土著细菌对江汉平原浅层含水层沉积物中砷迁移的影响

Influence of Indigenous Bacteria on Arsenic Migration in Shallow Aquifer Sediments of Jianghan Plain

对江汉平原水文地质调查发现,该地区地下水砷含量已远超国家饮用水标准。以沉积物培养的土著细菌混合液为生物材料,以江汉平原高砷含水层沉积物为研究对象,在实验室内模拟地下水系统,研究厌氧环境条件下,不同生物量土著细菌和pH值对沉积物中砷迁移转化的影响,以及土著细菌活动下砷在不同沉积物中的迁移转化。结果表明,不同生物量菌悬液都能促进沉积物中As的释放,增加总As和As(III)的浓度,但150mL处理组,在研究后期,总As和As(III)的浓度呈现减缓趋势;在初始生物量一定的条件下,沉积物中As含量越高,细菌活动下总As相对释出量就越低,而且As(III)占所释出总As的比值就越高,但两个高砷含量沉积物组的差异较小;在初始pH值为5、7和9的培养条件下,细菌都能加速砷的迁移,但pH值为5的处理组(简称pH5处理组)最弱,在前8天,pH9处理组较pH7处理组的低,随后超过pH7处理组。研究表明,土著细菌悬液能加速As从沉积物中释出,并且释出的As以As(III)为主;在耐受的弱碱性环境条件下,细菌对砷的迁移和转化随环境的pH值增加而增强。

High arsenic groundwater has been found in Jianghan Plain, in which the arsenic concentration exceeded the national standard for drinking water. To investigate the effects of microbial activities as well as pH on arsenic migration and speciation in shallow aquifers under anaerobic condition, the experiments were carried out using a groundwater simulation system with the indigenous bacteria cultured into high arsenic aquifer sediments from Jianghan Plain. Nutrient broth medium (NB medium) was used for bacterial growth in this work. Results showed that arsenic can release from sediment in all treatment groups with bacteria. Except 150 mL-treatment group, total As and As(III) concentrations increased with the increasing of initial bacterial biomass. As(III) was the predominant arsenic species in the total arsenic. Under certain conditions of biomass, the content of arsenic release in high arsenic sediment was relatively lower than that in low arsenic sediment. While the ratio of As(III) release in total As from high arsenic sediment was higher than that from low arsenic sediment. There was nearly no difference of arsenic release between the two high arsenic sediments. Arsenic release in the treatment group with initial pH 5 was the lowest among the three pH-treatment groups (pH 5, 7 and 9). Arsenic release in the treatment group with initial pH 9 was lower than the treatment group with initial pH 7 during the first eight days. Then the former exceeded the latter in the following incubation. It implied that indigenous bacteria promoted arsenic releasing from aquifer sediments, and most of arsenic release was As(III). Alkalescent condition is helpful for bacteria to release arsenic. The content of arsenic release increased with the increasing of pH under bacteria as well as alkalescent conditions.