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Decision support in disinfection technologies for treated wastewater reuse
Journal of Cleaner Production 17 (2009) 1504–1511
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Decision support in disinfection technologies for treated wastewater reuse M.D. Go´mez-Lo´pez a, J. Bayo b, *, M.S. Garcı´a-Cascales a, J.M. Angosto b a b
Group of Management and Aid Decision Support in Project Engineering, Technical University of Cartagena, Spain Department of Chemical and Environmental Engineering, Technical University of Cartagena, Spain, Paseo Alfonso XIII, 48, E-30203 Cartagena, Spain
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 March 2009 Received in revised form 18 June 2009 Accepted 30 June 2009 Available online 7 July 2009
The environmental and social impact derived from treated wastewater reuse is an intrinsically complex multidimensional process, which involves multiple criteria and multiple stakeholders. This paper presents the use of multicriteria decision through the TOPSIS method, applied to six different methodologies concerning the disinfection of treated wastewater before reusing. Results have shown that the best disinfection technique for treated wastewater has been chlorination with 4 ppm, if this water is to be destined to an urban, agricultural or industrial use, due to a large weight given to cost and environmental criteria. Conversely, in recreational and environmental uses, the alternative of ultraviolet light disinfection was the chosen alternative. Economic criteria showed priority in the most entrepreneurial uses of the water, although social and political cost had a greater weight in the case of environmental or recreational uses. The inclusion of environmental and social assessment in the disinfection technique decision support clearly provides a cleaner and more sustainable production. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Wastewater reuse Multicriteria decision making Disinfection Environmental criteria Social criteria
1. Introduction The recovery of treated wastewater for different uses is an interesting practice that can contribute to a better management of water resources all over the world. This fact is especially important in arid and semi-arid zones, where water resources are becoming both quantitatively and qualitatively scarce [1,2]. One of them is the Region of Murcia, situated in the South East of Spain, where industrial wastewater disposal accounts for up to 50% of all wastewater discharged into municipal collectors. In all cases, water quality standards are becoming more and more stringent. The reuse of treated wastewater from wastewater treatment plants (WWTP) is an international practice with a large variety of applications, i.e., irrigation, urban and recreational uses, groundwater recharge, aquaculture, and industrial uses, among others. For all of these, the quality of the water should be taken into account. Disinfection is considered to be the essential process for the inactivation and destruction of waterborne pathogens, in order to protect human health and also the environment [3]. Chlorination has been the traditional and most common wastewater disinfection chemical system used around the world [4]. However, it has proved to show secondary effects due to the formation of disinfection by-products (DBP), such as trihalomethanes (THM) and haloacetic acids (HAA) [5]. Nowadays, the trend is * Corresponding author. Tel.: þ34 968 327 077; fax: þ34 968 325 435. E-mail address: [email protected] (J. Bayo). 0959-6526/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jclepro.2009.06.008
to move to ultraviolet irradiation (UV) as a safe physical procedure for water and wastewater disinfection. This technology efficiently eliminates enteric bacteria, without producing DBP at UV doses usually used in wastewater disinfection [6]. However, this method also has some disadvantages, such as the lack of a bacteriostatic effect and the possibility of repairing UV-damaged DNA, with further bacteria regeneration [7]. A combination of both technologies has also been reported, being beneficial in reducing treatment times needed for inactivation and also minimizing bacteria regeneration [8]. Disinfection techniques other than chlorination and UV are rarely applied at full-scale. Ever since the world has existed, people have found themselves involved in taking decisions that concern their daily life. For many years, researchers have been interested in the analysis of how the human being carries out this task. Thus, we study the alternatives that can be chosen, as well as the criteria on which we are going to evaluate these alternatives. This, which at first sight seems to be simple, forms part of the whole discipline that is called Multiple Criteria Decision Making (MCDM) [9,10]. MCDM is a procedure that consists in finding the best alternative among a set of feasible alternatives. MCDM methodologies have been widely used for the resolution of sophisticated problems that should involve both quantitative and qualitative factors, as well as the evaluation of different actors. The environmental decision context demands multicriteria evaluation models, where quantitative data and individual weights provided by technical experts and users are taken into account. In these models the inclusion of environmental
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criteria in the enterprise decision should be taken into account, as highlighted by Tsoulfas and Pappis [11]. In the literature, various studies have been performed to solve environmental problems through the use of MCDM. Examples of this include the work of Spengler et al. [12], in which life cycle assessment and multicriteria techniques are combined for the environmental evaluation of different recycling techniques. Montanari [13] also proposes a methodology, based on the TOPSIS method, to estimate the environmental efficiency of 15 thermal energy power plants. With regard to the selection of treatments in the disinfection of wastewaters, those works which employ different multicriteria techniques should be highlighted; these include the works of AbuTaleb [14], Georgopoulou et al. [15], Flores et al. [16], Gabzdylova et al. [17] and recently of Aragone´s-Beltra´n et al. [18], who used MCDM for the selection of the treatment of textile wastewater. Similarly it is becoming increasingly necessary to include social criteria in the decision support systems. On this aspect and associated to the reutilisation of the water, we find the works of Panebianco and Pahl-Wostl [19] who evaluated habits and prejudices from different agents when new wastewater treatment techniques are introduced in Germany, Menegaki et al. [20] who investigated the social acceptability and the evaluation of recycled water use in Crete, and Urkiaga et al. [21], who affirm the need for social and environmental implementation in this type of decisions. However, there are few references about the evaluation of disinfection procedures for treated wastewater with a multiple attribute decision making technique. This paper presents the use of multicriteria decision techniques applied to six different methodologies concerning the disinfection of treated wastewater before reusing. For this purpose, quantitative data about water quality and qualitative value judgments provided by technical experts were taken into account. The inclusion of environmental and social factors in the decision support is particularly relevant in this work. In order to identify the best disinfection alternative for treated wastewater reuse in five different final uses, data were processed through the TOPSIS method.
2. Sample collection and treatments The study was carried out with urban wastewater treated in the WWTP of Cartagena (Spain). This plant consists of a conventional system, with a primary treatment and two activated-sludge reactors. Wastewater samples from the secondary effluent were collected in sterile glass bottles for microbiological analyses, and in a plastic collector for physicochemical parameter determinations. For chlorination experiments, wastewater samples were first buffered with phosphate buffer at pH 7. A 5% w/v solution of chemically pure sodium hypochlorite (NaOCl) was obtained from Panreac Quimica (Barcelona, Spain) and diluted to obtain final concentrations of 4 mg/L and 6 mg/L. Chlorinated samples were monitored for 30 min. The UV radiation was applied using a low-pressure UVC lamp of 8 Watts (400 mm length and 85 mm diameter) (Messner Benelux, Belgium), with a flow-rate from 500 to 1100 L/h, and a wavelength of 254 nm. The installation was designed to be used with 1000 mL of sample, irradiated for short periods of 5 and 10 min, providing doses of 37 mJ/cm2 and 73 mJ/cm2, respectively. Before each treatment, the lamp was cleaned up with bidistilled water. All disinfection tests were conducted at room temperature. Samples were analysed for the following physicochemical parameters: pH, conductivity, turbidity, BOD5, and chlorides. All of them were analysed in laboratory according to the methods prescribed by the APHA handbook [22].
