Foaming in anaerobic digesters caused by Microthrix parvicella

Three large wastewater treatment plants in the greater Stockholm area have experienced serious anaerobic digester foaming. Microscopic studies of the sludge from the foam phase showed a network of the filamentous organism Microthrix parvicella. The morphology of the long, coiled filament appeared to be affected by the anaerobic conditions where it became broken up into to shorter and thicker filaments. The operating strategy to prevent foam in the anaerobic digesters at these plants is to control the growth of M. parvicella in the activated sludge tanks by increasing the sludge load. Top installed stirrers and the addition of poly-aluminium salt have also been used to prevent foam formation.     

In situ characterization of substrate uptake by Microthrix parvicella using microautoradiography

Microthrix parvicella is a filamentous microorganism responsible for bulking and foaming problems in many activated sludge treatment plants. The problems have increased with the introduction of nutrient removal in many countries, and presently, there is no reliable control strategy for M. parvicella. Little is known about the physiology of M. parvicella, and conflicting data exist about its preferred organic substrates, and whether it is able to be physiologically active under anaerobic and anoxic conditions. In this study, the ability of M. parvicella to take up various radioactively labeled organic compounds was investigated in situ at three nutrient removal plants using a microautoradiographic technique. Of 12 compounds tested under aerobic conditions only the long chain fatty acids (LCFA), oleic acid and palmitic acid, and to some extent a lipid, trioleic acid, were assimilated. None of the simple substrates such as acetate, propionate, butyrate, glucose, ethanol, glycine and leucine were taken up. Furthermore, the uptake of oleic acid was compared under anaerobic, anoxic and aerobic conditions, and it was demonstrated that in addition to aerobic conditions M. parvicella was also able to take up oleic acid under anaerobic and anoxic conditions. No difference in substrate uptake pattern for M. parvicella was found among the tested activated sludge plants. The results strongly indicate that a better control strategy against M. parvicella must rely on a better understanding of presence and availability of triglycerides and LCFA, and an improved knowledge of the physiology of M. parvicella under anaerobic and anoxic conditions.     

Influence of temperature and sludge loading on activated sludge settling,especially on Microthrix parvicella

During recent years modern full scale wastewater treatment plants with biological nitrification, denitrification and phosphorus removal have had increasing problems with foam formation on the surfaces of aerobic tanks and with bulking activated sludge. The results of a survey in 1995 (Kunst and Knoop, 1996) showed that most often the filamentous bacterium Microthrix parvicella is responsible for these problems. Up to today there is only little knowledge about its selection criteria in activated sludge. Therefore several expenments were done in full scale activated sludge plants and in laboratory systems under defined conditions to investigate the influence of low (< 0.1 kg/(kg·d)) and high (≤ 0.2 kg/(kg·d)) BOD₅-sludge loading rates on the growth and morphology of M. parvicella and the settlement of activated sludge. Furthermore the influence of temperatures of 5°C, 12°C and 20°C on the growth of M. parvicella was investigated. It was shown that M. parvicella grows at low BOD₅-sludge loading rate and low temperature and is the main causative organism of bulking and foaming sludge in nutrient removal plants. On the basis of this investigation it was concluded that the growth of M. parvicella and the settling problems of the activated sludge resulting from excessive growth of this filament will always appear in modern municipal wastewater treatment plants with BOD₅-sludge loading rate ≤ 0.1 kg/(kg·d) especially under low temperature conditions.     

Causes of,and control strategies for,Microthrix parvicella bulking and foaming in nutrient removal activated sludge systems

Bench and pilot scale nutrient removal activated sludge units were used to examine the effect of factors such as temperature, substrate type (easily biodegradable in the form of acetate and slowly biodegradable in the form of oleic acid) on Microthrix parvicella growth. The configurations examined include complete mix with and without selectors (anoxic and anaerobic) and plug flow reactors. The results indicate that low temperatures and substrates in the form of long chain fatty acids favour the growth of M. parvicella. With respect to reactor configuration, a plug flow configuration was shown to be quite effective in controlling the growth of M. parvicella and producing a sludge with good settling characteristics, while the presence of a selector, either anoxic or anaerobic, had no significant effect on the growth of M. parvicella.     

