Assessing amendment and fertilizing properties of digestates from anaerobic
digestion through a comparative study with digested sludge and compost
Fulvia Tambone
, Barbara Scaglia, Giuliana D’Imporzano, Andrea Schievano, Valentina Orzi, Silvia Salati,
Fabrizio Adani
Gruppo RICICLA, Dipartimento di Produzione Vegetale, Università degli Studi di Milano, Via Celoria 2, 20133 Milano, Italy
a r t i c l e
i n f o
Article history:
Received 22 April 2010
Received in revised form 13 August 2010
Accepted 17 August 2010
Available online 9 September 2010
Keywords:
Amendment properties
Anaerobic digestion
Digestate
Fertilizer properties
CP MAS
13
C NMR
Principal component analysis
a b s t r a c t
Digestate, with biogas represents the final products of anaerobic digestion (AD). The methane-rich biogas
is used to produce electricity and heat, whereas the digestate could be valorized in agriculture. Contrarily
to well-recognized biomasses such as digested sludge and compost, the properties of the digestate are
not well known and its agricultural use remains unexplored.
In this work, a first attempt to study the agronomic properties of digestates was performed by compar-
ing the chemical, spectroscopic, and biological characteristics of digestates with those of compost and
digested sludge, used as reference organic matrices. A total of 23 organic matrices were studied, which
include eight ingestates and relative digestates, three composts, and four digested sludges.
The analytical data obtained was analyzed using principal component analysis to better show in detail
similarities or differences between the organic matrices studied.
The results showed that digestates differed from ingestates and also from compost, although the start-
ing organic mix influenced the digestate final characteristics. With respect to amendment properties, it
seems that biological parameters, more than chemical characteristics, were more important in describing
these features. In this way, amendment properties could be ranked as follows: compost ffi dige-
state > digested sludge ingestate.
As to fertilizer properties, AD allowed getting a final product (digestate) with very good fertilizing prop-
erties because of the high nutrient content (N, P, K) in available form. In this way, the digestate appears to
be a very good candidate to replace inorganic fertilizers, also contributing, to the short-term soil organic
matter turnover.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
The inputs of organic matter (OM) in the soil play a central role
in the productivity of arable land by providing nutrients, through
decomposition, and by maintaining soil fertility through OM turn-
over (
). The benefits of a balanced fertilization,
using organic amendment (e.g., crop residues, manure, compost)
in maintaining soil OM level in soils, have been increasingly
emphasized by researchers (
). At the same
time in the last decades, the use of organic wastes to produce or-
ganic fertilizers, with the aim of reducing dumping in landfill sites,
has grown a lot. Recycling of organic waste materials helps main-
tain soil nutrient levels, stimulating various aspects of soil fertility
(
Iakimenko et al., 1996; Tambone et al., 2007
). However, the
efficient and appropriate use in agriculture of organic fertilizers
coming from organic wastes requires more in-depth knowledge
both in terms of quality and fertilizer value (
).
Only in this way will it be possible to support crop production
and protect the environment, saving the soil resource (
). Recently, in European countries, among the biological
processes applied to treat organic wastes, interest in AD has in-
creased (
). AD is an anaerobic biological digestion
by which, in the absence of oxygen, OM is transformed into biogas,
which principally consists of methane (50–80 vol.%) and carbon
dioxide, the former used to produce energy and heat (
). AD also produces a final biologically stable and partially hy-
gienic organic product, the digestate (
AD has been reported to produce benefits by increasing the
agronomic value of the biomasses treated. For example, with re-
spect to animal slurry, AD allows the production of a digestate with
a higher proportion of mineral N and less decomposable OM
(
). This point is very important if one
considers that the N-fertilizing effect of slurry or similar material
is roughly equal to ammonium content and that the N leaching
0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:
10.1016/j.chemosphere.2010.08.034
⇑
Corresponding author. Tel.: +39 02 50316547.
⇑⇑
Corresponding author. Tel.: +39 02 50316545.
E-mail addresses:
(F. Tambone),
(F. Adani).
Contents lists available at
Chemosphere
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 / c h e m o s p h e r e
from organic N mineralization depends on organic content (
No less important are the effects of the anaerobic digestion on
the environment. AD-reduces emissions of greenhouse gas such
as methane and nitrous oxide (
). In addi-
tion AD contributes to global warming savings, not only from sub-
stitution of fossil fuel by biogas but also from carbon storage in the
soil and inorganic fertilizer substitution (
).
Therefore, a strong contributing factor to the success of AD comes
from the valuation of the digestate in agriculture (
). Nevertheless, in contrast to well-recognized biomasses such
as digested sludge (DS) and compost, the digestate is not well
known and its agricultural use remains an unexplored field in re-
search. Digestates, in fact, have not undergone scientific examina-
tion that will reveal their configuration in agronomic terms.
Whether digestates could act more as fertilizer or amendment or
both is still not clear. Having amendment properties implies that
the organic matrices contain organic fractions that can contribute
to SOM turnover, as this latter process influences biological, chem-
ical, and physical soil characteristics (
). On the other hand,
fertilizer properties refer to the amount of nutrient elements con-
tained in the organic matrices and their chemical forms (
).
DSs, for example, have been extensively studied in the past (
) and, because of their high N and P content
and low C:N, they represent an organic matrix used more for its
fertilizer properties, with amendment effects being visible only at
very high dosage (
).
On the other hand, compost is used more for its amending prop-
erties because of its low nutrient content and high OM quality
(
Giusquiani et al., 1995; Tambone et al., 2007
). Research has shown
that compost may improve the chemical and physical properties of
the soil by increasing nutrient and water capacity, OM content, pH,
and cation exchange capacity (
Giusquiani et al., 1995; Leifeld et al.,
) and that the effects of compost depend on the dose used
(
).
