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Models for the optimization of regional wastewater treatment systems
Abstract
The problem of the optimization of regional wastewater systems may be generally formulated as follows: to define the transport and treatment system in a region or water basin, which assure compliance with given pollution control criteria, with minimum cost. In addition, one may try to satisfy other objectives, such as minimum environmental impact, better effluent reuse or adequate phasing. From the optimization point of view, the two main problems that render the solution difficult are the dimensionality and the concavity of cost functions. The matter has been dealt with by many authors, who have produced varied techniques to try to solve this problem. This paper begins with a brief review of the work of those authors who have produced models specifically designed to study the problem. Then, solution strategies are discussed concerning three major items: definition of the objective function and constraints, optimization method and practical applicability of the models. The paper concludes with the discussion of topics for future research.
... Waste sludge is a waste product that originated in the wastewater treatment process. Wastewater treatment consists of a series of physical, chemical, and biological processes that have the purpose of eliminating the contaminants present in the water [1,2]. The wastewater treatment process usually has three stages (primary, secondary, and tertiary). ...
... However, the P released (organic P to inorganic P) from the biosolids increased in the soil depending on the application rate of the biosolids. organic matter present in wastewater [1][2][3]. This stage is carried out f a biological nature that have in common the use of microorganisms to nic matter [4]. ...
... In the third oxidation is continued. Phases two and three are called aerobic stability al sludges are called biosolids and can be used as soil improvers and mply with the established regulations [1,3,9]. olids during urban effluent treatment has increased in Mexico, as there number of urban wastewater treatment plants (UWWTPs). ...
Biosolids are waste from wastewater treatment and have a high content of organic matter and nutrients. In this study, not conventional physicochemical and biological properties of biosolids produced during different seasons of the year were evaluated. These properties are not considered in environmental regulations; however, they are of agronomic interest as indicators of quality and functionality in soils. Also, molecular analysis by Fourier-transform infrared (FTIR) was conducted, enzymatic analysis using the APIZYM® system was performed and two indices of functional and microbial diversity were established. The results showed that the biosolids had a high content of total organic carbon, total nitrogen, P, and K. FTIR analyses showed that chemical composition of biosolids was similar during all year. The C and N of microbial biomass demonstrated presence of active microorganisms, as well as a uniformity in its richness and abundance of species that could present a positive synergy with soil microorganisms. The enzymatic activities showed that the biosolids contained an enzymatic machinery available to promote the mineralisation of the organic matter of biosolids and could even transcend into the soil. Finally, biological properties can be used as indicators of quality and functionality of biosolids before being used as an organic amendment, especially in agricultural soils.
... Quanto ao objetivo, a função deve incluir custos de transporte, contemplando a inserção de estações elevatórias, quando necessário, e dos condutos. Assim, a solução conterá a localização e capacidade das ETEs, o diâmetro da tubulação em cada trecho, bem como a disposição dos sistemas de transporte e a localização das elevatórias quando necessárias (CUNHA et al., 2009;MELO;CÂMARA, 1994;ZE-FERINO, 2011). Assim, a junção desses dois aspectos constitui uma lacuna científica nesta área de pesquisa. ...
... Quanto ao objetivo, a função deve incluir custos de transporte, contemplando a inserção de estações elevatórias, quando necessário, e dos condutos. Assim, a solução conterá a localização e capacidade das ETEs, o diâmetro da tubulação em cada trecho, bem como a disposição dos sistemas de transporte e a localização das elevatórias quando necessárias (CUNHA et al., 2009;MELO;CÂMARA, 1994;ZE-FERINO, 2011). Assim, a junção desses dois aspectos constitui uma lacuna científica nesta área de pesquisa. ...
No Brasil, os níveis de cobertura dos serviços de tratamento de esgotos ainda são considerados baixos. Os custos de implantação, operação e manutenção de sistemas de tratamento de esgotos são, em geral, elevados e variam consideravelmente conforme o tipo de tecnologia a ser implementada. Assim, modelos matemáticos capazes de auxiliar o processo de alocação da carga orgânica e o consequente processo de seleção dessas tecnologias são de grande valia para a gestão adequada dos recursos hídricos. Diante da relevância do assunto, este artigo tem como objetivo realizar uma revisão sistemática das principais publicações relacionadas ao Problema de Alocação de Efluentes Sanitários (PAES). O intuito é analisar publicações recentes e identificar abordagens de solução, cenários de aplicação, características incorporadas aos modelos de otimização e lacunas científicas existentes. Palavras-chave: Problema de alocação de efluentes sanitários. Modelo de qualidade de água. Tratamento de esgoto. Sistemas de águas residuárias. Otimização.
... The 1970s brought a more mature use of such DSSs due to the application of more dynamic concepts regarding the wastewater treatment, which includes transport systems and the integration of different treatment levels (Converse, 1972;de Melo and Camara, 1994). Although this decade was important for the development of mathematical model-based DSSs, a certain difficulty in their application to real cases is reported (de Melo and Camara, 1994). ...
... The 1970s brought a more mature use of such DSSs due to the application of more dynamic concepts regarding the wastewater treatment, which includes transport systems and the integration of different treatment levels (Converse, 1972;de Melo and Camara, 1994). Although this decade was important for the development of mathematical model-based DSSs, a certain difficulty in their application to real cases is reported (de Melo and Camara, 1994). The use of cost functions within the models is also reported (Hahn et al., 1973;Wanielista and Bauer, 1972) with the aim to integrate operational quality and cost optimization to more complex algorithms, e.g. ...
The use of decision support systems (DSS) allows integrating all the issues related with sustainable development in view of providing a useful support to solve multi-scenario problems. In this work an extensive review on the DSSs applied to wastewater treatment plants (WWTPs) is presented. The main aim of the work is to provide an updated compendium on DSSs in view of supporting researchers and engineers on the selection of the most suitable method to address their management/operation/design problems. Results showed that DSSs were mostly used as a comprehensive tool that is capable of integrating several data and a multi-criteria perspective in order to provide more reliable results. Only one energy-focused DSS was found in literature, while DSSs based on quality and operational issues are very often applied to site-specific conditions. Finally, it would be important to encourage the development of more user-friendly DSSs to increase general interest and usability.
... Many modelling approaches are also applied to different types of fluids such as gas, hydrogen or oil (Marcoulaki et al. 2012, Baufumé et al. 2013. Commonly, network layouts are generated with aid of shortest-path algorithms, topographic details and the existing road network because of the correlation between De Melo and Câmara (1994) exemplary list in addition to achieving minimum economic costs the following criteria: ...
... Heuristic optimisation approaches such as simulated annealing, evolutionary algorithms and hierarchical clustering are consequently often used to determine approximate solutions. Heuristic approaches using detailed cost or geographic information as their input have long been suggested as the way forward in sanitation planning, because the theoretical optimum is usually not of primary interest and finding approximate solutions is already a big step forward (inter alia de Melo andCâmara 1994, Eggimann et al. 2015). ...
