Biogas

Biogas is a mixture of gases, mostly methane (CH₄) and carbon dioxide (CO₂) produced by the digestion of organic materials in oxygen constrained conditions. This process is called Anaerobic Digestion (AD).

What is biogas made from?

Biogas is made from a mixture of water and organic waste, which is commonly known as “feedstock.”

Organic waste can be obtained from the following sources:

• Animal manure from cattle, goats, pigs and poultry;
• Crop residues including maize cobs, banana stems, rice husks.
• Kitchen waste from leftover foods in households and restaurants.
• Market waste such as rotting foodstuffs, food husks and peelings, and others.
• Sewage and human waste from sewage and faecal sludge treatment and containment facilities.
• Industrial organic effluent from dairy processing facilities, breweries, sugar processing industries and agro-processing industries.

What is the process of biogas production?

1. Collection & mixing: Organic Waste is collected and mixed with water to make a porridge like mixture and poured into an inlet tank. Some feedstock instantly forms the porridge like mixture i.e. animal dung, while solid waste requires soaking in water for a period of 12 – 24 hours.
2. Anaerobic digestion: The mixture proceeds to a sealed digester (fermentation tank), usually by gravitational flow. In the sealed digester, microbes break down the organic matter in the absence of oxygen. The breakdown has four (4) progressive stages i.e. hydrolysis → acidogenesis → acetogenesis → methanogenesis.
3. Collecting the biogas: The biogas progressively accumulates above the mixture in the digester as breakdown progresses. Then, the gas is either piped to a gas storage tank or used directly by piping to a kitchen or bulb.
4. Utilisation: Biogas is cleaned/conditioned as needed and used for cooking, heating, lighting or to generate electricity (via a gas engine/CHP).
5. Digestate management: After biogas has been extracted from the mixture, there is a left over solid/liquid, called digestate. This digestate is piped out of the system through gravitational flow. After removal of the biogas, the mixture is converted to a stable digestate and can be used directly as organic fertiliser.

How does one optimize biogas production from different feedstock?

1) Animal Manure (Cattle, Goats, Pigs, Poultry)

Challenge: Some manures (especially poultry and pig waste) have high nitrogen, causing excess ammonia. Excess ammonia slows down the biogas production process and affects the quality and quantity of biogas produced.

Optimization Practices:

• Mix poultry and pig manure with waste that is rich in carbon so as reduce the production of ammonia. Carbon rich feedstock includes cow dung, crop residues, kitchen waste, sawdust and dry leaves.
• Dilute with water to reduce ammonia concentration, particularly for poultry droppings.
• Pre-treat with anaerobic storage/composting for 1–2 weeks to reduce pathogens and stabilize organic matter.
• Maintain appropriate moisture, especially for drier manure (goat dung), by mixing with wetter feedstock.

2) Crop Residues (Maize cobs, Banana stems, Rice husks)

Challenge: These contain too much lignocellulose. The excessive lignocellulose makes it hard the waste to be degraded.

Optimization Practices:

• Size reduction: The residues are chopped, shredded, hammered to increase their surface area. Size reduction could be coupled with the following practices:
• Biological pre-treatment: by soaking in enzymes like cattle urine to break the fibers.
• Combine with nitrogen-rich wastes such as poultry waste, piggery waste.

Challenge: Rice husks should not be used in excess. Excessive use rice husks cause accumulation of silica.

Optimization practices:

• Always mix the rice husks with wet organic waste.

Why biogas?

Energy & household benefits

• Provides a clean cooking fuel that reduces indoor air pollution and associated health risks from traditional biomass stoves.
• Can be used for cooking, lighting, and electricity generation (through biogas-fired generators), increasing household energy access and resilience.

Agricultural co-benefits

• Digestate from anaerobic digestion is a nutrient-rich organic fertiliser that can improve soil fertility and crop yields, supporting smallholder agriculture and reducing reliance on chemical fertilisers.

