507308
search-article2013
WMR311210.1177/0734242X13507308Waste Management & ResearchBakkali et al.
Original Article
Characterization of bottom ash from two hospital waste incinerators in Rabat, Morocco
Waste Management & Research 31(12) 1228–1236 © The Author(s) 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X13507308 wmr.sagepub.com
Meriem EL Bakkali1,2*, Meriem Bahri1*, Said Gmouh3, Hassan Jaddi1, Mohammed Bakkali2, Amin Laglaoui2 and Mohammed EL Mzibri1
Abstract The uncontrolled disposal of bottom ash generated by the incineration units of hazardous and infected wastes in developed countries are the main cause of significant damage, such as contamination of the soil, as well as surface and underground waters, which may put both the environment and public health at risk. In Morocco, little information is available on the chemical properties of the resulting ashes. In this study, 16 hospital waste ash samples were collected from the incinerators of the two main hospitals in Rabat: Ibn Sina and Cheikh Zayd. A series of tests was conducted, including particle size distribution, mineralogical and chemical composition, and heavy metal leaching behaviour. The results showed that the samples were composed mainly of P2O5 (18%), SiO2 (17%), Na2O (16%), CaO (14%) and SO3 (10%). Moreover, chemical analysis clearly demonstrated that medical waste (MW) contains large amounts of waste generated by domestic activities in the hospital, with a lack of sorting system in the monitoring of MW. Furthermore, the ashes contained high concentrations of heavy metals such as zinc, lead, chromium and nickel with a vast range of 0.5–25071 mg/kg. Leaching tests showed that the extracted amounts of all the heavy metals were lower, with concentrations < 2.85 mg/kg. Comparison of the corresponding heavy metal concentrations with the limit values set by the Council Decision 2003/33/EC allowed us to conclude that bottom ashes meet the waste acceptance criteria regarding these heavy metals. Keywords Hospital waste, incineration, bottom ashes, waste management, heavy metals
Introduction Medical activities have increased worldwide during the last few decades as a result of the the emergence of various diseases, the development of new drugs and the construction of many hospitals to meet the increasing demand. This development has been accompanied by greater production of medical waste (Kuo et al., 1999). Medical service providers, including public and private hospitals and infirmaries, municipal surgery centres, military hospitals, blood donation centres, diagnostic laboratories, microbiological laboratories, veterinary clinics and veterinary diagnostic laboratories can be the origin of infectious hospital waste (HW), which may be the cause of dangerous diseases that can be transmitted to health and waste disposal personnel, patients and the general population (Kougemitrou et al., 2010). Hospital waste is physically and chemically varied. The majority is based on plastic polymers, including polyvinylchloride (PVC), which is an inherently rigid material that requires the addition of plasticizers to give it flexibility—in particular, di2-ethylhexyl phthalate (CNIID, 2008). Hospital wastes also contain polypropylene, polyamide 6, polystyrene and polyethylene (Dauphin, 1988). Incinerating HW offers a 70% reduction in mass and 90% reduction in volume of the waste (Stegemann et al., 1995) and degrades the infectious materials (Velzy et al., 1990). However,
this practice generates solid residues, such as bottom and fly ash, as well as air pollution control residues with high levels of heavy metals, including lead, copper, chromium, nickel, zinc and cadmium (Mulder 1996; Stucki and Jakob, 1997), inorganic salts and other organic compounds (Dong et al., 2002; Linak et al., 1993). The subsequent transformation and vaporisation of volatile metals are influenced by the incineration conditions. Some metals may be adsorbed by incombustible materials and left in bottom ash (Wei, 1998). A recent study reported that these metals were highly leachable (Valavanidis 2008). Other metals may escape with flue gas when passing through their dew-points to form nuclei, or they may condense around existing particles, which 1Unité
de Biologie et Recherche Médicale, Cnesten, Rabat, Morocco de Recherche Biotechnologies et Génie des Biomolécules (ERBGB), Faculté des Sciences et Techniques, Tanger, Morocco 3Unités d’Appui Techniques à la Recherche Scientifique, Centre National pour la Recherche Scientifique et Technique, Rabat, Morocco *These authors contributed equally. 2Equipe
Corresponding author: Mohammed EL Mzibri, Biology and Medical Research Unit, Centre National de l’Energie, des Sciences et Techniques Nucléaires, (CNESTEN), BP 1382 RP, 10001 Rabat, Morocco. Email: [email protected]
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1229
Bakkali et al. can be removed by an air pollution control device as fly ash (Wei et al., 1998). The partitioning of heavy metals in incineration systems depends on their physical and chemical properties, such as saturated vapour pressure and boiling point. Heavy metals with higher saturated vapour pressure (e.g. mercury, cadmium and lead) are easily volatilised and enter the flue gas after combusting, which accounts for their greater content in fly ash than in bottom ash. However, metals with higher boiling points (e.g. chromium, magnesium and copper) primarily remain in the bottom ash (Linak et al., 1993; Vogg et al., 1986). Heavy metals can react with chlorine and oxygen during incineration process to subsequently produce various compounds. The chlorine content and form in wastes play an important role in the partitioning of heavy metals in the incineration system (Fournier et al., 1991; Greenberg et al., 1978). Bottom and fly ashes create a significant risk for the environment and human health (Lo and Liao 2007). The uncontrolled disposal of ash in a landfill can cause the contamination of soil and groundwater by leached heavy metals (Eusden et al., 1999; Shim et al., 2005; Wang and Chiang, 1999). In addition, most of these chemical compounds are believed to be carcinogenic, and they have been implicated in other potential health problems, such as endocrine disruption (Lemieux and Ryan, 1998; Lemieux et al., 2002) and severe acute respiratory syndrome (Zhao et al., 2010). For these reasons, medical waste requires special management (Alba et al., 1997). Previous studies have shown that bottom ash is less contaminated with heavy metals than its corresponding fly ash (Stegemann et al., 1995); nevertheless, the Council of the European Union considers both bottom and fly ashes to be dangerous waste materials. However, bottom and fly ashes require characterisation to determine whether or not they are hazardous (EC, 2000). Currently, many studies on HW are available—most of them focus on the emission of organic pollutants during the incineration process and their impact on the environment and human health. In Morocco, like other developing countries, there is a need to evaluate both bottom and fly ashes after incineration in order to establish necessary measures to minimise the leaching of hazardous components into the environment (Woolley et al., 2001) and facilitate the application of an appropriate management program before disposal in a landfill. Management of HW in Morocco is governed by Decree 2-09-139 of 18 June 2009 on the management of medical waste and pharmaceuticals. This Moroccan regulation defines various categories of medical waste and pharmaceuticals, as well as the packaging, collection, transport and the elimination of these products. It also determines the measures, terms and processes for the handling of medical waste in order to protect public health and the environment. Incineration is the major process used in the treatment of HW in Morocco, and the resulting ashes are mainly disposed of by landfilling or piling up near the incineration plants. Currently, approximately 5000 tons of HW are produced every year, which
contains large amounts of disposed metallic or plastic materials (DHSA, 2002; Levendis et al., 2001). The main objectives of this study were to examine the chemical composition of HW ashes, especially the major elements and heavy metal concentrations, and to determine the leachability of the heavy metals found in HW ashes in order to evaluate their environmental impacts and develop a global environmental protection strategy.