Efficient infrastructure planning is essential to achieve a more sustainable future. This includes aiming for optimal and economically more efficient infrastructures in the field of urban water management (UWM). Especially network-based infrastructures need special attention as they are generally very cost intensive and have distinctly demanding planning characteristics. Today’s historically evolved UWM practices tend to be network-based as in the last century enormous investments have been made to build-up vast sewer networks and large central wastewater treatment plants which centrally connect very high population percentages in many countries. The construction of large network infrastructures has resulted in a dominant centralised planning paradigm and heavily centralised wastewater management systems (WMS). However, this strong central planning paradigm is increasingly being questioned with respect to sustainability challenges and the call is becoming louder for innovative and radical approaches to address future challenges in the field of UWM. One such innovative approach is the decentralised treatment of wastewater by decentralised WMS, although in countries with high central connection rates this has so far been seen mainly as a stopgap solution. Today, connection rates differ significantly across countries: Great differences exist not only between high-income and low-income countries but also within OECD countries. It is unclear to what degree centralised or decentralised WMS should be installed in a region from the point of view of economic efficiency. Whereas the UWM literature presents specific cost assessments, there is a paucity of tools and methods to assess the costs of WMS consisting of centralised and decentralised systems (hybrid WMS). There are also few cost assessments of decentralised WMS with respect to their operation and maintenance costs. This dissertation uses an economic geospatial model-based approach to address the challenging research question of the optimal degree of centralisation. Conceptually, especially the spatially explicit full-cost modelling and the socio-technical conceptualisation of WMS are of special relevance. The basic trade-off between wastewater transportation and treatment is modelled in a geographically explicit way, economies of density for decentralised systems are assessed and a framework is presented to assess different optimal connection rates for hybrid systems. This framework is then used to assess economically sustainable connection rates in order to promote the economic argumentation for a possible sustainability transition in UWM.
This dissertation demonstrates that the use of models is a promising way to address the question of the optimal number, geographical placement and dimensioning of infrastructures, and that space has a significant influence on the costs of centralised, decentralised and hybrid WMS. Another major finding is the importance of the co-evolution of institutional, organisational and technological innovation in the field of UWM. This thesis also indicates ‘threshold-effects’, i.e. when transitioning towards lower connection rates, cost differences between the central and decentral systems within a region may become negligible from certain connection rates onwards, which could potentially lead to an increase in the transition dynamics towards new system configurations. On the basis of the findings of this thesis, the introduction of more explicitly spatial price differentiation to facilitate the installation of decentralised WMS is recommended: central networks should be regulated to ensure that they only connect households as long as the average central costs of all households connected to a network decrease. The results suggest that regulations such as the mandatory connection rule should be reconsidered in countries such as Switzerland. Finally, even though the focus of this thesis is on wastewater infrastructures, the argument is made that the research challenge of determining the optimal degree of centralisation is generic and applies to many different infrastructure sectors.
... 8,9 The water quality should meet standard requirements before leaving the wastewater treatment plant. 10,11 reviewed the problems that developed for planning regional wastewater systems. The problem aspects are divided into three objectives: (1) distribution, (2) emission, and (3) water quality. ...
This study proposes a novel optimization model for planning strategy for regional wastewater systems in conditions of water quality. The model seeks to minimize the total costs of installing, maintaining, and operating wastewater treatment plant (WWTP) locations and the operation of sewer layout. The constraints are (1) continuity constraint, (2) connectivity constraint, (3) WWTP capacity constraint, and (4) water quality constraints. The model is created by applying a 0–1 integer nonlinear programming (INLP) issue created in the general algebra modeling system. The model is applied to simple examples for validation and accuracy, and the results are discussed.
... Relevant studies have been made in the past with [1] offering a detailed review of them. The different approaches include the minimization of the environmental impact and the maximization of system reliability and flexibility under uncertainty conditions. ...
Wastewater treatment (WWT) is a very important issue affecting both the environment and public health in the twenty-first century. The increasing earth’s population together with the growing urbanism leads to the need of redesigning effective WWT. In this paper, the problem of optimal Waste Water Treatment Network
Design (WWTND) is addressed. To this end, various parameters affecting the problem have been taken into consideration, such as the distance between the residential
areas and the treatment plants, estimations for the future population of towns, and costs
of expanding the existing network or building a new one. The last parameter of cost
has a lot of components (pipeline cost, treatment plant cost, etc.), all of which are
non-linear functions depending on the amount of wastewater produced and treated
within the network. The authors have developed a mathematical model for the solution of the WWTND problem and have applied piecewise linearization in order to deal
with the non-linear terms. The developed model has been implemented in an area
in Luxemburg, for which data were collected. The results prove the model’s validity
and usefulness, while its solution is computationally afordable.
... The use of this method in decision making includes optimizing the allocation of water resources [1], [2], [3]. This model is also used to optimize wastewater management [4], [5], [6], [7], [8], [9]. Meanwhile, optimization for more specific purposes can also use linear programming models [10], [11], [12], [13]. ...
Linear programming is one of the operation research techniques to optimize certain cases. In terms of the environment, one application of programming is the case of the disposal of industrial waste into the rivers. This programming is a tool for making waste disposal decisions by considering the interests of many parties. In this linear programming, industrial interests become "objective functions", namely "Minimize the amount of reduced pollution load" with 28 equations as constraints including ten constraints related to stream standards, nine constraints related to effluent standards, and nine constraints related to the efficiency of wastewater treatment plants. The results of linear programming modeling show optimal conditions, i.e. the level of wastewater treatment that must be done by each industry before being discharged into the river so that the river is not polluted.
... linear programming (Deininger 1965;Loucks et al. 1967); dynamic programming (Converse 1972;Klemetson & Grenney 1985); non-linear programming (Graves et al. 1972); convex programming (Deininger & Su 1973); linear mixed-integer programming (Wanielista & Bauer 1972;Joeres et al. 1974;Brill & Nakamura 1978); and different types of heuristic techniques (McConagha & Converse 1973;Weeter & Belarti 1976;Lauria 1979;Smeers & Tyteca 1982;Câ mara 1985;Melo 1992;Voutchkov & Boulos 1993). Regardless of the potential interest of these models, in practice they have been utilized only to a very small extent. ...
A regional wastewater system planning problem consists of finding the minimum-cost configuration for the system needed to drain the wastewater produced at the communities located within a region, while meeting the quality standards defined for the receiving water bodies and complying with all (other) relevant regulatory aspects. There are several possible solutions to this kind of problem. They range from solutions where each community treats its wastewater separately, to solutions where all the wastewater produced in the region is sent to a single treatment plant. It is likely that the most effective solution both in terms of public expenditure, equipment reliability, and environmental impact will be found somewhere between these two extremes. This paper presents an optimization approach to wastewater systems planning at regional level. The approach applies only to sanitary sewer networks. A simulated annealing algorithm is used to solve the optimization model upon which the approach is based. For the application of this approach a user-friendly computing tool was developed. Within this tool, both the acquisition of data and the output of results are made through a flexible GIS interface.
... The planning of regional wastewater treatment systems is a classic multi-attribute problem. The goals of such problems may generally be formulated as follows (De Melo and Câmara, 1994): ...
For sustainable wastewater management, it is essential to consider social, environmental, geological and
technical features as well as economic feature in the decision-making process. A limitation of many of the
earlier works on wastewater management is that they take into account only financial criteria to make a
decision for a given problem. Moreover, the decision-makers’ (DMs) attitude to risk, or optimism degree,
when faced with uncertainty is not considered. In this paper, we study the application of risk-based
multi-attribute decision-making (RB-MADM) methods to achieve sustainable wastewater management.
Consideration of uncertainty, value tradeoffs, and different risk attitudes of decision makers are the
important features of the developed methodology. A case study on the Iranian city of Niasar is presented
to illustrate how this methodology can be applied to select the most preferred alternative for wastewater
management among a set of options. The most preferred option is selected with respect to nine attributes
under different optimism/pessimism degrees, using six different MADM methods. The results show that
the ranking of options is sensitive to the optimism degree of the DMs. The proposed approach may help
policy makers to achieve sustainable wastewater management.
... Systems models borrowed from operations research have previously been used to study the potential for and the effects of regionalization of water and wastewater utilities. One study reviewed the system models literature on regionalizing wastewater utilities (de Melo & Camara, 1994). The models found by these authors were mainly focused on meeting water quality standards at minimum cost through regionalizing wastewater treatment utilities, while some models attempted to optimize other objectives, including reliability, environmental impacts, and effluent reuse. ...
