原位注射硝酸钙修复污染底泥过程中无机氮的迁移与转化

发布时间：2018-06-21 18:33

本文选题：污染底泥 + 原位修复　；参考：《哈尔滨工业大学》2015年硕士论文

【摘要】：污染底泥作为河道的内源污染源,是改善河道水系环境的重要环节。在多种底泥治理技术中,原位生化修复技术因其工程量小,修复效果好,受到广泛的关注和应用。其中,硝酸钙在底泥原位生化修复技术中工程应用最为广泛。然而,已有研究数据表明,投加硝酸钙后会引起底泥硝态氮和氨氮的快速释放,可能会对河道生态环境造成一定的影响。因此,有必要对原位注射硝酸钙修复污染底泥过程中硝态氮在底泥中的迁移与转化规律进行研究,以期为原位投加硝酸钙修复污染底泥技术的应用改进以及后续环境影响监控提供参考。本文研究通过使用耙式给药装置投加硝酸钙至底泥,考察硝酸钙在不同颗粒粒径分布底泥中的扩散,并分析投药耙投药效率;通过小试研究投加硝酸钙后,生化修复过程中底泥硝态氮迁移转化规律;通过柱实验模拟各种河道场景,分析向颗粒尺寸分布不同、挥发性硫化物AVS(acid volatile sulfide)浓度不同的底泥投加硝酸钙,并考虑不同水位变化的条件下,上覆水的变化及影响。研究结果表明,使用耙式给药装置向底泥注射硝酸钙溶液,底泥颗粒尺寸大小不同,硝态氮在底泥中的扩散规律不同。在投药24 h至48 h后可观察到,在粗砂颗粒粒径分布的底泥中,药剂主要集中在垂向断面上层,水平方向扩散范围为10 cm,投药效率仅为43%;在粉砂颗粒粒径分布的底泥中,药剂主要集中的垂向断面上层,水平方向扩散范围为10 cm,投药效率可达到78%;在粉土颗粒粒径分布的底泥中,药剂主要集中的垂向断面中间层,水平方向扩散范围为5 cm,投药效率可达到80%以上。投加硝酸钙药剂后,底泥生化修复过程中硝态氮还原为氮气的硫自养反硝化过程占硝态氮总还原量的90%,还原硝态氮为氨氮的异化反硝化过程仅占5%-10%。进一步探究生化修复过程中硝态氮的迁移规律,观察到底泥AVS浓度越高,由自养反硝化还原硝态氮为氮气产生的气腔驱动越大,硝态氮在底泥中越容易表现为向上迁移的趋势。当底泥AVS浓度越高、颗粒粒径越粗,投加硝酸钙生化修复过程,容易引起底泥硝态氮、亚硝氮、氨氮的释放,带来的环境风险也越大。此外,相比于水体持续流动更替的场景,在水体流动受限的场景下,底泥生化修复过程更容易引起上覆水无机氮的积累。
[Abstract]:As an internal pollution source, polluted sediment plays an important role in improving the environment of river system. Among various sediment treatment technologies, in situ biochemical remediation technology is widely concerned and applied because of its small amount of engineering and good restoration effect. Among them, calcium nitrate is most widely used in sediment in situ biochemical restoration technology. However, some research data have shown that adding calcium nitrate can cause the rapid release of nitrate-nitrogen and ammonia-nitrogen from sediment, which may have a certain impact on the ecological environment of river channel. Therefore, it is necessary to study the migration and transformation of nitrate nitrogen in contaminated sediment during in-situ injection of calcium nitrate. In order to provide reference for the application and improvement of in-situ calcium nitrate for remediation of contaminated sediment and subsequent monitoring of environmental impact. In this paper, the diffusion of calcium nitrate in sediment with different particle size distribution was investigated by adding calcium nitrate to sediment in a rake dispensing device, and the feed efficiency of rake was analyzed. In the process of biochemical remediation, the transport and transformation of nitrate in sediment were simulated by column experiment, and the calcium nitrate was added to the sediment with different particle size distribution and volatile sulfide concentration. The change and influence of overlying water are considered under the condition of different water level change. The results show that when calcium nitrate solution is injected into the sediment with rake dispensing device, the particle size of the sediment is different, and the diffusion law of nitrate nitrogen in the sediment is different. After 24 h to 48 h, it was observed that in the sediment with coarse sand particle size distribution, the fungicides were mainly concentrated in the upper layer of vertical section, the horizontal diffusion range was 10 cm, and the dosing efficiency was only 43%, and in the sediment with silty sand particle size distribution, The upper layer of vertical section is mainly concentrated, the horizontal diffusion range is 10 cm, the dosing efficiency can reach 78%, and in the sediment of silt particle size distribution, the intermediate layer of vertical section is mainly concentrated. The horizontal diffusion range is 5 cm and the dosing efficiency is over 80%. After adding calcium nitrate, the sulfur autotrophic denitrification process of reducing nitrate nitrogen to nitrogen accounted for 90% of the total reduction amount of nitrate nitrogen, and the dissimilatory denitrification process of reducing nitrate nitrogen to ammonia nitrogen accounted for only 5-10% of the total reduction amount of nitrate nitrogen. It is observed that the higher the AVS concentration of sediment, the greater the gas chamber driven by autotrophic denitrification to reduce nitrate nitrogen into nitrogen, and the more easily the nitrate nitrogen is transported upward in the sediment. When the concentration of AVS in sediment is higher, the particle size is thicker, and the biochemical remediation process of adding calcium nitrate is easy to cause the release of nitrate nitrogen, nitrite nitrogen and ammonia nitrogen, and the environmental risk is also greater. In addition, under the condition of limited water flow, the accumulation of inorganic nitrogen in overlying water is more likely to be caused by the biochemical remediation process of sediment than in the scenario of continuous water flow replacement.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X52

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