| Industrial wastewater contains large quantities of pollutants with high toxicity and low biodegradability. These pollutants are hard to be removed after traditional secondary biological treatments. The effluent of industrial wastewater plant after biological treatment still contains considerable concentrations of the toxic compounds, which has posed great challenges to environmental safety and public health. Therefore, the advanced treatment of industrial wastewater is urgently needed.Electrochemical technology is a significant advanced treatment technology. The effects of primary operational parameters on the performance of the electrochemical reactors were investigated in this study. The results showed that the best operational parameters in two-dimensional electrode system were current density=5mA/cm2, with initial pH=8.7, without aeration and the electrodes distance =4cm. The best operational parameters in three dimensional electrode system were current density=5 mA/cm2, with initial pH=8.7, without aeration, the electrodes distance =12cm and the volume ratio of activated carbon and quartz sand=1:1. The removals of CODCr and NH3-N in the three-dimensional electrode system were higher than that in two-dimensional electrode system under the same conditions. The Instantaneous current efficiency (ICE) decreases with the increase in current density in both the two-dimensional electrode system and three-dimensional electrode system, and the Specific energy consumption (Esp) increases with the increase in current density in both systems. The degradation of CODCr fit pseudo-first-order kinetics, while the degradation of NH3-N fit pseudo-second-order kinetics under low current density in both systems.The removal of organics was mainly degraded by indirect oxidation in the two-dimensional electrode system. The reaction zone analysis showed that the pollutants were mainly degraded in the boundary layer between the electrode surface and the bulk solution. And the aeration decreased the thickness of the boundary layer, and resulted in performance decline of the reactor's.Acute biotoxicity of wastewater was found to increased rapidly (more than 95% inhibition) after 30 min in three-dimensional electrode system. And the acute biotoxicity was primarily caused by the generation of the oxidants (such as active chlorine). The concentration of total chlorine and free chlorine could reach as high as 3 and 1 mg/L, respectively during the treatment. On the other hand, the successful inactivation of the bacterium was observed in three-dimensional electrode by the active chlorine generated. The total bacteria count was reduced to near 100 CFU/mL with a 3-log reduction after 30 min. Therefore, the three-dimensional electrode system performs well in the removal of CODCr combined with disinfection.The removal of CODCr in three-dimensional biofilm electrode reactor was higher than that in biofilm reactor. And the dominant became larger under higher current density. The CODCr in the effluent of three dimensional biofilm electrode reactor could reach 40 mA/cm2 (the removal can reach 35%), and the pH of the effluent was nearly neutral under the current density of 0.5mA/cm2. The energy consumption of three-dimensional biofilm electrode reactor is much lower than that of three-dimensional electrode reactor, when the CODCr of the effluent reach the same degree (45mg/L). But the performance of nitrate and total nitrogen treatment was not obvious. The biomass was stable under the current density between 0.1250.5mA/cm2, while it decreased when the current density was beyond 1mA/cm2, which might be due to the inhibition effects of chlorine generated by higher current density. |
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