反硝化条件下河流沉积层中苯胺降解的微环境实验

Microcosm Study on Aniline Degradation in Weihe Riverbed Sediments under Denitrification Conditions

为研究反硝化条件下河流沉积层中苯胺降解及NO3-、有机碳与苯胺初始浓度等的影响,采集了渭河河流沉积物及西安某自备井的地下水,进行了微环境实验研究。结果发现,在厌氧条件下,河流沉积层中苯胺可以通过反硝化微生物代谢而降解,但其降解速率随苯胺初始浓度和NO3-浓度的增加而增大,随有机碳含量的增加而减小。表明反硝化微生物通过生长代谢的方式降解苯胺,环境中有机质抑制反硝化微生物降解苯胺,而NO3-则具有促进作用。

Our aim is to study the degradation of aniline in Weihe Riverbed sediments, which is situated in Shaanxi province and close to the populous city of Xi＇an, China. Aniline is a deadly substance; the amount of new aniline that goes into polluting the environment has been estimated at 30 000 tons per annum. Aniliners half-life is about 10 years in anaerobic sediments. It is important to study the degradation of aniline in anaerobic conditions to protect water and soil from aniline pollution and to treat the polluted. Much research has been carried out in aerobic conditions but little in anaerobic environment. This paper is devoted to study in denitrification conditions for it is the most common type one of the anaerobic environment in the world. We took riverbed sediments from Weihe River and groundwater from a well in Xi＇an and put them into 1 000 mL brown bottles. And aniline, nitrate and other reagents are added to the bottles （based on the test design） which are flushed with nitrogen for 8 min and then sealed immediately with rubber stoppers; thus microcosms in anaerobic environment are formed in these bottles. The microcosm tests were conducted and aniline, nitrate and chemical oxygen demand （COD） were monitored to research aniline degradation in denitrification conditions. During the test with nitrate as electron acceptor, we observed three phenomena： （1） the concentration of aniline was steady but COD decreased in microcosm with sediments; （2） the concentrations of aniline and nitrate and COD were steady in the microcosm with NaN3（500 mg/L）; and （3） these concentrations and COD decreased simultaneously in the microcosm with nitrate（50 mg/L）. Therefore, aniline was degraded by the denitrifers. During the test on the effect of nitrate on the degradation of aniline with concentration of 47 mg/L, aniline degradation rate constant was 0. 001 14 d^-1 in the microcosm without nitrate, and the constants were 0. 004 58 d^-1 and 0. 044 27 d^-1 in the microcosms with 50 mg/L and 400 mg/L nitrate respectively. These proved that nitrate could enhance the degradation of aniline in the studied conditions. During the test on the effect of organic carbon on aniline degradation and still with nitrate as electron acceptor, the rate constant was 0. 155 03 d^-1 in the microcosm with sediments which had been soaked in H202 for 48 h; the constants were 0. 021 13 d^-1 and 0. 048 26 d^-1 in the microcosm with sediments when the nitrate was 50 mg/L and 400 mg/ L respectively; the constants were 0. 019 25 d^-1 and 0. 006 78 d^-1 in the microcosms with sediments again when the nitrate was 50 mg/L and 400 mg/L respectively but with 50 mg/L acetate added. These data implied that organic carbon which was already in sediments or added inhibited aniline degradation. The degradation of aniline in the microcosm with sediments which had been soaked in H2O2 showed that the denitrifier used aniline as the sole carbon source to grow. During the test on the effect of aniliners initial concentration on its degradation, the rate constants were 0. 001 13 d^-1, 0. 002 31 d ^-1 and 0. 002 49 d^-1 when the initial concentration was 45. 55 mg/L, 46. 96 mg/L and 65. 77 mg/L respectively. These indicated that increasing the initial concentration might be useful to the microbes and accelerate the degradation of aniline, and that the lag period would become longer with increasing initial concentration. Since riverbed sediments often are anaerobic, nitrate respiration may be an important process in degradation of aniline.