Millions of small biogas plants are used by rural households across Africa and India, saving families from the arduous work of gathering wood for fuel – and saving trees too.
Now policymakers are recognising that by developing large biogas plants they can provide energy for their ever-expanding urban populations.
‘Biogas’ refers to the gases – mainly methane and carbon dioxide – produced when organic matter is broken down in the absence of oxygen in an enclosed chamber (‘anaerobic digestion’) or by fermentation. The process is potentially a virtuous circle: it disposes of biodegradable waste, produces a valuable fuel and leaves residues which can be put back on the land as high quality fertiliser. Production is generally carbon-neutral, depending on the waste matter used.
The manure from just two to four cows can be enough to produce gas for all a household’s cooking needs, often with spare left over for lighting too.
From rural to industrial use
In industrial-scale applications, there is another biogas bonus: it can be cleaned and upgraded to the quality of natural gas for vehicle fuel and other uses. More than just cow dung can feed the plant, of course – feedstocks are generally municipal solid waste, domestic organic waste, harvest surplus or dedicated ‘energy crops’. In Germany, which leads the way in European biogas production (though the UK has some ambitious plans, as we reported last July), the feedstock is typically manure mixed with corn.
A company in Kenya announced in February that its national grid-connected biogas plant, the first of its kind in Africa, is to begin producing power ‘within weeks’. Half the electricity generated will be sold to Kenya Power, with the rest powering the plant itself and the farm that supplies the corn.
However, it is another crop, namely sugar, that feeds India’s largest biogas plant, set up in Maharashtra in partnership with Germany. While 80% of the gas produced is upgraded to form compressed biogas, the rest is sold to the cooperative which supplies the sugar as a fuel for industrial use.
Process monitoring in a biogas plant is important in order to identify potential problems in a digester well before a malfunction occurs. If the amount of organic matter fed to the plant exceeds the ability of the microbes to break it down, an ‘overload’ can take place. The resulting acidification reduces the amount of biogas produced.
The cost of basic monitoring, usually performed by gas flow meters, is almost always much lower than the cost of rebooting a destabilised plant.