This paper identifies opportunities to enhance management capacity for small community water systems through cooperative management. Shared management is a non-structural form of regionalization that would not require reluctant water system owners to give up ownership of their systems, thereby eliminating two of the main obstacles to regionalization. This paper provides a background on various aspects of small water systems, performance, and regionalization in North Carolina, before exploring the shared management regionalization alternative. We identify opportunities for cost savings through capturing economies of scale in this unique regionalization alternative by recognizing the tasks and duties of running a water system that would be affected by consolidation of management and operations. Finally, the feasibility of implementing a shared management regionalization effort is explored.
... To address issues related to water reclamation and reuse, a wide range of studies have been carried out in recent years. These issues include financing of water reuse projects (Starkl et al. 2009); reclaimed water pricing (Cuthbert and Hajnosz 1999); risk, performance and environmental impact assessment (Nilsson and Bergstrom 1995;Balkema et al. 2002;Benedetti et al. 2008); water reclamation and reuse infrastructure design and planning (De Melo and Cfimara 1994;Jodicke et al. 2001); choice of treatment system such as on-site, central plant, clustering, and use of natural or constructed wetlands (Orona et al. 1999;Verhoeven, and Meuleman 1999;Chung et al. 2008); choice of treatment technology in wastewater treatment plants (with aerobic, activated sludge, filtering, and disinfection processes) and optimal control of treatment operations (Lessard and Beck 1991;Andrews 1994;Alvarez-Vazquez et al. 2008); and water reuse and wastewater treatment locations analysis and capacity planning (Vasiloglou et al. 2008;Almasri and McNeill 2009). ...
Water reclamation and reuse practices are recently receiving growing attention due to increasing water scarcity, concerns about the effect of wastewater discharges on receiving water, and availability of high-performing and cost-effective water reuse technologies. However, incorporation of water reuse schemes into water/wastewater infrastructure systems is a complex decision making process, involving various economical, technological, and environmental criteria. System dynamics (SD) allows modeling of complex systems and provides information about the temporal and feedback behavior of the system. In this sense, a SD model of the existing water/wastewater system in Kalamazoo-Michigan, an urban area in the Great Lakes region, was created with the hypothetical incorporation of water reuse. The model simulates and optimizes the overall water system cost (including water, wastewater and water reuse components), accounting for future scenarios of population, economic growth and climate change. Results indicate significant levels of water reuse after an infrastructure build delay. The model also indicates that a decision to implement water reuse yields remarkably lower water withdrawals and lower water treatment costs even in a location with a relatively abundant water supply like Kalamazoo. This study emphasizes the fact that a true understanding of the practice of water reuse cannot be achieved without taking regional and climatic parameters into account.
... Formerly, traditional optimization methods were often used to solve regional wastewater systems planning problems. Melo & Câ mara (1994) present a wide-ranging survey of the literature in this domain (41 papers are quoted). The methods most commonly used are as follows: ...
A regional wastewater system planning problem consists of finding the minimum-cost configuration for the system needed to drain the wastewater produced at the communities located within a region, while meeting the quality standards defined for the receiving water bodies and complying with all (other) relevant regulatory aspects. There are several possible solutions to this kind of problem. They range from solutions where each community treats its wastewater separately, to solutions where all the wastewater produced in the region is sent to a single treatment plant. It is likely that the most effective solution both in terms of public expenditure, equipment reliability, and environmental impact will be found somewhere between these two extremes. This paper presents an optimization approach to wastewater systems planning at regional level. The approach applies only to sanitary sewer networks. A simulated annealing algorithm is used to solve the optimization model upon which the approach is based. For the application of this approach a user-friendly computing tool was developed. Within this tool, both the acquisition of data and the output of results are made through a flexible GIS interface.
This article briefly presents how to monitor a technological process in a municipal WWTP, in order to better understand the treatment processes. Monitoring the parameters of wastewater in a treatment plant, involves monitoring the quality of wastewater through measuring and control equipment, sampling wastewater as accurately and as many points as possible, the ideal case being after each technological object or treatment step and analysis of wastewater samples as accurately as possible, also the ideal case being compliance with well-defined methodologies. Following the monitoring of wastewater parameters, data and study results are obtained that can be used to evaluate the technological process, make graphs and tables or to optimize technological processes. The research methodology consists in the presentation of the way of monitoring the wastewater parameters with the measuring and control equipment, the presentation of the sampling method and the analysis method, after which the obtained data will be presented graphically and tabularly.
Centralized wastewater treatment has been the favorite wastewater treatment strategy until a few decades ago, in order to exploit each possible scale economy. Nowadays, water stress and resource scarcity, due to population growth and climate change, call for water reuse and resource recovery, and these goals do not often find in centralization the best solution. Today, the reuse of reclaimed water can take place at different levels and represents an option of primary importance; therefore, in some cases, centralized systems may be economically and environmentally unsustainable for this additional purpose, and the search for the optimal infrastructure centralization degree must take into account these goals. This review analyzes studies that investigated the search of the best centralization level of wastewater collection and treatment, focusing on the methodologies applied to take the decision and highlighting strengths and weaknesses of the different approaches and how they have evolved over time. The final goal is to guide planners and decision-makers in choosing and handling the most suitable method to assess the centralization level of wastewater infrastructures, based on the objectives set out. The reviewed studies cover a period of twenty years. The differences found along this time span show an ongoing paradigm shift towards hybrid systems, which combine centralized and decentralized wastewater treatments that promote the storage of treated water and various forms of local water reuse and resource recovery. The protection of human health and the environment (which primarily promotes water reuse and resource recovery) has become the main challenge of wastewater treatment systems, that will presumably improve further their economic, social and environmental sustainability to achieve urban development in the context of the water-energy-food security nexus.
Microalgae have been theoretically described as a sustainable feedstock for biofuel production. However, there are still some concerns and obstacles that need to be overcome in order to translate the theoretical promise into commercial and economic success. These obstacles include a high requirement for nutrients and sustainable water source and the identification of affordable cultivation conditions. It has been suggested that growing microalgae in wastewater can potentially offset some of these obstacles. Microalgae can perform a dual role for remediation of nutrient pollutants and biomass production when grown in wastewater. However, there are huge challenges to overcome before this route can be exploited in an economically and environmentally sustainable manner. In the present chapter, the potentials and challenges of growing microalgae in wastewater and its future implications are discussed in detail.
Die Sicherung der großen Werte der Einrichtungen der Abwasserwirtschaft und deren Anpassung an die sich ändernden Randbedingungen erfordern ein geordnetes Vorgehen. Ein Masterplan ist hierfür ein wirksames Instrument.
Wastewater systems are of crucial importance to the promotion of sustainable development. Through an integrated planning approach, the costs can be minimized and the resulting benefits maximized. A planning approach at regional level exploits the economies of scale, while achieving a better environmental performance. In this paper we set out a decision support approach for the planning of regional wastewater systems. Optimization models are used, aimed at finding optimal configurations for the location, type and size of the system's infrastructure: sewers, pump stations, and wastewater treatment plants. Solutions are evaluated in terms of the cost of installing, operating and maintaining the infrastructure, and the water quality in the river that receives the treated wastewater. The river water quality varies in accordance with the effluent discharges, and is assessed using environmental parameters. The models are solved with a simulated annealing algorithm complemented by a local improvement procedure. Its application is illustrated through a case study in the Una river basin region, in Brazil.
