Pollutants production, energy recovery and environmental impact of sewage sludge co-incineration with biomass pellets

This study describes the production of pollutants, energy recovery and environmental impact of the co-incineration of sewage sludge and biomass pellets. The main objective of this study is to describe the use of energy generated by co-incineration and to assess the environmental impact of emitted pollutants. Co-incineration takes place in five different blended. The combustion takes place in a fluidised bed reactor with an average combustion temperature of 915–939 °C. The combustion process is mapped by Fourier transform infrared spectroscopy, Continuous Mercury Monitoring Systems, thermocouples, pressures, and flows sensors. The results show that the concentrations of harmful substances, namely SO2 and NOX, reach values of 12.39–1730.33 mg∙m–3N for SO2 and 93.30–1156 mg∙m–3N for NOX. This means that the emission limits are exceeded 40 times for SO2 and 8 times for NOX in the worst case. Regarding heat recovery, the resulting value of potential energy recovery from the flue gas is 5.35–7.69 MJ∙kg–1, and as the sewage sludge content in the fuel increases, the heat recovery value decreases. The resulting values of pollutant concentrations are also analyzed using a life cycle assessment approach using the GaBi software. The results show that sewage sludge incineration has the greatest impact on climate change, terrestrial ecotoxicity, and human toxicity. Again, as the sewage sludge content in the fuel decreases, the hazardousness of the discharged flue gas decreases. This study presents a relatively promising option to use sewage sludge as a secondary fuel in large combustion sources under certain conditions.