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题名: 改性土壤湖泊综合修复技术对富营养化水体甲烷释放控制的研究
作者: 施文卿
学位类别: 博士
答辩日期: 2016-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 潘纲
关键词: 改性土、藻去除、沉积物覆盖、厌氧修复、甲烷释放 ; Modified soil, algal removal, sediment capping, anoxia remediation, methane emission
其他题名: Manipulating methane emission in eutrophic waters using the modified local soil technology
学位专业: 环境工程
中文摘要:       近年来,气候变暖导致干旱、洪涝、飓风等极端天气条件频发。甲烷作为第二大温室气体对温室效应贡献达20%。天然水体被认为是甲烷释放的重要源头之一。当水体发生富营养化时,藻类大量繁殖,其腐烂分解耗竭水体溶解氧,“营造”的厌氧环境促进甲烷释放。为减少富营养化水体甲烷释放,进行厌氧修复是关键。改性土壤湖泊综合修复技术作为湖泊地质工程措施之一受到了越来越多的关注。本技术中,改性土沉降除藻协同沉积物原位覆盖可实现良好的水环境改善效果,这可能会调控微生物群落,进而实现水体甲烷释放的削减。本论文中,我们提出了一种新的改性土沉降除藻方法,并研究了藻沉降后沉积物覆盖对甲烷释放的影响。首先合成了价格低廉、可生物降解的阳离子淀粉用作土改性剂,并在藻沉降效果、絮凝机理、絮体特征、对水体溶解性有机物影响等方面开展了系列研究;其次,考察了藻沉降后土壤、沸石和活性炭材料覆盖沉积物对水环境及甲烷释放的影响;最后,探索了藻沉降后载氧材料覆盖沉积物对水环境改善及甲烷释放控制的效果,并利用分子生物学手段揭示了相关作用机理。本研究主要结果如下:
    (1)经阳离子淀粉改性,土壤颗粒等电点由pH 0.5大幅度提升至pH 11.8,使其在天然水环境下带有正电荷,从而具有沉降除藻能力。在土剂量为100 mg L-1条件下,若阳离子淀粉剂量为10 mg L-1,86%铜绿微囊藻可在30 min内沉降去除。阳离子淀粉剂量过高或过低,藻沉降效果均下降。当阳离子淀粉剂量为5 mg L-1和80 mg L-1时,铜绿微囊藻沉降效率分别为71%和45%。在pH 4.0-10.0范围内,改性土沉降除藻效果受pH影响较小,但藻絮体稳定性受pH影响较大。与中性条件相比,酸性和碱性条件下形成的藻絮体易于破碎。阳离子淀粉价格低廉、易生物降解,可降低改性土沉降除藻成本并解决了残留问题。
    (2)阳离子淀粉改性土沉降除藻后,水体DOC出现下降现象。当阳离子淀粉表面电荷密度为0.052 meq g-1、0.140 meq g-1和0.293 meq g-1时,藻沉降后水体DOC分别从3.4 mg L-1降至3.0 mg L-1、1.8 mg L-1和1.7 mg L-1。三维荧光及UV254分析表明,在沉降除藻过程中,阳离子淀粉改性土对水体溶解性有机物也具有去除作用;所用阳离子淀粉表面电荷密度越高,对水体溶解性有机物去除效率越高。但是阳离子淀粉表面电荷密度过低时,改性土沉降除藻具有增加水体溶解性有机物的风险。当阳离子淀粉表面电荷密度为0.044 meq g-1时,水体DOC由3.4 mg L-1升高至3.9 mg L-1,这是由于达到最佳藻沉降效果时所需阳离子淀粉投加量过高所致。此研究结果表明,当有机大分子絮凝剂用作土改性剂沉降除藻时,可通过调控其表面电荷密度方式来控制处理水体溶解性有机物含量。
    (3)藻沉降去除后,沉积物覆盖处理可一定程度地缓解水环境厌氧状况,但不同覆盖材料的效果存在差异。土壤和沸石覆盖的效果相似,但均不及活性炭覆盖。对照体系水体溶解氧(DO)和沉积物界面氧化还原电位(ORP)在实验运行期间分别维持在低于2.0 mg L-1和-125 mV水平。土壤、沸石和活性炭覆盖后,水体DO分别上升至4.0 mg L-1,4.6 mg L-1和3.1 mg L-1,沉积物界面ORP分别上升至-19.8 mV、-8.4 mV和167.5 mV。沉积物覆盖对水环境的调控改变了碳素循环,进而对甲烷释放产生影响。土壤、沸石和活性炭覆盖后,水体向沉积物的DOC通量由0.11 g m-2d-1分别升高至0.12 g m-2d-1、0.21 g m-2d-1和0.45 g m-2d-1,沉积物向水体的DIC通量由0.73 g m-2d-1分别升高至0.98 g m-2d-1、0.82 g m-2d-1和1.18 g m-2d-1。水-气界面甲烷释放通量出现一定程度的削减现象,其中活性炭覆盖的削减效果最佳,在整个实验期间一直维持在3.1 × 10-6 mol h-1m-2较低水平。
     (4)蓝藻暴发末期,藻体腐烂分解诱发水体缺氧,引起甲烷大量释放。甲烷的释放量为1.35 g m-2,最大甲烷释放速率达到215.3 × 10-3 g d-1m-2。藻沉降后,利用沸石颗粒覆盖沉积物,水环境改善效果较为理想,但对甲烷释放控制效果有限,这是因为覆盖层下藻体腐烂分解形成厌氧环境促进甲烷产生、释放。甲烷的释放量为1.13 g m-2,最大甲烷释放速率达到183.6 × 10-3 g d-1m-2。当沸石载氧后进行沉积物覆盖,水环境改善效果进一步提升。与对照相比,甲烷释放量降低了3.2倍,为0.32 g m-2,最大甲烷释放速率为57.1 × 10-3 g d-1m-2。载氧沸石覆盖到沉积物表层之后,逐渐向周围环境释放氧气,“营造”富氧环境,从而降低了产甲烷菌丰度,减少甲烷产生,同时提高了甲烷氧化菌丰度,增加甲烷氧化消耗,最终实现甲烷释放量的削减。本研究结果为富营养水体厌氧修复及甲烷释放控制提供了一种策略,利用缓解气候变暖。
