Organic pollutants pro
filing of wood ashes from biomass power plants
linked to the ash characteristics
Ledicia Rey-Salgueiro
, Beatriz Omil
, Agustín Merino
, Elena Martínez-Carballo
, Jesús Simal-Gándara
,
a
Nutrition and Bromatology Group, Department of Analytical and Food Chemistry, Food Science and Technology Faculty, University of Vigo
— Ourense Campus, 32004 Ourense, Spain
b
Sustainable Forest Management Unit, Department of Soil Science and Agricultural Chemistry, University of Santiago de Compostela
— Lugo Campus, 27002 Lugo, Spain
H I G H L I G H T S
• The sum of BTEX+S varied from non-
detected to 30 mg/kg.
• Total amounts of PAHs (total PAHs)
ranged
between
non-detected
to
422
μg/kg.
• The larger T50 (with more burned or-
ganic matter), the higher BTEX + S
levels.
• The higher the QMO (or lower combus-
tion), the higher presence of PAHs.
• The ashes are suitable for soil applica-
tions, as an organic amendment.
G R A P H I C A L
A B S T R A C T
a b s t r a c t
a r t i c l e i n f o
Article history:
Received 2 September 2015
Received in revised form 3 November 2015
Accepted 25 November 2015
Available online 8 December 2015
Editor: D. Barcelo
Purpose: Wood ash, characterized by high content of certain nutrients and charcoal, can be applied to soils as a
means of managing this waste product improving the soil quality. The associated environmental risk must be
assessed. The objective of this study was to characterize the bottom and
fly ash collected from 15 biomass
power plants in Spain by determining the benzene, toluene, ethylbenzene, xylene and styrene (BTEX + S),
PAHs and aliphatic hydrocarbon contents of both types of ash. Biochar was also used for comparison purposes.
Methods: Gas chromatography
–mass spectrometric methods were used for the identification and determination
of both BTEX+S and aliphatic hydrocarbon contents in bottom and
fly ashes, as well as biochar. High perfor-
mance liquid chromatography with
fluorescence detection was used for PAHs measurements. Multivariate cor-
relation analysis was used to determine the relationship between sample characteristics and pollutants identi
fied
by partial least squares regression analysis.
Results and discussion: In general, the degree to which organic matter in the sample is burned increases with T50
or the
“50% burn off” temperature (possibly due to the addition of fuel), and the BTEX+S also tended to increase.
However, as the Q/MO (the heat of combustion divided by organic matter mass) increased, the combustion de-
creased or proceeded with less oxygen, which appears to be related to an increased presence of PAHs. The results
con
firm that the amounts of organic pollutants (PAHs and BTEX+S, together with total aliphatic hydrocarbons)
Keywords:
Wood ash and biochar
BTEX
Styrene
PAHs
Total aliphatic hydrocarbons
Soil impact
Science of the Total Environment 544 (2016) 535
⁎ Corresponding author at: Nutrition and Bromatology Group, Department of Analytical and Food Chemistry, Food Science and Technology Faculty, University of Vigo, Spain.
E-mail address:
(J. Simal-Gándara).
http://dx.doi.org/10.1016/j.scitotenv.2015.11.134
0048-9697/© 2015 Elsevier B.V. All rights reserved.
Contents lists available at
Science of the Total Environment
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v
in the wood ash do not exceed limits established for different soil or industrial uses.
Conclusions: Both types of ash, together with biochar, may therefore be suitable for application to soil as a fertil-
izer and an organic amendment, taking into account the target organic pollutants.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
The wood ash generated in biomass power plants contains high
levels of nutrients and charcoal and can be applied to soils
(
Augusto et al., 2008; Omil et al., 2013
). These studies showed that
application of wood ash to land increased the soil pH and nutrient
levels. In addition, because the signi
ficant content in charcoal, this
practice may also help to improve the SOM content, enhance soil mi-
crobiology activity and enhance the C stocks of degraded agricultural
soils. Incineration greatly reduces the volume of the waste disposed
(
). Fly and bottom ashes are the main
by-products from the combustion of solid biomass, representing
5.0% and up to 30% of initial weight of waste, respectively (
). Fly powdered ash, suspended in the
flue gases, is the
finest part and is typically light grey. Fly ash represents up to 40%
of the total ash. Bottom ash (or mixed wood ash), which settles
under the grate of the combustion chamber, is the coarsest compo-
nent of the combustion by-products. Bottom ash is generated in
wood
fired furnaces and contains significant amounts of charcoal
(
Melotti et al., 2013; Santalla et al., 2011
).
Large volumes of plant residues are burned in industrial power
plants, at a combustion temperature from 500 to 800 °C, under oxic con-
ditions. The concentrations of PAHs in wood ash vary depending on the
boiler operating conditions and on differences in the origin and compo-
sition of biomass (
Pérez-Gregorio et al., 2010; Rey-Salgueiro et al.,
) and could range from 15 to 733
μg/kg (
). Nevertheless, the organic compounds possibly present are not
usually addressed and in these kinds of samples, it is important to
know not only the inorganic but also the organic toxic substances
(
). Sixteen PAHs are listed as priority pollut-
ants by the United States Environmental Protection Agency (
). Benzene, toluene, ethylbenzene, the ortho, para and meta xylenes
(BTEX) and styrene (S) are petroleum-derived volatile organic com-
pounds, and can occur in wood ash. BTEX has been adopted by state
agencies as an
“indicator” from petroleum products. Combustion of ag-
ricultural residue-derived fuels leads to BTEX emissions (
2009; Krugly et al., 2014; Sinha et al., 2006
). They can also remain in the
combustion residue. Most previous research has focused on PAHs in
fly
ash (
Masto et al., 2015; Straka and Havelcová, 2012
), and very few have
characterized organic pollutants in bottom ash from biomass power
stations.
