Simultaneous total organic carbon and humic acid removals for landfill leachate using subcritical water catalytic oxidation based on response surface methodology

Total organic carbon (TOC) and humic acid (HA) are very strong contamination potential components in landfill leachate, which were treated by subcritical water catalytic oxidation technology with a batch reactor. Response surface methodology (RSM) was used to evaluate the effects of temperature (180–260 °C), peroxide coefficient (2–3), pH (4–8), and their interactive effects on TOC and HA removal efficiencies. The results demonstrated that RSM was an effective method for the optimization of experimental parameters in the treatment of landfill leachate. The results indicated that the effects on TOC removal efficiency were in the order temperature > pH > peroxide coefficient and that the order on HA removal efficiency was pH > temperature > peroxide coefficient. The experiments were performed in different heterogeneous (CuO, ZnO) and homogeneous (CuSO₄·5H₂O, FeSO₄·7H₂O, and Cu(NO₃)₂·3H₂O) catalysts; the optimal parameters within the experimental range were temperature of 260 °C, pH of 4.0, peroxide coefficient of 3.0, and Cu(NO₃)₂·3H₂O of 0.03 M. Under the optimum conditions, the TOC and HA removal efficiency can reach 86.42 and 66.10 %, respectively. Using gas chromatography coupled with mass spectrometry (GC-MS) to analyze the composition of liquid, 89 and 76 kinds of principal organic components were detected in the landfill leachate before and after treatment, respectively. In the raw landfill leachate, there were five kinds of organic matters, which belong to the US Environmental Protection Agency (USEPA) list of priority environmental pollutants. After the treatment, the toxic organics were not detected. In summary, the results suggested that the subcritical catalytic oxidation technology can be used as an effective method for the treatment of landfill leachate.