Toxic Environmental Releases from Medical WasteIncineration: A Review

Satnam Singh & Vinit Prakash

Received: 4 July 2006 /Accepted: 15 September 2006 / Published online: 13 February 2007# Springer Science + Business Media B.V. 2007

Abstract Toxic releases from medical waste inciner-ation comprising organic emissions such as poly-chlorinated dibenzo-dioxin/furan (PCDD/Fs) andpolycyclic aromatic hydrocarbons (PAHs), inorganicemissions and ashes containing toxic metals havebeen reviewed. Attempts made by various investiga-tors to reduce/eliminate emissions have also beenincluded. Legislations concerning emission standardsfor medical waste incinerators have been discussed.

Keywords Dioxins . Furans . Polycyclic aromatichydrocarbons . Organic emissions .

Inorganic emissions

1 Introduction

Increased standard of living is creating a great risk to theenvironment by generating a large quantity of waste.Depending upon the nature and source of waste, it maybe classified as medical, industrial, agricultural, munic-ipal, vehicular waste etc. Incineration of waste results inthe reduction of mass by ∼70% and volume by ∼90%(Allsopp et al. 2001; Grochowalski 1998; Rao and

Garg 1994; Stegemann et al. 1995). Incineration is anengineered process, which employs thermal decompo-sition via thermal oxidation at high temperatures(usually 900°C or greater) to destroy organic fractionof the waste (Oppelt 1987; Penner 1989; Saxena andJotshi 1996) and is considered to be one of the fourprimary ways to manage solid wastes, in conjunctionwith source reduction and reuse, recycling–compost-ing, and landfilling (Dempsey and Oppelt 1993;Gochfeld 1995; Lee et al. 2000). Incineration ofmedical waste was identified as the most preferreddisposal method and has been widely practiced (Janget al. 2006). However, inadequate incineration, orincineration of materials unsuitable for incinerationresult in the release of toxic pollutants into the air inlarge concentration and these may travel long distancesbefore they return to earth. Incineration of waste alsoleads to bottom and fly ashes, which contain toxicorganic and inorganic compounds.

Several reviews available on incineration are: For-mation of polychlorinated dibenzodioxins (PCDDs)and polychlorinated dibenzofurans (PCDFs) in munic-ipal solid waste (MSW) incineration and its inhibitionmechanisms (Tuppurainen et al. 1998), chloroaromaticformation in incineration processes (Taylora and Lenoir2001), dioxin characterization, formation and mini-misation during MSW incineration (McKay 2002),dioxin levels in wood combustion (Lavric et al.2004), dioxin releases to land and water in UK (Dykeet al. 1997), formation of dioxins in combustion

Environ Monit Assess (2007) 132:67–81DOI 10.1007/s10661-006-9503-3

S. Singh (*) :V. PrakashSchool of Chemistry & Biochemistry,Thapar Institute of Engineering & Technology(Deemed University), Patiala 147004, Indiae-mail: dsstietp@yahoo.com

systems (Stanmore 2004), polycyclic aromatic hydro-carbon (PAH) emissions from energy generation(Mastral and Callen 2000), formation of polycyclicaromatic hydrocarbons and their growth to soot – areview of chemical reaction pathways (Richter andHoward 2000), medical waste incineration/manage-ment (Lee and Huffman 1996), meeting the newregulations for medical waste incinerators – a reviewof current technologies (Norris and Patterson 1998),industrial and medical waste practices in Dar esSalaam city (Mato and Kaseva 1999) and approachto incineration technology for medical waste in China(Chen 2002). There are not many reviews onmedical waste and its incineration, except few(Chen 2002; Lee and Huffman 1996; Mato andKaseva 1999; Norris and Patterson 1998), which onlytouch upon few aspects of the subject. Therefore,there is a need to prepare an updated detailedreview on medical waste incineration. This reviewdeals with polychlorinated dibenzo-dioxin/furan(PCDD/Fs), polycyclic aromatic hydrocarbons(PAHs) inorganic acidic gases and ashes containingtoxic metals. However, it does not include the fateof radioactive materials and cytotoxic agents presentin medical waste. The coverage of literature is upto 2005.

2 Classification of Medical Waste

World Health Organization released the first globaland comprehensive guidance document on SafeManagement of Wastes from Health-Care Activitiesin 1999 (WHO 1999). It addresses aspects such asregulatory framework, planning issues, waste mini-mization and recycling, handling, storage and trans-portation, treatment and disposal options, andtraining. The wastes from health-care activities in-clude immunizations, diagnostic tests, medical treat-ments and laboratory examinations. Almost 80% oftotal wastes generated by health-care activities arecomparable to domestic waste and can be disposedthrough regular municipal waste methods. Theremaining 20% of wastes are considered hazardousand have been classified into nine categories: infec-tious waste, pathological waste, sharps, pharmaceuticalwaste, genotoxic waste, chemical waste, waste withhigh contents of heavy metals, pressurized containersand radioactive waste (WHO 2003a, b).

US Environmental Protection Agency (US EPA2004) defines medical waste as any solid waste that isgenerated in the diagnosis, treatment, or immuniza-tion of human beings or animals, in research pertain-ing thereto, or in the production or testing ofbiologicals, including but not limited to: blood-soakedbandages, culture dishes and other glasswares, dis-carded surgical gloves, discarded surgical instru-ments, needles, cultures, stocks, swabs used toinnoculate cultures, removed body organs and lancets.

