Municipal solid waste incineration bottom ash: Characterization and kinetic studies of organic matter

Article abstract of DOI:10.1021/es980193e

Bottom ash is the main solid residue (in weight) which is produced by municipal solid waste incineration (MSWI) facilities. To be reused in public works, it has to be stored previously a few months. This material is composed primarily of a mineral matrix but also contains unburnt organic matter. The mineral content and its change in the course of aging are relatively well- known, in contrast with the organic content. So in order to detect the phenomena responsible for changes in organic matter and their effects during aging, the concentrations of the main organic compounds previously characterized, the number of microorganisms, and the release of carbon dioxide were followed kinetically (over 13 months) in model laboratory conditions (mass, particle size, humidity, temperature, aerobiosis). The results showed that the aging process led to the natural biodegradation of the organic matter available in bottom ash, composed essentially of carboxylic acids and n-alkanes (steroids and PAH's to a lesser extent), and consequently that it would improve the bottom ash quality. Furthermore these results were confirmed by the study of aging Conducted in conditions used in the industrial scale (over 12 months).

Full text of DOI:10.1021/es980193e

Environ. Sci. Technol. 1999, 33, 1110-1115
draining and evaporation. The main chemical reactions
Municipal Solid Waste Incineration
Bottom Ash: Characterization and
Kinetic Studies of Organic Matter
involved in the transformation of MSWI bottom ash inorganic
matter are the oxidation of scrap iron (highly exothermal),
the hydroxylation of metals, the carbonation of alkaline and
alkaline earth metals, and the dissolution of lime and calcium
sulfate (3). Few published studies (5) have dealt with changes
in organic matter during aging, as well as the role of
microorganisms, even though the MSWI bottom ash milieu
S . D U G E N E S T , * , † J . C O M B R I S S O N , ‡
†
H . C A S A B I A N C A , A N D
M . F . G R E N I E R - L O U S T A L O T
(
water, temperature, pH, organic matter) seems able to
†
support bacterial development. The presence of metals can
also preferentially favor the growth of some bacterial species.
Microorganisms could thus act on the MSWI bottom ash,
particularly on the organic matter via oxidation or dehy-
drogenation reactions of organic components (6).
Service Central d’Analyse, Centre National de la Recherche
Scientifique, USR 059, BP 22, 69390 Vernaison, France, and
Laboratoire d’Ecologie Microbienne du Sol, UMR-CNRS 5557,
Universit e´ Claude Bernard-Lyon I, 69622 Villeurbanne, France
Consequently, we investigated changes in organic matter
related to the development of microorganisms in the milieu
during aging. Two conditions of aging were tested: in
conditions existing at the industrial scale (open pile of 300
tons) and in controlled conditions at the laboratory scale
Bottom ash is the main solid residue (in weight) which is
produced by municipal solid waste incineration (MSWI)
facilities. To be reused in public works, it has to be stored
previously a few months. This material is composed
primarily of a mineral matrix but also contains unburnt
organic matter. The mineral content and its change in the
course of aging are relatively well-known, in contrast
with the organic content. So in order to detect the phenomena
responsible for changes in organic matter and their
effects during aging, the concentrations of the main organic
compounds previously characterized, the number of
microorganisms, and the release of carbon dioxide were
followed kinetically (over 13 months) in model laboratory
conditions (mass, particle size, humidity, temperature,
aerobiosis). The results showed that the aging process
led to the natural biodegradation of the organic matter
available in bottom ash, composed essentially of carboxylic
acids and n-alkanes (steroids and PAH’s to a lesser
extent), and consequently that it would improve the bottom
ash quality. Furthermore these results were confirmed
by the study of aging conducted in conditions used in the
industrial scale (over 12 months).
(
aerobiosis, temperature 30 or 70 °C, 80 or 160 g samples).
Laboratory simulation of aging for 13 months enabled us to
kinetically follow the concentrations of target organic
compounds, the number of microorganisms, and the release
of carbon dioxide (at 30 °C). The latter is a significant marker
of the oxidation of organic compounds by microorganisms
in MSWI bottom ash during aging. Concerning aging in in
situ conditions, only the kinetics (for 12 months) of organic
compounds could be done.
