can be seen that men's (a) suits reflected the highest environmental load of the three garment types in terms of water resources, followed by men's (b) suits and blouses.

In summary, the main results from the LCA polygon calculations are the following:

• (a)

  The WF_AET is the main driving factor for the environmental load in terms of water resources related to the production of the three types of clothing. The viscose staple fiber production stage had the biggest impact on the WF_AET and the WF_AET of men's suits was approximately three to five times that of blouses.

• (b)

  The WF_SC is the secondary driving factor related to the environmental load in terms of water resources related to the three types of garments. However, there are differences among three types that caused water scarcity. In terms of blouses, it is mainly influenced by the washing of blouses by consumers. With respect to men's suits, it is attributed to the viscose staple fiber production as well as dyeing and finishing. The WF_SC of the viscose staple fiber production accounted for approximately 74% of the total WF_SC of the men's suits (a) and 61% of the total WF_SC of the men's suits (b).

• (c)

  The WF_AC and WF_AL had relatively smaller impact on the environmental load in terms of water resources related to the three types of garments compared with the two indicators mentioned above. The water acidification of the three types of clothing stemming from the production of viscose staple fiber was mainly due to H₂SO₄ in the wastewater discharged from the two-bath, acid-station, and scouring processes. Furthermore, it is the combined efforts of base input in the production of viscose staple fiber and fabric dyeing and finishing that caused water alkalization. Apparently, the WF_EU had the smallest impact on the size of the LCA polygon area. The water eutrophication was caused by the chemicals used in the production and consumption processes. Therefore, measures can be taken to reduce the use of chemicals and control pollution can effectively reduce the environmental load in terms of water resources by improving production and post-processing technology or adjusting product development strategies.

The LCA polygon of each production process of viscose staple fiber is shown in Figure 12, and the areas of presoaking, washing, stock solution, two-bath, acid-station, and scouring were 13.67, 0.52, 3,121.60, 292.86, 433.55, and 5,536.03. From our results, it can be seen that the scouring process showed the highest environmental load in terms of water resources followed by the stock solution, acid-station, two-bath, presoaking, and washing process. In summary, the main results from our LCA calculations are the following:

• (a)

  The scouring process has four types of environmental impacts, with the actual value of each quantitative indicator being relatively large, resulting in the highest environmental load in terms of water resources.

• (b)

  The highest water consumption and wastewater emission was related to the presoaking process, with wastewater containing a large amount of COD, BOD₅, and NaOH, resulting in the largest WF_SC, WF_EU, and WF_AL. However, as the presoaking process only involved these three types of environmental impacts, it only ranked fifth in terms of the environmental load related to water resources.

Therefore, our results indicate that the magnitude of the environmental load in terms of water resources is not only related to the actual value of the environmental impact quantitative indicators, but also to the number of environmental impact types involved. Industrial wastewater pollutants often exhibit diverse characteristics, which explains why traditional wastewater treatment models that focus on large quantities of conventional pollutants or heavy metals with high microtoxicity often result in a one-off treatment of wastewater and ignore the potential environmental impacts of other pollutants. To better reduce the environmental load related to water resources, wastewater treatment models should focus on the different characteristics of industrial wastewater pollutants.

The following conclusions can be drawn from our investigations and results:

• (a)

  Sub-module calculations related to the water footprint of viscose fiber clothing showed good results in terms of calculation accuracy and the identification of various pollution factors and sources. Viscose staple fiber production showed the most significant environmental load in terms of water resources with its water footprint accounting for more than 50% of the total water footprints of the three types of clothing.

• (b)

  In this study, the viscose staple fiber production as well as fabric dyeing and finishing processes showed the highest water alkaline footprint with NaOH and Na₂CO₃ being the main pollutants. The water alkaline footprints related to blouses as well as men's (a) and (b) suits were 11.55, 55.90, and 38.33 kg OH^-eq/1,000 pieces, respectively.

• (c)

  The results from our calculation of the environmental load in terms of water resources were directly related to the number of types of environmental impacts and the actual value of the quantitative indicators. The water degradation footprint had a greater impact than the water scarcity footprint on environmental load in terms of water resources, with the water ecotoxicity footprint being the main driving factor, and Zn²⁺ and CS₂ the main pollutants.

• (d)

  According to the results from our calculations of environmental load in terms of water resources for viscose staple fiber clothing, we suggest relevant management departments adjust pollutant discharge limit standards or increase the list of wastewater pollutant discharge limits as appropriate. Furthermore, we suggest that, based on the results of certain calculations and analyses, relevant production departments carry out technological improvements such as the recovery rate of black liquor in the presoaking process, improving the production processes and equipment to reduce the input of water and chemicals such as ZnSO₄ and other additives, appropriately adjusting the product development plan or production ratio to reduce the viscose staple fiber content of the product, and the development of household dry-cleaning machines.

The authors are grateful to the Zhejiang Provincial Natural Science Foundation of China (LY20G030001), the National Key R&D Program of China (2018YFF0215703), Excellent Graduate Thesis Cultivation Foundation (201920401009), Science and Technology Innovation Activities of University Students in Zhejiang Province (2020R406074) for providing funding support to this research.

All relevant data are included in the paper or its Supplementary Information.