Removal of chemical oxygen demand and ammonia nitrogen from high salinity tungsten smelting wastewater by one-step electrochemical oxidation: From bench-scale test, pilot-scale test, to industrial test

In recent years, electrochemical oxidation (EO) shows the characteristics of green and high efficiency in removing chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) from wastewater, which has been favored by researchers. However, at present, most of current studies on EO remain in laboratory stage, reports about pilot-scale or even industrial tests with large treatment capacity are few, which slowing down the use of the advanced technology to practical application. In this study, bench-scale tests, pilot-scale tests (treatment capacity 200-500 L/h), and industrial tests (treatment capacity 100 m3/h) were carried out by EO technology in view of the characteristics of tungsten smelting wastewater (TSW) with high salinity (NaCl), COD, and NH3-N. Results showed that the removal of COD and NH3-N was a competitive reaction in the EO process, and COD could be removed more preferentially than NH3-N. When NH3-N content was low, the influent pH had a minimal effect on its removal, and when NH3-N content was high, increasing the influent pH was beneficial to its removal. Industrial tests showed that the one-step removal of COD and NH3-N in TSW met the standard, and the power consumption per cubic meter of wastewater was only 4.2 kW h, and the treatment cost was much lower than the two-step process of "breaking point chlorination to remove NH3-N and adding oxidant to remove COD". This study has successfully realized industrial application of EO technology in TSW treatment for the first time and provided a successful case, which is helpful to accelerate the popularization and application of this technology in the field of high salinity organic ammonia nitrogen wastewater treatment.