This thesis deals with durable household electronic appliances collection. Regarding legislative constraints that force disposal of so-called « ultimate » products from july 2002, recycling appears to be an ecologic and economic promising solution. Economic stability of recycling depends among other things on the costs management and the development of secondary markets, in order to add value on materials, spare parts and recycled products. This perspective leads us to consider the management and the planning of collection, the main supplier of reverse logistics and the responsible of a consequent part of system global costs. Once the principal characteristics of the logistics system are identified, the collection at home keeps our attention, and is modelled as a vehicle routing problem : the « pickup and delivery problem with time windows ». This Operational Research problem is then algorithmly resolved, successively considering the single vehicle and the multiple vehicle cases. Main algorithm is based on probabilistic and deterministic tabu searchs, and give excellent results in terms of execution time and quality. Finaly, a way is shown for easily integrating heuristics in a decision support module of collection operational planning, where the human operator has to define the collection plan to be executed. Module integration is modeled using the unified modelling language UML.
Regional wastewater systems are used for the collection and treatment of the wastewater generated in a region and aimed at guaranteeing surface water quality. The volumes of wastewater to process depend on future population and thus are affected by the uncertainty inherent to population dynamics. In this article, we present a robust approach to the planning of regional wastewater systems under population dynamics uncertainty. The approach searches for the optimal configuration of the sewer networks and for the best location, type, and size of the possible pump stations and treatment plants to include in the system. It assumes uncertainty to be described by a given number of discrete scenarios of known probabilities and relies on discrete nonlinear optimization models whose objective is to minimize the expected regret of solutions with respect to total costs. As demonstrated through a case study developed for the North Baixo Mondego area in central Portugal, the results obtained through the proposed approach provide clear insights into the wastewater system planning decisions to make and do not require excessive computational effort.
Regional wastewater systems are aimed at guaranteeing surface water quality by properly collecting and treating the wastewater generated in the population centers of a region. But the most suitable planning regions are often divided by political or social boundaries and may include upstream-downstream surface water quality conflicts. A cross-border planning approach allows for the coordination of pollution control and can embrace both economic and environmental considerations. In this paper, a methodology for wastewater system planning across borders is presented. An optimization model is used to identify reference solutions for negotiation between parties, regarding the layout of the infrastructure to be included in the system. The model takes into account costs and water quality in the receiving water body, and is therefore able to meet surface water quality standards in the shared waterway. A heuristic method is used to solve the model, based on a simulated annealing algorithm enhanced with a local improvement procedure. A region designed to replicate a real-world problem containing two countries is used as a case study. The transboundary wastewater system planning approach is compared with the consideration of separate systems for each country. The features of the transboundary solutions are discussed, with particular focus on the basis of the asymmetries in willingness to pay and different cost allocations.
This volume presents a selection of the main contributions made to the international conference on Integrated Water Resources Management (IWRM) entitled ‘Management of Water in a Changing World: Lessons Learnt and Innovative Perspectives’ that was held from 12 to 13 October 2011 in Dresden, Germany. The book summarise the main messages issuing from the conference and contains selected papers which were presented during the conference, either as keynote lectures in plenary sessions or as submitted papers in one of the thematic sessions. The key themes of the book are:
The book provides an overview on important issues concerning the conceptual framework of integrated water resources management (IWRM). All presentations and abstracts and the corresponding PowerPoint presentations as well as a video recording of the panel discussion are available at the conference website ; Readers are encouraged to complete their review of the conference and its messages by consulting this interesting on-line source of accompanying scientific material.
ISBN: 9781780405278 (eBook)
ISBN: 9781780405261 (Print)
The wastewater generated in urban areas is one of the main sources of water pollution, particularly in regions characterized with large population density and high urbanization degree. In this paper, we present an optimization model for regional wastewater systems planning. The model is aimed at helping to determine the best possible configuration (layout of sewer networks, location of treatment plants, etc.) for the wastewater system of a region taking economic, environmental, and technical criteria explicitly into account. It can be used separately, or as a building block of a broad decision-support tool designed to cover all (or most of) the issues involved in the implementation of an Integrated Water Resources Management approach. The model is solved through a simulated annealing algorithm. The type of results that can be obtained through the application of the model is illustrated for three case studies.
A decision support system for the water-quality management of the Tejo estuary, named Hypeitejo, is presented. Hypertejo is based on a chain of data bases, dispersion, nonpoint pollution, and regional water-quality management models. Due to large running times of some of the models, making their interactive use impossible, Hypertejo was designed as a synthesis of the interconnected data bases and models. This synthesis was achieved by applying descriptive statistics and transfer function concepts. The system, implemented using HyperCard, provides answers to questions posed by three levels of users: member of the government, mayor, and technical manager. Hypertejo implementation for a pilot zone in the estuary is used to illustrate the potential applications of similar systems in waterquality management studies.
Introduction
Optimization of Wastewater Systems
References
In the present discussion of sustainability centralised water infrastructures are exposed to new challenges, which may cause a conceptual alteration in urban water management. If technologies for closing urban water and nutrient cycles are to at least partially replace existing systems, then intensive reconstruction work becomes essential. The paper presents the development and implementation of a mathematical approach to minimise environmental impact and economic costs on the way to more source-controlled future states in urban water management. To find an optimal transformation strategy, a simultaneous project scheduling and network flow problem was defined as a bi-criteria mixed-integer program. An optimal solution is found by minimising two objective functions concurrently - the economic costs and 'ecologic costs' for the period of consideration. This paper discusses the influence of the weighting of these two costs on optimal transformation strategies for a real catchment in Germany. The results show that the approach can very well support decision makers when showing all impacts of transformation processes in detail. All in all, the developed model can be seen as a first step in strategy-finding for transformations in existing urban water systems.
This paper presents integer programming models for the determination of (a) optimal sequences of wastewater treatment processes, and (b) minimum cost, energy efficient composite wall and roof structures. The first model has been used to determine optimal sequences of wastewater treatment processes for a combined industrial and sanitary wastewater facility in Kuwait. The second model was used to assist design engineers in meeting government standards for the thermal resistance of building structures. Remarkably, the two models have essentially the same structure: a shortest path model with additional linear side constraints. The two practical applications are described and solved, and computational experience is discussed.
Operational Research has been usefully applied to a wide variety of environmental problem areas including water resources management, water quality management, solid wastes operation and design, cost allocation for environmental facilities, and air quality management. Despite almost four decades of such activity, challenging operational research problems remain in all of these areas. The problems include the design of rationing strategies in a system of parallel reservoirs, hydropower production planning from parallel reservoirs, simultaneous siting and efficiency determination of wastewater treatment plants, design of the sequence of facilities in a solid wastes collection/disposal system, the achievement of equity as well as rationality in cost allocation, the planning of cost allocations when demands change in time, and the siting of air quality monitoring stations.
Economic growth is frequently considered to be in conflict with sustainable development and environmental quality. Therefore, a decision maker needs to know how to deal with the environmental issues that come around. This article aims to inform Operational Researchers of the possibilities of incorporating environmental issues when analyzing industrial supply chains and to inform environmental scientists more generally of the value of using OR models and techniques in environmental research.
