Hydraulic performance of sewer pipes with deposited sediments.

This paper investigates in-sewer sediment deposit behaviour and its influence on the hydraulic performance of sewer pipes. This evaluation is based on experimental results regarding the mobility of non-cohesive and partly cohesive deposits in a partially full circular pipe. The focus of these tests is on the development of bed forms and friction characteristics. In particular, it is investigated to what extent the bed forms from the non-cohesive and (partly) cohesive sediments affect a sewer's discharge capacity. Based on the laboratory study results and on the existing criteria for sewer design, a generic assessment of a sewer's hydraulic performance is made. The relative discharge factor for a pipe with sediment deposit is analysed in terms of the thickness and roughness of the deposit.     

雨水干管污染物输送规律研究

根据城市汇水面源头污染物的径流冲刷规律 ,进一步从理论上推导分析了降雨径流通过任意多个雨水口汇入雨水干管后的污染物输送数学模型及规律 ,并结合现场取样分析数据对输送规律进行了验证 ,分析了部分实测数据与理论模型存在一定偏差的原因。基本掌握了城市雨水管系中污染物的输送规律 ,为进一步研究有效的控制措施提供了理论和试验依据     

Modeling stochastic load variations in sewer systems.

In wastewater treatment and environmental risk assessments increasing attention is paid to the fate of micropollutants. These are time-consuming, expensive and difficult to detect and quantify. If a substance's load or concentration is subject to high dynamic fluctuations, it is demanding to take representative samples, especially when the "variation" is unknown. Therefore, we developed a concept to model stochastic load variations in sewer systems. We gathered readily available information from existing databases (population and consumption data) and combined it with the characteristics of household activities and appliances. We succeeded in predicting realistic short-term variations of benzotriazole (contained in dishwasher detergents) and validated them with a high-frequency measuring campaign. Benzotriazole stands as an example for other household chemicals, which cannot be measured so easily. All required information used within this case study is also available for other substances and catchments. This allows the forecast of stochastic load variations for many chemical compounds of interest. It helps to plan measuring campaigns, to estimate discharged loads from combined sewer overflows and to have a characteristic input for modeling purposes.     

Control of sewer systems and wastewater treatment plants using pollutant concentration profiles

On-line measurements of pollutants in the wastewater combined with grey-box modelling are used to estimate the amount of deposits in the sewer system. The pollutant mass flow at the wastewater treatment plant is found to consist of a diurnal profile minus the deposited amount of pollutants. The diurnal profile is found to be a second order harmonic function and the pollutants deposited in the sewer are identified using first order ordinary differential equations.     

正弦余弦算法-投影寻踪水污染物总量分配模型

基于水资源禀赋条件、效率原则和尊重现状的原则,构建水污染物总量分配指标体系和水污染物分配投影寻踪(PP)模型。针对PP模型最佳投影方向难以确定的不足,利用正弦余弦算法(SCA)搜寻PP模型最佳投影方向,构建SCA-PP模型对云南省文山州壮族苗族自治州8县(市)水污染物控制总量进行分配。并通过6个典型测试函数对SCA算法进行仿真验证,仿真结果与蚁群优化(ACO)算法、模拟退火算法(SA)、文化算法(CA)、布谷鸟搜索(CS)算法和人工蜂群(ABC)算法进行对比。结果表明:(1)SCA算法寻优效果明显优于ACO、SA、CA、CS和ABC算法,具有模型简单、调节参数少、收敛速度快、寻优精度高、全局寻优能力强以及收敛稳定性与收敛可靠性好等特点。(2)SCA-PP模型水污染物控制总量分配结果符合区域经济社会发展和水污物染削减客观要求。模型及方法具有一定的可操作性和有效性,可为水污染物分配提供新的途径和方法。     

合流制排水系统雨季污染物溢流的截流与调蓄控制研究

截流式合流制排水系统是我国主要的排水体制之一。以昆明市主城区明通河合流制排水系统为背景,研究了雨季产污及迁移规律及削减入湖污染物的措施,并进行了工程示范。示范研究结果表明,在CODCr截留率小于80%、截流倍数n0=1~3、调蓄量2~20 mm(以不透水地面计),提高截流倍数或调蓄量均可显著提高污染物截留率。截流倍数与调蓄量可表述为截留系数的函数,截流倍数增加1等效于调蓄量增加8 mm,截留系数为CODCr截留比率的幂函数。     

Monitor-based evaluation of pollutant load from urban stormwater runoff in Beijing.

