Potential use of faecal sludge derived char briquettes as an alternative cooking energy source in Dar es Salaam, Tanzania

Abstract

Coprophobia characterizes faecal sludge (FS) as an unpleasing raw or partially digested faecal waste with no recycling value. However, this so-called waste is claimed to have tremendous recycling values after being pyrolyzed. This study hypothesized that char briquettes made from FS might have the potential of replacing charcoal consumption in Dar es Salaam, Tanzania. Quantitative methods were used to examine the proximate, emissions and environmental benefits of faecal sludge char briquettes in comparison to wood charcoal from Dalbergia melanoxylon (locally known as Mpingo). Results revealed that FS collected during the dry season exhibited a higher total solids content (26%) compared to that collected during the rainy season (20%). This difference was statistically significant (p = 6.12405E-14 at α=0.05). Dewatering and further drying the FS to a minimum of 90% total solids yielded an energy value of 11-12 MJ/kg, which was lower than that of uncarbonized wood (firewood) at 19 MJ/kg. Production of FS char briquettes bonded by paper waste has a lower energy value (13 MJ/kg) than that bonded by cassava starch (14.6 MJ/kg). The average energy value of FS char briquettes is almost half that of wood charcoal (26 MJ/kg), meaning that the replacement of 1 kg of charcoal consumption would require 2 kg of FS char briquettes is required. Nevertheless, due to an ineffective collection of FS to be used in the production of char briquettes, only 8% of charcoal consumption in the city can be replaced. It is recommended to use the produced briquettes in open kitchens with ample oxygen circulation, as they emit carbon monoxide levels exceeding the allowable limits set by the Tanzania Bureau of Standards.