La logistique inverse des déchets techniques encombrants de type blanc ou brun se développe de nos jours afin de répondre aux contraintes législatives fortes qui n’autorisent à partir de juillet 2002 que la mise en décharge des déchets dits « ultimes ». Le recyclage noble apparaît comme une solution prometteuse, économiquement viable et écologique, où la collecte, approvisionneuse exclusive du processus de récupération des déchets, doit être appréhendée et planifiée dans l’objectif de maîtrise des coûts. Après avoir identifié les caractéristiques principales des systèmes de collecte existants, nous nous attardons sur le ramassage à domicile des produits usagés de la population. Afin de pouvoir établir une planification opérationnelle, ce mode de collecte est modélisé comme un problème de routage de véhicules : le problème de chargement et de déchargement avec contraintes de fenêtres temporelles, de précédence et de capacité. Ce problème d’Optimisation Combinatoire est ensuite résolu de manière algorithmique, en considérant successivement le cas d’un véhicule, puis de plusieurs véhicules. La résolution du problème se base sur la recherche tabou et la recherche tabou probabiliste, et fournit des résultats très satisfaisants sur le plan qualitatif et en temps d’exécution. Finalement, nous décrivons, grâce au langage de modélisation unifié orienté objet UML, une manière d’intégrer nos résultats algorithmiques dans un module d’aide à la décision pour la planification opérationnelle de la collecte, où l’opérateur humain est chargé de définir le plan de collecte à exécuter.
Pollen data from China for 6000 and 18,000 14C yr bp were compiled and used to reconstruct palaeovegetation patterns, using complete taxon lists where possible and a biomization procedure that entailed the assignment of 645 pollen taxa to plant functional types. A set of 658 modern pollen samples spanning all biomes and regions provided a comprehensive test for this procedure and showed convincing agreement between reconstructed biomes and present natural vegetation types, both geographically and in terms of the elevation gradients in mountain regions of north-eastern and south-western China.
The 6000 14C yr bp map confirms earlier studies in showing that the forest biomes in eastern China were systematically shifted northwards and extended westwards during the mid-Holocene. Tropical rain forest occurred on mainland China at sites characterized today by either tropical seasonal or broadleaved evergreen/warm mixed forest. Broadleaved evergreen/warm mixed forest occurred further north than today, and at higher elevation sites within the modern latitudinal range of this biome. The northern limit of temperate deciduous forest was shifted c. 800 km north relative to today.
The 18,000 14C yr bp map shows that steppe and even desert vegetation extended to the modern coast of eastern China at the last glacial maximum, replacing today’s temperate deciduous forest. Tropical forests were excluded from China and broadleaved evergreen/warm mixed forest had retreated to tropical latitudes, while taiga extended southwards to c. 43°N.
Numerous mathematical approaches have been taken toward solution of the regional wastewater treatment plant optimization problem. It is questioned whether seeking an optimum solution to this problem is justified, given cost uncertainties, environmental impact questions, and other considerations. The programming techniques involve a considerable amount of mathematical sophistication. Modification of these programs by planning agencies for some alteration to the system would be extremely difficult, if not impossible. Secondly, most of the techniques require long computational times, resulting in added coasts and inefficient use of the computer. Finally, the programs have various flaws when trying to apply their technique to an actual situation.
An economic optimization model for selecting least-cost regional wastewater treatment facility locations, interceptor routes, and capacity expansion schedules is developed. The model explicitly considers the interaction between facility location and capacity expansion decisions on total system cost. Cost functions for treatment facilities and interceptors and growth patterns for future wastewater flows may be of any form. The model is solved with a three-phase heuristic procedure that makes strong use of dynamic programming. In comparison with a mixed integer programming model on a large-scale problem the procedure demonstrates significant advantages in computational time, accuracy, and user requirements. The model is applied to facilities planning in a 208 study area of Massachusetts to demonstrate how the economic impacts of alternative management objectives and demographic projections can be assessed.
Economic safety factors have been developed to provide a hedge against errors inherent in using population forecasts. Optimal treatment plant expansions were calculated by minimizing the expected value of long-term investment costs. Factors considered were growth rate, forecast uncertainty interest rate, inflation, and learning-curve effect, and construction cost economy-of-scale. When a linear growth rate is anticipated, the interest rate and the economy of scale factor M determine the design period, the growth rate does not. However, when the growth rate is uncertain, it is possible to hedge against the possible cost of selecting the wrong period of design by reducing the design capacity 5 to 10%. Exponential growth always yields a shorter design life than the linear growth pattern. Therefore, even when a linear growth in demand is not expected, it may be helpful to use the linear growth expansion criterion to establish an upper bound on the design capacity.
Several models are reported in the technical literature for deciding the optimal capacity of water systems. Many require use of numerical techniques and the computer for solution. Simple approximating equations are presented for calculating the optimal design periods of two models particularly relevant to sanitary engineering; one pertains to capacity expansions and the other to initial construction where facilities have not yet been built. The principal contribution of this paper is a model for determining the optimal waiting period prior to constructing new systems; an approximating equation is presented for the optimality conditions to avoid use of numerical methods. Model assumptions are appropriate for both economically advanced and developing countries. The penalty cost of not satisfying demands is shown to be a key model parameter; a method is presented for inputting its value. Numerical examples are included.
Waste load allocation for rivers has been a topic of growing interest. Dynamic programming based algorithms are particularly attractive in this context and are widely reported in the literature. Codes developed for dynamic programming are however complex, require substantial computer resources and importantly do not allow interactions of the user. Further, there is always resistance to utilizing mathematical programming based algorithms for practical applications. There has been therefore always a gap between theory and practice in systems analysis in water quality management. This paper presents various heuristic algorithms to bridge this gap with supporting comparisons with dynamic programming based algorithms. These heuristics make a good use of the insight gained in the system's behaviour through experience, a process akin to the one adopted by field personnel and therefore can readily be understood by a user familiar with the system. Also they allow user preferences in decision making via on-line interaction. Experience has shown that these heuristics are indeed well founded and compare very favourably with the sophisticated dynamic programming algorithms. Two examples have been included which demonstrate such a success of the heuristic algorithms.
The tendency today is toward regionalization in water supply and waste water disposal. When developing new methods for the planning of regional water and waste water systems, it is absolutely necessary to consider the aspects of updating and renewing existing individual plants for the purpose of forming regional systems. In this paper, a new method is described for determining the optimal solution in the planning of regional waste water management systems. In order to demonstrate the necessary steps of this new method, a problem with three municipalities is discussed. To solve the problem, the following information is considered: quantity and quality of waste water produced at each point; all costs and possible limitations for each individual connection between the various matrix points; and costs for treatment of waste water at each individual point under consideration. The final structure of the overall network is determined with an optimization procedure, whereby optimization in this context means a 'selection of one solution from a group of several alternatives in such a way that a predefined purpose is realized as best as possible.' It is shown that the optimization procedure will give the practicing engineer a method to find the true optimal solution by means of mathematical optimization algorithms and in connection with large scale computation centers. It is understood that the costs of writing and testing such programs are considerable and should be expanded only if the program will be used more than once. The optimization techniques demand of the practicing engineer a knowledge of existing solution algorithms as well as an understanding of the possibilities and limitations of such methods.
Because of the trade off between the cost of collection and the savings obtained from the decreasing unit costs of treatment as the amount treated is increased, there is an optimal extent to community services that involve collection and treatment such as in the case of wastewater. The heuristic algorithm presented yields, in most cases, the optimal collection treatment system for a set of sources located in an arbitrary spatial arrangement; that is, it allows branched collection systems. Convergence is always obtained, but the answer is dependent on the starting conditions. In the systems studied to date, however, the algorithm has always yielded the minimum cost solution when the assumed starting configuration is treatment at each source with no collection.
A heuristic algorithm has been developed for engineers and planners to make cost evaluations during regional wastewater planning in regard to the location, timing, and scale of treatment plants, sewers, and pumping stations. The algorithm is an iterative procedure which consists of both spatial and temporal cost comparisons in the search for optimality in wastewater planning. While spatial comparisons explore the possibility of combining two or more spatially distinct plants, temporal comparisons consider the possibility of combining two or more temporally distinct plants and transport lines. The algorithm yields quickly a sequence of good or perhaps least-cost solutions with modest machine and user requirements.
