Probabilistic modelling of combined sewer overflow using the First Order Reliability Method.

This paper presents a new and alternative method (in the context of urban drainage) for probabilistic hydrodynamical analysis of drainage systems in general and especially prediction of combined sewer overflow. Using a probabilistic shell it is possible to implement both input and parameter uncertainties on an application of the commercial urban drainage model MOUSE combined with the probabilistic First Order Reliability Method (FORM). Applying statistical characteristics on several years of rainfall, it is possible to derive a parameterization of the rainfall input and the failure probability and return period of combined sewer overflow to receiving waters can be found.     

Impact of sewage treatment plants and combined sewer overflow basins on the microbiological quality of surface water.

In a small river catchment, microbiological quality of different sewage treatment plants under regular conditions and in case of heavy rainfall, when combined sewage overflow basins (CSOs) are activated, was examined regarding microbial indicators and pathogens. In the watercourse, no self-cleaning effects could be observed. Small compact treatment plants discharge treated wastewater with a poor microbiological quality compared to river water quality and the quality of treated wastewater of larger plants. During storm water events, concentrations of microorganisms downstream of sewer overflows were approximately two logs higher than during dry weather conditions. Concentrations of parasites decreased slowly during the overflow, in parallel to filterable matter and particle-bound substances. The annual load of microorganisms originating from CSOs significantly exceeds the load from treated effluent of the sewage plants. Thus, an improved hygienic quality of the water course could be achieved by preventing overflows and by enhancing sewage treatment plants.     

Possibility of sewage and combined sewer overflow reuse with biological aerated filters.

The secondary effluent from municipal plants in Korea generally represents higher BOD with lower SS. Therefore, more soluble forms of organics and NH4-N need to be removed to improve its effluent for reuse. In this study reuse possibility of secondary effluent and CSO (combined sewer overflow) using BAF (biological aerated filter) was evaluated. The tertiary application with 1.2 h EBCT, SS, BOD and COD showed stable concentrations less than 1.3, 1.3 and 6.2 mg/L, respectively. Nitrogen could be nitrified even at 7 degrees suggesting BAF can be used for a water reuse method as well as an effective add-on facility in cold regions. However, BAF was not stable with CSO application at increased flow rates suggesting CSO must be equalised prior to application. Disinfection was necessary even during normal weather conditions.     

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.     

截流式合流制排水管网设计新思路

提出了一种以溢流井为分界线,将截流式合流制排水管网分解为一系列小型完全合流制排水管网的设计新思路,并以管网关联矩阵和节点连接特性矩阵为基础,以节点平衡原理和节点递归算法为核心,实现完全合流制排水管网的流量计算和水力计算.该方法能有效减小管网计算模型的规模,降低程序设计难度,提高程序的实用性.     

合流制溢流控制指标与标准制定研究

合流制溢流(combined sewer overflow,CSO)控制是城市水环境质量改善的关键一环,相关指标及标准制定尚显薄弱.基于技术的排放控制指标主要包括溢流频次、溢流体积控制率、污染物排放浓度限值、CSO效率及稀释度等,因这些指标缺乏对CSO水质水量控制效果的综合评价,进而提出雨季CSO污染负荷占比的指标;基...     

合流制溢流污染控制系统决策

合流制溢流(CSO)污染控制以削减溢流进入受纳水体的污染物总量为目标。由于合流制排水系统的复杂性以及污染物传输、溢流过程的随机性和多变性,CSO污染控制涉及一系列错综复杂的理论与工程实际问题,因而需要进行科学的系统决策,以降低投资、提高效益。首先分析我国城市CSO污染控制存在的主要问题;再从解析合流制及其溢流污染控制系统的组成关系入手,从宏观、系统的角度分析CSO污染的产生与传输过程,构建CSO污染控制系统,并对几个主要子系统进行分析;最后提出CSO污染的系统控制原理,探讨子系统的合理衔接、匹配和控制方案的优化选择问题,为我国城市CSO污染控制提供一个清晰的思路。     

