Utilizing settling tests to design a conventional upflow settling tank modified with inclined plates

This paper examines the relationships between the turbidity removal efficiency (TRE), the surface overflow rate (SOR), and the detention time (D(t)) in settling column and jar tests, as well as the performance of a conventional upflow settling tank modified with inclined plates in the upper zone. The experimental results showed that the SOR obtained from the flocculent settling column test can be increased by 30% and the corresponding D(t) can be decreased by 75% with a variation in TRE of less than 7%. The TRE of flocculent settling in the jar test coincided with the performance of the modified upflow settling tank, while the results of the settling column test were slightly different. For plain settling, the SOR obtained from jar and settling column tests should be divided by 3 and 2, respectively, before possible use in the design of the modified upflow settling tank. Two empirical models with 1.0% error in the TRE predictions were developed to facilitate the design of the modified upflow settling tank.     

Monitoring in inline storage sewers for stormwater treatment to determine efficiencies.

A special structure of combined sewer overflow tanks is the inline storage sewer with downstream discharge (SKU). This layout has the advantage that besides the sewer system, no other structures are required for storm water treatment. Consequently only very little space is required and compared to combined sewer overflow tanks, there is an enormous potential in reducing costs during construction. To investigate the efficiency of an inline storage sewer, a monitoring station was established in Dortmund-Scharnhorst, Germany. The monitoring station was in operation for a period of 2.5 years. Within this period water samples were taken during a total of 20 discharge events. Besides the complete hydraulic data collection, seven water samplers took more than 5,000 water samples during dry and wet weather. This adds up to a total of more than 20,000 individual lab analyses. The average of the total efficiency for the SKU-West is 86%. 29% of this efficiency can be attributed to the throttle flow. The remaining 57% can be divided into a part of 48% that can be attributed to the process storage and 9% that can be attributed to sedimentation and erosion process.     

Measurement of flow velocity profiles in tank structures using the prototype device OCM Pro LR

Generally, studies investigating the treatment efficiency of tank structures for storm water or waste water treatment observe pollutant flows in connection with conditions of hydraulic loading. Further investigations evaluate internal processes in tank structures using computational fluid dynamic (CFD) modelling or lab scale tests. As flow paths inside of tank structures have a considerable influence on the treatment efficiency, flow velocity profile (FVP) measurements can provide a possibility to calibrate CFD models and contribute to a better understanding of pollutant transport processes in these structures. This study focuses on tests carried out with the prototype FVP measurement device OCM Pro LR by NIVUS in a sedimentation tank with combined sewer overflow (CSO) situated in Petange, Luxembourg. The OCM Pro LR measurement system analyses the echo of ultrasonic signals of different flow depths to get a detailed FVP. A comparison of flow velocity measured by OCM Pro LR with a vane measurement showed good conformity. The FVPs measured by OCM Pro LR point out shortcut flows within the tank structure during CSO events, which could cause a reduction of the cleaning efficiency of the structure. The results prove the applicability of FVP measurements in large-scale structures.     

Research of the performance of pulse electrohydrodynamics in blockage removal

In line with contemporary trends and seeking to develop new methods and technologies, a new, original technology was explored and designed based on a non-conventional process of electrical pulse discharge in a water chamber, referred to as 'Pulse Electrohydrodynamic Technology' (PELHYDT). The application of the PELHYDT in sewer blockage removal is presented in this paper. Existing machinery can remove two blockages of gully pot connections per hour. Three blockages of pipe conduits are generally removed during an 8-h working day. Applying PELHYDT technology, which allows for high rates of removal of mechanical obstructions, it is possible to achieve operating fluid pressures in the order of 10(3)-10(4) bars, a velocity of 100 m/s, a deformation acceleration of the model material structure of 10(6)-10(7) m/s2, and high-frequency hydraulic shock waves with a frequency of 10(3)-10(4) Hz. The applicability of this efficient technology in sewer blockage removal was proven under laboratory conditions at operating fluid pressures from 50 to 160 bars, which are standard for sewer maintenance. Water velocities generally achieved in sewers using existing flushing technologies range between 1 and 3 m/s and usually do not exceed 9 m/s. PELHYDT creates waves whose velocity is at least 100 m/s, and is therefore about ten times more efficient than existing technologies. PELHYDT generates an electrohydrodynamic wave very quickly, virtually in the form of an explosion. It was proven under laboratory conditions that the application of this technology for blockage removal in practice will not result in any sewer damage.     

