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题名: 复合垂直流人工湿地系统中有机物积累及设计应用研究
作者: 徐栋
答辩日期: 2007-01-06
导师: 吴振斌
授予单位: 中国科学院水生生物研究所
授予地点: 水生生物研究所
学位: 博士
关键词: 复合垂直流人工湿地 ; 有机物积累 ; 腐殖酸 ; 堵塞 ; 设计与应用
摘要: 通过一种新型复合垂直流人工湿地(IVCW)在受污染城市湖泊水体富营养化治理与水体生态系统恢复中的应用与实践,就该系统长效安全运行问题,以小试系、中试系统为基础,结合实际设计与应用开展相关研究,深入了解人工湿地堵塞现象发生的过程和变化特征,从系统有机物积累的角度探讨堵塞的可能的机理,分析堵塞发生的原因以及适合的对策,尝试建立人工湿地系统健康发育的指标评价体系,提出有效的堵塞解决对策,指导人工湿地设计、运行与维护管理,结合实际设计与应用开展研究,为人工湿地系统的长期、高效运行提供理论依据与实践示范,具有较大的理论意义和实践价值。 1.通过文献综述了人工湿地技术的发展及面临的挑战,从系统有机物积累的角度探讨了湿地堵塞现象及其研究进展。 2.比较了两种有机物积累的测定分析方法,灼烧失重法只适用于有机物含量较高的砂性壤土,重铬酸钾容重法作为测定湿地中有机物含量的方法具有较好的适用性,两者可用Y=1.497X,(R=0.937)来换算。 3.IVCW中有机物积累主要发生在基质表层和上层0-50mm处,表层有机物含量明显高于其它各层,有机物含量与基质深度成负指数关系递减,基质越深,有机物含量越少;有机物积累主要发生部位受湿地运行时间和方式影响;在进水有机负荷较高时有机物积累主要发生在下行池。 4.借鉴土壤有机质SOM(Soil Organic Matter)分组技术提取了其中的腐殖酸组分,通过元素分析及多种光谱分析技术对基质中提取的有机物组分腐殖酸(Humic Acid, HA)进行系统研究和比较,结果表明IVCW不同单元基质表层提取的有机物均出现了一定程度上的腐殖化,不同的吸收波长显示有机物的来源不同,基质表面的有机物具有更高的腐殖酸芳香缩合程度,下行流单元表层基质有机物提取HA絮凝极限较低,更易于和湿地进水中的Ca2+、SO42-发生共同沉淀形成难溶性物质并造成堵塞。 5.人工湿地对于CODCr、BOD5均具有一定的去除能力,组合工艺Z7、Z2系统对CODCr的平均去除率分别为18.7%与49.2%,对BOD5的平均去除率分别为35.7%与68.8%。有机物降解主要发生在IVCW系统下行流的上层区域,其中CODCr沿水流方向基本呈现逐步降低趋势。在Z2系统下行流湿地中层CODCr浓度最低,在下行流底层和上行流湿地中层略有提高,但出水时仍可以保持较低浓度。基质类型对人工湿地去除有机物影响较大。 6.官桥湿地系统中不同基质层面上DOC分布变化说明湿地中存在着一定程度的内源性有机物的释放。较大的水力负荷会导致相当多的有机物从表层迁移到基质中层和下层,湿地植物增加了系统中溶解性有机碳(DOC)的释放。官桥湿地系统中不同基质层面上SUVA值变化说明人工湿地出水中DOC组成发生了一定程度的改变。 7.天然有机物积累会对对湿地系统中有机污染物环境行为迁移、转化造成一定影响,通过模拟光化学反应系统,对有机污染物多环芳烃在湿地表面水环境中可能发生光化学反应作了探讨,经过模拟日光的照射,水中Fe(III)-HA配合物表现出较强的光氧化性能,HA促进了Fe(III)-HA配合物中光-Fenton反应的进行,光降解的效率与体系的pH值和Fe(III)/HA配比以及光源强度有密切关系;光降解速率随着水溶液中2-萘酚初始浓度的增加而降低;增加反应体系中溶氧会获得更好的去除率;使用苯作为自由基探针测定了有无Fe(III)加入的HA溶液中羟基自由基的生成产率,表明Fe(III)是该体系中光化学反应机制进行的关键,在一定范围内,较高HA浓度有更高的自由基产率,光解过程中的体系得紫外-可见光谱及荧光光谱变化表明有新的光解产物产生。 8.通过5项具体的人工湿地设计应用案例介绍,总结了IVCW技术在生活污水处理、城市面源污染控制、湖泊水生态系统恢复等方面的推广应用情况;从设计、营建、运行与管理等多方面加以详细阐述了设计参数、理念、系统运行参数,为IVCW系统长期健康运行以及优化与完善提供有益的支持。
英文摘要: Constructed wetlands (CW) are engineered systems that have been designed and constructed to utilize natural processes involving wetland vegetation, soils and the associated microbial assemblages to assist in treating wastewaters. As their high purification efficiency and relatively low capital investment and treatment cost, constructed wetlands wastewater treatment systems have been popular, and are being increasingly applied in many countries. However, there are many problems and challenges to the long-term safety of CW system. Substrate clogging is by far the biggest operational problem of constructed wetlands, which leads to permanent ponding and to anaerobic conditions within CW. Prolonged clogging can cause variation in hydraulic characteristics and malfunction of the system. The reasons for the clogging can be very complex and there is no simple cause-and-effect chain. Accumulation of organic solids is a typical feature in CW system treating domestic sewage and organic wastewater. The accumulated organic solids provide a long-term storage of carbon (C) and nutrients and a sustainable supply of C for microbial denitrification. However, they may clog wetland pore spaces, thus leading to a decline in wastewater retention time and the efficiency of nutrient removal from wastewaters. Aimed to the long-term safety of a new CW, Integrated Vertical Flow Constructed Wetland (IVCW) and the mechanisms, parameters, consequences, and possible strategies of clogging are reviewed and the relationships with clogging phenomenon and accumulation of organic solids