羟基自由基氧化降解水中土臭素的效率与机制

土臭素(Geosmin,GSM)是一种由蓝绿藻及放线菌产生,具有令人讨厌土霉味的化合物.地表水中存在土臭素,尽管量少,但因传统水处理工艺难以去除,大大降低了饮用水的感官质量.本文采用大气压强电场电离放电结合水力射流空化方式制备的羟基自由基(Hydroxyl radicals,·OH)对水中GSM进行氧化降解,研究了氧化剂投加剂量、接触时间因素的影响,并根据气相色谱-质谱(GC-MS)全扫描获取的中间产物探讨了·OH氧化降解GSM的机制.实验结果表明:当氧化剂投加剂量为0.8 mg·L~(-1),管路中接触反应6 s,可把初始浓度100 ng·L~(-1)的GSM降解到10 ng·L~(-1)以下;提高氧化剂投加量至2.6 mg·L~(-1),接触反应180 s,可氧化降解500 ng·L~(-1)的GSM至10 ng·L~(-1)以下,达到我国《生活饮用水卫生标准》(GB5749—2006).在GSM水样中加入叔丁醇(Tertiary butyl alcohol,TBA)·OH淬灭剂,GSM氧化降解效果明显降低,间接证明了降解GSM的主要物质为·OH.对氧化降解GSM的中间产物分析表明·OH可以破坏GSM双环结构并最终将其矿化成CO_2和H_2O.

Performance and mechanism of oxidative degradation of geosmin in water by hydroxyl radicals

Geosmin (GSM), a compound with undesirably earthy and musty odours, is produced by several species of cyanobacteria and actinomycetes. Although it is less in surface water, GSM greatly reduces the sensory quality of drinking water because it is resistant to conventional water treatment technology. In this paper, the oxidative degradation of GSM was performed using hydroxyl radicals (·OH) generated from a strong ionization discharge at atmosphere pressure combined with the effects of water jet cavitation. The dose effect and contact time of·OH determined by the concentration of total reactive oxidants (TRO) were studied. The oxidative degradation mechanism of GSM using several intermediates from GC-MS full scan was also discussed. Experimental results show that when the TRO concentration reached 0.8 mg·L^-1, the GSM with an initial concentration of 100 ng·L^-1 could be degraded to less than 10 ng·L^-1 in 6 s. Increasing the TRO concentration to 2.6 mg·L^-1, GSM with 500 ng·L^-1 could also be degraded to less than 10 ng·L^-1 in 6 s, which achieved China''s "Standards for drinking water quality" (GB5749-2006). Addition of·OH scavengers (tertiary butyl alcohol, TBA) remarkably reduces the degradation effects of GSM, which indicates that·OH should be the main oxidants for GSM degradation. The identified intermediates showed that·OH could destroy the double loop structure of GSM, leading to ring opening, and finally mineralize formation of CO₂ and H₂O.