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Research Paper

Anaerobic digestion of ammonia-pretreated cornstover

Hairong Yuan a, Rongping Li b, Yatian Zhang c, Xiujin Li a,*, Chunmei Liu a,Ying Meng a, Meina Lin a, Ziyi Yang a

a Center for Resources and Environmental Research, Beijing University of Chemical Technology, Beijing 100029,

Chinab Beijing Environmental Sanitation Engineering Research Institute, Beijing 100028, Chinac Capital Aerospace Machinery Company, Beijing 100076, China

a r t i c l e i n f o

Article history:

Received 19 March 2014

Received in revised form

28 August 2014

Accepted 17 September 2014

Published online

Keywords:

Anaerobic digestion

Ammonia-pretreated

Moisture content

Corn stover

* Corresponding author. Tel.: þ86 136 6107 0E-mail address: xjli@mail.buct.edu.cn (X.

http://dx.doi.org/10.1016/j.biosystemseng.2011537-5110/© 2014 Published by Elsevier Ltd o

The effect of ammonia pretreatment on the anaerobic digestibility of corn stover was

investigated. Corn stover with different moisture contents (30%, 50%, 70%, and 90%) was

pretreated with three concentrations of ammonia (2%, 4%, and 6%) at 35 ± 2 �C for the

following batch digestion. Results showed that the reagent of 4% ammonia and 70%

moisture content could achieve the highest anaerobic digestibility. In comparison with the

untreated, the time needed to produce 90% of the maximum digester gas production (T90)

shortened from 52 d to 37 d. The total biogas production and the unit volatile solids (VS)

biogas yield were 20,740 ml and 427.1 ml respectively, both 26.70% higher than the un-

treated. It was found that the digesters with high moisture contents of 70% and 90% were

more stable and had shorter acidification periods relative to the low moisture contents of

30% and 50%. The decreases in cellulose, hemicelluloses and lignin indicated that

ammonia pretreatment could destroy the lignocellulose (LCH) structure and furthermore

enhance the biogas production. Following anaerobic digestion, 80.6% of cellulose and

68.52% of hemicelluloses were consumed where there was 4% ammonia and 70% moisture

content, indicating why these conditions produced the highest level of biogas.

© 2014 Published by Elsevier Ltd on behalf of IAgrE.

1. Introduction

China is one of the largest agricultural countries in the world,

where approximately 0.79 billion tonnes of crop residues were

generated in 2013. Corn is one of major crops, totalling 0.28

billion tonnes of residues (National Bureau of Statistics of the

People's Republic of China, 2013). Although there are various

methods for corn stover reutilisation such as energy

453; fax: þ86 10 6443 228Li).4.09.010n behalf of IAgrE.

production, animal feed, and return to agriculture as fertiliser,

etc., more than 50 %e60 % of corn stover currently remains

unused. Energy utilisation using corn stover as raw material

has recently received more attention from researchers in

China and in other countries.

Corn stover is lignocellulosic biomass. The complex

structure of lignocellulosic biomass provides a primary pro-

tective barrier that prevents cell destruction by chemical or

1.

Nomenclature

L/C ratio of lignin to cellulose

TC total carbon

LCH lignocellulose, including lignin, cellulose, and

hemicellulose

TN total nitrogen

MLSS mixed liquor suspended solids

TS total solids

T90 time needed to produce 90% of the maximum

digester gas production

VS volatile solids

b i o s y s t em s e ng i n e e r i n g 1 2 9 ( 2 0 1 5 ) 1 4 2e1 4 8 143

biological methods (Chen, Zhen, Luo, Zou, & Fang, 2010),

leading to lower digestion rate and biogas yield. Pretreatment

prior to anaerobic digestion had been proven to be one of

simple and effectivemethods to improve biodegradability and

increase biogas production (Bruni, Jensen, & Angelidaki, 2010;

Zhong, Zhang, & Luo, 2011; Zhong, Zhang, & Wei, 2011). There

were a number of methods available for the pretreatment of

crop residues, such as ammonia treatment, acidic and alka-

line treatment, fungal biodegradation, etc. Ammonia treat-

ment has the advantage of increasing nitrogen content

and conditioning the C/N ratio making the corn stover

more biodegradable. Oji, Etim, and Okoye (2007) reported

that ammonia pretreatment could enhance the nitrogen

content of corn stover effectively, while decreasing the cel-

lulose and hemicellulose contents. Zhang and Zhang (1999)

found that compared to the untreated whole straw, 2%

ammonia treatment resulted in 17.5% higher biogas yield. Ma

et al. (2011) reported that a 4% ammonia pretreatment of rice

straw produced 34.8% higher biogas yield than the untreated

straw.

