Approaches for the evaluation of future-oriented technologies and concepts in the ﬁ eld of water reuse and desalination Uncorrected

Against the background of drastically rising global water demand and increasing pollution and overexploitation of regional water resources, the demand-driven water supply of households and industry is of central importance. Water reuse and desalination are seen as key technologies to overcome potential regional and local water shortage. In the joint projects funded by the German Federal Ministry of Education and Research (BMBF) ‘ Future-oriented Technologies and Concepts to Increase Water Availability by Water Reuse and Desalination (WavE) ’ , evaluation approaches for analysing innovative technologies and concepts are being developed and assessed. All evaluation methods and criteria used were selected based on the decision situation at hand and the decision-maker´s preferences. Based on the analysis of six multi-criteria evaluation concepts used in selected WavE projects, this paper presents a general approach for comparative multi-criteria evaluation of water reuse systems consisting of prerequisites, minimum requirements, evaluation criteria (qualitative, semi-quantitative or quantitative) and a ﬁ nal aggregation of results. Exemplary sets of criteria for the application in a more industrial, municipal and/or international context are presented as an aid for the application of holistic evaluation approaches for (process) concept and technology selection in the context of water reuse and desalination. (cid:129) Exemplary sets of criteria for the application in a more industrial, municipal and/or international context are presented as an aid for the application of holistic evaluation approaches for concept and technology selection in the context of water reuse and desalination. (cid:129) Finally, possible data sources, challenges in using them and indicators to measure data quality are presented to give guidance on data collection.


INTRODUCTION
The need for targeted and safe water reuse solutions is increasing worldwide. However, the implementation of water reuse solutions is still very limited compared to their potential due to a number of factors, e.g. low economic attractiveness and lack of public acceptance of reuse solutions, low awareness of technological advantages and poor coordination of actors from industry, authorities and the water companies. Decisions on the implementation of innovative technologies and concepts for water reuse and desalination are regularly marked by conflicting goals between economic, technical, environmental and socio-political considerations.
In order to inspire decision-makers to use new technologies and to convince sceptics of the viability of innovative approaches, transparent, sound decision criteria are required.

VALUATION ISSUES IN WAVE
In the joint projects of the funding measure 'Future-oriented Nevertheless, the individual evaluation procedures have some aspects in common, which result from the value system of the decision-makers and/or the respective object of evaluation. Context-specific factors, such as the region of application, can also lead to overlapping procedures.
The aim of this paper is to assist decision-makers in identifying the best possible source of water supply by providing a generic approach for comparative process assessment (section Valuation issues in wave) and providing a structured overview of assessment criteria with high relevance to the topic of water reuse and desalination (section Evaluation framework). Based on the generic flow chart and the list of criteria, which were derived from six multi-criteria evaluation concepts used in selected WavE projects, it is possible to compile an evaluation methodology together with a set of criteria, tailored to a specific subject of evaluation and the decision-maker(s). If necessary, further application-or country-specific criteria can be added to the list. In section Evaluation criteria, Multi-criteria decision analysis (MCDA), cost-benefit analysis (CBA) and LCA are presented as exemplary evaluation methods for identifying preferred solutions. Finally, possible data sources and methods for addressing uncertainty are presented and discussed with regard to their applicability (section Evaluation methods and selection of preferred solutions).

