Novel strategies for analyzing sewage sludge incineration: Pyrolysis derived products and image analysis technologies

The disposal of municipal sewage sludge (SS) through incineration holds promise for promoting resource circularity, environmental conservation, and the development of an affordable and sustainable energy strategy in line with the United Nations' sustainable development goals. However, numerous structural, chemical, and physical challenges often result in low energy yield and the release of gases and pollutants. This study utilized an innovative flame image analysis method to investigate the effects of biochar (BC) and pyrolysis oil (PO) on enhancing the fuel properties and combustion behavior of SS. Various biomass blends were created by combining SS with BC at 25% (T1), 50% (T2), and 75% (T3), and were compared with pure SS (T0) as the control. Additionally, parallel samples were mixed with 10% pyrolysis oil to improve the energy content and self-ignition rate. Increasing the proportion of BC and adding PO resulted in higher fuel volatiles and lower moisture and ash content. Furthermore, the addition of BC and PO led to an increase in the higher heating value (HHV) from 14.14 to 24.59 MJ kg−1. Additionally, the addition of PO increased the carbon and hydrogen content, thereby improving the biofuel indices. The flame image analysis, which included flame size and red color intensity, effectively differentiated the biomass burning behavior. It was observed that the flame volume and red color intensity of the SS blends improved by approximately 30.0% to 49.4% compared to pure SS. Moreover, adding BC to the blends reduced CO formation and decreased SO2 and NOx emissions by 36%, 41%, and 32% respectively, while the addition of pyrolysis oil further reduced CO emissions, albeit to a lesser extent than biochar. Ultimately, these findings demonstrate that the synergistic integration of biochar and pyrolysis oil overcomes the inherent limitations of sewage sludge incineration, offering a highly efficient, low-emission pathway to optimize waste-to-energy conversion and advance global circular economy objectives.