Materials and methods Hospital incinerators Samples were collected from two typical hospital waste incinerators (HWI) in Rabat, Morocco. The first incinerator (LEMER et CIE, type LV-N°30734; ZINANTE, Quarrefou, France), which is characterised by a combustion temperature reaching 1200°C, is located in the university hospital Ibn Sina (CHU), which is the main public hospital in Morocco. The second incinerator (Ati Muller, type CP50; Champoulet, France), which is located at the private international hospital Cheikh Zayed (CHZ), has a combustion temperature of 800°C. The two incinerators have the same form and operating mode, are not equipped with flue-gas cleaning systems and have no assured monitoring of atmospheric emissions. Each incinerator is expected to treat 50 kg/h of solid waste. The CHU and CHZ hospitals produce household, packaging, gardening, cleaning and medical waste, which contains various infectious materials like the specific waste from care services covering dressings, compresses, pungent and sharp elements, sharps, plaster and the hazardous waste from operating, laboratories, dialysis and imaging services.
Sampling and particle preparation Eight samples of ash were collected from CHU and eight samples were collected from CHZ. Sampling from CHU was made available weekly from April to June, and samples from CHZ were taken between July and August. Sampling was done using the quartering procedure (Smith and James, 1981) and was limited to bottom ashes from the combustion chambers. The samples were cooled at room temperature. Before the analysis, all samples were dried at 105°C for 24 h.
Particle size distribution The dried samples were ground into particles ranging from 0.05 to 5 mm. To minimise the error due to sampling and to promote the exchange between residue phases and the extraction solutions (Buchholz, 1993; Guérin 2000), a second grinding was done to create particles with small sizes. The bottom ash particles were segregated into different fractions using a shaker fitted with standard meshes that corresponded to different sizes. Samples were sieved into particle size classes: 1.60–1.00; 1.00–0.25; 0.25–0.16 and < 0.16 mm.
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1230
Waste Management & Research 31(12)
Figure 1. Mass percentages of the particle size distributions in the bottom ash samples from Ibn Sina (CHU) (A) and Cheikh Zayed (CHZ) (B).
Chemical composition X-ray fluorescence spectrometry analysis. The major elements in the ashes were determined using X-ray fluorescence (XRF) spectroscopy. Seven samples from CHU and five samples from CHZ were prepared by grinding the bottom ash and then pressing it into a cake. An S2 Ranger EDS (Philips, Almelo, Netherlands) was then used to qualitatively analyse the chemical composition of the bottom ash in order to measure the amount of unknown elements, which provided the basis for quantitative analysis of the elements to an accuracy of 0.1%. The results are expressed as the mean of percentages of the chemical contents obtained from 12 samples. Inductively coupled plasma atomic emission spectroscopy analysis. The heavy metals (minor and toxic elements) were analysed using inductively coupled plasma–optical emission spectroscopy (ICP–AES; Ultima 2-Jobin Yvan, Villeneuved’Ascq, France) after HNO3/H2SO4 digestion (NF EN ISO 15589, 2012). In order to ensure the quality and precision of the data, the element analyses were calibrated using certified reference materials (the TraceCERT, Saint-Quentin Fallavier, France). Laboratory quality control procedures included sampling in triplicates. Averages of the triplicates and the detection limits for each element are presented.
Mineralogical determination: X-ray diffraction Two samples from CHU and two from CHZ were randomly analysed by X-ray diffraction (XRD) to determine the mineralogical properties of the bottom ash. The samples were ground and backfilled into the sample holder for analysis by the X’Pert Pro MPD (Panalytical, Almelo, Netherlands) machine with a copper target (λ = 15.406 nm). A diffraction angle of between 4° and 90° (2θ) and a scanning rate of 4°/min were utilised to analyse the crystal phases of the bottom ash. Diffraction patterns were manually analysed utilising the Joint Committee on Powder Diffraction standards.
Leaching toxicity of ashes In this study, standard test (DIN 38414, 1987) was applied to evaluate the leaching of heavy metals in eight samples: four from CHU
and four from CHZ. Powdered bottom ashes were agitated with distilled, de-ionized water for 24 h, maintaining a 10:1 liquid-tosolid ratio. About 100 ml of each leachate was recovered and filtered through a 0.45-µm membrane filter. The pH of each batch extraction was measured. Leachates were then acidified with 1 M HCl and subjected to ICP–AES for elemental analysis.
Results and Discussion Particle size distribution in bottom ash samples The mass percentages of the particle size distributions in the bottom ash samples are shown in Figure 1. The majority of the particles in the bottom ash ranged from 0.25 to 1.00 mm. These particles constitute 53% (w/w) of the total particles in the sample from CHU and 58.2% (w/w) of the sample from CHZ. The masses of the large particles (> 1.6 mm) were negligible, representing < 1% of total particles. The percentage of the particles sized 0.16–0.25 mm was considerably reduced in the CHU sample, representing only 7.34% of the total sample. The bottom ash contained a high proportion of heavy particles (with 79% of the CHU samples and 71% of the CHZ samples having a total weight > 250 µm). The particle size distribution of the bottom ash is in close agreement with previous studies regarding the grain size of bottom ash coming from municipal solid waste (MSW) incinerators (Chang and Wey, 2006).
Chemical composition of bottom ash samples by XRF XRF is a standard technique used for element analysis. This technique was used in this study to evaluate the major elements present in the HW. For CHU samples, XRF analyses of the bottom ashes revealed that 75% of the total amount of bottom ash consisted of the major elements (P2O5, SiO2, Na2O, CaO and SO3). The results, as shown in Figure 2, indicate that the samples were composed mainly of P2O5 (18%), SiO2 (17%), Na2O (16%), CaO (14%) and SO3 (10%). However, in the CHZ samples, the main
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1231
Bakkali et al.