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Total coliforms (TC) and faecal coliforms (FC) were analysed by means of the membrane filtration method. The membrane filter selected, with a pore size of 0.45 mm, was always within the acceptable range, i.e., 20–80 colonies of TC and 20–60 colonies of FC. Total coliforms were cultured on Tergitol agar and incubated at 35 C for 24 h. Faecal coliforms were cultured in the same media, and incubated at 44 C for 24 h. After the incubation period, colonies were counted and the results calculated as colony forming units (cfu) per 100 mL of sample. The surviving number of total and faecal coliforms at each UV dose was investigated. 3. Application of MCDM models In this paper, an MCDM model has been implemented for the evaluation of different disinfection technologies for treated wastewater reuse, for this purpose two different groups of experts were involved in the process, MCDM and wastewater reuse experts. The selection of an ideal wastewater disinfection treatment for different uses (i.e., urban, agricultural, industrial, recreational and environmental) is associated with different criteria which should be evaluated. Fig. 1 summarises the steps to be carried out. In the first step, data were available from experts, and after a brain storming process, a set of six alternatives and four criteria with different levels of subcriteria were established. These criteria and alternatives were the same in the five uses. Five decision-making processes were proposed according to the different uses. In order to elaborate the decision matrix, each decision maker was provided with a survey (see Appendix A) in which a series of different questions were made on the behaviour of each alternative, in terms of each criterion and the importance given by the decision maker to each criterion. In the second step, the translation of these data to the TOPSIS method allowed us to obtain the best alternative. 3.1. The TOPSIS method The Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) approach is an MCDM method for the arrangement of preferences to an ideal solution by similarity [23]. The basic principle is that the chosen alternative must have the shortest distance to the positive ideal solution and the farthest distance to the negative ideal solution [24]. The mathematical procedure of TOPSIS is carried out in a series of steps, which can be seen in Hwang and Yoon [23]. It should be pointed out that within the model, and since several experts have been consulted, a decision process is carried out separately for each expert, with the aim of studying the individual choice, and also a group decision process, using the first
Wastewater reuse experts Wastewater reuse experts DATA ACQUISITION
MCDM experts MCDM experts Decision makers
DATA EVALUATION
MCDM experts
Brain storming
Problem identification Alternative and criteria selection Survey for decision makers Survey answer
TOPSIS methodology
Fig. 1. Optimal alternative identification for wastewater disinfection treatment by means of multicriteria decision making.
M.D. Go´mez-Lo´pez et al. / Journal of Cleaner Production 17 (2009) 1504–1511
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process (aggregating the information of the experts in origin) for the purpose of studying the final decision. Since 1993 there have been more than 150 references in international journals related to the application of TOPSIS; Shih et al. [25] provide a review of these applications, with a notable increase in recent years, above all with the implementation of fuzzy techniques. Among these, and focusing on the inclusion of environmental criteria in the methodology, the works of Chen et al. [26]; Janic [27]; Cheng et al. [28]; Montanari [13]; Li et al. [29]; Kandakoglu et al. [30]; Xuebin [31] should be emphasized, and only two papers (Janic [27]; Cheng et al. [28]) have been found which also consider social factors amongst others. If we focus on the choice of one method as opposed to another, there are numerous works which compare methodologies, although, the qualitative MCDM techniques generally used are focused on both TOPSIS and AHP. In Zeydan and Çolpan [32] and Shih et al. [25], an extensive study of these MCDM methods was made. They conclude that there are some advantages and disadvantages when compared with each other. But, mostly, they think that there are more advantages of TOPSIS than of AHP. Some of these main reasons are defined as follows:
disinfection of treated wastewater with maximum general profits. Level 1 shows the overall objective of the decision problem: the selection of a disinfection system for treated wastewater reuse. Level 2 consists of four main criteria, namely: water quality; capital cost; socio-economic; and environmental criteria, and their associated subcriteria. Level 3 consists of the wastewater treatment options. Water quality, as a technical parameter, and economic cost have been traditionally used as performance criteria for the optimisation of wastewater treatments [34]. But socio-economic and environmental aspects should not be isolated and taken into account for a better acceptance of the disinfection treatment used. As previously stated by different authors [19–21], public acceptability is a prerequisite for society to establish and promote water reuse projects. The four criteria chosen in our study were subdivided into different subcriteria, with the following optimisation tendency: (C1) Water quality criterion, with seven subcriteria: (C11) pH (pH units): between 6.5 and 7.5. (C12) Conductivity (mS/cm): to a minimum. (C13) Turbidity (NTU): to a minimum. (C14) BOD5 (% reduction): to a maximum. (C15) Chlorides (mg/L): to a minimum. (C16) Total coliforms (% reduction): to a maximum. (C17) Faecal coliforms (% reduction): to a maximum. (C2) Economic criterion, with two subcriteria: (C21) Disinfection system implementation: to a minimum. (C22) Maintenance cost: to a minimum. (C3) Social criterion, with one subcriteria: (C31) Enterprise image: to a maximum (means by which the enterprise chose the disinfection technique in its process production). (C4) Environmental criterion, with three subcriteria: (C41) Energy saving: to a maximum. (C42) Residues from disinfection processes: to a minimum. (C43) Emissions (gases and vapours): to a minimum.
TOPSIS method is intuitive, easy to understand and to implement. TOPSIS is simple and it yields a highly reliable preference order. TOPSIS logic is rational and understandable. The computation processes are straightforward. The concept permits the pursuit of best alternatives for each criterion depicted in a simple mathematical form. The importance weights are incorporated into the comparison procedures. It is a method which allows working with different scales and types of information (i.e., linguistic evaluations, experimental data). It should be highlighted that although the works cited finally select TOPSIS as the method to apply, the discussion made by Shih et al. [25] and Aragone´s-Beltra´n et al. [33] emphasizes that the method chosen depends to a great extent on the characteristics of the problem posed. 3.2. Evaluation of criteria and alternatives Fig. 2 illustrates a hierarchical system of wastewater disinfection alternatives’ selection. The overall objective is to achieve
Level 1 Problem
All the subcriteria have been valued qualitatively, according to qualitative labels, except criteria C12–C17, which were valued quantitatively. We have to point out that criterion C11, pH, although it is a criterion defined in a quantitative form, the optimum range of its use leads to defining a qualitative valuation of its weight. On the other hand, six different alternatives were chosen in relation to disinfection procedures:
Disinfection system alternative selection
Level 2 Criteria and subcriteria
C1 WATER QUALITY · pH · BOD5 · conductivity · chlorides · turbidity · TC, FC
C2 CAPITAL COST · system implementation · maintenance cost
C3 SOCIO-ECONOMICS · enterprise image
C4 ENVIRONMENTAL · energy saving · residues · emissions
Level 3 Alternatives
A1 UV1
A2 UV2
A3 UV + CL1
A4 UV + CL2
A5 CL1
A6 CL2
Fig. 2. The hierarchical structure of disinfection system alternative selection for treated wastewater reuse.
´ mez-Lo´pez et al. / Journal of Cleaner Production 17 (2009) 1504–1511 M.D. Go Table 1 Linguistic labels and weights used for the evaluation of different criteria and alternatives. Linguistic label type 1
Linguistic label type 2
Label
Description
Weights, wj
Label
Description
Weights, wj
vL L mL m mH H vH
Very low Low Medium low Medium Medium high High Very high
0 0.1 0.3 0.5 0.7 0.9 1
vG G mG m mB B vB
Very good Good Medium good Medium Medium bad Bad Very bad
0 0.1 0.3 0.5 0.7 0.9 1
(A1) Treated wastewater disinfected with 254 nm wavelength ultraviolet light for 5 min. (A2) Treated wastewater disinfected with 254 nm wavelength ultraviolet light for 10 min. (A3) Treated wastewater disinfected with chlorine ranging from 0.35 up to 0.70 mg/L and irradiated with 254 nm wavelength ultraviolet light for 5 min. (A4) Treated wastewater disinfected with chlorine ranging from 0.71 up to 0.87 mg/L and irradiated with 254 nm wavelength ultraviolet light for 5 min. (A5) Treated wastewater chlorinated with sodium hypochlorite to a final concentration of 4 mg/L for 30 min. (A6) Treated wastewater chlorinated with sodium hypochlorite to a final concentration of 6 mg/L for 30 min.
