生物絮凝泥沙的絮凝结构实验分析

泥沙絮凝是黏性泥沙动力学中的一个重要课题,相关的研究主要关注于各种有机絮凝和无机絮凝的形成机理、影响因素、泥沙物理化学条件等方面。但近几十年,泥沙的生物絮凝逐渐引起更多的关注,大多数研究集中在各种生物学因子和沉积学因子之间的相互关系。本文借助于最新发展的研究工具和相关的显微镜方法来桥连生物絮凝泥沙中泥沙颗粒和微生物活动及其代谢产物生物膜之间的关系,以利于更好地理解聚合物质生物膜在微絮凝结构及其外部絮凝行为中的作用。研究表明,生物絮凝泥沙包含了复杂的生物膜网络,呈现出复杂的絮凝结构。生物膜覆盖泥沙表面充斥于颗粒孔隙之中,在生物絮凝中起到主要的桥连作用,并对生物絮凝泥沙的表面形貌、结构特征、力学性质等产生重要影响。     

生物絮凝泥沙运动输移数学模型

近几十年来,河流中生物絮凝泥沙的运动输移对河流生态系统与水工建筑物等造成的影响,已逐渐成为一个研究热点。本文将泥沙运动输移模型与生物絮凝机理模型耦合起来,构建生物絮凝泥沙运动输移数学模型,以预测富营养水生态系统中生物絮凝泥沙运动输移过程中的浓度及水位变化。模型中,通过求解一维非恒定流圣维南方程来计算水流,将生物絮凝视为导致悬浮泥沙絮团粒径变化的主要因素,通过不饱和非均匀输沙(泥沙/絮团)方法来模拟生物絮凝泥沙的运动。利用文献数据和室内水槽实验来验证生物絮凝泥沙运动输移数学模型,模拟结果与实验数据吻合较好,表明所构建的一维数学模型可以较好地模拟生物絮凝泥沙的输移特性。     

泥沙颗粒生长生物膜后沉降的实验研究(Ⅱ)——沉降速度计算

泥沙生长生物膜后相应的物理特性将会发生改变，本文主要探讨泥沙颗粒在微生物生命活动的影响下沉降特性的改变情况。通过将官厅水库的泥沙分为六组，使用天然水和营养液的混合液对泥沙进行培养，用来模拟富营养水体中泥沙颗粒特性的发展变化情况。对于生长生物膜后的絮体颗粒在各个不同培养时间的沉降运动，实验采用先进的图像采集观测系统进行拍摄采样，并利用图像分析测量颗粒大小和沉速的变化，推导了生长生物膜后的颗粒沉速计算公式。研究表明生物膜极大的改变了颗粒的表面特性，使得颗粒下沉阻力增大，与同等大小无生物膜粘连的泥沙颗粒相比沉速明显减小。     

泥沙颗粒生长生物膜前后表面变化的试验研究

以泥沙颗粒为载体,以天然水配置营养液进行生物膜培养试验,采用环境扫描电子显微镜观察泥沙颗粒生长生物膜前后的形貌变化,并用图像处理和梯度计算的方法对获得的灰度图片进行分析,发现泥沙颗粒因生物膜的生成而发生较大变化,群体泥沙互相粘连,形成网状结构或絮状结构等,单颗粒泥沙因为生物膜的存在使得长膜沙相比原状沙其表面导数更多地集...     

泥沙颗粒生长生物膜后沉降的实验研究Ⅱ：沉降速度计算

泥沙生长生物膜后相应的物理特性会发生改变。本文主要探讨泥沙颗粒在微生物生命活动的影响下沉降特性的改变情况。将官厅水库的泥沙分为6组,使用天然水和营养液的混合液对泥沙进行培养,用来模拟富营养水体中泥沙颗粒特性的发展变化情况。对于生长生物膜后的絮体颗粒在各个不同培养时间的沉降运动,实验采用先进的图像采集观测系统进行拍摄采样,并利用图像分析测量颗粒大小和沉速的变化,推导了生长生物膜后的颗粒沉速计算公式。研究表明生物膜极大地改变了颗粒的表面特性,使得颗粒下沉阻力增大,与同等大小无生物膜黏连的泥沙颗粒相比沉速明显减小。     