英文摘要:       Over the past decades, global warming has intensified extreme weather events, such as hurricanes, heat waves and floods. Methane is the second most important greenhouse gas, contributing 20% of global warming effect. Freshwaters are considered as „hot spots‟ of methane emission. When eutrophication occurs, algae often proliferate as dense floating mats. As these blooms die, they decay and deplete water oxygen. This algae-induced anoxic environment favors methane production and increases methene emission to the atmosphere. Anoxia remediation is the key to achieve methane emission reduction from eutrophic waters. Recently, the modified local soil technology has triggered much interest as a lake geo-engineering tool for eutrophic lake restoration. In this method, the sedimentation removal of algal blooms and sediment capping can achieve water environment improvement, which may manipulate microbial process and offer the prospect of methane emission control in eutrophic waters. In this work, we developed a new local soil modification method for algal removal and tested the effect of sediment capping after algal removal on methane emission reduction. Firstly, a cheap and biodegradable cationic starch (CS) was produced as the soil modifier for algal removal. The algal removal effect, flocculation mechanism, floc properties and its impacts on the dissolved organic matters in the treated water were studied. Then, sediment capping using different materials (soil, zeolite and activated carbon) were investigated after algal removal to control methane emission. Finally, oxygen loaded capping materials were tested to remediate anoxia and reduce methane emission. The associated mechanism was also studied using the molecular method. The main results are listed as follows:
      (1) After CS modification, the isoelectric point of soil particles was remarkably increased from pH 0.5 to 11.8, which made CS modified soil particles positively charged and obtained algal flocculation ability under natural water conditions. At the soil concentration of 100 mg L-1, when the CS modifier was 10 mg L-1, 86% of Microcystis aeruginosa cells were removed within 30 min. Lower or higher CS dosage led to limited algal removal. About 71% and 45% of Microcystis aeruginosa cells were removed within 30 min when CS was 5 mg L-1 and 80 mg L-1, respectively. As water pH changed in the wide range of 4.0-10.0, algal removal effect showed no significant differences, but algal floc stability differed. Algal flocs formed at acid and alkaline conditions were more prone to be broken than those at the neutral condition.