Growing controversy over "wise international water governance".

This article takes the perspective that when political relationships are strained, there seem to be few examples of wise international water resources governance. The Middle East is a striking example. Much effort has been put into policy development and the design of international principles, but very little into the translation of those into concrete and lasting governance. One of the theses of the article is that politics--whether domestic or international--in most cases overrides these principles and standards. Moreover readymade regional co-operation models of water managements are not directly applicable to every geographical, political, economic and social setting. Certain factors are often under-estimated in international water negotiations, such as: the complexity of any hydro-political negotiations, and need to develop commonly accepted standards; the difficulty of translating policy--either politically or legally--into an operational and realistic negotiations strategy; the format of the procedures and meetings; recognition that third parties should have a long-term perspective on any conflict they get involved in. With reservations, the lessons learned indicate that the following factors have an impact on grid locked situations, such as: new substantive information; new trade-offs between the parties; and changed political climate or relationship with external power-brokers.     

Modelling faecal coliforms dynamics in the Seine estuary, France.

A model describing the dynamics of faecal coliforms (FC) in the Seine estuary has been developed and coupled with a three-dimensional hydrodynamic model. As input to this model three types of FC sources were considered: (1) FC transported by the Seine river flow at the estuary entrance at Poses dam; (2) FC brought in through the tributaries of the Seine estuary; and (3) the outfalls of the treated effluents of the WWTPs located along the estuary. As previous studies in the Seine estuary showed that a large proportion of FC was attached to SM, two pools of FC were considered separately in the model: free FC and FC attached to SM. Two main processes controlling the fate of FC in the estuary were considered: mortality and settling. The model calculates for a given discharge of the Seine river at Poses the longitudinal distribution of FC along the estuary. The model was validated by comparison of model calculations with experimental data in various hydrological conditions. The model also correctly reproduced the impact of the main river flow rate on the level of estuarine water's contamination. Finally, the model was used to test different scenarios of sanitation, suggesting priorities for sanitation efforts.     

Heat exchanges and temperatures within a salmon spawning stream in the Cairngorms,Scotland: seasonal and sub‐seasonal dynamics

Stream temperatures are often used to predict salmonid embryo development; but there are very few medium‐term studies of the heat exchanges determining water column and bed temperatures. Furthermore, no research exists on the energy balance for sub‐arctic Scottish rivers. This paper reports results of a hydrometeorological study of a Cairngorm stream (Girnock burn, northeast Scotland) over the salmon spawning–hatch season (late October 2001 to mid‐April 2002) that aims: (1) to characterize seasonal and sub‐seasonal stream energy budget and thermal dynamics; and (2) to explain these variations with respect to meteorological and hydrological factors. In terms of average energy flux contributions, sensible heat (38.7%), the bed heat flux (37.0%) and friction at the stream bed and banks (24.3%) are heat sources, while latent heat (73.1%) and net radiation (26.9%) are heat sinks. All energy losses and 38.7% of heat gains occur at the air–water interface; and 61.3% of energy gains (including friction) take place at the water–channel bed interface. Typically, temperatures increase (+1.97°C) and show dampening of thermal response from the water column to depth in the stream bed. The most salient findings include: (1) the stream bed (atmosphere) is the dominant energy source (sink) for heating (cooling) channel water, which may be attributed to inferred heat advection by groundwater up‐welling into the bed of this upland stream; (2) sensible heat is the primary atmospheric energy source due to limited net radiation; (3) friction at the stream bed and banks is an important heat source. Energy budget terms and temperatures exhibit (sub‐)seasonal changes in response to meteorological and hydrological conditions; a schematic diagram is presented to summarize these results. This paper clearly illustrates the need for further medium‐ to long‐term empirical stream energy balance research to characterize heat flux dynamics and, thus, understand and predict water temperature variations over time‐scales of relevance to biological studies. Copyright © 2004 John Wiley & Sons, Ltd.     

