Technology selection for infectious medical waste treatment using the analytic hierarchy process

ABSTRACT

The overall objective of this paper was to evaluate five different technologies used for infectious medical waste treatment and select the optimum one by means of multicriteria analysis. Steam disinfection was selected as the optimum treatment technology, among others using incineration, microwave disinfection, chemical disinfection with sodium hypochlorite, and reverse polymerization with microwaves. The evaluation was based on four groups of criteria, specifically, environmental, economic, technical, and social criteria, using the analytic hierarchy process. Selection among four commercial systems using steam disinfection was not possible, because it required additional site-specific criteria, e.g., loading capacity and requirements of local regulations.

Implications: The paper can help health care facilities to select the system for infectious waste treatment that best fits their needs. It was concluded that steam disinfection was the optimum technology, using environmental, economic, technical, and social criteria.

Introduction

The system of hazardous medical waste (HMW) treatment is the heart of any higher-order management system. This is where the HMW will undergo the appropriate physical, chemical, biological, or thermal processes or combination thereof, in order to decrease their volume and eliminate or reduce their hazardous characteristics. Treatment technologies can be classified into (1) low-heat technologies (e.g., autoclaves, retorts, and microwave treatment), (2) medium-heat technologies (e.g., reverse polymerization), and (3) high-heat technologies (e.g., excess air incineration, pyrolytic incineration). Low-heat technologies can be used for treating infectious waste, but are inappropriate for chemical and pharmaceutical waste and anatomical parts without previous mechanical treatment (e.g., shredding). Medium-heat technologies can treat the same waste as low-heat technologies and also pathological waste including anatomical parts. High-heat technologies are appropriate for all kinds of health care waste, including chemotherapy waste, solvents, and chemical and pharmaceutical waste (Diaz et al., 2005; Health Care Without Harm [HCWH], 2001). Due to potential emission of persistent organic and inorganic pollutants by incinerators, Health Care Without Harm recommends the use of nonincineration technologies (HCWH, 2001, 2004).

In most cases, hospitals do not treat their own waste in house, but they outsource medical waste treatment and disposal to private companies. This is a way to reduce cost for construction, operation, and maintenance of the treatment facility inside the hospital. It is the responsibility of the private company to comply with the regulations concerning environmental and public health protection. There are a large number of companies offering treatment technologies, and the hospitals have to make a selection for the most appropriate one for their waste. Some key factors to consider for technology selection include loading capacity, waste type, microbial inactivation, environmental emissions and residues, compliance with regulations, size of the system and space requirements, reduction of waste mass and volume, degree of automation, technical reliability, health and safety considerations, and cost (HCWH, 2001). Multicriteria assessment methods have been used to select the most appropriate company or treatment technology for infectious medical waste (e.g., Karagiannidis et al., 2010; Dursun et al., 2011; Ho, 2011; Ozkan, 2013), which is a subcategory of HMW. Evaluated technologies included steam disinfection, microwave disinfection, incineration, and sanitary landfilling. However, two important technologies, chemical disinfection and reverse polymerization, were not evaluated, and the criteria used by different authors were not the same. Thus, there is a need to evaluate all five treatment technologies, using the same criteria.

The objective of this paper was to evaluate five different treatment technologies (incineration, steam disinfection, microwave disinfection, reverse polymerization, and chemical disinfection) used for infectious medical waste treatment and select the optimum one by means of multicriteria analysis. The evaluation was based on four groups of main criteria, specifically, environmental, economic, technical, and social criteria. Several subcriteria were included in each main criterion. The characteristics of several commercial systems were also considered in this technology evaluation. Decision makers are the hospital administrators, who can use this paper to select the treatment system that best fits their needs.