are discussed by characterize organic matter (OM) fractions collected from above and within substratum in the small sale plots (SSP), medium scale plot (MSP) and Guanqiao CW systems (GQS). Detailed investigations were carried out at pilot-scale constructed wetlands (PSCWs) using a variety of methods: e.g. soil physical-chemical investigations, spectrums analysis methods, and various analysis methods of drinking water and wastewater. The main contents included: 1.Clogging phenomenon and its research development are reviewed by summing up present references. Also, the index appraisal system and evaluation standard of long-term healthy and safety development of CW system are put forward. Some possible strategies and effective techniques are summarized. 2.Two analytical methods are selected and compared which are to determine the quantity of accumulated organic matters at different depth of CW substrates. Loss On Ignition (LOI) is suitable for the sandy soil which have higher organic matter quantities only. High errors are brought out with large grain gravels media. Calculated capacity react to potassium dichromate is more applicable to determine the quantity of accumulated organic matters at different depth of CW substrates. The ration of two methods are normalized by the equation of Y=1.497X (R=0.927). 3.The organic matter accumulation (OMA) at different depth in MSP and GQS is measured and organic matter distribution is discussed. The results show that organic matter is mainly accumulated at the surface and 0~50mm upper layer in IVCW chamber. The equation describing the relation between OMA and substrate depth is y=7.2126e-0.1168x + 0.1675. Different positions where OMA take place results from the runtime of CW system and influent sewage composition. High organic loading result in more OMA occurs in down-flow chamber in early experiments and the impact of wetland vegetation (Rhizoma Acoori Graminei) seems change this trend. 4.A practicable isolation method of humic acid (HA) has been built up in accordance with open literature which describes the relative fractionation procedures of natural organic matter (NOM) in soil. Compared with one commercial product, two humic acids were extracted and prepared from different chamber substrate surface, and characterized by Elemental analysis, UV-Vis, FTIR, 3DEEM fluorescence spectra. Characteristic data of functional groups and flocculation values were also determined. The results showed the elemental compositions, UV-Vis spectra and FTIR spectra of the three humic acids were all similar to each other. Humic compounds from CW system are slightly low polycondensation extent and saturation of double bonds of C and H. It is suggested that lowly colloidal and amorphous materials with lower water holding and physical binding properties than Aldrich HA. While 3DEEM fluorescence spectra had obvious differences reflecting the differences of the structures and conformations of humic acids. This work indicates that the fluorescence characteristic can be applied to disclose differences in structure of HAs from different sources. Higher C/N and E4/E6 of HA from substrate of up-flow chamber than down-flow chamber applies that the special lignose spectra of aromatic and polysaccharide structures which have relative lower bio-degradation characteristic. Lower flocculation limits of HA from substrate of up-flow chamber shows that the OM is liable to react with the Ca2+、SO42- in influent of CW systems, and coagulative precipitation and deposition of CaCO3 or CaSO4 result in blocking of pore space in substrate. 