3.3. Elaboration of the survey This type of methods may require consulting experts who can enrich the decision with their judgments regarding the problem and this was provided by a survey. Three experts in the sector of wastewater reuse in the South East of Spain were consulted. Two of the three wastewater reuse experts were researchers in this subject, and were asked in the process of the problem definition and in the survey. Another wastewater reuse expert is a technical employee of a wastewater treatment plant and was only involved in
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the survey step. The survey was carried out at two levels: for the first level, concrete questions were used to obtain a ranking for criteria according to each expert, and at the second level, experts were asked to value each criterion for each alternative (see Appendix A). In this level, questions were designed for all qualitative criteria. Table 1 shows the qualitative labels used for the ratings of the alternatives according to the importance weighting of each subcriterion. Each label was associated to a weight in order to simplify further statistical analyses.
3.4. Data analysis Tables 2 and 3 present the data of the weights that each expert gave to the groups of criteria and subcriteria, respectively, as well as the results of the original weights obtained for the group after the primary aggregation. If we take into account the weights of the group we can see (Table 2) that the social criterion has the lowest weight in urban, agricultural and industrial uses. In urban and agricultural uses, a greater weight is given to the quality criteria, giving them an importance similar to the cost and environmental criteria. It should be highlighted that in industrial use the preferential criterion is that of cost, in contrast to what occurs in recreational use, perhaps due to the profitability associated to the use of water in these activities. In the ecological use the experts have attributed a similar weight to the different criteria. A somewhat homogeneous pattern can be seen in the weights that the experts have given to each group of criteria. For each of the uses we can highlight: For urban use of the water Experts 1 and 2 and the group give a greater weight to the quality criteria and a lower weight to the social criteria. However Expert 3 considers that the quality, costs and social criteria all have a similar weight, higher than that for the environmental criteria. For agricultural use of the water the three experts and the group coincide in giving the greatest importance to quality, although Expert 2 shares that importance with the environmental criteria. As for the lowest weight, they give it to the social criteria.
Table 2 Normalised weights for each group of criterion and water uses, according to experts (E1–E3) and group decision (G). Water uses
Experts and group
Criteria C1 quality criterion
C2 economic criterion
C3 social criterion
C4 environmental criterion
UU
E1 E2 E3 G
0.36 0.40 0.27 0.35
0.27 0.20 0.27 0.25
0.09 0.10 0.27 0.15
0.27 0.30 0.18 0.25
AU
E1 E2 E3 G
0.33 0.31 0.33 0.32
0.25 0.23 0.25 0.24
0.17 0.15 0.17 0.16
0.25 0.31 0.25 0.27
IU
E1 E2 E3 G
0.25 0.29 0.25 0.26
0.33 0.29 0.33 0.32
0.17 0.21 0.17 0.18
0.25 0.21 0.25 0.24
RU
E1 E2 E3 G
0.31 0.31 0.29 0.30
0.15 0.15 0.21 0.17
0.23 0.23 0.29 0.25
0.31 0.31 0.21 0.28
EU
E1 E2 E3 G
0.29 0.36 0.29 0.31
0.21 0.18 0.21 0.20
0.21 0.18 0.29 0.23
0.29 0.27 0.21 0.26
UU: urban use; AU: agricultural use; IU: industrial use; RU: recreational use; and EU: environmental use.
M.D. Go´mez-Lo´pez et al. / Journal of Cleaner Production 17 (2009) 1504–1511
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Table 3 Normalised weights for each subcriterion and water uses, according to experts (E1–E3) and group decision (G). Water uses
Experts and group
Subcriteria C11
C12
C13
C14
C15
C16
C17
C21
C22
C31
C41
C42
C43
UU
E1 E2 E3 G
0.08 0.03 0.04 0.05
0.00 0.05 0.02 0.02
0.09 0.07 0.06 0.07
0.03 0.06 0.03 0.04
0.00 0.05 0.00 0.02
0.09 0.07 0.06 0.07
0.09 0.07 0.06 0.07
0.13 0.09 0.11 0.11
0.14 0.11 0.16 0.14
0.09 0.10 0.27 0.15
0.19 0.07 0.11 0.13
0.06 0.10 0.06 0.07
0.02 0.13 0.01 0.05
AU
E1 E2 E3 G
0.05 0.04 0.02 0.04
0.05 0.05 0.04 0.05
0.06 0.06 0.06 0.06
0.01 0.02 0.03 0.02
0.04 0.03 0.06 0.04
0.06 0.06 0.06 0.06
0.06 0.06 0.06 0.06
0.12 0.11 0.13 0.12
0.13 0.12 0.12 0.12
0.17 0.15 0.17 0.16
0.12 0.15 0.09 0.12
0.07 0.08 0.13 0.09
0.07 0.08 0.04 0.06
IU
E1 E2 E3 G
0.05 0.05 0.03 0.04
0.04 0.04 0.03 0.03
0.05 0.05 0.05 0.05
0.01 0.03 0.02 0.02
0.03 0.02 0.02 0.02
0.05 0.05 0.05 0.05
0.05 0.05 0.05 0.05
0.17 0.14 0.18 0.16
0.17 0.14 0.16 0.16
0.17 0.21 0.17 0.18
0.13 0.09 0.10 0.11
0.07 0.05 0.09 0.07
0.04 0.07 0.05 0.06
RU
E1 E2 E3 G
0.03 0.03 0.04 0.03
0.05 0.04 0.01 0.03
0.06 0.06 0.07 0.06
0.03 0.05 0.01 0.03
0.03 0.02 0.00 0.02
0.06 0.06 0.08 0.06
0.06 0.06 0.08 0.06
0.10 0.08 0.12 0.10
0.05 0.08 0.09 0.08
0.23 0.23 0.29 0.25
0.10 0.06 0.10 0.09
0.10 0.12 0.07 0.10
0.10 0.12 0.05 0.09
EU
E1 E2 E3 G
0.04 0.04 0.03 0.04
0.02 0.04 0.02 0.03
0.05 0.07 0.05 0.06
0.04 0.05 0.06 0.05
0.02 0.02 0.01 0.02
0.05 0.07 0.05 0.06
0.05 0.07 0.06 0.06
0.09 0.09 0.14 0.11
0.12 0.09 0.08 0.10
0.21 0.18 0.29 0.23
0.10 0.09 0.11 0.10
0.10 0.09 0.08 0.09
0.10 0.09 0.03 0.07
UU: urban use; AU: agricultural use; IU: industrial use; RU: recreational use; EU: environmental use.