Ammonia treatment technology has been widely applied

for conversion of organicwastes into animal feed and biomass

conversion. During the ammonia pretreatment moisture

content influences the hydrolysis of LCHs (lignocellulose) and

the pretreatment efficiency. Commonly, 30 %e40 % moisture

content has been used in most of studies. Caneque and

Velasco (1998) found that with 40% moisture content at a

temperature of 35 �C the best results were achieved for the

digestibility and degradability of the lignocellulosic feed.

Abdellatif, Santi, Florian, Abderrahim, and Xavier (2014)

investigated dry chemo-mechanical pretreatments of ligno-

cellulosic biomass with the moisture content of 30%. Kim and

Lee (2007) showed that the treated corn stover exhibited

enzymatic digestibility of 85% and 78% for glucan and xylan

following soaking in aqueous ammonia at moderate temper-

ature and 1:6 of solid: liquid ratio (equivalent to moisture

Table 1 e Characteristics of corn stover and inoculum sludge.

TS (%) VS (%) Total carbon (%) Total ni

Corn stover 94.5 88.16 42.59 1

Inoculum sludge 8.45 5.29 30.13 3

content was 85.7%). However, limited research has been car-

ried out to investigate the effect of combined effect of

ammonia and moisture content on the pretreatment of corn

stover for anaerobic biogas production.

Therefore, the objective of this study was to further

investigate the effect of ammonia pretreatment and moisture

content on anaerobic digestibility. Using corn stover as raw

material, different reagents with ammonia additions of 2%,

4%, 6% andmoisture contents of 30%, 50%, 70%, and 90%were

applied to batch digestion. The pretreatment time, biogas

production, digester stability, and corn stover composition

changes were analysed.

2. Materials and methods

2.1. Materials

Corn stover was obtained from farmland at Beijing suburb of

Shunyi. It was dried with the natural air and ground to <5mm

for later use. The amount of corn stover was calculated in

accordancewith total solids (TS) quality. The anaerobic sludge

was collected from an operating anaerobic digester as inoc-

ulum sludge. The amount of inculum inoculant was calcu-

lated in accordance with the mixed liquor suspended solids

(MLSS) quality. The characteristics of corn stover and inoc-

ulum sludge were presented in Table 1.

2.2. Experimental methods

The ammonia used in this study was 25%with 13.33mol l�1 at

20 �C. According to ammonia content, the additions of

ammonia were respectively 2%, 4%, and 6% of dry weight of

the corn stover. Different amounts of water were added to

make sure samples of the corn stover had moisture contents

of 30%, 50% and 70%, 90%. After the ammonia and water, were

added the corn stover was put into a bottle and sealed and

stored at the temperature of 30�C ± 2 �C. After pretreatment,

the corn stover was dried and then used for the anaerobic

digestion.

Batch anaerobic digestion was used in this study. The

pretreated corn stover of 65 g [TS] l�1 was loaded in a 1 l bottle.

The inoculum sludge content in each bottle was15 [MLSS] g l�1

with an effective volume of 0.8 l. Some corn stover that was

dried at 105 �C in drying oven for 12 h was digested as the

control without any ammonia and water.

After feeding, the 1 l bottles were placed in a shaker (Tai-

cang DHZ-DA, China) and connected with the water

displacement. The shaker kept at a mesophilic temperature

(35 ± 2 �C) at 120 rpm shaking speed and 3 min h�1 frequency.

