**2. Comparative analysis of municipal solid waste systems: Cracow case study**

There is a need to develop, master, and implement a simple, but reliable tool that would help the decision makers select the Municipal Solid Waste Management (MSWM) system. There are number of mathematical municipal solid waste models that might be used to solve the problem, where the objective function is the cost of waste disposal. The environmental elements (the recycling schemes) have appeared in the models beginning in the 1980s [6, 7]. Also there is a group of models, which include the environmental factors in the form of constrains of the economic models [8]. Some of the models are based on the concept of Life Cycle Analysis (LCA) while other focus only on different environmental elements such as traffic or noise [8] or CO2 emissions from waste delivering vehicles [9]. The review of different models can be found in Refs. [10–12], but so far no model fits fully the decision makers' expectations.

Probably the group of models which, in the best way, reflects the idea of sustainable devel‐ opment is a group of Life Cycle Analysis (LCA) models. The examples of such models are the US-EPA [13], WISARD [14], MIMES/Waste [15], ORWARE [16], ISWM tool Canada, LCA-IWM [17] and Integrated Waste Model (IWM) [14]. IWM (Integrated Waste Model) was first published in 1995 as an IWM-1 (in form of an Excel spreadsheet). IWM-2 was developed to improve certain aspects of IWM-1 and to make the model more global by including new set of data. IWM-1 was rather a European development [18]. IWM-2 was published in more userfriendly SQL-Database environment, which unfortunately is less transparent hence less useful for in-depth analysis. The authors chose IWM-1 model considering it to be transparent, flexible and simple.

The results of IWM-1 model are numerous and detailed, which makes them not convenient for the inexperienced decision makers, who are interested in the clear and simple answer which MSWM system is the best. To help with this issue, the authors integrated IWM-1 results using the LCA impact categories and later, implementing simple, but sound multiobjective AHP method. Described methodology allowed to compare two MSWM systems for the city of Cracow, Poland (population: 742,000).

#### **2.1. Description of the compared MSWM systems**

The authors compared two MSWM systems. The real system applied in Cracow, Poland, in year 2001, based on the landfill as the main option of waste disposal (called "system A"), and the hypothetical system based on the assumption that the waste recycling is improved and the main way of rest-waste disposal is incineration. This was the planned system for Cracow at that time. In the analysis, this system is called "system B." The case study is based on real data. The information regarding waste and systems' description was cited after Kopacz [19].

The key data for the MSWM analysis are the amount and composition of waste. Waste input data, the same for system A and system B, divided into categories required by the IWM-1 model presents (**Table 1**).


**Table 1.** Composition of different parts of Municipal Solid Waste in analyzed Cracow case.

In system A, landfilling is the main disposal method and there are also 150 recycling material banks for metal, polyethylene terephthalate (PET) bottles, paper and glass. Additionally to the system of recycling banks, there is a system of "bring and earn" collection points and the composting facility with the throughput of 6000 tons per year. A number of charity organiza‐ tions run the system of collection points for the textile waste.

In system B, the annual throughput of 200,000 tons of waste is assumed for the incinerator. The incinerator generates only electricity with the 20% efficiency. Contrary to the real Cracow plans, the waste heat recovery is not modeled because IWM-1 model does not have such an option. This blurs the final results, but in reality the incinerator generates the heat for the municipal district heating system, substituting the waste heat from the power plants. If the city decides to utilize the heat from the incinerator, the power plants have the problem of "what to do" with their by-product, hence the environmental benefits of incinerator's waste heat utilization are problematic. Additionally, in system B, the number of collection banks is increased up to 450, and thanks to the increase of public awareness, the amount of recyclables collected in each bank is increased by 25%. System B assumes the development of the recycling program. Material Recovery Facility ready to handle 20,000 tons of recyclables along with two composting facilities for 6000 and 9000 tons of green waste is commissioned. Also, in some parts of the town, the "wet" and "dry" waste collection systems are introduced.

As a result of those changes, the amount and quality of waste disposed at the landfill change significantly. The exact results, for both systems, calculated using IWM-1 model are presented in **Table 2**. In system B, the amount of waste disposed at the landfill is reduced by five times (from 247 ktons in system A to 49 ktons in system B). Also in system B, the diversion from


landfill is eight times higher than in system A, and the amount of recyclables is increased more than twice. The economic and environmental results of the two systems are also very different.

