Stove working with biogas. (Christoph Kaufmann (Centre for Development and Environment CDE))

Biogas system at household level fed daily with cattle manure (Cambodia)

ប្រពន្ធ័ឡជីវៈឧស្ម័នប្រើសំរាប់គ្រួសារប្រចំាថៃ្ងដោយប្រើលាមកគោ (Khmer)

Description

Small-scale biogas systems fed with cow manure and water are implemented in order to supply the household with energy for cooking and lighting, as well as to produce fertilizer.

In this case-study, a small-scale biogas system was introduced in order to generate both energy for home consumption and fertilizer. Small-scale biogas systems are implemented in different parts of the world, however the layout thereof varies considerably.
The model used in this case-study consists of different components (cf. technical drawing). First, there is an inlet where the land user puts cow manure mixed with water. On the bottom of the inlet, there is a board which closes the access to the bio-digester situated beneath the inlet. The board can be opened manually by pulling a string. Once the board is open, the fluid components go through a pipe which leads to the bio-digester. In the bio-digester, bacteria transform the organic matter into biogas (mainly methane and CO2) and slurry. At the other end of the digester, there is another pipe (outlet). The outlet is lower than the inlet, and due to the difference in pressure, the slurry is pushed out of the digester. The slurry is dried and applied to the fields two to three times a year with the help of an ox cart. It has similar effects on the plant growth as chemical fertilizer as it does not build up the soil organic matter as much as compost. The biogas, however, is pushed to the pipe situated on top of the digester and can be utilized for domestic uses. The gas is used for cooking and lighting.

The use of biogas allows reducing the expenses on charging batteries for the lighting, as well as reducing the firewood use (usually from deforestation) for cooking. The slurry reduces the expenses on chemical fertilizer in the fields and has the advantage of killing the weed and rice seeds present in the manure and crop residues.

For building the biogas system, there is governmental and NGO support. These two actors finance half of the construction costs. The other half is paid by the land user. Building a biogas system is quite costly, with about 400 $, and not all of the land users in the area can afford paying 50% of its price. However, the costs borne by the land user are paid off within a few years due to reduced expenses on firewood, chemical fertilizer, and charging batteries. The construction itself was undertaken by local companies.
The costs are paid off within a few years due to the reduced expenses on firewood, chemical fertilizer and battery charging.

The analysed area is flat (slope < 2%), tropic (dry and wet season), and the soils are mostly sandy or loamy. The soils contain little organic matter (low soil fertility, acidification, small amount of cattle, area has been deforested a long time ago) and the groundwater table is rather high (1-3 m during the dry season, on the surface during wet season).
Due to climate change, the rainfalls are more erratic, temperatures rise and droughts are more recurrent. Rice is the predominant crop grown in the area, since it serves as staple food (mix subsistence and commercial activities). Rice is often grown in monocultures and harvested once a year. Once the rice is harvested (dry season), the cattle are released to the paddy fields. The cattle is often replaced by hand tractors, which effects the production of manure but allows a higher amount of crop residues on the fields.
As an addition to rice, most land users grow vegetable and fruits in small home gardens (subsistence) and complement their income by producing handicrafts or through off farm income / remittances from family members working in other places. The increasing migration rate (the young generation leaves the villages to work in the cities, garment industry or abroad) results in a decrease of available labour force in the area which has detrimental effects on the agricultural activities. Furthermore, the civil war in the 1970s (Khmer Rouge) led to the loss of agricultural knowledge which different NGOs try to re-establish.