泥沙颗粒生长生物膜后沉降的实验研究Ⅰ：实验设计及粒径变化

天然河道与湖泊的水污染问题日益受到广泛的重视,对泥沙颗粒的基本特性的研究也开始与水体污染物质的吸附解析、微生物的吸附成膜等水环境生态方面结合起来。本文通过对官厅水库的泥沙分组进行培养,并采用先进的图像采集观测系统,对泥沙生长生物膜后的絮体在沉降时进行拍摄采集,探讨了颗粒级配的变化情况。同时利用得到的颗粒特征值,推导了水体不同营养条件下的粒径变化公式。数据表明泥沙在生物膜的作用下形成新的泥沙生物絮体颗粒,能够在水沙交界面上形成粒径范围很宽的颗粒组使得级配变化显著。     

悬浮泥沙环境下微塑料颗粒的絮凝特征研究北大核心CSCD

微塑料颗粒与悬浮泥沙的絮凝特征研究,尤其在天然水体环境中生物膜附着的情况下,对于微塑料颗粒在紊动水体中与悬浮泥沙的沉积动力学过程具有科学意义。选用高岭土作为悬浮泥沙的代表,与聚乙烯微塑料颗粒在紊动剪切率可控的搅拌槽中进行絮凝试验,并采用非侵入式絮凝体观测系统进行观测,分析絮团在不同悬浮泥沙浓度及不同紊动剪切率条件下的絮凝特征。试验结果表明,随着紊动剪切率和悬浮泥沙浓度的增加,絮团的特征粒径总体呈现出先增大后减小的规律。利用Winterwerp模型对试验数据进行拟合,数值模拟结果较好地印证了试验的结果。     

生物膜泥沙床面对水体紊动影响的实验研究

泥沙床面生长生物膜后水流紊动特性将发生变化,进一步影响到泥沙的起动,悬浮和输移特性。本文采用d500.1 mm的天然沙,对相同水流条件下无生物膜生长和有生物膜生长床面以上的水流内部结构进行研究。实验中采用多普勒声学流速仪(ADV)测量了垂向流速,对比分析了生物膜生长前后,时均流速、雷诺应力、紊动强度以及紊动猝发事件在垂向上的变化,并初步分析了这些变化对泥沙运动的影响。结果表明:生物膜生长后,同流量条件下的垂向平均流速增加,床面阻力减小;对比无膜沙床面,有膜沙床面在发生冲刷的水力条件下,雷诺应力、紊动强度均有所减小,从而会影响到悬沙的浓度分布;同时猝发事件发生率在垂向上的变化也使得生物膜泥沙床面的泥沙起动更加困难。     

黏性泥沙絮凝研究综述与展望

絮凝是黏性泥沙最重要的特性之一,也一直是泥沙基本理论和运动规律研究的重点和难点课题,对絮凝过程与机制的研究是理解、模拟和预测黏性泥沙及其携带物质输运规律的关键。总结了黏性泥沙絮凝机制、絮团特性和影响絮凝因素方面的研究成果与进展,并分析提出了现有研究的不足,主要有三方面:对黏性泥沙生物絮凝过程与作用机理的精细化研究薄弱;对絮团有效密度和结构特性变化及其影响因素、影响方式等问题的认识不足;已有研究仍主要以单因子影响为主,难以准确反映影响因子复杂多变的天然水环境的絮凝特性。今后需要深化黏性泥沙生物絮凝的基础研究、加强研究不同絮凝环境及絮凝过程对絮团结构的影响方式与机理以及开展多因子共同作用的复合絮凝体系内黏性泥沙絮凝过程与控制机制研究。     

水库泥沙絮凝机理研究

天然水体泥沙絮凝的作用力主要来源于颗粒表面的电荷作用,其絮凝的基本原理可以采用DLVO理论分析研究。以三峡水库中的水体环境因素为基础,通过DLVO理论量化了颗粒之间的作用能和作用力。通过对颗粒之间位能曲线上特征值与泥沙颗粒相对运动具有的动能之间的对比,得到了泥沙颗粒能够形成絮凝的水动力条件。对比三峡水库具体的水动力因素发现,坝前水深较大,当泥沙处于水体的中层时更容易产生絮凝;水库中泥沙的絮凝体均较为疏松,颗粒之间相互作用力较小,容易在水流中被剪切破坏。最后通过力的平衡关系得到了絮凝体的极限下沉速度,沉速等于絮凝体极限下沉速度的单颗粒泥沙粒径即为絮凝临界粒径,约为0.019 mm,小于临界粒径的单颗粒泥沙的沉速需要考虑絮凝因素而进行修正。     