Biochar is generated by biomass pyrolysis at temperatures ranging
from 350 °C to 1000 °C, in oxygen-limited conditions (unlike bottom
and
fly ash). Feedstock for biochar production may comprise purpose-
grown biomass or waste material from forestry or agriculture,
guaranteeing compliance with all environmental threshold values and
declaring all product properties for its agricultural use (
). Biochar may also become contaminated with
PAHs or BTEX during pyrolysis (
Brown et al., 2006; Fabbri et al., 2012;
Hale et al., 2012; Nakajima et al., 2007
).
The objective of the current study was to obtain basic information
about concentrations of PAHs, total petroleum hydrocarbon (TPH),
BTEX and S in bottom and
fly ash produced in different industrial
power plants in which different combustion systems are used. Commer-
cial biochar samples were also analysed and used as reference samples
for comparison. The relationship between pollutant variables and indi-
ces of the samples was also considered.
2. Materials and methods
2.1. Sampling design
Ash samples were collected from 15 biomass power stations in
Spain. Pine and eucalyptus branches and bark were used as the main
types of feedstock in the power plants. However, in some of them
waste wood was also employed.
For this study three types of burnt plant biomass were selected:
a) Fly wood ash (FWA): Nine samples of FWA were collected from Cir-
culating Fluidized Bed (CFB) boilers. The feedstock of this type of WA
was eucalyptus branches, which were burnt at temperature of 750 to
900 °C.
b) Mixed wood ash (MWA): 18 samples obtained in conventional
grate-
fired combustion boilers and 9 samples obtained in water-
tube boilers. The feedstock of this type of WA was pine branches
(18) and waste wood (9), which were burnt at temperature of 400
to 500 °C. Since MWA samples were very heterogeneous, in order
to know if composition was dependent on the particle size/
granulometry, MWA samples were fractionated in three fractions:
b2 mm, 2–5 mm and N5 mm.
All wood ash samples were collected by the following procedure, to
ensure that they were representative of the ash produced. Thus,
about 2.0 kg of ash was collected three times a day during one
week and these subsamples were mixed thoroughly.
c) Five commercial biochar samples (pine branches) were also
analysed for comparative purposes. They were pyrolyzed at 600 °C
for 5 h. Each fraction was weighed and characterized to determine
the organic matter content and quality, PAHs, TPH and 9. For each
determination, three replicates were analysed per sample.
2.2. Characterization of the organic matter in wood ash
Samples of wood ash were dried at 40 °C to constant weight. All sam-
ples were ground to a powder. The organic matter (OM) content of the
wood ash was calculated by loss-on-ignition (LOI), as follows:
LOI
%
ð Þ ¼ Weight
105
−Weight
600
ð
Þ=Weight
105
ð
Þ 100
where Weight
105
is the weight of samples after heating at 105 °C and
Weight
600
is the weight of sample after ignition at 600 °C. To obtain in-
formation about the molecular characteristics of the charred material,
the samples were milled and analysed by differential scanning calorim-
etry (DSC). The DSC experiments were performed under dry air at a
flow rate of 2.1 kg/cm
2
and a scanning rate of 10 °C/min, with ash
samples (10 mg) placed in open pans. The temperature range was
50
–600 °C. Samples of indium (mp: 157 °C) were used to calibrate the
calorimeter. The
“50% burn off” temperature (T50) (
) was
determined as the temperature at which the weight loss of a sample
reached the half of the overall weight loss due to oxidative decomposi-
tion in the temperature range 200
–550 °C. The heat of combustion (Q, in
J/g) was determined by integrating the DSC curves over the exothermic
region (150
–600 °C). Data recorded at b150 °C were discarded, thus ob-
viating weight losses and energy changes associated with moisture loss.
The Q values were divided by the mass loss (both measured between
536
L. Rey-Salgueiro et al. / Science of the Total Environment 544 (2016) 535
–543
150 and 550 °C) in each measurement (energy density of the soil organic
matter-OM, Q/OM or QMO, in J g
−1
OM; (
)). The areas
under the DSC curves were divided into three groups representing dif-
ferent degrees of resistance to thermal oxidation (
): labile organic matter, mainly carbohy-
drates and other aliphatic compounds (200
–375 °C); recalcitrant organ-
ic matter, such as lignin and other polyphenols (375
–475 °C); and
highly recalcitrant organic matter, such as polycondensed aromatic
forms (475
–550 °C).
2.3. Chemicals and reagents
A commercial mixture containing benzene (B), toluene (T), ethyl
benzene (E) and o-, m- and p-xylene (X) (BTEX), a commercial TPH
mixture and the styrene (S) standard were supplied by Sigma
–
Aldrich. The following PAHs were also supplied by Sigma-Aldrich:
fluo-
ranthene
(F),
pyrene
(P),
benzo(b)
fluoranthene
(B(b)F),
benzo(k)
fluoranthene
(B(k)F),
benzo(a)anthracene
(B(a)A),
benzo(a)pyrene (B(a)P), benzo(ghi)perylene (B(ghi)P), indeno(1,2,3-
c,d)pyrene (I(1,2,3-c,d)P), dibenzo(a,h)anthracene (DB(a,h)A) and
chrysene (Chr). All solvents used to analyse BTEX, S; TPH and PAHs
contained n-hexane, ethyl acetate and acetonitrile (HPLC-gradient
grade) and all were purchased from Sigma
–Aldrich. Silica SPE cartridges
for PAHs analysis were obtained from Phenomenex.