Location

Location: Sre Ouk Samlor Sap/Taing Krasaing/Rolear Pha,er, Kampong Chhnang, Cambodia

No. of Technology sites analysed:

Geo-reference of selected sites
  • 104.62859, 12.05603

Spread of the Technology: evenly spread over an area (approx. 0.1-1 km2)

In a permanently protected area?:

Date of implementation: less than 10 years ago (recently)

Type of introduction
Manure and water are added to this top part of the biogas system. (Christoph Kaufmann (Centre for Development and Environment CDE))

Classification of the Technology

Main purpose
  • improve production
  • reduce, prevent, restore land degradation
  • conserve ecosystem
  • protect a watershed/ downstream areas – in combination with other Technologies
  • preserve/ improve biodiversity
  • reduce risk of disasters
  • adapt to climate change/ extremes and its impacts
  • mitigate climate change and its impacts
  • create beneficial economic impact
  • create beneficial social impact
Land use

  • Cropland
    • Annual cropping
    Number of growing seasons per year: 1
  • Settlements, infrastructure - Settlements, buildings
    other (specify): biogas system
Water supply
  • rainfed
  • mixed rainfed-irrigated
  • full irrigation

Purpose related to land degradation
  • prevent land degradation
  • reduce land degradation
  • restore/ rehabilitate severely degraded land
  • adapt to land degradation
  • not applicable
Degradation addressed
  • chemical soil deterioration - Cn: fertility decline and reduced organic matter content (not caused by erosion), Ca: acidification
  • biological degradation - Bs: quality and species composition/ diversity decline
SLM group
  • energy efficiency technologies
SLM measures
  • structural measures - S11: Others
  • management measures - M6: Waste management (recycling, re-use or reduce)

Technical drawing

Technical specifications
Biodigester. Inlet: top left; gas outlet: top centre; digestion chambre: centre; and outlet: right. For the comlete building instructions contact the NBP.
Technical knowledge required for field staff / advisors: high (The most challenging part is the construction of the construction of the Biodigester.)
Technical knowledge required for land users: low
Main technical functions: increase in nutrient availability (supply, recycling,…)
Secondary technical functions: increase in organic matter

Structural measure: Biodigester. Round shape. Tiles and concrete.
Width of ditches/pits/dams (m): 4 m^3
Structural measure: Connecting pipes made of plastic
Construction material (concrete): Tiles are covered in concrete.
Construction material (other): The most challenging part is the construction of the Biodigester.
Other type of management: Change of energy supply system for home consumption.
Author: National Biodigester Programm, www.nbp.org.kh

Establishment and maintenance: activities, inputs and costs

Calculation of inputs and costs
  • Costs are calculated:
  • Currency used for cost calculation: Riel
  • Exchange rate (to USD): 1 USD = 4000.0 Riel
  • Average wage cost of hired labour per day: 5.00
Most important factors affecting the costs
The most costly part of this Technology is the construction of the biodigester. Once the system is installed, the costs borne by the land user are low. Also, the land user can save money since he doesn’t need to buy firewood any more.
Establishment activities
  1. Construction of the biodigester by external experts. The land user did not help with the construction, he only paid 200 US$. The other 200 US$ were paid by the National Biodigester Program. (Timing/ frequency: Dry season, when water table is low.)
Establishment inputs and costs
Specify input Unit Quantity Costs per Unit (Riel) Total costs per input (Riel) % of costs borne by land users
Construction material
Construction of biodigester 1.0 400.0 400.0 50.0
Total costs for establishment of the Technology 400.0
Total costs for establishment of the Technology in USD 0.1
Maintenance activities
  1. Add manure and water to the inlet (Timing/ frequency: once per day all year round)
  2. Collect residuals from biodigester, spread it out and let it dry, and finally put it on the field. (Timing/ frequency: 3 times/year)
Maintenance inputs and costs
Specify input Unit Quantity Costs per Unit (Riel) Total costs per input (Riel) % of costs borne by land users
Labour
Labour 1.0 121.5 121.5 100.0
Total costs for maintenance of the Technology 121.5
Total costs for maintenance of the Technology in USD 0.03