In industrial use the greatest weight is given in all cases to the quality criteria, with Expert 2 sharing this weight with the quality criteria. The lowest weight is given to the social criteria and Expert 2 also considers the same weight for the environmental criteria. The recreational use of the water presents greater disparity between the experts. Experts 1 and 2 give a greater weight to the quality and environmental criteria and Expert 3 to the quality and social criteria. The group gives priority only to quality criteria. All experts coincide in giving a lower weight to the costs criteria, which Expert 3 shares with the environmental criteria. It is with the environmental use where the greatest discrepancy exists. All the experts coincide in giving priority to the quality criteria, but Expert 1 shares it with the environmental criteria and Expert 3 with the social criteria. Likewise all give the lowest weight to the costs criteria, but Experts 1 and 2 share it with the social criteria, and Expert 3 with the environmental criteria. Table 4 presents the data for the quantitative quality criteria (except the pH), obtained analytically for each of the alternatives proposed. Table 5 presents the data of the criteria that do not have a quantitative valuation, and the experts have valued each of the alternatives with the qualitative labels defined in Table 1. Fig. 3 presents a graphic representation of the values of relative proximity (R), obtained for each of the alternatives for each of the uses considered. It can be observed that in the urban, agricultural and industrial uses, the best disinfection method chosen is Alternative 5 (chlorination at 4 ppm). For recreational and environmental uses Alternative 1 has been obtained (UV, 5 min) as the best
disinfection option. In both cases the tendencies of the curves are similar, which indicates a similar pattern in the decision. If we centre our attention on the values obtained in the group decision, in uses such as urban, agricultural and industrial the choice of a chlorination system seems to be due to the large weight conferred on the costs and environmental criteria. In this sense, although the UV system provides good quality water, its cost and energy consumption are greater than those for chlorination. However, for recreational and environmental uses, the lowest weight has been given to the cost criteria, a fact which has led to a change in the final decision with regard to the other uses and, therefore, to choose the UV method as the best. It should be highlighted that in cases in which water is an important cost within the activity, such as for agricultural and industrial uses, there is little dispersion between values obtained by each of the experts, and thus for the group decision. In these cases the cost of the disinfection method is decisive, therefore, the cheapest (chlorination) is the one chosen by all the experts. On the other hand, as can be appreciated in the urban, recreational and environmental uses, a greater dispersion exists between the values obtained from each expert. We must point out that these uses are associated to the service sector or to the administration, in which both the social aspects as well as the environmental aspects have a greater weight than the costs, although it should be mentioned that in the recreational and environment uses, the dispersion is marked above all by Expert 3 who gives the costs and environmental criteria similar and high weights. If we analyse the decisions of this expert,
Table 4 Values of water quality subcriteria for each disinfection alternative. Subcriteria
C12, C13, C14, C15, C16, C17,
conductivity (mS/cm) turbidity (NTU) BOD5 (% reduction) chlorides (mg/L) total coliforms (% reduction) faecal coliforms (% reduction)
Alternatives A1
A2
A3
A4
A5
A6
2647.0 1.3 49.7 533.8 96.2 97.8
2592.0 1.8 44.4 522.3 99.4 100.0
2458.0 2.0 25.0 463.0 94.5 95.0
2490.0 2.8 27.1 455.2 91.4 95.0
2296.0 5.7 77.5 309.4 99.6 99.2
2210.0 4.9 87.0 299.3 100.0 82.6
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we can see that he does not suggest much discrimination between the different disinfection methods for the different uses. At this point in the analysis of the data obtained it is important to see how social aspects, such as the rejection of chlorination by the users of golf courses, because of the chlorine smell, leads the managers of said golf courses to reject these methods, to preserve the company’s image and, therefore, the user’s acceptance. Likewise, if we focus on the environmental aspects of all the sustainability programmes and the compliance with the Kyoto protocol, they advocate greater energy efficiency, so from that point of view the UV method would be a more viable alternative if it were possible to power it by means of renewable energy, thus solving the problem. As can be seen, social and environmental aspects are becoming increasingly important, which coincides with Panebianco and PahlWostl [19], Menegaki et al. [20] and Urkiaga et al. [21], who affirm the need for social and environmental implementation in this type of decisions. Similarly, decision making in this field would be enriched by consulting agents from all the fields implicated (businessmen, users and managers). With regard to methodological aspects, we can say that the implementation of the group decision algorithms has enriched the decision. As an example of this we see that if the decision had been taken by Expert 3 alone, the chosen method would have been chlorination for all the uses, yet this is unviable in recreational uses for the social aspects previously commented. But the opinion of this expert has been considered and is reflected in the final group decision in the same proportion as the rest. In relation to the application of the TOPSIS method we have been able to check that the inclusion of qualitative labels has
Table 5 Linguistic variables for each alternative and subcriteria according to three experts. Subcriteria
Alternatives A1
A2
A3
A4
A5
A6
Expert 1 C11 pH C21 disinfection system implementations C22 maintenance cost C31 enterprise image C41 energy saving C42 residues C43 emissions
vG m m mG L L L
G mH mH mG L L L
G mH H M m mL m
m H vH mB m m mH
B mL mL B H mH H
mB m mL B mH H H
Expert 2 C11 pH C21 disinfection system implementations C22 maintenance cost C31 enterprise image C41 energy saving C42 residues C43 emissions
G mL mL G L vL L
G M m G L vL L
G mH mH mG m L mL
mG H H m mL mL m
mB L L mB H m mH
m mL mL mB mH mH H
Expert 3 C11 pH C21 disinfection system implementations C22 maintenance cost C31 enterprise image C41 energy saving C42 residues C43 emissions
G H H vG mH vL vL
G H vH vG m vL vL
vG vH vH G L mL L
mG vH vH G vL mL L
mB mH M mG m H L
mG mH H mG mL H L
0.8
0.8
0.6
0.6
0.4
0.4 0.2
0.2
AGRICULTURAL USE
URBAN USE 0
A1
A2
A3
A4
A5
0.0
A6
0.8
0.8
0.6
0.6
0.4
0.4
A1
A2
A3
A4
A5
A6
0.2
0.2
RECREATIONAL USE
INDUSTRIAL USE 0
1509
A1
A2
A3
A4
A5
0
A6
A1
A2
A3
A4
A5
A6
0.8 0.6 0.4 0.2 ENVIRONMENTAL USE 0 A1
A2
A3
A4
A5
A6
Fig. 3. Results of the relative proximity, R, for Expert 1 (thin line), Expert 2 (dashed line), Expert 3 (dotted line), and Group (thick line) for the selection of disinfection system for treated wastewater reuse in five different uses.
M.D. Go´mez-Lo´pez et al. / Journal of Cleaner Production 17 (2009) 1504–1511
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allowed the experts to value aspects which are difficult to quantify and, as we can see, the decision has benefited to a great extent.
B. Value the importance of each subcriteria of the group ‘‘water quality’’, in the election of treated water for agricultural use, using the linguistic label type 1.
4. Conclusions In our problem, qualitative and quantitative information was available as this was the type of data provided by the experts. We, therefore, decided to approach the problem using the widely accepted TOPSIS process for dealing with complex decision problems. In terms of the results obtained the best disinfection technique for treated wastewater chosen for urban, agricultural and industrial uses was the technique of chlorination 4 ppm, because a large weight has been given to the costs and environmental criteria. Conversely, for recreational and environmental uses, in which less importance is given to the cost, and the weight for environmental factors has been increased, the alternative with UV light was chosen. We can conclude that in this type of decisions, economic criteria continue to dominate, above all when we refer to business uses in which the water is an input in the company. However, when the social and political cost is given a greater importance such as in the case of ecological and recreational uses, the most costly method (ultraviolet), but which has fewer problems in terms of residual contamination in comparison with the chlorination methods (chlorine compounds and smells), is that which prevails. In terms of environmental factors, of all the methods proposed, it is only the energy consumption of the UV methods which has led the experts to opt for chlorination methods, which could be solved with the introduction of renewable energy resources. As for future lines to follow, we propose the use of fuzzy numbers in the modelling of the linguistic labels, being able to compare both methodologies, and the study and comparison of the different aggregations to determine how they affect the final and partial decision for each expert.
C11, pH: vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
C12, CE:
C13, Turbidity:
C14, DBO5:
C15, Chlorides:
C16, CT:
C17, CF:
2. Evaluation of the alternatives for each qualitative criterion A. With respect to criterion C11 (pH), value the different alternatives, using linguistic label type 2:
A1 (UV1) vG
G
mG
m
mB
B
vB
vG
G
mG
m
mB
B
vB
vG
G
mG
m
mB
B
vB
vG
G
mG
m
mB
B
vB
vG
G
mG
m
mB
B
vB
vG
G
mG
m
mB
B
vB
A2 (UV2)
A3 (UV þ CL1)
Acknowledgements We are indebted to the anonymous referees for their critical review and suggestions that enabled us to obtain this paper. This research was financed by DGICYT (Project TIN2008 – 06872 – C0404) and the Fundacio´n Se´neca (Project 8824/PPC/08).
A4 (UV þ CL2)
A5 (CL_4 ppm)
A6 (CL_6 ppm)
Appendix A. Questionnaire TOPSIS Example of questionnaire (agricultural use; criterion: pH):
References
1. Importance of the criteria. A. Write the degree of importance that you believe that each of the criteria should have when selecting the best disinfection technique for treated wastewater for agricultural use, using the linguistic label type 1.