2.4. Gas chromatography of BTEX+S, S and TPH
The pre-analytical treatment was based on a procedure for the de-
termination of BTEX and TPH in soil (
et al., 2009; Cortes et al., 2012
). Each sample (0.50 g) was subjected to
ultrasound-assisted solvent extraction with 3.0 × 2.5 mL n-hexane:
ethyl acetate (1:1) for 10 min. The phases were separated by centrifuga-
tion at 1500 rpm for 10 min and a 2.0
μL aliquot of the organic phase was
analysed by GC. The three eluates obtained from each sample were
analysed individually. Chromatographic conditions were optimized for
the simultaneous determination of BTEX+ S, and TPH. These analytes
were separated and identi
fied on a Trace GC instrument equipped
with a PolarisQ ion trap mass selective detector (ITMS) furnished with
an AS 3000 automatic injector (Thermo Finnigan: Rodano, Italy) and
interfaced to a PC computer running Xcalibur 1.4 software (Thermo Sci-
enti
fic). Chromatographic separations were carried out on a HP-Innovax
fused-silica capillary column (60 m × 0.25 mm ID, 0.25 lm
film thick-
ness). Helium carrier gas was circulated at 1.0 ml/min in constant
flow
mode. A split/splitless injector was used in splitless mode (split time:
1.0 min). The injected volume was 2.0
μL and the injector temperature,
200 °C. The oven temperature programme was as follows: 40 °C for
5 min; 2 °C/min ramp to 80 °C, 30 °C/min ramp to 250 °C and held for
5 min. The transfer line temperature was 250 °C and the ion-trap man-
ifold temperature 200 °C. The ion energy for electron impact remained
constant at 70 eV. The volatile compounds (BTEX+S) were identi
fied
by comparing the GC retention times and mass spectra over the mass
range 50
–200 amu for the samples against those of pure standards
analysed under the same conditions. Mass detection was performed in
the selected ion recording (SIR) mode for quanti
fication: 77 + 78 for
B, 91 + 92 for T, 91 + 106 for E and X, and 78 + 104 for S. For TPH,
the MS was scanned from 50 to 550 amu at 0.47 scan/s in full-scan
mode. The TPH in a sample from the same GC run was quanti
fied on
the basis of total chromatographic area counts. To obtain the total area
of a total ion chromatogram manual integration along the lowest-
point baseline approach was used (
Bernardo et al., 2009; Cortes et al.,
).
2.5. Liquid chromatography of PAHs
The methods used to extract, purify, identify and quantify the PAHs
in the ash are described in detail by
. Brie
fly,
0.50 g of ash was extracted with 10 mL n-hexane for 20 min in an ultra-
sonic bath, and the extraction process was repeated 3 times, with subse-
quent centrifugation for 5 min at 1500 rpm. The liquid fraction was then
evaporated to dryness under a stream of nitrogen and re-dissolved to
5.0 mL with hexane before the clean-up stage. The 5.0 mL extract was
cleaned directly with sep-pack silica plus cartridges, and additional
15 mL n-hexane was added. The eluate was evaporated to dryness
under a stream of nitrogen and made up to a
final volume of 0.50 mL
with acetonitrile, for LC-FD analysis. The liquid chromatographic system
used was HPLC-Fluorescence (Thermo Separation Products P2000 bina-
ry pump equipped with an AS1000 autosampler, a SCM1000 vacuum
membrane degasser and a Jasco FP-1520
fluorescence detector), as pre-
viously described (
García-Falcón et al., 2006; Rey-Salgueiro et al., 2004;
Rey-Salgueiro et al., 2009; Pontevedra-Pombal et al., 2012
).
2.6. Statistical treatment
Statistical analysis was performed using the Statgraphics Plus v. 5.1
statistical software package (Manugistics, Rockville, MD, USA). Signi
fi-
cant differences in the parameters measured (concentrations of pollut-
ants) in the different variables (separated by sample type: bottom ash
or biochar; boiler: grate-
fired or water-tube; starting material: pine or
recycled wood; and particle size:
b2, 2–5, and N5 mm) were detected
by one-way and two-way analysis of variance (ANOVA), at the 95% con-
fidence level. A Fisher's least significant difference (LSD) test was also
used to detect interactions between variables, at the 95% con
fidence
level. Pearson product
–moment correlation coefficients between ash
characteristics and organic pollutant levels were determined. The data
were analysed by partial least squares regression (PLSR2), implemented
with The Unscrambler v. 9.7 statistical software package (Camo Process
AS), to evaluate the relationship between pollutant variables and qual-
ity indices of the samples.
3. Results and discussion
3.1. Organic matter content and quality in wood ash
The OM content and certain thermal properties may re
flect the de-
gree of aromatization/carbonization of charred compounds, which
could be related with the generation of organic contaminants (
). OM contents of the three types of charred material (bottom
ash,
fly ash and biochar) used in this study are shown in
. The
mean OM content of the selected samples decreased as follows: biochar
(68
–93%) N bottom ash (4.4–78%) N fly ash (1–34%) (
). The OM
content of the bottom ash samples varied widely and was usually low-
est in the
fine fraction (b2 mm) and highest in the coarsest fraction
(
N5 mm).
The DSC curves of selected samples of the different type of material
employed in the present study are shown in
. Only one peak was
distinguished in both biochar and bottom ash samples. The peak ap-
peared at between 450 and 550 °C. In the biochar samples, the thermo-
grams for biochar showed a higher Q (integration area), re
flecting
higher OM contents. The average position of the peak was 504 °C and
the T50 (temperatures at which 50% of the energy is released during
the DSC analysis) values, higher that 475 °C. These values indicate the
presence of highly polycondensed aromatic compounds, as a result of
the no complete combustion (
Leifeld, 2007; Merino et al., 2015
). The
thermogram for wood ash showed a lower Q (integration area),
re
flecting the lower OM contents. For bottom ash, the peaks ranged be-
tween 460 and 490 °C, and T50 similar than biochar, indicating also an
important degree of aromatization/carbonization. In the case of
fly
wood ash, Q is much lower, re
flecting the lower OM in this type of
wood ash. The locations of the peaks for the
fly ash were highly variable
(435
–550 °C). In many cases the T50 values and Q/OM (energy density)
were higher than in biochar and bottom ash. In these samples the Q is
much lower, re
flecting the low OM. All these properties (lower OM,
537
L. Rey-Salgueiro et al. / Science of the Total Environment 544 (2016) 535
–543
higher aromatization/carbonization) would re
flect the higher tempera-
ture of the combustion. All these results indicate the presence of ther-
mally stable compounds in the wood ash, including aromatic moieties
(
Leifeld, 2007; Merino et al., 2015; Omil et al., 2013
).
