New alternative energy pathway for chemical pulp mills: From traditional fibers to methane production

•Brown, oxygen delignified and bleached pulp were tested for methane potential.•Highest methane yields correspond to fiber samples, particularly of bleached pulp.•Degradability was found to be in the following order: bleached>brown>delignified.•Energy and cost estimations were evaluated. Chemical pulp mills have a need to diversify their end-product portfolio due to the current changing bio-economy. In this study, the methane potential of brown, oxygen delignified and bleached pulp were evaluated in order to assess the potential of converting traditional fibers; as well as microcrystalline cellulose and filtrates; to energy. Results showed that high yields (380mL CH4/gVS) were achieved with bleached fibers which correlates with the lower presence of lignin. Filtrates from the hydrolysis process on the other hand, had the lowest yields (253mL CH4/gVS) due to the high amount of acid and lignin compounds that cause inhibition. Overall, substrates had a biodegradability above 50% which demonstrates that they can be subjected to efficient anaerobic digestion. An energy and cost estimation showed that the energy produced can be translated into a significant profit and that methane production can be a promising new alternative option for chemical pulp mills.