In both situations of aging, mechanisms involved in
organic matter changes could be suggested.
An analytical methodology was first developed to identify
and quantify organic components of MSWI bottom ash,
involving two extraction techniques: supercritical fluid
extraction (SFE) and hot solvent extraction (Soxtec). The
samples recovered were analyzed by using two state-of-the-
art analytical tools: gas chromatography coupled to a mass
spectrometry detector (GC-MSD) and gas chromatography
with microwave-induced plasma atomic emission detection
(
GC-MIP-AED).
Conventional techniques were used to enumerate mi-
croorganisms in solid media: both direct counting using a
fluorochrome and an indirect plate counting involving
bacterial growth (7).
Introduction
Experimental Section
In France, 37% of the municipal solid waste are eliminated
by incineration with or without energy recovery (1). Municipal
solid waste incineration (MSWI) produces large quantities
of bottom ash (2.7 milliontons/ year) as solid residue. MSWI
bottom ash is composed primarily of silica, metal oxides,
silicates, chlorides, and sulfates, but also contains nonneg-
ligible concentrations of heavy metals including Zn, Pb, Cu,
Ni, Cr, and Cd, and small amounts of unburnt organic matter
MSWI Bottom Ash Sam pling. The nature of MSWI bottom
ash is closely linked to the nature of the solid waste, the type
of incinerator, and the combustion conditions. We have
selected one facility having a high incineration capacity and
consequently producing high amounts of bottom ash.
The facility is located near an urban area. As a result of
the French customs (1), municipal solid waste include paper-
cardboard (30%), fermentable matter (25%), glass (12%), fines
(
2). In some European countries, bottom ash can be used in
(
10%), plastics (10%), metal (6%), textiles (2%), and undefined
road building, but has to be stored a few months before
reuse (1). Published data indicate that the aging process leads
to an overall improvement in the environmental qualities of
MSWI bottom ash (3-5). It has been shown that aging reduces
the leaching of heavy metals and total organic carbon in
parallel to a decrease of pH from highly alkaline to nearly
neutral values (5). This is done by stockpiling large amounts
of MSWI bottom ash in the open air, which allows some
materials (5%) (mean composition). The nature and the
volume of solid waste are relatively constant from day to
day.
The incinerator is one of the most common type of MSWI
system in use today. It has been operated since 1989, and its
rated incineration capacity is 12 tons/ h. Before combustion,
solid waste were not preprocessed to remove materials
including ferrous or nonferrous metals and glass. They were
fed into the combustion chamber via gravity and transported
through the furnace via a system consisting of six rollers
disposed on a slightly inclined plane. Inside the furnace, the
air supply was controlled, and the gas temperature reached
*
Corresponding author phone: 04-78-02-22-55; fax: 04-78-02-
7
1-87.
†
‡
Centre National de la Recherche Scientifique.
Universit e´ Claude Bernard-Lyon I.
1
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 33, NO. 7, 1999
10.1021/es980193e CCC: $18.00

1999 Am erican Chem ical Society
Published on Web 04/01/1999

roughly 1200 °C. In furnace exit, bottom ash was collected
by an extractor using water to cool it. Then elements larger
than 30 mm were separated, and ferrous metal was mag-
netically recovered with an over-band. At last, bottom ash
was deposited in a pit.
The MSWI bottom ash sample was collected over a 7 day
time period, in October. It reached about 400 tons distributed
into 20 dumper-trucks. The initial sample (500 kg) was pre-
pared by collecting two buckets from each truck. It was com-
posed of particles whose diameter ranged from 0 to 30 mm,
and high amounts of unburnt paper, metal containers, and
glass were not observed. Its moisture content was 16.3 wt %.
Several representative samples of 80 and 160 g of MSWI
bottom ash, whose multi-millimeter particle size distribution
was less than 4 mm, were prepared from the initial sample,
by drying (30 °C), grinding, and quartering. Four of these
samples were submitted to analysis in order to characterize
the initial state of the bottom ash, and the others were aged
in standardized laboratory conditions.
