Effect of carbonisation on combustion characteristics of faecal sludge and sawdust blended briquettes

In Malawi, biomass briquettes are used as alternative fuels to firewood and charcoal. Briquettes are produced by the densification of waste biomass using various processes. This study was undertaken to assess the effect of carbonization process on the combustion characteristics of briquettes made from different ratios (9:1, 4:1 and 2.3:1) of faecal sludge and sawdust. Proximate and ultimate combustion characteristics analyses were done. The combustion characteristics of the carbonised briquettes competed favourably with firewood and charcoal which are the main energy means for cooking and heating in Malawi. The highest calorific value was recorded in the ratio of 2.3:1 (20.79 MJ/kg). The carbonised briquettes had a moisture content of 6.40% with an ash content of less than 4% (ratio 9:1). The overall mean water boiling times for the un-carbonised and carbonised briquettes were 720.17 and 374.83 s respectively. The mean burning rates for the un-carbonised and carbonised briquettes were 1.65 and 0.81 g/min respectively. Low emissions from the combustion of the carbonised briquettes were observed as compared to the un-carbonised briquettes. The study concluded that the carbonised briquettes from all ratios had better quality in terms of the physical and combustion characteristics. By being more environmentally friendly than the uncarbonized briquettes, the carbonised briquettes are more suitable to be used as an alternative energy source to the commonly used fuels (firewood and charcoal).