Nitrogen removal mechanisms and effect enhancement of N-containing organic matters in supercritical water

Nitrogenous organic compounds in wastewater are highly toxic and harmful to ecological environment. Supercritical water oxidation (SCWO) is a promising technology for removing nitrogenous organic compounds efficiently with the formation of environment-friendly reaction products. However, few studies have been conducted to systematically summarize denitrogenation mechanisms of organic matters in supercritical water. In this work, the effects of operating parameters on nitrogen removal are analyzed. Denitrogenation mechanisms of five main types of N-containing organic matters (i.e., amino, nitro, diazonium, nitrogen heteroatom and mixed groups) in SCWO are discussed deeply. The results show that organic matters with different N-containing functional groups produce various intermediates, such as NH₃–N and NO₃⁻. The conversion rate of intermediates to N₂ affects the degradation rate of nitrogenous organic matters. It is necessary to incorporate enhanced technologies in SCWO, such as using catalysts, adding auxiliary fuels and sorption. Catalysts allow reactions to proceed under mild SCWO conditions and convert organic nitrogen to harmless products. Oxidation with auxiliary fuels can provide free radicals and reaction heat for nitrogen removal from organic matters.