Sam ples Aged in Standardized Laboratory Conditions.
The granulometric heterogeneity of MSWI bottom ash was
conserved in the studied samples, at the same time as
reducing grain size for laboratory scale tests. By analogy with
soil incubation techniques, the samples were moistered at
a level equivalent to 60% of their water holding capacity, i.e.,
FIGURE 1. Physicochemical characterization methodology of MSWI
bottom ash.
the outside temperature varying between 12 and 18 °C.
Temperatures inside the pile varied from 30 to 70 °C.
Following this initial rise, temperatures decreased throughout
the pile, stabilizing between 7 and 12 months at around 30
6
0 mL/ kg. Each sample was placed in a beaker of appropriate
°
C at the surface and 25 °C in the core. A further decrease,
size (100 mL for 80 g samples, 250 mL for 160 g). The beakers
were then placed in a 1 L (80 g) or 3 L (160 g) jar. The
dimensions of the aging system were selected to ensure
aerobic conditions (i.e., available oxygen amount and good
diffusion of oxygen in the sample). The water content of the
MSWI bottom ash was maintained by adding ultrapure water
to the bottom of the jar. The jars were placed in constant-
temperature incubators at 30 or 70 °C and opened from time
to time to admit fresh air and thus maintain aerobiosis
throughout aging. The carbon dioxide release was followed
at 30 °C. A bottle containing 0.1 N sodium hydroxide was
placed inside each jar to trap carbon dioxide released from
the MSWI bottom ash.
resulting from the atmospheric temperature, was then
observed.
A water balance of the aging pile was established by
measuring rainfall and the volume of water in the recovery
basin. At the onset of aging, draining of the bottom ash pile
produced 30 m3 of water. Afterward, the moisture content
of MSWI bottom ash remained relatively stable around 17
wt %.
After 7 and 12 months of storage, samples were taken
from the pile by core drilling at two points (at each extremity)
through its entire depth. These core samples were used to
prepare two 80 g MSWI bottom ash samples with particle
sizes less than 4 mm (as were prepared the laboratory
samples): one was from the surface down to a depth of 1 m
and the second was from a depth of 1 m to the bottom,
corresponding to the core of the pile.
A total of 22 samples of MSWI bottom ash were aged at
3
0 or 70 °C for 1, 4, 9, or 13 months. Periodically, two 80 g
samples of MSWI bottom ash aged in each temperature
condition, and sometimes one supplementary 160 g sample,
were removed from the jar and processed for analysis. The
volume of sodium hydroxide for trapping carbon dioxide
was removed periodically to measure carbonates and bi-
carbonates and replaced by a fresh volume of trapping
solution. From these measurements, the carbon dioxide
released (micrograms of carbon) per mass unit of dry bottom
ash (grams) was determined.
Characterization of Organic Com pounds. Figure 1 il-
lustrates the methodology for the physicochemical charac-
terization of MSWI bottom ash. Each sample was first
screened into six particle size classes, whose diameters were
included in the interval indicated in millimeters. A sample
of about 5 g of classes 1-5 was then prepared by manual
quartering. Fraction 6 was divided into two samples.
The seven samples were first extracted with supercritical
carbon dioxide for 30 min, using a Hewlett-Packard (HP)
Model 7680 apparatus. With the conditions of pressure (318
bar) and temperature (120 °C) chosen, the density of the
Sam ples Aged in On-Site Conditions. At the industrial
scale, 300 tons of MSWI bottom ash (from the same on-site
sample used to prepare the laboratory samples) were
deposited as a conical pile in open air. A basin for recovering
water draining from the MSWI bottom ash was located
downstream from the pile. The site was previously prepared
by installing a geomembrane covering the drainage ditch
and the emplacement for the pile. The surface of the bottom
3
supercritical fluid was relatively high (0.61 g/ cm ) and was
thus able to solubilize efficiently different types of com-
pounds. This first extraction step yielded seven 1 mL extracts
of double-distilled hexane (SDS, HPLC grade), which were
then pooled and subjected to a silica cleanup separation.
Finally, three purified SFE extracts were obtained.