Figure 2. Chemical composition (wt %) of the bottom ashes using the X-ray fluorescence spectrometry.
components of the bottom ashes made up about 58% of the ashes: SiO2 (23%), CaO (20%) and Al2O3 (15%). Interestingly, our two medical waste bottom ashes had a silicon/calcium ratio < 3, which is lower than the ratio reported in other studies of medical waste incineration ash (Idris and Saed, 2002; Li et al., 2004). This ratio is characteristic of MSW and indicates that MW contains large amounts of waste generated by domestic activities in the hospital, due to the lack of a sorting system in the monitoring of medical waste at both CHU and CHZ. Overall, our results show the difference in the composition of ashes from the two hospitals’ incinerators. This can be explained by differences in their physical and chemical natures, as well as the quantity of hospital waste from the two different hospitals, the wastes of which vary depending on the nature of the activities in each health facility. The concentration of calcium and chlorine in the CHZ samples was higher than in CHU samples, whereas the opposite trend was observed for sodium. The high amounts of sodium in CHU samples, and of calcium and chlorine in CHZ samples could be due to the intrinsic chemical composition of the waste, including NaCl, which is frequently used in medical treatment in Morocco, and PVC polymer (e.g. disposable infusion devices) (Birpinar et al., 2009; Cheng et al., 2009; Coker et al., 2009). Globally, the chemical compositions of the ashes in the two HWI are in agreement with previous studies, including the contents of the bottom ash produced at HWIs in Germany (Gidarakos et al., 2009), Italy (Filipponi et al., 2003), Malaysia (Idris and Saed 2002) and China (Zhao et al., 2003).
Heavy metal composition of HWI bottom ashes In the medical field, heavy metals, such as cadmium, chromium, nickel, lead and zinc, are generally used in medicines, photographic materials and medical tools. Therefore, they are present in the HW waste stream and appear in high concentrations in the
resulting incineration ashes. Moreover, it is widely accepted that these heavy metals may pose threats to human health and are the origin of several diseases (Kuo et al., 1999; Sukandar et al., 2006). Worldwide, many studies have indicated that MW bottom ash contains high amounts of toxic chemicals that persist in the environment (Ibañez et al., 2000; Kuo et al., 1999). The heavy metal composition of HWI bottom ashes in Morocco was limited to arsenic, cadmium, chromium, nickel, lead, tin and zinc. The heavy metal composition of the bottom samples was analysed by ICP–AES owing to its high sensitivity and specificity. The complete qualitative analysis of the bottom ash samples is shown in Table 1. The metallic element concentrations in the HW ash samples were quite different between the bottom ashes from CHU and CHZ. Both were enriched with large amounts of heavy metals, such as zinc, lead, chromium and nickel. These heavy metals are commonly used in medical facilities (such as for metal alloys, needles and syringes) and have high mobility—this may allow their association with environmental CO2 to be transformed to exchangeable and carbonate forms (Costa et al., 2007; Ibañez et al., 2000; Lombardi et al., 1998; Sukandar et al., 2006). However, toxic metals, such as tin and cadmium, were present in minor amounts, with concentrations < 50 mg/kg. The concentrations of arsenic ranged from 2 to 229 mg/kg. The samples from CHU (mean: 92.45 mg/kg) were more concentrated than those from CHZ (mean: 48.19 mg/kg). Globally, the concentrations of heavy metals in the bottom ash from CHU and CHZ are in agreement with previously reported data from various HWIs (Zhao et al., 2008). There is evidence that the concentrations of most toxic heavy metals (e.g. cadmium, lead and zinc), usually found in small medical tools, are underestimated. Indeed, these heavy metals either have high volatility or can easily form highly volatile compounds, such as CdCl2, ZnCl2 and PbCl2. Thus, we can assume that the high concentrations of chloride in our samples would facilitate the formation of these compounds, which can lead to their transfer into fly ash during the incineration process (Dirk and Alfons, 1996; Idris and Saed, 2002; Jung et al., 2004; Shim et al., 2005; Sukandar et al., 2006).
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1232
Waste Management & Research 31(12)
Table 1. Metal concentrations of the bottom ash using inductively coupled plasma–optical emission spectroscopy. Element
CHU
CHZ
Range of metal concentration from eight samples (mg/kg)
Average (mg/kg)
Range of metal concentration from eight samples (mg/kg)
Average (mg/kg)
Arsenic Cadmium Chromium Nickel Lead Tin Zinc
2.75–229 0–2 0.50–786.50 27.75–546.25 48.50–4063.25 1.25–14.75 281.75–13612.50
92.45 0.73 316.07 138.35 1043.67 4.45 3638.37
11.75–127.5 0.5–9.5 4–355 23.5–49.5 217.75–2960.5 3.55–32.37 630.25–25071.50
48.19 3.81 185.15 31.14 862.60 11.97 8236.26
CHU: Ibn Sina; CHZ: Cheikh Zayed.
Figure 3. Amount of heavy metals in the different particle size classes: chromium (A), nickel (B), lead (C) and zinc (-D-). CHU: Ibn Sina (black filled bars); CHZ: Cheikh Zayed (grey bars).
The concentrations of chromium were similar to that reported by Zhao et al. (2008) and considered to be high; this may have come from infectious wastes, such as needles and syringes (Kuo et al., 1999). In addition, high concentrations of chromium were found in plastic wastes from a hospital (Shim et al., 2005). Chromium is generally not thermally mobile during the incineration process and thus mainly remains in the bottom ash (Jung et al., 2004). The distribution of four heavy metals (chromium, nickel, lead and zinc) according to particle size is reported in Figure 3. Chemical analysis identified that there was no correlation between the particle sizes and the chemical composition of the bottom ash. Nickel prevails in particles < 0.16 mm in the samples from both CHU (189.79 mg/kg) and CHZ (177.18 mg/kg).
In CHU samples, chromium is most predominant in particles < 0.16 mm (590 mg/kg), whereas in CHZ sampleschromium is equitably distributed between all size ranges (160.50–237.56 mg/kg). In CHU samples, lead was more predominant in small (< 0.16 mm) (1548.17 mg/kg) and large samples (> 1 mm) (1458.31 mg/ kg), whereas in the CHZ samples, the concentration of lead was higher in particles between 0.16 mm and 0.25 mm, as well as large particles (> 1 mm) (935.17 and 1090.39 mg/kg). The concentration of zinc was higher in the CHZ bottom ashes than in the CHU bottom ashes. Moreover, the most concentrated particles in the CHZ samples were > 1 mm (11,083.00 mg/ kg), whereas in CHU samples, the zinc concentration was equally distributed between all particles (3331.18–4189.43 mg/kg).
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1233
Bakkali et al. The zinc and lead concentrations in this study were significantly higher than the values reported from other studies on hospital waste incinerator ashes, which may be attributed to differences in the raw HW materials (Idris and Saed, 2002; Sukandar et al., 2006). HW in Morocco usually contains large amounts of plastic, which contain heavy metals that are commonly used as additives.
