Experimental research on medical wastewater disposal by supercritical water oxidation

The oxidation of medical wastewater in supercritical water was investigated experimentally in a batch reactor. The results show that the COD removal rate of medical wastewater obviously increases with the increases of reaction time and temperature rise; whereas it scarcely changes with pressure in the range of 25-27 MPa. Both MnSO₄ and CuSO₄ are active catalysts for COD removal rate of the wastewater, and CuSO₄ offers greater influence when reaction time is less than 7 min. Ammonia-nitrogen mass concentration has no evident variation under various reaction conditions. The experimental data under the conditions of 420-480°C, 25 MPa, and oxidant stoichiometric ratio 300% were used to fit the rate of reaction in a non-linear regression analysis, with the parameter values determined as follows: activation energy (170.025±11.692)kJ/mol, pre-exponential factor (4.98±0.01)×10⁸ min^-1·mg^-0.918·L^0.918 and reaction order of wastewater (based on COD) 1.918±0.256, and the confidence level of such kinetics modeling is 93%. Based on the enthalpy changes of the reaction mediums, the reaction heat of the medical wastewater in supercritical water oxidation (SCWO) was studied. The results indicate that the reaction heat is 296.63 kJ/kg when the organics are completely oxidized.