Ministry of Environment and Forests uses the term“biomedical waste” in India, which means any waste,generated during the diagnosis, treatment or immuni-zation of human beings or animals or in researchactivities pertaining thereto or in the production ortesting of biologicals, and is classified into 10categories: human anatomical waste, animal waste,microbiology and biotechnology waste, waste sharps,discarded medicines and cytotoxic drugs, soiledwaste, solid waste, liquid waste, incineration ash andchemical waste (MEF 1998).

Many terms like “health-care waste,” “hospitalwaste,” “medical waste,” “infectious waste,” veteri-nary waste” and “clinical waste” are used in theliterature. These terms have significantly differentmeanings between institutions, regulatory agenciesand countries. However, medical waste has beenconsidered as a subset of hospital waste and significantquantities of waste from other non-hospital sourcessuch as clinics, health-care establishments, laboratoriesand research centers, mortuary and autopsy centers,animal research and testing laboratories, blood banksand collection services, and nursing homes.

3 Medical Waste Incinerators

Medical waste incinerators (MWIs) are divided intothree categories on the basis of waste burningcapacity: small (less than or equal to 90 kg h−1),medium (between 90 and 225 kg h−1) and large(greater than 225 kg h−1) (Gochfeld 1995).

Lee and Huffman (1996) described two types ofMWIs: Modular and Rotary kilns. Modular incinera-tor can be starved air or excess air type. Starved airincinerator contains two furnace chambers, primaryand secondary. In primary chamber, the waste is firedwith less air than the stoichiometric requirement andthe off gas is allowed to burn in secondary chamber

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with 100–140% of the stoichiometric air requirement.In excess air incinerators, waste is fired in the primarychamber and the secondary chamber provides theresidence time, temperature and supplementary fuelfor combustion of the unburned organics. Theincinerator contains multiple internal baffles to guidethe combustion gases through 90° turns in both lateraland vertical directions. At each turn, ash drops fromthe gas stream. The air is injected into the primary andsecondary combustion chambers through the supple-mentary fuel burners.

The rotary kiln is a horizontal refractory linedcylinder that rotates about horizontal axis. Waste ischarged directly into the kiln. Air, typically in excessof the stoichiometric requirement, is provided to thekiln to burn the waste. A secondary combustionchamber is part of the kiln system. Off-gas from thekiln contains volatiles from the waste that have notburnt out and their burning is completed in secondarychamber.

4 Incinerator Releases

Incineration of medical waste results into organic andinorganic releases in the form of stack gases, bottomash and fly ash.

4.1 Organic releases

Organic releases comprise polychlorinated dibenzo-p-dioxin/dibenzofuran and polycyclic aromatichydrocarbons.

4.1.1 Polychlorinated dibenzo-p-dioxinand dibenzofuran (PCDD/Fs)

PCDD/Fs are mainly formed during anthropogenicactivities and are usually referred to as dioxins. Theseare extremely potent toxic chemicals, producing effectsin humans and animals at extremely low doses. Beingpersistent in the environment, these chemicals accu-mulate in the food chain and are distributed globally.Every member of the human population is exposed tothem, primarily through the food supply and mother’smilk. PCDD/Fs are carcinogenic and affect thedevelopment, reproduction and immune system(Thornton et al. 1996). Olie et al. (1977) were the

first to discover the presence of these chemicals in theflue gases and fly ashes of incinerators. Since thentheir emission from various sources became a seriousissue. The emissions of PCDD/Fs have been observedin the waste combustion sources, chemical-industrialsources and other thermal sources (Eduljee and Dyke1996; Fledler 1993; Luthardt et al. 2002; Takeda et al.2000, 2001; Wevers and De Fre 1995). The primarycause of “iatrogenic” PCDD/F produced by theincineration of MW was organically bound chlorinein polyvinyl chloride (Thornton et al. 1996).

The emissions from most combustion processescontained mixtures of 75 PCDD and 135 PCDF conge-ners (Buekens et al. 2000). The most toxic and humancarcinogen congener is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The amount of PCDD/Fs is presentedas toxic equivalents (TEQ) relative to 2,3,7,8-TCDD.PCDD/Fs emission factors depend on composition,type, classification, segregation practice, and manage-ment methodology of incinerated waste, (Alvim-Ferraz et al. 2003a, b, c).

Combustion of organic matter in the presence ofchlorine and metals is recognized as a major source ofPCDD/Fs in the environment. Tuppurainen et al.(1998) explored some of the reaction pathways suchas high-temperature pyrosynthesis, low-temperaturede novo formation from macromolecular carbon andorganic or inorganic chlorine present in the fly ashmatrix and formation from different organic precur-sors such as chlorophenols. The mechanisms involvedin the emission of PCDD/Fs from incinerators can beexplained by three theories: PCDD/Fs are alreadypresent in the incoming feed and are incompletelydestroyed or transformed during combustion, PCDD/Fs can be formed during combustion, and PCDD/Fscan be formed by de novo mechanism that is in thelow-temperature post-combustion zone of incineratorsthrough some heterogeneous catalytic reactions thatoccur in the flue gas-fly ash environment (Stieglitzet al. 1991; Stieglitz et al. 1989). The mechanism offormation of PCDFs is different from that of PCDDs(Cains et al. 1997; Luijk et al. 1994). The reactionsbetween PCDDs and PCDFs are found to bekinetically inhibited (Tan et al. 2001). The PCDDformation occurs by condensation reactions andassociated Smile’s rearrangements of a small set ofchlorophenol precursors (Luijk et al. 1994). Theformation pathways from 2,4,5-trichlorophenol(TCP) to PCDDs were considered by direct intermo-

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lecular condensation and those via radicals (Okamotoand Tomonari 1999). The pathways by direct con-densation are preferred to those via radicals (Wanget al. 2003b).