EVALUATION FRAMEWORK
Despite project-specific differences, a common generic structure was identified, which applies to all six WavE projects involved. Three levels of assessment can be distinguished: prerequisites, minimum requirements and evaluation criteria ( Figure 1).
Examining that prerequisites (here n ¼ 4), such as fulfilling legal boundary conditions for the intended purpose of use, local availability of the raw water flows required for reuse, general openness of the decision-makers towards the solutions and a ascertained demand for water reuse, are fulfilled, represents the first step of this process. These four prerequisites lie outside the sphere of influence of the project. Failure to meet them can significantly impede the implementation and use of the investigated technologies or systems and thus leads to the exclusion of the alternative in question from the decision-making process.
Furthermore, before the actual evaluation begins, the general suitability of the alternatives is examined on the basis of various minimum requirements (here: n ¼ 3). In contrast to the prerequisites, the test criteria, which are represents the assessment basis for the characteristic con- cerned. An example of this is the integrability, which needs to be given in principle (test criterion) but should also be evaluated qualitatively on the basis of the effort involved (evaluation criterion).
The remaining alternatives can then be subjected to a comparative evaluation for decision-making, which can be based on a quantitative evaluation (e.g. using material or energy balances, Environmental Impact Assessment, life cycle costing) or a qualitative evaluation of individual evaluation aspects (e.g. using stakeholder analyses) or can combine elements of both evaluation methods in the form of a holistic, multi-criteria decision support approach (see section Evaluation criteria).
If the examination of some test criteria is more complex than determining the evaluation criteria, a screening for promising alternatives and/or rejection of undesirable ones can be carried out first based on the evaluation criteria, before compliance with the (remaining) test criteria is ensured.
The aim of the evaluation is to uncover strengths and weaknesses of the compared alternatives and to identify the system solution that is most suitable for a specific site. The number of evaluation criteria asked for in each project varies between 20 and 30. In total, around 50 different criteria were compiled from the participating projects covering the following aspects.
Interactions between water treatment plant and environment are recorded on the basis of resource and land use (including land use, energy and water requirements, chemical consumption), emissions into soil, water and air, and the contribution to maintaining or increasing ecosystem services (e.g. volume of additionally provided water).
The social acceptance and compatibility of a water supply alternative can be described, among other things, based on the transparency and acceptance of the decisionmaking process (qualitative), the acceptance of water reuse and the products manufactured (qualitative), the creation of new jobs, political legitimacy, the potential for raising awareness for sustainable resource use, nuisances caused by the operation of the system (noise, aesthetics), conflict potential due to competition over resources and land, user friendliness and affordability.
In the economic dimension, the economic profitability, in only a few projects, such as the potential for opening up additional markets, the potential for automation and the potential for the creation of ecosystem services or the creation of jobs. An overview of the different criteria is given in Figure 2.
Criteria that are important primarily from an economic/ business perspective or from the perspective of public services of general interest are indicated by corresponding symbols.
Adopting the different criteria presented in Figure 2, it should be noted that from different perspectives, some criteria may have partly opposite implications for the evaluation. One example is the criterion 'creation of new jobs', which is seen positively from a social perspective but is viewed rather negatively from an economic perspective due to the associated personnel costs. In addition, the allocation of criteria is not  systems is increasingly coming into focus. The public administration has a supporting, regulating, but also monitoring role in the implementation of these criteria (OECD ).
Taking these framework conditions into account, the WavE collaborative projects have included evaluation criteria in their assessment tools that take into account important aspects of water supply in the context of public services of general interest.
The goal of the WaKap project, for example, is the development and piloting of an innovative, energy-efficient, modular combination process for the desalination of seawater and brackish or groundwater treatment. The background of the project is that the water supply in Vietnam and other Southeast Asian countries is increasingly facing challenges, such as the influence of climate change, the strong regional population growth and additional water demand due to economic development. For a permanent, sustainable use, safety-relevant and social aspects play an outstanding role in this project, in addition to ecological, technical and economic aspects.  (2002)).
• Competition for resources and land: The use of natural resources and land has a variety of social impacts in addition to the consequences for the environment. Competition for land and resources with the existing environment should therefore be carefully examined, e.g. with regard to natural areas, areas for local recreation or areas for alternative uses. In this context, attention should be paid to the quality and quantity of resources and land required for a planned facility. In terms of land quality, for example, this means that natural areas with a high availability of biodiversity must be protected in particular.