The cost and biodegradability concerns may be largely reduced through the use of CS modified local soils in algal bloom removal.
      (2) After algal removal using CS modified soils, the DOC content in water showed a decrease. When CS with the charge density of 0.052, 0.102 and 0.293 meq g-1 were used, DOC was decreased from 3.4 to 3.0, 2.3 and 1.7 mg L-1, respectively. The excitation-emission matrix fluorescence spectroscopy and UV254 analysis indicated that CS modified soils exhibited an ability to remove some soluble organics, which potentially contributed to the DOC reduction; and the use of higher charge density CS yielded a higher organic removal performance. However, the use of low charge density CS posed a potential risk of DOC increase. When CS with the charge density of 0.044 meq g-1 was used, DOC was increased from 3.4 to 3.9 mg L-1 due to the high CS loading for effective algal removal. This study suggested that, when organic polymers are used as soil modifers for algal bloom removal, the content of dissolved organic matters in the treated water can be controlled by optimizing the charge density.
      (3) After algal blooms settled, sediment capping potentially alleviated anoxia in eutrophic waters, which varied among different capping materials. Soil and zeolite capping yielded the similar remediation effect, but were less effective than acitivated carbon capping. In the control system, the dissolved oxygen (DO) in water and redox potential (ORP) at the sediment-water interface maintained below 2.0 mg L-1 and -125 mV, respectively, throughout the experiment. After sediment capping using soil, zeolite and activated carbon, the DO in water was increased to 4.0, 4.6 and 3.1 mg L-1; and the ORP at the sediment-water interface was increased to -19.8, -8.4 and 167.5 mV, repectively. The water environment manipulation by sediment capping affected carbon cycles and thereby methane emission. Water to sediment DOC flux was increased from 0.11 to 0.12, 0.21 and 0.45 g m-2d-1, and sediment to water DIC flux was increased from 0.73 to 0.98, 0.82 and 1.18 g m-2d-1 in the soil, zeolite and activated carbon capping treated systems, respectively. Methane emission reduction was observed across the water-air interface after sediment capping. Compared with soil and zeolite capping, the activated carbon capping achieved a greater methane emission reduction, and the methane flux maintained below 3.1 × 10-6 mol h-1m-2 throughout the experiment.
      (4) As algal blooms die, they decay and induce hypoxia/anoxia, leading to a significant methane emission. Over the algal deposition period, 1.35 g m-2 of methane was emitted to the atmosphere, and methane flux across the water-air interface reached a maximum of 215.3 × 10-3 g d-1m-2. After algal blooms settled, sediment capping using zeolites yielded the reasonably oxic water environment but limited methane emission reduction, due to the occurrence of algae-induced anoxia under zeolite capping layer. Methane emission was 1.13 g m-2, and methane flux maximally reached 183.6 × 10-3g d-1m-2. The remediation effect of zeolite capping was enhanced after oxygen was loaded onto zeolites. Methane emission was reduced by a factor of 3.2 (0.32 g m-2) compared to the control. Methane flux maximally reached 57.1 × 10-3 g d-1m-2. After delivered, oxygen loaded zeolites potentially served as oxygen suppliers for the surroundings. The created oxygen enriched environment decreased methanogen abundance and simultaneously increased methanotroph abundance, leading to the methane emission reduction. The results provide a possible strategy for anoxia/hypoxia remediation and methane emission control in eutrophic waters, which can benefit global warming mitigation.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/36952
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施文卿. 改性土壤湖泊综合修复技术对富营养化水体甲烷释放控制的研究[D]. 北京. 中国科学院研究生院. 2016.
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