Simultaneous carbon capture and nitrogen removal during supercritical water oxidation

Carbon dioxide emission and nitrogen pollution caused by nitrogen-containing wastes have become global environmental issues in recent years. To simultaneously reduce the discharge of carbon dioxide and reactive nitrogen during the conventional supercritical water oxidation (SCWO), we have developed an advanced SCWO process involving the treatment of nitrogen-containing wastewater. By introducing Ca(NO3)2 to the reactor inlet and Ca(OH)2 to the reactor outlet, 94% of the carbon and 95% of the reactive nitrogen in acrylonitrile (C3H3N) were simultaneously converted to solid CaCO3 and innocuous nitrogen gas at 250 bar and 420 °C. In situ formed CaCO3 in the reactor acted as a catalyst for the decomposition of acrylonitrile. Furthermore, CaCO3 with average particle size of 1.72 μm can either be used for industrial applications or reconverted to Ca(NO3)2, which can be recycled to the reactor, and carbon dioxide, which can be injected into deep geological formations. This novel method provides inherently cleaner SCWO process which offers an attractive solution for the capture of carbon dioxide and reduction of total nitrogen (TN) from nitrogen-containing wastewater, as well as the removal of total organic carbon (TOC).

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► The conventional supercritical water oxidation (SCWO) emits carbon dioxide.
► An advanced SCWO without carbon dioxide emission and nitrogen pollution is proposed.
► Ca(NO3)2 and Ca(OH)2 were fed to the reactor (250 bar, 420 °C, 10 s) continuously.
► 94% carbon and 95% reactive nitrogen of acrylonitrile were converted to CaCO3 and N2.
► This in situ formed CaCO3 during SCWO acts as a catalyst to decompose acrylonitrile.