Analysis the sewage sludge recycling strategy based on real-time pyrolysis performance and pyrochar characteristics

Abstract

Co-pyrolysis with waste biomass is an effective strategy for the disposal of huge amounts of sewage sludge. A thermogravimetric-infrared-mass spectrometry real-time monitoring system is utilized to study the co-pyrolysis of sludge and coffee grounds (CG). By fitting thermodynamic models, the addition of CG favored the thermal initiation process by increasing the effective collision frequency required. The release of NO2, SO2, C2HCl3, and C6H6 was concentrated at 330–500 °C and was suppressed when the blending ratio (CG: sludge) was 3:7. Furthermore, as pyrolysis proceeding, the P form in the pyrochar converted from poly-P to pyrophosphate or Al-P, and eventually to Ca-P. The blending of CG as calcium source furthered the proportion of Ca(H2PO4)2 reached up to 44% when the blending ratio was 3:7 at pyrolysis temperature of 500 °C. Therefore, the quality of the value-added product (pyrochar) was related to the pyrolysis temperature, while the mitigation of volatiles was more influenced by the blending ratio of biomass. By studying the co-pyrolysis process, we deepen the understanding of the effect of waste biomass on sewage sludge treatment, and laid the foundation for optimizing the means of pyrolysis treatment, controlling the co-pyrolysis as well as resource utilization.