In relation to the increased degree of aromatization, thermal analysis
showed that burning generated compounds with higher Q
N 475 °C and
T
50
values, indicating greater thermal stability. However, re
flecting the
persistence of labile compounds after burning, such as O-alkyl com-
pounds, the T50 values were lower than those measured in highly
polycondensed aromatic compounds (
). Other authors have also found that thermal analysis is useful
for characterizing soil organic matter, including black carbon
(
Dell'Abate et al., 2002; Leifeld, 2007; Merino et al., 2014
). In these stud-
ies, certain indices of Thermal stability, measured as Q1 (Q
b 375 °C) or
T50, were signi
ficantly correlated with the H/C (r = 0.85, −0.70, re-
spectively; P
b 0.01) and O/C (r = 0.80, −0. 68, respectively; P b 0.01)
ratios.
3.2. Organic pollutants
3.2.1. Quality control validation of the analytical methods used for
BTEX+S, TPH and PAHs
3.2.1.1. BTEX+S and TPH. The number of re-extraction steps is often op-
timized to enhance the extraction ef
ficiency of solid–liquid extraction.
We applied the same reasoning to the ultrasound-assisted solvent ex-
traction (UASE) and evaluated this critical parameter to optimize per-
formance of the BTEX + S extraction. An ash sample was extracted
four consecutive times by UASE and each fraction was analysed sepa-
rately. A mixture of n-hexane: ethyl acetate (1:1) was used as the ex-
traction solvent. Extraction in three steps increased the total amounts
of all compounds extracted. The three eluates obtained from each ex-
traction were analysed individually to avoid excessive dilution of the
analytes and a poorer analytical response.
External standard calibration with multicomponent standards was
used to quantify analyte values for GC-MS. Linear calibration curves
were constructed in the range of 0.075
–10 mg/L, with eight concentra-
tion levels. For statistical validation of the regression analysis, the linear-
ity was veri
fied by the Mandel fitting test (P = 99%) (
).
Acceptable linearity was obtained for each compound evaluated, with
a correlation coef
ficient N 0.9985 for the target compounds. Limits of de-
tection and quanti
fication (LODs and LOQs, respectively) were calculat-
ed in an unforti
fied peat sample following the signal-to-noise criteria
(S/N = 3 and S/N = 10 for LODs and LOQs, respectively) (n = 4)
(
). The estimated LODs ranged from 0.025 to
0.042 mg/kg, whereas the LOQs ranged from 0.075 to 0.125 mg/kg for
the tested analytes.
For TPH, chromatograms may typically demonstrate the effect of
physicochemical and biochemical weathering on the chemical composi-
tion of hydrocarbons by comparison of the retention time and elution
pro
files of unknown samples with the commercial TPH mixture. The
gross chromatogram of a product thus becomes increasingly dominated
by an unresolved complex mixture (UCM) of hydrocarbons and by hy-
drocarbons with high carbon numbers. The UCM is represented by a
large hump in the chromatogram. We did not obtain any typical elution
pro
files from the analysed samples (
Bernardo et al., 2009; Cortes et al.,
).
3.2.1.2. PAHs. Validation of the extraction procedure involved determi-
nation of linearity and limits (LODs and LOQs) in accordance with the
methods used in a previous study (
). External
standard calibration with multicomponent standards was used to quan-
tify analyte values for LC
–FD. The 6-point calibration line (each point in
duplicate) showed good linearity, with correlation coef
ficients higher
than 0.998 for all PAHs studied. The LODs and LOQs were evaluated on
the basis of the noise obtained from the analysis of unforti
fied ash sam-
ples (n = 4) and were de
fined as the concentration of the analyte that
produced signal-to-noise ratios of 3 and 10, respectively. The values
Table 1
Ash characteristics, mean, min and max concentrations of BTEX+S and PAHs (S.D.) (n = 3) in the 41 samples in relation to established variables: type of sample, boiler, starting material,
and particle size. PAH ratios (F/P and F/(F + P)) for source diagnostics are also shown.
Sample
Boiler
Feedstock
Fraction size
(mm)
% OM
(S.D.)
T50
(S.D.)
Q/SOM (J
gOM
−1
)
Tot BTEXS (mg/kg)
Tot PAHs (
μg/Kg)
PAH ratios
Mean
(S.D.)
Min
–max Mean
(S.D.)
Min
–max F/P
F/(F +
P)
Bottom ash
Grate-
fired boilers
Waste wood
b2.0
6.3 (5.6)
428 (35)
14,203 (5623)
0.054 (0.11)
–0.22 2.9 (3.5)
n.d.
–6.73 0.16 0.14
2.0
–5.0
4.4 (2.9)
443 (36)
17,537 (4217)
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
N5.0
6.2 (6.8)
441 (63)
14,623 (8623)
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
Bottom ash
Grate-
fired boilers
Pine
b2.0
26 (28)
476 (15)
8721 (3151)
0.20 (0.28)
n.d.
–0.40
211 (298)
n.d.
–422
0.26
0.24
2.0
–5.0
43 (56)
472 (32)
8263 (624)
0.25 (0.35)
n.d.
–0.50
42 (59)
n.d.
–84
0.28
0.22
N5.0
78
442
8178
n.d.
n.d.
n.d.
n.d.
0.39
0.28
Bottom ash
Water-tube boilers
Pine
b2.0
32 (0.30)
462 (23)
21,787 (2901)
0.74 (0.28)
0.54
–0.93 n.d.
n.d.
n.d.
n.d.
