What is Biogas?

Biogas is the product of the breakdown of organic matter such as food, garden, sewage, animal and organic waste and is produced through bio-digesters installed in compounds. Bio-digesters are used to digest organic materials using anaerobic bacteria. During the process the bacteria breaks down the complicate carbon compounds in to simple substrates and emits Methane gas.

Bio-digesters have been used in Sri Lanka since 1970’s and the oldest functioning unit is at the Trinity farm Kandy which was built in 1976 by Mr G.K Upawansa.

Since 1970 over 10000 biogas units have been built in Sri Lanka for various types of feed waste, the industry has developed in many areas today and has systems that can cater to any type of organic feed material and had many modern appliances than can make effective end use of the gas produced.


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Financing for Biogas Units

Currently, there are two financing schemes available for biogas units made available through the Regional Development Bank branches in North Western Province and Sanasa Development Bank branches island wide.

Regional Development Bank – North Western Province

The loan scheme in place is at a 6% interest rate for cattle farmers and 6-8% for hoteliers, households, industries and piggeries.

Sanasa Development Bank

With an 8% interest rate for industries and a repayment period of three years, Sanasa Development Bank offers equally competitive rates for households and hotels.

Biogas Units in Sri Lanka

Continuous flow fixed dome biogas systems (Chinese)
Most common biogas systems found in Sri Lanka
This type of biogas systems works well if animal dung and human excreta are used.
Input material has to be fed continuously on a daily basis if biogas is used daily.
The slurry would generally be in the semi-liquid form.

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Plug flow biogas systems
There are only a few of this type of biogas systems in the country.
Their length is comparatively long as against the width (typically five times longer than they are wide).
Most suitable for materials that do not mix with water that well.
Most of this type of biogas systems in operation in Sri Lanka use food waste, (canteens, restaurants) and waste generated at kitchens.

Continuous flow floating drum biogas systems (Indian)
The construction of this type of biogas system involves a permanent well like pit for organic matter that produces biogas.
Input material has to be fed continuously on a daily basis if biogas is used daily. In such cases, biogas is also produced continuously, almost constantly.
The slurry would generally be in the semi-liquid form.

Compact biogas systems
This type of biogas systems is especially suitable for household kitchen and food waste.
The system must be fed with smaller size input material and the biogas produced may be adequate to meet only a portion of the total energy demand of the households.
Readily available in the local market.

Dry batch biogas systems (Sri Lankan)
Material that produces biogas is fed into the system only as batches and from time to time. Hence, the material produces biogas over a period of time
The typical cycle time would vary depending on the type of input material. An indicative cycle time for municipal garbage is 16 weeks and for paddy straw a period of 24 weeks.
There are no inlet or output chambers and this type of biogas systems are most suitable for agricultural residues, market garbage and that of which cannot easily be mixed with water.

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