Production of sustainable fuel briquettes from the co-carbonization of sewage sludge derived from wastewater treatment and wood shavings as a sustainable solid fuel for heating energy

• Sewage sludge biochar as a sustainable and safe heating fuel. • Low environmental and health impact carbonized sewage sludge and saw-dust briquettes. Dried sewage sludge is an appealing biomass fuel for industrial kilns, because of its availability, affordability and has a positive effect on improving the symbiotic sustainable circularity of liquid waste treatment plants. The study investigated the fuel characteristics (efficiency, environmental and human safety) of biochar produced from sewage sludge for utilization as heating energy and compared the fuel performance to charcoal produced from wood sources using the Water Boiling Test method and X-ray Fluorescence Spectroscopy. Biochar briquette with equal ratio of carbonized sludge and wood shavings grants a solid fuel with good quality in terms of the burning rate (10.51 g/min.), specific fuel consumption (107.13 g/l) and emission levels of CO (59.64 g kg -1 of fuel) and PM 2.5 (4.76 g kg -1 of fuel). This fuel compared favourably with other biomass fuels used in Ghana. Also, no adverse impact on the environment and human health was observed in the use of the biochar with the low air quality index (35.23) recorded when the fuel is used in a well-ventilated cooking environment as well as showed low potential ecological risk (121.54) in terms of the heavy metals in the residual ash when disposed of in the soil. The positive energy balance (2.35 MJ/kg) of the production is indicative the potential carbon savings.