Both amendment and fertilizer properties of organic matrices
can be revealed by long-term, full-field studies (
). Nevertheless, this approach is very expensive and
time-consuming. In this work, a first attempt to investigate the
agronomic properties of digestates was performed by studying
their chemical, spectroscopic and biological characteristics in com-
parison with those of compost and DS, which were used in this
work as reference organic matrices. Results obtained in this work
could be of help in the preparation of a guidelines for the digestate
use in agriculture. By now, there is not a EU regulation for the use
of digestate and only local and on volunteer basis guidelines have
been proposed. For example the
British Standards Institution (BSI)
, published a volume in which indications for a correct use of
digestate are reported. On the other hand, the European Commis-
sion is considering proposing minimum standards and guidelines
for use of digestate in agriculture via the revision of the Sewage
Sludge Directive.
2. Material and methods
2.1. Organic matrices studied
The biomasses studied (
) were as follows: eight inge-
states (I) and the corresponding eight digestates (D) (
), four DS, and three composts (C), for a total of 23 sam-
ples. The ingestates and digestates were sampled in 2008 at three
different AD plants that produce biogas.
Anaerobically treated and dried DSs came from two municipal
wastewater treatment plants. The composts were collected from
three full-scale plants: one produces green compost from ligno-
cellulosic residues, and two produce mixed composts from ligno-
cellulosic residues plus the organic fraction of municipal solid
waste (OFMSW) obtained by separate collection, in a 1:2 (v/v) fresh
matter ratio.
2.2. Chemical analyses
All samples collected, about 5 kg each, were brought to the lab-
oratory, dried for 24 h at 40 °C and then for another 24 h at 105 °C
(
), shredded in a blender and passed through a 1-mm
mesh. The samples were successively subjected to biological,
chemical, and spectroscopic analyses. NH
3
and TKN were detected
on fresh samples.
Fresh matter (FM), total solids (TS), volatile solids (VS), and total
organic carbon (TOC) were determined following standard proce-
dures (
). Ammonia and TKN were determined using
the analytical method for wastewater sludges (
Organic N was calculated as the difference between TKN and
NH
3
. Total P and K contents were determined by inductively cou-
pled plasma mass spectrometry (Varian, Fort Collins, USA). Stan-
dard samples (National Institute of Standards and Technology,
Gaithersburg, MD, USA) and blanks were run with all samples to
ensure precision in the analyses. P and K detection was preceded
by acid digestion (
) of the biomass samples. All analyses
were performed in triplicate.
2.3. CP MAS
13
C NMR analysis
The solid-state Cross Polarization Magic Angle Spinning
13
C Nu-
clear Magnetic Resonance (CP MAS
13
C NMR) spectra of the sam-
ples were acquired at 10 kHz on a Bruker AMX 600 spectrometer
(Bruker BioSpin GmbH, Rheinstetten) using a 4-mm CP MAS probe.
The pulse repetition rate was set at 0.5 s, the contact time at 1 ms,
and the number of scans was 3200. The chemical shift scale of CP
MAS
13
C NMR spectra were referred to tetramethylsilane
(d = 0 ppm). Spectra were elaborated using TOPSPIN 1.3 software
(Bruker BioSpin GmbH, Rheinstetten, Germany).
2.4. Biological stability determination
Biological stability was determined by a long-term degradation
test (60 d) using the anaerobic potential biogas production test
Table 1
Composition of the biomasses studied.
Composition
w/w fresh matter
I1
I2
80% OFMSW + 20% pig slurry
I3
I4
48% Pig slurry + 24% milk serum + 14% cow slurry + 10% maize
silage + 4% rice residues
I5
I6
I7
65% Pig slurry + 20% blood industry residues + 15% maize silage
I8
C1
Green compost: 100% ligno-cellulosic residues
v/v fresh matter
C2
Mixed composts: ligno-cellulosic residues plus OFMSW in a 1:2 ratio
C3
DS1
Anaerobically treated and dried digested slurries from municipal
wastewater
DS2
DS3
DS4
578
F. Tambone et al. / Chemosphere 81 (2010) 577–583
(ABP test) (
). Anaerobic test has been re-
ported to describe OM degradability well (
In brief, in a 100 mL serum bottle, 0.62 g of dried sample
(Ø < 1 mm) was added to 37.5 mL of inoculum and 22 mL of deion-
ized water. The batch tests were carried out with 60 mL samples
(about 35 g kg
1
TS) and 40 mL of headspace. The fresh feedstock
and inoculum percentages of TS were respectively 35% and 65%.
Control blanks were prepared using 60 mL of inoculum.
All batches were sealed with Teflon hermetic caps, flushed with
an N
2
atmosphere, and incubated at 37 ± 1 °C, until no further bio-
gas production was detected (normally around 60 d).
2.5. Statistical approach
Chemical analyses were performed in triplicate on each bio-
mass sample taken from 5 kg representative mass. Since chemical
analyses were performed on three analytical samples withdrawn
from the 5 kg composite bulk sample, standard deviation values
calculated from the data for three replications were estimates of
the variability caused by both the analytical method and the bulk
sample homogeneity. Average and standard deviation values from
chemical analyses were calculated according to standard proce-
dures and the results analyzed by ANOVA. Tukey’s test was used
to compare mean values and to assess the significance of the differ-
ences between mean values.
Biomass similarity was studied by using chemical, spectro-
scopic, and biological parameters detected for each biomass. Thus,
the large amount of information required a reduction in dimen-
sionality (generally two dimensions). As a consequence, the analyt-
ical data obtained were elaborated by multivariate analysis. In this
work, principal component analysis (PCA) was used to compare
biomasses qualitatively. PCA has been conducted on the log-trans-
formed data (
). The determinant value, Bartlett’s
test of sphericity, and the Kaiser–Meyer–Olkin test of sampling
adequacy were initially performed on the data to evaluate the
appropriateness of conducting PCA. The size of each component
was identified by the eigenvalue: the earlier (and more significant)
the component, the larger its size. Only the PCs with eigenvalues
>1 were retained (
Kaiser, 1960; Brejda et al., 2000
). All statistical
analyses were carried out using SPSS statistical software (vers.
