Modeling air flow in sanitary sewer systems: A review

Current designs of sanitary collection systems normally only consider the transport of wastewater without attention on the air movement in the sewer airspaces. Under anaerobic conditions, hydrogen sulfide (H₂S) can be generated in the liquid phase in sewer systems. H₂S is corrosive to concrete and steel structures and odorous or even toxic to human, which can cause corrosion and sewer odor issues. To develop a feasible sewer corrosion and odor control strategy, it is necessary to understand the mechanisms of air flow in sewer systems for developing practical tools to predict and control the air flow. This paper comprehensively reviewed previous efforts on modeling the air flow in sewer systems and provided recommendations on predicting the air flow for engineering applications. The air flow in a single pipe was firstly reviewed followed by the air flow in sewer structures as well as air flow models in sewer networks. Some other considerations such as temperature driven flow, transient water flow, and wind effect were also reviewed. The knowledge gaps were then identified, and recommendations on the further studies were provided.     

Model-based knowledge acquisition in environmental decision support system for wastewater integrated management

The main goal of the Water Framework Directive is to achieve good chemical and ecological status of water bodies by 2015. The implementation of integrated river basin management, including sewer systems, wastewater treatment plants and receiving water bodies, is essential to accomplishing this objective. Integrated management is complex and therefore the implementation of control systems and the development of decision support systems are needed to facilitate the work of urban wastewater system (UWS) managers. Within this context, the objective of this paper is to apply integrated modelling of an UWS to simulate and analyse the behaviour of the 'Congost' UWS in Spain, and to optimize its performance against different types of perturbations. This analysis results in optimal operating set-points for each perturbation, improves river water quality, minimizes combined sewer overflows and optimizes flow lamination from storm water tanks. This is achieved by running Monte Carlo simulations and applying global sensitivity analysis. The set-points will become part of the knowledge base composed of a set of IF-THEN rules of the environmental decision support system being developed for this case study.     

Sewer System Design Using Simulated Annealing in Excel

An optimization procedure has been developed for branching storm and sanitary sewer systems with a pre-determined layout for determining the minimum total cost. The model was developed within Microsoft Excel using simulated annealing as the optimization procedure. The total cost of the storm sewer system that was obtained with this optimal design procedure was compared to the total cost of the system as obtained from the conventional straight slope design procedure. Applying the simulated annealing optimizer to the design of the branching storm sewer network resulted in a cost savings of over $77,100 or about 7 % (a reduction from $1,117,700 to $1,040,600). These significant savings were realized by simply going an extra step and implementing an optimization technique during the design phase. Use of Excel should enhance the availability and the usage of such an optimization model for the design of storm and sanitary sewer systems by consulting engineers and various agencies.     

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.     

Japan's sewerage system

This paper traces the history of sewer construction in Japan. The first sewers were built for flood control, and as late as the end of the Second World War there were only six cities enjoying sewer systems with treatment facilities. Rapid industrialization increased pollution problems and led to accelerated sewer development. Advances in the technology of sewage treatment are outlined. Today 30% of Japan's population is served by sewer systems, and identifying cost‐effective means of increasing that proportion is a major priority. The Experimental Sewer System, developed in Tokyo, is described. Finally, a new method for the estimation of peak flow in sewer pipes, entitled grid analysis, is presented.     

Decision making in flood risk based storm sewer network design

It is widely recognised that flood risk needs to be taken into account when designing a storm sewer network. Flood risk is generally a combination of flood consequences and flood probabilities. This paper aims to explore the decision making in flood risk based storm sewer network design. A multiobjective optimization is proposed to find the Pareto front of optimal designs in terms of low construction cost and low flood risk. The decision making process then follows this multi-objective optimization to select a best design from the Pareto front. The traditional way of designing a storm sewer system based on a predefined design storm is used as one of the decision making criteria. Additionally, three commonly used risk based criteria, i.e., the expected flood risk based criterion, the Hurwicz criterion and the stochastic dominance based criterion, are investigated and applied in this paper. Different decisions are made according to different criteria as a result of different concerns represented by the criteria. The proposed procedure is applied to a simple storm sewer network design to demonstrate its effectiveness and the different criteria are compared.     

Automation model of sewerage rehabilitation planning.

