 INTRODUCTION

Urbanization and rapid population growth are the main issues worldwide
creating increased generation of solid waste per unit area. Particularly, urban
and semi-urban areas of developing and poor countries are facing great
challenges in managing solid waste .
Organic waste such as kitchen waste is regarded as waste and thrown, which
then becomes the source of the pollution. This pollution results in many
environmental problems as well as health problems leading to many diseases .
For the management of the food waste, people prefer to compost the waste
for using as manure in the field and ignore the energy that could be obtained
from the waste. In this context, anaerobic digestion of organic waste could be
better solution, as it minimizes the volume and mass of organic waste and also
recovers energy at source at the same time.

Biogas is a renewable energy source that is produced by the anaerobic

digestion of organic matter such as animal waste, plant residues, and
biodegradable waste. It primarily consists of methane (CH₄) and carbon dioxide
(CO₂), along with trace amounts of other gases like hydrogen sulfide (H₂S).

Composition of Biogas

 Methane (CH₄): 50–75%

 Carbon Dioxide (CO₂): 25–50%
 Other Gases:
o Hydrogen (H₂): 0–1%
o Nitrogen (N₂): 0–10%
o Hydrogen Sulfide (H₂S): 0–3%
o Oxygen (O₂): 0–2%

Anaerobic digestion is the process of decomposition of biodegradable

substance by microorganisms in the absence of oxygen. The end-products of
anaerobic digestion are gas containing mainly methane and carbon dioxide,
referred to as biogas.

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  MATERIALS AND METHODS
The study was carried out with the support via materials provided by Solid
Waste Management Technical Support Centre (SWMTSC), Pulchowk, Lalitpur.
SWMTSC lies in Lalitpur Metropolitan City, Province no. 3. The SWMTSC falls
under Ministry of Federal Affairs and Local Development (Ministry of Federal
Affairs and Local Development (MOFALD).
The urban biogas plant has fixed digester and its capacity is 1,275 litres (Fig. 1).
For total trapping of gas, biogas plant was insulated with plastic sheet and glass
wool.

fig. bio gas plant

 Composition of organic waste collected

The food (kitchen waste) was collected in the four buckets provided to the
canteen of SWMTSC. Composition of the collected waste was identified by
visual estimation. With the help of the eyes, the composition of the waste was
identified and categorized according to its amount present in the collected
waste.

Sampling of waste and slurry sample

For the representative waste sample, 50 g of waste, each from four buckets,
was kept together and mixed. This sample was air dried, ground, and sieved.
Thus, prepared waste sample was used for laboratory analysis. The bio-slurry

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was also air dried, ground, and sieved. This sample was used for laboratory
analysis.

a) Laboratory analysis
The laboratory analysis of waste and bio-slurry sample was done for three
times at an interval of one week. It was performed using standard methods and
instruments

Table 1: Parameters, methods and instruments for lab analysis

S.N. Parameters Methods Instruments

1. Total solid Oven drying Hot air oven and desiccator
2. Volatile solid Gravimetric Muffle furnace and desiccator
3. Organic matter Modified Walkley & Black Burette, pipette
4. Nitrogen Kjeldahl Digestion Kjeldahl distillation assembly
5. Carbon Modified Walkley & Black –
6. C:N ratio from 4 and 5 (Division) –
7. Phosphorus Ammonium molybdate Spectrophotometer
8. Potassium Ammonium acetate Flame photometer 4
9. pH Potentiometric pH meter

b) Field analysis
Various parameters and instruments used for field parameters analysis are shown in Table 2

Table 2: Parameters and instruments for field analysis

S.N. Parameters Instruments

1. Temperature Lab thermometer

2. Volume of methane and CO2 Gas analyser

3. Pressure Pressure gauze

4. Volume of biogas Gas flow meter

c) Statistical analysis

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Data collected were analysed using R-programming. To test the normal
distribution of the population Shapiro Wilk normality test was performed as
the sample number was less than 50. Simple linear regression was performed
to determine the relationship between ambient temperature and biogas
production.

d) Economic analysis
Economic analysis was performed on the basis of energy content and market
price of fuels with assumptions. Simple payback period was determined by
dividing total cost of the biogas plant to the total cost savings. Average rate of
return was calculated by dividing the subtracted value of current and original
cost of biogas plant with the original cost of biogas plant and multiplying the
obtained value with 100, as given in the equation.
Average rate of return = (Current cost -Original cost of biogas plant /Original
cost of biogas plant) x 100