16) (SPSS, Chicago, IL).
3. Results
3.1. Chemical characteristics
The chemical characteristics for ingestates, digestates, DSs and
composts are reported in
. Results, reported as average of
sample data composing each organic matrix, showed that the inge-
states had the highest TOC and VS contents. These data support the
fact that ingestates did not undergo any kind of biological process.
In contrast, anaerobic (digestates) or aerobic (composts) or the
combination of the two biological treatments (digestate sludge)
were responsible for the partial mineralization of OM, thus the
lower TOC and VS contents of digestates, DSs, and composts (
et al., 2006; Tambone et al., 2009
). Composts, in particular, showed
the lowest TOC values, indicating a great degree of mineralization
of OM (
), although both TOC and VS were affected also by
the composition of the starting organic matrices used to produce
the compost.
Table 2
Chemical and biological characteristics of the samples studied in this work.
TS
(g kg
1
FM)
VS (g kg
1
TS)
TOC
(g kg
1
TS)
TKN
(g kg
1
TS)
NH
3
–N
(g kg
1
TS)
NH
3
–N
(% TKN)
(g kg
1
TS)
C:N
P
2
O
5
(g kg
1
TS)
K
2
O
(g kg
1
TS)
ABP (normal
L kg
1
VS)
I1
110 ± 10
823 ± 8
451 ± 7
55 ± 1
17 ± 1
32
37
12
15 ± 1
27 ± 2
649 ± 50
I2
112 ± 4
873 ± 9
482 ± 2
32 ± 1
8 ± 1
26
24
20
10 ± 1
16 ± 3
732 ± 58
I3
123 ± 6
920 ± 18
510 ± 5
39 ± 2
19 ± 2
48
20
25
12 ± 1
18 ± 1
714 ± 21
I4
119 ± 7
883 ± 5
473 ± 2
28 ± 1
12 ± 2
43
16
29
27 ± 2
13 ± 1
631 ± 4
I5
146 ± 7
882 ± 3
492 ± 4
24 ± 1
11 ± 2
45
13
37
27 ± 0
19 ± 2
596 ± 26
I6
144 ± 8
849 ± 2
492 ± 9
27 ± 2
16 ± 1
59
11
46
35 ± 1
39 ± 1
375 ± 14
I7
115 ± 3
822 ± 11
477 ± 6
44 ± 2
23 ± 1
51
21
22
27 ± 1
55 ± 1
449 ± 12
I8
127 ± 9
852 ± 18
494 ± 5
44 ± 1
18 ± 1
41
26
19
25 ± 0
49 ± 1
396 ± 13
Mean
n = 8
124 ± 14b
863 ± 33c
484 ± 18c
37 ± 11ab
15 ± 5b
43 ± 11c
21 ± 8b
26 ± 11b
22 ± 9a
30 ± 16c
568 ± 142b
D1
45 ± 3
707 ± 1
397 ± 9
135 ± 2
87 ± 3
63
48
8
17 ± 2
59 ± 1
399 ± 27
D2
38 ± 6
685 ± 17
384 ± 11
145 ± 2
97 ± 1
68
48
8
21 ± 1
48 ± 1
396 ± 56
D3
31 ± 12
681 ± 19
378 ± 10
151 ± 1
98 ± 1
65
53
7
35 ± 2
58 ± 2
372 ± 79
D4
32 ± 8
696 ± 28
367 ± 8
103 ± 1
63 ± 2
61
41
9
52 ± 2
29 ± 2
240 ± 48
D5
44 ± 3
702 ± 30
383 ± 2
83 ± 2
45 ± 2
54
38
10
53 ± 2
36 ± 2
281 ± 15
D6
53 ± 1
667 ± 1
387 ± 8
85 ± 2
51 ± 2
61
34
11
58 ± 1
82 ± 0
211 ± 6
D7
63 ± 1
722 ± 1
418 ± 7
86 ± 3
54 ± 1
62
32
13
53 ± 1
67 ± 2
184 ± 15
D8
60 ± 0
735 ± 3
421 ± 9
92 ± 1
61 ± 2
67
31
14
50 ± 1
55 ± 2
193 ± 65
Mean
n = 8
46 ± 12a
670 ± 22b
392 ± 19b
110 ± 29c
69 ± 21c
63 ± 4d
41 ± 8c
10 ± 2a
43 ± 16ab
54 ± 17d
284 ± 92a
C1
769 ± 4
362 ± 5
184 ± 8
12 ± 1
1 ± 0
10
11
17
6 ± 1
9 ± 2
517 ± 58
C2
731 ± 7
679 ± 11
284 ± 5
19 ± 0
2 ± 0
10
17
16
29 ± 1
21 ± 2
323 ± 26
C3
711 ± 11
415 ± 7
200 ± 3
17 ± 1
2 ± 0
10
15
13
31 ± 1
16 ± 1
472 ± 58
Mean
n = 3
737 ± 30d
485.5 ± 170.0a
222 ± 54a
16 ± 4a
2 ± 0a
10 ± 0a
14 ± 3a
15 ± 3ab
22 ± 14a
15 ± 6b
437 ± 102ab
DS1
176 ± 5
765 ± 12
412 ± 10
73 ± 1
14 ± 0
19
59
7
52 ± 1
5 ± 0
438 ± 15
DS2
145 ± 3
743 ± 9
363 ± 9
55 ± 0
10 ± 2
19
45
8
50 ± 1
7 ± 1
385 ± 18
DS3
185 ± 6
682 ± 14
357 ± 11
50 ± 2
9 ± 2
18
41
9
40 ± 1
4 ± 0
359 ± 58
DS4
131 ± 11
660 ± 7
340 ± 3
50 ± 2
9 ± 1
19
41
8
42 ± 2
6 ± 0
394 ± 29
Mean
n = 4
159 ± 25c
712 ± 50b
368 ± 31b
57 ± 11b
11 ± 2b
18 ± 0b
47 ± 9c
8 ± 0a
46 ± 6ab
5 ± 1a
394 ± 33ab
a
Calculated as TKN–NH
3
–N.
b
Calculated as TOC/org-N.
c
Means followed in the same column by the same letter are not statistically different (p < 0.05) according to Tukey’s test.