Mineralogical determination of bottom ash samples by XRD Mineralogy is of great interest for understanding the status of the elements in the ashes. In addition to the concentrations of polluting elements, the speciation of the pollutant elements and the nature of the host phases are necessary to evaluate the toxicity of solid MSW incineration residues (Forestier and Libourel, 1998). Therefore, a detailed knowledge of the mineralogy of these solid residues is required. In this study, four samples were analysed— two from CHU and two from CHZ. The major fractions of the samples retained for analysis were between 0.25 and 1.00 mm. The XRD analyses are reported in Figure 4. Overall, the bottom ashes contained a considerable percentage of amorphous mass, which led to a high background signal in each sample (see Figure 4). As shown in these diagrams, the mineralogy of the solid residues is very mixed. This complex mineralogy of the solid residues results from several processes, including vaporisation, melting, crystallisation and vitrification. The height of the corresponding peaks in the XRD diagrams give an idea about the abundance of the different compounds identified by XRD (Remond et al., 2002). The results of XRD showed that the bottom ash samples are heterogeneous. Different minerals were found in the four samples, and results from the CHU and CHZ samples were not in agreement with each other. Moreover, the bottom ashes of CHU and CHZ are characterised by a variability of quantity and nature of crystalline compounds. The results of the XRD patterns were different for the two samples from CHU. Different components were found in these two samples, which highlighted the evidence that different kinds of waste were sent for incineration. Sample 1 from CHU was characterised by a large quantity of mullite (3 Al2O3 2 SiO2), quartz (SiO2) and corundum (Al2O3); the second sample, however, had considerable amounts of halite (NaCl), calcite (CaCO3) and sylvite (KCl). The mineralogy results of the two samples of bottom ashes from CHZ were certainly alike owing to the presence of calcite, halite and anhydrite (CaSO4). The presence of CaCO3, CaSO4, NaCl, KCl and SiO2 was previously reported in the mineralogy of medical waste incineration ashes by Forestier and Libourel (1998). Other researchers have demonstrated that the main minerals present in bottom ash are quartz, halite, anhydrite, anorthite, calcite and hematite (Chang and Wey 2006; Saikia et al., 2008). The compounds determined by XRD were in good agreement with the chemical analysis results (Figure 2) and with previous studies (Gidarakos et al., 2009; Klika et al., 2001).
In this regard, the Al2O3 and SiO2 contents of the bottom ashes from the CHZ incinerator, as well as the bottom ashes from the CHU incinerator, are important, as reported in Figure 2. Many solid residues from the two incinerators had high CaO contents, and XRD analysis showed the presence of CaCO3. In addition, large fractions of Na2O and chlorine were present in the bottom ashes from the two incinerators; correspondingly, a large amount of NaCl was found by XRD. However, the small amount of K2O found explains the small fraction of KCl present in the diagrams. Moreover, heavy metal-containing compounds, which are dangerous to the environment, would typically be below detection limits, and are not shown in the XRD diagram (Remond et al., 2002).
Leaching test of heavy metals Land disposal of solid waste can lead to environmental impacts associated with the leaching of pollutants to surface and ground water. Therefore, leaching tests play a major role in assessing the possibility of their use within regulatory limits (Ibañez et al., 2000; Reijnders, 2005). The heavy metal concentrations were evaluated in the leachates of four bottom ash samples from CHU and four samples from CHZ. The leached amounts of heavy metals were compared with the corresponding limits set by Council Decision 2003/33/ EC (EC, 2002). As shown in Table 2, the extracted amounts of all the heavy metals were lower than the standards limits set by the Council Decision 2003/33/EC (EC, 2002). During the leaching process, the dissolution of basic metal salts caused the pH to increase in the leachate. The amounts of CaCO3, CaO and Al2O3 in the solid residues, as well as the dissolution of CO2 in water, determine the equilibrium pH (Andac and Glasser, 1999; Van Herck, 2000). There are considerable amounts of CaO and Al2O3 in the solid residues of incinerators (Figure 2). CaO and Al2O3 dissolve in the leachate when the solid residues come into contact with water, which causes the pH to increase. Therefore, the pH values of the leachates were measured and the values are reported in Table 2. For both CHU and CHZ, the pH values of the leachates were moderately alkaline. It is widely accepted that pH extremes (≤ 2 and ≥ 11.5) may indicate corrosive effects; however, in our study, the pH values did not allow us to assess whether the wastes should be classified as hazardous by their corrosive/irritant properties. However, it is widely accepted that hospital waste management by means of incineration processes generates solid residues with high levels of organic compounds (Gidarakos et al., 2009). Worldwide, characterisation of bottom ash from medical waste incineration reveals high amounts of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) (Lee et al., 2002; Johansson and Bavel, 2003a; Wheatley and Sadhra, 2004; Valavanidis et al., 2008). Organics that are present in bottom ash might be formed during incomplete combustion (e.g. polychlorinated dibenzo-dioxins, polychlorinated dibenzo-furans, PCBs,
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1234
Waste Management & Research 31(12)
Figure 4. The X-ray diffraction patterns for samples of medical waste bottom ashes from Ibn Sina (CHU) (A) and Cheikh Zayed (CHZ) (B).
1, Halite, Syn (NaCl); 2, Calcite (Ca(CO3)); 3, Anhydrite (Ca(SO4)); 4, Sylvite,Syn (KCl); 5 ,Mullite (3 Al2O3 2 SiO2); 6, Quartz (SiO2); 7, Curundum (Al2O3).
PAHs) (Johansson and Bavel, 2003a, 2003b; Levendis et al., 2001; Wagner and Green, 1993).
Conclusion The bottom ashes produced by medical waste incinerators contain high concentrations of NaCl, Al2O3, SiO2 and CaCO3, and are significantly contaminated by waste generated from domestic
activities in hospitals. This clearly demonstrates the necessity of establishing an efficient sorting system to monitor medical waste at both CHU and CHZ. Moreover, HW contains relatively large amounts of heavy metals, including arsenic, cadmium, chromium, nickel, lead, tin and zinc. However, these heavy metals are sparingly soluble; therefore, only small proportions of the total concentrations are leached and cannot contaminate the groundwater. To establish a more comprehensive waste management
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1235
Bakkali et al. Table 2. Amounts of heavy metals leached from four medical waste bottom ash samples. Element
L/S= 10 l/kga
L/S= 10 l/kga
CHU (n = 4)
CHZ (n = 4)
mg/kg dry substanceb
mg/kg dry substancec
Range of metal concentration. (mg/kg)
Average (mg/kg)
Range of metal concentration (mg/kg-1)
Average (mg/kg)
Arsenic Cadmium Chromium Nickel Lead Tin Zinc
2.0 1.0 10.0 10.0 10.0 0.7 50.0
25 5 70 40 50 5 200
0.05–1.20
search-article2013
WMR311210.1177/0734242X13507308Waste Management & ResearchBakkali et al.