 RESULTS AND DISCUSSION

a) Composition of organic waste
The collected organic waste was composed of both raw and cooked foods (Fig.
3). The organic waste contained highest percentage of vegetables peels and
leftover. The feeding material consisted of mixed organic waste generated daily
in the kitchen. Values of physicochemical parameters of input waste and bio-
slurry.
The average values of physicochemical parameters of input waste and bio-
slurry are shown in Table 3. For the production of biogas, pH of the input
material should be in between 6 and 7, C: N ratio should be 20-30:1 and total
solid should be 5-10%. The obtained value of pH of waste was 5.99 which was
found to be within the range and was suitable for the production of biogas.
This meant that pH of waste was appropriate for the survival of methane
producing bacteria. Similarly, the pH of bio slurry was found to be alkaline (pH
8.99). Methanogenic bacteria best thrive under neutral to alkaline condition.
The pH of bio-slurry indicated that methane producing bacteria are growing
and digesting the waste to produce biogas.
Organic matter and carbon content in bio-slurry were found to be less in
compared to waste. This may be because of the utilization of organic matter by

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the methanogenic bacteria for the digestion process. This also indicated that
there was proper digestion of feeding materials. The C:N ratio was 19.85:1
which lied within the range reported suggesting waste to be suitable for the
biogas production. While, the total solid was found to be 14%, which was little
higher, may be because of lesser moisture content in the waste. Similarly, the
digested slurry contains 1.60% nitrogen, 1.55% phosphorus and 1.00%
potassium.
The obtained value of nitrogen was 1.69% which was little higher than this
range and the value of phosphorus was found to be 0.88% which is lesser.
However, these values were near to the range indicating that the bio-slurry
could be used as a fertilizer for crop production.

Fig.3 Composition of organic waste

b) Measurement of biogas production

The total volume of biogas within the data collection period (48 days) was
calculated to be 5,782 litres and the total weight of waste fed in the digester
within that period was calculated to be 262.50 kg. Hence, 1 kg of waste was
capable of generating 22.03 liters of biogas in average. Obtained 32.12 l/kg of
biogas from kitchen waste. Municipal organic waste contains 0.5-0.8 m3 /kg of
Volatile Solid (VS). The obtained volume of biogas in this study was found to be
less than both studies. The low production of biogas may be because of the
improper digestion of the waste, overfeeding of the waste in the digester and
the shade of the tree located behind the biogas plant preventing the direct sun

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rays to the bio-digester. Similarly, the data collection period was 48 days.
Hence, it was calculated that the biogas plant was capable of producing 120.46
litres of biogas in a day which could boil four litres of water.

c) Composition of methane and carbon dioxide

The average methane content was calculated to be 48.89% and that of carbon
dioxide was calculated to be 39.11%. Normally, biogas consists of 50-70% of
methane and 30- 40% of carbon dioxide. The obtained percentage of methane
was near to the range and carbon dioxide was within the range. Lesser volume
of methane may be due to presence of carbohydrates like potato peels, cooked
rice and food leftover in the feeding material.

d) Reduction in CO2 emission from the biogas plant

The annual reduction of CO2emission from the operation of the biogas plant is
shown in Table 4. Since the government had fixed 100 days as public
holidays;100 days have been deducted from annual days (365 days) i.e. for 265
days. The Table 4 showed that using urban biogas plant, 3.20 tonnes of
CO2equivalent could be reduced in a year from 262.50 kg of waste. It revealed
that even a small volume of bio-digester can help in reduction of carbon
dioxide.

Table 4 CO2 Equivalent calculation from the biogas plant

Weight of canteen’s waste 262.50 Kg

collected in 48 days

Conversion factor* 2.20 kg of CO2equivalent

Total CO2equivalent in 48 days 0.58 Tonnes of CO2equivalent

Total CO2equivalent/annum 3.20 Tonnes of CO2equivalent

e) Economic analysis
The calculated cost-benefit estimation of kerosene, firewood or LPG
substitution in terms of biogas has been shown in Table 7, 8 and 9 respectively.
The cost benefit estimation showed that if the benefits obtained from bio-
slurry is also considered, the invested money will be returned in less than one
year to substitute kerosene or firewood or LPG by a biogas plant. This indicated

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that this biogas plant is beneficial from investment point of view and is
economically suitable.

f) Statistical data
The result of Shapiro-Wilk normality test is presented in Table 5. The p-value
obtained in all the data was found to be >0.05 suggesting that the collected
data was acceptable, good and normal. Here, the obtained p-value was This
showed that there was significant relationship between ambient temperature

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and biogas production. Using simple linear regression, the output is shown in
table 6.

Table 5 Shapiro-Wilk normality test value

Data p-value
Weight 0.2124
Biogas production 0.0875
Ambient temperature 0.9315
Inlet’s temperature 0.1298

 CONCLUSION
The obtained values of physicochemical parameters of waste indicated that
kitchen waste is an appropriate material for anaerobic digestion. So, if this kind
of biogas plant is kept in the household of urban areas, the problem of organic
waste management faced by the municipalities could be solved. Another
important benefits provided by anaerobic digestion is the production of energy
or fuel, i.e. biogas which can be used for cooking and the residue, i.e. bio-slurry
can be used for crop production.
The study showed that biogas produced in a day was able to boil 4 litres of
water daily. So, the energy produced can act as a supplement fuel for cooking
purpose for urban people suffering from energy crisis. During the study, bio-
slurry produced was found to be blackish with lesser odour and within
optimum values of NPK. Hence, this residue could be used as a fertilizer in the
garden. Besides these benefits to the people, biogas also helps to protect
environment from the GHGs emission.
The study showed that even a small quantity of waste (262.50 kg) fed in the
biogas plant was able to reduce a greater quantity of carbon dioxide emission