The duration of anaerobic digestion was 65 d.

trogen (%) Cellulose (%) Hemicellulose (%) Lignin (%)

.22 38.81 29.50 7.10

.27 N/A N/A N/A

b i o s y s t em s e n g i n e e r i n g 1 2 9 ( 2 0 1 5 ) 1 4 2e1 4 8144

2.3. Analytical methods

Daily biogas production was recorded using the water

displacement method. Methane in the biogas was measured

using gas chromatography (Shimadzu corporation, GC-2014,

Tokyo, Japan) equipped with a 2 m � 3 mm stainless steel

column (Shimadzu corporation, TDX-01, Tokyo, Japan) and a

thermal conductivity detector. Temperatures of the detector,

injector, and oven were 150, 150, and 120 �C, respectively. TS,VS (volatile solids) , pH, ammonia nitrogen, and alkalinity

were determined according to the standard methods (APHA.,

1998). The total carbon (TC) was analysed with the TC analy-

ser (Skalar Primacsslc, The Netherlands). Total nitrogen (TN)

was analysed with a total Kjeldahl nitrogen analyser (Foss

Scino (Suzhou) Co. Ltd, Scino KT260, Suzhou P.R., China). The

cellulose, hemicellulose, and lignin contents were analysed

according to the procedure of Van Soest (Van Soest & Wine,

1968).

3. Results and discussion

3.1. Ammonia pretreatment time

Pretreatment time is an important indicator (Garba, 1996). The

pH value declined with consumption of ammonia. When

there was no consumption, the pH value of the system tended

to be stable. The change in pH with different pretreatments of

corn stover with 30%, 50%, 70%, and 90% moisture content

showed the same trend. Taking 30% moisture content for

example, pH values at different ammonia additions were

measured, as shown in Fig. 1. After adding ammonia the pH

values were within the range of 9.3e10.2 at the beginning of

the process. With the processing of ammonia pretreatment,

the pH values declined and finally stabilised after four days.

From the 4th day to 7th day, pH values in 2%, 4%, and 6%

ammonia pretreatment were 8.6 ± 0.1, 8.7 ± 0.2, and 8.9 ± 0.1,

respectively. From the view point of pH changes, the pre-

treatment time would be completed within 4 d. However, to

ensure complete ammonia reaction, 5 d was recommended in

this study.

7.5

8

8.5

9

9.5

10

10.5

0 1 2 3 4 5 6 7Time (d)

pH v

alue

Fig. 1 e Changes of pH values in pretreatment of corn

stover with ammonia at 30% moisture content with

different ammonia additions: (⋄ 2% ammonia, ▵ 4%ammonia,£ 6% ammonia).

3.2. Daily biogas production

During the batch experiment, biogas production with each

pretreatment condition showed three or four peaks, as can be

seen in Fig. 2. The first peaks appeared between the first to the

fourth days. The daily biogas production with 2% and 6%

ammonia at 30% moisture content showed the first peak at

660 ml, 38.5% and 46.6% higher than pretreatment with 90%

Fig. 2 e Daily biogas production in the cases of different

ammonia additions (⋄ 2% ammonia, ▫ 4% ammonia, ▵ 6%ammonia,£ untreated) at different moisture contents: (a)

30%, (b) 50%, (c) 70%, (d) 90%.

(a)

0

10

20

30

40

50

60

70

80

90

0 5 10 15 20 25 30 35 40 45 50 55 60 65

Digestion time (d)

Met

hane

con

tent

s(%

)

(b)

0

10

20

30

40

50

60

70

80

90

0 5 10 15 20 25 30 35 40 45 50 55 60 65

Digestion time (d)

Met

hane

con

tent

s(%

)

(c)

0

10

20

30

40

50

60

70

80

90

0 5 10 15 20 25 30 35 40 45 50 55 60 65

Digestion time (d)

Met

hane

con

tent

s(%

)

(d)

0

10

20

30

40

50

60

70

80

90

0 5 10 15 20 25 30 35 40 45 50 55 60 65

Digestion time (d)

Met

hane

con

tent

s(%

)

Fig. 3 e Methane content during the anaerobic digestion of

corn stover with different pretreatment parameters (⋄ 2%

ammonia, ▫ 4% ammonia, ▵ 6% ammonia,£ untreated) at

different moisture contents: (a) 30%, (b) 50%, (c) 70%, (d)