As a major pollutant source to urban receiving waters, the non-point source pollution from urban runoff needs to be well studied and effectively controlled. Based on monitoring data from urban runoff pollutant sources, this article describes a systematic estimation of total pollutant loads from the urban areas of Beijing. A numerical model was developed to quantify main pollutant loads of urban runoff in Beijing. A sub-procedure is involved in this method, in which the flush process influences both the quantity and quality of stormwater runoff. A statistics-based method was applied in computing the annual pollutant load as an output of the runoff. The proportions of pollutant from point-source and non-point sources were compared. This provides a scientific basis for proper environmental input assessment of urban stormwater pollution to receiving waters, improvement of infrastructure performance, implementation of urban stormwater management, and utilization of stormwater.     

Identification of overall degradation in sewer systems from long-term measurements and consequences for WWTP simulations.

In-sewer transformation processes affect significantly design and operation of large wastewater treatment plants. Especially for long-term simulations the degradation has to be considered in order to avoid over- and underestimation. In this paper a method is presented to derive the overall degradation from available operation data. The application of the results in a long-term simulation of a WWTP shows the relevance of the degradation for design and operation of an activated sludge plant.     

Simulation of a subsurface vertical flow constructed wetland for CSO treatment.

Constructed wetlands (CWs) have proved to be a highly effective measure to reduce the ecological impact of combined sewer overflows (CSOs) on receiving waters. Due to the stochastic nature of the loading regime and the multitude of environmental influences, assessment of the performance of such plants requires detailed mathematical modelling. A multi-component reactive transport module (CW2D) was applied to simulate the flow, transport and degradation processes occurring in a CW for CSO treatment. CW2D was originally developed to simulate the treatment of municipal wastewater in subsurface flow CWs. Loading and operational conditions in CSO treatment differ fundamentally from the conditions occurring for wastewater treatment. Despite these differences, first results from the simulation of lab-scale experiments show, that the model is generally applicable to this type of plant. Modelling of adsorption, degradation processes, and influent fractionation, however, require further research.     

Sampling for representative micropollutant loads in sewer systems.

Most commercially available auto-sampling devices do not support a continuous flow-proportional sampling mode, which would conceptually be the best for collecting representative composite samples. Instead different discrete sampling modes are available. Household chemicals can show considerable random short-term variations. With the anticorrosive benzotriazole, relating to a middle-frequent household activity, we show that, besides an accurate flow meter, mainly three factors are decisive for the representativeness of a substance's average load: the substance's load pattern, the sampling frequency and the length of the composite sample. When the sampling intervals are 10 minutes or longer, errors in the order of +/-40% (standard deviation) or more have to be accepted, if the substance of interest is contained in a low number of wastewater pulses (i.e., the level of household activity). This particularly holds true for specific pharmaceuticals e.g. carbamazepine. Ammonium would be less critical, because it relates to a larger number of sources in the same catchment.     

Long term monitoring of sewer sediment accumulation and flushing experiments in a man-entry sewer.

This paper presents continuous field experiments carried out during 4 years in a man-entry egg-shaped combined sewer in Lyon, France in order to contribute to the knowledge and the modelling of sediment accumulation and sediment removal by means of a Hydrass flushing gate. The 250 microm sediments are mainly mineral, and their physical and chemical characteristics appear as rather stable in time and space. Long-term sediment monitoring reveals: (i) a regular asymptotic increase of both the sediment mass and the slope of its longitudinal profile, (ii) a clear correlation between local sediment profile irregularities and sewer ancillaries but without significant influence on the global and long term accumulation. Simple sediment accumulation modelling shows: (i) a good suitability of a three parameters conceptual model to reproduce asymptotic sediment volume accumulation, and (ii) a good suitability of the Velikanov model to reproduce sediment profiles. Both models reproduce observations with an acceptable margin of uncertainty for operational management purposes but are very sensitive to input data and parameter values. The Hydrass flushing gate is efficient and it appeared that the mass of sediments moves downstream linearly with the number of flushes.     

Constructed wetlands for CSO treatment: an overview of practice and research in Germany.

Vertical flow treatment wetlands have been developed as very useful tools for treatment of combined sewage overflow. Several systems have been in operation for over 15 years. Based on recent research work, new technical guidelines now recommend systems with a drained filter of sand 0/2 mm and a throttled outflow. COD, NH4-N and SS removal rates of 85-99% can be expected from this type of filter. SS loadings that are too high and very long or frequent inundation affect the performance adversely. Information for successful long-term operation were derived from various existing plants.     