The SFE residues of classes 1, 2, and 3, and the two class
6 SFE residues, were mixed, respectively, and then extracted
with 100 mL of methanol (Chromanorm, HPLC grade) for 2
h, using a Soxtec apparatus (Tecator). The SFE residues of
classes 4 and 5 were extracted separately as above. The second
extraction step yielded four 1 mL methanol extracts.
Each extract was analyzed by GC-MSD and GC-MIP-AED.
Chromatographic separation was achieved on an HP Model
5890A Series II gas chromatograph (GC), equipped with a 30
m 5% phenyl (equivalent) polysilphenylene siloxane capillary
column with a 0.22 mm i.d., and 0.25 µm film thickness (BPX5,
2
ash pile was 126 m (8 m × 16 m), and its height at the center
was 3 m. In the course of storage, the bottom ash pile was
subjected to a number of uncontrolled factors, including
outside temperature, surrounding atmosphere, precipitation,
light, microorganisms, vegetation, etc.
Internal temperature was monitored with thermal sensors
placed at different depths in the bottom ash pile. During the
first month of storage, the temperature of the entire pile
increased, probably due to the oxidation of scrap iron present
(
3). The highest temperature increase occurred at the surface
and reached 70-80 °C, undoubtedly because of the pre-
dominance of scrap iron and better oxygenation in this layer,
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SGE). The instrument was equipped with an HP Model 7673A
programmable automatic injector. The injector was main-
tained at 280 °C in the splitless mode (1 µL). After an initial
plateau of 5 min at 60 °C, the oven temperature was increased
at the rate of 10 °C/ min up to 315 °C, followed by a 15 min
plateau at that temperature. For steroid determination, the
initial GC oven temperature was 150 °C.
The GC-MSD coupling configuration was equipped with
an HP Model 5972 Series MSD mass detector (electron impact,
7
0 eV). The transfer line was maintained at 280 °C. The mass
interval scanned was from 40 to 450 amu at a rate of 1.8
scans/ s. The quantitative analysis of specific aromatic
compounds, polyaromatic hydrocarbons (PAH’s) and ste-
roids, was carried out in the SIM mode with external
standards, selecting ions characteristic of the target molecule.
In both cases, the relative error of quantification was included
between 5 and 10%.
GC-MIP-AED coupling involved an HP Model 5921A
microwave-induced plasma atomic emission detector. Com-
pounds were quantified on the carbon emission line at 193
nm (very sensitive). The helium makeup flow rate was 60
mL/ min. Inlet pressures of the makeup gas and reactant
gases (oxygen and hydrogen) were 400, 160, and 200 kPa,
respectively. A nitrogen flow rate of 3 L/ min was maintained
inside the spectrometer (purge). The transfer line temperature
was maintained at 280 °C. The microwave cavity was under
a pressure of 10.3 kPa, and the temperature was 280 °C. The
elemental response of the detector was calibrated with three
reference products (Aldrich) widely used in the laboratory.
The carbon detection limit calculated as 3 times the standard
deviation of the noise was 0.1 ng. The relative error of
quantification was estimated at about 10%.
FIGURE 2. Concentration profiles of (a) carboxylic acids and (b)
n-alkanes.
The methodology for characterizing organic compounds
in MSWI bottom ash was developed for the 80 g samples of
crude MSWI bottom ash < 4 mm. It was applied to the
different samples (80 or 160 g) aged in laboratory conditions
and to samples (80 g) aged in on-site conditions.
often elevated relative standard deviations). The same was
true for the results of enumeration of microorganisms.
The principal organic compounds present initially in the
extractable matter from MSWI bottom ash were carboxylic
acids (total concentration 73 µg/ g), n-alkanes (14.1 ( 1.6
µg/ g), steroids (24.1 ( 0.2 µg/ g), phthalates (about 6 µg/ g),
and PAH’s (from 130 to 210 ng/ g).