Waste load allocation for rivers has been a topic of growing interest. Dynamic programming based algorithms are particularly attractive in this context and are widely reported in the literature. Codes developed for dynamic programming are however complex, require substantial computer resources and importantly do not allow interactions of the user. Further, there is always resistance to utilizing mathematical programming based algorithms for practical applications. There has been therefore always a gap between theory and practice in systems analysis in water quality management. This paper presents various heuristic algorithms to bridge this gap with supporting comparisons with dynamic programming based algorithms. These heuristics make a good use of the insight gained in the system's behaviour through experience, a process akin to the one adopted by field personnel and therefore can readily be understood by a user familiar with the system. Also they allow user preferences in decision making via on-line interaction. Experience has shown that these heuristics are indeed well founded and compare very favourably with the sophisticated dynamic programming algorithms. Two examples have been included which demonstrate such a success of the heuristic algorithms.
A new methodology to optimize regionalized wastewater treatment systems is presented. The approach, developed for the River Ave basin, relies upon a clustering analysis algorithm to identify independent sub-sets of polluting sources within the basin. Then for each cluster, heuristic methods are used to generate a network representing the most promising configurations for the regional system, auxiliary models are applied to estimate detailed costs, and a k-shortest path algorithm is used to specify the configurations minimizing cost while achieving a pre-defined efficiency level. To illustrate the proposed method, an application to a sub-section of the basin with seven textile industry units is included.
A water quality evaluation of regional wastewater system centralization was undertaken to test the hypothesis that water quality improvement may result from the spatial and temporal variations in wasteloads attributed to decentralized regional systems. The evaluation employed water quality models developed for both deterministic and stochastic analyses. Each analysis considered a set of experiments which involved a determination of the water quality resulting from alternative degrees of regional wastewater centralization. Water quality was measured in terms of the minimum dissolved oxygen concentrations experienced by alternative systems. It was concluded that decentralized regional wasterwater systems may result in significantly higher stream water qualities than that achieved by highly centralized systems.
Swedish environmental policies have aimed at connecting even small point source discharges to tertiary treatment plants, either by large scale collection and treatment systems or by small scale separate plants. The cost-effectiveness of the strategy for a number of urban areas with less than 1000 inhabitants was evaluated in one municipality (115,000 inhabitants) in the south of Sweden. By combining the total cost regression equations, a relationship was established to show treatment capacities and distances at which local tertiary treatment was economically equivalent to the centralized system for two different cost allocations. Average costs per person for small separate tertiary treatment plants were about the same magnitude as those for connection to the main municipal system at the present level of capacity utilization. A different on-site treatment technique, the wetland filter, which has been experimentally adapted to Swedish conditions, was compared to the existing system. In the wetland filter, pre-sedimented wastewater is applied by surface irrigation to reed sweetgrass, Glyceria maxima, growing in loamy sand. Part of the nutrients is recovered by the harvest of the grass. Besides reaching tertiary requirements for phosphorus and BOD removal, the wetland filter removed more nitrogen than the ordinary treatment plants. Investment costs for wetland filters were estimated to be somewhat lower than those for the existing technology. Operation and maintenance costs would be considerably lower. Further, there are potential revenues from the utilization of the grass for forage or energy purposes by integrating wastewater treatment into a farming system. The principal differences in regarding wastewater constituents as pollutants to be removed or resources to be managed are discussed.
An economic optimization model for selecting least-cost regional wastewater treatment facility locations, interceptor routes, and capacity expansion schedules is developed. The model explicitly considers the interaction between facility location and capacity expansion decisions on total system cost. Cost functions for treatment facilities and interceptors and growth patterns for future wastewater flows may be of any form. The model is solved with a three phase heuristic procedure that makes strong use of dynamic programming. In comparison with a mixed integer programming model on a large scale problem the procedure demonstrates significant advantages in computational time, accuracy, and user requirements. The model is applied to facilities planning in a 208 study area of Massachusetts to demonstrate how the economic impacts of alternative management objective and demographic projections can be assessed.
This work presents an approach to water quality management in areas where a variety of urban and agricultural pollutants are discharged into a body of water. The Utah Lake drainage area is considered in which the urban and agricultural return flows from four districts of the Utah Valley are discharged into the Lake. A model of salinity and biochemical oxygen demand control is used which coordinates the pollution control activities of the urban and agricultural sectors in each district. The model consists of a waste water treatment system and a desalting plant in the urban sector, and a combination of structural and practice improvements in the irrigation system of the agricultural sector. The objective is to minimize the costs of maintaining certain biochemical oxygen demand and salt reduction standards in the districts' aggregate effluents to the Lake under two assumptions: that each district is to maintain the standards independently, and that the salinity-biochemical oxygen demand control efforts of the individual districts are regionally coordinated. The results indicate that savings can be achieved through regional coordination of pollution control efforts.
A model is presented for solving the problem of simultaneously determining the conveyance system, and the number, location, size and treatment degree of a set of plants for treating at minimal cost wastewaters from various origins, while meeting quality standards at various points of the river basin under consideration. -from Authors
In developing an optimization model for regional water quality management, in which certain entities such as stream flows are stochastic, it does not seem logical to assume that the water quality constraints for the stream reach absolute satisfaction. A more logical approach is the chance-constrained programming model presented in this paper, which consists of specifying degrees of satisfaction for the constraints. A zero-order decision rule chance-constrained programming model for regional water quality management yields a deterministic equivalent that is a straightforward programming problem easily solvable by the available algorithm. The model also includes a reliability parameter that provides a tradeoff between a desired water quality and the degree of satisfaction for a given annual operating budget.
Municipal wastewater warrants increased attention as a potential environmental pollution and a possible irrigation water source. A long-run mathematical programming model aimed at regional optimization with regard to plant capacity, treatment level, allocation of the effluent to the participating farms, and cropping patterns at each farm is presented. The model is applied to an agricultural region in Israel which includes a town and several farms. The results indicate the necessity of a subsidy for regional cooperation and provide a regional setup of reusing municipal wastewater for irrigation. The optimal solution enables each farm to reallocate the freshwater quota among the different land sections, to cultivate new land areas, and to expand the irrigated crops by using effluent. The acceptability of the regional optimal solution by the town and the farms is discussed in another paper.
This paper reports on a set of paleoclimate simulations for 21, 16, 14, 11 and 6 ka (thousands of years ago) carried out with the Community Climate Model, Version 1 (CCM1) of the National Center for Atmospheric Research (NCAR). This climate model uses four interactive components that were not available in our previous simulations with the NCAR CCM0 (COHMAP, 1988Science, 241, 1043–1052; Wright et al., 1993Global Climate Since the Last Glocial Maximum, University of Minnesota Press, MN): soil moisture, snow hydrology, sea-ice, and mixed-layer ocean temperature. The new simulations also use new estimates of ice sheet height and size from (Peltier 1994, Science, 265, 195–201), and synchronize the astronomically dated orbital forcing with the ice sheet and atmospheric CO2 levels corrected from radiocarbon years to calendar years. The CCM1 simulations agree with the previous simulations in their most general characteristics. The 21 ka climate is cold and dry, in response to the presence of the ice sheets and lowered CO2 levels. The period 14–6 ka has strengthened northern summer monsoons and warm mid-latitude continental interiors in response to orbital changes. Regional differences between the CCM1 and CCM0 simulations can be traced to the effects of either the new interactive model components or the new boundary conditions. CCM1 simulates climate processes more realistically, but has additional degrees of freedom that can allow the model to ‘drift’ toward less realistic solutions in some instances. The CCM1 simulations are expressed in terms of equilibrium vegetation using BIOME 1, and indicate large shifts in biomes. Northern tundra and forest biomes are displaced southward at glacial maximum and subtropical deserts contract in the mid-Holocene when monsoons strengthen. These vegetation changes could, if simulated interactively, introduce additional climate feedbacks. The total area of vegetated land remains nearly constant through time because the exposure of continental shelves with lowered sea level largely compensates for the land covered by the expanded ice sheets.
