The accumulation of post-consumer textile waste (PCTW) in municipal landfills has emerged as a significant challenge to a more sustainable economy. The Environmental Research and Education Foundation (EREF) recently released a new Grant Report entitled Converting Textile Waste to Pumpable Slurry for Biogas Production. The report addresses this pressing issue by exploring innovative solutions for the bioconversion of PCTW.
Led by Dr. Sonja Salmon, and funded by EREF, a research team at North Carolina State University investigated a potential new textile recycling method. By focusing on the transformation of common textile materials like cotton and polyester/cotton blends into valuable biogas through enzymatic hydrolysis, it delves into a novel approach that not only aims to mitigate the environmental impact of textile waste but also contributes to the generation of sustainable energy resources.
Enzymatic hydrolysis is a biochemical process where enzymes are used to break down complex molecules into simpler ones through the addition of water. In the context of this research, enzymatic hydrolysis specifically refers to the use of cellulase enzymes to decompose the cellulose in cotton textiles. By employing enzymatic hydrolysis, the research team successfully separated cotton fibers from polyester fibers and created a pumpable slurry that could be used for biogas production.
Dr. Salmon’s team focused on various cotton and cotton blend textiles, which were processed in different forms to simulate real-world waste. One of the primary variables studied was the effect of different dye treatments on the hydrolysis process and how they affected the breakdown of cotton fibers into pumpable slurries. Cotton fabrics were treated with different types of fiber reactive dyes which are known for their complex molecular structures that can hinder enzyme activity.
In addition to dyes, the team also explored the impact of other fabric treatments, particularly durable press finishes. These finishes, commonly applied to textiles to reduce wrinkling, involve the use of cross-linking agents that can significantly impede the enzymatic degradation of cotton. They assessed the effectiveness of enzymatic hydrolysis in breaking down these chemically treated fibers and explored various pre-treatment methods to enhance the process. The outcomes demonstrated the necessity of adapting the enzymatic treatment to accommodate the chemical complexity introduced by dyes and finishes.
The project yielded several promising findings, most notably the capability to convert both dyed and undyed cotton fabrics into slurries under mild conditions (pH 5 and 50°C) within 24 hours. When tested in lab scale anaerobic digesters by co-PI Dr. Doug Call’s team, the cotton fiber fragment (CFF) slurries did ultimately produce biogas, although methane production was lower than expected potentially due to a non-acclimated microbial sludge consortium. This suggests that the method could be viable with more research.
Researchers were able to cleanly separate cotton from cotton blends and synthetic fibers, thereby isolating pure synthetic fibers suitable for recycling. This not only underscores the efficiency of the process but also its potential to contribute to sustainable textile management.
Another important aspect of the research, led by co-PI Dr. Nelson Vinueza, was understanding the fate of dyes and chemicals in the process. The findings indicated that increased enzyme treatments led to higher concentrations of dye-related compounds in the slurries. However, these levels did not significantly impact the efficiency of the anaerobic digestion process, suggesting the presence of dyes and chemicals will not impede the bioconversion process.
While the initial project’s value proposition focused on biogas generation, a preliminary feasibility assessment suggested that savings from diverting waste from landfills, combined with the value of recycled synthetic fibers or potential value from CFFs, could offer a commercially favorable opportunity for the enzymatic fiber separation process.
“Complex problems like textile waste require creative and multidisciplinary solutions,” said Salmon, “we appreciate the support by EREF that allowed us to form such a team and make tangible progress on news ways to approach solid waste management.”
The implications of this research suggest that future textile waste could be managed by using enzymes to degrade organic fabrics, and the products of that process could be used to generate energy or other manufacturing inputs, and then recovering the synthetic fibers for recycling. This could represent a positive step toward both managing textile waste and generating renewable energy.