Enum eration of Microorganism s. A subsample of about
1
0 g was taken from the 80 and 160 g samples of MSWI bottom
ash, for the enumeration of microorganisms. The direct
counting method was based on staining bacteria with a DNA
intercalating agent, acridine orange (AO), that fluoresces
green when excited by UV irradiation (8). Serial dilutions of
the sample were done in 8‰ sodium chloride. One milliliter
of each dilution was stained with 100 µL of AO solution (0.1%)
over a 2 min time period. Then the stained suspension was
filtered on 0.2 µm polycarbonate membrane filters (Nucle-
pore, Costar) before mounting on a glass slide. Enumeration
was carried out with an inverse epifluorescence microscope
The acid concentration profile determined in crude MSWI
bottom ash (Figure 2a) shows that there was a predominance
of compounds containing an even number of carbon atoms,
especially C16 and C18 (palmitic and oleic acids). The short
chain acids, from 6 to 10 carbon atoms, account for a much
lower proportion of the total quantity of acids.
The concentration profile of n-alkanes in MSWI bottom
ash (Figure 2b) shows a bimodal distribution with a short
mode of C14-C20 and a pseudo-normal distribution from
C21 to C36. This profile presents some analogies with that
of a petroleum paraffin series, such as heavy diesel fuel, whose
distillation range is between 254 °C (bp of C14) and 496 °C
(
Zeiss Universal) by counting at least 100 bacterial cells on
each slide.
The indirect counting method involved the plate growth
(
bp of C36). In light of these results, MSWI bottom ash could
of microorganisms on an unselective agar nutrient (Trypticase
Soy Agar at 4 g/ L) containing cycloheximide to inhibit fungi
development. The number of colonies is directly related to
the number of bacteria cultured during a 5 day incubation
period at 30 °C.
Microorganisms were enumerated in two different samples
of crude MSWI bottom ash and in all the samples aged in
the laboratory (mentioned above), including two additional
assays from 17 months of aging at 30 °C.
be so compared to natural products as oils.
Six steroids were identified and quantified: 4,6-choles-
tadien-3â-ol, cholesterol, â-sitosterol (both major com-
pounds), cholestanol, ergosterol, and stigmasterol. These
compounds are considered as excellent biomarkers.
Seven phthalates were also identified in extracts of crude
MSWI bottom ash. Dibutyl phthalate and bis(2-ethylhexyl)
phthalate were the major compounds. The concentrations
of the other phthalates identified [dimethyl, diethyl, bis(2-
methylpropyl), nonyloctyl, decyloctyl] were lower than 1 µg/
g. These toxic compounds are relatively stable chemically
and resistant to biodegradation, contrary to steroids.
Highly toxic, PAH’s are usually generated when organic
matter is treated in conditions of pyrolysis, i.e., incomplete
combustion or combustion without oxygen, explaining their
presence in MSWI bottom ash. The most commonly found
types [from naphthalene to dibenz[a,h]acridine] were identi-
Results and Discussion
In all MSWI bottom ash samples (crude or aged), each organic
compound identified was quantified. To define the concen-
tration of each organic compound for one state of aging (initial
or in the course of laboratory aging), we have taken into
account the mean of the results obtained with different
samples (2, 3, or 4) but having the same age (explaining the
1
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FIGURE 4. Evolution during standardized aging of total carboxylic
acid concentration (s0s)at 30°C and (- - - ! - - -)at 70°C, of acid
C8 concentration (×40) (s4s) at 30 °C and (- - - 3 - - -) at 70 °C,
of acid C16 concentration (sOs) at 30 °C and (- - - x - - -) at 70
FIGURE 3. Evolution of carbon dioxide release and bacteria number
during standardized aging at 30 °C. The release of carbon dioxide
was measured from samples (0) 3, (]) 4, (O) 6, (4) 8, (x) 2, (3) 9,
°
C. Relative standard deviation: 2-17%.
(
×) 1, (/) 5, (!) A, (+), B, (*) C. The mean numbers of (^) viable
and (&) total bacteria were determined from measurements in each
This temperature does not totally inhibit microbial develop-
ment in a milieu, but it can result in an initial latency period
during which the microorganisms must adapt to the imposed
temperature before developing. In addition, direct enumera-
tion of microorganisms in samples aged at 70 °C for 9 months
showed a nonpersistent development, probably thermophilic
bacteria. Many of thermophiles have an optimum growth
temperature between 50 and 60 °C, but some of them indeed
grow at temperatures well above 90 °C (9).
sample aged.
fied in MSWI bottom ash, including phenanthrene (27%),
fluoranthene (21%), and pyrene (17%). Their total concen-
tration in the MSWI bottom ash studied was relatively low.