5.Comparisons of removal rates of main organic contaminations between combination plots (Z2, Z7) and GQS show that the capability of removing CODCr、BOD5 in CW systems. The average CODCr removal rates of Z7 and Z2 are 18.7% and 49.2%. The average BOD5 removal rates of Z7 and Z2 are 35.7% and 68.8%. The main removal field of organic matter is located in the upper layer of down-flow chamber of IVCW. CODCr deceases along the direction of inflow. The substrate of CW has already become a major limiting factor on the degradation of OM. 6.The distribution of dissolved organic carbon (DOC) changes in different substrate layer shows the autochthonous OM release to a certain extent. Many OMs are transferred from the upper layer to the bottom layer with the high hydraulic loadings and vegetation of CW may contribute to the increase of DOC in bottom layer of substrate. The changes of Specific ultraviolet light absorbance(SUVA)in pore water at different layer of substrate imply the changes of the proportion of refractory fractions in plant litter and applied organic wastewater of outfluent of CW. Accumulation of organic solids includes some stable fractions which are consist of dead plants roots and stems. 7.The OMA in CWs have great influence on environmental behaviors of organic pollutants such as polycyclic aromatic hydrocarbons (PAHs). The photodegradation of the carcinogenic pollutant 2-naphthol in aqueous solution containing Aldrich humic acid (HA) and ferric ions (Fe(III)) under simulated solar irradiation was investigated. The photooxidation efficiencies were dependent on the pH values, light intensities and Fe(III)/HA concentration in the water, with higher efficiency at pHs 3-4, and 50 μmol l-1 Fe(III) with 20 mg l-1 HA under 250 W HPML. The initial rate of photooxidation increases with increasing the initial concentration of 2-naphthol from 10 μmol l-1 to 100 μmol l-1, while do not change at 50 and 100 μmol l-1. However, higher removal efficiency of 2-naphthol is achieved at its lower initial concentration of 10 μmol l-1, and initial rate of photooxidation is 0.193 μmol l-1min-1. Dissolved oxygen (DO) plays an important role in the system containing Fe(III)-HA complexes in which Fenton and photo-Fenton reactions were enhanced in the environment. Hydroxyl radicals produced in HA solution with or without ferric ions were determined by using benzene as free radical scavenger and phenol as scavenging products proportional to hydroxyl radicals. By using UV–Vis and excited fluorescence spectrum techniques, the main photooxidation products, which have higher absorption in the region of 240-340 nm, were found, and the mechanisms for the oxidative degradation is proposed. 8.Particular parameters of thedesign, operation and performance of six cases in design and application of constructed wetland are described carefully, all these application of IVCW to the rehabilitation of fresh water (lake and river) ecology、to control non-point pollution in urban surface runoff and to treat sewage in scenery spot are summarized, the widely use of IVCW proved that IVCW can run safely for a long time if sound design strategies and measures are taken to prevent substrate from clogging.
语种: 中文
内容类型: 学位论文
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