Correlation of combined sewer overflow reduction due to real-time control and resulting effect on the oxygen concentration in the river

Real-time control of the sewer system is a frequently applied measure for the abatement of pollution caused by urban runoff in the receiving water. Although the goal is an improvement of the water quality the actual aim of real-time control is usually formulated as the reduction/avoidance of combined sewer overflow. However, testing a virtual drainage system by means of a three-month rain series, hardly any correlation between the combined sewer overflow reduction and the resulting effect on the oxygen concentration in the river has been found. The efficiency of real-time control for pollution abatement by means of artificial performance criteria has to be doubted.     

Column studies to determine mercury settling in road runoff

A study was performed using a settling column to remove mercury (Hg) from road runoff. The emphasis was placed on the relationship between Hg removal and critical settling velocities, as well as the distribution of total suspended solids (TSS). The impact of rainfall characteristics and temperature on Hg removal was also discussed. Results indicated that Hg removal was significant within the initial 30 min of the settling process. The Hg removal rate increased with the decrease of critical settling velocity, and this trend became gradually significant, which could be used as an important reference for the optimization of sedimentation basin design. Hg removal at different settling times was significantly related to initial distribution of TSS. The impact of rainfall intensity on Hg removal was greater than other parameters of precipitation features, followed by rainfall. In addition, Hg removal was moderately related to temperature. The effect of antecedent dry periods on Hg removal was restricted by rainfall and rainfall intensity.     

The Actiflo method

The Actiflo method is a compact physico-chemical water treatment method. The method has for many years been used in waterworks for the treatment of surface water to produce drinking water, but is now to an increasing extent being used for treating wastewater and combined sewer overflows (CSO). The method works as weighted settling combined with lamella settling. Typical treatment efficiency: suspended solids 85%, COD 60%, Kjeldahl N 18% and total P 85%. The method also permits efficient removal of heavy metals. Krüger has a mobile pilot plant with a capacity of 80–120 m³/h in Scandinavia and a similar pilot plant in the USA. As an Actiflo plant can be started up in less than 15 minutes, it has many applications. Several applications may also be combined, e.g. treatment of overflows during rain and treatment of lake water in the recipient nearby in dry weather. As an alternative to detention basins in combined sewer systems the Actiflo method is often a competitive method.     

基于CCHE的重力沉砂池结构布置参数比选研究

为了提高重力沉砂池水沙分离效率,对重力沉砂池相关结构参数进行优化使各项结构参数取得较优值,并研究了侧向溢流堰长度与位置对重力沉砂池最终水沙分离效率的影响,且取得较优的侧堰长度与位置。基于CCHE软件采用混合掺长紊流模型建立CCHE2D重力沉砂池数学模型,得到重力沉砂池内水流流速、泥沙沿程分布及最终水沙分离效率,在已有研究成果基础上分析得到较优的重力沉砂池侧向溢流堰长度及位置。研究结果表明:改变侧向溢流堰长度及位置可将传统重力沉砂池水沙分离效率显著提高。当溢流堰长度取4 m并向上游移动1 m时可将水沙分离效率提高至71.20%。当侧向溢流堰向上游移动一段距离可以阻挡由沉砂池末端产生回流、漩涡等流态而卷起的泥沙,避免其流向清水池,从而提高重力沉砂池水沙分离效率。移动距离不可过前,否则距离过于靠前由于沉砂池边壁的阻挡容易使沉砂池末端形成一段"死水区",使沉砂池有效沉降距离减少,从而降低重力沉砂池水沙分离效率。     

Detailed observation and measurement of sewer sediment erosion under aerobic and anaerobic conditions.

A greater understanding of the erosion behaviour of sewer sediments is necessary in order to reliably estimate the amount and nature of the sewer sediments released from deposits in sewers and transported either to waste water treatment plants or discharged into the environment. Research has indicated that microbial activity in sediment can influence the physical release of sediment from in-pipe deposits. This paper reports on a series of erosion tests in which sewer sediments from different sewer networks are kept under different environmental conditions and their resistance to erosion is examined. The erosion tests are carried out under aerobic and anaerobic conditions and two temperatures, one representing ambient sewer temperatures and a lower temperature that significantly suppresses bacterial activity.     

On the effect of spatial variances in historical rainfall time series to CSO performance evaluation.

