沙漠研究 19-1, 145- 148 (2009 )Journal of Arid Land Studies“Desert Technology IX ”
Refereed Paper

Enhancing Plant Residue Composting using Bacillus sp. in Semi-Arid Regions
Kotaro TAKARADA1, Machito MIHARA2
Abstract: This study dealt with the effects of water content and microorganisms added on
fermentation process including reduction of greenhouse gas emission.
Experimental
composting was conducted in the glass house. Initial water content was controlled at 60% as
standard water content for Run A and B, and then Bacillus sp. was added for Run B but not for
Run A. Also initial water content was controlled at 45% as lower one for Run C and D, andthen Bacillus sp. was added for Run D but not for Run C. Based on the results ofexperimental composting, carbon-nitrogen ratio in compost with Bacillus sp. became 88% or
84% of the initial stage of composting, although the ratio in compost without Bacillus sp. wasonly 94% or 96%, respectively. There was a significant difference in carbon-nitrogen ratio at
99% confidence interval between compost with Bacillus sp. and that without Bacillus sp. underlower water content at 45%. Also, in the experimental results of gas analysis, there was nosignificant difference in gas emissions of carbon dioxide or methane gas between compostingwith Bacillus sp. and that without Bacillus sp. under either water content. However, methanegas emission from composting under lower water content at 45% was significantly lower thanthat under standard water content at 60%.
Keywords: Bacillus sp., Carbon dioxide, Compost, Methane, Plant residue

1. Introduction
Frequent drought and low fertility of soils are the fundamental agricultural problems in semi-arid
regions of Asia. Composting has been an effective way in agriculture to improve land productivity. The
composting of tree branches or leaves pruned is a process of promoting the fermentation bymicroorganisms. Although water content in materials is one of the necessary requirements forfermentation process by microorganisms, it is difficult to supply enough water for fermentation during dry
season in semi-arid regions of Asia. Also, greenhouse gas emission such as carbon dioxide or methanegas occurs during composting. There were some studies concerning greenhouse gas emission duringcomposting and reported suitable strategies to overcome the problems. Hellebrand (1998) suggested thatabout 80% of initial carbon mass (initial mass of the compost heap was 14,800 kg with carbon content of4,300 kg) was transformed by microorganisms into carbon dioxide during composting of grass and green
waste. Also methane was produced 1.5-2.0% of initial one. Also, Shiraishi et al. (2006) reported thatthe initial water content should be controlled at 55% to reduce greenhouse gas such as nitrous oxide andmethane. Kuroda (2002) suggested the addition of Bacillus sp. was effective to reduce malodor emission
during composting. Therefore, research interests have been focused on the changes in fermentation orgreenhouse gas emission with water content or microorganism addition during composting.
So, the objectives of this study are to investigate the effectsof water content and microorganism addition on the fermentation
process including the reduction of greenhouse gas emission.
2. Materials and Methods
Experimental composting was conducted from 15 October to
14 November 2007 in the glass house. The composting of tree
branches or leaves pruned was done by the heaping method
generally used as a method of the composting pruned one. The
plastic box of 50 cm long, 40 cm wide and 40 cm high was used as
a compost box and the temperature was not controlled. Initialwater content was controlled by adding water at 60% as standard
12Fig. 1. Bacillus sp.

Graduate School of Agriculture, Tokyo University of Agriculture, Tokyo, Japan
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan.
E-mail: m-mihara@nodai.ac.jp, Tel: 03-5477-2338, Fax: 03-5477-2620

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water content for Run A and B, and then Bacillus sp. (Fig. 1) was added for Run B but not for Run A.
Also initial water content was controlled at 45% as lower water content for Run C and D, and thenBacillus sp. was added for Run D but not for Run C. Bacillus sp. was isolated from the matured compostof tree branches or leaves pruned. The amounts of Bacillus sp. added to compost were 1.2 × (108-109) cfu/g(dry mass). The amounts of Bacillus sp. were measured by the dilution plate counting method.
Gases produced during composting and composting materials were sampled and analyzed at certain
interval. Carbon dioxide and methane gas concentration were analyzed from sampled gases at every 2days by vacuum method using gas detection tube. Also water content, carbon and nitrogen concentrationfrom sampled composting materials were measured at every 10 days. Water content was measured by theoven dry method, total carbon by ignition loss method, total nitrogen by absorption spectrophotometry
after decomposition with potassium peroxodisulphate.
3. Results and Discussion
3.1. Carbon-nitrogen ratio
The results of changing carbon-nitrogen ratio during experimental composting were summarized inFigures 2 and 3. In the experimental composting, carbon-nitrogen ratio decreased gradually for all Runs.
It was considered the fermentation during composting has advanced. But there was no significant
difference in changing carbon-nitrogen ratio between decomposed with Bacillus sp. and without Bacillus
sp. under standard water content at 60%.