Technology description

Detailed technology description with their advantages and shortcomings has been presented in previous studies (HCWH, 2001; Diaz et al., 2005; Yang et al., 2009; Ozkan, 2013). Therefore, only a short description of the technology and the respective commercial systems is presented below. The information for the commercial systems was provided by the manufacturers and/or published in the respective Web pages. Although many manufacturers were conducted, only nine provided the requested information and price quotes. These nine commercial treatment systems were coded with letters A–I, to maintain anonymity. Two of the commercial systems compared use incineration, four use steam disinfection, one microwave disinfection, one chemical disinfection with sodium hypochlorite, and one reverse polymerization with microwaves. The common characteristics of the nine treatment systems, as claimed by their manufacturers, are compared in Table 1.

Table 1. Comparison of common characteristics of the nine commercial treatment systems, on the basis of information provided by the manufacturers.

Commercial Treatment System	Pathogen Inactivation	Volume Reduction	Treatment Temperature, °C	Treatment Time	Mode of Operation
A (Incineration)	100%	90–95%	Primary chamber: Controlled air at 800–900 °C	4–6 hr batch cycle	Batch/continuous feed
			Secondary chamber at 900–1200 °C	Residence time for combustion gases: 2 sec
B (Incineration)	100%	90–95%	Primary chamber: Starved air at 820 °C	Residence time for combustion gases: 2 sec	Batch/continuous feed
			Secondary chamber at 760–1100 °C
C (Steam disinfection)	8log10	80% with shredding	138 °C at 3.8 bar	40–60 min per cycle	Batch
D (Steam disinfection)	6log10	85% with shredding	121 °C for 30 min	15–30 min contact time	Batch
			132 °C for 15 min
E (Steam disinfection)	6log10	70% with shredding	135 °C at 75 psi	60 min contact time	Batch
F (Steam disinfection)	6log10	40–80% depending on shredding	138–140 °C at 38 psig	30 min contact time	Batch
G (Microwave disinfection)	7log10	80% with shredding	95–100 °C	≥30 min contact time	Batch
H (Reverse polymerization)	6log10	80% with shredding	180–370 °C	50–80 min per cycle	Batch
I (Chemical disinfection)	6log10	Not available	95–155 °C	25 min exposure	Batch

Incineration

It is a high-heat treatment technology used to convert waste materials in a noncombustible residue (ash) and exhaust gases. According to the Greek regulations (CMD, 2012), it is suitable for treatment of all types of hazardous health care waste, reducing significantly their volume and weight. On the other hand, incineration produces toxic air pollutants, including chlorinated dibenzodioxins and dibenzofurans. The description of the two commercial incineration treatment systems (A, B) follows.

The treatment system A is a multiple-chamber, controlled-air thermal oxidizer, with intermittent or continuous feed capacity. Air pollution control is provided by oxidizing exhaust gases in a baffled secondary combustion chamber. Temperature can be maintained with auxiliary fuel. The company claims 100% microbial destruction and 90% mass reduction. However, it may produce hazardous air contaminants (dioxins, furans, etc.), which are emitted into the atmosphere. There is a high degree of automation and flexibility with respect to waste capacity, but the public acceptance of an incineration system in Greece is potentially limited, compared with other treatment technologies.

The treatment system B uses the combustion technology for medical waste treatment. It is a controlled-air, multiple-chamber thermal oxidation system with intermittent or continuous feed capacity. The primary chamber maintains a starved air atmosphere at approximately 820 °C. Temperature in the secondary chamber varies in the range 760–1100 °C, depending on local regulations. It claims 100% pathogen inactivation. The other characteristics of the technology are comparable to those of technology A.

Steam disinfection

It is a low-heat treatment technology used to disinfect infectious health care waste, resulting in level III inactivation of 6log₁₀, according to State and Territorial Association on Alternative Treatment Technologies (STAATT) (HCWH, 2001). The treated waste is disposed of in a sanitary landfill. The description of the four commercial steam disinfection systems (C–F) is presented below.