2.0
–5.0
65 (13)
484 (9.9)
18,134 (1322)
0.98 (0.40)
0.69
–1.3
0.52 (0.74)
n.d.-1.0
n.d.
n.d.
N5.0
52 (42)
464 (8.6)
20,038 (6447)
0.82 (0.29)
0.62
–1.0
n.d.
n.d.
n.d.
n.d.
Biochar
–
–
b2.0
87 (6.0)
473 (12)
13,495 (7128)
18 (17)
6.2
–30
118 (3.3)
116
–120
0.26
0.21
2.0
–5.0
93 (2.5)
482 (16)
14,739 (4622)
11 (12)
2.7
–20
16 (23)
n.d.
–33
0.29
0.22
N5.0
68
474
15,964
10
10
n.d.
n.d.
n.d.
n.d.
Fly ash
Fluidized bed boilers
Eucalyptus
b2.0
11 (4.9)
495 (16)
236,401 (70,300)
1.6 (2.80)
n.d.
–8.99
14 (34.5)
n.d.
–105
0.22
0.18
a
n = 1.
b
n = 9.
Fig. 1. Comparison of DSC curves for representative samples of the type of the three types
of carbonized samples studied: biochar, bottom and
fly ash.
538
L. Rey-Salgueiro et al. / Science of the Total Environment 544 (2016) 535
–543
were then tested experimentally by spiking blank samples at these
levels. The LODs ranged from 0.010 to 1.7
μg/kg and LOQs ranged from
0.020 to 2.5
μg/kg for B(k)F and P, respectively.
3.2.2. Evaluation of organic pollutants in the ash samples
The concentrations of the BTEX+S in the samples ranged from un-
detected to 30 mg/kg ash (
). Benzene was detected in all the
samples, accounting for 10
–38% of the total BTEX+S. The abundance
of the individual compounds followed the order T
N E N X N S. To our
knowledge, no reference levels of BTEX+S in wood ash generated by
biomass combustion have been reported in the literature. Nevertheless,
several studies report that BTEX are released due to burning of biomass
fuel, including wood (
Galbally et al., 2009; Krugly et al., 2014; Sinha
). The total PAH values ranged from non-detected to
422
μg/kg ash (
), which is similar to the range reported by
(15
–733 μg/kg) for ash samples collected
from power plants in which wood chips, sawdust, bark and straw were
combusted. These values were much lower than the total PAHs reported
by other authors for wood ash (
Masto et al., 2015; Sarenbo, 2009
). Al-
though re-burning of the ash reduced the concentration of PAHs to
0.24 mg/Kg (
), this is still higher than the concentrations
determined in the present study. These concentrations are all below the
limits established by USEPA and different European countries
(
European Communities, 2001; USEPA, 2002
) for biosolids used for ap-
plication to land. They are also much lower than the levels proposed by
the European Biochar Certi
ficate (
).
The Galician Government (NW Spain) has issued general guidelines
for different potential uses of residues, including different types of ash
(
Technical instruction of waste ITR/01/08, 2008
) and it was set limit
values of BETX + S (60 mg/kg), PAHs (23 mg/kg) and TPH
(50 mg/kg). The concentrations of PAHs and BTEX + S in all samples
analysed in the present study were low enough for the bottom ash sam-
ples to be considered suitable for application to soil. However, the levels
of BTEX+S in biochar and some
fly ash samples were only adequate for
reclamation of industrial soils, and were not suitable for agriculture use.
For a better understanding of the results obtained, the target
analytes were evaluated by two-way ANOVA followed by a test of mul-
tiple comparisons considering factors such as particle size, boiler type
and starting materials. The concentrations of BTEX+ S were higher in
the lower particle size fraction of the biochar. The effect of the
Fig. 2. (a) Total BTEX+S levels of samples of biochar and bottom ash, (b) samples generated in grate-
fired and water-tube boilers, (c), and samples generated from starting materials of
pine and recycled wood (always separated by particle size).
539
L. Rey-Salgueiro et al. / Science of the Total Environment 544 (2016) 535
–543
interaction between sample type (biochar or bottom ash) and particle
size was signi
ficant (
a). The pollutant levels were therefore
lower in bottom ash than in the biochar. Regarding the type of boiler
(
b), the concentrations of BTEX+S were higher in samples from
water-tube boilers, independently of particle size. Considering the
type of starting material (pine or recycled wood), we observed only a
very slightly higher levels of BTEX +S in the pine-derived ash than in
the waste wood ash (
c). Regard to BTEX + S contaminants
(
a and
b) concentration levels were dominated by benzene and
toluene in bottom and biochar ash samples. Bottom ashes shown the
highest levels in pine ashes from water-tube boilers, the levels were
similar for the selected particle sizes. However, for biochar (
b),
the concentration of benzene was twice that of toluene, and the highest
levels corresponded to the
b2.0 mm particle size fraction. An inverse
Fig. 3. Levels of BTEX+S in (a) bottom ash, (b) biochar, and (c)
fly ash.
Fig. 4. Levels of low molecular weight PAHs in (a) bottom ash, (b) biochar, and (c)
fly ash.