F. Tambone et al. / Chemosphere 81 (2010) 577–583
579
Total N content differed among the biomasses studied (
)
and followed this order: digestates > DSs > ingestates > composts.
Data in
reflected the typical N contents of these biomasses,
which depended on both the composition of the starting organic
matrix and the biological processes that the matrices underwent.
The higher N content of the digestate with respect to the ingestate
was a consequence of the N concentration effect, because of carbon
degradation to CO
2
and CH
4
and N preservation during AD (
). More interesting were the data on the reparti-
tion of TKN into ammonia and organic N (
). During AD,
OM mineralization led to the organic transformation of the organic
N into ammonia, with the consequent increase in NH
3
content in
the digestate. The low TKN content and, above all, the low NH
3
content measured in the composts were expected, as the aerobic
treatment determined ammonia losses by its stripping during
composting if pH is high (
). On the other hand,
the low TKN and ammonia of the DS was due to the drying process
that occurred at the end of the wastewater treatment, allowing
ammonia to be volatilized.
Among the mechanisms that regulate OM mineralization and
conservation in the soil, a determinant role is assumed by the
C:N ratio (
). The C:N values (
) were
calculated, taking into account only the organic N fraction as the
NH
3
fraction did not contribute to the medium and long-term N
turnover in the soil; this fraction was rapidly lost because of plant
uptake, ammonia volatilization in the air, or nitrate leaching into
the soil (
). The C:N of digestates and DSs
were similar and much lower than those of composts (
Concerning the P (P
2
O
5
) content of organic matrices, digestates
and DSs showed the same concentrations of this element (
),
twice that of the compost, that was similar to that of the ingestates.
Digestates also had the greatest concentration of K (K
2
O) of all the
other organic matrices (
3.2. CP MAS
13
C NMR analysis
CP MAS
13
C NMR provides qualitative and quantitative informa-
tion on the composition of the ingestates, digestates, DSs and com-
posts. It identifies the main C type that comprises OM (
). Here, this technique was applied to verify the changes in
macromolecular composition that occur in the ingestates through
AD treatment and to measure the differences and/or similarities
between digestates, composts, and DSs.
Five types of carbon can be distinguished in the NMR spectrum
): (i) short chain aliphatic carbon, e.g., volatile fatty acids
(VFAs) and steroid-like molecules (
) (0–
28 ppm); (ii) long chain aliphatic carbon (e.g., plant aliphatic bio-
polymers) (
) and proteins (
(28–47 ppm); (iii) O-alkyl carbon (e.g., polysaccharides) (
) (47–113 ppm); (iv) aromatic carbon (e.g., lignin)
) (113–160 ppm); and (v) carbonyl car-
bon in aliphatic esters, carboxyl groups, and amide carboxyl
(160–210 ppm).
The ingestates’ NMR (
) were well-characterized by the
presence of the 0–47 ppm area, which indicated the presence of
both long chain linear structures (e.g., suberin, cutin, waxes, fatty
acid) (peaks at 30–33 ppm) derived from animal slurry, municipal
solid waste, and energy crops (
Dignac et al., 2000; Pichler et al.,
) and of branched or short chains (peaks at 24–25 ppm), such
as steroid-like molecules, most likely derived from animal slurry
preserved during the biological treatments (
What was interesting in the spectra of ingestates was the presence
Table 3
CP MAS
13
C NMR integrated area of the samples studied in this work.
C-type
Aliphatic-C bonded to other aliphatic chain or to H
Total aliphatic-C
O–CH
3
or N-alkyl
O-alkyl-C di-O-alkyl-C
Aromatic-C phenol or
phenyl ether-C
Carboxyl-C keto-C
Short chain
Long chain
Band d range (ppm)
0–28
28–47
0–47
47–113
113–160
160–210
I1
12.7
9.3
21.9
60.7
6.6
10.7
I2
13.4
16.4
29.8
56.9
5.1
8.1
I3
17
8.9
26
59.6
3.7
10.7
I4
11.1
7.7
18.9
67.2
6.8
7.2
I5
11.2
7.1
18.4
66.6
7.1
7.8
I6
9.1
10
19.2
67.8
7.7
5.3
I7
10.9
8.9
19.7
64.8
8.7
6.8
I8
9.2
11.4
20.6
64.9
7.6
6.8
Mean n = 8
11.8 ± 2.6
10 ± 3
21.8 ± 4a
63.6 ± 4c
6.7 ± 1.6a
7.9 ± 1.9a
D1
19.5
23.3
42.8
37.5
8.5
11.2
D2
23.6
23.1
46.7
32.7
7.5
13.1
D3
21.1
22.9
44
36
7.7
12.2
D4
11.9
13.7
25.6
59.4
7.9
7.1
D5
13.4
14.8
28.1
55.3
8.1
8.4
D6
13.2
17.1
30.3
54.4
8
7.2
D7
18.2
20.3
38.5
44.1
7.7
9.6
D8
12.2
16.6
28.8
55.2
8.6
7.4
Mean n = 8
16.6 ± 4.5
19 ± 4
35.6 ± 8.3b
46.8 ± 10.5ab
8 ± 0a
9.5 ± 2.4ab
C1
nd
nd
25
53.4
12.8
8.8
C2
nd
nd
22.3
56
13.14
8.5
C3
nd
nd
17.9
56.9
15.72
9.5
Mean n = 3
nd
nd
21.7 ± 3.6a
55.4 ± 1.8bc
13.9 ± 1.6b
8.9 ± 0.5ab
DS1
17.5
20.3
37.8
42.8
7
12.3
DS2
18.5
18.6
37.1
44.8
6.3
11.8
DS3
17.1
18.7
35.8
44.7
7.2
12.3
DS4
17.9
20.4
38.3
42.8
7
11.8
Mean n = 4
17.7 ± 0.6
19.5 ± 1
37.3 ± 1.1b
43.8 ± 1.1a
6.9 ± 0.4a
12.1 ± 0.3b
a
Means followed in the same column by the same letter are not statistically different (p < 0.05) according to Tukey’s test.
