Application of hydrothermal treatment to affect the fermentability of Pinus radiata pulp mill effluent sludge

•Significant removal of lignin and hemicellulose components.•Reduction in the concentration of extractive compounds, such as resin acids, >99%.•Some resistance to degradation of the cellulose component.•No demonstrable increase in biological VFA or methane after pre-treatment.

A hybrid technique incorporating a wet oxidation stage and secondary fermentation step was used to process Pinus radiata pulp mill effluent sludge. The effect of hydrothermal oxidation at high temperature and pressure on the hydrolysis of constituents of the waste stream was studied. Biochemical acidogenic potential assays were conducted to assess acid production resulting from anaerobic hydrolysis of the wet oxidised hydrolysate under acidogenic conditions. Significant degradation of the lignin, hemicellulose, suspended solids, carbohydrates and extractives were observed with wet oxidation. In contrast, cellulose showed resistance to degradation under the experimental conditions. Extensive degradation of biologically inhibitory compounds by wet oxidation did not show a beneficial impact on the acidogenic or methanogenic potential compared to untreated samples.