The major steps of sewerage rehabilitation include inspection of sewerage, assessment of structural conditions, computation of structural condition grades, and determination of rehabilitation methods and materials. Conventionally, sewerage rehabilitation planning relies on experts with professional background that is tedious and time-consuming. This paper proposes an automation model of planning optimal sewerage rehabilitation strategies for the sewer system by integrating image process, clustering technology, optimization, and visualization display. Firstly, image processing techniques, such as wavelet transformation and co-occurrence features extraction, were employed to extract various characteristics of structural failures from CCTV inspection images. Secondly, a classification neural network was established to automatically interpret the structural conditions by comparing the extracted features with the typical failures in a databank. Then, to achieve optimal rehabilitation efficiency, a genetic algorithm was used to determine appropriate rehabilitation methods and substitution materials for the pipe sections with a risk of mal-function and even collapse. Finally, the result from the automation model can be visualized in a geographic information system in which essential information of the sewer system and sewerage rehabilitation plans are graphically displayed. For demonstration, the automation model of optimal sewerage rehabilitation planning was applied to a sewer system in east Taichung, Chinese Taiwan.     

Heuristic Optimization Model for the Optimal Layout and Pipe Design of Sewer Systems

The design of urban stormwater systems and sanitary sewer systems consists of solving two problems: generating a layout of the system and the pipe design which includes the crown elevations, slopes and commercial pipe sizes. A heuristic model for determining the optimal (minimum cost) layout and pipe design of a storm sewer network is presented. The hierarchical procedure combines a sewer layout model formulated as a mixed-integer nonlinear programming (MINLP) problem which is solved using the General Algebraic Modeling System (GAMS) and a simulated annealing optimization procedure for the pipe design of a generated layout was developed in Excel. The GAMS and simulated annealing models are interfaced through linkage of Excel and GAMS. The pipe design model is based upon the simulated annealing method to optimize the crown elevations and diameter of pipe segments in a storm sewer network using layouts generated using GAMS. A sample scenario demonstrates that using these methods may allow for significant costs saving while simultaneously reducing the time typically required to design and compare multiple storm sewer networks.     

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.     

Failure of sewage pumps: statistical modelling and impact assessment.

Sewage pumping stations are directly responsible for affecting performance, i.e. failing pumps may result in combined sewer overflows or flooding. However, failures of sewage pumps are not yet incorporated in sewer assessments due to lack of knowledge and data. This paper presents the analysis of pump failure data provided by two sewer management authorities in The Netherlands. Pump failures have been studied accounting for the nature of the failures, the operation and maintenance procedures of the management authority, the ageing of the pumps and the changes in the environment of pumps. The analysis shows that sewage pumps fail relatively often due to the composition of sewage and the discontinuous operation of the pumps. The interarrival time and the duration of failures are highly variable and independent of the pump type and the specific function of the pump. The results also indicate that the serviceability of sewer systems is significantly affected by failing pumps. As a consequence, part of the environmental damage due to CSOs (combined sewer overflows) can be avoided by improving maintenance of pumping stations.     

An integrated approach for improving the wastewater discharge and treatment systems

Since treatment plants have been built all over Germany during the last decades, the water quality of receiving streams has been improved remarkably. But there are still a lot of quality problems left, which are caused e.g. by combined sewer overflows (CSO), treatment plant effluents or rainwater discharges from separate sewer systems. At present different efforts are undertaken to control sewer systems in order to improve the operation of urban drainage systems or more generally, design processes. The Emschergenossenschaft and Lippeverband (EG/LV) are carrying out research studies, which are focusing on a minimization of total emissions from sewer systems both from wastewater treatment plant (WWTP) effluents and from CSO. They consider dynamic interactions between rainfall, resultant wastewater, combined sewers, WWTP and receiving streams. Therefore, in an advanced wastewater treatment, a model-based improvement of WWTP operation becomes more and more essential, and consequently a highly qualified operational staff is needed. Some aspects of the current research studies are presented in this report. The need and the use of an integrated approach to combine existing model components in order to optimize dynamic management of combined sewer systems (CSS) with a benefit for nature are outlined.     

Probabilistic modeling of sewer deterioration using inspection data.

Accurate prediction of current and future conditions of sewer systems is crucial to manage the sewer system wisely, cost-effectively and efficiently. The application of historical databases of visual inspection data to sewer deterioration modeling seems common sense. However, in The Netherlands, sewer inspection data is only used to determine the direct need for rehabilitation. This paper outlines the possibilities of using inspection data for deterioration modeling and discusses the problems encountered. A case study was performed on the modeling of the condition aspect 'surface damage by corrosion or mechanical action' using a Markov model.     

A dynamic ventilation model for gravity sewer networks

To implement any effective odour and corrosion control technology in the sewer network, it is imperative that the airflow through gravity sewer airspaces be quantified. This paper presents a full dynamic airflow model for gravity sewer systems. The model, which is developed using the finite element method, is a compressible air transport model. The model has been applied to the North Head Sewerage Ocean Outfall System (NSOOS) and calibrated using the air pressure and airflow data collected during October 2008. Although the calibration is focused on forced ventilation, the model can be applied to natural ventilation as well.     

