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城市河道在人居生活和景观调节中发挥着重要作用。近年来,随着我国水环境治理相关政策体系的不断完善,特别是自《水污染防治行动计划》(“水十条”)发布和“污染防治攻坚战”开展以来,我国的水环境质量得到较大改善。2020年底全国地级以上城市2 914个黑臭水体消除比例达到98.2%[1],2021年底3641个国家地表水考核断面中水质劣V类仅占2.1%。然而,环保专项督查发现各地均有出现黑臭污染反弹现象;督查报告指出,水体底泥的内源污染未有效解决是黑臭污染反弹的主要原因之一[2]。
底泥是河流生态系统的重要组成部分,但长期污染已使其成为营养盐、难降解有机物、重金属等污染物的蓄积库[3]。即使外源污染得到有效控制,底泥中的污染物释放仍可能对水体产生“二次污染”[4]。目前,污染底泥治理思路分为异位处置和原位治理两类。异位处置主要指底泥清淤及后续处置,在水环境治理工程中被广泛采用,但实践中存在工程成本高、施工难度大、二次污染控制难度大等弊端[5]。原位治理的思路则是通过向底泥定向投加微生物、化学剂等,在泥水界面乃至底泥中对底泥污染物进行氧化和分解,以达到重建底泥生境,恢复底泥生态功能的目的。相较异位处置,原位治理技术所需费用一般较低,并可避免清淤处置过程的二次污染等问题,符合生态文明建设目标,已得到广泛研究及应用[6-8]。
硝酸盐介导的底泥修复技术是一种底泥原位治理技术。在硝酸盐刺激下,反硝化细菌的活性被激活,其中异养反硝化菌利用硝酸盐为电子受体降解底泥中的有机物(NO3− + OM
$\to $ N2 + CO2)[9-10],自养反硝化菌以硝酸盐为电子受体氧化底泥中的硫化物(NO3− + S2−$\to $ N2 + SO42−)[11-12],达到消除底泥黑臭(H2S、FeS等)和有机污染物的效果。硝酸盐底泥修复法可解决传统曝气充氧难以突破泥水界面的难题,利用硝酸盐的强水溶性和对反硝化菌的强化特性深度氧化黑臭底泥[13-15],是极具潜力的底泥原位治理方法;但由于硝酸盐的添加可能对水体引入营养污染风险[16-17],而限制了其应用推广。本研究通过室内泥柱、原位泥柱和现场中试实验,探索硝酸钙修复黑臭底泥过程中河道水相水质的影响和响应,客观评价硝酸钙底泥修复法的效果与风险,为底泥原位治理技术的应用提供参考。
硝酸钙缓释颗粒原位修复黑臭底泥的作用机制及其应用
Mechanism and application of in situ remediation of black and smelly sediment by calcium nitrate sustained-release particles
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摘要: 为解决水体中沉积底泥的内源污染释放问题,亟需高效底泥修复技术。硝酸盐为底泥微生物的电子受体,可通过反硝化作用氧化底泥的黑臭物质,是极具潜力的底泥修复剂。为探明硝酸盐在实际工程中的修复效果和潜在问题,结合实验室模拟和实际修复工程,分析了投加硝酸钙颗粒对黑臭底泥原位修复的环境过程。结果表明,投加硝酸钙缓释颗粒产品能显著提高底泥氧化还原势能(以Fe(II)/Fe(III)表征),促进黑臭物质转化,实际硫化物氧化率达85.2%,使得底泥由黑转黄,最终实现修复目标。同时,硝酸钙修复底泥的过程不受上覆水水质影响,且因修复过程消耗了大量底泥耗氧物质(硫化物和易降解有机质),使水体整体复氧能力提高。另一方面,钙离子的加入使磷素以较为稳定的钙磷形态转化,能改变水相总磷的归趋(TPSedCaN < TPCK,p < 0.01)。然而,由于反硝化产气增加了底泥孔隙,增加了泥水界面表面积和污染物扩散通量,故在修复初期存在底泥污染物和硝酸盐向其浓度较低的水相扩散,产生了一定风险,而实际上这也有利于泥相污染物的加速释放。因此,建议在可控工程段,联合覆盖法阻断污染物扩散或联合曝气加速水相污染物氧化,以确保在控制风险的前提下达到最优的底泥修复效果。Abstract: In order to solve the problem of endogenous pollution release of sediment in water body, the efficient sediment remediation technology is urgently needed. Nitrate is the electron acceptor of sediment microorganisms, which can oxidize the black-odor substance through denitrification process, therefore it is a potential agent for sediment remediation. In order to explore the remediation effects and potential problems of nitrate in practical engineering, this study conducted laboratory and field experiments to explored the environmental processes in in-situ sediment remediating by adding calcium nitrate pellets (SedCaN pellets). The results showed that the addition of calcium nitrate could significantly increase the redox potential in sediment (characterized by Fe(II)/Fe(III)) and promote the transformation of black-odor substances, meanwhile the