580
F. Tambone et al. / Chemosphere 81 (2010) 577–583
of the peaks at 21 ppm, indicating the presence in the biomass of
VFAs, which were probably formed during biomass storage under
semi- or anaerobic condition. This peak disappeared in the dige-
state, indicating VFA degradation during AD (
). The ingestates’ spectra were also dominated by the pres-
ence of carbohydrate molecules (e.g., hemicelluloses, celluloses,
and simple sugars) (see 47–113 ppm area) (
). The strong
reduction of this area in the digestates suggests that AD proceeded,
above all, through the degradation of the carbohydrate fraction
(
As a consequence of the degradation of the labile organic mol-
ecules during AD (i.e., VFAs and O-alkyl-C), the digestates’ spectra
(
) showed an increase in NMR signals in the 0–47 ppm and
130–160 ppm regions. This means that the more recalcitrant frac-
tions (plant biopolymers, steroid-like molecules, and lignin) con-
tained in the starting organic mixtures were concentrated
(
DSs showed a macromolecular composition similar to that of
digestates. The presence of recalcitrant biogenic molecules such
as steroids from human feces (
) and those of
non-biogenic origin in the domestic wastewaters (
) were probably responsible for the high alkyl-C content in
DSs (see 0–47 ppm region) (
The composts (
) showed macromolecular compositions
different from other organic matrices studied, i.e., higher O-alkyl-
C and aryl-C contents and lower alkyl-C content, than those of
other organic matrices (
). Lignocellulosic materials used in
the starting mixer as bulking agents determined higher lignin-like
and O-alkyl-Cs contents in the final products (composts) (
et al., 1998; Ussiri and Johnson, 2003
) than those in both digestates
and ingestates.
3.3. Biological stability
The ABP production of the organic matrices studied (
)
showed that the ingestates were the less degraded biomasses
(
Schievano et al., 2008; Tambone et al., 2009
). On the contrary, bio-
logically treated biomasses such as composts, DSs, and digestates
showed lower biogas production than ingestate (
) Dige-
states showed ABP values lower than both compost and above all
DS, although average values were not statistically different (
), and similar to those reported in a previous study (
). In particular digestate data indicate a high degree of
biological stability (
).
3.4. PCA
In this study, PCA was applied to two different data sets with
the aim of studying both amendment (PC
AM
) and fertilizer proper-
ties (PC
F
) of the biomasses.
Data sets relative to OM contents (VS and TOC), biological sta-
bility (ABP test) (
), and macromolecular composition (CP
MAS
13
C NMR) (
) were considered useful for measuring
the amendment properties. The second data set, related to the fer-
tilizing properties, included TKN, NH
3
, org-N, C:N, total P
2
O
5
, and
total K
2
O contents (
).
The determinant values (0.00004 and 0.0001 for PC
AM
and PC
F
,
respectively) and the results of Bartlett’s test of sphericity (signif-
icance of 0.0001 for both PC
AM
and PC
F
) confirmed the appropriate
level of correlation to perform PCA (
). In addi-
tion, the Kaiser–Meyer–Olkin test of sampling adequacy measure,
which was 0.5 for both PC
AM
and PC
F
, confirmed the sampling ade-
quacy of the data set used (
).
The PCA of amendment properties gave two principal compo-
nents that are able to explain 79% of the total variability of the sys-
tem (
). The use of the data set relative to fertilizing properties
and the successive application of PCA allowed the extraction of two
principal components (PC
F1
and PC
F2
) that explained 82% of the
system’s total variability (
4. Discussion
Anaerobic processes are conducted with the aim of producing
biogas. In this way and in order to maximize biogas production,
easily degradable biomasses such as animal slurries, OFMSW,
energy crops, and agro-industrial residues are used alone or in
mixture. AD, if correctly performed, proceeds by the high degrada-
tion of OM (
). Consequently, starting organic
matrices are transformed during AD. OM transformation involves
the preservation of recalcitrant molecules that are concentrated
(
). CP MAS
13
C NMR gave evidence of that,
indicating that both lignin-like material and complex lipids and
steroids became concentrated during AD. These molecules have
been reported to be humus precursors (
), playing
an important role in the short-term SOM turnover. On the other
hand, because of mineralization of OM and of the anaerobic
Fig. 1. PCA plots for amendment properties (a) and fertilizer properties (b).
F. Tambone et al. / Chemosphere 81 (2010) 577–583
581
condition in which AD is performed, the preservation and concen-
tration of inorganic nutrients, such as P and K and N, occurred
(
). In addition, organic N is transformed into
ammonia (
).
The data of this study confirmed that digestates are very differ-
ent from ingestates and, both OM quality and fertilizing element
content of the digestates suggest its usefulness in agriculture
(
). In this study, to know the digestate’s
amendment and fertilizing properties, a comparison was made be-
tween digestates and well known organic matrices. Thus compost
was used in the study as it is one of the most classical organic
amendments studied and DS was chosen because it has a high con-
tent of nutritional elements such as N, P, and K.
The results of this study reveal differences in the chemical com-
position of OM and nutrients contained in the digestate and the
ingestate and, more importantly, differences with respect to the
DSs and composts. Considering that compost is an organic amend-
ment and that DS is a nutrient fertilizer, the chemical, spectro-
scopic, and biological data of the samples studied were analyzed
using multivariate analysis (PCA) to detect similarities or differ-
ences among the four types of biomasses.
