Integrated valorization of hop vine chaff silage by steam pulping and explosive decompression enabling coupled fiber production, methane generation and viroid mitigation

This study evaluated steam-assisted pulping with explosive decompression (SE) as an integrated strategy for fractionating ensiled hop vine chaff into papermaking fibers and a methane-potential-rich liquid fraction for anaerobic digestion, while reducing hop latent viroid RNA. The process was investigated using a central composite design across temperature (140–170 °C), holding time (10–30min), and dry matter content (10–20%). The treatment caused a redistribution of organic matter into the liquid phase, which showed a high specific methane yield of 0.359 ± 0.014 m 3 CH 4 kg −1 ODM, while the solid fraction showed a lower yield of 0.176 ± 0.015 m 3 CH 4 kg −1 ODM. Up to 30.1% of the total methane potential was recovered in the liquid phase, with temperature and dry matter content identified as controlling factors. Fiber quality improved markedly, with tear length increasing from 0.15 ± 0.03 km in untreated silage to a maximum of 1.35 ± 0.06 km after treatment. Acetic acid recovery increased to 146 ± 23%, indicating hydrothermal formation of soluble intermediates and contributing to lower liquid phase pH. Thermal treatment substantially reduced detectable hop latent viroid RNA, and no viroid RNA was detected after anaerobic digestion of the liquid fraction. Pilot-scale validation confirmed process transferability. Overall, steam-assisted pulping represents a promising approach for the coupled production of papermaking fibers and methane-rich process liquor from hop vine chaff within a decentralized biorefinery concept. However, overall methane potential recovery after SE was limited to 79.4 ± 5.9%, and further fiber optimization or blending with other pulps would be required, while residual metal fragments remain a practical challenge for feedstock preparation.