effect of caco3 pretreatment on methane production from anaerobic digestion of rice straw
TRANSCRIPT
Effect of CaCO3 Pretreatment on Methane Production from Anaerobic
Digestion of Rice Straw
Benlin Dai1, 2, a, Anfeng Zhu2, b, Feihu Mu1, 2, c, Ning Xu1, d and Zhen Wu1, e 1Jiangsu Key Laboratory for Biomass-based Energy and Enzyme Technology, Huaiyin Normal
University, Huaian, Jiangsu, 223300, China
2Jiangsu Key Laboratory for Chemistry of Low-Dimensional Material, Huaiyin Normal University,
Huaian, Jiangsu, 223300, China
Keywords: Anaerobic Digestion, Biogas, Methane Production, CaCO3 Pretreatment, Rice Straw.
Abstract. The chemical pretreatment of rice straw was achieved via the liquid-state dissolution of
CaCO3. Pretreatment effects on the biodegradability and subsequent anaerobic production of methane
were investigated. The results showed that the peak value of biogas production was attained of 4%
CaCO3 pretreatment on the 20th
day, which is 1 589 mL. The test daily methane content of different
pretreatment conditions mainly ranges from 3.4% to 47.4%. The cumulative biogas production of 6%
CaCO3 pretreatment was the highest, about 19 917 mL.
Introduction
Straw is a kind of important lignocellulosic biomass resources, can provide biological transformation
(such as bio-diesel, biogas, bio-ethanol, bio-hydrogen) provides polysaccharide rich [1]. In China,
agriculture waste large quantity, variety, waste produced about 8 × 108 ton annual agricultural crops
[2]. If the use of anaerobic fermentation into methane and biogas slurry or application of biogas
residue recycling mode to make full use of the agricultural waste, not only ease the nervous energy in
rural areas, but also can improve the ecological environment, contribute to the structural adjustment
of our country agriculture, to achieve the transition to sustainable agriculture as soon as possible [3].
Straw cellulose and hemicellulose can be degraded biogas produced in the anaerobic fermentation
conditions, while the lignin is difficult to be degraded and utilized. Because in the straw cellulose
lignin and hemicellulose wrapped, lignin in the fiber, hindered the microbial and enzymatic
degradation of cellulose and easy contact, causing resistance material on anaerobic digestion [4].
Visible damage, hydrolysis lignin structure and cellulose and hemicellulose are the raw material of
biotransformation rate limiting step.
The pretreatment methods to enhance the biogas yield were widely used in the conventional sole
anaerobic digestion on the rice straw [5-6]. The objective of this study was to evaluate the biogas
production and methane content enhancement capacity by using batch anaerobic reactors, when
pretreating the rice straw substrate with four different weight percentages (2%, 4%, 6% and 8%) of
CaCO3. The test pH value, biogas production and methane content were examined. It provides
relevant technical reference to biogas production technology and equipment research and
development of the rice straw during anaerobic digestion in this study.
Materials and Methods
Experimental Materials. Rice straw waste was used as the biodegradable substrate. The substrate
was pulverized into particles of diameters of 2 - 3 mm. Anaerobic biogas slurry was collected from
rural fecal pool in Xinji town, Huaian city, Jiangsu province, China. The substrate was washed and
filtered before the experiment, and then cultured under mid-temperature for one week. No other
strains were added in the experiment, and the components of the backfill material are illustrated in
Table 1.
Applied Mechanics and Materials Vols. 587-589 (2014) pp 208-211Online available since 2014/Jul/04 at www.scientific.net© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.587-589.208
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Table 1 Composition of rice straw waste and anaerobic biogas slurry [%]
Digestive material Rice straw waste Anaerobic biogas slurry
Total solids (g TS g-1
wet) 91.2 8.3
Volatile solids (g VS g-1
TS) 83.3 3.2
C/N 69.3 25.8
Experimental Design. Semi-continuous anaerobic reaction was adopted in the experiment.
Different pretreated substrates, water and anaerobic biogas slurry at a certain proportion were put in a
sealed glass bottle with continuous stirring, the maximum volume of which is 2000 mL. The digester
was then put in a water bath, the temperature of which could be adjusted. The temperature was
maintained between 35.0±0.5℃. The test cycle was set to 30 d. The initial pH value was adjusted to
about 7. The mixture in the reactor was collected on time so that the indicators were monitored, and
the same amount of anaerobic biogas slurry was added.
Analytical Methods. Total solids (TS) and volatile solids (VS) were determined according to
Standard Methods 2540B, 2540E [7]. The pH was measured every day using a Leici PHS-3C pH
meter (Leici, Shanghai, China). Gas produced was collected daily in a 1000 mL volumetric bottle,
with biogas samples obtained on a daily basis and then analyzed. Biogas volumes were measured a
water displacement bottle containing acidified (pH = 2) tap water. Volumes were collected for
moisture content and converted to standard temperature and pressure (273 K, 105 Pa). Methane
content in the biogas (% CH4) was measured in a gas chromatograph fitted with flame ionization
detection (GC-FID-2014, Shimadzu, Japan). The analytical column, Rtx-WAX (30 m × 0.25 mm ×
0.25 um), was used for CH4 determination. A standard gas was used to calibrate the system and this
had the following composition: 30% CO2; 30% N2; 40% CH4.