540
L. Rey-Salgueiro et al. / Science of the Total Environment 544 (2016) 535
–543
relationship between concentration and particle size has been shown
for other organic compounds in biochar and
fly ash, but not bottom
ash, and was attributed to the small particle size and high speci
fic sur-
face area (
Arditsoglou et al., 2004; Masto et al., 2015
). In general, a gra-
dient was observed in the relative organic pollution based on BTEX+S:
small particle size
N large particle size (in biochars), water-tube
boilers
N grate-fired boilers (in bottom ash), and pine N recycled wood
(in bottom ash). These results are consistent with the
findings reported
by
No signi
ficant differences were found in the PAH levels for the vari-
ables selected: particle size (
b2.0, 2.0–5.0, or N5.0 mm), type of boiler
and starting material. The PAHs (
) were generally detected
at
μg/kg levels (n.d.–422), with larger amounts of low molecular weight
PAHs (
˂4 rings) than high molecular weight PAHs (N4 rings). According
to the previous studies, anthracene, F, P, B(a)A and Chry are the pre-
dominant PAHs generated during combustion of biomass fuels (
). Our results are consistent with this, as the most abundant
PAHs detected in wood ash were P, Chry and F. The pattern of low mo-
lecular weight PAHs was similar in bottom ash, biochar and
fly ash as P
predominated and was found at highest levels in the
b2.0 mm particle
size fraction. In bottom ash (
a), Chr was the second most abundant
compound, and it was found at the highest levels in pine ash from grate-
fired boilers. Nevertheless, in biochar (
b) and
fly ash (
c), the
second most common compound was F, and it was also found at highest
levels in the
b2.0 mm particle size fraction. With regard to the high mo-
lecular weight PAHs, the highest levels were found for pine ash from
grate-
fired boilers (in the case of bottoms ash) (
a) and in the
b2.0 mm particle size fraction (in the case of biochar) (
b). No
high molecular weight PAHs were detected in
fly ash.
Although no signi
ficant differences were observed in the PAH levels
for the variables selected, an inverse relationship between concentra-
tion and particle size was observed for PAHs (particularly the lighter
compounds) in bottom and
fly ash and in biochar. This is consistent
with previously reported
findings (
Arditsoglou et al., 2004; Masto
). Fine-particulate
fly ash usually has a higher specific surface
area than coarse-particulate ash (bottom ash), and more condensed
PAHs can therefore be absorbed than those adsorbed by coarse particles.
However, this does not explain the higher concentration of PAHs in bot-
tom ash than in
fly ash detected in the present study. The PAHs are likely
to be associated with the unburnt carbon in the ash (
Ruwei et al., 2013; Straka and Havelcová, 2012
).
who also found higher PAH levels in bottom ash than
fly ash, observed
a strong correlation between total organic carbon and the high PAH con-
tent in bottom ash and attributed this to the remains of unburnt carbon.
The formation and release of PAHs arising from combustion process de-
pends on the properties of the fuel and on the operating conditions.
Thus, poor combustion yields high levels of unburnt carbon and high
levels of PAHs in the ash. Temperatures above 1000 °C promote com-
plete decomposition of pollutants (
). However, the
operating temperature of the incinerators considered here was around
500
–800 °C.
reported that the colour of
the ash may indicate the presence of unburnt carbon. In the present
study, bottom ashes were much darker in colour than the
fly ashes,
and the PAHs content was higher. This may explain the higher concen-
tration of PAHs in bottom ash than in
fly ash.
Usually, in environmental studies, the molecular patterns of PAHs
are like
fingerprints, that make possible to hypothesise about which
processes generate them by studying their distribution in samples
(
Orecchio and Papuzza, 2009; Mansuy-Huault et al., 2009
). The ratios
commonly used in the literature are F/P, F/F + P, B[a]A/Chr and B[a]A/
B[a]A + Chr (
). The F/F + P ratio covers the gaseous
as well as the particle-transported PAHs (
),
and both compounds have comparable physicochemical properties.
reported that the F/F + P ratio was
below 0.50 for most petroleum samples (gasoline, diesel and fuel oil
combustion), and higher than 0.50 for most coal, grass and wood com-
bustion samples. Generally, F/F + P ratios higher than 0.40 belong to py-
rolytic sources. The same consideration could be applied to the F/P
ratios, whose values greater than 1.0 are classically related to pyrolytic
origins, namely, to coal combustion (
). Thus, the F/P
and F/(F + P) ratios were determined experimentally, yielding
values
b 1.0, which indicates the petrogenic origin of PAHs in the select-
ed samples (
Bucheli et al., 2004; Yunker et al., 2002
). Hence,
we can postulate that the PAHs were derived from the use of petroleum
derivatives during the combustion process. The use of petroleum deriv-
atives may also explain the presence of BTEX + S in the analysed
samples.
3.3. Regression analysis (PLSR2) for sample descriptors and pollutants
We applied partial least squares regression analysis to two data ma-
trices (PLSR2;
), to show the relationship between the total pollut-
ants (Y data) and the sample characteristics (X data). A biplot of the
samples and their characteristics was obtained using The Unscrambler
programme, which automatically extracted two latent variables. The
biplot explained 41% of the variation in Y-variables. Validation of the
model ability was carried out by the root-mean-square error for predic-
tions (RMSEP). The RMSEP was below 10 for the total pollutants de-
scriptors. The relationship between pollutants and the other variables
Fig. 5. Levels of high molecular weight PAHs in (a) bottom ash and (b) biochar.
541
L. Rey-Salgueiro et al. / Science of the Total Environment 544 (2016) 535
–543
demonstrated the existence of positive and negative relationships be-
tween the two sets of variables, with a positive relationship between
BTEX + S and T50. As T50 increased, the degree to which the organic
matter in the sample was burned increased, possibly because of the ad-
dition of more fuel, which tended to increase the BTEX+S. In contrast,
an inverse relationship between PAHs and Q/OM was observed. Thus,
as Q/OM increased, the degree of combustion decreased or occurred
with less oxygen, which is related to a higher presence of PAHs. This is
consistent with a previous report of high concentrations of these com-
pounds in biochar containing highly aromatic compounds (
4. Conclusions
In this study, the potential environmental risk of using wood ash as a
soil fertilizer was assessed by determining the PAH and BETX+S con-
tents of different types of ash. Bottom ash is generally considered to
be safer than
fly ash, although neither of these materials contain dan-
gerous levels of pollutants and do not pose environmental risks. In gen-
eral, the degree to which organic matter in the sample is burned
increases with T50 (possibly due to the addition of fuel), and the
BTEX + S also tended to increase. However, as the combustion de-
creased or proceeded with less oxygen, it was found an increased pres-
ence of PAHs. The results con
firm that the amounts of organic pollutants
(PAHs and BTEX+S) in the wood ash do not exceed limits established
for different soil or industrial uses. The study
findings also show that
both types of ash may therefore be suitable for application to soil as a
fertilizer and an organic amendment, taking into account the target or-
ganic pollutants.
