Elsevier

Minerals Engineering

Volume 23, Issue 3, February 2010, Pages 157-174
Minerals Engineering

Management of the Web of Water and Web of Materials

https://doi.org/10.1016/j.mineng.2009.08.009Get rights and content

Abstract

The European Water Framework Directive (EWFD) demands a detailed analysis to determine which changes and measures within the surface water system are required, which actors require detailed scrutiny, and which technology has to be developed in order to guarantee that the quality of the surface water is complying with this Directive.

This paper will discuss a holistic model developed for the optimization of the surface water system for a water authority in The Netherlands, which is influenced by (i) waste water streams originating from e.g. households, industry, agricultural and transport activities among others and (ii) the end-of-pipe technology of waste water treatment plants, while interfacing with (iii) thermal treatment and minerals and metallurgical processing for the recovery of specific elements from waste water sludge and other residues created during waste water treatment.

The paper develops a fundamental basis that can feed factual information such as optimal combination of measures (technology and policy) into sustainability frameworks or the implementation of the EWFD. This optimization is affected by quality constraints, costs, energy, environment and interactions between the various materials present in the different streams in the water system. By incorporating these parameters into the model a tool is provided that provides metrics to measure the ‘sustainability’ of the Web of Water (WoW), while linking to and harmonising with the Web of Materials/Metals (WoM).

The WoW optimization model links material cycles from e.g. food, transport, agriculture and industry to the recovery of materials from the water cycle with the pyrometallurgical and thermal processing of minerals/materials, hence quantifying resource conservation and sustainability on the interface between aquatic and product manufacturing systems and the process industries.

Introduction

The European Water Framework Directive (EWFD, 2000) defines targets for the quality of surface and ground water in Europe. At the same time social and political drive for sustainable development puts strong emphasis on the ‘sustainable’ operation of the water system. This includes the environmentally conscious and economically efficient use and/or selection of waste water and sludge treatment processes linked to the energy and metallurgical process industries.

The quality of the surface water and environmental impact of the (waste) water system are determined by the emissions/outflows originating from various sources and the actual inflow of streams into the surface water, their composition as well as end-of-pipe technology of Waste Water Treatment Plants (WWTP) combined with thermal and metallurgical sludge treatment processes (for which the efficiency is determined by separation physics, thermodynamics and the technology itself). All of these can reduce the inflow of substances into the surface water and environment. In order to improve and optimize the quality of the surface water as well as the eco-techno-environmental performance of the surface water system the different (created) flows, substances and technologies have to be considered simultaneously when assessing the surface and waste water system.

Expanding on the authors’ work with regard to the optimization of recycling and metal processing (industrial ecological) systems; this work links the Web of Materials/Metals or WoM (Reuter et al., 2005) to the Web of Water or WoW. This paper will discuss an optimization model for the WoW in order to link all the actors within the surface water system with the objective to analyse the system in its totality. This is an expansion of the usual focus on only one aspect or a selected sub-system of the waste and surface water system.

The optimization and management of waste water treatment networks are discussed by for example Statyukha et al. (2008). Erbe and Schütze (2005) present an integrated modelling concept with the aim to analyse fluxes through the total wastewater system, whereas and Hoppe et al. (2004) links simulation models of sewer, waste water treatment plant and river quality for immission based water quality management. Other research focuses on the modelling and/or optimization of a specific processes or plants (Corsano et al., 2006, Sechi and Sulis, 2009, Johansson et al., 2008, Tiana et al., 2008, Frederico et al., 2007). Detailed WWTP process models are discussed among others by Brdjanovic et al., 2000, Smolders et al., 1994, Hao et al., 2001, van Veldhuizen et al., 1999, Uhlenhut et al., 2001, Uhlenhut et al., 2008).

