Oxidative Degradation of Lurgi Coal Gasification Wastewater: Optimization Using Response Surface Methodology

摘要

Lurgi coal-gasification wastewater with an initial total organic carbon (TOC) of 5000 mg/L and ammonia nitrogen (NH_3-N) of 1500 mg/L was treated by supercritical water oxidation technology to make the effluent reach the national wastewater discharge standard I in China (TOC ＜ 20 mg/L, NH_3-N ＜ 15 mg/L). Response surface methodology method combined with central composite design and regression analysis were used to statistically analyze and optimize the operating parameters. The effect degree of the parameters on TOC and NH_3-N decreasing were in the following order: temperature (440-600℃) ＞ oxygen ratio (OR) (1-5) ＞ reaction time (20-300 s) ＞ pressure (22.2-30.2 MPa). The interactive effects of temperature and OR were significant on both COD and NH_3-N decreasing. The optimum conditions within experimental ranges were: 540℃, 27 MPa, OR of 3, and reaction time of 219 s. Under these conditions, the experimental TOC and NH_3-N decreasing efficiencies were 99.69 and 99.07%, respectively. The effluent can reach the waste-water discharge standard 1. The main intermediate products of the pollutants during the oxidation process were detected and possible degradation pathways were also proposed.