Modelling the influence of seiche-events on phosphorous-loading dynamics in three Lake Ontario coastal wetlands

Coastal Wetlands (CWs) provide critical ecosystem services that maintain biogeochemical processes and habitats in the coastal zone of the Great Lakes. When nutrient-laden surface waters flow into CWs from their watersheds, internal physical, chemical, and biological processes can alter the final nutrient loadings to the lake. However, CWs can periodically be inundated with lake water from seiche events, and little is known about the impacts of seiches on nutrient processing and loadings from CWs. To evaluate the influence of lake seiches on CW phosphorous-loading dynamics, we built a multi group structural equation model (SEM) using climatic and wave data, and interannual (2009–2018) estimated sediment and phosphorous loadings from three CWs on the north-shore of central Lake Ontario (Rouge Marsh, Duffin’s Marsh, and Carruthers Marsh). Wind speeds, lake levels, and an increased peak period of wave spectra were significant explanatory variables of seiche events (p-value < 0.001). We identified that seiche events caused significant sediment resuspension (p-value < 0.001) in CWs, which contributed to a significant increase of phosphorous loading to the coastal zone of Lake Ontario (p-value < 0.001). Our results indicate that lake-seiche events can influence CW phosphorous-loadings to Lake Ontario, and should be considered when modelling water quality in the nearshore zone.     

Anthropogenic and seasonal influences on the dynamics of selected heavy metals in Lake Naivasha, Kenya

Lake Naivasha is a freshwater lake in the Eastern Rift Valley of Kenya (0°45′S and 36°20′E). It has no surface outlet and is perceived to be under anthropogenic stress. Being situated at the basin of the rift valley, the lake acts as a sink for wastes from the town of Naivasha and the surrounding horticultural industry. Flux experiments were conducted to investigate the dynamics of heavy metals between the sediment–water interface in Lake Naivasha. In situ benthic flux experiments were conducted at two sites, one near the municipal wastewater inflow to the lake (site SS), and one at the papyrus field near the horticultural farms (site SH). Sediment samples from the exposed riparian land were collected during the dry season after the lake has receded, and the fluxes of selected metals were determined in the laboratory under simulated conditions. Aluminium in situ benthic flux at site SS averaged 7 mmol m^?2 h^?1, and was correlated positively with pH (Pearson correlation coefficient (r) = 0.89). While the in situ benthic flux of aluminium at site SH averaged 1 mmol m^?2 h^?1. In situ benthic fluxes of copper and manganese were predominantly positive at site SS, but not at site SH. The papyrus field at site SH played an important role in buffering of the lake in regard to the selected metals investigated in this study. Redox‐sensitive metals were precipitated in the benthic flux experiment for this site.     

Modelling and prediction of phyto- and zooplankton dynamics in Lake Kasumigaura by artificial neural networks

An artificial neural network model was developed for Lake Kasumigaura to predict timing and magnitudes for chlorophyll a, five species of blue-green algae and three zooplankton groups. The model was trained by 8 years of limnological time series and validated by two independent years. The validation showed the potential of neural networks as predictive tools for highly non-linear phenomena such as blue-green algal blooms in freshwater lakes.     