Environmental assessment of the water system or selected sub-system thereof is discussed by Jeppsson and Hellström, 2007, Icke et al., 1999, Bertrand-Krajewski et al., 2000. The control of water quality (in view of the EWFD) is discussed by e.g. Achleitner et al., 2007, Butler and Schütze, 2005. Correljé et al. (2007) present an overview of policy principles that play a role as basic assumptions in water management. Water resources management is discussed by many authors such as Zhang et al., 2008, Mitchell et al., 2003, Zhao and Chen, 2008, Wilson et al., 1997, Maqsood et al., 2005, Ekinci and Konak, 2009, Sherali and Smith, 1997, Jacovkis et al., 1989, Wan Alwia et al., 2008. These approaches focus on a specific part of the water cycle, being isolated from the total water system, in which a extensive range of actors and processes play a role, which are not addressed in these studies. Fu et al. (2008) discusses a more detailed work on the integrated urban wastewater cycle. Closing of water and material cycles is not possible using this type of modelling, system definition and processing detail. Modelling and optimization of the urban water cycle, as one aspect of the water system, has been described by Hardy et al., 2005, Mitchell et al., 2001, Mitchell et al., 2007, Mitchell and Diaper, 2005, Mitchell and Diaper, 2006.

In contrast to this briefly discussed published work, the proposed holistic system model simultaneously establishes an efficient solution for the technological configuration of processes and streams as well as (policy driven) measures on the reduction of the systems input. This is all done as a function of all substances, their concentrations, in- and output streams and processes present in the system, which is a significant step further in the system modelling of a large-scale water system in The Netherlands. The term WoW defines the interlinked and interdependent Industrial Ecological system of all processes, streams (in- and output and intermediate) and substances (originating from various sources and actors) in the waste and surface water system and links these to the WoM i.e. the metal, material and waste processing systems. This approach considers the treatment of waste water and its recycling back into the surface water, and its link back to the environmental and industrial system. At the same time it brings together industry and household waste water with the end-of-pipe treatment of waste water purification sludges in for example metals production and waste processing industries. This makes the WoW an excellent example of Industrial Ecology as discussed by Reuter et al., 2005, Capra, 1996, Ayres and Ayres, 1996, Graedel and Allenby, 1995. It illustrates the interwoven and interdependent nature of complex industrial systems requiring a ‘systemic’ approach in order to make these as sustainable as possible. Fig. 1 gives a simplified overview of the WoW. This figure not only schematically illustrates the streams and actors playing a role in the sustainability of the water cycle, but reveals at the same times the essential role of minerals and materials processing in view of material cycle closure (through the recovery of e.g. P from waste water treatment sludge (Scheepers et al., 2006)). A similar systemic and holistic as illustrated in Fig. 1 for the WoW has been developed and extensively applied in industry by the authors in the field of material and product recycling (cars, consumers electronics, etc.). The concepts of the WoM (Reuter and van Schaik, 2008b, Reuter et al., 2005) discuss the interconnectedness of material, metal and product systems. This basis has been used to model these combined systems.

A large variety of assessment methods/models and indicators for the optimization or assessment of individual processes or the entire water system have been developed. The environmental assessment of different facets of the water system and water resource management, as well as the development and application of various sustainability indicators is discussed by many authors (Ashley and Hopkinson, 2002, Remy and Jekel, 2008, Sarang et al., 2008 and Weigert and Steinberg, 2002). The sustainability of waste water treatment systems is topic of many papers e.g. by Balkema et al., 2001, Lim and Park, 2009, Malmqvist and Palmquist, 2005, Muga and Mihelcic, 2008, Palme et al., 2005. The development and application of these single models and indicators raise the question, which of these methods or indicator should best be applied to express and improve sustainability. The developed system optimization model for the WoW as presented in this paper, provides a framework to adopt, combine and compare these different indicators for measuring sustainability, hence providing a generic structure to incorporate and apply existing measurements as well as to ensure that future measurements are fundamental enough to calibrate this type of modelling basis.

At the same time technological and detailed models for the modelling, improvement and understanding of waste water treatment processes, and metallurgical and thermal sludge treatment operations exist. The developed system optimization model does not replace these existing models, however provides a framework in which the knowledge (figure/data derived from detailed process models) can be integrated in a simplified manner, for all processes at the same time. This allows optimization of the system as a function of all processes, and more important, allows a sensitivity analysis in which the crucial processes and parameters to be investigated or improved are pinpointed. This approach is different from the general applied scenario analyses, in which a solution is being selected out of a set of a priori fixed options/scenarios (STOWA, 2005-26, 2005).