Layout and Component Size Optimization of Sewer Network Using Spanning Tree and Modified PSO Algorithm

In the paper, a new method is introduced for optimally solve the problem of the layout and component size determination of sewer network. Simultaneously Layout and component size optimization of sewer network problem consists of many hydraulic constraints which are generally nonlinear and discrete; which creates a challenge even to the modern heuristic search methods. An algorithm generation of a predefined number of spanning trees is introduced to generate a predefined number of sewer layouts of a base sewer network in order of increasing length. These generated layouts are sorted in ascending order of total cumulative flow and sorted layouts are individually optimized for sewer components sizing. It has been found that the optimal sewer layout for total system optimization is one where the total cumulative flow has the minimal value. The modified particle swarm optimization (MPSO) algorithm has been used to optimally determine the component sizes of the selected layouts. The proposed method is applied to the Sudarshanpura sewer network (situated in Jaipur, India) design problem. The results are presented for optimal cost vs cumulative flow of the layouts. Further results of MPSO has been compared with the original PSO algorithm.     

地下排水管道流量检测技术进展

排水管道属于资金密集型市政基础工程.准确掌握管道内水流状况,是改善排水系统管理、科学制定管道系统改扩建方案的必要条件,也是今后利用先进技术建立管道系统模型、实现计算机实时控制的基础.系统总结了排水管道流量测试的常规技术,提出了适用性评估方法,介绍了目前国际上较为先进实用的排水管道流量检测设备及其在上海的应用,以期推动国内排水管道的流量检测与排水系统的管理水平.     

Occurrence and fate of organic pollutants in combined sewer systems and possible impacts on receiving waters.

Selected organic pollutants are classified based on an intensive literature survey. Two wastewater parameters (COD and ammonium) and six selected organic pollutants (polycyclic aromatic hydrocarbons (PAH), diethylhexylphthalate (DEHP), estradiol (E2), ethinylestradiol (EE2), ethylenediamine tetraacetic acid (EDTA) and nitrilo triaceticacid (NTA)) are specified. As a result, for the first time representative concentrations in dry weather flow, surface runoff and effluent of wastewater treatment plants (WWTPs) in combined sewer systems (CSS) are stated. The second part of the paper presents a first estimation of main emission out of a combined sewer system and possible receiving water impacts in terms of (1) annual discharged loads calculated by pollution load simulations in a hypothetical catchment and (2) concentrations calculated in combined sewer overflows (CSO) discharges and resulting receiving water concentrations.     

Modelling Sewer Systems Costs with Multiple Linear Regression

The aim of this paper is the establishment and validation of cost functions for the various assets of sewer systems, namely gravity and raising pipes, manholes and pumping-stations. Costs are defined as a function of the main physical characteristics of the assets, such as, the pipe material and diameter, excavation depth and percentage of pavement (for sewer pipes), the manhole depth (for manholes) and flow rate, pump head and pump power (for pumping stations,). A four-step methodology was followed: 1) data collection, processing and analysis, 2) present value calculation, 3) key parameters identification and cost functions estimation, and 4) cost functions validation. Cost and infrastructure data for construction contracts of sewer systems managed by Águas de Portugal (AdP) were analyzed. Cost functions were estimated based on multiple linear regression analysis and compared with the ones obtained in previous studies.     

枚举法和动态规划法在污水管网布置优化中的应用

用VB语言编写污水管网布置优化计算程序,从污水有向网络图出发,以污水管网系统费用最低为优化目标,并结合图论理论知识,应用枚举法将污水管网的所有可能的布置形式全部列出,同时利用水力参数优化计算,进行动态规划剪枝,选出污水管网最优的布置形式及其相应的最优水力参数.     

Experimental analysis of the hydrass flushing gate and laboratory validation of flush propagation modelling.

Periodical cleansing operations prove necessary inside sewer systems in order to reduce hydraulic and environmental problems owing to the accumulation of deposits on the bottom of channels. For this objective, new effective hydraulic devices based on the scouring effects of flushing waves have been recently set up and adopted in many sewer systems. In this paper, the results of an experimental and numerical investigation on the hydraulic operation of the Hydrass flushing gate are reported. The experimental analysis has been carried out using a laboratory channel and a reduced scale model of the gate, in order to characterise the flushing waves generated by the device. The numerical analysis has been performed using a mathematical model specifically developed for the simulation of flushing waves inside sewer channels. The comparison of numerical results and experimental data has allowed evaluation of the applicability under unsteady flow conditions of the outflow relations determined for the Hydrass gate in a previous investigation under steady flow conditions.