Original Article
Characterization of bottom ash from two hospital waste incinerators in Rabat, Morocco
Waste Management & Research 31(12) 1228–1236 © The Author(s) 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X13507308 wmr.sagepub.com
Meriem EL Bakkali1,2*, Meriem Bahri1*, Said Gmouh3, Hassan Jaddi1, Mohammed Bakkali2, Amin Laglaoui2 and Mohammed EL Mzibri1
Abstract The uncontrolled disposal of bottom ash generated by the incineration units of hazardous and infected wastes in developed countries are the main cause of significant damage, such as contamination of the soil, as well as surface and underground waters, which may put both the environment and public health at risk. In Morocco, little information is available on the chemical properties of the resulting ashes. In this study, 16 hospital waste ash samples were collected from the incinerators of the two main hospitals in Rabat: Ibn Sina and Cheikh Zayd. A series of tests was conducted, including particle size distribution, mineralogical and chemical composition, and heavy metal leaching behaviour. The results showed that the samples were composed mainly of P2O5 (18%), SiO2 (17%), Na2O (16%), CaO (14%) and SO3 (10%). Moreover, chemical analysis clearly demonstrated that medical waste (MW) contains large amounts of waste generated by domestic activities in the hospital, with a lack of sorting system in the monitoring of MW. Furthermore, the ashes contained high concentrations of heavy metals such as zinc, lead, chromium and nickel with a vast range of 0.5–25071 mg/kg. Leaching tests showed that the extracted amounts of all the heavy metals were lower, with concentrations < 2.85 mg/kg. Comparison of the corresponding heavy metal concentrations with the limit values set by the Council Decision 2003/33/EC allowed us to conclude that bottom ashes meet the waste acceptance criteria regarding these heavy metals. Keywords Hospital waste, incineration, bottom ashes, waste management, heavy metals
Introduction Medical activities have increased worldwide during the last few decades as a result of the the emergence of various diseases, the development of new drugs and the construction of many hospitals to meet the increasing demand. This development has been accompanied by greater production of medical waste (Kuo et al., 1999). Medical service providers, including public and private hospitals and infirmaries, municipal surgery centres, military hospitals, blood donation centres, diagnostic laboratories, microbiological laboratories, veterinary clinics and veterinary diagnostic laboratories can be the origin of infectious hospital waste (HW), which may be the cause of dangerous diseases that can be transmitted to health and waste disposal personnel, patients and the general population (Kougemitrou et al., 2010). Hospital waste is physically and chemically varied. The majority is based on plastic polymers, including polyvinylchloride (PVC), which is an inherently rigid material that requires the addition of plasticizers to give it flexibility—in particular, di2-ethylhexyl phthalate (CNIID, 2008). Hospital wastes also contain polypropylene, polyamide 6, polystyrene and polyethylene (Dauphin, 1988). Incinerating HW offers a 70% reduction in mass and 90% reduction in volume of the waste (Stegemann et al., 1995) and degrades the infectious materials (Velzy et al., 1990). However,
this practice generates solid residues, such as bottom and fly ash, as well as air pollution control residues with high levels of heavy metals, including lead, copper, chromium, nickel, zinc and cadmium (Mulder 1996; Stucki and Jakob, 1997), inorganic salts and other organic compounds (Dong et al., 2002; Linak et al., 1993). The subsequent transformation and vaporisation of volatile metals are influenced by the incineration conditions. Some metals may be adsorbed by incombustible materials and left in bottom ash (Wei, 1998). A recent study reported that these metals were highly leachable (Valavanidis 2008). Other metals may escape with flue gas when passing through their dew-points to form nuclei, or they may condense around existing particles, which 1Unité
de Biologie et Recherche Médicale, Cnesten, Rabat, Morocco de Recherche Biotechnologies et Génie des Biomolécules (ERBGB), Faculté des Sciences et Techniques, Tanger, Morocco 3Unités d’Appui Techniques à la Recherche Scientifique, Centre National pour la Recherche Scientifique et Technique, Rabat, Morocco *These authors contributed equally. 2Equipe
Corresponding author: Mohammed EL Mzibri, Biology and Medical Research Unit, Centre National de l’Energie, des Sciences et Techniques Nucléaires, (CNESTEN), BP 1382 RP, 10001 Rabat, Morocco. Email: [email protected]
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1229
Bakkali et al. can be removed by an air pollution control device as fly ash (Wei et al., 1998). The partitioning of heavy metals in incineration systems depends on their physical and chemical properties, such as saturated vapour pressure and boiling point. Heavy metals with higher saturated vapour pressure (e.g. mercury, cadmium and lead) are easily volatilised and enter the flue gas after combusting, which accounts for their greater content in fly ash than in bottom ash. However, metals with higher boiling points (e.g. chromium, magnesium and copper) primarily remain in the bottom ash (Linak et al., 1993; Vogg et al., 1986). Heavy metals can react with chlorine and oxygen during incineration process to subsequently produce various compounds. The chlorine content and form in wastes play an important role in the partitioning of heavy metals in the incineration system (Fournier et al., 1991; Greenberg et al., 1978). Bottom and fly ashes create a significant risk for the environment and human health (Lo and Liao 2007). The uncontrolled disposal of ash in a landfill can cause the contamination of soil and groundwater by leached heavy metals (Eusden et al., 1999; Shim et al., 2005; Wang and Chiang, 1999). In addition, most of these chemical compounds are believed to be carcinogenic, and they have been implicated in other potential health problems, such as endocrine disruption (Lemieux and Ryan, 1998; Lemieux et al., 2002) and severe acute respiratory syndrome (Zhao et al., 2010). For these reasons, medical waste requires special management (Alba et al., 1997). Previous studies have shown that bottom ash is less contaminated with heavy metals than its corresponding fly ash (Stegemann et al., 1995); nevertheless, the Council of the European Union considers both bottom and fly ashes to be dangerous waste materials. However, bottom and fly ashes require characterisation to determine whether or not they are hazardous (EC, 2000). Currently, many studies on HW are available—most of them focus on the emission of organic pollutants during the incineration process and their impact on the environment and human health. In Morocco, like other developing countries, there is a need to evaluate both bottom and fly ashes after incineration in order to establish necessary measures to minimise the leaching of hazardous components into the environment (Woolley et al., 2001) and facilitate the application of an appropriate management program before disposal in a landfill. Management of HW in Morocco is governed by Decree 2-09-139 of 18 June 2009 on the management of medical waste and pharmaceuticals. This Moroccan regulation defines various categories of medical waste and pharmaceuticals, as well as the packaging, collection, transport and the elimination of these products. It also determines the measures, terms and processes for the handling of medical waste in order to protect public health and the environment. Incineration is the major process used in the treatment of HW in Morocco, and the resulting ashes are mainly disposed of by landfilling or piling up near the incineration plants. Currently, approximately 5000 tons of HW are produced every year, which
contains large amounts of disposed metallic or plastic materials (DHSA, 2002; Levendis et al., 2001). The main objectives of this study were to examine the chemical composition of HW ashes, especially the major elements and heavy metal concentrations, and to determine the leachability of the heavy metals found in HW ashes in order to evaluate their environmental impacts and develop a global environmental protection strategy.
