Influence of aeration on CH4, N2O and NH3 emissions during aerobic composting of a chicken manure and high C/N waste mixture.

Abstract

Co-composting of chicken manure, straw and dry grasses was investigated in a forced aeration system to estimate the effect of aeration rates on NH(3), CH(4) and N(2)O emissions and compost quality. Continuous measurements of gas emissions were carried out and detailed gas emission patterns were obtained using an intermittent-aeration of 30 min on/30 min off at rates of 0.01 (A1), 0.1 (A2) and 0.2 (A3) m(3)min(-1)m(-3). Concentrations of CH(4) and N(2)O at the low aeration rate (A1) were significantly greater than those at the other two rates, but there was no significant difference between the A2 and A3 treatments. CH(4) and N(2)O emissions for this mixture could be controlled when the composting process was aerobic and ammonia emissions were reduced at a lower aeration rate. Comparison of CH(4), N(2)O, NH(3) emissions and compost quality showed that the aeration rate of the A2 treatment was superior to the other two aeration rates.

Full text

Page 1

This article appeared in a journal published by Elsevier. The attached
copy is furnished to the author for internal non-commercial research
and education use, including for instruction at the authors institution
and sharing with colleagues.
Other uses, including reproduction and distribution, or selling or
licensing copies, or posting to personal, institutional or third party
websites are prohibited.
In most cases authors are permitted to post their version of the
article (e.g. in Word or Tex form) to their personal website or
institutional repository. Authors requiring further information
regarding Elsevier’s archiving and manuscript policies are
encouraged to visit:
http://www.elsevier.com/copyright

Page 2

Author's personal copy
Influence of aeration on CH4, N2O and NH3emissions during aerobic composting
of a chicken manure and high C/N waste mixture
Yujun Shena,b, Limei Renb, Guoxue Lib,⇑, Tongbin Chena, Rui Guob
aCenter for Environmental Remediation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, PR China
bCollege of Resource and Environmental Science, China Agriculture University, Beijing 100193, PR China
a r t i c l e i n f o
Article history:
Received 24 March 2010
Accepted 12 August 2010
Available online 2 October 2010
a b s t r a c t
Co-composting of chicken manure, straw and dry grasses was investigated in a forced aeration system to
estimate theeffectof aerationrates onNH3,CH4and N2O emissions and compost quality. Continuousmea-
surements of gas emissions were carried out and detailed gas emission patterns were obtained using an
intermittent-aeration of 30 min on/30 min off at rates of 0.01 (A1), 0.1 (A2) and 0.2 (A3) m3min?1m?3.
Concentrations of CH4and N2O at the low aeration rate (A1) were significantly greater than those at the
other two rates, but there was no significant difference between the A2 and A3 treatments. CH4and N2O
emissions for this mixture could be controlled when the composting process was aerobic and ammonia
emissions were reduced at a lower aeration rate. Comparison of CH4, N2O, NH3emissions and compost
quality showed that the aeration rate of the A2 treatment was superior to the other two aeration rates.
? 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Composting is an effective way to manage livestock manure.
However, mismanagement of the composting process results in
emissions of harmful gases and corresponding environmental
problems (Hassouna et al., 2008; Szanto et al., 2007). Ammonia
(NH3) emission due to aerobic degradation of organic matter leads
to nutrient loss and acidification. Nitrous oxide (N2O), released
from nitrification or denitrification, and methane (CH4) produced
in anaerobic conditions cause large greenhouse gas effects with
global warming potentials over a 100-year time horizon of 23
times for CH4and 296 times for N2O per mole of gas compared
to CO2(Fukumoto et al., 2003; Molodovskaya et al., 2008).
The aerobic condition during composting process is a critical
factor determining the discharge of unwanted emissions (Haug,
1993; Smet et al., 1999). High oxygen levels can be maintained
by choosing different aeration systems and designing various aer-
ation rates and on/off cycles (de Guardia et al., 2008; Keener et al.,
2005; Kim et al., 2009; Li et al., 2008; Michel et al., 1996). Three
different systems of aeration, pile turning, forced aeration of a sta-
tic pile, and passive aeration of a static pile are commonly applied
(Solano et al., 2001). The pile turning system produces lower CH4
and N2O emissions than does passive aeration of a static pile that
has an assured aerobic environment. Composting by forced aera-
tion gives even lower CH4and N2O emissions than that by turning
due to the more plentiful oxygen supply (Hao et al., 2001). For
composting involving the forced aeration of a static pile, whether
time-continuous or intermittent ventilation of the pile are used
also influences greenhouse gas emissions. The impact on gas emis-
sion of different aeration rates in a time-continuous ventilation
system have been previously studied (Osada et al., 2000; Sommer
and MØller, 2000). However, intermittent ventilation can reduce
some greenhouse gas emissions compared with time-continuous
ventilation (Hong et al., 1998; Keener et al., 2001). But little infor-
mation is available on how the aeration rates of intermittent ven-
tilation systems relate to CH4and N2O emissions. Studies have
shown that an increased aeration rate was responsible for an in-
crease in NH3 emissions (de Guardia et al., 2008; Elwell et al.,
2001; Kim et al., 2009; Osada et al., 2000). Remarkably, however,
it was found that NH3emission at an aeration rate of 0.50 L/min kg
VS was higher than that at other aerations such as 0.125, 0.25 and
0.75 L/min kg initial VS.
In this study, chicken manure, straw and dry grasses were co-
composted with forced aeration composting to examine the influ-
ence of aeration rates with intermittent ventilation on NH3, CH4
and N2O emissions and to obtain an optimal aeration rate for
reducing gas emissions and improving compost quality.
2. Materials and methods
2.1. Materials and experimental design
Chicken manure, straw and dry grasses taken from the China
Agricultural Academy of Science were used in each experiment.
Straw was cut using a saw in order to keep pieces with dimensions
ranging from 1 to 5 cm. The total carbon, total nitrogen and mois-
0956-053X/$ - see front matter ? 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.wasman.2010.08.019
⇑Corresponding author. Tel.: +86 010 62733498; fax: +86 64889303.
E-mail addresses: shenyj.09b@igsnrr.ac.cn (Y. Shen), ligx@cau.edu.cn (G. Li).
Waste Management 31 (2011) 33–38
Contents lists available at ScienceDirect
Waste Management
journal homepage: www.elsevier.com/locate/wasman