Hell et al. (2000) conducted experiments on twodifferent matrices with 2,4,6-TCP as a precursor toPCDD/Fs and found that at low TCP concentrations,PCDFs are formed primarily de novo from theresidual carbon of the fly ash. As TCP concentrationincreases, the condensation reaction of 2,4,6-TCP toPCDD exceeds the de novo reaction. Two non-substituted phenol moieties present in the ash/residuecondense to dibenzofuran followed by chlorination/dechlorination reactions during the formation ofPCDFs (Cains et al. 1997). Wikstrom and Marklund(2000) suggested that PCDFs are formed by non/lowchlorinated precursor followed by further chlorina-tion/dechlorination reactions. During the formation ofPCDD/Fs from PAHs, the formation of PCDFsdominated every homologue with a PCDD/Fs ratioof approximately 10 (Iino et al. 1999). Perylene gavea higher yield of PCDFs than activated carbon gaveunder the same conditions. The effect of chlorinecontent in the feeding waste on formation mecha-nisms of PCDD/Fs remains unclear as it is difficult toperform studies concerning formation mechanisms ofPCDD/Fs in complex systems like full scale inciner-ators (Wang et al. 2003b). However, incinerationsystems that are similar with respect to compositionof the waste feed (chlorine content in the waste),types of furnaces and air pollution control devices(APCDs) should have similar PCDD/F emissions (USEPA 1998).

The distributions of PCDD/Fs congeners incombustion gases were found to be similar in 18MWIs by Grochowalski (1998). In order to clarifythe effects of chlorine content in the waste on theformation mechanisms of PCDD/Fs in full scaleincinerators, Wang et al. (2003b) proposed theprincipal component analysis to compare the conge-ner profiles of PCDD/Fs in the stack flue gases of 17emission sources including five MWIs. The forma-tion mechanisms of PCDD/Fs are found to beinfluenced by the chlorine content with a thresholdvalue of 0.8–1.1% in the feeding waste than by otherfactors, like furnaces or APCDs. Below thresholdvalue, the formation of PCDDs dominates, whileabove this value, the formation of PCDFs increasedfaster. Oh et al. (1999) analyzed the sample of stack

gases for PCDD/Fs emissions in MW containing lesschlorine content in MWI and found their concentra-tion to be 5.86 ng TEQ Nm−3.

An empirical model for de novo formation ofPCDD/Fs in MWIs for a chlorine-rich gas phase,based on diffusion of HCl to the fly ash surface hasbeen developed by Stanmore and Clunies-Ross(2000). The burning of MW showed that amounts ofPCDD/Fs formed on cooling from 900°C to ambientair were almost proportional to residence time intemperature range 400–200°C. The empirical globalmodel for their de novo formation on fly ash in MWIand MSWI was extended to include the precursormechanism and a gas phase formation component,with separate rate expressions for PCDD and PCDF(Stanmore 2002). The formation of PCDD/Fs throughprecursor and de novo routes were found to be inboth the gas phase at temperatures above 600°C andon the surface of fly ash in the temperature range400–225°C.

Pandompatam et al. (1997) compared PCDD/Fsemissions from MWIs and hog fuel boilers. The2,3,7,8-TCDD/Fs emission followed the same trendas in case of bark combustion and MW incineration.In Taiwan, 18 MWIs treated a total of 61.2 ton ofMW daily and released 260 ng TEQ of PCDD/Fsyear−1. An average emission factor of 37,400 ng TEQton−1 obtained from a study of PCDD/Fs stackemissions of MWIs, and used for the calculation of16 MWIs (Chen 2004). Seventeen PCDD/Fs likecompounds and three coplanar polychlorinatedbiphenyls were studied from fly ashes of MW,MSW and electrical power plant incinerators by Lingand Hou (1998). The TEQ values of fly ashes fromMWIs (13.9 ng g−1) and small MSWIs (29.3 ng g−1)were much higher than those from large MSWI(2.1 ng g−1) and electrical power plant (0.3 ng g−1)incinerators.

A plume model developed and tested in the windtunnel with a scale model of incinerator stackpredicted that average PCDD/Fs formed in the plumeexceeded up to 40 times, the stack emission regu-lations of 0.2 ng TEQ Nm−3 in South Africa (Brentand Rogers 2002). By the use of model simulations,Lohman and Seigneur (2001) investigated the relativefractions of PCDD/F emissions deposited locally(within 100 km from the source) and transported atregional/global scales (i.e., beyond 100 km from thesource) from eight sources including two MWIs. The

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small fraction of PCDD/Fs emissions were depositedlocally from the sources having tall stack and/or highplume rise than other sources such as MWIs andMSWIs where the greater fraction of PCDD/Fs werebeing deposited locally and the majority of theirPCDD/Fs emissions tended to be transported at globalscale. Bennett et al. (1998) calculated the characteristictravel distance of 2,3,7,8-TCDD to be in the range100–1,000 km on assuming a mean wind speed of4 m s−1. Van Pul et al. (1998) obtained residencetimes for TCDD and octachloro-dibenzofuran corre-sponding to travel distances of 1,900 and 370 km,respectively. Travel distance of 810 km for TCDDand 460 km for octachloro-dibenzodioxin has beencalculated (Beyer et al. 2000). Baker and Hites (1999)suggested that a large fraction of the PCDD/Fsemissions settle close to the source because most ofPCDD/Fs are associated with large particles that settleto the ground rapidly.

