IJERD – International Journal of Environmental and Rural Development (2021) 12-1

Research article
erd

Effects of adding Rice Husk Biochar on GHG Emission andCompost Quality during Cow Manure Composting
SARVESH MASKEY
Graduate School of Agriculture, Tokyo University of Agriculture, Tokyo, Japan
Email: smaskey27@gmail.com

MACHITO MIHARA*
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan
Email: m-mihara@nodai.ac.jp
Received 31 December 2020

Accepted 30 June 2021(*Corresponding Author)

Abstract Agriculture is a major anthropogenic source of Green House Gases (GHG) andcontributes 24% of total GHG emitted (IPCC, 2014). Livestock sector forms a significant partof agriculture and is responsible for major GHG emission. According to FAO, 2016, livestock
manure contributes 23% to total GHG emitted in agricultural sector. N2O, CO2 and CH4 areimportant GHG emitted during management of livestock manure. Against the background of
global warming, there is increased motivation in reducing GHG emission. Therefore, this study
deals to see the effects in N2O, CO2 and CH4 emission by adding 5%, 10% and 15% of rice husk
biochar during cow manure composting. In addition, degradation rate and C/N ratio of manuresamples were analyzed for determining the final compost quality. Subsequently, a composting
experiment was conducted using rice husk biochar and gases emitted were measured
periodically with static gas chamber method. The experimental results indicated that biochar
was effective in reducing N2O and CO2 emissions. The cumulative emission of N2O was
reduced by 40% in 5% treatment, 46% in 10% treatment and 60% in 15% treatment. Similarly,
there was decrease of CO2 by 69% in 5% treatment, 68% in 10% treatment and 48% in 15%
treatment. Biochar’s well developed pore structure and adsorption capacity reduced the gas
emission. Furthermore, addition of biochar enhanced degradation rate and better C/N ratio.
Biochar addition provided necessary nutrients and habitat, facilitating growth of various
microorganisms. The results of CH4 emission did not show any significant difference between
the treatments. The obtained results indicate that rice husk biochar addition is beneficial in
reducing GHG emission and improving compost quality with faster degradation and better C/Nratio.
Keywords GHG emission, cow manure composting, rice husk biochar, compost quality

INTRODUCTION AND BACKGROUND
As the human civilization has evolved, the global climate change has been continuously changing. In
recent years, global climate change issues and its relation to human activities has gathered widespreadattention. IPCC, 2007, IPCC, 2013, states that global warming is significantly affected by humanactivities. Furthermore, these reports states that fossil fuel use and land use change are the major
contributor of GHGs. AFLOU, which represents agriculture, forestry and other land uses is a majoranthropogenic source of GHGs emission and contributes 24% of total GHG emitted (IPCC, 2014).
GHGs are mainly composed of CO2 (76%), CH4 (16%), N2O (6%) (IPCC, 2013). Agricultural activities
contributes 20% of CO2, 70% CH4 and 90% of N2O (Cole et al., 1997; Yousefi, Damghani andKhoramivafa, 2016). Livestock sector forms a significant part of agriculture and is responsible formajor GHGs emission. FAO, 2016, reports that management of livestock manure contributes 23% toⒸ ISERD

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total GHGs emitted in agricultural sector. Generally, livestock manure has been used as a soil
amendment in the form of compost. Composting is an efficient way of manure management, but also
releases GHGs. N2O, CO2 and CH4 are important GHGs emitted during composting of livestock
manure. In recent years, biochar has gained significant interest in various environmental applications.
Biochar is a product of pyrolysis characterized with microscopic structure having large surface areaand has affinity to absorb nutrients, ions etc. (Dünisch et al., 2007; Major et al., 2009), and has been
applied in soil to mainatain soil fertility and reducing GHG emission (Van Zwieten et al., 2015). Dueto its unique properties, it is an efficeint, cost effective and environmentally friendly material fordiverse purposes. Against the background of global warming, there is increased motivation in reducing
GHG emissions. Therefore, this study focus to see the effects of adding rice husk biochar during cow
manure composting in reducing GHG gases emission and better compost quality.

Fig. 1 GHGs contributor in agricultural sector (FAO, 2016)
METHODOLOGY
Compost Box and Gas Chamber
A glass container of dimension 30 cm3 was used as a compost box. The box was covered with styrofoam sheets of thickness 2 cm on five sides for minimizing the heat loss (Fig. 2) during compostingprocess. A static gas chamber made up of acrylic sheet was used to measure the gas flux. Acrylic sheet
was used as it is inert to the target gases. A digital thermometer and a fan were attached inside thechamber for measuring temperature and uniform circulation of air during measurement of gas
respectively (Fig. 2 and 3). The volume of air inside the chamber was calculated as 0.017705 m3.