Natural environment

Average annual rainfall
  • < 250 mm
  • 251-500 mm
  • 501-750 mm
  • 751-1,000 mm
  • 1,001-1,500 mm
  • 1,501-2,000 mm
  • 2,001-3,000 mm
  • 3,001-4,000 mm
  • > 4,000 mm
Agro-climatic zone
  • humid
  • sub-humid
  • semi-arid
  • arid
Specifications on climate
1486.45 mm 2013 in Kampong Chhnang
27° to 35°C, 1486.45 mm 2013 in Kampong Chhnang
Slope
  • flat (0-2%)
  • gentle (3-5%)
  • moderate (6-10%)
  • rolling (11-15%)
  • hilly (16-30%)
  • steep (31-60%)
  • very steep (>60%)
Landforms
  • plateau/plains
  • ridges
  • mountain slopes
  • hill slopes
  • footslopes
  • valley floors
Altitude
  • 0-100 m a.s.l.
  • 101-500 m a.s.l.
  • 501-1,000 m a.s.l.
  • 1,001-1,500 m a.s.l.
  • 1,501-2,000 m a.s.l.
  • 2,001-2,500 m a.s.l.
  • 2,501-3,000 m a.s.l.
  • 3,001-4,000 m a.s.l.
  • > 4,000 m a.s.l.
Technology is applied in
  • convex situations
  • concave situations
  • not relevant
Soil depth
  • very shallow (0-20 cm)
  • shallow (21-50 cm)
  • moderately deep (51-80 cm)
  • deep (81-120 cm)
  • very deep (> 120 cm)
Soil texture (topsoil)
  • coarse/ light (sandy)
  • medium (loamy, silty)
  • fine/ heavy (clay)
Soil texture (> 20 cm below surface)
  • coarse/ light (sandy)
  • medium (loamy, silty)
  • fine/ heavy (clay)
Topsoil organic matter content
  • high (>3%)
  • medium (1-3%)
  • low (<1%)
Groundwater table
  • on surface
  • < 5 m
  • 5-50 m
  • > 50 m
Availability of surface water
  • excess
  • good
  • medium
  • poor/ none
Water quality (untreated)
  • good drinking water
  • poor drinking water (treatment required)
  • for agricultural use only (irrigation)
  • unusable
Water quality refers to:
Is salinity a problem?
  • Ja
  • Nee

Occurrence of flooding
  • Ja
  • Nee
Species diversity
  • high
  • medium
  • low
Habitat diversity
  • high
  • medium
  • low

Characteristics of land users applying the Technology

Market orientation
  • subsistence (self-supply)
  • mixed (subsistence/ commercial)
  • commercial/ market
Off-farm income
  • less than 10% of all income
  • 10-50% of all income
  • > 50% of all income
Relative level of wealth
  • very poor
  • poor
  • average
  • rich
  • very rich
Level of mechanization
  • manual work
  • animal traction
  • mechanized/ motorized
Sedentary or nomadic
  • Sedentary
  • Semi-nomadic
  • Nomadic
Individuals or groups
  • individual/ household
  • groups/ community
  • cooperative
  • employee (company, government)
Gender
  • women
  • men
Age
  • children
  • youth
  • middle-aged
  • elderly
Area used per household
  • < 0.5 ha
  • 0.5-1 ha
  • 1-2 ha
  • 2-5 ha
  • 5-15 ha
  • 15-50 ha
  • 50-100 ha
  • 100-500 ha
  • 500-1,000 ha
  • 1,000-10,000 ha
  • > 10,000 ha
Scale
  • small-scale
  • medium-scale
  • large-scale
Land ownership
  • state
  • company
  • communal/ village
  • group
  • individual, not titled
  • individual, titled
Land use rights
  • open access (unorganized)
  • communal (organized)
  • leased
  • individual
Water use rights
  • open access (unorganized)
  • communal (organized)
  • leased
  • individual
Access to services and infrastructure
health

poor
x
good
education

poor
x
good
technical assistance

poor
x
good
employment (e.g. off-farm)

poor
x
good
markets

poor
x
good
energy

poor
x
good
roads and transport

poor
x
good
drinking water and sanitation

poor
x
good
financial services

poor
x
good

Impacts

Socio-economic impacts
Crop production
decreased
x
increased


Dried residues are put in the garden (cucumber, pumpkin, watermelon) which increases nutrient availability.

energy generation (e.g. hydro, bio)
decreased
x
increased

expenses on agricultural inputs
increased
x
decreased


He saves 50 $ on chemical fertilizer per year.

