Degradation Efficiency Of Nitrate In The Sulfite/Vacuum Ultraviolet Process

Nitrate has quite strong persistence and harmfulness in the aqueous environment due to its stable chemical property,raising a great concern worldwide.The usual removal techniques are difficult to acquire good effects at present.Efficient and harmless denitrification is a challenge for water treatment.Sulfite/vacuum ultraviolet(SO32-/VUV)can remove most recalcitrant contaminants efficiently without secondary pollution.It's based on the strong reducibility of hydrated electron(eaq-)from water molecule that photolyzed under VUV irradiation at 185 nm and sulfite photo-ionized under UV irradiation at 254 nm.With the strong reduction efficiency of SO32-/VUV,degradation and denitrification of nitrate were done in this study.The degradation kinetics of nitrate was analyzed and the activation energy was calculated.The influence of typical factors on the degradation of nitrate was investigated.The function of reactive species(eaq-and H.)and the reduction mechanism of nitrate were explored.Comparing with the VUV photolysis directly,the degradation of nitrate was accelerated obviously in the SO32-/VUV process.Analyzing the degradation kinetics of nitrate in the SO32/VUV process,the initial degradation rate of nitrate had a linear growth with the increasing concentrate of sulfite(0?3 mM).Temperature mainly had a slight influence on the effective quantum of the photochemical reaction,and the apparent activation energy was about 15.1 kJ-mol-1.The influence of pH was quite significant,the degradation of nitrate was enhanced obviously with increasing pH at the range of 6?8 but only slight promoted by further raising pH.Dissolved oxygen and natural organic matter both had inhibition on the degradation of nitrate.Chloride,bicarbonate and ferrous all had no evident influence on the degradation of nitrate.The SO32-/VUV process was also effective for the degradation of nitrate in realistic surface water,while the efficiency was declined,which mainly owned to the consumption of eaq-by organic carbon and the absorption of UV by contaminants in realistic water.The primary degradation mechansism was investigated by the competitive kinetics analysis.The degradation of nitrate in the SO32-/VUV process was mainly depended on eaq-,and the contribution of H was negligible.In the degradation,nitrate firstly restored to nitrite quickly,and nitrite also reacted with eaq-rapidly for further reduction.There was no formation of ammonia during the whole process.SO32-/VUV reductive process is an efficient technique for the degradation of nitrate with no secondary pollution,having good application prospect.