Seasonal effect on ammonia nitrogen removal by constructed wetlands treating polluted river water in southern Taiwan

A pilot-scale constructed wetland (CW) system, combining a free water surface wetland and a subsurface wetland in series, was used to purify highly polluted river water. The concentrations of constituents varied seasonally. The effects of season-dependent parameters, such as temperature, mass loading rate and inflow salinity, on the removal of ammonia nitrogen (AN) in the wetland system were examined at a constant hydraulic loading rate, based on data from June 1998 to February 2000. AN removal of the CW varied cyclically with the seasons. The removal efficiency and the first-order volumetric removal rate constant (k(V)) increased exponentially with water temperature, yielding a high temperature coefficient (theta). However, the mass removal rate decreased exponentially as temperature increased. These contradictory results made the actual effect of temperature uncertain. The inhibition of high water salinity on AN removal was also unclear because k(V) (as well as k(V20)) and mass removal rate were inversely proportional to salinity. However, mass loading rate (MLR) predominantly affected both the removal efficiency and the mass removal rate of AN, both of which were factors that explicitly determined seasonality. A power equation, k(V20)' alpha MLR(-n), was proposed to correct the variation of the mass loading rate in estimating k(V) and thus in designing a constructed wetland.     

人工湿地中的SND机理以及DO、pH对其的影响

人工湿地中的水生植物向系统中输送大量的DO,并为系统中的微生物提供栖息地,使得系统中连续同时发生硝化和反硝化（SND）反应。DO的高低直接影响到人工湿地系统SND的效果,根据SND的发生机理,可采用复合植物床（系统前端栽种泌氧能力强、后端泌氧能力稍弱的水生植物）和间歇运行的的方式来改善整个系统的脱氮能力。pH过高或过低都会抑制人工湿地系统的SND作用,最适宜值为7．0,据此可以选择适当pH的湿地填料来提高系统的SND作用。     

污水生物脱氮过程硝化阶段N2O动力学模型

通过耦合导致N2O产生的亚硝酰基（NOH）化学分解和氨氧化细菌（AOB）反硝化途径,构建了一种包含10个组分和7个生化过程的硝化阶段N2O动力学模型。与此同时,利用MATLAB和Excel软件工具,完成了对所有动力学参数的相对灵敏度分析,并在此前提下实现了对模型关键参数的拟合,完成了对模型的模拟与验证过程,进而确定了一种不同于已有活性污泥模型计算软件的模型计算方法。并且通过对模型数据和实验数据之间相关系数（R2）的考察,证明本模型不仅对硝化阶段含氮组分具有良好的模拟效果,同时也与机理研究相符。     

同步硝化反硝化工艺中DO浓度对N2O产生量的影响

采用序批式生物膜反应器（SBBR）,在连续曝气全程好氧的运行条件下,考察不同溶解氧浓度对同步硝化反硝化脱氮性能及N2O产量的影响。控制溶解氧浓度恒定在1、2、2.5和3 mg/L。结果表明,DO为2 mg/L和2.5 mg/L时,氨氮去除率分别为97.9%和98.5%,同步硝化反硝化率均为99%。DO为2 mg/L时,系统中N2O产生量最低,为0.423 mg/L,占氨氮去除量的1.4%;DO为3 mg/L时N2O的产生量最高,为2.01 mg/L,是DO为2 mg/L时的4.75倍。系统中亚硝酸盐的存在可能是高溶解氧条件下N2O产量增加的主要原因,同步过程中没有NOx-的积累即稳定的SND系统有利于降低生物脱氮过程中N2O的产生量。     

SBBR工艺硝化过程中DO对N2O产生量的影响

利用生物膜序批式反应器(SBBR),考察不同溶解氧(DO)条件下硝化过程中N2O产生及释放过程。研究结果表明:DO浓度增大有利于控制系统中N2O的产生;DO浓度分别为(1.92±0.14)mg/L、(2.34±0.11)mg/L和(2.70±0.11)mg/L时,硝化过程中N2O释放因子(N2O总产量与NH4+-N转化量的比值)分别为5.47%、5.36%和4.77%。分析其原因主要是DO浓度的减小使DO对生物膜的穿透力降低,氧传递能力减弱后生物膜系统内易发生以N2O为产物的氨氧化细菌(AOB)反硝化反应。同时,在研究的3种不同的DO条件下,低DO运行条件更有利于SBBR实现亚硝酸盐型同步硝化反硝化。     