The PCDD/Fs emission rates for the crematorysource were found to be ∼9.1, 1–35 and 1.3–3.8×109 ng TEQ year−1, in US (US EPA 2001), UK(Eduljee and Dyke 1996) and Japan (Takeda et al.2001), respectively. The estimated PCDD/Fs emissionrate for all crematories in Taiwan was found to be0.838×109 ng TEQ year−1 accounting for 227 and112% of the annual emissions from all MWIs andMSWIs, respectively (Wang et al. 2003a). ThePCDD/Fs like potencies and extractable organohal-ogens in MW, MSW and domestic waste incineratorashes in Japan have been studied (Matsui et al. 2003).The PCDD/Fs in the ashes ranged between 2.33 and12.29 ng TEQ g−1 (dry weight). Relative rangesestimated by ethoxyresorufin-O-deethylase assay inthe medical incinerator ashes were 3.8–17.6 timeshigher than the results of conventional chemicalanalysis. The mean PCDD/Fs emission from thecrematory without APCD and the crematory with abag filter were 2.36 and 0.322 ng TEQ Nm−3,respectively (Wang et al. 2003a).

MWIs were found to be major source of PCDD/Fs followed by MSWIs into the atmosphere (Brzuzyand Hites 1996; Jones et al. 1994; Pandompatam et al.1997). These generate relatively large amounts ofPCDD/F due to lack of optimal APCDs and highfraction of chlorine containing combustibles (Brzuzyand Hites 1996). The concentrations of PCDD/Fs incombustion gas were much higher than the legal limit(0.1 ng TEQ Nm−3) for the MWIs having no or

efficient APCDs (Alvim-Ferraz et al. 2000, 2003a).However, MWIs having very efficient APCDs emitthe exhaust fumes containing PCDD/Fs at levelsbelow 0.1 ng TEQ Nm−3 (Grochowalski 1998).APCDs needed to be made compulsory for MWIs indeveloping countries (Brent and Rogers 2002). Linderet al. (1990) studied PCDD/Fs emissions from eightMWIs in California and reported that wet scrubbers(WSB) achieved an emissions control efficiency of95% while bag house less than 30% in removingPCDD/Fs. The PCDD/Fs emissions from variousMWIs and effect of APCDs have been summarizedin Table 1. To comply with the PCDD/Fs regulations,Fritsky et al. (2001) developed a catalytic filtersystem for MWIs which destroy PCDD/Fs withoutadsorption. Yufeng et al. (2003) developed a newpyrolysis technology and equipment for treatment ofMW and municipal household.

4.1.2 Polycyclic aromatic hydrocarbons (PAHs)

PAHs are two- to eight-ring semi-volatile organiccompounds formed mainly during incomplete com-bustion from natural and anthropogenic sources(Benner et al. 1989; Bjorseth and Ramdahl 1985;Freeman and Cattel 1990). Their emissions aredirectly affected by incineration temperature (Mastralet al. 1999; Singh and Prakash 2006). PAHs areubiquitous environmental pollutants, many of whichhad been shown to be carcinogenic and mutagenic(IARC 1984). The US Environmental ProtectionAgency (US EPA 1997a) has fixed 16 PAHs aspriority pollutants which are: naphthalene (Nap),acenaphthene (Acp), acenaphthylene (AcPy), fluorene(Flu), phenanthrene (PA), anthracene (Ant), fluoran-thene (FL), pyrene (Pyr), benzo[a]anthracene (BaA),chrysene (CHR), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), benzo(g,h,i)perylene (BghiP), dibenzo(a,h)anthracene(DBA) and indeno(1,2,3-c,d)pyrene (IND). The Inter-national Agency for Research on Cancer (IARC)classifies carcinogens into group 1, 2A, 2B, 3 and 4for designating human carcinogens, probable humancarcinogens, possible human carcinogens, not classi-fiable for human carcinogenicity and probably notcarcinogenic to humans, respectively. BaP, DBA andBaA are classified as Group 2A while BbF, BkF andIND are classified as Group 2B (IARC 1983, 1987).IARC (2002) has evaluated Nap and reclassified it in

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Group 2B. However, National Toxicology Program(NTP 2004) has evaluated Nap and classified it as“reasonably anticipated to be a human carcinogen.”

The main contributions to the environmental PAHlevel are the human activities. Investigations regard-ing PAH emissions include motor vehicle exhausts inurban and suburban areas (Baek et al. 1991), vehi-cular emissions and tobacco smoking (Benner et al.1989; Handa et al. 1979; Lee et al. 1995; Mi et al.1996; Nasrin et al. 1995; Smith and Harrison 1996;Venkataraman et al. 1994; Westerholm et al. 1991),industrial processes (Griest and Tomkins 1986;Natusch 1978) and in stack gases of incinerators(Colmsjo et al. 1986; Davies et al. 1976; Eicemanet al. 1981; Ingrld et al. 1993; Magagni et al. 1991;Yasuda et al. 1989; Yasuda and Takahashi 1998).Waste composition, temperature and excess air duringincineration process determine the quantity of PAHsemitted by a given facility. High emissions of PAHshave been observed during start-up of incinerators(Yasuda and Takahashi 1998).