90%.

b i o s y s t em s e ng i n e e r i n g 1 2 9 ( 2 0 1 5 ) 1 4 2e1 4 8 145

moisture content and that of the untreated. Varying degrees

of acidification occurred after the first peaks. This was espe-

cially serious pretreatments with 30% and 50% moisture

content. The daily biogas production rapidly reduced to 100ml

or less and pH values dropped to 5.4e5.9 within 3e5 d after the

first peaks. Calcium hydroxide was added to increase the pH

value to around 7.5. Five to nine days later the digestion sys-

tem returned to normal and second peaks occurred between

the 19th and 23rd day. Due to short acidification period, the

second peaks with 6% ammonia at 70% and 90% moisture

content pretreatment appeared between the 11th and 13th

days, 8e10 d and 15e17 d earlier than for 30% and 50 %

moisture contents and the control respectively. In the case of

6% ammonia addition at 30% moisture content, the second

peak was the highest, reaching 1300 ml. Among other pre-

treatment conditions, 4% ammonia at 90% moisture content

was 32.65% of the control and 39.78% of the minimum daily

production of 930 ml. In the cases of 70% and 90% moisture

content, because of the early second peak, the third and fourth

peaks appeared 5e7 d earlier than the low moisture content

treatments and the control. The daily biogas production of the

third peak ranged from 600 ml to 800 ml, which was lower

than the second peak. The above results showed that an in-

crease in the moisture content of the ammonia pretreatment

can not only bring forward the peaks in production effectively

but also increase daily biogas production.

3.3. Methane content

Methane contents in anaerobic digestion of corn stover were

measured at different pretreatment conditions, as shown in

Fig. 3. Methane content firstly increased then gradually

became stable. In the cases of 30% and 50% moisture content,

the methane content was 11 %e15 % over the first day of

anaerobic digestion, while the methane content rapidly

increased to 33%e43 % with high moisture content and 18 %e

32 % with low moisture content. With the progress of anaer-

obic digestion, acidification appeared in the digester with 30%

and 50% moisture content pretreatments. In the following

5e7 d, methane content kept increasing slowly, about 20%.

However, the pretreatments with 70% and 90% moisture

content were relatively stable; the methane content increased

to 35 %e45 % around the 3rde4th day and was above 60%

within the following 5 d. The methane content stayed be-

tween 60% and 70% over the stable period of anaerobic

digestion. The methane content in the pretreatments with 4%

ammonia and 70% moisture content increased to 60% at the

10th day, 11 d earlier than that of the untreated control. The

maximum methane content reached was 73%, 12% higher

than that of the untreated. The ammonia pretreatment

therefore contributes to increasing methane content for the

anaerobic digestion of corn stover. When the moisture con-

tent increased to 70% and 90%, the digester system was more

stable and the methane content rapidly increased and was

maintained at a higher level.

3.4. Total biogas production and digestion time

The total biogas production was significantly different

(p < 0.05) for the anaerobic digestion with 2%, 4%, and 6%

ammonia pretreatment under different moisture conditions

(Table 2).Withmoisture content of 30%, 50%, 70% and 90% and

with 4% ammonia, total biogas production was 19,540 ml,

19,390 ml, 20,740 ml and 20,140 ml respectively, rises of

19.36%, 18.45%, 26.70% and 23.03% respectively compared to

Table 2 e Comparison of anaerobic digestion performance of corn stover pretreated with different conditions.a

Ammonia (%) Moisturecontent (%)

T90 (day) Total biogasproduction (ml)

Unit VS biogasyield (ml)

VS conversionrate (%)

