The relevance of sewer deterioration modelling to support asset management strategies

Deterioration modelling can be a powerful tool to support utilities in planning efficient sewer rehabilitation strategies. However, the benefits of using deterioration models are still to be demonstrated to increase the confidence of utilities toward simulation results. This study aims at assessing the performance of a statistical deterioration model to estimate the current condition and predict the future deterioration of a sewer network. The prediction quality of the deterioration model GompitZ has been assessed using the extensive data-set of 35,826 inspections performed in the city of Braunschweig, Germany. The performance of the statistical model has been compared with the performance of a simple model based only on the condition of observed sewers. Results show that the statistical model performs much better than the simple model for simulating the deterioration of the network. The findings highlight the relevance of using modelling tools to simulate sewer deterioration and support strategic asset management.     

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.     

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.     

基于管道沉积物控制的CSOs污染负荷削减分析

管道沉积物是合流制排水系统溢流(CSOs)污染的重要来源,因此控制沉积物对于削减CSOs污染具有重要意义。在合流制排水系统截流泵站的上游管道中安装穿孔管,给穿孔管提供高压水产生7.5 m/s以上的射流以冲洗管道,同时在截流泵站内设置旋流分离系统来去除冲洗水中的沉积物。对于水层较浅、管径为DN400、管长为40 m、沉积层厚度为3 cm的管道,可使管道流中的SS从冲洗前的75～170 mg/L增加到2 500～3 000 mg/L,且在2～3 min内冲洗干净。旋流分离器对冲洗水中SS的去除率达到55.6%。两周一次的管道例行清洗维护,可使CSOs中污染物降低25%左右,减轻了受纳水体的污染负荷。     

雨污分流改造保留合流管为雨水管的工程实例

在将城市排水合流管改造为雨、污分流管道的过程中，如条件允许可将合流管局部或整体保留用做雨水管，再另外新建污水管道。结合苏州市中心城区完善污水管网工程，介绍了在该市吴县新村内的应用实例。实践表明，保留的合流管能有效地排放正常年份的降雨，甚至是台风暴雨时产生的地面径流。该措施不仅能节约工程投资、缩短工期，还能减少因地面开挖对居民生活造成的不利影响。     

On hydraulic and pollution effects of converting combined sewer catchments to separate sewer catchments

The overall objective of this paper is to contribute to the standing debate concerning the advantages of separate sewer systems compared to traditional combined sewer systems. By a case study this investigation reveals that transformation of part of a town from being serviced with combined sewer systems to become serviced with separate sewer systems decreases the volumes of storm water and pollutants diverted to the waste water treatment plant and discharged as combined sewer overflow. This happens at the expense of an increase in volumes of storm water and pollutant loads diverted to local receiving waters when detention ponds are not built-in the new separate sewer systems. It is concluded that consequences can be fatal for receiving waters, if no retention of pollutants is integrated into the system.     

Statistical comparison of the performance of data-based models for sewer condition modeling

Abstract

The present article proposes a methodology to consider the uncertainty intrinsic to data-based models when comparing their performance. The goal is to provide a quantification of the variability of this type of models due to the random nature of the calibration process and enable a statistical comparison of the models’ performance when attempting to identify the best. The methodology proposed doesn’t provide an alternative metric to determine the models’ performance, but it expands the traditional deterministic comparison to a stochastic comparison. The methodology builds on the current standard approach for developing data-based model and its application is demonstrated to model sewer condition using data from 4 trunk sewers of the SANEST – Saneamento da Costa do Estoril sewer system, corresponding to 25?km of sewer pipes. The data-based models were developed using artificial neural networks, support vector machines, bootstrapping aggregation and least squares support vector machines. For the case study, the highest and average misclassification performance records are similar for all models (23% to 24% and 31% to 33%, respectively) but the lowest performance varied more significantly (39% to 62%). This demonstrates that selecting a model based on its maximum single realisation performance alone may be misleading.     

