Measuring surplus capacity for multiobjective optimal design of foul sewer systems

ABSTRACT

This paper proposes a new performance index of foul sewer systems, i.e. sewer conveyance capacity (SCC) index, to quantify the surplus capacity for multi-objective optimization design problems. The use of the new SCC index is demonstrated using a hypothetical network and a real-world foul sewer network. Results obtained show clear trade-offs between SCC and the other two objectives considered, i.e., capital and operational costs and greenhouse gas emissions. The results show that the upstream sewers in the system often have a relatively large surplus capacity, while the sewer mains operate close to the design capacity. Moreover, SCC is compared with three common indicators at both individual sewer and system-wide levels. Strong correlations between SCC and other indicators are revealed, implying that SCC is a good representation of system performance and can provide a more comprehensive picture of the foul sewer system performance.     

Reliability-based layout design of sewage collection systems in flat areas

The sewer layout in flat areas significantly influences the final design which is desired to be optimized for the construction and operational costs. This study introduces a model for designing the layout of sewer networks considering their reliability. A reliability criterion is introduced and optimized using a simple simulated annealing scheme. The best layout with the maximum reliability represents an optimum sewer layout in which clogging in a sewer has the least effect on its upstream lines. A case study is solved using the proposed model. Then, for the obtained layout, the sewer specifications are designed using a dynamic programming model. The reliability somehow reflects the operational costs that can be taken into account in the system design by the proposed model. Furthermore, it is concluded that the network's reliability and construction cost are in conflict with each other such that more reliable layouts lead to more expensive designs.     

Grey-box modelling of pollutant loads from a sewer system

Using a compact measuring unit with on-line meters for UV absorption and turbidity, it is possible to determine concentrations of organic load (chemical oxygen demand (COD) and suspended solids (SS)) anywhere in a sewer system. When measurements of the flow are available as well, the pollutant mass flow at the measuring point can be calculated.The measured data are used to estimate different models describing the load of pollutants in the sewer. A comparison of the models shows that a grey-box model is most informative and best in terms measured by the multiple correlation coefficient. The grey-box model is a state-space model, where the state represents the actual amount of deposition in the sewer, and the output from the model is the pollutant mass flow to the wastewater treatment plant (WWTP). The model is formulated by means of stochastic differential equations. Harmonic functions are used to describe the dry weather diurnal load profiles. It is found that the accumulation of deposits in the sewer depends on previous rain events and flows.By means of on-line use of the grey-box models, it is possible to predict the amount of pollutants in a first flush at any time, and hence from the capacity of the plant to decide if and when the available detention basin is to be used for storage of wastewater. The mass flow models comprise an important improvement of the integrated control of sewer and WWTP including control of equalisation basins in the sewer system. Further improvements are expected by the introduction of an additive model where dry weather situations and storm situations are modelled separately before addition to the resulting model.     

城市污水管道维护优化决策模型的研究

在研究污水管道维护费用函数的基拙上,提出了城市污水管道维护优化决策模型,并运用该优化决策模型对四川岳池城东新区123段城市污水管道进行了维护优化决策.优化决策结果为:需采取维护措施的污水管道共19段,约占总管段数的15.44%,其中两段污水管道采取"更新"方案、两段污水管道采取"软管内衬"方案、巧段污水管道采取"清淤"方案;其余104段污水管道无需采取维护措施而只例行检查.实例计算结果表明:应用城市污水管道维护优化决策模型得到的决策是有效的,可为污水管道的维护提供决策支持.     

