Financial and economic performance of domestic biogas installations
SNV Dom. Biogas Programs
3. Dairy and biogas
• Traditionally, small scale biogas and small scale dairy have always
been having tight links.
• => From a biogas point of view: zero stabled- dairy cows / overnight
stabling, are the producer of the substrate for the biogas installation.
• => From a dairy perspective: a biogas installation contribute to a
proper and hygienic management of cow dung, the production of
energy for hot/warm water to clean milking equipment and cattle
before and after milking, nutrients cycling….
Biochemical processes and
The dairy cow
Mature “developed (!)” dairy cow Live weight 635 kg
Milk production 20 – 35 kg / day
Main dung characteristics:
Daily fresh manure production: 51 kg per day (61 litres / day)
Total solids: 6.4 kg (TS (= DM) ~ 13% of fresh wght)
Macro nutrients: Micro nutrients / trace elements
Phosphorus P: 0.04 kg
Potassium K: 0.16 kgTypical substrates
Cow dung 0.025 0.050
Pig dung 0.040 0.070
Poultry litter 0.065 0.120
Nigh soil 0.030 0.070
•Weight <250 kg
•Milk production 1-5 kg/day
•TS >20% of fresh wght
4. Bio-slurry as fertilizer
Improved soil fertility:
• Higher yield kg/ha
• Better quality, higher price/kg
• Savings on chemical fertilizer
• Savings on pesticides
Bio-slurry can be used fresh or
mixed with agricultural
residues to make compost!
Often the financial benefits of
bio-slurry is greater than that
Slurry use for aqua culture
• Food for fish
• Fast uptake of inorganic
materials by plankton
• Plankton food for fish
• Little use of O2, better water
• Less risks for fish diseases
• Increase in fish growth of 15-
30% compared to fresh dung
• Dehydrated digested sludge can be used as feed supplement
for pig and poultry.
• Mushroom farming: increase in yields of 15% more compared
to that of usual medium using bio-slurry and reducing pick time
by 7 days.
Bio-slurry use matters!
Small fraction of soils: < 2 % (in tropics)
• Living organisms: roots, fungi, earthworms, etc.
• Dead material: plant residues, fym, compost, humus, etc
• Soil structure (roots, air)
• Water retention capacity
• Soil fertility (CEC = cation exchange capacity)
• Buffers soil pH
• Resistance to erosion
5. Energy use for dairy farmers
• Use of biogas for heating of water to clean milking equipment
and cattle before and after milking.
• To a lesser extent, biogas-energy has been applied for on-farm
milk processing, mainly pasteurizing raw milk
• Innovative idea; use of biogas for milk chilling at HH level
both micro-scale (6-16 M3) and medium sized digesters (24-60
- special designed milk coolers operating on biogas
- use of generators operating on biogas
Preliminary calculations indicate that the per-head production of
cattle dung produces sufficient energy to cool down the per head
energy to the
• The impact of a biogas installation on the dairy quality is high;
- improved hygienic conditions and cleanness
• - energy for heating, pasteurisation and possible chilling
• - organic potential fertilizer for crops / fodder grasses /
• - reduced GHG emissions by saving NRM fuels.
• => resulting that Nestle supported the construction of bio-
digesters for all its farmer-producers in Indonesia.
SNV - Kenya
Peter Bos, Senior Advisor Renewable Energy
For more information, please
• Primary: nitrogen (N), phosphorus (P), potassium (K)
• Secondary: calcium (Ca), magnesium (Mg), sulphur (S)
Micronutrients (trace elements)
• boron (B), copper (Cu), iron (Fe), chloride (Cl), manganese
(Mn), molybdenum (Mo), zinc (Zn)
• hydrogen (H), oxygen (O), carbon (C)
Measured: dry weight in % or g/kg or ppm (= parts per million)
• proteins, enzymes and metabolic processes.
• chlorophyll ⇨ photosynthesis.
• rapid growth, seed and fruit production, quality.
• photosynthesis rapid growth.
• formation of all oils, sugars, starches, etc.
• encourages blooming and root growth.
• building of protein, photosynthesis, fruit quality.
• reduction of diseases.
Broad range of nutrients
Low in N-P-K
Long term effect (indirect)
Soil organic matter content
Short term effect (direct)
High in N, P or K
Integrated Soil Fertility Management:
Optimal combination of organic and chemical fertilizers
Domestic biogas & carbon
Manure handling modality
Methane emissions per animal type “i” in “j” systems:
i = ∑j Bo
i x VSi x MS%ij x MCFj
CH4= Methane emissions [kgm-3]
Bo= Biodegradability [m3 CH4 (kgVS)-1]
MS%= Manure management system usage [%]
MCF= Methane conversion factor [%]
VS= Volatile solids [kgyr-1]
Domestic biogas & carbon
Biomass and fossil fuel substitution
Baseline emissions for thermal energy for one household:
BEth, h = ∑j (( F i,bl,h) x NCVi x EFco2
Beth,h = Baseline hh emissions from thermal energy [t CO2eq]
Fi, bl, h= Amount of fuel i in baseline situation per hh [kg, m3 or ltr]
NCVi = Net calorific value fuel i [GJkg-1etc]
i= CO2 emission factor for fuel i [tCO2kg-1]