Historical, high-resolution rain series are the backbone of modern combined sewer overflow (CSO) structure design. These rain series are the input to the computational estimation of the performance of the measures with respect to CSO pollution abatement. However, those historical precipitation measurements are available at only a few locations. Frequently rain series have to be used from gauging stations at a significant distance. In order to judge and to compensate for this influence an estimate between rain characteristics and combined sewer outflow (CSO) performance indicators would be useful. In this paper such correlations have been sought for a collection of 37 rain series covering large areas of Europe. It was found that the mean annual rain volume can explain most of the variances for the performance indicators Number of overflows and CSO volume. For explaining the spatial differences in the efficiency of the CSO structure another rain characteristic, i.e. the maximum event with a return period of one year, is to be used.     

固体颗粒的群体沉降速度分析

从流体力学原理出发，数值模拟非均匀沙随机分布对流场的影响，推导出固体颗粒群体沉速的理论解。该公式不仅量纲和谐，浓度变化不超过极限浓度值，能反映含沙量与非均匀沙级配变化对群体沉速的影响，而且可避免其它公式量纲不和谐，计算中出现负值或降得过快的缺点。采用黄河实测资料对该公式进行了验证，计算结果与实测资料基本符合。     

排沙漏斗流场特性与排沙机理研究

排沙漏斗是一种截沙率高、耗水率小的二级泥沙处理设施。为了进一步探明排沙漏斗的流场特性和排沙机理,该文采用声学多普勒流速仪(ADV)对排沙漏斗立轴螺旋流进行了三维流场测试,采用雷诺应力模型(RSM)和VOF方法数值模拟了排沙漏斗内清水流场,计算的水流时均流速分布与实测结果吻合良好。通过数值模拟方法得到了全面详细的排沙漏斗流场结构信息,并据此分析了排沙漏斗的排沙机理,提出二次流是排沙漏斗能够顺畅高效排沙的关键。     

Influence of characteristics on combined sewer performance

Elements of combined sewer systems are among others sub-catchments, junctions, conduits and weirs with or without storage units. The spatial distribution and attributes of all these elements influence both system characteristics and sewer performance. Until today, little work has been done to analyse the influence of such characteristics in a case unspecific approach. In this study, 250 virtual combined sewer systems are analysed by defining groups of systems, which are representative for their different characteristics. The set was created with a further development of the case study generator (CSG), a tool for automatic generation of branched sewer systems. Combined sewer overflow and flooding is evaluated using performance indicators based on hydrodynamic simulations. The analysis of system characteristics, like those presented in this paper, helps researchers to understand coherences and aids practitioners in designing combined sewers. For instance, it was found that characteristics that have a positive influence on emission reduction frequently have a negative influence on flooding avoidance and vice versa.     

黄河高含沙水流的高效输沙特性形成机理(黄河下游河道存在巨大的输沙潜力)

利用黄河主要干支流渭河、北洛河、黄河下游及三门峡水库大量实测资料,结合高含沙水流流变特性分析得出:河道中的高含沙水流的阻力与低含沙水流相同,均可用曼宁公式进行阻力计算;由于黄河泥沙组成较细,d50=0.03~0.10mm,随着含沙量的增加颗粒的沉速大幅度降低,泥沙在垂线上分布变得更加均匀,当含沙量大于200kg/m3以后发生改变;从泥沙存在对水流结构,流速在垂线上的分布特性上分析,含沙量200kg/m3左右时输送最困难,并得到河道实测资料的证实。由于粘性的增大,粗颗粒泥沙在河道中也能顺利输送,洪水期实测含沙量可达800~900kg/m3,表现出高含沙水流的高效输沙特性;黄河下游艾山以下河段实测洪水的最大含沙量为200kg/m3,在流量2 000~3 000m3/s时,高含沙洪水均可顺利输送。利用河道输送高含沙水流入海的主要障碍是改造宽浅游荡河段为窄深稳定的河槽。     

过水设施水流噪声的形成机理及影响因子研究综述

为提高水流噪声对过水设施运行状态的监测效率，需明确水流噪声形成的机理及其与过水设施运行及结构参数之间的相互关系。分析和总结了河道与水电站常用过水设施水流噪声的形成机理及影响因子，指出常用过水设施水流噪声特征与其运行工况及流道结构特征密切相关，水流流速、流量与形成的水流噪声声级呈正相关关系；流道结构形式越复杂则水流紊动越激烈，水流噪声形成机理也越复杂。过水设施水流噪声声级和频率随流道水动力特性和结构边界特性同步变化，可作为过水设施运行及流道状态的信号源，实时监测过水设施的运行状态和安全，保障过水设施的安全。     

Impact of dimension uncertainty and model calibration on sewer system assessment.