Carbon-nitrogen ratio

4035302505101520253035day
Run A 60% un-added
Run B 60% added

4 Run C 45% un-added
4 Run D 45% added

Fig. 2. Changes in carbon-nitrogen ratio during experimental composting.

Carbon-nitrogen ratio

353331292725Run ARun BRun C

Run D

60% un-added 60% added 45% un-added 45% added

Fig. 3. Carbon-nitrogen ratio in the period of experimental composting.

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However, under lower water content at 45% such as Run C and D, the changes in carbon-nitrogenratio of decomposed with Bacillus sp. of Run D tended to be lower than that without Bacillus sp. of Run C.
Also, in the results of carbon-nitrogen ratio of experimental composting, there was a significant difference
at 99% confidence interval in carbon-nitrogen ratio in Run C and that in Run D. It means the addition ofBacillus sp. was effective to enhance the composting of tree branches or leaves pruned only under lower
water content at 45%. It was considered that many kinds of microorganisms worked actively understandard water content at 60%, but not under lower water content at 45%. So, it was considered that
addition of Bacillus sp. was clearly effective for composting under lower water content at 45%.
3.2. Gas concentration
According to the results of gas analysis, there was a tendency for the emission of carbon dioxide to beremarkably high at the initial stage of composting process, but gradually decreased with the time. But
there was no significant difference in carbon dioxide emission among Run A to D as shown in Figure 4.
Additionally, although there was a tendency for methane gas emission from Run B and D with Bacillus sp.
to be lower than that from Run A and C without Bacillus sp., there was no significant difference inmethane gas emission between composting with Bacillus sp. and that without Bacillus sp.. It means theaddition of Bacillus sp. was not effective to reduce the emissions of carbon dioxide or methane gas duringcomposting.
However, methane gas emission from composting under lower water content at 45% such as Run Cand D were significantly lower than that under standard water content at 60% such as Run A and B as
shown in Figure 5. Shiraishi et al. (2006) reported the methane gas emission occurred mainly in the earlyphase of beef cattle manure composting, and could be reduced by lowering the initial water content. Also,
Osada et al. (1997) suggested that it was possible to reduce the emission of methane gas and nitrous oxidethrough maintaining the aerobic condition. On the basis of these reports, it was considered the emissionof methane gas was due to insufficient aerobic condition. In this study, the emission of methane gas fromstandard water content at 60% such as Run A and B were higher than that from lower water content at 45%
such as Run C and D. So, it was considered that standard water content at 60% of insufficient aerobic
condition in composting process resulted higher emission of methane gas.
Accordingly, it was concluded that in composting process of tree branches or leaves pruned, it isimportant to maintain in aerobic conditions to reduce the emission of methane gas.

120000CO2 vol ppm

100000
80000
60000
40000
20000
0051015Run A 60% un-added
Run B 60% added

20253035
day

4 Run C 45% un-added
4 Run D 45% added

Fig. 4. Changes in carbon dioxide concentration during experimental composting.

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1800

CH4 vol ppm

1600
1400
1200
1000
800
600
400
2000510Run A 60% un-added
Run B 60% added

1520253035day

4 Run C 45% un-added
4 Run D 45% added

Fig. 5. Changes in methane concentration during experimental composting.

4. Conclusions
This study dealt with the effects of water content or microorganisms added on fermentation processincluding reduction of greenhouse gas emission. The difference in carbon-nitrogen ratio in compost
between fermented at 60% water content as standard one and fermented at 45% water content as lower one
was not apparent; however carbon-nitrogen ratio in compost with Bacillus sp. was lower than the ratio incompost without Bacillus sp. under lower water content at 45%. It means the addition of Bacillus sp. waseffective for composting especially under lower water content at 45%.
In the experimental results of gas analysis, there was no significant difference in gas emissions ofcarbon dioxide or methane gas between composting with Bacillus sp. and that without Bacillus sp. undereither water content. However, methane gas emission from composting under lower water content at 45%
was significantly lower than that under standard water content at 60%.
So, it was concluded the addition of Bacillus sp. was effective for composting especially under lower
water content at 45%, but for decreasing the emission of methane gas in composting process, the important
was to maintain aerobic conditions of compost under lower water content at 45%.
References
Hellebrand H.J. (1998): Emission of Nitrous Oxide and other Trace Gases during Composting of Grass and Green Waste. Journal
Agriculture Engineering Research, 69: 365-375.
Shiraishi M., Osada T., Takimoto E., Wakimoto N., Kitamura N., Okuda K. (2006): Method of Controlling Generation of Nitrous
Oxide and Methane. Bulletin of the Okayama Prefectural Center for Animal Husbandry and Research, 16: 31-37.
Kuroda K. (2002): Application of Microorganisms for Reducing Malodor Emissions from Composting Treatment of Animal Wastes.
Soil Microorganisms, 56(2): 69-74.