Materials and methods Hospital incinerators Samples were collected from two typical hospital waste incinerators (HWI) in Rabat, Morocco. The first incinerator (LEMER et CIE, type LV-N°30734; ZINANTE, Quarrefou, France), which is characterised by a combustion temperature reaching 1200°C, is located in the university hospital Ibn Sina (CHU), which is the main public hospital in Morocco. The second incinerator (Ati Muller, type CP50; Champoulet, France), which is located at the private international hospital Cheikh Zayed (CHZ), has a combustion temperature of 800°C. The two incinerators have the same form and operating mode, are not equipped with flue-gas cleaning systems and have no assured monitoring of atmospheric emissions. Each incinerator is expected to treat 50 kg/h of solid waste. The CHU and CHZ hospitals produce household, packaging, gardening, cleaning and medical waste, which contains various infectious materials like the specific waste from care services covering dressings, compresses, pungent and sharp elements, sharps, plaster and the hazardous waste from operating, laboratories, dialysis and imaging services.
Sampling and particle preparation Eight samples of ash were collected from CHU and eight samples were collected from CHZ. Sampling from CHU was made available weekly from April to June, and samples from CHZ were taken between July and August. Sampling was done using the quartering procedure (Smith and James, 1981) and was limited to bottom ashes from the combustion chambers. The samples were cooled at room temperature. Before the analysis, all samples were dried at 105°C for 24 h.
Particle size distribution The dried samples were ground into particles ranging from 0.05 to 5 mm. To minimise the error due to sampling and to promote the exchange between residue phases and the extraction solutions (Buchholz, 1993; Guérin 2000), a second grinding was done to create particles with small sizes. The bottom ash particles were segregated into different fractions using a shaker fitted with standard meshes that corresponded to different sizes. Samples were sieved into particle size classes: 1.60–1.00; 1.00–0.25; 0.25–0.16 and < 0.16 mm.
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1230
Waste Management & Research 31(12)
Figure 1. Mass percentages of the particle size distributions in the bottom ash samples from Ibn Sina (CHU) (A) and Cheikh Zayed (CHZ) (B).
Chemical composition X-ray fluorescence spectrometry analysis. The major elements in the ashes were determined using X-ray fluorescence (XRF) spectroscopy. Seven samples from CHU and five samples from CHZ were prepared by grinding the bottom ash and then pressing it into a cake. An S2 Ranger EDS (Philips, Almelo, Netherlands) was then used to qualitatively analyse the chemical composition of the bottom ash in order to measure the amount of unknown elements, which provided the basis for quantitative analysis of the elements to an accuracy of 0.1%. The results are expressed as the mean of percentages of the chemical contents obtained from 12 samples. Inductively coupled plasma atomic emission spectroscopy analysis. The heavy metals (minor and toxic elements) were analysed using inductively coupled plasma–optical emission spectroscopy (ICP–AES; Ultima 2-Jobin Yvan, Villeneuved’Ascq, France) after HNO3/H2SO4 digestion (NF EN ISO 15589, 2012). In order to ensure the quality and precision of the data, the element analyses were calibrated using certified reference materials (the TraceCERT, Saint-Quentin Fallavier, France). Laboratory quality control procedures included sampling in triplicates. Averages of the triplicates and the detection limits for each element are presented.
Mineralogical determination: X-ray diffraction Two samples from CHU and two from CHZ were randomly analysed by X-ray diffraction (XRD) to determine the mineralogical properties of the bottom ash. The samples were ground and backfilled into the sample holder for analysis by the X’Pert Pro MPD (Panalytical, Almelo, Netherlands) machine with a copper target (λ = 15.406 nm). A diffraction angle of between 4° and 90° (2θ) and a scanning rate of 4°/min were utilised to analyse the crystal phases of the bottom ash. Diffraction patterns were manually analysed utilising the Joint Committee on Powder Diffraction standards.
Leaching toxicity of ashes In this study, standard test (DIN 38414, 1987) was applied to evaluate the leaching of heavy metals in eight samples: four from CHU
and four from CHZ. Powdered bottom ashes were agitated with distilled, de-ionized water for 24 h, maintaining a 10:1 liquid-tosolid ratio. About 100 ml of each leachate was recovered and filtered through a 0.45-µm membrane filter. The pH of each batch extraction was measured. Leachates were then acidified with 1 M HCl and subjected to ICP–AES for elemental analysis.
Results and Discussion Particle size distribution in bottom ash samples The mass percentages of the particle size distributions in the bottom ash samples are shown in Figure 1. The majority of the particles in the bottom ash ranged from 0.25 to 1.00 mm. These particles constitute 53% (w/w) of the total particles in the sample from CHU and 58.2% (w/w) of the sample from CHZ. The masses of the large particles (> 1.6 mm) were negligible, representing < 1% of total particles. The percentage of the particles sized 0.16–0.25 mm was considerably reduced in the CHU sample, representing only 7.34% of the total sample. The bottom ash contained a high proportion of heavy particles (with 79% of the CHU samples and 71% of the CHZ samples having a total weight > 250 µm). The particle size distribution of the bottom ash is in close agreement with previous studies regarding the grain size of bottom ash coming from municipal solid waste (MSW) incinerators (Chang and Wey, 2006).
Chemical composition of bottom ash samples by XRF XRF is a standard technique used for element analysis. This technique was used in this study to evaluate the major elements present in the HW. For CHU samples, XRF analyses of the bottom ashes revealed that 75% of the total amount of bottom ash consisted of the major elements (P2O5, SiO2, Na2O, CaO and SO3). The results, as shown in Figure 2, indicate that the samples were composed mainly of P2O5 (18%), SiO2 (17%), Na2O (16%), CaO (14%) and SO3 (10%). However, in the CHZ samples, the main
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1231
Bakkali et al.