Untreated e 52 ± 6 16,370 ± 130 337.11 ± 40.77 58.06 ± 11.11

2% 30% 47 ± 5 16,940 ± 257 348.85 ± 29.03 60.35 ± 8.82

50% 52 ± 4 18,430 ± 380 379.53 ± 10.65 66.80 ± 12.37

70% 38 ± 3 19,030 ± 330 391.89 ± 14.01 70.49 ± 5.32

90% 44 ± 6 18,880 ± 750 388.80 ± 10.92 73.26 ± 4.09

4% 30% 47 ± 5 19,540 ± 500 402.39 ± 24.51 72.74 ± 3.57

50% 50 ± 3 19,390 ± 372 399.30 ± 21.42 70.77 ± 7.06

70% 37 ± 2 20,740 ± 275 427.10 ± 49.22 75.29 ± 6.12

90% 48 ± 4 20,140 ± 225 414.74 ± 36.86 72.51 ± 3.34

6% 30% 52 ± 4 18,480 ± 135 380.59 ± 22.71 64.22 ± 4.95

50% 51 ± 6 18,410 ± 190 379.12 ± 21.24 66.42 ± 2.75

70% 38 ± 4 20,090 ± 628 413.71 ± 35.83 73.98 ± 4.81

90% 45 ± 2 12,110 ± 120 249.38 ± 25.58 74.35 ± 5.18

a Values are the means ± SD(n ¼ 3).

b i o s y s t em s e n g i n e e r i n g 1 2 9 ( 2 0 1 5 ) 1 4 2e1 4 8146

the control. When the moisture content was 70% the highest

total biogas production occurred and ammonia pretreatments

of 2%, 4% and 6% produced 19030 ml, 20740 ml and 20090 ml

respectively, increases of 16.25%, 26.70% and 22.72% respec-

tively over the untreated control.

Digestion time is defined as the time needed to produce

90% of themaximumdigester gas production (T90). Shortening

T90 can efficiently lower the operating cost and enhance pro-

ductivity. As shown in Table 2, for 70% moisture content, T90

reduced to 37e38 d, which was 7e14 d shorter than with other

moisture contents. In the case of 4% ammonia addition and

70%moisture content, T90 was 37 d, 10 d and 13 d shorter than

for 30% and 50% moisture contents respectively, and 15 d less

than that of the untreated. This was probably because the

high moisture content increased the surface contact of

ammonia and corn stover and improved the efficiency of the

ammonia pretreatment. Thorough pretreatment can not only

provide efficient nitrogen sources, but also neutralise the

organic acid produced in the earlier acidification stage, alle-

viating the inhibition of excess ammonia in anaerobic diges-

tion (Zhou, Zhang, & Lin, 2005).

3.5. Volatile solids conversion rate

Unit VS biogas yield is an important parameter to measure

biodegradability in anaerobic digestion. Here, it can represent

the efficiency of ammonia pretreatment. As shown in Table 2,

Unit VS biogas yields were not significantly different (p > 0.05)

with lower pretreatment moisture content (30 %e50 %). For

the pretreatment with 2%, 4% and 6% ammonia, but unit VS

biogas yields were increased when the moisture content

increased to 70%. With 70% moisture content unit VS biogas

yields for 2%, 4% and 6% ammonia pretreatment reached their

maximum values. The unit VS biogas yield for a 4% ammonia

treatment with 70% moisture content was 427.1 ml, 26.7%

more than that of the untreated. Similarly, the highest VS

conversion rates were obtained with 2%, 4% and 6% ammonia

pretreatment when themoisture content was 70%, which was

71%, 75% and 74% more than that of the untreated, respec-

tively. Such results followed the varying pattern of the biogas

production. The more corn stover that was consumed, the

higher the biogas produced. This indicated that ammonia

pretreatment with higher moisture content could release

more biodegradable matter, thus increasing the biogas pro-

duction and the utilisation of corn stover.

