Reduction of inhibitory effect of lignin via degradation and improvement of anaerobic digestion performance of maize straw by oxidative pretreatment with Fe2+-activated persulfate

The stable aromatic structure of lignin is one of the factors that limit the utilization of maize straw. In this study, pretreatment with Fe2+/persulfate (PS) was used to remove lignin while reducing the contents of lignin derivatives produced in the pretreatment. In comparison with the original straw, the lignin and hemicellulose contents of the pretreated straw were reduced to 54.58 % and 72.91 %, respectively. In the Fourier transform infrared spectrum, the characteristic peaks of both syringyl and guaiacyl units were significantly weaker after pretreatment with Fe2+/PS, which indicated that the pretreatment destroyed the structure of lignin. The pretreatment products were examined by gas chromatography–mass spectrometry, and the results indicated that the present pretreatment method reduced the contents of soluble inhibitors produced from lignin. After pretreatment, only levulinic acid, 4-hydroxybenzaldehyde, vanillin, 4-hydroxybenzoic acid, xylose, coumaric acid, and 4-coumaric acid were produce, whereas more than 20 soluble inhibitors are known to be produced from lignin. In anaerobic fermentation experiments, in comparison with the control group, the pretreated group exhibited higher gas production (an increase of 18.09 %) and a significantly higher methane content. This indicates that pretreatment with Fe2+/PS can improve the efficiency of the resource utilization of maize straw by degrading lignin.