Modelling inundation patterns and sediment dynamics in the extensive floodplain along the Tonle Sap River

The Tonle Sap River (TSR) serves as a natural medium for the reversal flow between Tonle Sap Lake (TSL) and the Mekong River to sustain productivity and biodiversity in the TSR floodplain and TSL. Understanding the hydrological connectivity and its dynamics in the TSR, including its floodplain, is therefore important to support activities that aim to maintain ecological services in the TSR–TSL system. Thus, the main objective of this study is to examine the hydrological connectivity of the TSR and its floodplain by a modelling approach that integrates inundation patterns and sediment dynamics. The Caesar–Lisflood model was applied to describe inundation, sediment erosion, transport, and deposition in the TSR for the period of 2003–2013. The inundation areas connected to the TSR ranged from 140 to 2,327 km², whereas the isolated inundation areas from the TSR ranged from 0.27 to 504 km². Sediment dynamics showed its influence on inundation patterns and hydrological connectivity and could alter the yearly inundation ratio (defined as a normalized inundation frequency with a value ranging from 0 to 1) up to 0.8. Our approach provides a quantitative way to determine key factors (e.g., total inundation areas, seasonality, and connectivity of inundation patterns) for further investigation of ecological processes in relation to the inundation patterns and sediment dynamics in the TSR and TSL.     

黄海冷水团的季节变化特征及其形成机制研究

在普林斯顿海洋模式(POM)的基础上,利用高精度卫星遥感得到的风和海表温度(SST)数据并考虑M2分潮的作用,模拟了黄、渤海海域三维热结构和环流的时、空变化;在此基础上,系统描述了黄海冷水团水文现象;并对黄海冷水团形成机制进行了探讨。研究结果表明:温跃层、潮混合、暖流和地形对黄海冷水团起着重要作用。     

Application of a 3D hydrodynamic-biological model for seasonal and spatial dynamics of water quality and phytoplankton in Lake Erie

In large lakes, temporal variability is compounded by strong spatial variability associated with mesoscale physical processes such as upwelling and basin-scale circulation. Here we explore the ability of a three dimensional model (ELCOM-CAEDYM) to capture temporal and spatial variability of phytoplankton and nutrients in Lake Erie. We emphasized the east basin of the lake, where an invasion by dreissenid mussels has given special importance to the question of spatial (particularly nearshore-offshore) variability and many comparative observations were available. We found that the model, which did not include any simulation of the mussels or of smaller diffuse nutrient sources, could capture the major features of the temperature, nutrient and phytoplankton variations. Within basin variability was large compared to among-basin variability, especially but not exclusively in the western regions. Consistent with observations in years prior to, but not after, the mussel invasion the model predicted generally higher phytoplankton concentrations in the nearshore than the offshore zones. The results suggest that the elevated phytoplankton abundance commonly observed in the nearshore of large lakes in the absence of dreissenid mussels does not have to depend on localized nutrient inputs but can be explained by the favourable light, temperature and nutrient environment in the shallower and energetic nearshore zone. The model is currently being extended to allow simulation of the effects of dreissenid mussels.     

Modelling of Meteo-Droughts

Water Resources Management - A simple stochastic model of meteorological droughts (meteo-droughts) is presented. All its components are analyzed and described, along with their probabilistic...     

Zooplankton dynamics in a Great Lakes connecting channel: Exploring the seasonal composition within the St. Clair-Detroit River System

The connecting channels linking the Laurentian Great Lakes provide important migration routes, spawning grounds, and nursery habitat for fish, but their role as conduits between lakes for zooplankton is less understood. To address this knowledge gap in the St. Clair–Detroit River System (SCDRS), a comprehensive survey of crustacean zooplankton was performed in both riverine and lacustrine habitats from spring to fall 2014, providing the first system-wide assessment of zooplankton in the SCDRS. Zooplankton density and biomass were greatest in northern reaches of the system (southern Lake Huron and the St. Clair River) and decreased downstream towards Lake Erie. The composition of zooplankton also changed moving downstream, transitioning from a community dominated by calanoid copepods, to more cyclopoids and cladocerans in the Detroit River, and to cladocerans dominant in western Lake Erie. Coincidentally, species richness increased as sampling progressed downstream, and we estimated that our single-year sampling regime identified ~88% of potential taxa. Other species assemblages have responded positively to recent water quality and habitat restoration efforts in the SCDRS, and this survey of the zooplankton community provides benchmark information necessary to assess its response to continued recovery. In addition, information regarding the lower trophic levels of the system is integral to understanding recruitment of ecologically and economically valuable fish species targeted for recovery in the SCDRS.     

