Biogenic coal-to-methane conversion can be enhanced with small additions of algal amendment in field-relevant upflow column reactors

•Algal amendment increased biogenic coal-to-methane conversion.•Produced gas exceeded full conversion of amendment, indicating coal-to-CH4 conversion.•13C analysis indicated <4% of amendment was converted to measurable gases.•A larger fraction of CO2 sorbed to coal than did CH4.•Continuous flow reactors appear to overcome some limitations of coal batch reactors.