The treatment system C uses saturated steam to disinfect infectious medical waste. The treatment cycle starts with shredding, followed by steam introduction and waste disinfection. The system operates on batch mode, with a total cycle time of 60 min. Then, moisture is removed by applying vacuum and discharged. The company claims that pathogen inactivation is 8log₁₀, which exceeds the 6log₁₀ (STAATT level III standard). It also claims that there are no significant air emissions by the disinfection process itself, except for small amounts of volatiles and odors in the work place. Volatile emission usually occurs when the treated waste is not source-separated, resulting in significant content of toxic compounds (e.g., waste pharmaceuticals) in the waste. Treatment of the latter compounds is not possible with this system, as well as with all steam disinfection systems. Internal shredding renders the waste unrecognizable and results in final volume reduction up to 80%. The public acceptance in Greece is considered higher than incineration systems.

The treatment system D is similar to treatment system C, but heat is supplied by steam introduction in the vessel jacket. Waste fragmentation occurs inside the vessel. During the process, the jacket steam condenses into clean and hot condensate, which is returned to the steam boiler. Independent testing showed 6log₁₀ units inactivation of the spores of Bacillus stearothermophilus. It also showed very low emissions of volatile organic compounds with respect to U.S. occupational exposure limits. The manufacturer claims 85% volume reduction with internal shredding.

The treatment system E is a steam disinfection system, which does not require preshredding. It operates using autoclavable carts draped with a polypropylene liner. The carts filled with medical waste are moved into the sterilizer chamber for treatment. At the end of the cycle, the carts are removed and the treated waste is compacted or shredded (optional) and disposed of in the landfill.

The treatment system F uses saturated steam to disinfect infectious medical waste. The system is designed utilizing multiple chambers lined up with a common load platform, conveyor, compactor, and roll-off container. After the disinfection cycle is completed, the waste within the treatment chamber is automatically discharged to the compaction chamber and compacted into the roll-off container. It claims 40% volume reduction, which can be increased to 80% with compaction, without shredding. Shredding is not required as part of the disinfection process. However, optional shredding can be applied after the disinfection process, to render the waste unrecognizable.

Microwave disinfection

This is essentially a steam-based technology, because it is based on moist heat and steam generated by microwave energy. The commercial system G is similar to system C, but it is using microwave disinfection to treat infectious waste. After loading, the waste is shredded and subject to microwave. The company claims better than 7log₁₀ pathogen inactivation. An independent study showed that volatile emissions are below standards of the Occupational Safety and Health Administration.

Reverse polymerization

This technology uses microwave energy to break down complex molecules and in this way to treat medical waste. The manufacturer of the commercial system H claims 6log₁₀ pathogen inactivation and 80% final volume reduction. Shredding is applied to the final sterilized carbon residue, which is stable and appropriate for sanitary landfill disposal. The disadvantages of the method include the use of NaOH and a scrubber to control gaseous emissions and the production of wastewater, which needs to be treated. The cost (indicative) of the method is the highest of the technologies studied and may affect negatively the public acceptance.

Chemical disinfection

The treatment system I uses a chemical technology with sodium hypochlorite as disinfectant. The waste is shredded before disinfection. The technology claims that it can accomplish 6log₁₀ units of pathogen inactivation. The levels of air emissions are low, because of a filter provided with the system, but significant production of liquid waste containing NaOCl. The public acceptance in Greece is expected to be limited, due to the use of chemicals for disinfection.

Assessment methodology

Analytic hierarchy process

The analytic hierarchy process (AHP) was used for technology evaluation in the present study. The method was developed by Saaty (1980) and has been applied to waste management applications, including evaluation of treatment technologies or companies (Hsu et al., 2008; Karagiannidis et al., 2010; Ho, 2011; Achillas et al., 2013). The AHP software Expert Choice 2000, version 2 (Expert Choice Inc., Pittsburgh, PA), was used for the analysis.

The hierarchy of the problem consisted of four levels, as shown in Figure 1. The first level was the goal of the problem, i.e., to select the most appropriate treatment technology for infectious medical waste treatment. The second level consisted of the main criteria, specifically, environmental, economic, technical, and social, that were used for the evaluation. The third level consisted of the subcriteria for each main criterion. The fourth level included the alternative technologies used for accomplishing the goal, after their evaluation against the main criteria and subcriteria.

Figure 1. View of the problem hierarchy.