Figure 2. Chemical composition (wt %) of the bottom ashes using the X-ray fluorescence spectrometry.
components of the bottom ashes made up about 58% of the ashes: SiO2 (23%), CaO (20%) and Al2O3 (15%). Interestingly, our two medical waste bottom ashes had a silicon/calcium ratio < 3, which is lower than the ratio reported in other studies of medical waste incineration ash (Idris and Saed, 2002; Li et al., 2004). This ratio is characteristic of MSW and indicates that MW contains large amounts of waste generated by domestic activities in the hospital, due to the lack of a sorting system in the monitoring of medical waste at both CHU and CHZ. Overall, our results show the difference in the composition of ashes from the two hospitals’ incinerators. This can be explained by differences in their physical and chemical natures, as well as the quantity of hospital waste from the two different hospitals, the wastes of which vary depending on the nature of the activities in each health facility. The concentration of calcium and chlorine in the CHZ samples was higher than in CHU samples, whereas the opposite trend was observed for sodium. The high amounts of sodium in CHU samples, and of calcium and chlorine in CHZ samples could be due to the intrinsic chemical composition of the waste, including NaCl, which is frequently used in medical treatment in Morocco, and PVC polymer (e.g. disposable infusion devices) (Birpinar et al., 2009; Cheng et al., 2009; Coker et al., 2009). Globally, the chemical compositions of the ashes in the two HWI are in agreement with previous studies, including the contents of the bottom ash produced at HWIs in Germany (Gidarakos et al., 2009), Italy (Filipponi et al., 2003), Malaysia (Idris and Saed 2002) and China (Zhao et al., 2003).
Heavy metal composition of HWI bottom ashes In the medical field, heavy metals, such as cadmium, chromium, nickel, lead and zinc, are generally used in medicines, photographic materials and medical tools. Therefore, they are present in the HW waste stream and appear in high concentrations in the
resulting incineration ashes. Moreover, it is widely accepted that these heavy metals may pose threats to human health and are the origin of several diseases (Kuo et al., 1999; Sukandar et al., 2006). Worldwide, many studies have indicated that MW bottom ash contains high amounts of toxic chemicals that persist in the environment (Ibañez et al., 2000; Kuo et al., 1999). The heavy metal composition of HWI bottom ashes in Morocco was limited to arsenic, cadmium, chromium, nickel, lead, tin and zinc. The heavy metal composition of the bottom samples was analysed by ICP–AES owing to its high sensitivity and specificity. The complete qualitative analysis of the bottom ash samples is shown in Table 1. The metallic element concentrations in the HW ash samples were quite different between the bottom ashes from CHU and CHZ. Both were enriched with large amounts of heavy metals, such as zinc, lead, chromium and nickel. These heavy metals are commonly used in medical facilities (such as for metal alloys, needles and syringes) and have high mobility—this may allow their association with environmental CO2 to be transformed to exchangeable and carbonate forms (Costa et al., 2007; Ibañez et al., 2000; Lombardi et al., 1998; Sukandar et al., 2006). However, toxic metals, such as tin and cadmium, were present in minor amounts, with concentrations < 50 mg/kg. The concentrations of arsenic ranged from 2 to 229 mg/kg. The samples from CHU (mean: 92.45 mg/kg) were more concentrated than those from CHZ (mean: 48.19 mg/kg). Globally, the concentrations of heavy metals in the bottom ash from CHU and CHZ are in agreement with previously reported data from various HWIs (Zhao et al., 2008). There is evidence that the concentrations of most toxic heavy metals (e.g. cadmium, lead and zinc), usually found in small medical tools, are underestimated. Indeed, these heavy metals either have high volatility or can easily form highly volatile compounds, such as CdCl2, ZnCl2 and PbCl2. Thus, we can assume that the high concentrations of chloride in our samples would facilitate the formation of these compounds, which can lead to their transfer into fly ash during the incineration process (Dirk and Alfons, 1996; Idris and Saed, 2002; Jung et al., 2004; Shim et al., 2005; Sukandar et al., 2006).
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1232
Waste Management & Research 31(12)
Table 1. Metal concentrations of the bottom ash using inductively coupled plasma–optical emission spectroscopy. Element
CHU
CHZ
Range of metal concentration from eight samples (mg/kg)
Average (mg/kg)
Range of metal concentration from eight samples (mg/kg)
Average (mg/kg)
Arsenic Cadmium Chromium Nickel Lead Tin Zinc
2.75–229 0–2 0.50–786.50 27.75–546.25 48.50–4063.25 1.25–14.75 281.75–13612.50
92.45 0.73 316.07 138.35 1043.67 4.45 3638.37
11.75–127.5 0.5–9.5 4–355 23.5–49.5 217.75–2960.5 3.55–32.37 630.25–25071.50
48.19 3.81 185.15 31.14 862.60 11.97 8236.26
CHU: Ibn Sina; CHZ: Cheikh Zayed.
Figure 3. Amount of heavy metals in the different particle size classes: chromium (A), nickel (B), lead (C) and zinc (-D-). CHU: Ibn Sina (black filled bars); CHZ: Cheikh Zayed (grey bars).
The concentrations of chromium were similar to that reported by Zhao et al. (2008) and considered to be high; this may have come from infectious wastes, such as needles and syringes (Kuo et al., 1999). In addition, high concentrations of chromium were found in plastic wastes from a hospital (Shim et al., 2005). Chromium is generally not thermally mobile during the incineration process and thus mainly remains in the bottom ash (Jung et al., 2004). The distribution of four heavy metals (chromium, nickel, lead and zinc) according to particle size is reported in Figure 3. Chemical analysis identified that there was no correlation between the particle sizes and the chemical composition of the bottom ash. Nickel prevails in particles < 0.16 mm in the samples from both CHU (189.79 mg/kg) and CHZ (177.18 mg/kg).
In CHU samples, chromium is most predominant in particles < 0.16 mm (590 mg/kg), whereas in CHZ sampleschromium is equitably distributed between all size ranges (160.50–237.56 mg/kg). In CHU samples, lead was more predominant in small (< 0.16 mm) (1548.17 mg/kg) and large samples (> 1 mm) (1458.31 mg/ kg), whereas in the CHZ samples, the concentration of lead was higher in particles between 0.16 mm and 0.25 mm, as well as large particles (> 1 mm) (935.17 and 1090.39 mg/kg). The concentration of zinc was higher in the CHZ bottom ashes than in the CHU bottom ashes. Moreover, the most concentrated particles in the CHZ samples were > 1 mm (11,083.00 mg/ kg), whereas in CHU samples, the zinc concentration was equally distributed between all particles (3331.18–4189.43 mg/kg).
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1233
Bakkali et al. The zinc and lead concentrations in this study were significantly higher than the values reported from other studies on hospital waste incinerator ashes, which may be attributed to differences in the raw HW materials (Idris and Saed, 2002; Sukandar et al., 2006). HW in Morocco usually contains large amounts of plastic, which contain heavy metals that are commonly used as additives.