碳氮比对人工湿地污水处理效果的影响

采用表面流人工湿地系统静态小试装置,考察了低、中、高3组不同进水COD/N(2,5,10)对系统中氮、磷及COD去除效果的影响。结果表明:进水C/N的变化对COD的去除率影响不大,平均去除率达到94.6%。TN的去除率随着COD/N的增大而逐渐升高,在C/N=5时达到63.8%,继续提高COD/N,TN的去除率变化不大。NH4+-N去除率随着COD/N的增加而降低。随着碳源的增加,释磷菌能够从进水中获得充足的碳源,从而可以比较充分地释磷,因此,磷的去除率随COD/N的增加而提高。     

不同DO下亚硝态氮氧化菌硝化系统N 2O减量化研究

采用序批式活性污泥反应器(SBR),在富集亚硝态氮氧化菌(NOB)的基础上,考察了DO对连续进水模式下硝化过程中N_2O减量化的影响。结果表明,在污泥氨氧化菌(AOB)和NOB的比耗氧速率(SOUR)分别为(2.36±0.31)、(7.62±0.43)mg/(L·h)条件下,不外加碳源进行小试实验,氨氮均小于1.0mg/L,亚硝态氮均小于0.5mg/L。DO由0.2mg/L增至3.0mg/L过程中,随着DO增加,积累的硝态氮浓度逐渐上升,而累计产生的N_2O浓度先上升后下降。DO为0.2mg/L时,积累的硝态氮和累计产生的N_2O浓度最低,可以实现N_2O的最大减量化。在进水连续投加氨氮的方式下,氨氮氧化速率不是引起N_2O生成的关键步骤,碳源缺乏的情况下NOB硝化系统中低DO可以有效控制N_2O的释放。     

污水硝化过程中N2O逸出控制的理论与实践

在污水生物脱氮工艺中,硝化过程是由自养硝化菌和异养硝化菌共同完成的.2类细菌的N2O生成机理及逸出量与系统中溶解氧的高低密切相关.了解硝化系统中的典型菌种自养菌Nitrosomonas europaea和异养菌Alcaligenesfaecalis生成N2O的机理是控制硝化过程中N2O逸出的理论基础,通过筛选优势菌种构建同步硝化-反硝化作用则是控制N2O逸出的新途径.     

Suppression of nitrification and N2O emission by karanjin--a nitrification inhibitor prepared from karanja (Pongamia glabra Vent.)

A laboratory incubation study was undertaken to study nitirification and N2O emission in an alluvial, sandy loam soil (typic ustochrept), fertilized with urea and urea combined with different levels of two nitrification inhibitors viz. karanjin and dicyandiamide (DCD). Karanjin [a furanoflavonoid, obtained from karanja (Pongamia glabra Vent.) seeds] and DCD were incorporated at the rate of 5%, 10%, 15%, 20% and 25% of applied urea-N (100 mg kg(-1) soil), to the soil (100 g) adjusted to field capacity moisture content. Mean N2O flux was appreciably reduced on addition of the inhibitors with urea. Amounts of nitrified N (i.e. (NO3- + NO2-)-N) in total inorganic N (i.e. (NO3 + NO2- + NH4+)-N) in soil were found to be much lower on the addition of karanjin with urea (2-8%) as compared to urea plus DCD (14-66%) during incubation, indicating that karanjin was much more potent nitrification inhibitor than DCD. Nitrification inhibition was appreciable on the application of different levels of karanjin (62-75%) and DCD (9-42%). Cumulative N2O-N loss was found to be in the range of 0.5-80% of the nitrified N at different stages of incubation. Application of karanjin resulted in higher mitigation of total N2O-N emission (92-96%) when compared with DCD (60-71%).     