泥沙颗粒生长生物膜前后表面变化的实验研究

微生物吸附及生物膜的形成是自然界中普遍存在的现象之一，其对河道、水库等水体环境中泥沙颗粒形貌及性质的影响目前研究尚少。本文采用环境扫描电子显微镜观察泥沙颗粒生长生物膜前后的形貌情况，并用图像处理和梯度计算的方法对获得的灰度图片进行分析，发现颗粒的表面微形貌因生物膜的生成而发生较大变化。     

Impact of the surface characteristics of rainwater tank material on biofilm development

In order to determine the impact of rainwater construction material on the development of a biofilm, three materials were tested: concrete, clay, and PVC. The biofilm attachment was initially more effective on clay coupons, but, after a period of three days, concrete coupons produced a greater quantity of biofilm than clay and PVC, in that order. The heterotrophic plate count in the rainwater indicated that this quantity tended to first increase following a rainfall, and then decrease. The new materials seemed to attach themselves to the existing biofilm on the wall and/or sediment in the form of small particles. The presence of fecal coliforms in the biofilm coupons was noted after major rainfall events, and this was correlated with the increase in fecal coliforms in the water. This study concluded that the most favorable support for biofilm development is concrete, clay, and PVC, in that order.     

Modelling biofilm-modified hydrodynamics in 3D.

A simulation-based study to predict the impact of biofilm growth on displacement distributions for flow of water through a supporting packed bed is presented. The lattice Boltzmann method and a directed random walk algorithm are used, and are applied to the system with and without biofilm being present. The aim of this simulation study is to model the anomalous transport dynamics induced by biofilm, as reported in the literature, and thus to study the impact of observation time, delta, on the shape of the displacement distributions (propagators). We believe that this is the first demonstration of a propagator simulation for flow through a complex porous structure modulated by biofilm growth. The propagator distributions undergo a transition from a pre-asymptotic to a Gaussian-shaped distribution with increasing delta. The propagators were simulated for a wide range of delta going up to 500 seconds. This transition occurs with and without biofilm, but is very significantly delayed when biofilm is present due to the consequential development of essentially stagnant regions. The transition can be classified into three stages: a diffusion-dominated stage, a "twin-peak" stage and an advection-dominated stage.     

Biofilm growth in response to various concentrations of biodegradable material in drinking water.

Biological stability is one of the most important aspects of safe drinking water. It depends crucially on the availability of biodegradable organic carbon (BDOC). Measurement of BDOC is time-consuming and only performed if an increase is suspected. In this study, a fibre optical sensor (FOS) was used to detect changes in BDOC, detected as an increase in biofilm growth. The FOS consists of a sending and a receiving optical fibre, the latter connected to a detector. When material is deposited at the tip of the fibre, an increase of backscattered light is detected. In a system fed with drinking water, the signal was correlated to biofilm growth which was confirmed by independent surface colonisation determination. When 1 and 3mgL(-1) of BDOC respectively was added, the increment of the FOS signal over a period of 1 week could be distinguished. Interference by planktonic components and humic substances could be excluded. The biofilm on the FOS could be used as a means to detect changes in BDOC in drinking water and the signal has an early warning capacity.     

A new mathematical model for chemotactic bacterial colony growth.

A new continuum model for the growth of a single species biofilm is proposed. The geometry of the biofilm is described by the interface between the biomass and the surrounding liquid. Nutrient transport is given by the solution of a semi-linear Poisson equation. In this model we study the morphology of a chemotactic bacterial colony, which grows in the direction of increasing nutrient concentration. Numerical simulations using the level set method and finite difference schemes are presented. The results show rich heterogeneous morphology.     

A membrane biofilm reactor achieves aerobic methane oxidation coupled to denitrification (AME-D) with high efficiency

Methane would potentially be an inexpensive, widely available electron donor for denitrification of wastewaters poor in organics. Currently, no methanotrophic microbe is known to denitrify. However, aerobic methane oxidation coupled to denitrification (AME-D) has been observed in several laboratory studies. In the AME-D process, aerobic methanotrophs oxidise methane and release organic metabolites and lysis products, which are used by coexisting denitrifiers as electron donors for denitrification. Due to the presence of oxygen, the denitrification efficiency in terms of methane-to-nitrate consumption is usually low. To improve this efficiency the use of a membrane biofilm reactor was investigated. The denitrification efficiency of an AME-D culture in (1) a suspended growth reactor, and (2) a membrane biofilm reactor was studied. The methane-to-nitrate consumption ratio for the suspended culture was 8.7. For the membrane-attached culture the ratio was 2.2. The results clearly indicated that the membrane-attached biofilm was superior to the suspended culture in terms of denitrification efficiency. This study showed that for practical application of the AME-D process, focus should be placed on development of a biofilm reactor.