4. Conclusion
Poplar processing residues are good substrate for methane production after NaOH treatment. The highest methane production of 271.9 L/kg VS was obtained at conditions of 35 g/L after 5.0% NaOH treatment, which was 113.8% higher than untreated one. However, methane production of 3.0% NaOH at the same concentration was 256.6 L/kg VS and only 12.1% less than that of the 5.0% NaOH. Con- sidering the costs efficiency, the 3.0% NaOH might the optimal dose for practical applications. Changes of chemical component and structures were beneficial for the improvement of biodegradability and enhancement of methane production.