The Wastewater Treatment Optimization Model (WTOM) was developed to analyze the wastewater treatment needs of large population centers or a group of small communities. Dynamic programming is used to evaluate the timing and capacity expansion decisions for regionalization and staging of treatment facilities. Among the factors considered were: the quantity and quality of wastewater and its change with respect to time; interest and inflation rates; capital, operation and maintenance costs; treatment efficiency; economy of scale; excess capacity; and service life. The model selects the best alternative treatment system to meet desired water quality objectives at the lowest future discounted costs.
In 1972, Congress mandated that wastewater management plans be completed for each area in the nation. One such area is Nassau County in Long Island, N. Y., where-in compliance with the federal guidelines-a study was undertaken utilizing a mixed integer model to screen wastewater management alternatives. This study resulted in a least-cost wastewater management plan that specified location, expansion, and upgrading for 25 wastewater treatment plants in the region. The model and its validation are discussed and conclusions are presented.
Correlation and regression analyses have been used to investigate the causes of effluent quality variability. In addition, the contribution of several variables to the observed effluent biochemical oxygen demand and suspended solids was analyzed. The effect of time-related trends or cycles, as well as the lag periods between influent and effluent also were examined. Considerations controlling plant performance, which change from plant to plant, accounted for most effluent variations.
An optimization procedure is described that can serve to identify
attractive regionalization plans for large wastewater treatment and
collection systems. Potential expansion of facilities in Western Suffolk
County, Long Island, New York is considered. A mixed integer programming
approach is utilized. Each system element cost, taken as a function of
wastewater flow, is represented by a linear variable cost plus a fixed
cost. The objective is to minimize total cost while ensuring that all
wastewater flow generated is treated. Political and administrative
feasibility and the location of effluent discharge constrain the model.
The Long Island problem is too large to be solved with a standard
formulation of wastewater network as a mixed integer programming
problem. To improve computational efficiency, additional constraints are
introduced on the minimum flow in each pipe and on the number of pipes
leaving each node. Network configurations obtained for Western Suffolk
County show that limiting development plans to 201 regions is not cost
effective. Regional solutions indicate a general trade-off between lower
costs for coastal discharge and increased groundwater recharge.
This paper details an application of mathematical programing to the
problem of optimal water quality control in an estuary. The mathematical
models allow for the possibilities of at-source treatment, regional
treatment plants, and by-pass piping. Actual data from the Delaware
Estuary are used to solve a large-scale problem and the solution is
given. The results indicate that a regional treatment system for the
Delaware Estuary is superior, in terms of total cost, to other proposed
schemes.
Numerous ad hoc methods are used to apportion the costs of a water
resource project among participants and/or purposes. Unfortunately these
procedures do not always work, i.e., they lead to unfair assignment of
costs. Accepted criteria for efficiency/financial analysis used in the
water resources field are expressed in axiomatic form. These criteria
are compared to accepted axioms of fairness from cooperative n-person
game theory. Similarities between the two approaches are identified. The
minimum costs, remaining savings (MCRS) method is proposed as an
improved method of financial analysis. The MCRS method can be viewed as
a generalization of the presently used separable costs, remaining
benefits method.
A nonlinear programing model for water quality management is developed
and applied to the case of the upper Hudson River. The model is
formulated as a geometric programing problem. It is shown that this
formulation permits the simultaneous consideration of waste treatment
processes, bypass piping, flow regulation, and artificial aeration in
determining a least-cost solution to a given water quality management
problem.
An optimization model is generally not a perfect representation of a
complex real world planning problem. Optimization models, however, can
be used to generate alternatives that are good and different so that
analysts and decision makers can examine a wide range of alternatives to
gain insight and understanding. Modeling to generate alternatives (MGA)
techniques have been designed to serve this purpose. This paper provides
a preliminary assessment of the capabilities of the Hop, Skip, Jump
(HSJ) method, a random method, and a branch and bound/screening (BBS)
method for generating good and different alternative solutions. These
three methods are illustrated using an example water resources planning
problem represented by a mixed integer programing model. Each method
yields sets of alternatives that are different from each other, but for
each method the alternatives are different in different ways. Given that
all three methods are efficient, it may be most fruitful to use more
than one method and thereby to consider alternatives that are not only
different, but different in different ways.
Since the mid-1970's, a number of research projects at Cornell
University have focused on the development and application of
interactive models and computer programs for studying water resources
and environmental management problems. These models and programs have
been adapted for use with computer graphics display devices. This
interactive computer-aided planning system has been designed to
facilitate data input, editing, and display; model building and
solution; and analysis and synthesis of alternative resource management
plans or policies. This paper discusses the approaches taken for
managing and displaying data that are needed for, and derived from, this
interactive modeling system. Several applications are presented and some
conclusions on how such systems might be developed or expanded in the
future are proposed.
A simplified method is proposed for analyzing multiperiod design of regional wastewater systems and other systems possessing a similar network flow structure. The primary objective of the method is generation of multiperiod locations and facility expansion timings. The method is based on several simplifying assumptions. The solution procedure involves a branch and bound algorithm specifically developed for integrating a set of solutions obtained using the initial design flow with a set of solutions obtained using the terminal design flow. A method for comparing the generated multiperiod alternatives is also proposed. The usefulness of the method is demonstrated, using as an example a hypothetical regional waste water system. A Fortran program was written to implement the method. The program is not in a form that would permit its transfer, but interested readers may contact the first author.
Interest has increased recently in water recycling and reuse. The possible economic feasibility of reuse and recycling dramatically increases the complexity of designing an optimal water delivery system. In this paper we present a nonlinear model which takes into account both flow requirements and water quality. Because of the model's transshipment formulation the solution technique seems to be effective in aiding the design decisions.
A regional model is developed to consider the trade-off between economies of scale inherent in waste water treatment plants and added pipe network collection costs. The resulting mixed integer programing model relies on piecewise linear approximations of concave cost curves and incorporates capacity limits dictated by maximum tolerable environmental impact at potential treatment plant sites. Cost savings possible for a region consisting of the central portion of Dane County, Wisconsin, are demonstrated.
Optimal wastewater plant capacity expansion is reexamined for the general case where effluent receiving water standards vary with time. A deterministic dynamic programing framework is used to find cost-minimizing expansion plans for wastewater treatment when hydraulic demand is assumed known and nondecreasing with time. The effect of discount rate, initial hydraulic capacity, and initial plant pollutant removal rate on expansion plan is investigated. Results show time-variable effluent receiving standards can significantly influence cost-minimizing expansion plans.
The problem of determining the optimal number, location, and level of treatment for regional domestic sewage treatment plants along an estuary or river is considered. The formulation is one of minimizing the sum of treatment and transport (piping and pumping) costs such that water quality improvement goals for dissolved oxygen are met. Restrictions may also be placed upon the overall level of treatment (required secondary, required uniform, or least cost) if desired. An optimization procedure is developed which utilizes dynamic programing, linear programing, and heuristic location techniques in a series of steps which lead to progressively improved (lower total cost) solutions. The location procedure is intended for use by an engineer-planner during the design stage and requires his participation and skilled judgment during the course of the algorithm. The technique is illustrated for the Delaware estuary for 22 domestic waste sources, nine potential regional sewage treatment plant sites, and 22 industrial waste sources. Results of the case study show considerable savings over previous nonregional treatment schemes.
