不同电子受体对无分子氧环境中苯微生物降解的影响

Effects of various electron acceptors on the oxygen-free biodegradation of benzene

为了考察提供氧分子以外的其它电子受体时微生物对石油污染的修复效果,在缺氧和厌氧条件下,采用批式试验方法研究了活性污泥在供给硝酸盐、亚硝酸盐、EDTA铁盐或硝酸盐+EDTA铁盐条件下对苯的降解效果,探讨了这些电子受体对缺氧和厌氧微生物降解苯的影响以及这些电子受体之间的相互作用.结果表明:①在供给硝酸盐时,苯的生物降解作用、硝酸盐还原和亚硝酸盐暂时累积现象同时出现;②当供给亚硝酸盐时,苯的生物降解作用不明显;③在供给EDTA铁盐为电子受体时,苯的生物降解作用明显,亚铁盐浓度逐渐升高;④当同时供给硝酸盐和EDTA铁盐时,苯的生物降解作用明显,并且没有出现明显的亚硝酸盐和亚铁盐累积现象.这表明,同时供给硝酸盐和EDTA铁盐时,伴随苯的降解首先硝酸盐和铁盐还原产生亚硝酸盐和亚铁盐,随后亚硝酸盐将亚铁盐氧化为铁盐,氧化产生的铁盐又继续作为苯降解的电子受体来降解苯;铁离子和亚铁离子之间构成的氧化还原循环,从而促进了苯的缺氧降解和硝酸盐还原.

Oxygen is one of the key control factors in petroleum hydrocarbon biodegradation in contaminated soil and water bodies since the biodegradation typically occurs under aerobic conditions. A potential method to improve bioremediation of petroleum contaminated soil and water bodies under oxygen-free conditions is to supply alternative electren aeeeptors for the biodegradation process. We performed batch tests using activated sludge to investigate the biodegradation of benzene under anoxic conditions （ using nitrate, nitrite and nitrate ＋ ferric-EDTA as electron acceptors） and anaerobic conditions （ using ferric-EDTA as electron aeceptor）. The results showed that （1） biodegradation of benzene, reduction of nitrate and accumulation of nitrite occurred simultaneously when nitrate was used as electron aeceptor, （2）insignificant benzene was removed when nitrite was supplied as electron aeceptor, （3）when ferric-EDTA was supplied as electron aceeptor, the amount of benzene removed significantly increased while the ferrous ion concentration gradually increased, （4）more benzene was removed when nitrate and ferric-EDTA were used as electron acceptors. It is implied that the nitrate and ferric ion were reduced into nitrite and ferrous ion firstly during benzene degradation, and then ferrous ion was further oxidized into ferric ion using nitrite as electron acceptor, so less nitrite and ferrous ion accumulated in the activated sludge system. Finally the resultant ferric ion acted as an electron acceptor in the benzene biodegradation process. A higher degree of benzene biodegradation and nitrate reduction could be achieved due to the iron ion reduction-oxidation cycle under oxygen-free conditions.