Fig. 2 Schematic diagram of composting box
and gas flux analysis

Fig. 3 Apparatus used during gas flux
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Conditions of the Experiment
The composting experiment was performed from 8 August 2019 to 7 October 2019 in Laboratory ofLand and Water Use Engineering, Tokyo University of Agriculture. The average temperature was
23.0 C̊ during the experiment period. Cow manure, rice straw and litter was used as main components
for composting. The nitrogen content in cow manure and rice husk biochar was 23695 mg/kg and 1241
mg/kg respectively at the start of the experiment. Rice husk biochar was added in three different
variations (Table 1). These variations were made to see the most effective composition. The initialwater content of the composting material was set at 70±2% for all the treatments.
Table 1 Composition of treatments
Composition

Control

5% Treatment

10% Treatment

15% Treatment

Cow manure (g)

3200

3200

3200

3200

Litter + rice straw (g)

1800*

1800*

1800*

1800*

250*

500*

750*

Rice husk bio-char (g)Note: * represents air-dry weight basis

Gas Flux Measurement
Gas flux was measured using static gas chamber method with photoacoustic spectrometer. The
spectrometer used in this study was INNOVA 1412 Photoacoustic Field Gas Monitor (Fig.3). Gas flux
was calculated using linear aggression method showed in Equation 1 (Minamikawa et al., 2015).
(1)
Where,F is gas flux (mg m-2 hr-1),
ρ is density of gas (kg m-3) where density of NH3 is 0.772 kg m-3 and of N2O is 1.96 kg m-3,
A is bottom surface area of chamber (m2),
V is volume of air inside the chamber (m3),△c/△t is average increase rate of gas density inside the chamber (10-6 m3 m-3 hr-1),
T is average temperature inside the chamber (K)Determination of Degradation Rate
Loss of organic content during a composting process is a measure of biological decomposition and isexpressed in the form of degradation rate. The degradation of composting substrates as a function oftime follows first order kinectics (Haug 1993, Kulcu and Yaldiz, 2004) and can be expressed asfollowing,= - kt(2)

Where,OM is mass of biodegradable organic matter at any time of composting,
OM0 is initial mass of biodegradable organic matter,Ⓒ ISERD

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t is time in day,kt is reaction rate constant in days-1
Compost Sampling and Analysis
Compost was sampled at 5, 10, 20, 30, 40 and 60 days to analyze its quality. Temperature of thecompost pile was measured using Custom CT-0580 data logger and digital thermometer on daily basis.
Organic content was analyzed using Ignition loss method. Carbon content was determined by using theformula C=0.580* IL. Total nitrogen was analyzed by absorption spectroscopy using HC-1000(Central Science Corp.) as measurement device (Mihara and Ueno, 2000).
RESULTS AND DISCUSSIONSBiochar Effect on Nitrous oxide Emission
Composting of high organic content materials has been shown to produce N2O by nitrification anddenitrification under aerobic and low oxygen conditions respectively. Fig. 4 shows the periodic change
in emission between the treatments. The cumulative gas emission (Fig. 5) was lowered by 40%, 46.4%
and 60.4% in 5%, 10% and 15% biochar added treatments compared to control. The result observed is
supported by that of Jeffery et al., 2015, which states that addition of biochar can decrease the emissionof nitrous oxide. Although the mechanisms of N2O formation during composting process of animal
manure is not studied in details, N2O emission is mainly associated with nitrification and denitrification
process (Sanchez-Monedero et al., 2010). These microbial process is regulated by the quantity ofmineral nitrogen, presence of carbon sources and oxygen concentration in composting maerial. Wanget al., 2013, showed 31% lower emissions in biochar treated piles and linked this result in reduction tochange in the abundance and composition of denitryfying bacteria. It has been well reported that
addition of biochar increases pile porosity, thus increasing oxygen content, weaking denitrification
enzyme activity and inhibiting denitrification reaction under anaerobic conditions (Singh et al., 2010).

Fig. 4 Periodic change in N2O flux

Fig. 5 Cumulative gas flux of N2O

Biochar Effect on Carbondioxide Emission
The result of periodic changes in CO2 flux is shown in fig 6. The concentration of CO2 was highest incontrol amongst the treatments which conincides to the studies from Awasthi et al., 2017 and Jiang etal., 2016, according to which biochar reduces CO2 emission. The periodic change in CO2 flux showed
an initial rise and fall at the later stage of the composting process, which was consistent with change intemperature.
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Fig. 6 Periodic change in CO2 flux

Fig.7 Cumulative gas flux of CO2

The cumulative gas flux (Fig.7) showed that there was decrease of CO2 by 69% in 5% treatment,
68% in 10% treatment and 48% in 15% treatment. According to the obtained results, biochar added
treatments could reduce the emission of CO2. This result coincides to the ones reported by Ngo et al.,2013, which states that biochar could increase carbon sequestration of exogenous organic matter whenapplied in compost mixtures.
Biochar Effect on Methane Emission
Fig. 8 shows the results of periodic change of CH4 flux and fig. 9 shows the cumulative gas flux
emission. CH4 emission was observed in early stage of the composting period for all the treatmentswith biochar added treatments having higher emission compared to control. The emission was seen
during first week of the experiment with no emission observed after a week for all the treatments.
Although, studies have shown that biochar addition enabled to inhibit CH4 emission in cow manure(Sonoki et al., 2013) and muncipal solid waste composting (Vandecasteele et al., 2013), similar results
could not be observed in our study. CH4 production during composting is mainly associated toanaerobic processes.

