Electrochemical oxidation of lignin by two typical electrodes: Ti/SbSnO2 and Ti/PbO2

• Electrochemical oxidation was used as the pretreatment of biotreatment.
• Possible lignin degradation mechanism has been proposed.
• Biodegradability enhancement depended strongly on the electrode material.
• Selective and nonselective electrochemical oxidation models were proposed.

The titanium based antimony doped tin dioxide electrode (Ti/SbSnO2) and titanium based lead dioxide electrode (Ti/PbO2) were used in the pre-degradation of a sodium lignosulphonate solution (2000 ppm). The performances of these two electrodes were compared by evaluating the change of water quality parameters (COD, biodegradability) and UV–Vis absorption. The parameters that influence effectiveness and efficiency of the pretreatment were investigated, including applied current, passed electric charge, solution temperature, and supporting electrolyte. Moreover, IR spectra, and GC–MS analysis were used for products analysis in order to explore the degradation mechanism. Results showed that the electrochemical oxidation is a promising approach for the pretreatment of lignin, and the aerobic or anaerobic biodegradability was enhanced significantly. Quinones and low-chain carboxylic acid were identified as important intermediate and main products, respectively. The oxidation effectiveness depends strongly on the electrode material. The Ti/SbSnO2 exhibited a better ability of UV–Vis absorption decrease and COD removal, while the Ti/PbO2 had a better capability to enhance biodegradability. Such differences could be interpreted by the theory of selective and nonselective oxidation.