C1, water quality: vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
C2, costs:
C3, socio-economics:
C4, environmental:
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Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Decision support in disinfection technologies for treated wastewater reuse M.D. Go´mez-Lo´pez a, J. Bayo b, *, M.S. Garcı´a-Cascales a, J.M. Angosto b a b
Group of Management and Aid Decision Support in Project Engineering, Technical University of Cartagena, Spain Department of Chemical and Environmental Engineering, Technical University of Cartagena, Spain, Paseo Alfonso XIII, 48, E-30203 Cartagena, Spain
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 March 2009 Received in revised form 18 June 2009 Accepted 30 June 2009 Available online 7 July 2009
The environmental and social impact derived from treated wastewater reuse is an intrinsically complex multidimensional process, which involves multiple criteria and multiple stakeholders. This paper presents the use of multicriteria decision through the TOPSIS method, applied to six different methodologies concerning the disinfection of treated wastewater before reusing. Results have shown that the best disinfection technique for treated wastewater has been chlorination with 4 ppm, if this water is to be destined to an urban, agricultural or industrial use, due to a large weight given to cost and environmental criteria. Conversely, in recreational and environmental uses, the alternative of ultraviolet light disinfection was the chosen alternative. Economic criteria showed priority in the most entrepreneurial uses of the water, although social and political cost had a greater weight in the case of environmental or recreational uses. The inclusion of environmental and social assessment in the disinfection technique decision support clearly provides a cleaner and more sustainable production. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Wastewater reuse Multicriteria decision making Disinfection Environmental criteria Social criteria
1. Introduction The recovery of treated wastewater for different uses is an interesting practice that can contribute to a better management of water resources all over the world. This fact is especially important in arid and semi-arid zones, where water resources are becoming both quantitatively and qualitatively scarce [1,2]. One of them is the Region of Murcia, situated in the South East of Spain, where industrial wastewater disposal accounts for up to 50% of all wastewater discharged into municipal collectors. In all cases, water quality standards are becoming more and more stringent. The reuse of treated wastewater from wastewater treatment plants (WWTP) is an international practice with a large variety of applications, i.e., irrigation, urban and recreational uses, groundwater recharge, aquaculture, and industrial uses, among others. For all of these, the quality of the water should be taken into account. Disinfection is considered to be the essential process for the inactivation and destruction of waterborne pathogens, in order to protect human health and also the environment [3]. Chlorination has been the traditional and most common wastewater disinfection chemical system used around the world [4]. However, it has proved to show secondary effects due to the formation of disinfection by-products (DBP), such as trihalomethanes (THM) and haloacetic acids (HAA) [5]. Nowadays, the trend is * Corresponding author. Tel.: þ34 968 327 077; fax: þ34 968 325 435. E-mail address: [email protected] (J. Bayo). 0959-6526/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jclepro.2009.06.008
to move to ultraviolet irradiation (UV) as a safe physical procedure for water and wastewater disinfection. This technology efficiently eliminates enteric bacteria, without producing DBP at UV doses usually used in wastewater disinfection [6]. However, this method also has some disadvantages, such as the lack of a bacteriostatic effect and the possibility of repairing UV-damaged DNA, with further bacteria regeneration [7]. A combination of both technologies has also been reported, being beneficial in reducing treatment times needed for inactivation and also minimizing bacteria regeneration [8]. Disinfection techniques other than chlorination and UV are rarely applied at full-scale. Ever since the world has existed, people have found themselves involved in taking decisions that concern their daily life. For many years, researchers have been interested in the analysis of how the human being carries out this task. Thus, we study the alternatives that can be chosen, as well as the criteria on which we are going to evaluate these alternatives. This, which at first sight seems to be simple, forms part of the whole discipline that is called Multiple Criteria Decision Making (MCDM) [9,10]. MCDM is a procedure that consists in finding the best alternative among a set of feasible alternatives. MCDM methodologies have been widely used for the resolution of sophisticated problems that should involve both quantitative and qualitative factors, as well as the evaluation of different actors. The environmental decision context demands multicriteria evaluation models, where quantitative data and individual weights provided by technical experts and users are taken into account. In these models the inclusion of environmental
´ mez-Lo´pez et al. / Journal of Cleaner Production 17 (2009) 1504–1511 M.D. Go
criteria in the enterprise decision should be taken into account, as highlighted by Tsoulfas and Pappis [11]. In the literature, various studies have been performed to solve environmental problems through the use of MCDM. Examples of this include the work of Spengler et al. [12], in which life cycle assessment and multicriteria techniques are combined for the environmental evaluation of different recycling techniques. Montanari [13] also proposes a methodology, based on the TOPSIS method, to estimate the environmental efficiency of 15 thermal energy power plants. With regard to the selection of treatments in the disinfection of wastewaters, those works which employ different multicriteria techniques should be highlighted; these include the works of AbuTaleb [14], Georgopoulou et al. [15], Flores et al. [16], Gabzdylova et al. [17] and recently of Aragone´s-Beltra´n et al. [18], who used MCDM for the selection of the treatment of textile wastewater. Similarly it is becoming increasingly necessary to include social criteria in the decision support systems. On this aspect and associated to the reutilisation of the water, we find the works of Panebianco and Pahl-Wostl [19] who evaluated habits and prejudices from different agents when new wastewater treatment techniques are introduced in Germany, Menegaki et al. [20] who investigated the social acceptability and the evaluation of recycled water use in Crete, and Urkiaga et al. [21], who affirm the need for social and environmental implementation in this type of decisions. However, there are few references about the evaluation of disinfection procedures for treated wastewater with a multiple attribute decision making technique. This paper presents the use of multicriteria decision techniques applied to six different methodologies concerning the disinfection of treated wastewater before reusing. For this purpose, quantitative data about water quality and qualitative value judgments provided by technical experts were taken into account. The inclusion of environmental and social factors in the decision support is particularly relevant in this work. In order to identify the best disinfection alternative for treated wastewater reuse in five different final uses, data were processed through the TOPSIS method.
2. Sample collection and treatments The study was carried out with urban wastewater treated in the WWTP of Cartagena (Spain). This plant consists of a conventional system, with a primary treatment and two activated-sludge reactors. Wastewater samples from the secondary effluent were collected in sterile glass bottles for microbiological analyses, and in a plastic collector for physicochemical parameter determinations. For chlorination experiments, wastewater samples were first buffered with phosphate buffer at pH 7. A 5% w/v solution of chemically pure sodium hypochlorite (NaOCl) was obtained from Panreac Quimica (Barcelona, Spain) and diluted to obtain final concentrations of 4 mg/L and 6 mg/L. Chlorinated samples were monitored for 30 min. The UV radiation was applied using a low-pressure UVC lamp of 8 Watts (400 mm length and 85 mm diameter) (Messner Benelux, Belgium), with a flow-rate from 500 to 1100 L/h, and a wavelength of 254 nm. The installation was designed to be used with 1000 mL of sample, irradiated for short periods of 5 and 10 min, providing doses of 37 mJ/cm2 and 73 mJ/cm2, respectively. Before each treatment, the lamp was cleaned up with bidistilled water. All disinfection tests were conducted at room temperature. Samples were analysed for the following physicochemical parameters: pH, conductivity, turbidity, BOD5, and chlorides. All of them were analysed in laboratory according to the methods prescribed by the APHA handbook [22].