Multiobjective optimisation algorithm for sewer network rehabilitation

Understanding of deterioration mechanisms in sewers helps asset managers in developing prediction models for estimating whether or not sewer collapse is likely. Effective utilisation of deterioration prediction models along with the development and use of life cycle maintenance cost analysis contribute to reducing operation and maintenance costs in sewer systems. This article presents a model for life-cycle maintenance planning of deteriorating sewer network as a multi-objective optimisation problem that treats the sewer network condition and service life as well as life-cycle maintenance cost (LCMC) as separate objective functions. The developed model utilises Markov chain model for the prediction of the deterioration of the network. A multi-objective genetic algorithm is used to automatically locate an appropriate maintenance scenario that exhibits an optimised tradeoff among conflicting objectives. Monte Carlo simulation is used to account for LCMC uncertainties. The optimisation algorithm provides an improved opportunity for asset managers to actively select near-optimum maintenance scenario that balances life-cycle maintenance cost, condition and service life of deteriorating sewer network. A case study is used to demonstrate the practical features of developed methodology.     

基于GIS的昆明主城区排水系统诊断研究

昆明主城区地处滇池流域北岸滨湖上游区域,污染负荷比重大,占流域污染负荷总量的约80%,目前昆明主城区二环路内区域为合流制排水系统,二环路外为分流制排水系统,在雨季雨、污合流污水溢流污染问题严重.在昆明市地下管线探测工作的基础上,对排水管网数据进行空间信息和属性信息处理,建立污染源与排水系统的拓扑关系,构建排水片区--子排水片区--排水单元结构网络.统计分析结果表明,昆明主城区的现状污水收集率约为81%;污水处理厂处理能力有限,在雨季大量合流污水不经处理而直接溢流排入河道,并汇入滇池.通过对典型排水区域船房河排水片区--第一污水处理厂纳污区域进行排水系统详查和污水产生--收集--处理全过程分析,确定依托沟渠主干的排水系统地下水渗入量约占系统收集总水量的35%,此截流式合流制与不完全分流制相结合的典型排水片区旱季污水收集率约为60%,在雨季典型降雨条件下,合流污水溢流率约为90%.此研究成果为昆明主城区排水系统的改造和污水处理厂的规划建设提供了一定依据,也为全面开展排水系统诊断工作奠定了基础.     

城市污水管道实际健康度评价模型及应用研究

根据现状管道破坏数据及其对环境影响的后果建立了城市污水管道实际健康度评价指标体系,基于属性理论提出了城市污水管道实际健康度属性综合评价模型,并运用此模型对四川岳池城东新区城市污水管道的实际健康度进行了综合评价.评价结果表明,运用城市污水管道属性综合评价模型得到的实际健康度,可以客观地反映城市污水管道实际整体健康状况,可为确定管道维护顺序和维护方案提供理论依据.     

城市污水管道预报健康度评价模型及其应用研究

根据现状管道破坏的可能性及其环境影响后果等因素,建立了城市污水管道预报健康度评价指标体系,基于灰色系统理论提出了城市污水管道预报健康度灰色关联综合评价模型,并运用此模型对四川岳池城东新区城市污水管道的预报健康度进行了综合评价.结果表明:运用灰色关联综合评价模型计算得到的预报健康度可为确定污水管道检测的优先次序提供依据,健康度较低的管道应优先被检测;在灰色关联评价法中,将模的大小与夹角的大小结合起来,可以较全面地反映污水管道与虚拟最健康管道的接近程度;采用多时段管道评价矩阵可避免评价模型的奇异性.     

An overview of the U.S. Environmental Protection Agency's storm and combined sewer program collection system research

A state-of-the-art and assessment of the USEPA'S Storm and Combined Sewer Program collection system research pertaining to management alternatives for wet- and dry-weather wastewater transport and interception is presented. These include: maintenance; catchbasins; new sewer design; sewer flushing; polymer injection; infiltration/inflow controls including inflow reduction. Insituform, impregnated concrete pipe and trenchless sewer; upstream storage/attenuation; flow routing and in-pipe storage; new types of flow regulators including swirl and helical bend regulator/concentrators, fluidic regulator and Hydrobrake; and a new rubber “duck-bill” tide gate. The emphasis is on optimal use of the existing sewerage system and optimal city-wide cost-effective strategy for the dual purpose of combined sewer drainage and overflow pollution control.     