Con
flict of interests
The authors declare no con
flict of interest.
Acknowledgements
Financial support for this work was provided by EU FEDER funds.
DSC analysis was carried out by Montse Gómez (RIAIDT, University of
Santiago de Compostela).
References
Arditsoglou, A., Petaloti, C., Terzi, E., Sofoniou, M., Samara, C., 2004.
trace elements and polycyclic aromatic hydrocarbons in
fired power plants. Sci. Total Environ. 323, 153–167.
Augusto, L., Bakker, M.R., Meredieu, C., 2008.
Wood ash applications to temperate forest
— potential benefits and drawbacks. Plant Soil 306, 181–198.
Bernardo, M.S., Gonçalves, M., Lapa, N., Barbosa, R., Mendes, B., Pinto, F., Gulyurtlu, I.,
2009.
Determination of aromatic compounds in eluates of pyrolisis solid residues
using HS-GC-MS and DLLME-GC-MS. Talanta 80, 104
Brown, R.A., Kercher, A.K., Nguyen, T.H., Nagle, D.C., Ball, W.P., 2006.
–333.
Bucheli, T.D., Blum, F., Desaules, A., Gustafsson, O., 2004.
bons, black carbon, and molecular markers in soils of Switzerland. Chemosphere
56, 1061
Calvelo Pereira, R., Kaal, J., Camps Arbestain, M., Pardo Lorenzo, R., Aitkenhead, W., Hedley,
M., Macías, F., Hindmarsh, J., Maciá-Agulló, J.A., 2011.
Contribution to characterisation
of biochar to estimate the labile fraction of carbon. Org. Geochem. 42, 1331
Cortes, J.E., Suspes, A., Roa, S., González, C., Castro, H.E., 2012.
bons by gas chromatography in Colombian waters and soils. Am. J. Environ. Sci. 8,
396
Danish Energy Agency. Energy Statistics, 2012. Available at
files/dokumenter/publikationer/downloads/energy_statistics_2012.pdf
(veri
fied
27 May 2015).
Dell'Abate, M.T., Benedetti, A., Trinchera, A., Dazzi, C., 2002.
file of two typic haploxerert. Geoderma 107, 281–296.
European Biochar Certi
ficate, 2012. Guidelines for a Sustainable Production of Biochar.
European Biochar Foundation 5th version Switzerland. Available at
european-biochar.org/biochar/media/doc/ebc-guidelines.pdf
(veri
fied 27 May 2015).
European Communities, 2001.
Disposal and Recycle Routes for Sewage Sludge. Part 1.
Sludge Use Acceptance. Part 2. Regulatory Report. European Communities, DG Envi-
ronment. Of
fice for Official Publications of the European Communities.
Fabbri, D., Torri, C., Spokas, K.A., 2012.
Analytical pyrolysis of synthetic chars derived from
–84.
Fernández, J.M., Plante, A.F., Leifeld, J., Rasmussen, C., 2011.
Galbally, I.E., Gillett, R.W., Powell, J.C., Lawson, S.J., Bentley, S.T., Weeks, I.A., 2009.
García-Falcón, M.S., Soto-González, B., Simal-Gándara, J., 2006.
trations of polycyclic aromatic hydrocarbons in burnt woodland soils. Environ. Sci.
Technol. 40, 759
Hale, S.E., Lehmann, J., Rutherford, D., Zimmerman, A.R., Bachmann, R.T., Shitumbanuma,
V., O'Toole, A., Sundqvist, K.L., Arp, H.P.H., Cornelissen, G., 2012.
Kloss, S., Zehetner, F., Dellantonio, A., Hamid, R., Ottner, F., Liedtke, V., Schwanninger, M.,
Gerzabek, M.H., Soja, G., 2012.
Characterization of slow pyrolysis biochars: Eff ects of
feedstocks and pyrolysis temperature on biochar properties. J. Environ. Qual. 41,
990
Fig. 6. Two-dimensional PLS2 (X-expl: 65%, 21%; Y-expl: 30%, 11%): correlations between loadings of X (5 sample characteristics) and Y variables (total PAHs and BTEX+S).
542
L. Rey-Salgueiro et al. / Science of the Total Environment 544 (2016) 535
–543
Krugly, E., Martuzevicius, D., Puida, E., Buinevicius, K., Stasiulaitiene, I., Radziuniene, I.,
Minikauskas, A., Kliucininkas, L., 2014.
Characterization of gaseous-and particle-
Lapa, N., Barbosa, R., Morais, J., Mendes, B., Méhu, J., Oliveira, J.S., 2002.
assessment of leachates from MSWI bottom ashes. Waste Manag. 22, 583
Lehndorff, E., Schwark, L., 2004.
Biomonitoring of air quality in the cologne conurbation
using pine needles as a passive sampler
— part II: polycyclic aromatic hydrocarbons
(PAH). Atmos. Environ. 38, 3793
Leifeld, J., 2007.
Thermal stability of black carbon characterised by oxidative differential
scanning calorimetry. Org. Geochem. 38, 112
MacDougall, D., Lal, J., Amore, F.J., 1980.
Guidelines for data acquisition and data quality
evaluation in environmental chemistry. Anal. Chem. 52, 2242
Mandel, J., 1964.
The statistical analysis of experimental data. Interscience-Wiley Pub-
lishers, Corrected and Reprinted. Dover Publications, New York.
Mansuy-Huault, L., Regier, A., Faure, P., 2009.