A pairwise comparison matrix was established to compute the weights for each hierarchy level. This was conducted among the subcriteria within each main criterion, among the main criteria, and among the treatment alternatives. The inconsistency ratio for each pairwise comparison was calculated and was found to be <0.1, indicating that the consistency principle was fulfilled.

The fundamental scale for pairwise comparison with intensity values of importance from 1 to 9 was used, defined as follows: Intensity of 1 indicates equal importance between the compared elements. Intensities of 3, 5, 7, and 9 indicate moderate, strong, very strong, and extreme importance between the compared elements, respectively. Intensities of 2, 4, 6, and 8 were used to express intermediate values.

Assessment criteria and subcriteria

The five different treatment technologies were assessed, using four groups of main criteria, specifically, environmental, technical, economic, and social criteria. Each of these groups was divided in subcriteria (Figure 1). The weights of assessment criteria and subcriteria were calculated by the AHP method, using pairwise comparison. The five technology alternatives were described above.

Sensitivity analysis

The base case of the study comprised the selection of the most appropriate treatment technology, using criteria weights computed according to AHP methodology. In addition to the base case comparison, a sensitivity analysis was conducted, in order to determine how the different weights of the assessment criteria influence the final solution of the problem. This was accomplished by changing the weights of the criteria and recording the resulting ranking of the treatment technologies. This is a way to incorporate the different opinions and priorities of decision makers in the process of technology selection. The following cases were studied and reported in this paper, which resulted in a total of 30 comparisons:

1. In all cases, two scenarios (A and B) for the subcriteria weights were considered. The weights in scenario A were calculated using Expert Choice software for the base case comparison. Equal weights for the subcriteria in each main criterion, simultaneously, were considered in scenario B.

2. Case 1: Only one of the four main criteria has a weight of 1 and all the remainder 0. This case resulted in four main combinations. However, because two sets of weights (scenarios A and B) were used for the subcriteria within each group of the main criteria, a total of eight comparisons were conducted in this case.

3. Case 2: All main criteria have equal weights (0.25 each), which resulted in one possible combination with two comparisons.

4. Case 3: Two of the main criteria at a time have weights of 0.5 each and the remainder 0. This resulted in six possible combinations with 12 comparisons.

5. Case 4: One analysis was conducted with the following main criteria weight combination: environmental 0.3, economic 0.25, technical 0.25, and social 0.2. This resulted in one combination with two comparisons.

6. Case 5: The following main criteria weights were used: environmental 0.3, economic 0.3, technical 0.2, and social 0.2. This resulted in one combination with two comparisons.

7. Case 6: The last combination was conducted with the following main criteria weights: environmental 0.3, economic 0.3, technical 0.3, and social 0.1. This also resulted in one combination with two comparisons.

Results and discussion

Comparison of treatment technologies against assessment criteria

A pairwise comparison was applied for each alternative technology against each assessment subcriterion. Quantitative information for technology comparison was used, based on relevant literature sources when available (e.g., Zhao et al., 2009; Ozkan, 2013; Karagiannidis et al., 2010; Tudor et al., 2009). The author’s judgment was used when specific information was partially available in the literature.

For example, with respect to pathogen inactivation, all five technologies studied in this paper claim pathogen inactivation of at least 6log₁₀. However, a higher degree of pathogen inactivation was assigned to incineration, due to the much higher treatment temperatures. Therefore, the used order of decreasing pathogen inactivation was incineration > steam disinfection ≈ microwave disinfection ≈ reverse polymerization ≈ chemical disinfection.

Disposal cost was considered higher for incineration residues, which were considered hazardous waste, whereas the remainders were considered municipal waste (HCWH, 2001; Department for Environment, Food & Rural Affairs [DEFRA], 2013; European Commission, 2014; Windfeld and Brooks, 2015; Sabbas et al., 2003). For example, the European Waste Catalogue lists several wastes from waste incineration as hazardous, including filter cake from gas treatment (code 19 01 05*), aqueous liquid waste from gas treatment and other aqueous liquid wastes (code 19 01 06*), solid wastes from gas treatment (code 19 01 07*), and fly ash containing hazardous substances (19 01 13*) (European Commission, 2014). The basis of grading is explained in Table 2.

