Study Of The Enhancement Of H₂O₂ In-situ Production In Bio-electro-Fenton Systems

Bio-electro-Fenton?BEF?is a new type of electro-Fenton?EF?technique.BEF takes advantage of the electrically active microorganisms attaching and growing on the surface of anode to provide electrons for the cathodic oxygen reduction reaction?ORR?to in-situ generate H₂O₂.BEF possesses the advantages of mild operation condition and low energy consumption.However,the accumulated concentration of H₂O₂ in BEF systems is much lower than that of the EF system,leading to a lower degradation efficiency against contaminants,which hinders its industrialized application.For the BEF system,factors affecting H₂O₂ in-situ production include cathodic material,anodic electron output?namely,cathodic electron supply?,electrolyte pH,aeration,and so forth,among which the anodic electron output,and the 2e^-ORR activity of cathodic material are the most significant influence factors.Accordingly,in this study,H₂O₂in-situ production was enhanced through the following aspects:Multi-anode BEF system was built up to enhance the electron output from anode,namely to increase the electron supply for the cathodic ORR;Utilizing thermo-treated candle ash?CS?as a novel cathodic catalyst to enhance the 2e^-ORR activity of the cathode and significantly increase the H₂O₂ in-situ accumulated concentration and the efficiency of pollutants degradation.The main research content and conclusions are as follows:?1?Cheap and easily accessible carbon materials,active carbon?AC?,carbon black?CB?and graphite?GC?were used as cathodic ORR catalysts.The 2e^-ORR catalytic activity of the above catalysts were evaluated by electrochemistry measurements.The current output and H₂O₂ in-situ generating performance of the BEF systems with the cathodes prepared with the three common carbon catalysts were preliminarily investigated.Experiment results manifested that on the surfaces of the CB and GC air-cathodes,2e^-pathway was the main ORR process,but CB showed a higher 2e^-ORR catalytic activity.For BEF-CB system,the anodic average output current(I_ave)and cathodic H₂O₂ accumulated concentration were?0.39 mA and 3.4 mg/L,respectively.?2?More electrons were supplied for cathodic ORR via construction of multi-anode BEF system to enforce electron output from anodes,to enhance the H₂O₂ in situ production.The influences of number of anode,connecting forms and anodic structure on electricity generation and H₂O₂ in-situ production of the BEF system were investigated.Experiment results demonstrated that the parallel connection of multi-anodes exert a more obvious influence on electricity generation and H₂O₂ in-situ generating capacity of BEF system in comparison to the series connection.Compared with BEF-1?0.38 m A?,I_ave of the BEF-P2?0.52 mA?and BEF-P3?0.55 mA?increased by 36.8%and 44.7%,respectively.Finally,In BEF-P2 and BEF-P3systems,H₂O₂ accumulated concentrations increased from 3.40 mg/L to 4.22 mg/L and4.66 mg/L,respectively.The restriction of mass transportation in multi-anodes BEF system can be reduced with the utility of perforated anodes,and therefore the current output and H₂O₂accumulated concentration were boosted.The I_ave of BEF-P2P and BEF-P3P increased from0.52 mA?BEF-P2?and 0.55 mA?BEF-P3?to 0.57 mA and 0.72 mA.The H₂O₂ accumulated concentrations increased from 4.22 mg/L?BEF-P2?and 4.66 mg/L?BEF-P3?to 4.95 mg/L and5.14 mg/L.Compared with the double-anode BEF,neither the I_ave nor the H₂O₂ accumulated concentration of the three-anode BEF system were evidently increased,but its electrodes cost was relatively higher.Hence,the BEF with double perforated anodes connected in parallel is the optimal system.?3?Thermo-treated CS was utilized as 2e^-ORR catalyst to enhance the H₂O₂ in-situ accumulated concentration.Experimental results indicated that the thermo-treatment increased the hydrophilicity and the BET surface area of the CS.The CS-400 which was thermally treated at 400°C exhibited the highest mesoporous ratio and surface oxygen-containing groups percentage.Its electron transfer number is close to 2,indicating it was a 2e^-ORR catalyst.In the BEF-CS system with double perforated anodes and a CS-400 air-cathode,provided a H₂O₂accumulated concentration of 32.02 mg/L,and the RhB and SMX removal rates of 100%and83.0%within 40 h.