During combustion, the mechanisms of PAHformation are classified into two processes: pyrolysis

(Mastral et al. 1996) and pyrosynthesis (Barbella et al.1990; Bjorseth and Ramdahl 1985; Bonfanti et al.1994; Williams et al. 1986). Organic compounds arepartially cracked to smaller and unstable fragmentsupon heating (pyrolysis). These fragments, mainlyreactive free radicals lead to more stable PAHformation through recombination reactions (pyrosyn-thesis). During thermal decomposition of organicfractions of waste, propargyl (C3H3·) and cyclopenta-dienyl (C5H5·) radicals also play significant role in theformation of first aromatic rings (Richter and Howard2000). PAH formation and sequential growth of PAHtake place by reactions with stable and radical species,including single-ring aromatics, lower molecularweight PAH and acetylene, followed by the nucle-ation or inception of small soot particles, soot growthby coagulation and mass addition from gas phasespecies, and carbonization of the particulate material.

Liow et al. (1997) investigated PAHs from twoMWIs, a mechanical grate incinerator (MG-MWI) forinfectious waste and a fixed-bed incinerator forpathological waste. The total PAHs concentration instack flue gas from MG-MWI (1,290 μg m−3) was

Table 1 PCDD/Fs releases from MWIs

No. ofsourcesstudied

Type ofsources

APCDs PCDD/Fs,(ng I-TEQNm−3)

TotalPCDD/Fs(ng m−3)

Remarks Reference

18 5 MWIs LE 9.7–32 ... At temperature from 500–1,000°C, PCDD/Fsin bottom ash varies 8.5–45 μg TEQ kg−1.

Grochowalski (1998)8 MWIs VES 0.015–0.09 ...5 MWIs NVE 0.13–3.9 ...

16 1 MWIs B-WS-BF 5.86 132 PCDD/Fs in fly ash 179 ng g−1. Oh et al. (1999)11MSWIs ... 0.07–36.5 8.56–2,1003 SIs ... 0.25–43.3 16.5–1,7001 IWIs ... 0.03 1.51

1 1 MWI CFS <0.1 ... CFS destroys PCDD/Fs to form CO2, H2Oand HCl with RE of 98.4%.

Fritsky et al. (2001)

17 2 MWIs QC-VS-PBS ... ... The formation of PCDD/Fs influenced bythe chlorine content in the feeding waste.Threshold chlorine content is 0.8-1.1%.

Wang et al. (2003b)1 MWIs DSI-FF ... ...1 MWIs ... ... ...1 MWIs WS-BF-FF ... ...8 MSWIs ... ... ...2 VFS ... ... ...2 PVC ... ... ...

2 1 C1 ... 2.36 ... ... Wang et al. (2003a)1 C2 BF 0.322 ... The RE of BF 55.1%.

1 1 NPTE ... <0.1 ... NPTE obeys the emission standard Yufeng et al. (2003)

B Boiler, BF bag filter, C crematory, CFS catalytical filter system, DSI dry sorbent injection, FF fabric filter, IWI industrial wasteincinerator, LE low efficient, NPTE new pyrolysis technology and equipment, NVE not very efficient, PBS packed bed scrubber, PVCpolyvinylchloride vent combustors, QC quench chamber, RE removal efficiency, VES very efficient system, VFC vehicle fuelcombustion, VS venturi scrubber, SIs small size incinerators, WS wet scrubber, ... not reported

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two times higher than that from fixed-bed incinerator,mainly due to large amount of plastic in infectiouswaste. Chen et al. (2003) investigated PAH emissionsfrom two batch-type animal carcass waste inciner-ators, one in a hog farm and the other in a livestockdisease control center, along with a fixed grateincinerator (FG-MWI) for the disposal of biologicalMW in Taiwan. Lee et al. (2002, 2003) investigatedemission of PAHs from two batch-type MWIs, oneMG-MWI and the other FG-MWI for the disposal ofgeneral MW and special MW, respectively.

Wang et al. (2002) conducted Laboratory experi-ments in a two-stage horizontal muffle furnace tomonitor emissions from batch combustion of polysty-rene, a dominant component of MW and MSWstreams and identified conditions to minimize them.Levendis et al. (2001) explored PAH and sootemissions from burning components of surgical glovesand cotton pads in a laboratory scale horizontal mufflefurnace. The batch combustion of shredded latexgloves in fixed beds resulted in higher magnitude ofPAHs comparable to those emitted from batch com-bustion of tire-derived fuel, a little higher than thoseemitted from batch combustion of fixed beds of apulverized, bituminous coal and soot than those frombatch combustion of cotton pads. The condensed-phase PAH from latex and cotton was about 1 of 10 anda few percent of the particulate mass, respectively. Thegas-phase PAHs from the combustion of cotton werehigh relative to those in the condensed phase, with thethree-membered ring PAHs (PA and Ant) reachingvalues even higher than those from latex.

The concentrations of 21 PAHs in the stack fluegas, bottom ash and WSB effluent from two batch-type animal carcass waste incinerators and a FG-MWIwere analyzed. In addition to 16 priority pollutants(US EPA 1997a), various other PAHs determinedwere cyclopenta(c,d)pyrene (CYC), benzo(e)pyrene(BeP), perylene (PER), benzo(b)chrycene (BbC), andcoronene (COR). The mean total-PAHs concentra-tions of the stack flue gas for hog farm and livestockdisease control center incinerators were 1.5 and 1.4times higher than MWI (391 g m−3), respectively. Theemissions of total-PAHs and carcinogenic potencies,the mean BaP, BbF and DBA exceeded 226.2 and2.3 kg day−1, respectively, during the outbreak offoot-and-mouth disease among pigs in Taiwan (Chenet al. 2003). PAHs emissions from various MWIs andeffect of APCDs are shown in Table 2.