Table 2. Comparison of treatment technologies against assessment criteria.

Criteria	Subcriteria	Rank	References
Environmental	Greenhouse gas emissions	Incineration > steam disinfection ≈ microwave disinfection > reverse polymerization > chemical disinfection	Zhao et al. (2009), author
	Environmental impact of other air emissions	Incineration > chemical disinfection > reverse polymerization > steam disinfection ≈ microwave disinfection	HCWH (2001), Diaz et al. (2005), Edlich et al. (2006), Zhao et al. (2009), author
	Environmental impact of liquid residues	Chemical disinfection > incineration > steam disinfection > reverse polymerization > microwave disinfection	HCWH (2001), Diaz et al. (2005), Zhao et al. (2009), author
	Environmental impact of solid residues	Incineration > chemical disinfection > steam disinfection ≈ microwave disinfection > reverse polymerization	HCWH (2001), author
	Energy consumption	Incineration > reverse polymerization > microwave disinfection > steam disinfection > chemical disinfection	Zhao et al. (2009), author
	Water consumption	Incineration > chemical disinfection > steam disinfection ≈ microwave disinfection > reverse polymerization	Zhao et al. (2009), author
	Volume reduction	Incineration > reverse polymerization ≈ steam disinfection ≈ microwave disinfection ≥ chemical disinfection	International Committee of the Red Cross (ICRC; 2011), author
	Pathogen inactivation	Incineration > steam disinfection ≈ microwave disinfection ≈ reverse polymerization ≈ chemical disinfection	Author, based on vendor information
Economic	Capital cost	Reverse polymerization > incineration > microwave disinfection > chemical disinfection ≥ steam disinfection	Karagiannidis et al. (2010), Ozkan (2013), Tudor et al. (2009), author
	Operation and maintenance cost	Incineration > microwave disinfection > reverse polymerization > steam disinfection ≈ chemical disinfection	Karagiannidis et al. (2010), Ozkan (2013), Tudor et al. (2009), author
	Disposal cost	Incineration > steam disinfection ≈ microwave disinfection ≈ reverse polymerization ≈ chemical disinfection	DEFRA (2013), European Commission (2014), HCWH (2001)
Technical	Treatment effectiveness	Incineration > steam disinfection ≈ microwave disinfection ≈ reverse polymerization ≈ chemical disinfection	Author, based on pathogen inactivation above
	Automation	Incineration ≈ steam disinfection ≈ microwave disinfection ≈ reverse polymerization ≈ chemical disinfection	HCWH (2001), author
	Need for skilled operators	Incineration > reverse polymerization > microwave disinfection > steam disinfection ≈ chemical disinfection	ICRC (2011), author
Social	Technology acceptance	Steam disinfection > microwave disinfection ≈ reverse polymerization ≈ chemical disinfection > incineration	HCWH (2001), author
	Cost acceptance	Steam disinfection > chemical disinfection > microwave disinfection > incineration > reverse polymerization	Karagiannidis et al. (2010), Ozkan (2013), Tudor et al. (2009), author

Calculation of criteria weights for the base case comparison

The weight of each hierarchy element was calculated, followed by the weight of the overall hierarchy. Pairwise comparison was applied to the main criteria, and the pair comparison matrix is presented in Table 3. The computed weights for the main criteria and subcriteria for the base case are presented in Table 4. It appears that the subcriteria with the highest weights are microbial inactivation and environmental impact of other (non-greenhouse gas) air emissions for environmental, capital cost for economic, treatment effectiveness for technical, and technology acceptance for social criteria.

Table 3. Pairwise comparison matrix for base case main criteria.

	Environmental	Economic	Technical	Social
Environmental	1	1	3	3
Economic	1	1	3	3
Technical	1/3	1/3	1	1
Social	1/3	1/3	1	1

Table 4. Computed weights of the main criteria and subcriteria, for the base case, using pairwise comparison, according to the AHP methodology.