The matrix of the components (
), with respect to amend-
ment properties, shows that the PC
AM1
(which explained 43% of to-
tal variability) was directly correlated to alkyl-C and carboxyl-C
contents and inversely correlated to the O-alkyl-C content, i.e., bio-
logical process-concentrated alkyl-C and carboxyl-C and degraded
O-alkyl-C.
The second component (PC
AM2
) (which explained 36% of total
variability) was directly correlated to VS, TOC, and inversely corre-
lated to the content of aromatic-C, i.e., the more the matrices were
mineralized, the more lignin-like molecules were contained.
The distribution of biomasses in the bi-dimensional space, de-
fined by the two PCPs, shows a clear distinction of the composts
from the other biomasses (
). This result can be attributed
not only to the different biological processes (aerobic vs. anaero-
bic) which the compost has undergone, but also to the presence
of lignocellulosic materials used as bulk agent in the mixers stud-
ied; this contributed greatly to the presence of aromatic-C in the
final compost (
). Digestates were posi-
tioned in the PCA bi-plot some what close to the DS (samples D1,
D2, and D3) (
) and partly intermediate between DS and com-
posts (samples D4, D5, D6, and D8) (
). Sample D7 was inter-
mediate between the two digestate groups. In
, five organic
matrix groups could be seen: C1–C3; D4, D5, D6, D8; D1, D2, D3,
D7, DS1, DS2, DS3, DS4; I1, I2, I3; and I4, I5, I6, I7, I8. The centroid
(
) for each organic matrix group was given
in
. Taking into consideration the Euclidean distances from
the compost centroid (
), one can surmise for each matrix
group a sort of ‘‘compost similarity”, which is as follows: C1, C2,
C3 > D4, D5, D6, D8 I4, I5, I6, I7, I8 ffi D1, D2, D3, D7, DS3, DS2,
DS1, DS4 > I1, I2, I3.
On the basis of these results, it can be suggested that digestates
show characteristics different (D4, D5, D6, D8 – D1, D2, D3, D7)
from those of compost. As D1–D3 digestates were derived from
I1–I3 ingestates, which were different from other ingestates in
terms of materials composing the mix (
) and chemical com-
position (
), it can be concluded that the origin and
composition of the organic matrices influenced the digestate’s
chemical characteristics. In particular, it seems that the presence
of the organic fraction of municipal solid wastes (
) gave dig-
estates characteristics much different from those of compost com-
pared with digestates obtained from a mix with animal slurry or
crop energy biomasses prevalent (
). These data appear
strange as two of the three composts were obtained from a mix
containing OFMSW (such as D1–D3), suggesting greater similarity.
On the other hand, the three composts studied did not show big
differences in composition among them, although C1 came from
lignocellulosic material and did not contain OFMSW. This fact indi-
cates that the lignocellulosic material present in the compost mix,
more than OFMSW, contributed to the final compost composition
and that this material strongly affected compost compositions
resulting in a material completely different from the other organic
matrices (
In any case, digestate properties seemed to be very different
from those of ingestates (see Euclidean distance between I and D
samples) (
). It was interesting to note that, with respect to
the compost (Euclidean distances) some digestates (samples D1,
D2, D3, D7) were similar to the ingestates (similar Euclidean dis-
tance). Nevertheless, the similarity was brought about by different
causes. Samples D1, D2, D3, and D7 were closer to the compost in
terms of biological stability (ABP) and OM content (VS and TOC
contents) (
), but they were far from it in terms of macromo-
lecular composition (alkyl-C and O-alkyl-C contents) (
). In
contrast, the ingestates were more similar to compost with regard
to macromolecular composition but not with OM and ABP (
The ability of an organic matrix to contribute actively to the
SOM in a short period depends on the presence of recalcitrant mol-
ecules (
). The degree of recalcitrance of
organic biomass can be measured by detecting its biological degra-
dability (biological stability) (
Adani et al., 2004; Scaglia et al.,
From the results of this study, it appears that macromolecular
composition is not a suitable approach to test the recalcitrance/
biological stability of OM. For example, ingestates showed very
low biological stability but a macromolecular composition similar
(e.g., alkyl-C content) to those of composts, which, contrastingly
showed low degradability. On the other hand, digestates D1, D2,
D3, and D7, although having a macromolecular composition differ-
ent from those of composts, showed high biological stability simi-
lar to that of composts. Therefore, it could be concluded that
chemical composition, such as the one detected in this work, did
not greatly contribute to elucidating the digestate amendment
properties by direct comparison with compost. Probably, biological
stability or biomass degradability is a more appropriate parameter.
In this work, ABP was chosen as a tool to detect biological stability.
On the basis of this parameter and taking into consideration
the average ABP data reported in
, the amendment proper-
ties could be ranked in the following manner: compost ffi
digestate > DS ingestate.
The matrix components (
) relative to the PCA performed
to study fertilizing properties of the organic matrices showed that
PC
F1
was directly correlated to TKN and organic N contents and in-
Table 4
Component loadings matrix of the PCAs for the amending properties (PC
AM
) and for
fertilizer properties (PC
F
) data sets.
Data sets
PC
AM
PC
F
PC
AM1
PC
AM2
PC
F1
PC
F2
VS
0.15
0.96
–
–
TOC
0.14
0.97
–
–
ABP
0.10
0.12
–
–
Total aliphatic-C
0.94
0.11
–
–
O–CH
3
or N-alkyl, O-alkyl C, di-O-alkyl C
0.96
0.13
–
–
Aromatic-C phenol or phenyl ether-C
0.21
0.88
–
–
Carboxyl-C and keto-C
0.91
0.1
–
–
TKN
–
–
0.83
0.53
NH
3
–N
–
–
0.18
0.94
Org-N
–
–
0.97
0.07
C/N
–
–
0.92
0.22
P
2
O
5
–
–
0.57
0.19
K
2
O
–
–
0.02
0.91
582
F. Tambone et al. / Chemosphere 81 (2010) 577–583
versely correlated to C:N. The second component (PC
F2
) was di-
rectly correlated to the NH
3
, P
2
O
5
, and K
2
O contents.