Optimizing tradeoffs among housing sustainability objectives

The sustainability of housing units can be improved by integrating green building equipment and systems such as energy-efficient HVAC systems, building envelopes, water heaters, appliances, and water-efficient fixtures. The use of these green building measures often improves the environmental and social performances of housing units; however they can increase their initial cost and life cycle cost. This paper presents a multi-objective optimization model that is capable of optimizing housing design and construction decisions in order to generate optimal/near-optimal tradeoffs among the three sustainability objectives of maximizing the operational environmental performance of housing units, maximizing the social quality of life for their residents, and minimizing their life cycle cost. The model is designed as a multi-objective genetic algorithm to provide the capability of optimizing multiple housing objectives and criteria that include minimizing carbon footprint and water usage during housing operational phase, maximizing thermal comfort, enhancing indoor air and lighting quality, improving neighborhood quality, and minimizing life cycle cost. An application example is analyzed to illustrate the use of the developed model and evaluate its performance. The results of this analysis illustrate the novel capabilities of the model in generating 210 near-optimal tradeoff solutions for the analyzed housing example, where each represents an optimal/near-optimal and unique tradeoff among the aforementioned three sustainability optimization objectives of maximizing the operational environmental performance of housing units, maximizing the social quality of life for their residents, and minimizing their life cycle cost. These novel capabilities of the developed model are expected to improve the design and construction of housing units and maximize their overall sustainability.     

微粒群多目标优化率定暴雨管理模型(SWMM)研究

针对SWMM存在模型参数多、率定困难的问题,采用微粒群算法(PSO0)对SWMM模型进行优化率定研究,完成了高维多目标优化率定过程.算例结果表明,微粒群算法可以有效地完成优化率定过程,并能实现多目标优化,这对模型率定和实际城市防汛工作具有一定指导意义.     

基于全寿命环境成本的工程结构维护方案优化

工程结构全寿命过程中存在有害气体、污水和固体废弃物排放等环境问题,但是由其造成的经济损失却很少在结构设计或工程决策过程中予以考虑。为此,将三类污染物排放的防治成本计入工程活动的环境成本中,得到了多种建筑材料、能源消耗、运输方式和建筑机械使用的环境成本。通过将环境成本与经典全寿命成本模型相结合,建立了包含环境成本的全寿命总成本模型。根据所提出的环境成本模型和全寿命总成本模型,以某一沿海高速公路桥梁结构为例,通过设置预防性维护措施和必要性维护措施,对其进行维护方案的多目标优化,分析环境成本对工程决策的影响。并对直接成本和环境成本的不确定性进行了分析,研究了环境成本折现率对环境成本影响。结果表明,在结构优化过程中考虑环境成本能够得到经济效益和环境综合性能更佳的工程方案。     

Fuzzy-based MOGA approach to stochastic time–cost trade-off problem

In construction projects, time and cost are manageable objectives with significant interdependencies for which sets of trade-offs may exist. This study presents a new approach for the solution of time–cost trade off problems in an uncertain environment. Fuzzy numbers are used to address the uncertainties in the activities execution times and costs. Fuzzy sets theory is then explicitly embedded into the optimization procedure. A multi-objective genetic algorithm is specially tailored to solve the discontinuous and multi-objective fuzzy time- cost model with relatively large search space. The proposed approach identifies the best set of implementation options defined by the sets of non-dominated solutions Accepted risk level and optimism of the decision maker are addressed using α-cut approach and optimism index (β) respectively. To illustrate the application and performance of the model, two case examples are presented, for which separate Pareto fronts are developed. The fuzzy presentation of the non-dominated solution helps the project manager to apply his own level of risk acceptance and degree of optimism in decision making process. Different risk acceptance level and/or optimism leads to different scheduling and sets of Pareto solutions from which the project manager may select his preferred options.     

