Air pollutant emissions from sludge-bituminous briquettes as a potential household energy source

To promote the sustainable and clean use of sewage sludge (SS) and bituminous coal (BC), BC was mixed with SS at 2%, 4% and 16% as sludge-coal briquettes (named by SBC1, SBC2 and SBC3) which were characterized in this study to evaluate combustion performance and emissions of hazardous air pollutants in an advanced residential stove. Fuel burning rate and modified combustion efficiency (MCE) were similar among the three fuels, while the emission factors of carbon monoxide (CO) and mercury (Hg) were significantly different (p < 0.05), with the highest emissions from the biomass-coal briquette with the sludge content of 4%. Ash content is a key factor affecting the emission factors (EFs) of CO and Hg. EFs of particulate matter with aerodynamic equivalent diameter ≤2.5 μm (PM2.5) was significantly correlated with the EFs of nitrogen oxides (NOx), cadmium (Cd) and total polycyclic aromatic hydrocarbons (tPAHs). It appears that by mixing sludge with briquettes at 16%, there were insignificant changes in emissions of most hazardous pollutants including Hg and PAHs compared with mixing sludge at 2%. This study suggested possibilities in support of high-efficient co-utilization of sludge and briquette coals especially in the residential sector.