Lee et al. (2002) determined the concentrations of21 PAHs contained in the stack flue gas, electrostaticprecipitator (ESP) fly ash, WSB effluent, and incin-erating ash of two batch-type MWIs, one MG-MWIand the other FG-MWI sharing same APCDs for thedisposal of general MW and special MW, respective-ly. Total-PAHs contained in stack flue gas weredominated by low molecular weight containing two-to three-ringed PAHs.

The effect of the afterburner in reducing PAHconcentrations from batch combustion of polystyrenewas observed by Wang et al. (2002). Lower molecularweight PAHs were having a higher fraction in liquidphase than that in the solid phase. The efficiency ofPAHs removal was found to be higher for WSB thanfor ESP (Liow et al. 1997). Lee et al. (2003, 2002)showed that MWIs sharing the same APCDs (ESPand WSB) results in reduction of the total PAHs andthe overall BaP+BbF+DBA concentrations or totalBaP equivalent emission of MWIs suggesting that theuse of proper APCDs during incineration results insignificant reduction of carcinogenic potencies asso-ciated with PAHs emissions.

The total PAHs concentrations in bottom ashes ofhog farm incinerator (737 ng g−1) were 1.6 and 1.8times higher than the livestock disease control center(470 ng g−1) and MWI (421 ng g−1). The total PAHsconcentration in WSB effluents for hog farm inciner-ator and MWI was 45.3 and 10.5 μg l−1 (Chen et al.2003). Lee et al. (2002) reported total PAH concen-tration in ESP fly ash, front bottom ash and bottomash for MG-MWI as 13,800, 3,170 and 162 ng g−1,respectively. However, the total PAH concentrationfor FG-MWI in ESP fly ash and bottom ash was47,000 and 3,480 ng g−1, respectively. Wheatley andSadhra (2004) studied 11 PAHs in solid residues fromclinical waste incineration and their total concentra-tion was found to be 449.3 μg kg−1.

4.2 Inorganic releases

Inorganic releases from MWIs include gases andashes containing toxic metals.

4.2.1 Gases

Inorganic acidic gases, notably hydrogen chloride,hydrogen fluoride, hydrogen bromide, sulphur oxides(SOx) and nitrogen oxides (NOx) are formed as a

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consequence of the elements chlorine, fluorine, bro-mine, sulphur and nitrogen being present in waste andare emitted by incinerators (Allsopp et al. 2001). NOx

are also formed as a result of the direct combination ofnitrogen and oxygen, a process that is accelerated athigh temperatures. HCl is emitted in greater quantitiesfrom incinerators due to chlorine in the waste, notablyin the form of plastics such as PVC.

Batch combustion of cotton resulted in CO yields,comparable to those from latex gloves and 10 times asmuch as those from tire derived fuel (TDF). However,CO2 yields were higher than those from latex glovesbut lower than those from TDF. No SO2 emissionswere detected, indicating the conversion of sulfur toH2S or sulfates in the soot (Levendis et al. 2001). Theemission factor for CO, SO2, NOx and HCl, associ-ated to the incineration of MW according to Portu-guese legislation were studied by Alvim-Ferraz et al.(2003b). The concentration of NOx was within thelimit whereas concentrations of CO, SO2, and HClwere higher than the legal limit. Zandaryaa et al.(2001) carried out a full-scale selective non-catalytic

reduction on a MWI in Italy by injecting anhydrousNH3 for NOx reduction into the first pass of the boiler.Reduction efficiency of NOx was found within amolar ratio of 0.9–1.5 for NH3/NO. The fraction ofNH3 used in NOx removal was found to decrease withrising NH3/NO molar ratio. Alvim-Ferraz et al.(2003b) recommended the control of CO, SO2 andHCl emissions by the use of APCDs for protectinghuman health. Incineration of segregated waste leadsto the smallest amount of SO2 and reduction of NOx

by 93%, and that of CO and HCl by more than 99%.

4.2.2 Metals

Heavy metals are emitted from all types of inciner-ators. Many heavy metals are known to be toxic atlow concentrations and some are persistent and bio-accumulative. Heavy metals enter the incinerator ascomponents of various materials in the raw waste. Aproportion of these toxic trace metals is emitted in thestack gases of incinerators to atmosphere. The majorproportion is generally present in fly ash and bottom

Table 2 PAHs releases from MWIs

No. and typeof sources

No. of PAHsstudied

APCDs BaP+BbF+DBAemission in μg m−3

Total PAHsin μg m−3

Remarks Reference

2 MWIs: Efficiency of WS washigher than ESP.

Liow et al. (1997)

1 MG ... ESP, WS ... 1,290a

1 FG ... ESP, WS ... 635a

2 MWIs: Total PAHs in ash: Lee et al. (2002)1 MG 21 ESP, WS 0.118b 1,290a 17,132 ng g−1.1 FG 21 ESP, WS 0.107b 587a 50,480 ng g−1

2 ACWIs: Total PAHs in ash: Chen et al. (2003)1 HF 21 WS 8.95 592a 737 ng g−1

1 LDCC 21 WS 5.46 527a 470 ng g−1

1 MWI (FG) 21 WS 1.18 39a 421 ng g−1

2 MWIs: Carcinogenic potencysignificantly reduced.

Lee et al. (2003)

1 MG 21 ESP, WS 30.2c 1,510d

1 FG 21 ESP, WS 19.8c 707d

1 MWI (CWI) 11 ... ... ... Total PAH in ash were499.3 μg kg−1.

Wheatley andSadhra (2004)

ACWIs Animal carcass waste incinerators, CWI clinical waste incinerator, HF in a hog farm, InWIs infectious waste incinerator, LDCCin a livestock disease control center, ... not reporteda In flue gasb Gram per daycBaPeq. Total conc. for individual PAH in flue gases, ESP and WSd In flue gases, ESP and WS

74 Environ Monit Assess (2007) 132:67–81

ash with the exception of mercury where the greaterproportion is vented via the flue stack. Mostly thetoxic metals associated with MW incineration arecadmium, lead, mercury, chromium and arsenic.National Research Council describes various typesof toxicity and health effects in humans for thesemetals (NRC 2000).