三联供与冰蓄冷耦合的复合系统优化设计

本文建立了一个冷热电三联供与冰蓄冷耦合的复合系统优化数学模型,以年总运行成本最小为目标函数,综合考虑了经济性、环保性、节能性评价指标对系统的影响。最后以上海某综合型超高层建筑为研究对象,利用LINGO软件进行多目标优化计算,提出了三联供耦合冰蓄冷系统的设备优化容量以及全年运行策略优化方案,并分析了电、气价格及二氧化碳排放税对系统的影响。     

基于遗传算法的建筑工程三大目标综合优化

工期、成本和质量是建筑工程的三大主要目标,他们能否顺利实现将直接影响项目总体目标的好坏,而以往提出的模型大都是侧重于对工期一成本两目标的综合优化,很少涉及质量目标,这显然是满足不了现实要求的。因此在这里提出了一个对三大目标综合优化的模型,它是在工期一成本、工期一质量为线性关系的基础上建立的,并且以综合目标函数作为适应度函数建立的依据,运用遗传算法进行求解。最后用一个实例验证了此模型的可行性,并且运算之后可以得到多组解,决策者可以根据自己的偏好选择自己满意的一组解。     

基于GPRS的市政下水道气体安全监测预警系统

为提高城市市政下水道气体环境监测的可靠性和实时性,开发了市政下水道气体安全监测预警系统,并应用于重庆市下水道.该系统是一种基于通用无线分组业务(GPRS)的下水道气体远程在线监测服务平台,由传感器模块、信号处理模块、数据传输模块以及监控中心处理层组成,可及时、准确地显示可燃气体(CH4)浓度超限的市政下水道所在位置.测试结果表明:该系统的年发送成功率达到99.0%,相对误差<2%.该监测预警系统的建设为防止下水道可燃气体泄漏引发爆炸、人员中毒等事故的发生提供了保障.     

Evaluation of an MBR-RO system to produce high quality reuse water: microbial control, DBP formation and nitrate

A membrane bioreactor and reverse osmosis (MBR-RO) system was developed to assess potential reuse applications of municipal wastewater. The objective of the study was to examine the water quality throughout the system with a focus on waterborne pathogens, disinfection by-products (DBPs) and nitrate. This paper will discuss the presence of these contaminants in MBR effluent and focus on their subsequent removal by RO. This study has shown that high quality reuse water can be produced from municipal wastewater through the use of an MBR-RO system. The water meets California Title 22 reuse regulations for non-potable applications and US EPA drinking water limits for trihalomethanes (THM) (80 microg/L), haloacetic acids (HAA) (60 microg/L), chlorite (1.0 mg/L), total coliform (not detectable), viruses (not detectable), and nitrate/nitrite (10 mg N/L). However, THM formation (182-689 microg/L) attributed to cleaning of the MBR with chlorine and incomplete removal by subsequent RO treatment resulted in reuse water with THM levels (40.2+/-19.9 microg/L) high enough to present a potential concern when considering drinking water applications. Nitrate levels of up to 3.6 mg N/L, which resulted from incomplete removal by the RO membrane, are also a potential concern. A denitrification step in the MBR should be considered in potable water applications.     

pH dynamics in sewers and its modeling

pH variation in sewers has a significant effect on hydrogen sulfide production and emissions, and hence its accurate prediction is critical for the optimization of mitigation strategies. In this study, the nature and dynamics of pH variation in a sewer system is examined. Three sewer systems collecting domestic wastewater were monitored, with pH in all cases showing large diurnal variations. pH in fresh sewage in all three cases had a very similar trend with maximum pH in the range of 8.5–8.7. pH variation in fresh sewage followed the same pattern as the sewage flow rate, suggesting that sewage pH is influenced by household water use. Nitrogen content of the wastewater was found to be the most influential factor causing pH variation in fresh sewage, with the total ammonium concentration variation well correlated with the pH variation. A methodology for predicting pH variation in sewers is developed and calibration protocols proposed. The methodology, which is based on the concept of charge balance, was validated using titration curves and field pH data. Measurement of the total ammonium concentration in fresh sewage was found necessary and adequate for the calibration of the charge balance-based pH model.