Results and Discussion
The pH Value Variation. As seen in Fig. 1, the test of pH value of different pretreatment conditions
is roughly the same trend, also is the first appearance of a valley, and then slowly rising, then the
second peak and trough. For the substrates pretreated with 6% and 8% H3PO4, the pH value decreased
rapidly from the initial value of 7.20 and 7.26 to the minimum acid point of 5.10 and 5.12 around the
5th
day during the anaerobic digestion, respectively. The test pH values of different pretreatment
conditions mainly ranges from 5.10 to 7.60.
0 5 10 15 20 25 30
5.2
5.6
6.0
6.4
6.8
7.2
7.6
0.02CaCO3 0.04CaCO
3
0.06CaCO3 0.08CaCO
3
pH
Time (days)
Fig. 1 pH change of each pretreated substrate in the digester
Effect of CaCO3 Pretreatment on Daily Biogas Production and Methane Content. Fig. 2 and
3 show that the changes of daily biogas production and methane (CH4) content of each pretreated
substrate in the digester. The test using different CaCO3 pretreatment conditions on rice straw is very
Applied Mechanics and Materials Vols. 587-589 209
slowly to enter the peak gas production of anaerobic digestion, the peak value of biogas production
was attained of 4% CaCO3 pretreatment on the 20th
day, which is 1 589 mL. In general, using CaCO3
pretreatment of rice straw biogas production is low. As seen in Fig. 3, the test of all the CaCO3
pretreated conditions show that similar variation trends in the methane content. The highest CH4
content was 47.4% for the 4% CaCO3- treated rice straw. The test daily methane content of different
pretreatment conditions mainly ranges from 3.4% to 47.4%.
0 5 10 15 20 25 300
300
600
900
1200
1500
1800 0.02CaCO3 0.04CaCO
3
0.06CaCO3 0.08CaCO
3
Bio
gas
pro
du
ctio
n (
mL
/d)
Time (days)
Fig. 2 Daily biogas production of each pretreated substrate in the digester
0 5 10 15 20 25 300
5
10
15
20
25
30
35
40
45
50
55 0.02CaCO3 0.04CaCO
3
0.06CaCO3 0.08CaCO
3
Rat
e o
f C
H4 (
%)
Time (days)
Fig. 3 CH4 content of each pretreated substrate in the digester
Effect of CaCO3 Pretreatment on Cumulative Biogas Production. The effect of the different
pretreatment on the cumulative biogas production in the digester is shown in Fig. 4. As seen in Fig. 4,
the cumulative biogas production of 6% CaCO3 pretreatment was the highest, about 19 917 mL,
which was followed by 4% CaCO3 (14 741 mL), 8% CaCO3 (9 562 mL), and 2% CaCO3 (9 240 mL).
The cumulative biogas production is increased significantly. This is due to the complex organic
compounds after CaCO3 pretreatment celluloses, hemicelluloses are degraded into soluble organic
matter, increase the substrate amount of acid producing bacteria, and the gas production increase.
210 Sustainable Cities Development and Environment Protection IV
0 5 10 15 20 25 300
4000
8000
12000
16000
20000 0.02CaCO
3
0.04CaCO3
0.06CaCO3
0.08CaCO3
Cu
mu
lati
ve
bio
gas
pro
du
ctio
n (
mL
)
Time (days)
Fig. 4 Cumulative gas production of each pretreated substrate in the digester
Conclusions
Here we may derive the following conclusions,
(1) The test pH values of different pretreatment conditions mainly range from 5.10 to 7.60.
(2) The test using different CaCO3 pretreatment conditions on rice straw is very slowly to enter the
peak gas production of anaerobic digestion, the peak value of biogas production was attained of 4%
CaCO3 pretreatment on the 20th
day, which is 1 589 mL. The test daily methane content of different
pretreatment conditions mainly ranges from 3.4% to 47.4%.
(3) The cumulative biogas production of 6% CaCO3 pretreatment was the highest, about 19 917
mL, which was followed by 4% CaCO3 (14 741 mL), 8% CaCO3 (9 562 mL), and 2% CaCO3 (9 240
mL).
Acknowledgements
This work was financially supported by Huaian Municipal Science and Technology Support Program
of China (HAS2013088), the Open Foundation of Jiangsu Key Laboratory for Biomass-based Energy
and Enzyme Technology of China (JSBEET1216), the Open Founds of Jiangsu Key Laboratory for
Chemistry of Low-Dimensional Materials of China (JSKC12117).
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Applied Mechanics and Materials Vols. 587-589 211
Sustainable Cities Development and Environment Protection IV 10.4028/www.scientific.net/AMM.587-589 Effect of CaCO3 Pretreatment on Methane Production from Anaerobic Digestion of Rice Straw 10.4028/www.scientific.net/AMM.587-589.208
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