Removal processes for arsenic in constructed wetlands

Arsenic pollution in aquatic environments is a worldwide concern due to its toxicity and chronic effects on human health. This concern has generated increasing interest in the use of different treatment technologies to remove arsenic from contaminated water. Constructed wetlands are a cost-effective natural system successfully used for removing various pollutants, and they have shown capability for removing arsenic. This paper reviews current understanding of the removal processes for arsenic, discusses implications for treatment wetlands, and identifies critical knowledge gaps and areas worthy of future research. The reactivity of arsenic means that different arsenic species may be found in wetlands, influenced by vegetation, supporting medium and microorganisms. Despite the fact that sorption, precipitation and coprecipitation are the principal processes responsible for the removal of arsenic, bacteria can mediate these processes and can play a significant role under favourable environmental conditions. The most important factors affecting the speciation of arsenic are pH, alkalinity, temperature, dissolved oxygen, the presence of other chemical species - iron, sulphur, phosphate -, a source of carbon, and the wetland substrate. Studies of the microbial communities and the speciation of arsenic in the solid phase using advanced techniques could provide further insights on the removal of arsenic. Limited data and understanding of the interaction of the different processes involved in the removal of arsenic explain the rudimentary guidelines available for the design of wetlands systems.     

2种人工湿地的水力停留时间及净化效果

以复合垂直流人工湿地(IVCW)和水平潜流人工湿地(HSCW)为研究对象,研究了2种湿地运行的季节性最佳水力停留时间(HRT)参数,并监测了2种湿地在最佳HRT参数下运行时对污水的净化效果。结果显示:(1)在IVCW中,最佳HRT在春、秋季为8～10 h;夏季为6 h;冬季为12 h。在HSCW中,最佳HRT在春、秋季为10～12 h;夏季为6～8h;冬季为24～36 h。(2)2种湿地对COD的去除率均无显著的季节性差异;湿地进水中NH4+-N/TN比值与TN去除率显著负相关;不同季节下IVCW对TN的去除效果均高于HSCW。(3)水温对TN、TP去除率的影响在IVCW中比HSCW中的明显;水温高时,2种湿地中的TN去除率较高,IVCW中的TP去除率也较高,但HSCW中的TP去除率则较低,它们间均未达到显著的相关性。     

Nitrous oxide emission from polyculture constructed wetlands: effect of plant species

Loss of nitrogen from the soil-plant system has raised environmental concern. This study assessed the fluxes of nitrous oxide (N2O) in the subsurface flow constructed wetlands (CWs). To better understand the mechanism of N2O emission, spatial distribution of ammonia-oxidizing bacteria (AOB) in four kinds of wetlands soil were compared. N2O emission data showed large temporal and spatial variation ranging from -5.5 to 32.7 mg N2O m(-2) d(-1). The highest N2O emission occurred in the cell planted with Phragmites australis and Zizania latifolia. Whereas, the lower emission rate were obtained in the cell planted with P. australis and Typha latifolia. These revealed that Z. latifolia stimulated the N2O emission. Transportation of more organic matter and oxygen for AOB growth may be the reason. The study of AOB also supported this result, indicating that the root structure of Z. latifolia was favored by AOB for N2O formation.     

Nitrogen transformations modeling in subsurface-flow constructed wetlands.

Subsurface-flow constructed wetlands (CWs) wastewater treatment typically results in satisfactory organics removal. However, the removal of nutrients, particularly nitrogen, is often unreliable, and typically less than desired, and nitrogen transformations in wetlands systems are not well-understood. The principal objective of this study was to establish a basis for quantification of nitrogen transformations through subsurface flow CW systems. Actual performance data from a full-scale facility located near Lincoln, Nebraska, were used to calibrate a proposed nitrogen transformations model, which, in turn, was used to replicate and predict the wetlands performance. To realize this objective, a compartmental analysis technique, which uses a set of differential equations and nonlinear optimization numerical methods, was used for solving nitrogen transformation rates and for predicting wetland performance. The model satisfactorily reproduced the mean effluent concentrations for organic nitrogen, ammonium-nitrogen, and nitrate-nitrogen, but with lesser accuracy with respect to peak high and low effluent concentrations. Nitrogen mass balance in the wetland was used to identify likely nitrogen transformation pathways. Generally, it was found that approximately one-third of the influent nitrogen mass was removed through nitrification and denitrification, one-third was removed through vegetative assimilation, and the remainder was discharged in the wetland effluent.     

