Toward the complete utilization of rice straw: Methane fermentation and lignin recovery by a combinational process involving mechanical milling, supporting material and nanofiltration.

•The complete utilization of rice straw was aimed.•Methane fermentation was performed in a bioreactor containing supporting material.•Mechanical milling (1.9MJ/kg-rice straw) increased methane production (3.5MJ).•Nanofiltration recovered lignin that was released from the residue.•2D NMR showed that lignin aromatic components were recovered.