Socio-cultural impacts
health situation
worsened
x
improved


No smoke from open fire.

Contribution to human well-being
decreased
x
increased


On the long term livelihood is improved, because he saves over 60 $ per year in firewood and battery charging for light, as well as 50 $ for chemical fertilizer.

Ecological impacts
water quality
decreased
x
increased


Pollution of groundwater due to washing out of nutrients.

soil organic matter/ below ground C
decreased
x
increased


Most of the carbon is transformed into methane, not available as organic matter.

reduced weed seeds
increased
x
reduced


Compost usually not completely decomposed, as well as raw manure, contain lots of weed seeds.

energy generation (eg hydro, bio)
decreased
x
increased


Before the installation of the biogas system, the land user bought firewood.

deforestation for firewood
increased
x
decreased

Off-site impacts
groundwater/ river pollution
increased
x
reduced


Sludge is left to dry outside, nutrients washed out into groundwater. Not measurable.

Cost-benefit analysis

Benefits compared with establishment costs
Short-term returns
very negative
x
very positive

Long-term returns
very negative
x
very positive

Benefits compared with maintenance costs
Short-term returns
very negative
x
very positive

Long-term returns
very negative
x
very positive

Climate change

Gradual climate change
annual temperature increase

not well at all
x
very well
Climate-related extremes (disasters)
local rainstorm

not well at all
x
very well
local windstorm

not well at all
x
very well
drought

not well at all
x
very well
general (river) flood

not well at all
x
very well
Other climate-related consequences
reduced growing period

not well at all
x
very well

Adoption and adaptation

Percentage of land users in the area who have adopted the Technology
  • single cases/ experimental
  • 1-10%
  • 11-50%
  • > 50%
Of all those who have adopted the Technology, how many have done so without receiving material incentives?
  • 0-10%
  • 11-50%
  • 51-90%
  • 91-100%
Number of households and/ or area covered
100% or 4 land user families
Has the Technology been modified recently to adapt to changing conditions?
  • Ja
  • Nee
To which changing conditions?
  • climatic change/ extremes
  • changing markets
  • labour availability (e.g. due to migration)

Conclusions and lessons learnt

Strengths: land user's view
  • Fertilizer production (sludge).
  • Saves money and time on the cooking fuel (previously wood) and electricity (charging batteries) for the light.
  • No weed seeds in the sludge compared to compost and raw manure if used as fertilizer.
Strengths: compiler’s or other key resource person’s view
  • Less deforestation for firewood.
Weaknesses/ disadvantages/ risks: land user's viewhow to overcome
  • The residue does not improve the soil as much as compost. Make compost in addition to biogas to enhance the soil organic matter.
  • The building costs are prohibitive Increase subsidies from state or NGOs.
  • At least 3-4 heads of cattle or 4-5 pigs have to be kept to produce enough manure. Diversify production with different animals.
  • Work has to be done each day to produce biogas.
Weaknesses/ disadvantages/ risks: compiler’s or other key resource person’s viewhow to overcome
  • Overgrazing could become a problem as more cattle needs to be kept. Add slurry as a liquid fertilizer
  • Part of nitrogen is volatilized during the drying of the sludge.

References

Compiler
  • Christoph Kaufmann
Editors
Reviewer
  • Deborah Niggli
  • David Streiff
  • Alexandra Gavilano
Date of documentation: Okt. 27, 2014
Last update: Maart 11, 2019
Resource persons
Full description in the WOCAT database
Linked SLM data
Documentation was faciliated by
Institution Project
Key references
  • NBP National Biodigester Program: www.nbp.org.kh
  • Lam et al. 2009. Domestic Biogas Compact Course. University of Oldenburg.: http://www.nbp.org.kh/publication/study_report/2_domestic_biogas%20.pdf
  • Gurung. 2009. Review of Literature on Effects of Slurry Use on Crop production. The Biogas Support Program:
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