Fig. 8 Periodic change in CH4 flux

Fig. 9 Cumulative gas flux of CH4

According to Sanchez et al., 2015, favourable conditions for CH4 emission can be found in theearly stages of composting process, where large amount of nutrients and organic matter are available
which enhances microbial growth, depleting the oxygen levels in the pile. Refering to the results oftemperature, (fig. 11) where biochar added treatments showed higher temperature gain, showes
increased microbial activity, creating anerobic environment. To support this, general bacteria count in
the early stage of composting showed higher microbial presence in biochar added treatments.
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Biochar Effects on Quality of Compost
C/N ratio and temperature profile are oftenly used as a criteria for determining the quality of compost.
C/N ratio is used as an indicator of compost stability and nitrogen availability. Wheareas, increased
temperature shows higher microbial activity and faster decompostion of organic substrates. The
periodic change of C/N ratio showed better values in biochar added treatments compared to control(Fig. 10).

Fig. 10 Periodic change in C/N ratio

Fig. 11 Periodic change in temperature

Better C/N ratio amongst the biochar added treatments compared to control may be due
increased surface area and moisture content favouring microbial activity for degradation andhumification of organic material. In addition, biochar increased sorption of nitrogeneouscompounds in its microspores, providing microorganism with sufficient nitrogen for their
metabolism.Temperature results (Fig. 11) showed rise in temperature in early stages of composting,followed by fall after one week and stabilising around 30 ºC at later stage of composting. Biochar
added treatments had higher temperature gain during early stages of composting compared to control
due to faster degradation due to reduced heat loss as addition of biochar filled the air pores (Zhang
and Sun, 2014). Khodadad et al., reports that adding of biochar increases the relative abundance ofActinobacteria, which are generally able to degrade more organic material, resulting in heatgeneration.
Biochar Effect on Degradation Rate
The results of degradation rate of organic substrates is shown in table 2. The highest biodegradability
after 5 days of composting was seen in 15% treatment with rate constant of 0.034 dˉ1, followed by 5%treatment with rate constant of 0.032 dˉ1, followed by 10% treatment with reaction rate of 0.031 dˉ1,
with the least in control having 0.013 dˉ1 of reaction rate. For 60 days of composting, the degradability
was in order of 10% treatment with 0.0056 dˉ1, 15% treatment with 0.0054 dˉ1, 5% treatment with
0.0052 dˉ1, followed by control with 0.0045 dˉ1. The obtained results shows that adding of biocharenhances decomposition of organic matter and degradation rate of the composting substrates. The
degradation rate was higher during early and decreased with time. The results of increased degradationin biochar added treatments also agree to that of Zhang and Sun, 2014, which states that biochar
amendment increased composting rate, increasing temperatures due to denser substrates with filledpore spaces reducing the heat loss that occurs because of greater air space. Moreover, adding of
biochar increased the oxygen uptake, moisture retention and increased the microbial activity resulting
in better degradation. Steiner et al., 2015, biochar is a highly porous material having high capacity toⒸ ISERD

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retain excess water, improve aeration conditions and provide suitable conditions for microorganisms,
promoting microbial activity and increasing organic matter degradation.
Table 2 Degradation rate at 5 and 60 days passed
Treatments

5 days kt (d-1)

60 days kt (d-1)

Control

0.013 a0.0045 a

5%
10%
15%

**

0.032 b0.031 c**0.034 c**0.0052 a
0.0056 a
0.0054 aNote: Significance difference at *:p<0.05, **:p<0.01

CONCLUSIONSThis study was conducted to see the effects of adding rice husk biochar in reducing GHG emission andenhancing final compost quality during cow manure composting. According to the results of this study,
addition or rice husk biochar was efficient in reducing GHG emission and significantly enhancing
degradation and mineralization of organic substrates during cow manure composting. In the given
conditions, addition of biochar was effective in decreased N2O and CO2 emission. However, nosignificance difference was seen in CH4 emission. On the other hand, compost quality with better
degradation and nitrogen mineralization was observed. Although, 15% treatment (750 g in 5 kg) had
highest reduction of GHG emission and enhanced compost quality, relatively small amount of 5% (250g in 5 kg) treatment was also effective. Considering these findings, rice husk biochar could be aneffective and beneficial practice for management of cow manure for reducing GHG emission and better
quality of cow manure compost.
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