The key data for the MSWM analysis are the amount and composition of waste. Waste input data, the same for system A and system B, divided into categories required by the IWM-1

169,346 19.9 7.8 2.9 14.4 6.1 36.2 12.7

107,806 45.0 5.0 4.1 12.0 1.0 30.0 2.9

**Table 1.** Composition of different parts of Municipal Solid Waste in analyzed Cracow case.

58 Applications and Theory of Analytic Hierarchy Process - Decision Making for Strategic Decisions

tions run the system of collection points for the textile waste.

Ferrous Non-Fe Film Rigid 65 35 44 56

Ferrous Non-Fe Film Rigid 60 40 80 20

In system A, landfilling is the main disposal method and there are also 150 recycling material banks for metal, polyethylene terephthalate (PET) bottles, paper and glass. Additionally to the system of recycling banks, there is a system of "bring and earn" collection points and the composting facility with the throughput of 6000 tons per year. A number of charity organiza‐

In system B, the annual throughput of 200,000 tons of waste is assumed for the incinerator. The incinerator generates only electricity with the 20% efficiency. Contrary to the real Cracow plans, the waste heat recovery is not modeled because IWM-1 model does not have such an option. This blurs the final results, but in reality the incinerator generates the heat for the municipal district heating system, substituting the waste heat from the power plants. If the city decides to utilize the heat from the incinerator, the power plants have the problem of "what to do" with their by-product, hence the environmental benefits of incinerator's waste heat utilization are problematic. Additionally, in system B, the number of collection banks is increased up to 450, and thanks to the increase of public awareness, the amount of recyclables collected in each bank is increased by 25%. System B assumes the development of the recycling program. Material Recovery Facility ready to handle 20,000 tons of recyclables along with two composting facilities for 6000 and 9000 tons of green waste is commissioned. Also, in some

parts of the town, the "wet" and "dry" waste collection systems are introduced.

As a result of those changes, the amount and quality of waste disposed at the landfill change significantly. The exact results, for both systems, calculated using IWM-1 model are presented in **Table 2**. In system B, the amount of waste disposed at the landfill is reduced by five times (from 247 ktons in system A to 49 ktons in system B). Also in system B, the diversion from

**Paper Glass Metal Plastic Textiles Organics Other**

**Paper Glass Metal Plastic Textiles Organics Other**

model presents (**Table 1**).

**Amount (t/year) Household waste composition (wt.%)**

**Amount (t/year) Commercial waste composition (wt.%)**

**Table 2.** Streams of waste and recovered materials for analyzed scenarios.

#### **2.2. Integration method of the IWM-1 results**

The IWM-1 model delivers results estimating the air emissions of 22 compounds and emission of 23 compounds into water. Additionally, the basic statistical and economical data about the systems' performance are also presented. This is a lot of detailed information not useful for the decision makers and has to be combined before implementation. The proposed integration method is based on impact assessment of LCA. To calculate these indicators, the authors used the methodology described in detail in Refs. [20–22]. The general assumption was to estimate the maximum possible number of LCA categories, which could be calculated based on the IWM-1 results. **Table 3** presents the list of the selected categories.


**Table 3.** Selected categories of the life cycle impact assessment.

Indicators for the different impact categories were selected based on the literature [23]. Unfortunately, not all recommended impact categories can be directly calculated from the IWM-1 result table. The obtained results are presented in **Table 4**. More detailed environmental analysis of the results can be found in reference [3].

The results show that, based on landfilling, system A is superior when the following criteria were analyzed: abiotic depletion, human toxicity, freshwater aquatic ecotoxicity, terrestrial ecotoxicity, acidification and eutrophication. The second scenario, system B, with advanced waste sorting and incineration, turned out to be better in categories of energy consumption, climate change, photochemical smog creation and odor creation.


**Table 4.** Results of the Integrated Waste Management model (IWM-1) analysis.

systems' performance are also presented. This is a lot of detailed information not useful for the decision makers and has to be combined before implementation. The proposed integration method is based on impact assessment of LCA. To calculate these indicators, the authors used the methodology described in detail in Refs. [20–22]. The general assumption was to estimate the maximum possible number of LCA categories, which could be calculated based on the

IWM-1 results. **Table 3** presents the list of the selected categories.

60 Applications and Theory of Analytic Hierarchy Process - Decision Making for Strategic Decisions

**Baseline categories**

ecotoxicity

Ecotoxicity: fresh water aquatic

**Other impact categories**

**Impact categories Characterization factor Unit**

(FAETP 100)

Acidification Acidification potential (AP) kg (SO2 eq.)

