In the present study, enhanced wet oxidation of excess sludge from pharmaceutical wastewater by NaOH as an alkaline homogeneous catalyst was investigated. The experiments were carried out in a stainless-steel batch autoclave reactor. The highest volatile suspended solids (VSS) removal rate, 95.2%, was achieved at 260 °C within 60 min with an initial oxygen pressure of 1.0 MPa and NaOH 0.5 g·L⁻¹. Simultaneously, the chemical oxygen demand (COD) removal rate of 57.3% was reached. The increase in volatile fatty acids (VFAs) demonstrated that the degradation of sludge was greatly accelerated by NaOH. Interestingly, the production of acetic acid, an intermediate by-product generated from the oxidation of organic compounds, increased significantly. These results illustrated that NaOH is a promising catalyst for the utilization of wet oxidation liquid of excess sludge as a carbon source for the treatment of wastewater.

The performance of catalytic wet oxidation of excess activated sludge derived from pharmaceutical wastewater treatment over a Cu/γ-Al₂O₃ catalyst was investigated. The experiments were performed with a stainless steel autoclave reactor by using the prepared Cu/γ-Al₂O₃ catalyst. The effects of reaction conditions were examined, including additional catalyst amount, reaction temperature, time, and initial oxygen pressure. Results demonstrated that the catalyst, fabricated via co-precipitating method, has excellent catalytic performance. Through the study on condition optimization, the highest removal rates of volatile suspended solids (VSS, 93.6%) and total chemical oxygen demand (TCOD, 76.5%) were acquired with the reaction temperature 260 °C, time 60 min, initial oxygen pressure 1.0 MPa, and the prepared catalyst 5.0 g/L. The volatile fatty acids (VFAs) produced from the wet oxidation of sludge included acetic (mainly), propanoic, isobutyric, and isovaleric acids, which have great potential for the utilization as organic carbon sources in biological wastewater treatment plant. These results demonstrated that the proposed method, catalytic wet oxidation over Cu/γ-Al₂O₃ catalyst, is effective for treating excess activated sludge and resource utilization of organic carbon in the sludge.

The wet oxidation of pharmaceutical sludge for the treatment and production of value-added materials was investigated. The experiments were carried out in a stainless-steel autoclave reactor with chemical synthetic pharmaceutical sludge. The highest removal rate of total suspended solids (90.1%) and volatile suspended solids (98.4%) was achieved at 260 °C for 60 min with an initial oxygen pressure of 0.8 MPa. Simultaneously, the total chemical oxygen demand removal rate (78.7%) and the soluble chemical oxygen demand removal rate (81.6%) were obtained. The volatile fatty acid concentration—including acetic acid, propanoic acid, isobutyric acid and isovaleric acid—increased to 4819 mg/L with pH 12.56, which indicated the possibility of improving the quality of wet oxidized sludge solution as a potential carbon source by adding reagents. Scanning electron microscopy images showed that the sludge became a loose porous structure after wet oxidation, which is beneficial for dewatering performance. Energy dispersive spectroscopy images illustrate that carbon elements in sludge migrate from solid to liquid phases during the wet oxidation process. These results provide meaningful data for the design of further works and demonstrate that wet oxidation is a promising method for the treatment of pharmaceutical sludge, and the produced volatile fatty acids, including acetic acid and propanoic acid, are potential carbon sources for the biological treatment of wastewater.