*3.1.3 Bioconversion processes*

Biodegradation can be featured as a method used by nature to recycle waste and to break down organic materials into compounds by microorganisms such as bacteria, fungi, insects, worms, and others. Through biodegradation processes, it is possible for nature to clean up wastes, to provide nutrients for the growth of new lives, and to produce the energy necessary for various biological processes [46]. Biochemical transformation via fermentation is an attractive way for utilizing recycling textile waste. Cotton is typically composed of 88–96% cellulose, and it is possible to hydrolyze waste cotton by enzymatic or chemical methods to obtain glucose and then ferment it into value-added products. Biogas production from textile waste via anaerobic digestion is an alternative route to utilize solid waste from textile industry. Organic compounds in solid waste can be used as a raw material to produce desired products via bioconversion processes. On the contrary, thermal and chemical processes can convert both organic and inorganic compounds to value-added products [47].

#### *3.1.4 Thermal and thermochemical conversion processes*

Conventional thermal processing refers to the combustion of solid waste and its conversion into energy. Since solid waste from the textile industry contains a high

energy content, it can be used as a raw material to generate heat energy [47]. Solid waste from the textile industry can be used as a raw material to produce briquette. The thermal processes that are performed at high temperature with inadequate oxygen could generate carbon monoxide, which is a greenhouse gas. Therefore, a thermochemical conversion process, such as pyrolysis, is applied. Pyrolysis is referred to the decompositional process with high temperature in the absence of oxygen condition [47]. Products from pyrolysis are various, such as activated carbon fiber, char, bio-oil, and syngas. The variation of product is related to pyrolysis condition.

Denim jeans are characterized by thick lapped seams that create problems during shredding and carding processes. The presence of elastane is another problem. It is more convenient to separate it before shredding and cutting, but this can only be done by chemical recycling. Recycling different colored jeans together results in a multicolored yarn that can create problems in dyeing. Recycled fibers might not meet the quality of virgin ones and could not be spun or woven properly.

*Understanding Denim Recycling: A Quantitative Study with Lifecycle Assessment Methodology*

Life cycle assessment (LCA) is a methodology where the environmental performance of a product or service is assessed starting from the raw material extraction point to the end of life of that product/service, i.e., from "cradle to grave." The

For a pair of denim jeans, the life cycle (**Figure 2**) starts with the production

methodology of LCA is defined under the ISO 14040/44 Standard [50].

of raw materials such as fibers and chemicals. These materials are then transported to fabric manufacturer and processed to become a fabric. During fabric production, energy and water are consumed in addition to raw materials while emission to air and to water and production waste are generated. The following process for the fabric is garment manufacturing in which the fabric is cut, sewn, washed, and accessorized (rivets, buttons, etc.) according to the design. Finally, the finished garment is sent to a warehouse or directly stores to be

sold. After it is bought, the garment is washed and dried (or dry-cleaned depending on its nature) many times throughout its use phase. When it completes its life span, the garment has various "end of life" scenarios such as

recycling, reused, refurbished, and disposed in landfill or incinerated, etc., which

Life cycle assessment (LCA) helps us analyze the environmental performance of denim production in a transparent and systematic way and identify the hot

**4. Life cycle assessment of a denim fabric**

*DOI: http://dx.doi.org/10.5772/intechopen.92793*

were discussed in the previous sections.

spots.

**Figure 2.** *Lifecycle of a jean.*

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