Farmers can turn trash into treasure by making briquette fuel from harvest waste for sale to both rural and urban residents.

Shelling coffee, wheat, maize, rice, beans, millet, maize, among others crops, chaff is always churned out as waste.

Together with maize stalks and rice and wheat straws from rice and other crops, these can be converted into cooking fuel that can generate extra income for the farmers, without much expertise.

Once one has the biomass to be used in the process, they will follow a few procedures to arrive at the fuel.

In simple terms, process can be described simply as sieving (crushing for big biomass), mixing, squeezing and carbonising biomass into fuel.

The first step is sieving the material to ensure the biomass in is the required size. This means big or long materials have to be sliced to a length of between 6 mm and 8 mm.

Soil or paper paste is used to bind the particles and should make about 10 per cent to 20 per cent of the whole biomass.

The content is taken through the second stage of drying. Drying will get rid of excess moisture content to 10 per cent, according to the Food for Agricultural Organisation.

Carbonisation will be done in the preheating process in an closed drum or kiln; they will turn black. 

During carbonisation, the biomass is enclosed in a vessel to limit the amount of oxygen supporting limited combustion.Fire is regulated, and because of the enclosure, the content will just turn black as it happens to charcoal burning.

Densification of the mass will be done by a simple compressing briquette machine, which costs about Sh25,000. 

The resultant 'balls' is cooled and packaged.

Unlike the ordinary charcoal, briquettes are hardy and can be transported for long distances without breaking.

Multiple statistics show that Nairobi residents consume at least 700 tonnes daily.  Out of this, approximately 88 tonnes of dust result from breakages during transportation from remote areas.

Innovative women and youth groups in Kibra, Kahawa Sukari and other informal settlements are mixing this dust with soil, before drying it to get the black 'balls' briquettes for sale.

On average a two-kilo tin of briquettes fetches about Sh50 while ordinary charcoal of similar quantity costs between Sh60 and Sh80 in Nairobi.

Considering the amount of charcoal consumed daily in Nairobi, briquettes have a place in the current set up.

Research by World Agroforestry Centre, briquettes of about  Sh3 can cook a traditional meal of maize and beans for five people. Cooking the same meal with charcoal or kerosene which would cost Sh26 and Sh45 respectively.

FAO describes briquettes as environmental friendly and clean energy.