Natural gas

Natural gas is widely available all over the world as one of the cleanest fossil fuels.  It can be used as a vehicle fuel either in its compressed form (CNG) or in its liquid form (LNG).  When used as a vehicle fuel, it has fewer greenhouse gas emissions than petrol or diesel, and none of the particulates associated with diesel.

 

Biogas

Biogas is a mixture of gases formed during the natural breakdown of organic materials (including food waste, animal manures, sewage, and energy crops) in a process known as anaerobic digestion.  During this process complex organic molecules are broken down by bacteria into their simplest forms, CO2, CH4 and H2S.  Biogas thus consists of a mixture of biomethane CH4 (60% - 70%) and carbon dioxide CO2 (30% - 40%) and minimal amounts of contaminants such as hydrogen sulphide H2S.  Biogas can be used in stationary reciprocating engines or gas turbines to generate electricity and heat, but is not suitable as a vehicle fuel.  Biogas is also produced in landfill sites, but then usually has a lower proportion of methane and may contain nitrogen and more contaminants than the biogas produced by dedicated anaerobic digestion plants.

Biomethane

Separating out the carbon dioxide and the contaminants from the biogas leaves biomethane.  Chemically this is the same as natural gas.  It can be dried and then fed into a natural gas grid, or pressurised for use as a vehicle fuel. 

Biomethane formed from organic waste is the world’s most environmentally friendly fuel.

Less than half of all the food grown in the world is actually eaten.  This means that more than half of all the food crops grown are available as an organic resource (the inedible leaves, stalks, skins, roots and peelings).  Normally these organic materials are regarded as wastes and they are thrown away to rot, or put into landfills, where they give off methane gas.  Capturing this and preventing the biomethane from escaping into the atmosphere to become a greenhouse gas some twenty one times worse than carbon dioxide, and using it as a renewable fuel, is improving the environment by preventing greenhouse gas emissions from these wastes.

Other ‘alternative’ or ‘renewable’ liquid biofuels such as biodiesel or bioethanol are simply ‘less bad’ for the environment than are fossil fuels, whereas using biomethane from wastes is actually doing ‘good’ for the environment.

(Source: Christopher Maltin, Organic Power Ltd.)