Micropollutants in stormwater runoff and combined sewer overflow in the Copenhagen area, Denmark

Stormwater runoff contains a broad range of micropollutants. In Europe a number of these substances are regulated through the Water Framework Directive, which establishes Environmental Quality Standards (EQSs) for surface waters. Knowledge about discharge of these substances through stormwater runoff and combined sewer overflows (CSOs) is essential to ensure compliance with the EQSs. Results from a screening campaign including more than 50 substances at four stormwater discharge locations and one CSO in Copenhagen are reported here. Heavy metal concentrations were detected at levels similar to earlier findings, e.g., with copper found at concentrations up to 13 times greater than the Danish standard for surface waters. The concentration of polyaromatic hydrocarbons (PAHs) exceeded the EQSs by factors up to 500 times for stormwater and 2,000 times for the CSO. Glyphosate was found in all samples whilst diuron, isoproturon, terbutylazine and MCPA were found only in some of the samples. Diethylhexylphthalate (DEHP) was also found at all five locations in concentrations exceeding the EQS. The results give a valuable background for designing further monitoring programmes focusing on the chemical status of surface waters in urban areas.     

The performance of a novel combined sewer overflow with perforated conical screen

Increasing concern over the discharge of sewer solids from combined sewer overflows (CSOs) has encouraged the introduction of installations which incorporate either mesh or bar screen arrangements, or both. Gross solids create visual and aesthetic pollution if they reach watercourses. An entirely new arrangement for a CSO with a perforated screen of 6 mm diameter apertures is described in the paper. The arrangement is circular, with tangential flow across the screen to facilitate its cleaning. High velocities across the screen holes ensure that solids which have been prevented from discharging are swept clear from the screen. As a result, a sufficient screen area remains free from trapped solids to permit discharge of flow. The device has been designed to meet all anticipated performance criteria for the removal of solids, and to require a minimum of maintenance.A thorough testing programme in different conditions is described. Laboratory testing utilised a wide range of gross solids and flows to determine efficiencies of solids removal under all anticipated operating conditions. The performance of the CSO in a sewer environment was evaluated at a sewage treatment works with flows up to 1801/s using both raw and treated sewage to simulate storm sewage of different strengths. Both the device and its testing are described, together with the results of the testing programme.     

Series of surveys for enteric viruses and indicator organisms in Tokyo Bay after an event of combined sewer overflow.

Combined sewer overflows (CSOs) have been recognised as one of the serious sources of pollution to the water environment during rain events, although field surveys to investigate the effect of their magnitude and duration on receiving waters have been very limited. The fates of enteric viruses (norovirus G1, G2, enteroviruses) and coliforms were determined in the wastewater treatment plant on a fine day and on a rainy day. Not all microorganisms were reduced in the primary treatment, but were reduced in the secondary treatment. Occurrences of enteric viruses and levels of coliforms were surveyed in the receiving coastal area after a CSO event, with the profiles of the enteric viruses in the coastal seawater being almost at the same positive ratio for 4 d after the CSO event.     

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。     

银川市某高密度城区合流制溢流污染特性研究

针对合流制管网系统溢流污染严重且易造成受纳水体出现黑臭现象等问题,以银川市第一污水处理厂片区为例,基于雨洪管理模型(SWMM),在短历时设计降雨和典型年长历时降雨条件下,模拟分析了研究区域溢流排口溢流量及溢流污染物负荷对不同降雨条件的响应关系及其对受纳水体水质的影响。结果表明：雨天合流制管网系统的溢流量及溢流污染负荷量较大,且无论是短历时还是长历时降雨条件下,均具有随着降雨量的增加而增大的特点;厂前溢流污染浓度大,超过受纳水体自净能力,短期内水体水质处于黑臭状态。本研究对银川市黑臭水体治理及溢流污染防治方案的制订具有重要的参考价值。     