The distribution of the biomasses in the bi-dimensional space,
defined by the two PC
F
s (
), resulted in a good separation of
the four typologies of biomasses. In particular, taking into account
the PCA results and the data in
, it can be concluded that all
digestate samples were characterized by the greatest TKN, NH
3
,
P
2
O
5
, and K
2
O contents and so they showed the highest nutrient
values. On the other hand, compost showed the opposite charac-
teristics as expected. The ingestate characteristics did not influence
the digestate properties.
Acknowledgements
This study was supported by Lombardy Region – National Pro-
grams for Biofuel (Probio Biogas Project – Regione Lombardia,
Italy) – and ARAL – Associazione Regionale Allevatori della Lom-
bardia contract N. Prot. USM 0032370.
References
Adani, F., Tambone, F., 2005. Long-term effect of sewage sludge application on soil
humic acids. Chemosphere 60, 1214–1221.
Adani, F., Confalonieri, R., Tambone, F., 2004. Dynamic respiration index as a
descriptor of the biological stability of organic wastes. J. Environ. Qual. 33,
1866–1876.
Adani, F., Tambone, F., Genevini, P.L., Montoneri, E., 2006. Compost effect on soil
humic acid: a NMR study. Chemosphere 65, 1414–1418.
Anderson, D., Plotnikoff, R.C., Raine, K., Cook, K., Smith, C., Barret, L., 2004. Towards
the development of scales to measure ‘‘will” to promote heart health within
health organizations in Canada. Health Promot. Int. 19, 471–481.
APHA, 1992. Standard Methods for the Examination of Water and Wastewater, 18th
ed. American Public Health Association, Washington, DC, USA.
Barrett, J.E., Burke, I.C., 2000. Potential nitrogen immobilization in grassland soil
across a soil organic matter gradient. Soil Biol. Biochem. 32, 1707–1716.
Brejda, J.J., Mooman, T.B., Karlen, D.L., Dao, T.H., 2000. Identification of regional soil
quality factors and indicators. I. Central and southern high plains. Soil Biol.
Biochem. 64, 2115–2124.
British Standards Institution (BSI), 2010. <
http://www.wrap.org.uk/downloads/
PAS110_vis_10.8c19f494.8536.pdf
> (08.11.10).
Cadena, E., Colon, J., Sànchez, A., Font, X., Artola, A., 2009. A methodology to
determine gaseous emission in a composting plant. Waste Manage. 29, 2799–
2807.
Conte, P., Piccolo, A., Van Lagen, B., Buurman, P., de Jager, P.A., 1997. Quantitative
aspects of solid-state
13
C NMR spectra of humic substances from soils of
volcanic systems. Geoderma 80, 327–338.
Dignac, M.F., Derenne, S., Ginestet, P., Bruchet, A., Kniker, H., Largeau, C., 2000.
Determination of structure and origin of refractory organic matter in bio-
depurated wastewater via spectroscopic methods. Comparison of conventional
and ozonation treatment. Environ. Sci. Technol. 34, 3389–3394.
Dinel, H., Schnitzer, M., Schulten, H.R., 1998. Chemical and spectroscopic
characterization of colloidal fraction separated from liquid hog manure. Soil
Sci. 163, 665–673.
EPA, 1998. Method EPA 3051. Microwave Assisted Acid Digestion of Sediments,
Sludges, Soils and Oils. Washington, DC.
Giusquiani, P.L., Pagliai, M., Gigliotti, G., Businelli, D., Benetti, A., 1995. Urban waste
compost: effects on physical, chemical, and biochemical soil properties. J.
Environ. Qual. 24, 175–182.
Huang, C.C., Chen, Z.S., 2009. Carbon and nitrogen mineralization of sewage sludge
compost in soil with different initial pH. Soil Sci. Plant Nutr. 55, 715–724.
Iakimenko, O., Otabbong, E., Sadovnikova, L., Persson, J., Nilsson, I., Orlov, D.,
Ammosova, Y., 1996. Dynamic transformation of sewage sludge and farmyard
manure components. 1. Content of humic substances and mineralization of
organic carbon and nitrogen in incubated soils. Agric. Ecosyst. Environ. 58, 121–
126.
IRSA CNR, 1994. Metodi Analitici per le Acque, Quaderni, N. 100. Istituto Poligrafico
e Zecca dello Stato, Rome, Italy.
Kaiser, H.F., 1960. The application of electronic computers to factor analysis. Educ.
Psychol. Meas. 29, 141–151.
Kogel-Knaber, I., 2002. The macromolecular organic composition of plant and
microbial residues as inputs to soil organic matter. Soil Biol. Biochem. 34, 139–
162.
Lal, R., 2001. World cropland soils as a source or sink for atmospheric carbon. Adv.
Agron. 71, 145–191.
Lee, C., 1992. Controls of organic carbon preservation: the use of stratified water
bodies to compare intrinsic rates of decomposition in oxic and anoxic systems.
Geochim. Cosmochim. Acta 56, 3323–3335.
Leifeld, J., Siebert, S., Kögel-Knabner, I., 2002. Changes in the chemical composition
of soil organic matter after application of compost. Eur. J. Soil Sci. 53,
299–309.
Lorenz, K., Lal, R., Preston, C.M., Nierop, K.G.J., 2007. Strengthening the soil organic
carbon
pool
by
increasing
contributions
from
recalcitrant
aliphatic
bio(macro)molecules. Geoderma 142, 1–10.