Corporate perspective
The business perspective is typically focused mainly on economic and technical aspects. Apart from costs and revenues, the stable and failure-free operation of processes is often of paramount importance. This is especially true for the supply of utilities, such as water, which do not directly generate any revenue but are required for most production processes. A reliable water supply, both in terms of quantity and quality, is crucial to ensure undisturbed production and thus prevent substantial financial losses due to production downtimes and impaired product quality.
Depending on the available water sources, water reuse can offer advantages but may also pose a risk in this regard. As the cost of water supply and wastewater treat- • Companies that provide water reuse and desalination technologies need to decide which technologies to include in their portfolio and/or develop. This is considered in the projects WEISS and DiWaL.
• Companies that want to implement water reuse and desalination on their own site need to decide on a suitable technical solutionas in the project WaReIp. There is a variety of methods that can support structured and transparent decision-making. They differ essentially in the selection of the evaluation aspects taken into account, the procedure for comparing and weighting the evaluation criteria and the determination of the best solution(s). Table 2 provides an overview of the advantages and limitations of the assessment methods used within the six projects that build the basis for this paper.

Multi-criteria decision analysis
The aim of multi-criteria evaluation is to identify the best solution or a manageable number of equally good alternatives. A complete ranking of all alternatives is not necessarily required for this, but may be the result, depending on the evaluation method used (Figueira et al. ).
Common to all multi-criteria evaluation methods is the

Cost-benefit analysis
As a rule, it is not only decisive what costs are caused by different decision options but also the benefits have to be seen in relation. In the so-called cost-benefit analysis (cf.  One tool for obtaining qualitative or semi-quantitative data is stakeholder and/or expert consultation. Here the aim is to bring together experiences and complementary knowledge from different perspectives. In order for this method to be successful, a common understanding of the facts to be evaluated and a common terminology is crucial.
Statistical data are used, for example, to estimate population figures, water demands or price indicesoften also to be able to forecast future developments. In addition to the challenge typical for statistical data of using a suitable sample size and distribution as a basis, extrapolations of past developments into the future need to be understood and should be presented as hypotheses.
As a basis for LCA, very large amounts of data on the environmental impacts of production, transport and disposal processes are required, which are usually not available or cannot be collected within a project. Proprietary databases such as the ecoinvent data base offer extensive information on these topics. If the data are to be extended by proprietary data sets, there is a risk that these will not be consistent with the existing data.
Laws and regulations supply information on effluent or discharge values and other emission limits to be complied.
These can vary greatly from region to region. In addition to the transferability from one site to another, which needs to be checked, this also means that the data are often not physically consistent. This can lead to the fact that an alternative that is considered to be sensible on the basis of the state of the art cannot be implemented or that legal requirements are physically contradictory.
Since the evaluation for decision support is carried out in the planning/design phase, the required data can usually not be collected on the real system. Therefore, the data used for the evaluation are subject to uncertainties that may also vary for different alternatives. How reliably prerequisites and minimum requirements can be fulfilled and evaluation attributes estimated, both for the expected use of the technology and with regard to future developments or unexpected boundary conditions, can therefore play an important role in the decision-making process. This is also reflected in some of the evaluation criteria, such as the TRL or the robustness and flexibility. A simple and intuitive way to consider uncertainties of the input data and/or the evaluation is to consider different predefined scenarios (i.e. different sets of input parameters or data sets). This method is often used to describe possible future developments, but it can also be used to map different plausible, mutually exclusive conditions for planning and evaluation (e.g. good/bad biodegradability of organic substances in the treated water, low/high population growth).
In A thorough consideration of technical, economic, ecological as well as social criteria are recommended to be considered in any decision case. In both public and corporate projects, ecological aspects have become increasingly important, although the motivation for including respective criteria in the decision-making process may not always be the same. In public projects, well-being and preservation of nature and resources seem to be more focused, whereas in corporate projects, green image and compliance are the environmental aspects that highest priority is assigned to.
In general, social and ecological aspects are less important for the assessment in corporate projects but are reflected in prerequisites that stem from laws and regulations.
A multi-criteria evaluation, which follows the generic approach of the WavE projects presented, helps to implement a clearly structured decision-making process. A