Using decision analysis to determine optimal experimental design for monitoring sewer exfiltration with tracers.

The tracer methods developed to assess exfiltration from sewers in the European project APUSS (assessment of the performance of sewer systems) have a high degree of freedom with regard to the choice of tracer and the dosing strategy. These can lead to very different degrees of uncertainty in the measured exfiltration ratio. In this study, we demonstrate how to select an optimal experimental design using decision analysis, which accounts for this uncertainty and its associated costs. Although the results are site-specific, we can conclude generally that, when NaCl is used as the tracer, the accuracy of the exfiltration estimate is most sensitive to the amount of tracer used and the starting time of the experiment.     

The hydraulic capacity of deteriorating sewer systems.

Sewer and wastewater systems suffer from insufficient capacity, construction flaws and pipe deterioration. Consequences are structural failures, local floods, surface erosion and pollution of receiving waters bodies. European cities spend in the order of five billion Euro per year for wastewater network rehabilitation. This amount is estimated to increase due to network ageing. The project CARE-S (Computer Aided RE-habilitation of Sewer Networks) deals with sewer and storm water networks. The final project goal is to develop integrated software, which provides the most cost-efficient system of maintenance, repair and rehabilitation of sewer networks. Decisions on investments in rehabilitation often have to be made with uncertain information about the structural condition and the hydraulic performance of a sewer system. Because of this, decision-making involves considerable risks. This paper presents the results of research focused on the study of hydraulic effects caused by failures due to temporal decline of sewer systems. Hydraulic simulations are usually carried out by running commercial models that apply, as input, default values of parameters that strongly influence results. Using CCTV inspections information as dataset to catalogue principal types of failures affecting pipes, a 3D model was used to evaluate their hydraulic consequences. The translation of failures effects in parameters values producing the same hydraulic conditions caused by failures was carried out through the comparison of laboratory experiences and 3D simulations results. Those parameters could be the input of 1D commercial models instead of the default values commonly inserted.     

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.     

Recent findings on sinks for sulfide in gravity sewer networks.

Sulfide buildup in sewer networks is associated with several problems, including health impacts, corrosion of sewer structures and odor nuisance. In recent years, significant advances in the knowledge of the major processes governing sulfide buildup in sewer networks have been made. This paper summarizes this newly obtained knowledge and emphasizes important implications of the findings. Model simulations of the in-sewer processes important for the sulfur cycle showed that sulfide oxidation in the wetted biofilm is typically the most important sink for dissolved sulfide in gravity sewers. However, sulfide emission and thereby potential hydrogen sulfide buildup in the sewer atmosphere is of particular importance in sewers constructed with large diameter pipes, in sewers constructed with steep slopes and in sewers conveying low pH wastewater. Precipitation of metal sulfides is only important when the sulfide concentration in the wastewater is low; i.e. less than 1 g Sm(-3).     

污染物浓度和水力负荷双重作用下人工湿地的净化效果

研究从徐州地区大沙河西人工湿地基地中筛选6种挺水植物系统和2种沉水植物作为室内实验的供试植物,从丰县康达污水处理厂出水取样作为实验用水,研究人工湿地的水生植物对不同污染程度水体和水力负荷条件下的净化能力.研究可为人工湿地的实际运行和处理效果提供理论依据.     

Solids separation efficiency of combined sewer overflows.

The removal of sewer solids at combined sewer overflow locations depends on the flow patterns inside the overflow structure on the one hand and on the sediment characteristics on the other hand. Flow conditions can be described by the residence time distribution; sewer sediments can be characterised by their settling velocity distribution. The combination of both distributions leads to a dimensionless efficiency curve, which gives the removal efficiency as a function of the Hazen number. For field conditions this efficiency curve is mainly influenced by the settling velocity distribution of the sewer sediments and, as a consequence, nearly identical efficiency curves are found for different types of prototype CSO structure. For design purposes, a methodology using return frequency analysis is proposed.     

Quantification of sewer leakage: a review.

One of the goals of the APUSS project (assessing infiltration and exfiltration on the performance of urban sewer systems) is to assess sewer exfiltration, in order to support cities and operators to define problem-oriented rehabilitation strategies. In this paper, we review various methods currently used for the estimation of exfiltration and discuss data needs and applicability for rehabilitation planning. Although each approach has its individual advantages and drawbacks, we identified pressure tests and tracer methods to have the highest potential for decision support in rehabilitation planning. With regard to future challenges (e.g., micropollutants) such methods might play a key role in integrated sewer management.