Level 2 Main Criteria	Main Criteria Weights	Level 3 Subcriteria	Subcriteria Weights		Inconsistency
			Local	Global	Test Values
Environmental	0.632	Greenhouse gas emissions	0.087	0.055	0.00578
		Environmental impact of other air emissions	0.245	0.154
		Environmental impact of liquid residues	0.087	0.055
		Environmental impact of solid residues	0.087	0.055
		Energy consumption	0.050	0.032
		Water consumption	0.050	0.032
		Volume reduction	0.151	0.095
		Microbial inactivation	0.245	0.154
		Sum	1.000	0.632
Economic	0.237	Capital cost	0.731	0.173	0.06
		Operation and maintenance cost	0.188	0.045
		Disposal cost	0.081	0.019
		Sum	1.000	0.237
Technical	0.079	Treatment effectiveness	0.731	0.058	0.06
		Automation	0.188	0.015
		Need for skilled operators	0.081	0.006
		Sum	1.000	0.079
Social	0.053	Technology acceptance	0.875	0.046	0
		Cost acceptance	0.125	0.007
		Sum	1.000	0.053
Sum	1.000			1.000

At the end, overall priorities for each alternative were computed, and the results are presented in Table 5 for the two scenarios of the subcriteria weights, i.e., scenario A with unequal (Table 4) and scenario B with equal subcriteria weights.

Table 5. Performance of alternative treatment technologies against main criteria for the base case.

	Incineration		Steam Disinfection		Microwave Disinfection		Reverse Polymerization		Chemical Disinfection
Main Criteria	Unequal Subcriteria Weights	Equal Subcriteria Weights	Unequal Subcriteria Weights	Equal Subcriteria Weights	Unequal Subcriteria Weights	Equal Subcriteria Weights	Unequal Subcriteria Weights	Equal Subcriteria Weights	Unequal Subcriteria Weights	Equal Subcriteria Weights
Environmental	0.201	0.148	0.211	0.210	0.229	0.230	0.209	0.237	0.150	0.176
Economic	0.071	0.067	0.406	0.341	0.163	0.166	0.076	0.140	0.283	0.286
Technical	0.356	0.232	0.168	0.221	0.157	0.176	0.152	0.151	0.168	0.221
Social	0.068	0.071	0.440	0.459	0.163	0.153	0.151	0.103	0.178	0.214
Overall	0.175	0.134	0.266	0.258	0.204	0.204	0.170	0.195	0.184	0.208

Selection of optimum treatment technology

Based on the AHP methodology, steam disinfection was the technology with the highest overall priority scores (OPS) for the base case (Table 5); therefore, it was selected as the technology of choice for infectious medical waste treatment, for the base case. Microwave disinfection and chemical disinfection appeared in ranks 2 and 3, respectively.

Finally, using the results of sensitivity analysis (Table 6), a comprehensive frequency table (Table 7) was constructed and used in the decision-making process. The results of the sensitivity analysis are presented briefly below.

• When only one of the main criteria has a weight of 1 and the remainder 0 (case 1), microwave disinfection appeared in rank 1 for unequal subcriteria weights (OPS = 0.229) and reverse polymerization in rank 1 for equal subcriteria weights (OPS = 0.237), on the basis of environmental criteria. Steam disinfection appeared in rank 1 with OPS = 0.406 for unequal subcriteria weights and OPS = 0.341 for equal subcriteria weights, on the basis of economic criteria. Steam disinfection appeared again in rank 1 on the basis of social criteria, with OPS = 0.440 and 0.459 (Table 6). Incineration appeared in rank 1 for unequal subcriteria weights (OPS = 0.356) and for equal subcriteria weights (OPS = 0.231), on the basis of technical criteria (Table 6).

• When all main criteria have the same weight (case 2), steam disinfection appeared in rank 1 and chemical disinfection appeared in rank 2.