1，2-二氯苯在3种基质中的吸附研究

采用平衡振荡法研究了1,2-二氯苯在3种人工湿地基质中的吸附情况。结果表明,1,2-二氯苯在12 h达到吸附平衡,可由Lagergren一级吸附动力学模型得出3种土壤的吸附速率常数分别为0.3338 h-1、0.2679 h-1和0.2537 h-1,壤土的吸附效果明显好于细砂、粗砂。30℃的吸附等温线既符合Freud...     

人工湿地系统微生物去除污染物的研究进展

人工湿地污水处理系统具有净化效果显著、建设和运行费用低廉、管理简便等优点,近年来越来越受到人们的重视。人工湿地是利用介质、植物和微生物构成的复合系统来处理污水。微生物在人工湿地系统净化污水过程中发挥着重要作用。介绍了人工湿地系统中微生物去除污染物的研究进展,重点讨论了人工湿地对污染物和特殊有机污染物的去除以及系统基质中微生物的种群和活性等内容,并结合我国研究现状展望了该领域的研究前景。人工湿地系统微生物对污染物去除将成为人工湿地生态系统服务功能评价、人工湿地生态系统健康与稳定的诊断的重要组成部分。     

构筑根孔湿地夏季浮游植物群落结构特征

湿地通过复杂的物理、化学、生物过程改变水质状态,而浮游植物能够快速、准确地反映环境变化并广泛应用于水质评价。2013年夏季对嘉兴市石臼漾构筑根孔湿地(运行5年)与贯泾港构筑根孔湿地(运行初期)的浮游植物群落结构进行了调查,分析了湿地内部浮游植物变化特征,识别其主要影响因素。结果表明,贯泾港湿地分布浮游植物5门70种(含变种),石臼漾湿地浮游植物6门68种(含变种)。绿藻门是贯泾港和石臼漾湿地浮游植物种类最主要的构成类群,分别占总种类数的46%和49%。贯泾港湿地浮游植物细胞数量在1 478.43×104~18 544.24×104 cells/L之间变化,均值为9 374.69×104 cells/L,变化幅度较大;石臼漾湿地浮游植物细胞数量整体低于贯泾港湿地,在598.58×104~3 587.71×104 cells/L之间变化,均值为2 526.36×104 cells/L。贯泾港湿地和石臼漾湿地水体水质处于β-中污型到α-中污型,整体上呈现出石臼漾湿地水质优于贯泾港湿地。研究表明,湿地不同的运行时期对浮游植物群落结构产生了影响。     

COD/N对潜流人工湿地脱氮效能及N2O排放的影响

人工湿地因其低能耗、易管理的优点被广泛应用于水处理和生态修复,尤其在发展中国家有其适用性。为探讨COD/N对潜流人工湿地脱氮效能及氧化亚氮（N2O）的排放影响,分别构建5组微型人工湿地CW1~CK,进水化学需氧量/总氮（COD/N）分别为20：1、10：1、7：1、4：1和0：1。结果表明,湿地出水DO浓度均低于0.5 mg·L-1,不同的COD/N下无显著差异,但pH表现为随COD/N的升高而降低。进水COD/N为10、7和4的湿地中COD去除率在80%以上,而进水COD/N=20的湿地中COD去除率不足70%。5组COD/N湿地中氨氮（NH4+-N）的平均去除率依次为（61±16.6）%、（23±14.1）%、（30±12.5）%、（28±14.5）%和（74±7.0）%,在碳源充足或无碳源的条件下有利于NH4+-N的去除。除COD/N=0外,其余湿地中出水未检测到硝态氮（NO3--N）。湿地中总氮（TN）的去除变化与NH4+-N相似。5组湿地系统中,N2O的平均释放通量和累积排放量,分别在0.83~11.84 mg·（m2·h）-1和30.65~490.80 mg·m-2之间。COD/N=4的人工湿地系统中,N2O的平均释放通量和累计排放量显著高于其他处理（p2O形态去除的氮占系统去除TN的百分比为4.87%。COD/N对潜流人工湿地的脱氮和N2O减量具有调控作用。     

Effects of biochar on nitrification and denitrification-mediated N2O emissions and the associated microbial community in an agricultural soil

Environmental Science and Pollution Research - Nitrous oxide (N2O) is a strong greenhouse gas, and it is of great significance for N2O reduction to study the effects of biochar on its production...