Mineralogical determination of bottom ash samples by XRD Mineralogy is of great interest for understanding the status of the elements in the ashes. In addition to the concentrations of polluting elements, the speciation of the pollutant elements and the nature of the host phases are necessary to evaluate the toxicity of solid MSW incineration residues (Forestier and Libourel, 1998). Therefore, a detailed knowledge of the mineralogy of these solid residues is required. In this study, four samples were analysed— two from CHU and two from CHZ. The major fractions of the samples retained for analysis were between 0.25 and 1.00 mm. The XRD analyses are reported in Figure 4. Overall, the bottom ashes contained a considerable percentage of amorphous mass, which led to a high background signal in each sample (see Figure 4). As shown in these diagrams, the mineralogy of the solid residues is very mixed. This complex mineralogy of the solid residues results from several processes, including vaporisation, melting, crystallisation and vitrification. The height of the corresponding peaks in the XRD diagrams give an idea about the abundance of the different compounds identified by XRD (Remond et al., 2002). The results of XRD showed that the bottom ash samples are heterogeneous. Different minerals were found in the four samples, and results from the CHU and CHZ samples were not in agreement with each other. Moreover, the bottom ashes of CHU and CHZ are characterised by a variability of quantity and nature of crystalline compounds. The results of the XRD patterns were different for the two samples from CHU. Different components were found in these two samples, which highlighted the evidence that different kinds of waste were sent for incineration. Sample 1 from CHU was characterised by a large quantity of mullite (3 Al2O3 2 SiO2), quartz (SiO2) and corundum (Al2O3); the second sample, however, had considerable amounts of halite (NaCl), calcite (CaCO3) and sylvite (KCl). The mineralogy results of the two samples of bottom ashes from CHZ were certainly alike owing to the presence of calcite, halite and anhydrite (CaSO4). The presence of CaCO3, CaSO4, NaCl, KCl and SiO2 was previously reported in the mineralogy of medical waste incineration ashes by Forestier and Libourel (1998). Other researchers have demonstrated that the main minerals present in bottom ash are quartz, halite, anhydrite, anorthite, calcite and hematite (Chang and Wey 2006; Saikia et al., 2008). The compounds determined by XRD were in good agreement with the chemical analysis results (Figure 2) and with previous studies (Gidarakos et al., 2009; Klika et al., 2001).
In this regard, the Al2O3 and SiO2 contents of the bottom ashes from the CHZ incinerator, as well as the bottom ashes from the CHU incinerator, are important, as reported in Figure 2. Many solid residues from the two incinerators had high CaO contents, and XRD analysis showed the presence of CaCO3. In addition, large fractions of Na2O and chlorine were present in the bottom ashes from the two incinerators; correspondingly, a large amount of NaCl was found by XRD. However, the small amount of K2O found explains the small fraction of KCl present in the diagrams. Moreover, heavy metal-containing compounds, which are dangerous to the environment, would typically be below detection limits, and are not shown in the XRD diagram (Remond et al., 2002).
Leaching test of heavy metals Land disposal of solid waste can lead to environmental impacts associated with the leaching of pollutants to surface and ground water. Therefore, leaching tests play a major role in assessing the possibility of their use within regulatory limits (Ibañez et al., 2000; Reijnders, 2005). The heavy metal concentrations were evaluated in the leachates of four bottom ash samples from CHU and four samples from CHZ. The leached amounts of heavy metals were compared with the corresponding limits set by Council Decision 2003/33/ EC (EC, 2002). As shown in Table 2, the extracted amounts of all the heavy metals were lower than the standards limits set by the Council Decision 2003/33/EC (EC, 2002). During the leaching process, the dissolution of basic metal salts caused the pH to increase in the leachate. The amounts of CaCO3, CaO and Al2O3 in the solid residues, as well as the dissolution of CO2 in water, determine the equilibrium pH (Andac and Glasser, 1999; Van Herck, 2000). There are considerable amounts of CaO and Al2O3 in the solid residues of incinerators (Figure 2). CaO and Al2O3 dissolve in the leachate when the solid residues come into contact with water, which causes the pH to increase. Therefore, the pH values of the leachates were measured and the values are reported in Table 2. For both CHU and CHZ, the pH values of the leachates were moderately alkaline. It is widely accepted that pH extremes (≤ 2 and ≥ 11.5) may indicate corrosive effects; however, in our study, the pH values did not allow us to assess whether the wastes should be classified as hazardous by their corrosive/irritant properties. However, it is widely accepted that hospital waste management by means of incineration processes generates solid residues with high levels of organic compounds (Gidarakos et al., 2009). Worldwide, characterisation of bottom ash from medical waste incineration reveals high amounts of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) (Lee et al., 2002; Johansson and Bavel, 2003a; Wheatley and Sadhra, 2004; Valavanidis et al., 2008). Organics that are present in bottom ash might be formed during incomplete combustion (e.g. polychlorinated dibenzo-dioxins, polychlorinated dibenzo-furans, PCBs,
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1234
Waste Management & Research 31(12)
Figure 4. The X-ray diffraction patterns for samples of medical waste bottom ashes from Ibn Sina (CHU) (A) and Cheikh Zayed (CHZ) (B).
1, Halite, Syn (NaCl); 2, Calcite (Ca(CO3)); 3, Anhydrite (Ca(SO4)); 4, Sylvite,Syn (KCl); 5 ,Mullite (3 Al2O3 2 SiO2); 6, Quartz (SiO2); 7, Curundum (Al2O3).
PAHs) (Johansson and Bavel, 2003a, 2003b; Levendis et al., 2001; Wagner and Green, 1993).
Conclusion The bottom ashes produced by medical waste incinerators contain high concentrations of NaCl, Al2O3, SiO2 and CaCO3, and are significantly contaminated by waste generated from domestic
activities in hospitals. This clearly demonstrates the necessity of establishing an efficient sorting system to monitor medical waste at both CHU and CHZ. Moreover, HW contains relatively large amounts of heavy metals, including arsenic, cadmium, chromium, nickel, lead, tin and zinc. However, these heavy metals are sparingly soluble; therefore, only small proportions of the total concentrations are leached and cannot contaminate the groundwater. To establish a more comprehensive waste management
Downloaded from wmr.sagepub.com at BRIGHAM YOUNG UNIV on March 15, 2015
1235
Bakkali et al. Table 2. Amounts of heavy metals leached from four medical waste bottom ash samples. Element
L/S= 10 l/kga
L/S= 10 l/kga
CHU (n = 4)
CHZ (n = 4)
mg/kg dry substanceb
mg/kg dry substancec
Range of metal concentration. (mg/kg)
Average (mg/kg)
Range of metal concentration (mg/kg-1)
Average (mg/kg)
Arsenic Cadmium Chromium Nickel Lead Tin Zinc
2.0 1.0 10.0 10.0 10.0 0.7 50.0
25 5 70 40 50 5 200
0.05–1.20