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Total coliforms (TC) and faecal coliforms (FC) were analysed by means of the membrane filtration method. The membrane filter selected, with a pore size of 0.45 mm, was always within the acceptable range, i.e., 20–80 colonies of TC and 20–60 colonies of FC. Total coliforms were cultured on Tergitol agar and incubated at 35 C for 24 h. Faecal coliforms were cultured in the same media, and incubated at 44 C for 24 h. After the incubation period, colonies were counted and the results calculated as colony forming units (cfu) per 100 mL of sample. The surviving number of total and faecal coliforms at each UV dose was investigated. 3. Application of MCDM models In this paper, an MCDM model has been implemented for the evaluation of different disinfection technologies for treated wastewater reuse, for this purpose two different groups of experts were involved in the process, MCDM and wastewater reuse experts. The selection of an ideal wastewater disinfection treatment for different uses (i.e., urban, agricultural, industrial, recreational and environmental) is associated with different criteria which should be evaluated. Fig. 1 summarises the steps to be carried out. In the first step, data were available from experts, and after a brain storming process, a set of six alternatives and four criteria with different levels of subcriteria were established. These criteria and alternatives were the same in the five uses. Five decision-making processes were proposed according to the different uses. In order to elaborate the decision matrix, each decision maker was provided with a survey (see Appendix A) in which a series of different questions were made on the behaviour of each alternative, in terms of each criterion and the importance given by the decision maker to each criterion. In the second step, the translation of these data to the TOPSIS method allowed us to obtain the best alternative. 3.1. The TOPSIS method The Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) approach is an MCDM method for the arrangement of preferences to an ideal solution by similarity [23]. The basic principle is that the chosen alternative must have the shortest distance to the positive ideal solution and the farthest distance to the negative ideal solution [24]. The mathematical procedure of TOPSIS is carried out in a series of steps, which can be seen in Hwang and Yoon [23]. It should be pointed out that within the model, and since several experts have been consulted, a decision process is carried out separately for each expert, with the aim of studying the individual choice, and also a group decision process, using the first
Wastewater reuse experts Wastewater reuse experts DATA ACQUISITION
MCDM experts MCDM experts Decision makers
DATA EVALUATION
MCDM experts
Brain storming
Problem identification Alternative and criteria selection Survey for decision makers Survey answer
TOPSIS methodology
Fig. 1. Optimal alternative identification for wastewater disinfection treatment by means of multicriteria decision making.
M.D. Go´mez-Lo´pez et al. / Journal of Cleaner Production 17 (2009) 1504–1511
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process (aggregating the information of the experts in origin) for the purpose of studying the final decision. Since 1993 there have been more than 150 references in international journals related to the application of TOPSIS; Shih et al. [25] provide a review of these applications, with a notable increase in recent years, above all with the implementation of fuzzy techniques. Among these, and focusing on the inclusion of environmental criteria in the methodology, the works of Chen et al. [26]; Janic [27]; Cheng et al. [28]; Montanari [13]; Li et al. [29]; Kandakoglu et al. [30]; Xuebin [31] should be emphasized, and only two papers (Janic [27]; Cheng et al. [28]) have been found which also consider social factors amongst others. If we focus on the choice of one method as opposed to another, there are numerous works which compare methodologies, although, the qualitative MCDM techniques generally used are focused on both TOPSIS and AHP. In Zeydan and Çolpan [32] and Shih et al. [25], an extensive study of these MCDM methods was made. They conclude that there are some advantages and disadvantages when compared with each other. But, mostly, they think that there are more advantages of TOPSIS than of AHP. Some of these main reasons are defined as follows:
disinfection of treated wastewater with maximum general profits. Level 1 shows the overall objective of the decision problem: the selection of a disinfection system for treated wastewater reuse. Level 2 consists of four main criteria, namely: water quality; capital cost; socio-economic; and environmental criteria, and their associated subcriteria. Level 3 consists of the wastewater treatment options. Water quality, as a technical parameter, and economic cost have been traditionally used as performance criteria for the optimisation of wastewater treatments [34]. But socio-economic and environmental aspects should not be isolated and taken into account for a better acceptance of the disinfection treatment used. As previously stated by different authors [19–21], public acceptability is a prerequisite for society to establish and promote water reuse projects. The four criteria chosen in our study were subdivided into different subcriteria, with the following optimisation tendency: (C1) Water quality criterion, with seven subcriteria: (C11) pH (pH units): between 6.5 and 7.5. (C12) Conductivity (mS/cm): to a minimum. (C13) Turbidity (NTU): to a minimum. (C14) BOD5 (% reduction): to a maximum. (C15) Chlorides (mg/L): to a minimum. (C16) Total coliforms (% reduction): to a maximum. (C17) Faecal coliforms (% reduction): to a maximum. (C2) Economic criterion, with two subcriteria: (C21) Disinfection system implementation: to a minimum. (C22) Maintenance cost: to a minimum. (C3) Social criterion, with one subcriteria: (C31) Enterprise image: to a maximum (means by which the enterprise chose the disinfection technique in its process production). (C4) Environmental criterion, with three subcriteria: (C41) Energy saving: to a maximum. (C42) Residues from disinfection processes: to a minimum. (C43) Emissions (gases and vapours): to a minimum.
TOPSIS method is intuitive, easy to understand and to implement. TOPSIS is simple and it yields a highly reliable preference order. TOPSIS logic is rational and understandable. The computation processes are straightforward. The concept permits the pursuit of best alternatives for each criterion depicted in a simple mathematical form. The importance weights are incorporated into the comparison procedures. It is a method which allows working with different scales and types of information (i.e., linguistic evaluations, experimental data). It should be highlighted that although the works cited finally select TOPSIS as the method to apply, the discussion made by Shih et al. [25] and Aragone´s-Beltra´n et al. [33] emphasizes that the method chosen depends to a great extent on the characteristics of the problem posed. 3.2. Evaluation of criteria and alternatives Fig. 2 illustrates a hierarchical system of wastewater disinfection alternatives’ selection. The overall objective is to achieve
Level 1 Problem
All the subcriteria have been valued qualitatively, according to qualitative labels, except criteria C12–C17, which were valued quantitatively. We have to point out that criterion C11, pH, although it is a criterion defined in a quantitative form, the optimum range of its use leads to defining a qualitative valuation of its weight. On the other hand, six different alternatives were chosen in relation to disinfection procedures:
Disinfection system alternative selection
Level 2 Criteria and subcriteria
C1 WATER QUALITY · pH · BOD5 · conductivity · chlorides · turbidity · TC, FC
C2 CAPITAL COST · system implementation · maintenance cost
C3 SOCIO-ECONOMICS · enterprise image
C4 ENVIRONMENTAL · energy saving · residues · emissions
Level 3 Alternatives
A1 UV1
A2 UV2
A3 UV + CL1
A4 UV + CL2
A5 CL1
A6 CL2
Fig. 2. The hierarchical structure of disinfection system alternative selection for treated wastewater reuse.
´ mez-Lo´pez et al. / Journal of Cleaner Production 17 (2009) 1504–1511 M.D. Go Table 1 Linguistic labels and weights used for the evaluation of different criteria and alternatives. Linguistic label type 1
Linguistic label type 2
Label
Description
Weights, wj
Label
Description
Weights, wj
vL L mL m mH H vH
Very low Low Medium low Medium Medium high High Very high
0 0.1 0.3 0.5 0.7 0.9 1
vG G mG m mB B vB
Very good Good Medium good Medium Medium bad Bad Very bad
0 0.1 0.3 0.5 0.7 0.9 1
(A1) Treated wastewater disinfected with 254 nm wavelength ultraviolet light for 5 min. (A2) Treated wastewater disinfected with 254 nm wavelength ultraviolet light for 10 min. (A3) Treated wastewater disinfected with chlorine ranging from 0.35 up to 0.70 mg/L and irradiated with 254 nm wavelength ultraviolet light for 5 min. (A4) Treated wastewater disinfected with chlorine ranging from 0.71 up to 0.87 mg/L and irradiated with 254 nm wavelength ultraviolet light for 5 min. (A5) Treated wastewater chlorinated with sodium hypochlorite to a final concentration of 4 mg/L for 30 min. (A6) Treated wastewater chlorinated with sodium hypochlorite to a final concentration of 6 mg/L for 30 min.
