In light of current fossil fuel shortages much focus has been placed on alternative sources of energy especially those that are renewable. Additionally, our environment is becoming more and more stressed as it is being contaminated by inappropriate disposal methods of organic and chemical wastes.  These factors significantly affect both the financial and social costs associated with agricultural production in Barbados.

WHAT IS BIOGAS DIGESTION?

Biogas digestion is the process in which biogas (a combustible gas) is produced as organic matter is broken down under anaerobic (lack of oxygen) conditions.  The process involves three basic steps.

1.  DECOMPOSITION

Complex compounds such as carbohydrates, fats and proteins are disintegrated into simple soluble compounds such as simple sugars and glycerol.

2.  ACID FORMATION

These simple compounds are then converted to simple and volatile acids such as acetic acid, lactic acid, propanic acid, butanic acid and methanol

3.  METHANE FORMATION

Acids formed, are now converted in to methane by methanogenic bacteria.

CONDITIONS THAT AFFECT BIOGAS PRODUCTION

ATMOSPHERIC CONDITIONS

The process will only occur under anaerobic conditions

TEMPERATURE

Three suitable temperature ranges have been noted for effective biogas gas production by various methanogenic bacteria.

                Psychrophilic digestion (10-200C)

                Mesophilic digestion (20-350C)

                Thermophilic digestion (50-650C)

pH LEVEL 

The methanogenic bacteria prefer a pH of 7(neutral). 

ORGANIC MATERIAL

The greatest level of gas produced occurs when the organic material has a high carbon to nitrogen ratio. (C/N of 20:1 or 30:1)

A demonstration video at Agrofest 2009

                     BIOGAS AS AN APPROPIATE TECHNOLOGY       

AGRICULTURIAL BENEFITS

Unlike fresh manure, effluent byproducts from the digestion process increase plant growth. During the digestion process gaseous nitrogen is converted to ammonia. In this compound form the nitrogen is readily available to plants. This process also makes available other vital nutrients required by plants. The sludge accumulating at the bottom of the digester can be mixed with soil mediums to improve water holding capacity and allow for better root growth.

CLEAN ENERGY

Biogas burns with a blue, smokeless flame. The gas produced can be used as a cooking gas. On some of the larger livestock farms enough gas is produced to fuel electrical generator capable supplying electricity to a power grid.

OFENSIVE ORDOUR REDUCTION

The anaerobic process reduces gaseous emission by deterring the growth of microbial organisms that would otherwise (aerobically) produce offensive orders.  Some projects have recorded up to 97% reduction in odours when using the biogas digestion system.           

PATHOGEN REDUCTION

A multiplicity of pathogens and bacteria such as Escherichia coli, Salmonella and Cryptosporidium are often found in animal manure.  These organisms are harmful to human health and are a potential source of sickness and disease.  Research has shown that the biogas digestion process reduces these pathogens by 99.99%.

ENVIRONMENTAL BENEFITS

Major pollution problems associated with waste are surface and groundwater contamination, and surface air pollution caused by odors, dust and ammonia. There is, moreover, a concern regarding the contribution of methane emissions to global climate change. The use of biogas digesters can significantly reduce the amount of pollutants entering the environment. According to latest research, methane is twenty-three times more potent than carbon dioxide in terms of its contribution to global warming. In a biogas system much of the methane is collected and burned. As such each molecule of the combustible gas produced is converted to one molecule of carbon dioxide which contributes less to global warming.