Trace element samples obtained from a MWI, acoal-fired cement kiln operation and a MSWI weremonitored for mercury (Stevens et al. 1996) andmeasured by the speciated Hg emission (US EPA1996). Significant amounts of soluble Hg(II) specieswere measured in the emissions from waste inciner-ation point sources with the Hg(II)/Hg(total) ratioranging from 0.75 to 0.95. The MWI emitted nearly95% of its emissions as Hg(II). Krivanek (1996)found that some facilities in US meet the standards forHg emissions from MWIs without additional controls(e.g. refuse derived fuel combustors) whereas most ofthe facilities did not conform to the standards.

Activated carbon injection, sodium sulfide injectionandwet scrubbing asmercury control technologies havebeen described. Dvonch et al. (1999) studied the use ofelemental tracers to source apportion mercury in SouthFlorida precipitation. An emission reconciliation foundthat local MWIs, emitted Hg(II) that could account forthe Hg wet deposition. The emissions from local urbanpoint sources played the dominant role in the wetdeposition of Hg to South Florida and Everglades.

A survey for the concentration of 22 elements inthe ashes of incinerators located at veterinary col-leges/animal disease diagnostic laboratories in sevenstates of US was conducted by Thompson et al.(1995). The variation in elemental composition ofashes collected over time from the same veterinarycollege incinerator in New York was reported for 24elements (Thompson et al. 1996). There was anindication that burned plastic wastes were a sourceof Pb in the ashes. Alvim-Ferraz et al. (2003c)reported the emission factors estimated for particulatematter, As, Cd, Cr, Pb, Mn, Hg, and Ni bysegregation of MW in different types according toPortuguese legislation. Comparison of the usual andrigorous practice of segregation suggested that rigor-ous segregation practice and adequate managementmethodology allowed reduction of ∼80% amount ofthe waste for incineration, thereby eliminating Hg andPb emissions and reducing those of As, Cd, Cr, Mn,and Ni.

The relationship between particle size and heavymetal concentrations in bottom ash and simulatedleachate from a MWI was determined (Racho and

Table 3 Relationship between particle size and concentrationof heavy metals in bottom ash of MWI

Mean Concentration (mg kg−1)

Particlesize

>9.5mm

4.75–9.5mm

0.5–4.75mm

<0.5mm

Pb 75.5 115.4 204.5 369.9Ag 13.2 49.1 172.6 93.1Fe 8,764.9 188,833.4 89,286.8 27,236.1Zn 1,115.8 3,418.5 5,681.8 8,494.6

Table 4 Toxic metal concentration in ashes from MWIs

Cadmium Lead Mercury Chromium Arsenic References

0.81–11.3 ppm 8.34–1,001 ppm 0.03–0.09 ppm 35.1–164 ppm 0.30–286 ppm Thompson et al. (1995)2.19–4.79 ppm 15.5–276 ppm ... 46.8–127 ppm 1.75–4.60 ppm Thompson et al. (1996)... ... 268±127 kg

year−1a... ... Dvonch et al. (1999)

0.25–0.85 ppm 1.83–102.98 ppm ... 0.89–2.51 ppm ... Kuo et al. (1999)1–56 μg g−1 192–5,866 μg g−1 ... 100–2,000 μg g−1 ... Abdulla et al. (2001)55–725 g year−1a 38–12,000 g year−1a 6–21,200 g year−1a 33–214 g year−1a 3–30.5 g year−1a Alvim-Ferraz et al. (2003c)... 765.3 mg kg−1 ... ... ... Racho and Jindal (2004)0.03–0.31 mgkg−1b

1.33–35.7 mg kg−1b ... 3.74–5.46 mg kg−1b ... Chen et al. (2004)

a Total emissionb Per kg of waste

... Not reported

Environ Monit Assess (2007) 132:67–81 75

Jindal 2004) and is summarized in Table 3. AveragePb, Ag, Fe and Zn concentrations in bottom ash were765.3, 327.9, 314,121.2 and 18,710.7 mg kg−1,respectively. The mean concentrations of heavy metalsfor bottom ash samples from three MWIs rangedbetween 192-5,866 μg g−1 of Pb, 100–2,000 μg g−1 ofCr, 138–1,988 μg g−1 of Cu, 31–928 μg g−1 of Mn,21–141 μg g−1 of Ni and 1–56 μg g−1 of Cd (Abdullaet al. 2001). Chen et al. (2004) found that the pig andanimal carcasses treating incinerators were havingmuch higher metal concentrations in stack flue gasesthan MWI.

On the basis of absolute concentration of heavymetals such as Cd, Cr, Cu, Ni, Pb and Zn in slags ofMW, Santarsiero and Ottaviani (1995) suggested thatthe landfilling of solid residues from MWI havingthese metals in slags need not be classified as toxic andharmful. However, Echegaray et al. (2002) observed

that the ash and slug fraction of MW incinerationrepresent a potential risk to human health due toheavy metal content (Cd, Cr, Pb, Hg, and Cu) andneed to be categorized as hazardous waste.

