Mini-household biogas plant

Biogas:

Biogas is a gaseous fuel consisting chiefly of methane, produced by the anaerobic decomposition of organic matter under controlled conditions. It is a clean fuel and a renewable source of energy with various applications.

Composition of biogas:

Sl.No	Composition of gas	Content (%)
1	Methane	55-65
2	Carbon-di-oxide	35-45
3	Hydrogen	trace
4	Hydrogen sulphide	trace
5	Ammonia	trace

Applications of biogas:

•      Fuel for cooking
•      Fuel for lighting
•      Automobile fuel (substitute for diesel / dual-fuel engines can also be used)
•      Enriched organic manure of agriculture and aquaculture (slurry)
•      Manure for mushroom cultivation (slurry)
•      Manure for seed coating (slurry)

Components of a biogas plant:

• Digester or fermentation chamber
• Gas holder or gas storage chamber
• Inlet (pipe or tank)
• Outlet (pipe or tank)
• Mixing tank
• Gas outlet pipe
• Inlet and outlet displacement Chambers
• Plant Dome or Arched Roof
• Inlet and outlet gates
• Manhole or Digester cover

Mini family-size household biogas plant:

Design:

Plant capacity: 1 m³

Daily feed: 25 kg

Hydraulic retention time: 30 days

Digester volume = HRT * Daily feed

                                      = 30 * 25

                                      = 750 kg ~ 750 l = 0.75 m³

Gas production = feed * 0.04

                                 = 25* 0.04 = 1 m³

Gas holder volume: 0.5 m³

Digester volume: 0.75 m³

Storage tank volume: 0.5 m³

Total volume: 1.25 m³

In general,

Yield from 1 m³ biogas plant = 1.5 -2.5 kWh electricity or 2.5-4 kWh of thermal power

Note:

These conditions are applicable for biogas production from cow dung. But the gas production from kitchen waste is considerably poor. The gas production capacity can be increased by varying the constituents of kitchen waste with materials that yield high quantity of biogas.

Thumb rule for initial feeding:

A 0.5 m³ biogas plant requires >100 kg of cow dung for initial feeding.

Similarly a 1m³ plant requires > 200-250 kg of cow dung for initial feeding.

Kitchen waste can be fed later.

But considerable amount of gas production starts only after 30 days.

Digested slurry can be collected time to time

Materials required for construction:

•          800 l container for digester
•          600 l container for gas holder
•          PVC pipes for inlet, outlet and slurry collection port
•          Funnel to connect to the inlet pipe to aid in feeding
•          Gas valve 

CAD of Mini biogas plant (Front View)

CAD of Mini Biogas plant (Isometric view)