Controlled anaerobic water retting of flax as part of an innovative biorefinery process

Abstract

Due to the increased interest in durable, sustainable and recyclable fabrics, natural fibres are currently experiencing a renaissance. This study investigated controlled anaerobic water retting of flax as a potential process step in a future biorefinery, allowing the simultaneous production of high-quality fibres, stalks, organic acids or biomethane. Anaerobic water retting of flax resulted in the formation of a retting effluent containing 1.745 ± 605 mg L−1 acetic acid, 1.051 ± 354 mg L−1 butyric acid, 145 ± 38 mg L−1 propionic acid and 190 ± 96 mg L−1 caproic acid. Furthermore, 38.0 ± 7.2 mL g oDM−1 hydrolysis gas with 41.6–54.2% CO2 and 45.3–58.1% H2 was produced. Anaerobic digestion tests resulted in a specific biomethane potential range of 221 ± 14 to 261 ± 13 mL CH4 g COD−1 for the retting effluent. The average yield of fibres and stalks from flax was 22% and 51%, respectively. The flax fibres obtained were mainly composed of cellulose (75.1% of dry matter). Hemicellulose and lignin accounted for 7.1 ± 0.3% and 1.9 ± 0.3%, respectively. The tensile strength and Young’s modulus of the fibres were 354 ± 130 MPa and 35 ± 8 GPa, respectively. The annual product yields for a cultivation area of 1 ha of flax were estimated at 0.67 t of fibres, 1.55 t of stalks and 117 m3 biomethane.