Researchers based in New Zealand and Australia have found that digesting discarded textiles alongside food waste can raise renewable methane output, offering textile makers and waste operators a route to cut landfill and incineration.
The study, by teams at the University of Auckland and James Cook University, tested cotton, polycotton and wool mixed with food waste in mesophilic batch reactors. It was accepted on July 3, 2026, by the journal Waste Disposal & Sustainable Energy.
About 92 million tonnes of textile waste are disposed of every year, and landfilling, incineration and recycling remain costly or environmentally problematic, the researchers said. Textiles are hard to digest alone because of imbalanced carbon-to-nitrogen ratios, tough keratin in wool and non-biodegradable polyester in blended fabrics.
Cotton performed best on its own, yielding 103 millilitres of methane per gram of volatile solids. Adding food waste lifted results, with the highest yield of 129.7 mL per gram coming from a 6:1 cotton-to-wool blend that had a balanced carbon-to-nitrogen ratio of 20.63.
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Synergy was strongest when food waste made up more than 80% of the feedstock, particularly with cotton. A 1:4 cotton-to-food-waste blend produced 111 mL per gram, and higher food waste shares shortened lag phases and sped up biogas production.
Polycotton and wool, by contrast, showed antagonistic effects. A 1:1 wool-to-food-waste mix produced almost no methane because of ammonia inhibition, while residual fatty acids and free ammonia above inhibitory thresholds hampered performance in those blends.
The authors said co-digestion works best when food waste dominates and the carbon-to-nitrogen ratio stays within an optimal window. Cotton-rich mixtures look most promising, while polycotton and wool need pretreatment or fibre separation, such as thermal hydrolysis or solvents that strip out polyester.
Most co-digestion treatments produced free ammonia within safe biofertiliser limits, the study also found.