The simultaneous consideration of all substances in the system is also required in order to be able to account for the chemical and thermodynamic interaction between the different elements present in a particular unit operation as well as end-of-pipe treatment technology. These interactions between substances can significantly influence (in a negative manner) the possibility to take up waste water treatment sludge into the process/unit operation in order to economically recover valuable elements, at the same time creating benign end products, residues, and slags that can be disposed of and or sold economically. The recovery of elements from the waste water treatment sludge by metallurgical and/or thermal processing not only decreases the inflow of substances into the surface water due to bleeding it off into benign products, but also contributes to keeping these materials in the resource cycle and reduces thereby the often energy-intensive production of e.g. metals from primary resources (ores) and the corresponding environmental impact. This implies that true material stewardship should at least embrace product systems (e.g. consumer products, fertilisers, pharmaceuticals, street furniture, landfill, etc.) and their link to the waste water, while considering the relationship to sludge and surface water cycles linked to the energy, minerals, metallurgical and recycling industries, hence supporting the implementation of a Cradle To Cradle approach in (waste) water and related material/energy systems (McDonough and Braungart, 2002).

The approach discussed in this paper being developed as a novel contribution to the waste and surface water system has already been extensively applied in industry by the authors for the modelling of recycling systems of cars in relation to product design and European Union directive on end-of-life vehicles and is being used within a EU 6th framework project ‘SuperLightCar’, carried out in cooperation with the European automotive industry (www.SuperLightCar.com). These recycling models are linked to Computer Aided Design tools of the automotive industry. The results of this work have also been used in a stakeholder discussion on the review of the recycling/recovery targets as imposed by this Directive. In addition a similar approach is being applied to model and optimize the recycling of Waste Electrical and Electronic Equipment (WEEE) and to control the dissemination of hazardous substances into the environment. These various examples illustrating the practical /industrial applicability of such a system model have been described extensively by van Schaik and Reuter and are referred to for further consultation and details (Reuter and van Schaik, 2008a, Reuter and van Schaik, 2008b, Reuter et al., 2006, Reuter et al., 2005, van Schaik and Reuter, 2007, van Schaik et al., 2004, van Schaik et al., 2002).

This paper evolves the above ideas into a description of a specific surface water system in The Netherlands and discusses the application of this approach (van Schaik et al., 2007). It is shown that this approach enables for example establishing a suitable balance between end-of-pipe processing and the technological limitations thereof. The quality constraints for the recovery of valuable materials from waste water treatment sludge (such as P and Zn) and the quantitative contribution of (policy) reductive measures to decrease the emissions/outflows of these materials originating from various sources are qualitatively indicated by Oranjewoud (2006) in view of the EWFD requirements for surface water quality. This paper elaborates on this on a first-principles basis. It will furthermore be shown that the developed approach could on the long term provide an objective and legally defendable basis for the assessment and definition of technological feasible and theoretically defendable EWFD targets. More important it can be a facilitator for levelling the playing field for different existing process and environmental models to determine the required focus within the water treatment industry. The systems approach allows determining the balance between reduction/control of inflows into the surface water originating from industry, farming and waste water treatment with required technology development to reduce the environmental impact of the water system and optimize surface water quality. The insights gained through this model based approach could pinpoint essential changes in product composition (from which materials are bleeding off into the waste/surface water) and/or legislative measures and restrictions to be imposed by governments in order to prevent or reduce environmental pollution from non-removable substances.

Section snippets

Web of Water – WoW optimization model

The (environmental) performance of the WoW, the quality of the surface water and the economic consequences thereof are affected by a large range of actors, streams, waste water and sludge treatment processes as well as measures to reduce the inflow of substances into the surface water. The extent of this system and the variety of parameters/actors affecting this require a fundamental, first-principles framework to incorporate, compare and optimize the system from a technological, environmental,

Case studies for the optimization of the WoW

Various case studies have been performed to demonstrate the applicability and possibilities of the developed WoW optimization model. These case studies are deliberately kept relatively simple in order to illustrate the various options of application and possibilities of the model. The lack of data from the different emission/outflows sources is also a reason for keeping the models simple at the stage. These cases attempt to indicate the possibilities of application of the holistic approach of

Conclusions

An approach to optimize and investigate the waste and surface water system has been developed. A optimization model for the ‘Web of Water’ (‘WoW’) has been developed, which simultaneously establishes an efficient solution for the technological configuration of processes and streams as well as (policy driven) measures on the reduction of the systems input providing a first principle basis for discussing, improving and implementing of the EWFD and measuring and implementing the ‘sustainability’

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