3.6. System stability

The factors affecting the stability of the anaerobic digestion

system include pH, ammoniacal nitrogen and alkalinity. All

the pH values following anaerobic digestion were in the range

of 7.3e7.7 (Fig. 4). The values were normal since they were not

beyond the range 6.5e7.8, which was found to be suitable for

methanogens to grow (Ren&Wang, 2004). Lay, Li, Noike, Endo,

and Ishimoto (1997) found that the NHþ4 concentration was a

major factor affecting themethanogen activity. Within the pH

range of 6.5e7.8, methanogen activity declined with

increasing ammoniacal nitrogen concentration, dropping to

10% at the maximum. Therefore the ammoniacal nitrogen

content and alkalinity of the anaerobic digestion solution

were important parameters in determining the stability of the

digestion system. As shown in Fig. 4, the lowest ammoniacal

nitrogen concentration (727 mg l�1) was observed in the un-

treated digestate solution. However, the pretreatments with

2%, 4% and 6% ammonia concentration with 90% moisture

content had the highest ammoniacal nitrogen concentrations,

1218e2870 mg l�1. The nitrogen in the anaerobic digestion

could enhance the anaerobic digestibility; however if the

ammonia nitrogen concentration reached 2000 mg l�1, it

would significantly suppress the activity of the methane

bacteria (Koster & Lettinga, 1988). For the corn stover pre-

treated with 6% ammonia and at 90% moisture content, the

ammoniacal nitrogen concentration was 2870 mg l�1; already

in the moderate inhibition range for anaerobic digestion (Ren

& Wang, 2004). This why the yield of biogas was the lowest.

The alkalinity of the corn stover digestion solution increases

with the growing moisture content during pretreatment as

well with increasing ammoniacal nitrogen. As shown in Fig. 4,

the alkalinity of the digestate solution was within the range of

6655e12,050 mg l�1. The alkalinity was slightly higher in the

Fig. 4 e Values of pH( ), ammoniacal nitrogen( ) and alkalinity( ) in the effluents with different ammonia additions and

moisture contents after anaerobic digestion.

b i o s y s t em s e ng i n e e r i n g 1 2 9 ( 2 0 1 5 ) 1 4 2e1 4 8 147

case of 90% moisture content, 12, 050 mg l�1 at maximum,

which was consistent with the trend for the ammoniacal

nitrogen.

3.7. Changes of main compositions

Comparisons of LCH content before and after pretreatment

with ammonia and after anaerobic digestion are shown in

Table 3. Prior to treatment the main components of corn

stover, cellulose and hemicelluloses, accounted for 38.8% and

29% respectively giving 67.8% in total. The content of the

lignin was lower, about 7.1%. Following ammonia pretreat-

ment, the proportion of hemicelluloses significantly

decreased to 28.01%e20.5%, which is 3.4%e29.34% lower than

that of the untreated control. The content of lignin also

decreased by 6.6 %e5.0%, which suggests partial lignin

Table 3 e Changes of lignocelluloses compositions after ammolignin/cellulose ratio).a

Pretreatedcondition

After ammonia pretreatme

Ammoniacontent %

Moisturecontent

Cellulose Hemi- Cellulose Lignin Lig(Lignand H

2 30 38.60 ± 0.34 28.01 ± 0.72 6.60 ± 0.31 7

50 36.92 ± 0.07 27.41 ± 0.19 6.55 ± 0.11 7

70 34.99 ± 0.34 27.22 ± 0.74 6.27 ± 0.29 6

90 32.99 ± 0.26 26.72 ± 0.26 5.57 ± 0.33 6

4 30 37.51 ± 0.41 27.68 ± 0.94 6.47 ± 0.13 7

50 36.09 ± 0.61 25.61 ± 0.30 6.46 ± 0.28 6

70 34.67 ± 1.67 24.81 ± 0.20 5.88 ± 1.39 6

90 32.01 ± 0.77 22.92 ± 0.16 5.71 ± 0.29 6

6 30 36.29 ± 0.09 21.08 ± 0.23 5.42 ± 0.07 6

50 35.47 ± 0.23 20.72 ± 0.35 5.45 ± 0.21 6

70 32.65 ± 2.03 20.49 ± 0.09 5.04 ± 1.19 5

90 32.80 ± 2.83 20.91 ± 0.60 5.73 ± 1.04 5

untreated 38.80 ± 0.75 29.00 ± 0.57 7.12 ± 0.63 7

a Values are the means ± SD (n � 3).

removal via the ammonia pretreatment. Lignin degradation

could release more cellulose and hemicelluloses, thus

increasing the biodegradability of the corn stover. Compared

to the untreated, the LCH content after pretreatment

decreased by 2.28 %e22.34 %. Scharer and Moo-Young (1979)

reported that the biodegradability of the substrate can be

evaluated using the ratio of lignin to cellulose (L/C). The lower

the L/C, the more readily biodegradable the corn stover is. The

L/C of corn stover following ammonia pretreatment was lower

than the untreated. This indicated that in the process of

ammonia pretreatment, increasing quantities of cellulose and

hemicelluloses released due to the removal of the lignin can

enable anaerobes to contact more of the digestible substrate

thus improving the performance of anaerobic digestion.