Page 3

Author's personal copy
ture content were measured before mixing. Properties of the mate-
rials are shown in Table 1.
The composting reactors were made of stainless steel and had
volumes of about 60 L (0.36 m in inner diameter, 0.6 m in height,
with the composting bed filled to about 0.5 m) (Fig. 1). A heat insu-
lation layer was provided to minimize heat loss to the surround-
ings. A stainless steel cap was fitted on the top of each reactor to
facilitate its filling and emptying. At the bottom of each reactor a
metal grid with small holes was fixed, which supported the com-
posting bed and facilitated the inflow of ambient air from the bot-
tom. Three sampling locations with plugs, each 5 cm in diameter,
at different heights (0.1, 0.3 and 0.5 m from the bottom) were pro-
vided. The samples taken from different height would be mixed
thoroughly. An oxygen analyzer (DH6511A) was placed in the cen-
ter of the composting bed from the middle sampling location to
analyze oxygen concentrations at different times (at days 0, 1, 2,
4, 7, 10, 13, 17, 20 and 25). Three ports in the cap were provided
for temperature sensors and collection of gas samples. A trap with
boric acid (H3BO3, 2% in mass), which was changed every day, was
provided for collecting ammonia. The other empty trap was pro-
vided for gas N2O and CH4collection. The experiments were per-
formed indoors at a temperature maintained at about 10 ?C.
Chicken manure, dry grasses and straw were added at a wet
mass ratio of 2.75:5.64:1.4. The initial moisture content was ad-
justed to 65% and the C/N ratio was adjusted to 20 in each exper-
imental run. The three reactors were run simultaneously until the
temperature of the composting material was around ambient. The
aeration was then stopped and the reactor emptied. Composting
lasted 25 days in this experiment. The materials were turned on
days 4 and 13, and water was added to keep the moisture content
of the mixture at 65%.
The Chinese Technical Specification for Static Aerobic Com-
posting (CJJ/T52-93) suggests that the optimum aeration rate
during composting should be about 0.05–0.2 m3min?1m?3in
order to maintain oxygen supply. In this study, three different
aeration treatments were investigated: A1, A2 and A3, with aer-
ation flows of 0.01, 0.1, and 0.2 m3min?1m?3, respectively. The
aeration rate of 0.01 m3min?1m?3was considered to represent
a weak aerobic condition and the other two rates were consid-
ered to represent increasingly aerobic conditions. The ventilation
of A1 was intermittent with aerating for 30 min and stopping for
30 min over the first seven days and then continuous for the rest
of the composting time. The ventilations of A2 and A3 were
intermittent over the whole composting period with 30 min
on/off periods.
2.2. Compost sampling and analytical methods
Samples of the composting solids were taken seven times dur-
ing the experimental period (at days 0, 3, 6, 9, 12, 20 and 25) at
the three sampling ports and mixed thoroughly. The samples were
divided into two, with one part being analyzed immediately, and
the other being air-dried and ground to pass a 1-mm sieve. Gas
samples for N2O and CH4measurement were taken from the col-
lection trap eight times during the experiment (at days 1, 2, 4, 7,
10, 13, 17 and 20). The N2O and CH4concentrations were measured
by gas chromatography (GC-9900, made in China). The ammonia
trapped in boric acid was titrated using sulphuric acid (H2SO4,
0.1 N).
Total nitrogen (TN) and total organic carbon (TOC) were ana-
lyzed in the air-dried samples. Total N was measured using the
Kjeldhal method (Lu, 2000). Total organic carbon (TOC) in the mix-
tures was measured by potassium dichromate (K2Cr2O7) and sul-
phuric acid (H2SO4) (Yeomans and Bremner, 1988). For pH
measurement, water extracts from the composting mixtures were
prepared at a 1:10 soil:water ratio (w/v) stirred for 1 h and then
centrifuged at 4000 rpm). The pH was measured with a pH meter.
Seed germination index (GI) was used to assess phytotoxicity of
the compost (Sellami et al., 2008). Twenty Brassica napus seeds
were distributed on filter paper in petri dishes (10 cm in diameter)
and moistened with 8 ml of the compost extract. Three replicate
dishes for each sample were incubated at 25 ?C for 3 days. The
number of germinating seeds and root length were measured. Dis-
tilled water was used as a control. The GI was calculated according
to the following formula:
Table 1
Properties of materials used in composting: values are means of triplicates (dry
weight basis), values in parentheses are standard error (n = 3).
Materials TOC (g kg?1) TN(g kg?1) C/NMoisture (%)
Chicken manure
Corn stalk
Dry grass
282 (2.91)
445.7 (3.78)
323.1 (3.01)
21 (0.73)
6.3 (0.03)
3.4 (0.01)
13.4 (0.21)
71 (0.61)
95 (0.82)
49 (0.38)
16.7 (0.18)
7.44 (0.07)
Fig. 1. Structure of the composting system.
34
Y. Shen et al./Waste Management 31 (2011) 33–38