3.3. Elaboration of the survey This type of methods may require consulting experts who can enrich the decision with their judgments regarding the problem and this was provided by a survey. Three experts in the sector of wastewater reuse in the South East of Spain were consulted. Two of the three wastewater reuse experts were researchers in this subject, and were asked in the process of the problem definition and in the survey. Another wastewater reuse expert is a technical employee of a wastewater treatment plant and was only involved in
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the survey step. The survey was carried out at two levels: for the first level, concrete questions were used to obtain a ranking for criteria according to each expert, and at the second level, experts were asked to value each criterion for each alternative (see Appendix A). In this level, questions were designed for all qualitative criteria. Table 1 shows the qualitative labels used for the ratings of the alternatives according to the importance weighting of each subcriterion. Each label was associated to a weight in order to simplify further statistical analyses.
3.4. Data analysis Tables 2 and 3 present the data of the weights that each expert gave to the groups of criteria and subcriteria, respectively, as well as the results of the original weights obtained for the group after the primary aggregation. If we take into account the weights of the group we can see (Table 2) that the social criterion has the lowest weight in urban, agricultural and industrial uses. In urban and agricultural uses, a greater weight is given to the quality criteria, giving them an importance similar to the cost and environmental criteria. It should be highlighted that in industrial use the preferential criterion is that of cost, in contrast to what occurs in recreational use, perhaps due to the profitability associated to the use of water in these activities. In the ecological use the experts have attributed a similar weight to the different criteria. A somewhat homogeneous pattern can be seen in the weights that the experts have given to each group of criteria. For each of the uses we can highlight: For urban use of the water Experts 1 and 2 and the group give a greater weight to the quality criteria and a lower weight to the social criteria. However Expert 3 considers that the quality, costs and social criteria all have a similar weight, higher than that for the environmental criteria. For agricultural use of the water the three experts and the group coincide in giving the greatest importance to quality, although Expert 2 shares that importance with the environmental criteria. As for the lowest weight, they give it to the social criteria.
Table 2 Normalised weights for each group of criterion and water uses, according to experts (E1–E3) and group decision (G). Water uses
Experts and group
Criteria C1 quality criterion
C2 economic criterion
C3 social criterion
C4 environmental criterion
UU
E1 E2 E3 G
0.36 0.40 0.27 0.35
0.27 0.20 0.27 0.25
0.09 0.10 0.27 0.15
0.27 0.30 0.18 0.25
AU
E1 E2 E3 G
0.33 0.31 0.33 0.32
0.25 0.23 0.25 0.24
0.17 0.15 0.17 0.16
0.25 0.31 0.25 0.27
IU
E1 E2 E3 G
0.25 0.29 0.25 0.26
0.33 0.29 0.33 0.32
0.17 0.21 0.17 0.18
0.25 0.21 0.25 0.24
RU
E1 E2 E3 G
0.31 0.31 0.29 0.30
0.15 0.15 0.21 0.17
0.23 0.23 0.29 0.25
0.31 0.31 0.21 0.28
EU
E1 E2 E3 G
0.29 0.36 0.29 0.31
0.21 0.18 0.21 0.20
0.21 0.18 0.29 0.23
0.29 0.27 0.21 0.26
UU: urban use; AU: agricultural use; IU: industrial use; RU: recreational use; and EU: environmental use.
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Table 3 Normalised weights for each subcriterion and water uses, according to experts (E1–E3) and group decision (G). Water uses
Experts and group
Subcriteria C11
C12
C13
C14
C15
C16
C17
C21
C22
C31
C41
C42
C43
UU
E1 E2 E3 G
0.08 0.03 0.04 0.05
0.00 0.05 0.02 0.02
0.09 0.07 0.06 0.07
0.03 0.06 0.03 0.04
0.00 0.05 0.00 0.02
0.09 0.07 0.06 0.07
0.09 0.07 0.06 0.07
0.13 0.09 0.11 0.11
0.14 0.11 0.16 0.14
0.09 0.10 0.27 0.15
0.19 0.07 0.11 0.13
0.06 0.10 0.06 0.07
0.02 0.13 0.01 0.05
AU
E1 E2 E3 G
0.05 0.04 0.02 0.04
0.05 0.05 0.04 0.05
0.06 0.06 0.06 0.06
0.01 0.02 0.03 0.02
0.04 0.03 0.06 0.04
0.06 0.06 0.06 0.06
0.06 0.06 0.06 0.06
0.12 0.11 0.13 0.12
0.13 0.12 0.12 0.12
0.17 0.15 0.17 0.16
0.12 0.15 0.09 0.12
0.07 0.08 0.13 0.09
0.07 0.08 0.04 0.06
IU
E1 E2 E3 G
0.05 0.05 0.03 0.04
0.04 0.04 0.03 0.03
0.05 0.05 0.05 0.05
0.01 0.03 0.02 0.02
0.03 0.02 0.02 0.02
0.05 0.05 0.05 0.05
0.05 0.05 0.05 0.05
0.17 0.14 0.18 0.16
0.17 0.14 0.16 0.16
0.17 0.21 0.17 0.18
0.13 0.09 0.10 0.11
0.07 0.05 0.09 0.07
0.04 0.07 0.05 0.06
RU
E1 E2 E3 G
0.03 0.03 0.04 0.03
0.05 0.04 0.01 0.03
0.06 0.06 0.07 0.06
0.03 0.05 0.01 0.03
0.03 0.02 0.00 0.02
0.06 0.06 0.08 0.06
0.06 0.06 0.08 0.06
0.10 0.08 0.12 0.10
0.05 0.08 0.09 0.08
0.23 0.23 0.29 0.25
0.10 0.06 0.10 0.09
0.10 0.12 0.07 0.10
0.10 0.12 0.05 0.09
EU
E1 E2 E3 G
0.04 0.04 0.03 0.04
0.02 0.04 0.02 0.03
0.05 0.07 0.05 0.06
0.04 0.05 0.06 0.05
0.02 0.02 0.01 0.02
0.05 0.07 0.05 0.06
0.05 0.07 0.06 0.06
0.09 0.09 0.14 0.11
0.12 0.09 0.08 0.10
0.21 0.18 0.29 0.23
0.10 0.09 0.11 0.10
0.10 0.09 0.08 0.09
0.10 0.09 0.03 0.07
UU: urban use; AU: agricultural use; IU: industrial use; RU: recreational use; EU: environmental use.