As a result, all carboxylic acids, n-alkanes, steroids,
phthalates, and PAH’s determined initially were selected as
target compounds for kinetic studies.
The biodegradation of organic matter down to the final
stage of totally inorganic was observed for different types of
organic compounds. The phenomenon was particularly
intense for aliphatic compounds, carboxylic acids, and
n-alkanes. In general, these compounds are preferentially
degraded in comparison to aromatic compounds (10).
Similarly, microorganisms metabolize preferentially lower
molecular weight compounds (10, 11). Laboratory aging led
to a rapid degradation of carboxylic acids in MSWI bottom
ash (Figure 4), regardless of chain length. During standardized
aging at 30 °C, degradation of acids occurred primarily during
the first month (60% degradation). When laboratory aging
was conducted at 70 °C, the slower development of micro-
organisms at this temperature resulted in a slower initial
decomposition of carboxylic acids. Nevertheless, during the
first 4 months of aging at 70 °C, acid degradation was 66%.
Fatty acid metabolism by most microorganisms involves a
sequence of reactions (6) (dehydrogenation, hydration,
dehydrogenation of alcohol), called â-oxidation. The bio-
degradation of acids occurred principally up to 4 months of
aging, and the phenomenon continued up to 9 months
At time zero, the MSWI bottom ash contained (6.01 (
4
0
.17) ×10 colony forming units (cfu) per gram of dry material
that were viable in the conditions chosen, among the (1.07
7
(
0.04) × 10 cells/ g of dry MSWI bottom ash counted by AO
microscopy. The greatest increase in the number of micro-
organisms living in the MSWI bottom ash and viable in vitro
was during the first month of the aging process at 30 °C
(
5
Figure 3). Microorganisms continued to develop until about
months. This was reflected by the considerable release of
carbon dioxide, significant of the capacity of microorganisms
to use organic carbon available in MSWI bottom ash. At 4
months, the number of microorganisms that could be
cultured nearly reached the total number of AO counted
cells present in MSWI bottom ash. All bacteria present were
thus viable and could be grown in a medium other than
MSWI bottom ash. The number of microorganisms that could
be cultured gradually decreased from 5 to 17 months of aging.
This decrease was initially very low (between 4 and 9 months),
accelerating during the last 4 months. In parallel, the total
number of cells increased slightly, suggesting that micro-
organisms could survive in the MSWI bottom ash, because
they were adapted to this material but no longer to the
nutrient broth. After 17 months, the number of microorgan-
(
overall degradation about 85%). Between 9 and 13 months
of aging at 30 and 70 °C, there was an increase in unsaturated
C18 (linoleic), C16 (hexadecenoic), and C14 (tetradecenoic)
acids in parallel to a decrease in oleic acid (C18) and saturated
C16 (hexadecanoic) and C14 (tetradecanoic) species. A large
number of microorganisms, however, are able to dehydro-
genate fatty acids; e.g., Tricholoma grammapodium trans-
forms oleic acid to linoleic acid (6).
6
isms that could be cultured stabilized around 10 cfu/ g of
dry bottom ash. During this period of regression of the
number of viable bacteria, carbon dioxide release continued
and tended toward a plateau that was reached after about
1
1 months. The quantities of carbon dioxide produced by
surviving microorganisms in MSWI bottom ash were much
lower at the end of aging. This low microbial respiration
could be due to the exhaustion of available carbon sources
in MSWI bottom ash.
Aging in on-site conditions also led to an overall degra-
dation of acids (80-90%) in MSWI bottom ash. The decreasing
acid concentration between 0 and 7 months could be partially
due to the leaching by rainwater from MSWI bottom ash in
the pile. The results at 12 months might suggest an increase
in the acid concentration at the end of aging.
