Modelling Real-Time Control Options on Virtual Sewer Systems

Article excerpt

Abstract: The study presents a benchmarking methodology to assess the performance of sewer systems and to evaluate the performance of real-time control (RTC) strategies by model simulation. The methodology is presented as a general stepwise approach. Two virtual sewer systems were modelled under four climate conditions. Catchment A represents a small system with medium RTC potential, while catchment B represents a large system with large potential according to PASST guidelines. The rain data represented Oceanic, Continental, Alpine and Mediterranean situations. Annual precipitation data was used. Tests included operation without RTC, and with two classic RTC strategies, aiming at, respectively, equal filling of storage tanks ("average filling"), and aiming at avoiding spilling just upstream of the treatment plant ("WWTP load"). The results have shown that similar RTC strategies perform differently under various climatic conditions and in sewer systems. The presented benchmarking methodology can be used to test the impacts of various climate scenarios on sewer systems that suffer from the limitations of static design.

Key words: real-time control, RTC in sewer, mathematical modelling, simulation, virtual sewer catchment.

Resume : Cette etude propose une methodologie de reference pour evaluer le rendement des systemes d'egout et des strate gies de controle en temps reel par simulation modelisee. La methodologie est presentee sous forme d'une approche generale progressive. Deux systemes d'egouts virtuels ont ete modelises pour quatre conditions climatiques. Le captage A represente un petit systeme presentant un potentiel moyen de controle en temps reel, alors que le captage B represente un grand systeme presentant un grand potentiel selon les lignes directrices PASST. Les donnees de precipitations representent des environnements oceaniques, continentaux, alpins et mediterraneens. Les donnees de precipitations annuelles ont ete utilise es. Les essais comprenaient le fonctionnement sans controle en temps reel et avec deux strategies classiques de controle en temps reel, visant respectivement le remplissage egal des reservoirs de stockage (<< remplissage moyen >>) et a eviter le deversement tout juste en amont de l'usine de traitement (<< charge WWTP >>). Les resultats ont montre que des strategies similaires de controle en temps reel ont des rendements differents selon les conditions climatiques et les systemes d'egouts. La methodologie de reference presentee peut etre utilisee pour analyser les impacts de divers scenarios climatiques sur les systemes d'egouts qui subissent les limitations de la conception statique.

Mots-cles : controle en temps reel, controle en temps reel dans les egouts, modelisation mathematique, simulation, captage virtuel des egouts.

[Traduit par la Redaction]

Introduction

The objectives of this work are the development and application of a stepwise methodology for evaluation of realtime control (RTC) alternatives for virtual sewer systems, in this study under varying climatic conditions. The presented simulations examine the potential of RTC to maintain or improve the performance of sewer systems designed according to "static" design rules on the basis of a design storm, but exposed to atypical loads or climates. It therefore permits to evaluate the adaptability of an RTC-augmented sewer system to deal with changing (climatic) conditions.

The work presented here is part of a larger project, CD4WC (Cost-effective development of urban wastewater systems for Water Framework Directive compliance, CD4WC 2006), and is thoroughly detailed in the project deliverable 6.1: "Real time control in the sewer system" (BIOMATH 2006).

Background

A methodology to optimize the sewer system is the use of RTC. Its operation requires objectives that can be defined by mathematical formulae, and which in the present case (and usually in urban drainage systems) is the reduction of volume and (or) number of combined sewer overflows (CSOs) without (volumetric) extension of the existing system. …