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(3.20 tons of CO2 equivalent per annum). So, if organic waste of the urban
households could be utilized for biogas production, reduction of carbon dioxide
emission could be even greater as compared to the present study value.
The urban biogas plant is economically feasible as well. The benefits obtained
from biogas and bio-slurry makes this plant suitable and profitable for the
investors. It can be concluded that biogas production is better solution to
manage organic waste.

 BIOGAS IN NEPAL
Biogas technology has been widely adopted in Nepal, particularly in rural
areas. The Biogas Support Program (BSP), launched in 1992, has helped install
thousands of household biogas plants across the country. Cow and buffalo
dung are the primary feedstocks in Nepal, making it an ideal energy solution
for rural communities.

 Current Condition of Biogas in Nepal

1. Adoption and Popularity:

o Nepal has over 400,000 household biogas plants installed,
primarily in rural areas.
o The Biogas Support Program (BSP) has significantly contributed to
its widespread adoption.
2. Feedstock Availability:
o Abundant availability of animal dung (cow and buffalo) due to
Nepal's agriculture-based economy.
o Kitchen and agricultural waste also serve as supplementary
feedstock.
3. Government Support:
o Subsidies provided by the Alternative Energy Promotion Centre
(AEPC) for biogas plant installation.
o Policy focuses on renewable energy under initiatives like the Rural
Energy Policy and National Renewable Energy Framework.
4. Environmental Impact:
o Reduction in firewood consumption, mitigating deforestation.
o Lower greenhouse gas emissions and indoor air pollution.
5. Challenges:
o High initial cost of biogas plants despite subsidies.

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 o Limited adoption in hilly and remote areas due to logistical
challenges and lack of technical expertise.
o Seasonal variations affect feedstock availability.

 Capability of Biogas in Nepal

1. Household Energy Supply:

o Biogas fulfils the cooking and heating needs of households,
reducing dependency on firewood and LPG.
2. Community-Level Usage:
o Larger biogas plants (institutional plants) can power schools,
hospitals, and community centres.
3. Agriculture Benefits:
o Byproduct digestate improves soil fertility and reduces chemical
fertilizer dependency.
4. Electricity Generation:
o Potential to use biogas for small-scale electricity production in off-
grid areas.
5. Tourism Industry:
o Hotels and lodges in eco-tourism zones can utilize biogas as an
eco-friendly energy source.
6. Environmental Conservation:
o Significant potential to reduce deforestation and promote
sustainable energy.

 Improvement Ideas for Biogas in Nepal

1. Technology Upgradation:
o Introduce high-efficiency digesters for better gas production.
o Implement temperature regulation systems for better biogas yield
in colder climates (hilly areas).
2. Awareness Campaigns:
o Conduct workshops and campaigns to educate rural communities
on the benefits of biogas.
o Promote biogas usage in urban areas by targeting institutions and
industries.
3. Policy Enhancements:
o Increase government subsidies and low-interest loans for biogas
plant installation.
o Offer tax incentives for industries and institutions using biogas.
4. Integration with Waste Management:

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 o Link urban biogas plants with municipal waste management
systems to utilize organic waste efficiently.
o Establish biogas plants near markets, schools, and hospitals for
waste-to-energy conversion.
5. Research and Development:
o Invest in research for alternative feedstocks like water hyacinth
and food waste.
o Explore the use of biomethane as a transportation fuel.
6. Scaling Up:
o Promote community-level biogas plants for shared benefits in
rural areas.
o Develop larger-scale plants for electricity production and supply in
off-grid regions.
7. Capacity Building:
o Train technicians to ensure proper installation and maintenance of
biogas plants.
o Establish service centres in remote areas for repairs and spare
parts.
8. Monitoring and Quality Assurance:
o Develop a robust system to monitor the performance of installed
biogas plants.
o Ensure quality standards for digesters and other equipment.

 References
1.Journal articles:

o S. Shrestha, N. P. Chaulagain, K. R. Shrestha(2017) - Biogas production for organic waste

management.
o Sara Tanigawa(2019) - Biogas: Converting Waste to Energy
o Jairo-Smith(2023) - Biogas production from organic solid waste through anaerobic
digestion: A meta-analysis

2. Other sources
o https://www.host-bioenergy.com/solutions/biogas-plants/organic-waste-biogas-plants/
o Text book
o YouTube

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 CONTENTS

HEADINGS: Page no.

 Introduction 1-2
 Materials and methods 2
 Sampling of curry sample 2-4
 Result and discussion 4-8
 Conclusion 8-9
 Biogas in Nepal 9-11
 References 11

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