Stratospheric ozone depletion Ozone depletion potential (ODP steady state) kg (CFC-11 eq.)

Eutrophication Eutrophication potential (EP) kg (PO4

Land competition Land use m2

Odor malodorous air Reciprocal of odor threshold value (1/OTV) m3

**Table 3.** Selected categories of the life cycle impact assessment.

analysis of the results can be found in reference [3].

climate change, photochemical smog creation and odor creation.

Photo-oxidant formation Photochemical ozone creation potential (POCP)

Depletion of abiotic resources Abiotic depletion potential (ADP) kg (antimony eq.)

Climate change Global warming potential (GWP 100) kg (carbon dioxide eq.)

Human toxicity Human toxicity potential (HTP 100) kg (1,4-dichlorobenzene eq.)

Freshwater aquatic ecotoxicity potential

Ecotoxicity: terrestrial ecotoxicity Terrestrial ecotoxicity potential (TETP 100) kg (1,4-dichlorobenzene eq.)

Indicators for the different impact categories were selected based on the literature [23]. Unfortunately, not all recommended impact categories can be directly calculated from the IWM-1 result table. The obtained results are presented in **Table 4**. More detailed environmental

The results show that, based on landfilling, system A is superior when the following criteria were analyzed: abiotic depletion, human toxicity, freshwater aquatic ecotoxicity, terrestrial ecotoxicity, acidification and eutrophication. The second scenario, system B, with advanced waste sorting and incineration, turned out to be better in categories of energy consumption,

kg (1,4-dichlorobenzene eq.)

kg (ethylene eq.)

3− eq.)

year

(air)

The obtained aggregated results still do not give a straight answer about the superiority of one specific system. There are many categories, measured by different units, and the analyzed systems fulfill various criteria in varying degree. Some of the categories are measured using the same units, but even in this case, the comparison between the different categories is impossible. For example, human toxicity, freshwater aquatic ecotoxicity and terrestrial ecotoxicity are all measured by 1,4-dichlorobenzene eq. in 100 years perspective. Even in this case, comparison among these categories is possible only when using the impact ratios.

The final evaluation of the analyzed scenarios was made using the AHP method.

#### **2.3. Multicriteria analysis of the Cracow MSW systems**

The authors used Analytic Hierarchy Process (AHP) as a method of further analysis with software prepared by Helsinki University of Technology [24]. Prepared hierarchy of criteria and assigned ratings are presented in **Figure 1**. Criteria were developed based on IWM-1 analysis and the ratings were assigned arbitrarily by the authors based on their experience. The goal of the model was to find the most sustainable solution and the selected hierarchy of criteria reflected this approach. The authors represented the whole spectrum of expertise in environmental engineering, environmental management and waste handling. The final ratings were reached at some point in the joined discussion.

**Figure 2** presents the final results of the analysis. The graph shows that system B is better evaluated than system A. The overall score of system A is 0.362 and system B is 0.638. This means that system B is almost two times better than system A and, in other words, meets all the expectations in 64%. System B is superior to system A, thanks to significantly better environmental performance. The more detailed comparison of the environmental performance of the two MSW systems is presented in **Figure 3**. System B is more friendly toward all three components of the environment: water, soil and air. It is superior to system A in all subcate‐ gories of air and water criteria. The environmental superiority of system B in subcategory "soil protection" is not so dominant. System B is better only in "land use" sub-criterion, but because this sub-criterion is so important, the total evaluation of system B in subcategory of "soil protection" is better than the performance of system A.

**Figure 1.** Objective hierarchy and ratings for the Cracow analysis.

**Figure 2.** Results of the AHP analysis for the two Cracow MSWM scenarios (criteria 1).

Application of the AHP Method in Environmental Engineering: Three Case Studies http://dx.doi.org/10.5772/63990 63

**Figure 3.** Results of the AHP analysis for the two Cracow MSWM scenarios (criteria 2).

A more detailed analysis of the obtained results allow to draw conclusion about how much the environmental performance of system B is increased by substituting the landfilling with the incineration and extension of the waste collection system. Also, the local and global environmental impacts can be distinguished [3].

The AHP analysis gives very clear answer that system B is superior to system A. Such a simple answer is expected by the decision makers, but the AHP analysis combined with the IWM-1 model also gives more detailed results justifying its overall score which can be useful in further analysis.

