Discovering the Importance of ClO~· in a Coupled Electrochemical System for the Simultaneous Removal of Carbon and Nitrogen from Secondary Coking Wastewater Effluent

摘要

Inorganic constituents in real wastewater, such as halides and carbonates/bicarbonates, may have negative effects on the performance of electrochemical systems because of their capability of quenching HO~·. However, we discovered that the presence of Cl~- and HCO_3~- in an electrochemical system is conducive to the formation of ClO~·, which plays an important role in promoting the simultaneous elimination of biorefractory organics and nitrogen in secondary coking wastewater effluent. The 6-h operation of the coupled electrochemical system (an undivided electrolytic cell with a PbO_2/Ti anode and a Cu/Zn cathode) at a current density of 37.5 mA cm~(-2) allowed the removal of 87.8% of chemical oxygen demand (COD) and 86.5% of total nitrogen. The electron paramagnetic resonance results suggested the formation of ClO~· in the system, and the probe experiments confirmed the predominance of ClO~·, whose steady-state concentrations (8.08 × 10~(-13) M) were 16.4, 26.5, and 1609.5 times those of Cl_2~(·-) (4.92 × 10~(-14) M), HO~· (3.05 × 10~(-14) M), and Cl~· (5.02 × 10~(-16) M), respectively. The rate constant of COD removal and the Faradaic efficiency of anodic oxidation obtained with Cl~- and HCO_3~- was linearly proportional to the natural logarithm of the ClO~· concentration, and the specific energy consumption was inversely correlated to it, demonstrating the crucial role of ClO~· in pollutant removal.