Why is the use of biomass to generate heat

(i) discouraged by burning it directly in ovens (chulhas) and

(ii) encouraged for obtaining biogas through a biogas plant.

1) The use of bio-mass to generate heat by burning directly in ovens is discouraged do not produce much heat on burning and a lot of smoke is given out when they are burnt. Therefore, it is important to improve the efficiency of these fuels before using them.

2) The use of bio-mass to obtain biogas is encouraged because biogas is clean fuel which does not produce any smoke on burning. Also it leaves no residue unlike burning of other fuels like coal, wood, etc and has high heating capacity. Secondly the slurry that is left behind is rich in nitrogen and phosphorus and hence can be used as a manure.