Production of low emission briquettes from carbonized faecal sludge as an alternative source of cooking energy

Abstract

Background

In Tanzania, firewood, charcoal, and agricultural waste play a crucial role in daily life as sources of cooking energy, especially in rural areas. Using these energy sources contributes to deforestation and the emission of harmful substances, leading to health problems. This study highlights the potential of faecal sludge briquettes as an innovative, environmentally friendly, and sustainable alternative to traditional energy sources to meet the increasing demand for cooking energy in Tanzania. The process involved sludge characterization, drying, sorting, carbonization, milling, briquette making, and characterization.

Results

A study was conducted to assess the presence of zinc (Zn), cadmium (Cd), and lead (Pb) in faecal sludge collected from households. The results indicates that the levels of these metals were all within the acceptable limits set by the Tanzanian Standards (TZS) for sludge disposal and use in the environment, which are 5.00 mg/L, 5.00 mg/L, and 30.00 mg/L, respectively. Septic tanks and pit latrines sludge had a concentration of 0.5 mg/L and 0.5 mg/L for Zn, 0.55 mg/L, and 0.6 mg/L for Cd, and 10.01 mg/L and 4.87 mg/L for Pb, respectively. Adding 75% charcoal dust improved the gross and net heating values from 10.47 and 10.16 to 19.29 and 18.86 MJ/kg, respectively. Similarly, adding 50% charcoal dust improved the gross and net heating values to 19.24 and 18.78 MJ/kg. The emission of particulate matter (micrograms/m³) was reduced from 30.4 and 35 to 10.3 and 11.8 for PM_2.5 and 7 and 8 for PM_10, while carbon monoxide emission decreased from 51.2 to 19.7 ppm.

Conclusion

The results strongly suggest that briquettes made of carbonized faecal sludge mixed with other biomass materials could offer an alternative to traditional solid fuels, with the added benefits of reducing greenhouse gas emissions, deforestation, and longer burning times.