排水管道淤积状况模拟分析

针对排水管道中沉积物淤积状况判断的实际需求,利用上下游检查井的水位测试,并借助排水管网水力模型,可判断管道淤积状况。通过分析淤积特征,提出水位相对变化指标概念;构建小型案例,从管道淤积平均断面面积和淤积平均长度、管长、管径、坡度、流量、管道粗糙系数7个方面分析其对上下游检查井水位的影响。模拟结果表明,开泵后淤积管道上下游水位差变化比无淤积管道明显;淤积平均断面积和淤积平均长度均对管道上下游水位差具有影响;管道淤积程度越大,水位相对变化指标K值越大;当K≥2时,则可判断管道存在淤积,淤积面积为30%以上。     

湍流各向同性回归过程的非线性模化

本文通过对不同湍流结构衰减过程的研究，发展一个成功描述“馅饼”湍流和“雪茄”湍流衰变的压力一应变相关项中的慢速项的模式。根据充模式应满足的可实现性条件，本文对各向性归过程模式进行了分析，得到了模式系数所必须满足的一个有普遍意义的重要等式。本模式满足了可实现性条件。通过计算本文验证了模式的瞬时行为，并与各向同性回归过程的实验数据进行了比较，结果表明本文模式成功地捕捉到了各向同性回归过程所表现的非线性     

分布式水文模型研究进展综述

简述分布式水文模型的优势和发展情况,归纳模型应用主要于降水——径流模拟,非点源污染,水资源开发利用等方面,并介绍各方面的应用方法,总结了常见的分布式水文模型,重点分析了SWAT模型,SHE模型,提出了模型未来发展需完善理论水平,提高技术支撑能力。     

Modelling physical characteristics of river habitats

The physical characteristics of river habitats constitute the setting in which fluvial biota dwell and thrive. Determining the spatial and temporal patterns of physical habitat characteristics and the main factors that control them is extremely important to increase the efficiency of river management, conservation, and restoration. This study determined spatial patterns of physical habitat characteristics for Atlantic and Mediterranean rivers in northern Spain and developed a river classification based on hydromorphological characteristics. Data gathered from almost 600 sites following a modified version of the River Habitat Survey methodology were used. In addition to the usual River Habitat Survey variables, the sequence of hydromorphologic units (i.e., areas exhibiting similar hydraulic characteristics, in terms of water velocity and depth), water depths, and widths were recorded. Unmodified reaches were selected computing the Habitat Modification Score. Multiple Linear Regression models were employed to test relationships between Principal Component Analyses that summarized physical river habitat characteristics with ecological relevance and environmental variables (i.e., climate, topography, land cover, and geology) at different spatial scales and used to predict physical habitat attributes for all river reaches. The density of hydromorphologic units, flow turbulence, substrate size, and channel dimensions were able to discriminate river classes within the river network, with topography being the main environmental driver of habitat characteristics (although climate, geology, and land cover were also relevant). This classification scheme could constitute a useful tool to restore physical habitat conditions in modified river reaches.     

季节冻结深度自动监测技术试验

通过测试土样初始冻结温度,建立野外现场温度自动化远程实时监测系统,利用初始冻结温度等温线深度代替冻结锋面,计算季节冻土层厚度,为冻土学冻结深度观测自动化提供依据。试验结果表明:冻结过程相关系数为0.97,融化过程相关系数为0.98,整个冻融过程相关系数为0.98;用温度场冻结点等温线观测冻深的方案是可行的,可以实现冻融过程自动化实时监测,且观测精度较高。