Disposal Disposal of incinerator ashes presents sig-nificant environmental problems, majority of ashbeing land filled, which results in contamination ofsub-soils and groundwater due to their leaching(Allsopp et al. 2001). The ash needed to be stored incovered containers and disposed of in a safe andproper manner at special landfill (Abdulla et al.2001). With a view to reduce leaching, these ashescan be stabilized in cement before disposal. Variousstudies have been carried out on solidification-stabilization of fly and bottom ash from MWIs withcement to render it less toxic and dispose of tolandfills in environmental friendly manner (Filipponi

Table 5 Comparison of incinerators emission standard for MWIs and hazardous waste combustors

Standards for incinerators: MEF 1998 US EPA 1997b EPA – MACT HWC 2004

Operating standards:CE 99.00% ... ...1°Chamber temp. 800±50°C ... ...2° Chamber temp. 1,050±50°C ... ...Residence time 1 s ... ...Stack height 30 m ... ...Emission standards: Existing units New unitsPM 150 mg Nm−3 34 mg dscm−1 34 mg dscm−1 1.6 mg dscm−1

NOx 450 mg Nm−3 250 ppmv ... ...HCl 50 mg Nm−3 100 ppmv 1.5 ppmv 0.18 ppmvVOCs ≤0.01%a ... ... ...CO ... 40 ppmv 100 ppmv 100 ppmvPCDD/Fs ... 2.3 ng TEQ dscm−1 0.40 ng TEQ dscm−1 0.20 ng TEQ dscm−1

SO2 ... 55 ppmv ... ...POHCs: ... ... ... ...a) PAHs ... ... 99.99%b 99.99%b

b) PCBs ... ... 99.9999%b 99.9990%b

Toxic metals:Cd 0.05 mg Nm−3 160 μg dscm−1 59 μg dscm−1 6.5 μg dscm−1

Pb 0.5 mg Nm−3 1200 μg dscm−1 59 μg dscm−1 6.5 μg dscm−1

Hg 0.05 mg Nm−3 550 μg dscm−1 130 μg dscm−1 8 μg dscm−1

Cr 0.5 mg Nm−3 ... 84 μg dscm−1 8.9 μg dscm−1

As 0.5 mg Nm−3 ... 84 μg dscm−1 8.9 μg dscm−1

Be ... ... 84 μg dscm−1 8.9 μg dscm−1

CE Combustion efficiency %CO2/%CO2+%CO×100, MACT maximum achievable control technology, PM particulate matter, ppmvparts per million by volume, dscm dry standard cubic meter, ... not reporteda Volatile organic compounds in ashb Destruction removal efficiency standard

76 Environ Monit Assess (2007) 132:67–81

et al. 2003; Gavasci et al. 1998; Genazzini et al. 2003;Lombardi et al. 1998). Table 4 shows the release oftoxic metals from the incineration of MW. The hightemperature melting treatment of incinerated MW ashproduces stabilized non-hazardous product “slag”leading to stabilization of metals which did not showleaching (Idris and Saed 2002).

5 Emission Standards

The growing public concern about the large volumeof toxic air pollutants released from numerouscategories of emission sources in US led to theAmendments of Clean Air Act in 1990 and promul-gation of new source performance standards (NSPS)and emission guidelines (EG) in 1997 to reduce airemissions from hospital/medical/infectious wasteincinerators (US EPA 1997b). EPA in 1999 promul-gated hazardous air pollutant (HAP) emissions stand-ards for Hazardous Waste Combustors HWCs /incinerators under the Clean Air Act Amendmentsand the Resource Conservation and Recovery Act(RCRA). Regulated pollutants include dioxins andfurans; mercury; total chlorine; semivolatile metals –lead and cadmium; low volatility metals – arsenic,beryllium and chromium; particulate matter; carbonmonoxide; and hydrocarbons. The standards require aminimum destruction and removal efficiency (DRE)of 99.99% for each principle organic hazardousconstituent and a minimum DRE of 99.9999% fordioxin-listed wastes.

For the disposal of bio-medical waste in India,Ministry of Environment and Forests has notifiedBio-Medical Waste (Management & Handling) Rules(MEF 1998) and these were amended in 2000 and2003 under the Environment (Protection) Act 1986.These rules prescribe the incineration of humananatomical waste; animal waste; microbiology andbiotechnology waste; discarded medicines and cyto-toxic drugs; and soiled waste. Emission standards forMWIs and hazardous waste combustors are summa-rized in Table 5.

6 Conclusions

MWIs are the major source of PCDD/Fs, PAHs andtoxic heavy metals to the environment. These com-pounds pass to air as vapors or stuck to the surfaces of

small solid particles and travel long distances beforethey return to earth in rainfall or particle setting. Theexposure of these compounds and metals to humanpopulation occur by inhalation or orally or throughskin contacts. Not only the incineration temperature,but their emissions are also related to the type ofwaste, APCDs, operating parameters, contents ofincineration and segregation of waste. Most of theincineration systems, which do not have efficientAPCDs and do not implement the segregationprocesses, do not obey the emission standards fororganic emissions. Catalytic filter system looks to beefficient, not only to remove PCDD/Fs but also todestroy it to CO2. Similarly the concentration of toxicheavy metals in the ash of MWI can be avoided tosome extent through segregation of the waste prior toincineration. The disposal of the ashes containingtoxic metals through solidification-stabilization of flyand bottom ash from MWIs with cement appears tobe the best method to render ash less toxic.

Acknowledgements The authors are thankful to CSIR, NewDelhi (India) for providing financial support to carry out workon the waste incineration.

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