Waste management & environmental benefits

• Converts organic waste (animal manure, food waste, crop residues, sewage) into usable energy, reducing open dumping, uncontrolled decomposition, and related greenhouse gas emissions.
• Properly managed systems reduce odour and pathogen loads compared with unmanaged manure piles.

Economic & social benefits

• Saves household time (less fuel collection) and money (reduced fuel purchases).
• Creates local jobs in construction, operation and maintenance of biogas systems and in supply chains for biogas services.

Uganda’s biogas potential — short facts and implications

• The Uganda National Livestock Census 2021 found that roughly 6.8 million households kept at least one type of livestock (about 72.8% of households), indicating a very large distributed source of animal manure that could be harnessed for biogas. This livestock ownership provides strong feedstock potential for household and community biogas systems across the country.

Safety & operation notes

• Biogas is flammable: installations must follow safe design, ventilation, proper piping, and include safety valves and flash arrestors.
• Systems require regular feeding and operator training to get consistent results.

BOQS For fixed Dome Systems

Quantity
ITEM	4M3	6M3		9M3	13M3	20M3
1.0 General Bulk Materials
1.1 (a) sand (plaster)	1 truck (Elf)	1 truck (Elf)	1 truck (Elf)		1 truck (Elf)	1 truck(forward)
(b) sand (Building)	1 truck (Elf)	1 truck (Elf)	1 truck (Elf)		1 truck (Elf)	1 truck(forward)
1.2 Gravel ¼*	5w/b	6w/b	10w/b		1 truck (Elf)	1 truck (Elf)
1.3 cement	10bags	14 bags	17 bags		22bags	40 bags
1.4 Bricks	800 pieces	100pieces	1200 pieces		2000pieces	3500pieces
1.5 Acrylic emulsion paint	3litres	4litres	5litres		6litres	10 liters
1.6 Welded/square mesh	1piece	1piece	1piece		1piece	3pieces
1.7Twisted bar (Y-12)	1piece	1piece	1piece		2pieces	4pieces
1.8 PVC piece 4”,20feet (medium)	1piece	1piece	1piece		1piece	1piece
1.9PCV Pipe½ (varies with distance)	1piece	2 pieces	3pieces		3pieces	5pieces
1.10Water drainage value (varies with distance)	2 pieces	2 pieces	2 pieces		2 pieces	2 pieces
1.11 fitting material and sundry	Lumpsum	Lumpsum	Lumpsum		Lumpsum	Lumpsum
1.12 Ring wire (8mm)	1piece	1piece	1piece		1piece	2 pieces
1,13 transport for bricks and cement	Lumpsum	Lumpsum	Lumpsum		Lumpsum	Lumpsum
1.14 waterproof cement	4kg	6kg	6kg		10kg	20kg
Sub-TOTAL
2.0 Biogas Materials &excavation
2.1 Dome gas pipe + valve	1piece	1piece	1piece		1piece	1piece
2.2Biogas stove +nozzle and horse pipe	1piece	1piece	2pieces		2pieces	3pieces
2.3Pressure gauge with accessories	1piece	1piece	1piece		1piece	1piece
2.4 Biogas filter	1piece	1piece	1piece		1piece	1piece
2.5 Excavation costs	Lumpsum	Lumpsum	Lumpsum		Lumpsum	Lumpsum
Sub-total
3.0 Company Service fees
3.1 Accommodation			To be provided by the biodigester owner
3.2 Meals for masons			To be provided by the biodigester owner
3.3 Quality control			To be provided by the biodigester company
3.4 Helpers/porters			To be provided by the biodigester owner
3.5 Annual maintenance fee (once a year)			To be provided by the biodigester company
Sub-total
4.0 Bio-digester commissioning
4.1 cow dung	1000	2,200	3,500		5,000	10,000
4.2 water	1000	2,200	3,500		5,000	10,000
4.3 Labor for initial feeding
Sub-total
5.0 Other Information
5.1 Hours for cooking per unit size	2	3	5		6.5	12
5.2 Quantity of dung / animal waste	30kgs or 1.5 basins	60kgs or 3 basins	120kgs or 6basins		160kgs or 8basins	300kgs or 15basins
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