城市河道溢流堰对水体溶解氧及氮和磷的影响

研究了河道溢流堰对水体DO及氮、磷的影响,结果表明:经溢流堰后,水体DO平均增加1.75 mg/L。当水温超过15℃,堰下DO低于4.00 mg/L时,堰下TN低于堰上,堰下DO高于4.00 mg/L时,堰下TN低于堰上。当水温低于15℃,堰下DO高于4.00 mg/L时,堰下TN高于堰上,TN升高。当DO增加较少时,堰下TP高于堰上,DO增加较多时,堰下TP低于堰上,TP得到一定降低。     

区域特征参数及降雨等级差异性对合流制系统溢流影响模拟研究

针对地形坡度、土壤渗透性能、不透水面积率、年径流总量控制率、截流倍数、截流井上游管段设计重现期六类合流制区域特征参数及降雨因素对合流制溢流总量及溢流频次的影响,利用S WMM模型模拟研究了合流制区域特征参数对溢流结果的影响权重、合流制区域特征参数组合正交方案的差异性及降雨因素与引入的溢流比概念的响应关系.结果表明,合流...     

Continuous measurement of dissolved sulfide in sewer systems

Sulfides are particularly problematic in the sewage industry. Hydrogen sulfide causes corrosion of concrete infrastructure, is dangerous at high concentrations and is foul smelling at low concentrations. Despite the importance of sulfide monitoring there is no commercially available system to quantify sulfide in waste water. In this article we report on our use of an in situ spectrometer to quantify bisulfide in waste water and additional analysis with a pH probe to calculate total dissolved sulfide. Our results show it is possible to use existing commercially available and field proven sensors to measure sulfide to mg/l levels continuously with little operator intervention and no sample preparation.     

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.     

A fate and transport model for Asian carp environmental DNA in the Chicago area waterways system

Detection of environmental DNA (eDNA) is widely employed to infer the presence of endangered or invasive species in the aquatic environment. Detection of eDNA, however, does not guarantee the presence of the species in question. The location, time, and nature of the eDNA source are unknown. An eDNA fate and transport model can help to address these unknowns. Construction of such a model requires resolution of multiple issues including: 1) Quantification of eDNA concentration in the environment; 2) Quantification of the eDNA source; 3) Quantification of decay rate; and, 4) Model application and validation. We address these issues and present the results of a fate and transport model for eDNA originating from an invasive species, silver carp (Hypophthalmicthys molitrix), in the Chicago Area Waterways System, USA. Results indicate the presence of roughly 4600?kg of silver carp, distributed along the major axes of the system, is required to produce the eDNA detected in routine monitoring. Positive detection of eDNA in a sample suggests a source within days and km of the sample time and location.     

Evaluation of total emissions from treatment plants and combined sewer overflows

Based upon the connection of a simulation program for combined sewer systems with the IAWQ-Activated Sludge Model No.l the new simulation tool GEMINI was developed, which allows the calculation of sewer and sewage treatment plant as a unit. Some obtained results are presented in an example. They suggest, that for every treatment plant a rate of inflow is determinable, which leads to a minimum of total emissions out of sewer and treatment plant. The optimal value of sewage treatment plant inflow in the example is distinctly greater than the design flow rate fixed in German design rules. So it is recognizable that a rigid flow management for sewer and treatment plant does not always fulfil the aim of minimization of total emissions.     

Combined sewer overflow emissions to bathing waters in Portugal. How to reduce in densely urbanised areas?

The current proposal for a revised European Directive concerning the quality of bathing water significantly increases the demands for the control of wet-weather discharges. A densely urbanised combined catchment was modelled for a 19-year long rainfall series in order to assess the current situation and to evaluate the benefits of potential solutions. Storage and advanced physical-chemical treatment of stormwater in the STP may significantly contribute for the reduction of the overflow volumes but reductions of the spill frequency under 2.5 spill days per bathing season are hardly obtained. This study reveals the severe strains that the local rainfall pattern may place on the control of the frequency of wet-weather discharges, pointing to serious technical, social and economical implications, at the local and at the national level, if the current proposal for a revised European Directive on Bathing Water is enforced.