Analyzing hydrocarbons in sewer to help in
PAH source apportionment in sewage sludges. Chemosphere 75, 995
Masto, R.E., Sarkar, E., George, J., Jyoti, K., Dutta, P., Ram, L.C., 2015.
fly ash and bed ash of biomass fired power plants. Fuel Process.
Mastral, A.M., Callén, M.S., García, T., 1999.
Polycyclic aromatic hydrocarbons and organic
matter associated to particulate matter emitted from atmospheric
combustion. Environ. Sci. Technol. 33, 3177
Melotti, R., Santagata, E., Bassani, M., Salvo, M., Rizzo, S., 2013.
into the physical and chemical properties of biomass ashes used as aggregate
for bituminous mixtures. Waste Manag. 33, 1906
Merino, A., Ferreiro, A., Salgado, J., Fontúrbel, M.T., Barros, N., Fernández, C., Vega, J.A.,
2014.
Use of thermal analysis and solid-state 13C CP-MAS NMR spectroscopy to diag-
nose organic matter quality in relation to burn severity in Atlantic soils. Geoderma
226-227, 376
Merino, A., Chávez-Vergara, B., Salgado, J., Fonturbel, M.T., García-Oliva, F., Vega, J.A., 2015.
Variability in the composition of charred litter generated by wild
Nakajima, D., Nagame, S., Kuramochi, H., Sugita, K., Kageyama, S., Shiozaki, T., Takemura,
T., Shiraishi, F., Goto, S., 2007.
Polycyclic aromatic hydrocarbon generation behavior
in the process of carbonization of wood. B. Environ. Contam. Tox. 79, 221
Omil, B., Piñeiro, V., Merino, A., 2013.
Soil and tree responses to the application of wood
ash containing charcoal in two soils with contrasting properties. For. Ecol. Manag.
295, 199
Orecchio, S., Papuzza, V., 2009.
fingerprint and daily intake of polycyclic aromatic
hydrocarbons (PAHs) in bread baked using wood as fuel. J. Hazard. Mater. 164,
876
Peng, T.H., Lin, C.L., Wey, M.Y., 2015.
Study of the low-temperature two-stage
fluence of the second-stage sand bed operating conditions on pol-
lutant emission. Appl. Therm. Eng. 75, 592
Pérez-Gregorio, M.R., García-Falcón, M.S., Martínez-Carballo, E., Simal-Gándara, J., 2010.
Pontevedra-Pombal, X., Rey-Salgueiro, L., García-Falcón, M.S., Martínez-Carballo, E.,
Simal-Gándara, J., Martínez-Cortizas, A., 2012.
Pre-industrial accumulation of
Rey-Algueiro, L., García-Falcón, M.S., Soto-González, B., Simal-Gándara, J., 2004.
Rey-Salgueiro, L., Pontevedra-Pombal, X., Álvarez-Casas, M., Martínez-Carballo, E., García-
Falcón, M.S., Simal-Gándara, J., 2009.
Comparative performance of extraction strate-
gies for polycyclic aromatic hydrocarbons in peats. J. Chromatogr. A 1216,
5235
Rovira, P., Kurz-Besson, C., Couteaux, M.M., Vallejo, V.R., 2008.
Ruwei, W., Jiamei, Z., Jingjing, L., Liu, G., 2013.
Levels and patterns of polycyclic aromatic
fired power plant bottom ash and fly ash from Huainan,
China. Arch. Environ. Contam. Toxicol. 65, 193
Santalla, M., Omil, B., Rodríguez-Soalleiro, R., Merino, A., 2011.
containing charcoal as a fertilizer for a forest plantation in a temperate region. Plant
Soil 346, 63
Sarenbo, S., 2009.
Wood ash dilemma-reduced quality due to poor combustion perfor-
mance. Biotechnol. Bioeng. 33, 1212
Shin, H.S., Kwon, O.S., 2000.
The simultaneous analysis of benzene, toluene, ethylbenzene,
Sicre, M.A., Marty, J.C., Saliot, A., Aparicio, X., Grimalt, J., Albaiges, J., 1987.
Singh, D.P., Gadi, R., Mandal, T.K., Saud, T., Saxena, M., Sharma, S.K., 2013.
Sinha, S.N., Kulkarni, P.K., Shah, S.H., Desai, N.M., Patel, G.M., Mansuri, M.M., et al., 2006.
Straka, P., Havelcová, M., 2012.
Polycyclic aromatic hydrocarbons and other organic com-
pounds in ashes from biomass combustion. Acta Geodyn. Geomater. 9, 481
Technical instruction of waste ITR/01/08, January 8th, 2008. The Directorate General for
Environmental Quality and Assessment, Concerning the Development of Soils (Tech-
no-soils) Derived From Waste. Available at
http://www.xunta.es/dog/Publicados/
2008/20080125/Anuncio58E2_es.html
(veri
fied 27 May 2015).
USEPA. Biosolids Applied to Land: Advancing Standards and Practices, 2002. Available at
http://water.epa.gov/scitech/wastetech/biosolids/upload/complete.pdf
(veri
fied 27
May 2015).
USEPA. Code of Federal Regulations (CFR), 40 CFR
— Chapter I — Part 423: Appendix A to
Part 423. 2013. Available at
http://www.gpo.gov/fdsys/pkg/CFR-2013-title40-vol30/
xml/CFR-2013-title40-vol30-part423.xml
(veri
fied 27 May 2015).
Yunker, M.B., Macdonald, R.W., Vingarzan, R., Mitchell, R.H., Goyette, D., Sylvestre, S.,
2002.
PAHs in the fraser river basin: a critical appraisal of PAH ratios as indicators
of PAH source and composition. Org. Geochem. 33, 489
543
L. Rey-Salgueiro et al. / Science of the Total Environment 544 (2016) 535
–543
Document Outline
- Organic pollutants profiling of wood ashes from biomass power plants linked to the ash characteristics
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