### **2.4. Sensitivity analysis and conclusions**

of the two MSW systems is presented in **Figure 3**. System B is more friendly toward all three components of the environment: water, soil and air. It is superior to system A in all subcate‐ gories of air and water criteria. The environmental superiority of system B in subcategory "soil protection" is not so dominant. System B is better only in "land use" sub-criterion, but because this sub-criterion is so important, the total evaluation of system B in subcategory of "soil

protection" is better than the performance of system A.

62 Applications and Theory of Analytic Hierarchy Process - Decision Making for Strategic Decisions

**Figure 1.** Objective hierarchy and ratings for the Cracow analysis.

**Figure 2.** Results of the AHP analysis for the two Cracow MSWM scenarios (criteria 1).

The sensitivity analysis is trying to give answer to the question: how much the obtained results change if there is a change in the input values? The final outcome of the AHP analysis depends on the assumed hierarchy of goals, on the assigned relative weights of the goals and on the performance of the analyzed alternatives, but the performance of the analyzed systems has far more limited impact on the final result. If only two options are compared, it is important if the performance in each category is superior, but not the level of this superiority.

The reason why system B performs better than system A is its significantly better performance in the category "impact on the natural environment." The performance in the AHP analysis is a product of relative weight of the category and estimated physical performance. The relative weight of this category was assumed to be equal to 0.67, but the sensitivity analysis indicates that if this weight is 0.48, both analyzed scenarios will be estimated as equally good (**Fig‐ ure 4**). If the weight for the natural environment equals 0.48, the other two weights should be in the same proportion to each other, and have the values 0.347 for the impact on the manmade environment and 0.173 for the economic performance. Also, the analysis shows that if the importance of the economic criterion increases from the present ratio 0.11 to 0.30, this will result in making the two analyzed systems equally good (**Figure 5**). The threefold increase of the economic criterion weight is not likely, but possible. The increased rating of the "manmade environment" from the present 0.22 to 0.47 will result in equalizing of the two systems performance. To change the ranks of analyzed scenarios, the weights have to change signifi‐ cantly. It is up to the decision makers to decide whether such a significant change of weights is possible.

**Figure 4.** Sensitivity analysis: the relative weight of the category "impact on the natural environment."

**Figure 5.** Sensitivity analysis: the relative weight of the category "economic performance."

Changing the weights of all components of the environment (water, air and soil) will change the final evaluation score, but will not change the rating of the systems' impact on the natural environment since all ratings' impact on the natural environment of the system B is better than those of the system A.

importance of the economic criterion increases from the present ratio 0.11 to 0.30, this will result in making the two analyzed systems equally good (**Figure 5**). The threefold increase of the economic criterion weight is not likely, but possible. The increased rating of the "manmade environment" from the present 0.22 to 0.47 will result in equalizing of the two systems performance. To change the ranks of analyzed scenarios, the weights have to change signifi‐ cantly. It is up to the decision makers to decide whether such a significant change of weights

64 Applications and Theory of Analytic Hierarchy Process - Decision Making for Strategic Decisions

**Figure 4.** Sensitivity analysis: the relative weight of the category "impact on the natural environment."

**Figure 5.** Sensitivity analysis: the relative weight of the category "economic performance."

is possible.

No change of water or air criteria ratings can change the two systems' performance in the subcategory "impact on water" and "impact on air" (**Figure 6**). In subcategory "impact on soil," changing the ratings of all subcategories can result in the switch of superiority of the two systems in the category "impact on soil," but the changes have to be substantial (**Figure 7**).

**Figure 6.** Sensitivity analysis: the relative weight of the subcategory "impact on water."

**Figure 7.** Sensitivity analysis: the relative weight of the subcategory "impact on soil."

Generally, the sensitivity analysis shows that the biggest impact on the final score have the weights assigned at the top level of hierarchy (natural environment, manmade environment, economic impact) and the weights assigned to category "impact on soil."

The AHP method combined with the IWM-1 model allowed the broad and thorough compar‐ ison of two different waste disposal systems. In this case, the system based on incineration looks like a better solution and shows superior environmental performance. This good environmental performance is the result of "avoided emissions," thanks to material and energy recovery. The economic performance of the traditional landfilling system is better than the performance of system based on incineration. The overall evaluation shows that the city should build the incinerator and implement advanced recycling programs. These conclusions are in tune with the common trends and regulations. Thanks to the integration of the AHP and IWM-1, the obtained results are clear and detailed simultaneously. This is a quality very much sought by the decision makers.