Page 4

Author's personal copy
GI ð%Þ ¼
Seed germination ð%Þ ? Root length of treatment
Seed germination of control ð%Þ ? Root length of control
? 100
2.3. Statistical analysis
The mean and standard deviation of the three replicates are re-
ported. One-way Analysis of Variance (ANOVA) was used to com-
pare the different composting treatments. Multiple comparisons
between treatments were compared using the Least Significant
Difference test (LSD-t). SPSS for Windows, release 15.0 (SPSS,
2007), was used for all statistical analyses.
3. Results and discussion
3.1. Temperature and pH profile
The temperature profiles from the different aeration rates dur-
ing composting are shown in Fig. 2. The temperature in the A1
treatment increased slowly with the maximum temperature dur-
ing the first 7 days being 37 ?C. Therefore, continuous aeration
was adjusted and the maximum temperature reached 39 ?C at
day 9. The temperature remained at around 30 ?C for the rest of
the composting time and did not reach the thermophilic phase. Re-
sults were different for the A2 and A3 treatments as temperatures
increased rapidly to the thermophilic phase by the second day.
After turning and moisture addition (at days 4 and 14), the temper-
atures rose again. The thermophilic phase lasted 10 and 8 days in
reactors A2 and A3 and reached a maximum temperature of 74
and 73 ?C, respectively, on day 5. These temperatures were suffi-
cient for pathogen elimination. After the early phase of compost-
ing, microbial activity and organic matter decomposition rates
slowed down and the temperature decreased gradually. The com-
post was emptied from the reactors at day 25 when the tempera-
tures were around 10 ?C. The temperature in the A3 treatment was
generally somewhat lower than in the A2 treatment probably due
to the cooling effect on the composting reactor caused by the
greater aeration rate. ANOVA showed no significant differences
among the three trials (F = 2.598, P = 0.081). However, the LSD-t
analysis showed no significant difference between the A2 and A3
treatments, but both were significantly different from the A1
treatment.
The pH of the three runs was maintained at 6.5–8 during the
composting processes (Fig. 3). The pH in the A1 treatment de-
creased in the initial phase of composting (days 0–2), and then in-
creased but remained below 7. We hypothesize that production of
organic acids due to anaerobic conditions caused by the low aera-
tion rate led to the relatively low pH, while, on the other hand, the
low ammonia emission (close to 0) was insufficient to promote a
pH increase (Fig. 5). In contrast, the pH in the A2 and A3 treatments
increased during the first several days and then decreased, but re-
mained above 7 as the compost matured. In accord with the date of
highest ammonia emission (Fig. 5), the maximum pH was at days 4
and 7 in the A2 treatment and A3 treatments, respectively. This is
suggested as being related to the low production of organic acids
and the large ammonia emissions under aerobic conditions
(Fig. 5) (Yu and Huang, 2009). One-way analysis of variance
showed a highly significant difference among the three treatments
(P = 0.0009).
3.2. Kinetics of O2concentration and emissions of N2O and CH4
Concentrations of O2, CH4and N2O at the outlet of the compost-
ing reactors are shown in Fig. 4. Oxygen decreased rapidly to 4.6%,
3.2% and 9.7% by day 2 for the A1, A2 and A3 treatments, respec-
tively. Oxygen concentrations in the A2 and A3 treatments in-