This paper speculates on the potential impacts of our increasing access to and use of computer technology and communication, especially with respect to planning and policy making. The focus of the discussion is on the interaction between the users of this expanding technology and the technology itself. Those involved in its development, whether it be the hardware or software of this technology, are in a position to make substantial contributions toward a more effective use of the models and their data bases by planners and policy analysts. Specific features of the technology and of environmental planning and policy-making processes are examined to identify where and how interactive computer-based models and associated hardware can best serve individuals, their organizations or institutions. Finally, the necessary conditions for the successful implementation of such tools and methods are identified.
A branch and bound method is presented for evaluating alternative regional wastewater treatment systems, taking into account economies of scale in constructing treatment plants and interceptor sewers. A branch and bound tree is ‘grown’ by using an algorithm which is very efficient computationally because it uses a powerful inspection step and a network algorithm to solve subproblems. Each infeasible solution found by using the method is converted to a feasible regional configuration of plants and interceptors. The alternative plans can be compared to examine tradeoffs between cost and other qualitative and quantitative planning objectives. Also the tree itself can be extended to generate additional planning alternatives. Rather than to find mathematically optimal solutions, the principal uses of the method are to generate systematically attractive alternative plans and potentially to assist in evaluating tradeoffs between different planning objectives.
Optimization models do not perfectly represent the real world. Therefore the mathematically optimal solution is not necessarily the “best” decision to implement. Water resources planning models tend to have many solutions that are nearly optimal in terms of objective function value, but which are significantly different decisions. Methods for generating nearly optimal solutions to linear programming models have been devised. The use of such methods is illustrated with an example problem involving the sizing of reservoirs and hydroelectric power plants and demands for municipal water supply and irrigation. The results show that the interactions among the decision variables and the economics of the system determine the range of choice among nearly optimal decisions. The examination of these interactions yields insight into the basic structure of the decision problem.
This paper presents a state of the art survey of network models and
algorithms that can be used as planning tools in irrigation and
wastewater systems. It is shown that the problem of designing or
extending such systems basically leads to the same type of mathematical
optimization model. The difficulty in solving this model lies mainly in
the properties of the objective function. Trying to minimize
construction and/or operating costs of a system typically results in a
concave cost (objective) function due to economies of scale. A number of
ways to attack such models are discussed and compared, including linear
programing, integer programing, and specially designed exact and
heuristic algorithms. The usefulness of each approach is evaluated in
terms of the validity of the model, the computational complexity of the
algorithm, the properties of the solution, the availability of software,
and the capability for sensitivity analysis.
The efficiency and equity of the separable costs-remaining benefits
(SCRB), alternative justifiable expenditure, and use of facilities
methods of cost allocation are examined. On efficiency grounds, only the
SCRB formula satisfied all three efficiency criteria. From an equity
viewpoint, no one method allocates costs so that each purpose shares
fairly in the savings from multiple-purpose development. The source of
inequity with the SCRB and alternative justifiable expenditure methods
arises because either separable costs or specific costs are subtracted
from justifiable costs on a 1:1 basis. Conceptual problems in defining
capacity preclude the use of facilities method from satisfying the
equity objective. An adjustment in the SCRB method is proposed which
will enable this procedure to satisfy both efficiency and equity
criteria.
The techniques of locations systems analysis are adapted to develop a
siting model for wastewater treatment facilities when the wastewater
sources and treatment facilities are in a chain or linear configuration.
The regional facility problem is considered as a special variant of the
fixed charge plant location model rather than the general transshipment
type model. The definition of the additional cost of a waste source
joining a regional facility and the development of sequential priority
constraints in the siting model allow the siting model to be
conveniently solved by widely available linear programming packages. The
model deals with the situation in which no current treatment is
provided, no bypassed plants are allowed, a fixed level of treatment is
required, and water quality constraints are either not included or are
not binding. The concave cost of treatment at a plant is approximated by
a fixed charge and one straight-line segment. Numerical examples are
included to demonstrate the computational efficiency of the siting
model.
This paper first examines three methods currently used for apportioning
the costs of joint waste water treatment facilities among users. The
methods are cost sharing based on the measure of pollution, cost sharing
based on single plant costs with a rebate proportional to the measure of
pollution, and cost sharing based on the separable costs remaining
benefit method. Through the use of numerical and theoretical arguments
it is demonstrated that often these methods do not provide an
apportionment that satisfies all the people involved and that a
potential participant may find it economically advantageous not to join
the regional plan and may thereby force the adoption of a system that
is, in total, more costly. These difficulties will frequently arise when
any plan is subjected to the pressures of `free market` bargaining. Two
additional methods relying on game-theoretic concepts are then
introduced to deal with the problem. These methods, which are practical,
can satisfactorily solve problems that are not tractable when other
techniques are used. Also, the basically perverse characteristics of
situations requiring cost sharing are demonstrated by using the
bargaining methods to prove that some cost-sharing problems have no
unique solutions and that others have no viable solution at all unless
the regional authority can obtain a subsidy.
A dynamic programming model that minimizes the cost of providing waste treatment to meet specified dissolved oxygen concentration standards in a stream is developed. The model is solved for a simplified example based on data from the Willamette River. Implications of the model on policy formulation are discussed. (Key words: Computers, digital; economics; oxygen; quality of water)
A growing number of studies suggest that vegetation changes can significantly influence regional climate variations. Herein we utilize a climate model (GENESIS) with a land surface vegetation package to evaluate the potential role of the very large vegetation changes that occurred during the last glacial maximum (LGM). In particular, we focus on the potential response to a significant reduction in the area of tropical rainforest. Simulations employed a global vegetation reconstruction for the LGM and Climate/Long-Range Investigation, Mapping and Prediction (CLIMAP) sea surface temperature (SST) estimates. Results indicate that expansion of dryland vegetation causes a 15-30% additional LGM cooling for Australia (0.4øC) and Africa (0.9øC), respectively. Turnover from conifer to tundra also causes cooling of 2ø-4øC or more in western Europe and Siberia. However, for the largest rainforest area (Amazon Basin), inclusion of realistic vegetation increased modeled temperatures 2ø-4øC and decreased precipitation by 10-35%. These latter results are similar to those obtained with sensitivity experiments of the effects of future Amazon deforestation. Initial assessment of the potential effect of decreased stomatal resistance due to lower ice age CO2 levels indicates little significant response to this effect. Comparison of model-predicted low-elevation LGM temperature changes with estimates from proxy data indicate that inclusion of realistic vegetation estimates for the LGM results in slightly more than 50% agreement between models and data for low-elevation sites in low-mid latitudes. Data at variance with model predictions would appear to be explainable by considering additional changes in vegetation, ice age dust, or a 1 ø-2øC cooling below CLIMAP values. This conclusion is at variance with a 3ø-4øC tropical cooling suggested by some studies for explaining estimated land temperature changes during the LGM. In some western European sites model temperatures are colder than proxy data by 2ø-8øC. This model-data discrepancy may be explained by less sea ice in the subpolar North Atlantic than stipulated by CLIMAP, a conclusion consistent with new marine data from that region.
A multiobjective goal programming method is proposed for use in analyzing problems involving a network flow structure which are commonly found in the wastewater and sludge management systems when cost functions are linear. The goals considered are the minimization of: (1) Costs, (2) water quality impact, and (3) land use impact. The model also selects interceptor routes, treatment plants, transport routes and sludge disposal sites, along with flow directions through these facilities under optimal solutions. A hypothetical example problem dealing with regional wastewater management is analyzed to demonstrate the potential usefulness of the method.