Mamo, M., Rosen, C.J., Halbach, T.R., 1999. Nitrogen availability and leaching from
soil amended with municipal solid waste compost. J. Environ. Qual. 28, 1074–
1082.
Miller, F.P., Wali, M.K., 1995. Soils, land use and sustainable agriculture: a review.
Can. J. Soil Sci. 75, 413–422.
Møller, J., Boldrin, A., Christensen, T.H., 2009. Anaerobic digestion and digestate use:
accounting of greenhouses gases and global warming contribution. Waste
Manage. Res. 27, 813–824.
Palm, C.A., Giller, K.E., Mafongoya, P.L., Swift, M.J., 2001. Management of organic
matter in the tropics: translating theory into practice. Nutr. Cycl. Agroecosys.
61, 63–75.
Pereira, M.A., Pires, O.C., Mota, M., Alves, M.M., 2005. Anaerobic biodegradation of
oleic and palmitic acids: evidence of mass transfer limitations caused by long
chain fatty acid accumulation onto the anaerobic sludge. Biotechnol. Bioeng. 92,
15–23.
Pichler, M., Knicker, H., Kögel-Knabner, I., 2001. Solid-state
13
C NMR spectroscopic,
chemolytic and biological assessment of pretreated municipal solid waste. J.
Ind. Microbiol. Biotechnol. 26, 83–89.
Pognani, M., D’Imporzano, G., Scaglia, B., Adani, F., 2009. Substituting energy crops
with organic fraction of municipal solid waste for biogas production at farm
level: a full-scale plant study. Process Biochem. 44, 817–821.
Réveillé, V., Mansuy, L., Jardé, E., Garnier-Sillam, E., 2003. Characterization of
sewage–sludge derived organic matter: lipids and humic acids. Org. Geochem.
34, 615–627.
Rowell, D.M., Prescott, C.E., Preston, C.M., 2001. Decomposition and nitrogen
mineralization from biosolids and other organic materials: relationship with
initial chemistry. J. Environ. Qual. 30, 1401–1410.
Scaglia, B., Adani, F., 2008. An index for quantifying the aerobic reactivity of
municipal solid wastes and derived waste products. Sci. Total. Environ. 394,
183–191.
Scaglia, B., Confalonieri, R., D’Imporzano, G., Adani, F., 2010. Estimating biogas
production of biologically treated municipal solid waste. Bioresour. Technol.
101, 945–952.
Schievano, A., Pognani, M., D’Imporzano, G., Adani, F., 2008. Predicting anaerobic
biogasification potential of ingestates and digestates of a full-scale biogas
plant using chemical and biological parameters. Bioresour. Technol. 99, 8112–
8117.
Schnaak, W., Küchler, T., Kujawa, M., Henschel, K.P., Süßenbach, D., 1997. Organic
contaminants in sewage sludge and their ecotoxicological significance in the
agricultural utilization of sewage sludge. Chemosphere 35, 5–11.
Sørensen, P., Møller, H.B., 2009. Fate of nitrogen in pig and cattle slurries applied to
the soil-crop system. In: Adani, F., Schievano, A., Boccasile, G. (Eds.), Anaerobic
Digestion: Opportunities for Agriculture and Environment. DiProVe University
of Milan, Milan, pp. 27–37.
Tambone, F., Genevini, P., Adani, F., 2007. The effect of short-term compost
application on soil chemical properties and on nutritional status of maize plant.
Compost Sci. Util. 15, 176–183.
Tambone, F., Genevini, P., D’Imporzano, G., Adani, F., 2009. Assessing amendment
properties of digestate by studying the organic matter composition and the
degree of biological stability during the anaerobic digestion of the organic
fraction of MSW. Bioresour. Technol. 100, 3140–3142.
Tani, M., Sakamoto, N., Kishimoto, T., Umetsu, K., 2006. Utilization of anaerobically
digested slurry combined with other waste following application to agricultural
land. Int. Congr. Ser. 1293, 331–334.
Ussiri, A.A.N., Johnson, C.E., 2003. Characterization of organic matter in a northern
hardwood forest soil by
13
C NMR spectroscopy and chemicals methods.
Geoderma 11, 123–149.
F. Tambone et al. / Chemosphere 81 (2010) 577–583
583
Document Outline
Wyszukiwarka
Podobne podstrony:
Skład chemiczny i właściwości nawozów mineralnych – oznaczanie różnych P 2 O 5 w nawozachx
właściwości fizyczne i skład chemiczny moczu, weterynaria, I semestr, Choroby zwierząt
Kosmetologia Budowa i skład chemiczny włosa Metody i środki do pielęgnacji różnych rodzajów włosó
Laborki surowce i procesy przemysłu nieorg Skład chemiczny i właściwości nawozów mineralnych nasze
Skład chemiczny biomasy wierzby zbieranej w różnych rotacjach 2 MS
Skład chemiczny biomasy wierzby zbieranej w różnych rotacjach 2 MS DN
Skład chemiczny popiołu biomasy wierzby zbieranej w różnych rotacjach 1
Skład chemiczny biomasy wierzby zbieranej w różnych rotacjach 2
Skład chemiczny biomasy wierzby zbieranej w różnych rotacjach DN 0321
Skład chemiczny biomasy wierzby zbieranej w różnych rotacjach DN 0326
TEORIA W-F, Teoria - pytania i odp., Skład chemiczny powietrza atmosferycznego: a)składniki stałe: a
TEORIA W-F, teoria, Skład chemiczny powietrza atmosferycznego: a)składniki stałe: azot(78%),tlen(21%
Skład chemiczny nukleotydu
PN EN 1744 1 2000 Badania chemicznych wlasciwosci kruszyw Analiza chemiczna
28b. SKLAD CHEMICZNY KOMOREK ORAZ WIAZANIA I ODDZIALYWANIA CHEMICZNE
skład chemiczny komorki
budownictwo ogolne specyfikacja róznych rodzajów stropów
więcej podobnych podstron