Assessments of sewer performance are usually based on a single computation of CSO (combined sewer overflow) volumes using a time series of rainfall as system loads. A shortcoming of this method is that uncertainties in knowledge of sewer system dimensions are not taken into account. Moreover, sewer models are rarely calibrated. This paper presents the impacts of database errors and model calibration on return periods of calculated CSO volumes. The impact of uncertainties is illustrated with two examples. Variability of calculated CSO volumes is estimated using Monte Carlo simulations. The results show that calculated CSO volumes vary considerably due to database errors, especially uncertain dimensions of the catchment area. Furthermore, event-based calibration of a sewer model does not result in more reliable predictions because the calibrated parameters have low portability. However, it enables removal of database errors harmonising model predictions and 'reality'.     

Modelling pathogen fate in stormwaters by a particle-pathogen interaction model using population balances

Stormwater is polluted by various contaminants affecting the quality of receiving water bodies. Pathogens are one of these contaminants, which have a critical effect on water use in rivers. Increasing the retention time of water in stormwater basins can lead to reduced loads of pathogens released to the rivers. In this paper a model describing the behaviour of pathogens in stormwater basins is presented including different fate processes such as decay, adsorption/desorption, settling and solar disinfection. By considering the settling velocity distribution of particles and a layered approach, this model is able to create a light intensity, and particle and pathogen concentration profile along the water depth in the basin. A strong effect of solar disinfection is discerned. The model has been used to evaluate pathogen removal efficiencies in stormwater basins. It includes a population of particle classes characterized by a distribution of settling velocities in order to be able to reproduce stormwater quality and treatment in a realistic way.     

雨水管道沉积物污染初期冲刷效应及初期雨水量研究

为了控制雨水管道沉积物在降雨径流的冲刷下再悬浮随雨水排入受纳水体而造成的污染,利用SWMM软件构建汇水面污染冲刷模型,耦合管道沉积物冲刷模型,分析在管道沉积物影响下的径流污染初期冲刷效应,并提出一种初期雨水量的动态计算方法。结果表明:管道沉积物的存在会削弱初期冲刷效应,需要控制比地面截流3～5mm更多的初期雨水,可根据对降雨径流污染的监测数据,结合初期雨水的汇流规律,通过图解法求得。     

Groundwater infiltration, surface water inflow and sewerage exfiltration considering hydrodynamic conditions in sewer systems

Sewer systems are closely interlinked with groundwater and surface water. Due to leaks and regular openings in the sewer system (e.g. combined sewer overflow structures with sometimes reverse pressure conditions), groundwater infiltration and surface water inflow as well as exfiltration of sewage take place and cannot be avoided. In the paper a new hydrodynamic sewer network modelling approach will be presented, which includes--besides precipitation--hydrographs of groundwater and surface water as essential boundary conditions. The concept of the modelling approach and the models to describe the infiltration, inflow and exfiltration fluxes are described. The model application to the sewerage system of the City of Dresden during a flood event with complex conditions shows that the processes of infiltration, exfiltration and surface water inflows can be described with a higher reliability and accuracy, showing that surface water inflow causes a pronounced system reaction. Further, according to the simulation results, a high sensitivity of exfiltration rates on the in-sewer water levels and a relatively low influence of the dynamic conditions on the infiltration rates were found.     

Interaction between the treatment plant and the sewer system in Halmstad: Integrated upgrading based on real time control

In Halmstad, Sweden great efforts have been made during the 1990's to improve the functionality and to reduce the environmental impact of the sewer system and the wastewater treatment plant The investment and rehabilitation program includes to a great extent an effective use of existing resources. The wastewater treatment plant is reconstructed to meet increased nutrient removal demands. A five year rehabilitation plan for the sewer system is under completion, where the measures mainly are motivated by the aim to reduce the combined sewer overflow volumes and to minimize the risk of local flooding. It was soon realized that an integrated use of storage volumes at the wastewater treatment plant and within the sewer system could improve the general conditions for the treatment at the plant. To implement this strategy a real time control system was introduced by installing controllable weirs and flow control devices in the main sewer. The article describes the background of the sewerage master plan, how the upgrading work has been carried out by means of simulations and measurement, gives examples of some expected potential benefits, and outlines plans for the future.