creased gradually after the third day and exceeded 15% after day
13. The pattern of oxygen concentrations in the A1 treatment
was very different to that in the A2 and A3 treatments with the
oxygen concentration continuing to fall after the second day, final-
ly stabilizing at about 0.5–1%. Inadequate oxygen supply in the A1
treatment would lead to the occurrence of anaerobic conditions
and would be disadvantageous to aerobic microbial activity.
For the three composting systems, the CH4content was high in
the first several days due to low O2concentration but relatively
low for the rest of the composting time. The emission patterns of
CH4in this study resemble those found by Osada et al. (1997)
and Fukumoto et al. (2003). However, CH4emissions from the A1
treatment were significantly higher than from the A2 and A3 treat-
ments. CH4increased sharply on the second day, reached a maxi-
mum concentration of 9% at day 4, and stabilized at 1.4–0.6% by
day 25. The maximum CH4concentrations from the A2 and A3
treatments were only 0.52% and 0.45%, respectively. The anaerobic
conditions in the A1 treatment due to the insufficient air supply led
to large CH4production, while the adequate air supply in the A2
and A3 treatments led to much lower CH4emissions. A different
Fig. 2. Changes in temperature during composting at different aeration rates.
Fig. 3. Changes in pH during composting at different aeration rates.
Y. Shen et al./Waste Management 31 (2011) 33–38
35

Page 5

Author's personal copy
intermittent ventilation cycle might reduce it even more in these
treatments. One-way analysis of variance showed a highly signifi-
cant difference among the three treatments (P < 0.05). However,
the LSD-t showed no significant difference between the A2 and
A3 treatments, but a significant difference from the A1 treatment.
Overall, CH4emission could be controlled when the aeration rate
exceeded 0.1 m3min?1m?3.
As for CH4emissions, N2O emissions were minimized when the
aeration rate increased. N2O emissions from the A1 treatment were
significantly higher than for the A2 and A3 treatments with mean
concentrations of 0.027%, 0.01% and 0.007%, respectively. One-way
analysis of variance showed a highly significant difference among
the three treatments (P = 0.000). However, the LSD-t showed no
significant difference between the A2 and A3 treatments, but a sig-
nificant difference from the A1 treatment. The relatively high pro-
duction of N2O from the A1 treatment may be related to lower
oxygen concentrations (von Schulthess et al., 1994). In the case
of the A2 and A3 treatments, sufficient oxygen supply provided
by greater aeration decreased N2O emissions (Kuenen and Robert-
son, 1994; Parkin, 1987). Furthermore, the aeration interval has
been confirmed as helping completion of denitrification and pre-
venting N2O accumulation and release (Béline and Martinez,
2002; Osada et al., 1995).
3.3. Emission of NH3
The emission patterns of ammonia were similar in the A2 and
A3 treatments (Fig. 5). Emission of ammonia increased sharply
with increasing temperature on days 1–3, which was caused by
ammonification of organic nitrogen compounds. The first peak in
the NH3emission rate was reached on day 3, and it then decreased
with the fall in temperature from days 4 to 5 (Fig. 2). However,
Fig. 4. Concentrations in O2, CH4and N2O in the different composting reactors.
Fig. 5. Emission of NH3in the different composting reactors.
36
Y. Shen et al./Waste Management 31 (2011) 33–38