In this study, the impact of NaOH on the hydrothermal oxidation of guaiacol was investigated. It was found that NaOH significantly accelerated the production of formic acid and acetic acid with H2O2 or CuO as the oxidant. With the strong oxidant, H2O2, the highest acetic acid yield (15.73%) and formic acid (5.64%) were obtained at 300 °C for 90 s with NaOH 1.0 mol·L−1 and a 100% H2O2 oxygen supply. In comparison, with CuO as the oxidant, the highest values of acetic acid (13.42%) and formic acid (4.21%) were acquired at 250 °C for 6 h with NaOH 1.0 mol·L−1. Formic acid and acetic acid were generated through the oxidation of intermediates, such as levulinic acid, fumaric acid, maleic acid, etc. These results demonstrated that NaOH catalytic hydrothermal oxidation has potential for the production of value-added chemicals from biomass materials. When CuO is used as the oxidant, this process could also be used as a green method for copper smelting along with the utilization of lignin biomass.

In this work, wet oxidation and catalytic wet oxidation of pharmaceutical sludge using homogeneous and heterogeneous catalysts were investigated. The results indicate that wet oxidation is a promising method for the highly efficient degradation of pharmaceutical sludge. Under optimal conditions, the highest removal efficiencies of volatile suspended solids (VSS) 86.8% and chemical oxygen demand (COD) 62.5% were achieved at 260 °C for 60 min with an initial oxygen pressure of 1.0 MPa. NaOH exhibited excellent acceleration performance on the VSS removal. The highest VSS removal efficiency of 95.2% was obtained at 260 °C for 60 min with an initial oxygen pressure of 1.0 MPa and 10 g·L−1 of NaOH. By using a Cu–Ce/γ-Al2O3 catalyst, the highest removal rates of VSS 87.3% and COD 72.6% were achieved at 260 °C for 60 min with an initial oxygen pressure of 1.0 MPa and 10 g·L−1 of catalyst. The wet oxidation reaction can be maintained itself owing to the exothermic heat. The produced low-molecular-weight carboxylic acids have potential commercial utilization as organic carbon sources in the biological wastewater treatment processes. The inorganic residues can be utilized for the building materials production. These results implied that the catalytic wet oxidation is a promising method for the volume reduction and resource utilization of pharmaceutical sludge.