color of sediment turned from black to yellow, which indicated that the remediation target was achieved. The actual sulfide oxidation rate was up to 85.2%. At the same time, the remediation was not affected by the quality of overlying water. A large number of oxygen-consuming substances (sulfide and easily degradable organic matter) were consumed in the process of repairing sediment, which improved the overall reoxygenation capacity of water body. The addition of calcium ions could stabilize the phosphorus as the form of Ca-P, which decreased the release of phosphorus from sediment to water phase (TPCaN < TPCK, p < 0.01). However, the gaseous nitrogen produced by denitrification increased the sediment porosity, which increased the diffusion flux of pollutants from sediment-water interface surface. At the initial stage of remediation, there was a certain risk due to the diffusion of sediment pollutants and nitrates, but in fact, it was also conducive to the accelerate the pollution release out of the sediment. Therefore, it was suggested to block the diffusion of pollutants by combining covering method or to accelerate the oxidation of water phase pollutants by combining aeration approaches in the controllable engineering section, so as to achieve the best sediment remediation effect on the premise of controlling the risk.
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Key words:
- black-odor sediment /
- calcium nitrate /
- in-situ remediation /
- pilot test applicaition /
- bioremediation.
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表 1 室内泥柱实验上覆水指标
Table 1. Overlying water index in indoor mud colum experiment
上覆水 DO/(mg·L−1) pH ORP/mV COD/(mg·L−1) 铵态氮/(mg·L−1) 硝态氮/(mg·L−1) 总磷/(mg·L−1) 黑臭原水 0.5 7.68 −219 64.00 13.39 N.D. 0.74 稀释水 0.4 7.89 −114 10.21 1.67 N.D. 0.09 注:N.D.表示浓度低于检测限。 表 2 室内泥柱实验上覆水指标的相关性与成对T检验差异
Table 2. The correlation and difference (paired T-test) of overlying water index from indoor mud column experiment
水样名称 水质指标 相关性r 相关的显著性Pr T检验的显著性Pt DO 原水 0.490 <0.01 0.042 DO 稀释水 0.684 <0.001 0.970 pH 原水 0.760 <0.001 0.001 pH 稀释水 0.844 <0.001 0.001 NH4+-N 原水 0.680 <0.001 0.988 NH4+-N 稀释水 0.770 <0.001 0.001 COD 原水 0.460 <0.01 0.281 COD 稀释水 0.570 <0.001 0.152 TP 原水 0.869 <0.001 <0.001 TP 稀释水 0.944 <0.001 0.233 表 3 现场泥柱实验上覆水指标的相关性与成对T检验差异
Table 3. The correlation and difference (paired T-test ) of overlying water index from field sediment column experiment
水质指标 相关性r 相关的显著性Pr T检验的显著性Pt DO 0.632 <0.001 0.355 pH 0.754 <0.001 <0.01 COD 0.344 <0.01 0.207 NH4+-N 0.343 <0.01 0.425 TP 0.114 0.388 <0.001 -
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