Treatment of high strength coking wastewater by supercritical water oxidation

Two kinds of coking wastewater were treated by supercritical water oxidation (SCWO) in a continuous-flow reactor using hydrogen peroxide (H2O2) as an oxidant. These wastewater contained high concentrations of ammonia nitrogen (NH3–N), phenol, chemical oxygen demand (COD) and inorganic salts. A salt separator was applied for the separation of salts in the SCWO process to solve the problem of reactor plugging due to salt precipitation. Experiments were conducted to investigate the effects of the temperature, pressure, excess oxygen and residence time on the destruction of pollutants (includes NH3–N, phenol and COD). The efficiency of the salt separator was also investigated. Results showed that both phenol and COD can be easily destructed in SCWO process. NH3–N was inert and its conversion increased noticeably as the temperature and excess oxygen increased. At the condition of 650 °C and 300% excess oxygen, the conversions of all pollutants were over 99.94% and the effluent met the first grade discharge standard of China. The results also indicated that the efficiency of salt separation increased with an increasing temperature. By controlling the temperature of salt separator at 600 °C, more than 87% of the salts were separated from coking wastewater.