• When environmental and economic criteria were assigned weight values of 0.5 each (case 3), steam disinfection appeared in rank 1 and chemical disinfection in rank 2.

• When environmental and technical criteria were assigned weight values of 0.5 each (case 3), incineration appeared in rank 1 for unequal subcriteria weights and steam disinfection in rank 1 for equal subcriteria weights.

• When environmental and social criteria were assigned weight values of 0.5 each (case 3), steam disinfection appeared in rank 1.

• When economic and technical criteria were assigned weight values of 0.5 each (case 3), steam disinfection appeared in rank 1 and chemical disinfection in rank 2.

• When economic and social criteria were assigned weight values of 0.5 each (case 3), steam disinfection appeared in rank 1 and chemical disinfection in rank 2.

• When technical and social criteria were assigned weight values of 0.5 each (case 3), steam disinfection appeared in rank 1.

• When the main criteria were assigned weight values according to case 4, steam disinfection appeared in rank 1 and chemical disinfection in rank 2.

• When the main criteria were assigned weight values according to case 5, steam disinfection appeared in rank 1 and chemical disinfection in rank 2.

• Similarly, when the main criteria were assigned weight values according to case 6, steam disinfection appeared in rank 1 and chemical disinfection in rank 2.

• The pooled data (Table 7) are based on the results of all cases of the sensitivity analysis (base case included) and showed that steam disinfection appeared in rank 1 with 83.3% frequency, followed by incineration (13.3% frequency), followed by microwave disinfection and reverse polymerization (3.3% frequency each). In rank 2, chemical disinfection appeared with frequency 70.0%, followed by microwave disinfection (16.7% frequency), followed by steam disinfection (10.0% frequency). In rank 3, microwave disinfection appeared with 63.3% frequency, followed by chemical disinfection (16.7% frequency), followed by incineration and reverse polymerization (6.7% frequency each). In rank 4, reverse polymerization appeared with 53.3% frequency, followed by incineration (23.3%), followed by microwave disinfection (16.7%), followed by chemical disinfection (6.7%). Finally, incineration appeared in rank 5 with frequency 56.7%, followed by reverse polymerization (36.7%) and chemical disinfection (6.7% frequency).

Table 6. Performance of alternative treatment technologies, based on sensitivity analysis.

	Main Criteria Weights
Main Criteria	Case 1-1	Case 1-2	Case 1-3	Case 1-4	Case 2	Case 3-1	Case 3-2	Case 3-3	Case 3-4	Case 3-5	Case 3-6	Case 4	Case 5	Case 6
Environmental	1	0	0	0	0.25	0.5	0.5	0.5	0	0	0	0.3	0.3	0.3
Economic	0	1	0	0	0.25	0.5	0	0	0.5	0.5	0	0.25	0.3	0.3
Technical	0	0	1	0	0.25	0	0.5	0	0.5	0	0.5	0.25	0.2	0.3
Social	0	0	0	1	0.25	0	0	0.5	0	0.5	0.5	0.2	0.2	0.1
Technologies	Technology Performance for Unequal Subcriteria Weights
Incineration	0.201	0.071	0.356	0.068	0.174	0.136	0.278	0.134	0.214	0.070	0.212	0.180	0.167	0.195
Steam disinfection	0.211	0.406	0.168	0.440	0.306	0.308	0.190	0.326	0.287	0.423	0.304	0.295	0.306	0.280
Microwave disinfection	0.229	0.163	0.157	0.163	0.178	0.196	0.193	0.196	0.160	0.163	0.160	0.181	0.182	0.181
Reverse polymerization	0.209	0.076	0.152	0.151	0.147	0.143	0.181	0.180	0.114	0.114	0.151	0.150	0.146	0.146
Chemical disinfection	0.150	0.283	0.168	0.178	0.195	0.217	0.159	0.164	0.226	0.231	0.173	0.194	0.199	0.198
Technologies	Technology Performance for Equal Subcriteria Weights
Incineration	0.148	0.067	0.231	0.071	0.129	0.107	0.189	0.109	0.149	0.069	0.151	0.133	0.124	0.140
Steam disinfection	0.210	0.341	0.220	0.459	0.308	0.276	0.215	0.334	0.281	0.400	0.340	0.296	0.301	0.278
Microwave disinfection	0.230	0.166	0.175	0.153	0.181	0.198	0.203	0.191	0.171	0.160	0.164	0.185	0.185	0.187
Reverse polymerization	0.237	0.140	0.154	0.103	0.159	0.188	0.195	0.170	0.147	0.122	0.129	0.165	0.165	0.169
Chemical disinfection	0.176	0.286	0.220	0.214	0.224	0.231	0.198	0.195	0.253	0.250	0.217	0.222	0.225	0.226

