土壤包气带强化反应层脱氮的控制因素与性能研究

包气带作为防止地下水硝酸盐污染的天然屏障,其反硝化效果通常受到碳源的限制。针对地下水硝酸盐污染防治技术现状,本文采用Ca(OH)₂处理的玉米芯作为反硝化的碳源材料,构建包气带强化反应层,用响应曲面法研究硝酸盐浓度、含水量和温度的交互作用对脱氮性能影响,并用硝态氮去除率、亚硝态氮累积、pH值变化以及溶解性有机碳(dissolved organic carbon, DOC)淋失通量综合评价脱氮性能,最后采用高通量测序揭示脱氮层中微生物变化。研究结果表明:温度、含水量以及温度和含水量交互作用对硝态氮去除率影响显著,其中温度是反硝化过程中最关键的因素;系统运行74天后,硝态氮去除率达到50%,亚硝态氮累积量(以N计)大多低于3 mg/L,pH值维持在7.0左右,DOC淋失通量(以C计)介于0.10.2 mg/(cm²·d);高通量测序发现,脱氮层中微生物的丰富度降低,而与反硝化和碳分解有关的微生物相对丰度提高,在碳源的刺激下微生物向有利于脱氮的方向演变。

Influencing factors and performance of enhanced denitrification layer in the vadose zone

The vadose zone is a natural barrier for preventing nitrate contamination of groundwater and its denitrification effect is limited by carbon contents. In order to control nitrate pollution in groundwater, the Ca(OH)₂-treated corn cobs were used as a carbon source to construct a reactive layer to speed up denitrification. The effects of interactions between nitrate concentration, humidity and temperature on denitrification performance were studied by response surface method. Denitrification performance was then comprehensively evaluated in terms of nitrate removal efficiency, nitrite accumulation concentration, pH value and leaching of dissolved organic carbon (DOC). The results show that the temperature and humidity as well as the interactions between them had significant effects on nitrate removal efficiency, with temperature being the most critical factor in this process. After 74 days, the nitrate removal efficiency reached 50% and the nitrite level was mostly lower than 3 mg(N)/L; the pH of the reactive layer maintained around 7.0; and the DOC leaching flux fluctuated between 0.1 and 0.2 mg(C)/(cm²·d). A high-throughput sequencing analysis shows an decrease of microbial richness in the denitrification layer and an increase of relative abundances of microorganisms related to denitrification and carbon source decomposition. The aborigine bacteria in the vadose zone are abundant, which is beneficial for denitrification under the effect of carbon source.