From the degradation rates of LCH following anaerobic

digestion, the degradation rates of cellulose, hemicelluloses,

nia pretreatment and anaerobic digestion (%, DM, except

nt After anaerobic digestion

nocellulosein, Cellulose,emicellulose)

L/C Celluloseconversion

rate

Hemi-cellulose

conversion rate

Ligninconversion

rate

3.21 ± 0.68 0.171 63.73 ± 1.40 58.21 ± 2.08 25.42 ± 0.70

0.88 ± 0.23 0.177 68.54 ± 2.46 63.51 ± 2.48 17.21 ± 3.60

7.48 ± 0.11 0.179 73.99 ± 1.45 67.97 ± 0.96 22.81 ± 4.35

5.28 ± 0.85 0.169 76.56 ± 3.37 67.32 ± 1.10 18.36 ± 2.04

1.66 ± 0.40 0.173 70.10 ± 1.43 61.94 ± 3.03 14.53 ± 2.54

7.16 ± 0.63 0.179 75.94 ± 1.71 62.85 ± 3.72 14.71 ± 0.67

2.39 ± 0.47 0.170 80.60 ± 1.05 68.52 ± 0.25 16.32 ± 0.84

0.64 ± 0.64 0.178 74.59 ± 1.79 64.97 ± 1.18 17.80 ± 1.00

2.79 ± 0.40 0.149 70.70 ± 1.64 64.60 ± 3.32 9.70 ± 2.90

1.64 ± 0.37 0.154 74.90 ± 0.13 65.25 ± 1.25 12.68 ± 1.67

8.18 ± 0.22 0.154 75.25 ± 1.97 65.15 ± 1.10 10.73 ± 0.08

9.44 ± 1.39 0.175 52.10 ± 0.39 58.76 ± 1.51 18.34 ± 1.23

4.92 ± 0.97 0.184 62.10 ± 0.02 54.38 ± 1.04 16.42 ± 0.28

b i o s y s t em s e n g i n e e r i n g 1 2 9 ( 2 0 1 5 ) 1 4 2e1 4 8148

and lignin under different ammonia pretreatment were 52.1

%e80.6 %, 54.38 %e68.52 %, and 9.7%e25.42%, respectively. In

the pretreatment with 4% ammonia at 70% moisture content,

cellulose and hemicelluloses had the highest degradation

rates, 80.6% and 68.52% respectively, which were 29.79% and

26% higher than that of the untreated. This indicated why the

highest unit VS biogas yield was achieved in the case of the

pretreatment with 4% ammonia at 70% moisture content.

4. Conclusions

In different ammonia pretreatment conditions, the corn sto-

ver pretreated with 4% ammonia at 70% moisture content

showed the highest anaerobic digestibility. Its T90 of 37 d was

the shorter, whichwas 15 d shorter than that of the untreated.

Its total biogas production and unit VS biogas yield were

20,740 ml and 427.1 ml, respectively, 26.7% higher than those

of the untreated.

Ammonia pretreatment effectively destroys the LCH

structure of corn stover. The LCH contents of the corn stover

following pretreatment were decreased by 2.28 %e22.34 %. For

the corn stover with, 4% ammonia at 70% moisture content,

80.6% of the cellulose and 68.52% of the hemicelluloses were

converted after anaerobic digestion. The LCHs results

demonstrated that ammonia pretreatment can help corn

stover be more readily biodegradable and consequently

improve the biogas production performance in anaerobic

digestion.

Acknowledgements

The author would like to acknowledge the financial support

from the Public Welfare Project of Ministry of Agriculture of

China (201303099 and 201303101), The “Eleventh Five” Science

and Technology Support Program of Ministry of Science and

Technology of China (2010BAC67B03 and 2010BAC67B05.), and

BUCT Inter-disciplinary Construction Plan (IPPBUCT201103).

r e f e r e n c e s

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