Table 7. Ranking with respect to percent frequency of appearance of alternative treatment technologies in the base case and all cases of sensitivity analysis.

	Rank
Technology	1	2	3	4	5	Sum
Steam disinfection	83.3	10.0	6.7			100
Chemical disinfection		70.0	16.7	6.7	6.7	100
Microwave disinfection	3.3	16.7	63.3	16.7		100
Reverse polymerization	3.3		6.7	53.3	36.7	100
Incineration	13.3		6.7	23.3	56.7	100

The above results suggested that steam disinfection was the best-performing technology; therefore, it was selected as optimum treatment technology for infectious waste treatment. This is in agreement with previous studies. For example, Ozkan (2013), using two multicriteria decision-making techniques, compared incineration, microwaving, off-site and on-site steam sterilization, and landfilling and concluded off-site sterilization to be the most appropriate. Dursun et al. (2011) evaluated incineration, steam sterilization, microwaving, and landfilling, using a fuzzy multicriteria group decision-making framework and concluded that steam sterilization was the best treatment method for Istanbul. Chemical disinfection and reverse polymerization, however, were not included in previous assessments.

Selection of optimum commercial system

Once steam disinfection was selected as the treatment technology for infectious medical waste (IMW), an attempt was made to select among the four steam disinfection commercial systems (C, D, E, F; Table 1) using the criteria of Table 2. However, this was not possible, because, based on the information provided by the manufacturers, the differences were rather small and there was a lack of specific information. A search through the respective Web pages was conducted and information provided directly by the manufacturers was considered biased, whereas results from independent testing were not available. A major decision criterion is cost, as long as this refers to the same capacity and same major features of the systems being evaluated.

At the end, a decision can be reached on the basis of additional criteria imposed by local conditions (e.g., amount to be treated) and local regulations. For example, Greek regulations require shredding before disinfection (CMD, 2012). The last two commercial systems (E, F; Table 1) do not use preshredding or have it optional at the end, thus resulting in additional cost increase. Therefore, the first two commercial systems (C and D), which use built-in shredding of infectious waste, could be recommended. Based on indicative cost quote provided by the manufacturers, company C was less expensive than company D. However, final cost offers are evaluated at the bidding process, when a purchase is pending, and therefore a final decision between C and D should be made at that point. An example on sizing, location, and economics of a treatment facility is presented in Voudrias and Graikos (2014).

Conclusions

Using multicriteria analysis (AHP methodology), five different treatment technologies (incineration, steam disinfection, microwave disinfection, reverse polymerization, and chemical disinfection with sodium hypochlorite) for IMW treatment were compared, against environmental, economic, technical, and social criteria. The following conclusions were drawn:

• Steam disinfection was selected as the optimum treatment technology for IMW. This is in agreement with previous investigations, which, however, did not evaluate chemical disinfection and reverse polymerization.

• Sensitivity analysis, incorporating a wide variety of assessment criteria weights in a total of 30 comparisons, showed that steam disinfection appeared in rank 1 with 83.3% frequency.

• Selection among four commercial systems using steam disinfection was not possible, because it required additional site-specific criteria, e.g., loading capacity and requirements of local regulations.

Additional information

Notes on contributors

Evangelos A. Voudrias

Evangelos A. Voudrias is a professor at the Department of Environmental Engineering, Democritus University of Thrace, in Xanthi, Greece.