Development And Experimental Study Of A Three-dimensional Electrode Reactor Packed With Catalyst-coated Granular Activated Carbons

In order to achieve high efficient advanced treatment of industrial secondaryeffluent and obtain a high organic pollutants removal rate, the objective of this study isto construct a pilot-scale three-dimensional electrode reactor (TDER) packed withcatalyst-coated granular activated carbons (GACs), which had high oxygen evolutionoverpotential and high hydroxyal radical production; to investigate preparation methodand process of catalyst-coated GACs; to optimize design parameter and operationalparameter of the reactor and to reveal mechanism of electrochemical oxidation reaction.The results showed that the TDER obtained a high and steady organic compoundsremoval rate in treatment of biologically treated citric acid wastewater.The effects of catalyst ratio, paperation method of catalyst-coated GAC on CODremoval, catalystic activity, catalytic stability, crystal characteristics as well aselectrochemical behaviours were investigated. The results showed that catalyst-coatedGACs (GAC-Ti-Sn/Sb), which had high oxygen evolution overpotential and highhydroxyl radical production rate, were prepared.Current distribution is of important in designing a three-dimensional electrodereactor. Thus, the effects of filling volume ratio, electrode distance and hydraulicretetion time on current distribution were investigated, and the treatability of variousorganics via GAC-Ti-Sn/Sb catalytic reaction was also studied. The results showed thatthe optimal design parameter (electrode distance of3cm, filling volume ratio70%)were determined. The degradation kinetics of rhodamine B, humic acid and citric acidduring electrolysis were all fitted to pseudo-first-order OH-mediated oxidationreaction.The treatability of a real wastewater (citric acid wastewater) in a GAC-Ti-Sn/Sbgranular electrodes packed continuous-flow three-dimensional electrode reactor(CTDER) was verified. The effects of hydraulic retetion time, current density, initial pHand airflow rate were investigated. We revealed that predominant refractory organiccompound (i.e., a humic acid-like substance) in citric acid wastewater was likelydegraded via indirect oxidation (OH-mediated and active chlorine-mediated oxidation)in bulk solution. A pilot-scale CTDER with capacity of3m3/d was constructed. The feasibility ofpilot-scale treatment of citric acid wastewater in this reactor and pilot-scale preperationof GAC-Ti-Sn/Sb granular electrodes were both verified. The results showed that thestable COD removals of70%, low energy consumption of90kWh/kgCOD and highcurrent efficiency of38%were obtained during13days operation. We also found thatorganic compounds were degraded primarily via oxidation of humic acid-likesubstances in the citric acid wastewater and then converted to aromatic proteinsubstances.