Degradation Of Methylene Blue Using Double-chamber Dielectric Barrier Discharge Reactor

With the development of society,water pollution has become an increasingly serious problem.As a new kind of sewage,aqueous organic pollutants treatment is widely studied in recent years,since organic wastewater is difficult to treat by conventional means.Dielectric barrier discharge?DBD?plasma technology combines the advantages of ozonation,ultraviolet degradation and other advanced oxidation process.With the characteristic of uniform and stable discharge,high electron density,low gas consumption,easy operation and low power consumption,DBD plasma technology can effectively breakdown organics in waste water,thus providing a new way for organic wastewater treatment.In this paper,methylene blue?MB?solution was used as simulated organic waste,double-chamber DBD reactor was self-designed to remove MB at room temperature and atmospheric pressure.The effects of reactor parameters,process parameters,atmospheres and additives on the degradation process of MB solution were investigated.The results of using double-chamber reactor with air bubbling showed that MB can be effectively decomposed by plasma with a low gas flow rate and a small input power.Under the optimum reaction conditions,degradation efficiency of MB solution(50 m L with initial concentration 50 mg·L^-1)reached 98.99% when the discharge lasted for 100 min,and the maximum energy efficiency of 0.14 g?kW·h?^-1 was obtained by 40 min discharge.Degradation efficiency of 50 mL of MB solution with initial concentration 100 mg·L^-1 can reach 99.98% within 20 min and COD removal rate can reach 72.37% within 40 min with oxygen plasma treatment.The double-chamber DBD reactor exhibits outstanding advantages with oxygen bubbling.Ozone play a major role in MB decomposition process,and the effects of ·OH and H₂O₂ cannot be neglected.There are huge differences in MB degradation processes between air and O₂ DBD plasma,the main cause of which is the reaction poisoning caused by air plasma?N₂ in air reacts with oxygen,which confines the oxidizing ability of reactive oxygen species?.Different additives are added to MB solution to investigate their effects on MB degradation.The addition of Na₂SO₄,NaNO₃ and NaCl has almost no effect on MB degradation,while the MB removal process was weaken by adding Na₂CO₃ and NaHCO₃.In addition,the degradation process was severely weakened by adding Na3PO₄ and NaNO₂ into MB solution.·OH radical scavenger can significantly weaken MB degradation,but the role of ·H radical scavenger in strengthen the MB removal process is very limited,which indicates that ·OH in oxygen plasma mainly come from the decomposition of ozone instead of water excitation.The degradation efficiency of MB was increased from 87% to 97% with the addition of Fe²⁺.H₂O₂ produced by plasma,and Fe²⁺ form Fenton reagent,promoting the formation of ·OH,thus strengthening the degradation process of MB by DBD plasma.According to the analytic results of O₂ plasma post-discharge MB solution within 10 min,we believed that the degradation of MB was the result of the synergistic effect of high-energy electron attack,ozonation as well as hydroxylation.