Fewer data could be obtained when the aging process
was run at 70 °C (enumeration of viable bacteria and trapping
of carbon dioxide released could not be done at this
temperature). It is nevertheless probable that bacteria also
developed in the MSWI bottom ash during aging at 70 °C.
At both temperatures (Figure 5), the biodegradation of
n-alkanes during the first month of standardized aging
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FIGURE 6. Evolution of bis(2-ethylhexyl) phthalate concentration
s0s)at 30°C and (- - - ! - - -)at 70°C during standardized aging
FIGURE 5. Evolution during standardized aging of total n-alkane
concentration (s0s)at 30°C and (- - - ! - - -)at 70°C, of n-alkane
C14 concentration (×30) (s4s) at 30 °C and (- - - 3 - - -) at 70 °C,
of n-alkane C32 concentration (×30) (sOs) at 30 °C and (- - -
x - - -) at 70 °C. Relative standard deviation: 1-30%.
(
(relative standard deviation: 1-14%), and (sOs) on the surface
and (- - - x - - -) in the core during real on-site aging.
catabolism (12). Then the relative concentration of naph-
thalene decreased between 1 and 4 months, perhaps due to
its volatilization, causing a decrease in its concentration and
an increase in the relative concentration of phenanthrene,
fluoranthene, and pyrene in MSWI bottom ash. It may also
have been partially degraded by microorganisms.
resulted in the formation of short-chain n-alkanes (C14 and
C16), as a result of microbial oxidation of n-alkanes having
longer alkyl chains (C32). After 1 month, n-alkanes degrada-
tion occurred without distinction of chain length. The
microbial oxidation process (R or â) of n-alkanes was thus
more intense between 1 and 4 months (degradation rate
about 50%). A large number of microorganisms can use
n-alkanes as substrate, in particular zymogenic bacteria
belonging to the genus Pseudomonas (10). It is highly probable
that these ubiquitous bacteria were present in MSWI bottom
ash. Changes in n-alkanes between 4 and 13 months of aging
were not significant because of the standard deviations
observed.
The kinetic changes in phthalate concentrations, espe-
cially that of bis(2-ethylhexyl) phthalate (Figure 6), revealed
no significant changes in these compounds during simulated
or on-site aging, suggesting that phthalates remain un-
changed during the aging process. Phthalates initially present
in MSWI bottom ash are probably not a sufficient and
available source of carbon for microorganisms in comparison
to carboxylic acids and n-alkanes, which in addition are more
easily degraded than aromatic compounds.
In the on-site experiment, the concentration profile of
n-alkanes in MSWI bottom ash samples aged for 7 months
differed from the results obtained in the laboratory experi-
ment. There were higher concentrations of short n-alkanes,
and there were nonnegligible levels of methylated n-alkanes.
Formed short n-alkanes could result from microbial me-
tabolism, but the contamination of the samples or the pile
of MSWI bottom ash, due to the proximity to highways, is
more probable. Nevertheless, the results at 12 months showed
the degradation of n-alkanes during aging (between 50% and
To conclude, changes in the organic matter of MSWI
bottom ash during aging are governed primarily by biotic
mechanisms. The first 4 months led to the biodegradation
of organic matter available in MSWI bottom ash, composed
essentially of carboxylic acids and n-alkanes (steroids and
PAH’s to a lesser extent). This organic matter was completely
transformed to inorganic substances, with the principal
metabolite detected being carbon dioxide. After 4 months,
residual organic matter changed little, since microorganisms
6
0%), with no relationship to chain length.
(
no mobility) exhausted available organic substrates (energy
In addition to the transformation of aliphatic organic
sources) and so activity decreased. Chemical reactions also
probably took place during aging in light of the presence of
metal catalysts, free radicals, and temperature effects in MSWI
bottom ash. The results of the present work suggest that
these phenomena are not very pronounced.
compounds, laboratory aging also caused the transformation
of steroids initially present in MSWI bottom ash. At 70 °C,
there was a rapid degradation (in 4 months) of all steroids
(
80%), in particular the three major compounds, 4,6-
cholestadien-3â-ol, cholesterol, and â-sitosterol. At 30 °C,
the aging process caused the transformation of 4,6-choles-
tadien-3â-ol and â-sitosterol, with no substantial decrease
in the total steroid concentration. The mechanisms involved
could be microbial dehydrogenation or hydroxylation reac-
tions (6). Steroids were not assayed in bottom ash aged
outdoors because of the abundance of sources of contami-
nation in proximity to the pile.