In industrial use the greatest weight is given in all cases to the quality criteria, with Expert 2 sharing this weight with the quality criteria. The lowest weight is given to the social criteria and Expert 2 also considers the same weight for the environmental criteria. The recreational use of the water presents greater disparity between the experts. Experts 1 and 2 give a greater weight to the quality and environmental criteria and Expert 3 to the quality and social criteria. The group gives priority only to quality criteria. All experts coincide in giving a lower weight to the costs criteria, which Expert 3 shares with the environmental criteria. It is with the environmental use where the greatest discrepancy exists. All the experts coincide in giving priority to the quality criteria, but Expert 1 shares it with the environmental criteria and Expert 3 with the social criteria. Likewise all give the lowest weight to the costs criteria, but Experts 1 and 2 share it with the social criteria, and Expert 3 with the environmental criteria. Table 4 presents the data for the quantitative quality criteria (except the pH), obtained analytically for each of the alternatives proposed. Table 5 presents the data of the criteria that do not have a quantitative valuation, and the experts have valued each of the alternatives with the qualitative labels defined in Table 1. Fig. 3 presents a graphic representation of the values of relative proximity (R), obtained for each of the alternatives for each of the uses considered. It can be observed that in the urban, agricultural and industrial uses, the best disinfection method chosen is Alternative 5 (chlorination at 4 ppm). For recreational and environmental uses Alternative 1 has been obtained (UV, 5 min) as the best
disinfection option. In both cases the tendencies of the curves are similar, which indicates a similar pattern in the decision. If we centre our attention on the values obtained in the group decision, in uses such as urban, agricultural and industrial the choice of a chlorination system seems to be due to the large weight conferred on the costs and environmental criteria. In this sense, although the UV system provides good quality water, its cost and energy consumption are greater than those for chlorination. However, for recreational and environmental uses, the lowest weight has been given to the cost criteria, a fact which has led to a change in the final decision with regard to the other uses and, therefore, to choose the UV method as the best. It should be highlighted that in cases in which water is an important cost within the activity, such as for agricultural and industrial uses, there is little dispersion between values obtained by each of the experts, and thus for the group decision. In these cases the cost of the disinfection method is decisive, therefore, the cheapest (chlorination) is the one chosen by all the experts. On the other hand, as can be appreciated in the urban, recreational and environmental uses, a greater dispersion exists between the values obtained from each expert. We must point out that these uses are associated to the service sector or to the administration, in which both the social aspects as well as the environmental aspects have a greater weight than the costs, although it should be mentioned that in the recreational and environment uses, the dispersion is marked above all by Expert 3 who gives the costs and environmental criteria similar and high weights. If we analyse the decisions of this expert,
Table 4 Values of water quality subcriteria for each disinfection alternative. Subcriteria
C12, C13, C14, C15, C16, C17,
conductivity (mS/cm) turbidity (NTU) BOD5 (% reduction) chlorides (mg/L) total coliforms (% reduction) faecal coliforms (% reduction)
Alternatives A1
A2
A3
A4
A5
A6
2647.0 1.3 49.7 533.8 96.2 97.8
2592.0 1.8 44.4 522.3 99.4 100.0
2458.0 2.0 25.0 463.0 94.5 95.0
2490.0 2.8 27.1 455.2 91.4 95.0
2296.0 5.7 77.5 309.4 99.6 99.2
2210.0 4.9 87.0 299.3 100.0 82.6
´ mez-Lo´pez et al. / Journal of Cleaner Production 17 (2009) 1504–1511 M.D. Go
we can see that he does not suggest much discrimination between the different disinfection methods for the different uses. At this point in the analysis of the data obtained it is important to see how social aspects, such as the rejection of chlorination by the users of golf courses, because of the chlorine smell, leads the managers of said golf courses to reject these methods, to preserve the company’s image and, therefore, the user’s acceptance. Likewise, if we focus on the environmental aspects of all the sustainability programmes and the compliance with the Kyoto protocol, they advocate greater energy efficiency, so from that point of view the UV method would be a more viable alternative if it were possible to power it by means of renewable energy, thus solving the problem. As can be seen, social and environmental aspects are becoming increasingly important, which coincides with Panebianco and PahlWostl [19], Menegaki et al. [20] and Urkiaga et al. [21], who affirm the need for social and environmental implementation in this type of decisions. Similarly, decision making in this field would be enriched by consulting agents from all the fields implicated (businessmen, users and managers). With regard to methodological aspects, we can say that the implementation of the group decision algorithms has enriched the decision. As an example of this we see that if the decision had been taken by Expert 3 alone, the chosen method would have been chlorination for all the uses, yet this is unviable in recreational uses for the social aspects previously commented. But the opinion of this expert has been considered and is reflected in the final group decision in the same proportion as the rest. In relation to the application of the TOPSIS method we have been able to check that the inclusion of qualitative labels has
Table 5 Linguistic variables for each alternative and subcriteria according to three experts. Subcriteria
Alternatives A1
A2
A3
A4
A5
A6
Expert 1 C11 pH C21 disinfection system implementations C22 maintenance cost C31 enterprise image C41 energy saving C42 residues C43 emissions
vG m m mG L L L
G mH mH mG L L L
G mH H M m mL m
m H vH mB m m mH
B mL mL B H mH H
mB m mL B mH H H
Expert 2 C11 pH C21 disinfection system implementations C22 maintenance cost C31 enterprise image C41 energy saving C42 residues C43 emissions
G mL mL G L vL L
G M m G L vL L
G mH mH mG m L mL
mG H H m mL mL m
mB L L mB H m mH
m mL mL mB mH mH H
Expert 3 C11 pH C21 disinfection system implementations C22 maintenance cost C31 enterprise image C41 energy saving C42 residues C43 emissions
G H H vG mH vL vL
G H vH vG m vL vL
vG vH vH G L mL L
mG vH vH G vL mL L
mB mH M mG m H L
mG mH H mG mL H L
0.8
0.8
0.6
0.6
0.4
0.4 0.2
0.2
AGRICULTURAL USE
URBAN USE 0
A1
A2
A3
A4
A5
0.0
A6
0.8
0.8
0.6
0.6
0.4
0.4
A1
A2
A3
A4
A5
A6
0.2
0.2
RECREATIONAL USE
INDUSTRIAL USE 0
1509
A1
A2
A3
A4
A5
0
A6
A1
A2
A3
A4
A5
A6
0.8 0.6 0.4 0.2 ENVIRONMENTAL USE 0 A1
A2
A3
A4
A5
A6
Fig. 3. Results of the relative proximity, R, for Expert 1 (thin line), Expert 2 (dashed line), Expert 3 (dotted line), and Group (thick line) for the selection of disinfection system for treated wastewater reuse in five different uses.
M.D. Go´mez-Lo´pez et al. / Journal of Cleaner Production 17 (2009) 1504–1511
1510
allowed the experts to value aspects which are difficult to quantify and, as we can see, the decision has benefited to a great extent.
B. Value the importance of each subcriteria of the group ‘‘water quality’’, in the election of treated water for agricultural use, using the linguistic label type 1.
4. Conclusions In our problem, qualitative and quantitative information was available as this was the type of data provided by the experts. We, therefore, decided to approach the problem using the widely accepted TOPSIS process for dealing with complex decision problems. In terms of the results obtained the best disinfection technique for treated wastewater chosen for urban, agricultural and industrial uses was the technique of chlorination 4 ppm, because a large weight has been given to the costs and environmental criteria. Conversely, for recreational and environmental uses, in which less importance is given to the cost, and the weight for environmental factors has been increased, the alternative with UV light was chosen. We can conclude that in this type of decisions, economic criteria continue to dominate, above all when we refer to business uses in which the water is an input in the company. However, when the social and political cost is given a greater importance such as in the case of ecological and recreational uses, the most costly method (ultraviolet), but which has fewer problems in terms of residual contamination in comparison with the chlorination methods (chlorine compounds and smells), is that which prevails. In terms of environmental factors, of all the methods proposed, it is only the energy consumption of the UV methods which has led the experts to opt for chlorination methods, which could be solved with the introduction of renewable energy resources. As for future lines to follow, we propose the use of fuzzy numbers in the modelling of the linguistic labels, being able to compare both methodologies, and the study and comparison of the different aggregations to determine how they affect the final and partial decision for each expert.
C11, pH: vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
C12, CE:
C13, Turbidity:
C14, DBO5:
C15, Chlorides:
C16, CT:
C17, CF:
2. Evaluation of the alternatives for each qualitative criterion A. With respect to criterion C11 (pH), value the different alternatives, using linguistic label type 2:
A1 (UV1) vG
G
mG
m
mB
B
vB
vG
G
mG
m
mB
B
vB
vG
G
mG
m
mB
B
vB
vG
G
mG
m
mB
B
vB
vG
G
mG
m
mB
B
vB
vG
G
mG
m
mB
B
vB
A2 (UV2)
A3 (UV þ CL1)
Acknowledgements We are indebted to the anonymous referees for their critical review and suggestions that enabled us to obtain this paper. This research was financed by DGICYT (Project TIN2008 – 06872 – C0404) and the Fundacio´n Se´neca (Project 8824/PPC/08).
A4 (UV þ CL2)
A5 (CL_4 ppm)
A6 (CL_6 ppm)
Appendix A. Questionnaire TOPSIS Example of questionnaire (agricultural use; criterion: pH):
References
1. Importance of the criteria. A. Write the degree of importance that you believe that each of the criteria should have when selecting the best disinfection technique for treated wastewater for agricultural use, using the linguistic label type 1.
C1, water quality: vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
vL
L
mL
m
mH
H
vH
C2, costs:
C3, socio-economics:
C4, environmental:
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