基于SWMM模型的截流倍数环境效应分析

由于对改造建设的重视程度、时序安排、经济条件、改造难度等许多主观和客观因素的限制,许多城市老城区的合流制排水系统保留至今。采用SWMM水力水质模型,对城市合流区的污染物削减情况进行模拟评价,以期为合流制排水系统的截流倍数取值及建设方向提供参考。结果表明,当截流倍数n≥2时,合流制排水系统即可达到分流制排水系统的污染物截流效果;但只有当截流倍数n≥5时,合流制排水系统才能达到分流制排水系统的污染物削减效果。城市合流区需尽快进行合改分建设,或加大末端处理设施的建设。     

自贡市截污管道工程设计

自贡市城市污水处理工程是国债支持的四川省城建环保工程重大项目，通过对其中最重要的子项工程——截污干管工程设计、建设经验的总结，介绍了管道结构形式的选型与城市景观的协调、截污干管穿越障碍物与因地制宜的设计、对附属构筑物采用的特殊处理形式等方面的经验，其对丘陵河谷城市的截污管道设计、建设具有很强的参考价值。     

合流制排水管道沉积物及其模型研究进展

在合流制排水系统中,管道沉积物不但影响系统的正常运行,而且在雨天时随着溢流排放被冲刷释放,造成雨天出流污染负荷的增加,成为水体面源污染的重要组成部分。因此,开展排水管道沉积物的研究不仅有利于改善排水系统的运行状况,也有利于水体污染的控制。介绍了排水管道沉积物的来源、构成、性质以及国外管道沉积物的模型研究进展,并总结了其中的不足,以期为我国开展此方面的研究提供参考依据、基础以及研究方向。     

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.     

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.     

污水管网的优化设计

对于污水管网的优化设计,采用了图论中树形结构的理论来描述污水管网,提出用三叉树的形式来处理污水管网的网络结构,把管段当作树的节点作为研究对象;利用树的遍历中的后序法(即节点递归算法)进行水力计算,在优化计算时采取了枚举标准管径法来选取管径,可以提高运算速度;在优化程序中寻求造价最低、最优的同时考虑了管道费用和泵站费用.采用Delphi语言编制了污水管网优化程序,并且用天津某一小区的污水管网对此程序进行了实例考核.其优化设计思路可推广到雨水管道.     

塑料排水检查井在住宅小区的应用前景

分析了传统排水检查井的缺点,介绍了塑料排水检查井的构造和特点(具有水力条件好、施工安装简便、占地面积小、节能、成本低等),探讨了其应用前景,并对塑料排水检查井在中国的推广提出了相关建议.     

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.     

排水管道检测技术的发展现状

对地下管道进行经常性的检测是避免其发生事故的有效措施,为此详细介绍了管道检测技术的现状、发展趋势及相关技术在国内的应用情况,并对我国排水管道检测的管理提出了改进建议.     

Optimal planning of decentralised storage tanks to reduce combined sewer overflow spills using particle swarm optimisation

The present study suggests an optimised method for planning multiple decentralised storage tanks which are designed to reduce combined sewer overflow (CSO) spills. Particle swarm optimisation (PSO) was applied for the optimal planning of the storage tanks in terms of location distribution and sizing. The framework for the storage optimal planning suggested in this study includes developing a simplified mathematical model that is, along with the PSO algorithm, for optimisation. In order to reduce the computational burden of PSO’s inherent iterative solution-searching process a simplified mathematical model was developed to simulate the complex hydraulic flows of a sewer network. Then, the optimisation model with the PSO algorithm was connected interactively with the mathematical model. A case study network was simulated to analyse its application in the planning of distributed CSO storage tanks, and the best available scenarios were suggested.     

Biofilm in the sediment phase of a sanitary gravity sewer

Microbial activity of the sediment phase in a 1.5-km-long concrete sewer section with a cement pipe in a 540-mm diameter was investigated in this paper. SEM examinations and elementary composition analyses of the sediment samples have identified the presence of a biofilm layer at the sediment surface. Bacterial counting results with a DNA-staining technique have revealed that the amount of bacteria in this layer was 2.1 x 10(11)cellg(-1) dry wt, which is close to that of activated sludge. ATP content in the sewer biofilm was found relatively high, demonstrating that the sewer biofilm is active. Throughout the entire 1.5-km sewer section, the biofilm activity was maintained at almost the same level. Lab-scale sediment oxygen uptake flux (SOUF) tests showed that the shear flow velocity above the sediment phase linearly increases the SOUF, which of the potential value was determined to be 32gO(2)m(-2) day(-1) at an estimated shear flow velocity of 0.055ms(-1) at 25 degrees C in the sewer line, provided that the mean flow velocity was 1.5ms(-1), and the mean water depth was 220mm. Such a high SOUF value further endorsed the existence of the active sewer biofilm.     

软土地基污水管道顶管设计

结合连云港市一工程的实际情况,对软土地基污水管道顶管工程作了初步分析。介绍了工程概况,具体叙述了管道设计中顶力计算的内容,还介绍了管道施工方式的确定、顶管管材选用及顶管操作坑的构筑方式等。