Overall, aging in on-site conditions confirmed the data
obtained in model conditions.
In light of the well-designed and operated facility, these
results should be furthemore representative of the evolution
of a widespread (in France at least) quality of MSWI bottom
ash.
The kinetic and mechanistic studies revealed the presence
of biogeochemical tracers such as carboxylic acids,n-alkanes,
and steroids, and stable tracers, e.g., phthalates. By analogy
with fossil mixtures in which observed alterations of organic
compounds are significant of the extent of biodegradation
of the mixture (13), the degree of degradation of organic
compounds (biomarkers) would be significant of the degree
of MSWI bottom ash aging.
PAH’s initially present in MSWI bottom ash were also
transformed during laboratory aging (at 30 and 70 °C),
primarily during the first 4 months. During this period, the
relative concentrations of the major compounds (phenan-
threne, fluoranthene, and pyrene) decreased first, while that
of naphthalene increased. This may have resulted from the
degradation of high molecular weight PAH’s by microorgan-
isms in MSWI bottom ash, with the formation of naphthalene,
probably due to inhibition of the mechanism before microbial
Thanks to its own material properties (including especially
its moisture content and temperature effects), aging would
1
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 33, NO. 7, 1999

naturally improve the MSWI bottom ash quality by reducing
its organic content and for extent its polluting character.
(3) Belevi, H.; St a¨ mpi, D. M.; Baccini, P. Waste Manage. Res. 1992,
0, 153.
1
(
4) Pascual, C.; Boos, B.; Troesch, O.; Beaurez, R.; Hermann, M.
Environ. Technique-Info-D e´ chets 1994, 140, 86.
Acknowledgments
This study received the financial support of the SITA group,
(
5) Steketee, J. J.; Urlings, L. G. C. M. In Environmental Aspects of
Construction with Waste Materials; Goumans, J. J. J. M., Van der
Sloot, H. A., Aalbers, T. G., Eds.; Elsevier Science: Amsterdam,
9
4 rue de Provence, BP 693-09, 75425 Paris Cedex 09, France,
1
994; p 233.
in the context of the thesis of St e´ phanie Dugenest. Biological
experiments and assays were carried out in cooperation with
the Laboratoire d’Ecologie Microbienne du Sol, UMR-CNRS
(
(
(
6) Fonken, G. S.; Johnson, R. A. In Oxidation in organic chemistry;
Belew, J. S., Ed.; Marcel Dekker: New York, 1972; Vol. 2.
7) Richaume, A.; Steinberg, C.; Jocteur-Monrozier, L.; Faurie, G.
Soil Biol. Biochem. 1993, 25(5), 641.
5
557, Universit e´ Claude Bernard-Lyon I, 69622 Villeurbanne,
France. Mrs. Lucile Jocteur-Monrozier is greatly thanked for
her contribution to the design of the laboratory experiments
and to the interpretation of results.
8) Hobbie, J. E.; Daley, R. J.; Jasper, S. Appl. Environ. Microbiol.
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977, 33, 1225.
(9) Tortora, G. J.; Funke, B. R.; Case, C. L. Microbiology: an
introduction, 4th ed.; Benjamin/ Cummings: Redwood City, CA,
1992.
Supporting Information Available
(
(
10) Sepic, E.; Leskovsek, H.; Trier, C. J. Chromatogr. A 1995, 697,
Two figures showing the evolution of carboxylic acid and
n-alkane contents in MSWI bottom ash, during aging in on-
site conditions. This material is available free of charge via
the Internet at http:/ / pubs.acs.org.
5
15.
11) Bailey, N. J. L.; Jobson, A. M.; Rogers, M. A. Chem. Geol. 1973,
1, 203.
(12) Evans, W. C.; Fernley, H. N.; Griffiths, E. Biochem. J. 1965, 95,
19.
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(
Received for review February 27, 1998. Revised manuscript
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