Co-pelletization of sewage sludge, furfural residue and corn stalk: Characteristics and quality analysis of pellets

Abstract In this study, pelletization of sewage sludge (SS), furfural residue (FR) and corn stalk (CS) and mixture of SS with FR and CS was performed, and various quality parameters and their dependency on process variables were investigated. Addition of SS in ratios of 20–40% to FR had not enhanced the pellet densities (e.g. particle and relaxed) of furfural residue sludge mixed pellets (FRSPs). However, mixing SS with CS in ratio of 20–80% had resulted in higher density, strength and hardness of corn stalk sludge mixed pellets (CSSPs). Addition of sludge to 20% with FR had resulted in higher strength and hardness (i.e. 7 ± 0.22 MPa and 508 ± 28.1 N/mm2) of pellets. While the highest strength and hardness i.e. 13.4 ± 0.12 MPa and 392 ± 5.96 N/mm2 were found for CSSPs-40 and CSSPs-80. Pelletization at 200 °C was found to be beneficial as it improved the mechanical characteristics of FRSPs and CSSPs and reduced the energy consumption. Energy consumption of pellets was decreased markedly with increasing sludge ratio and the lowest was found at SS proportion of 80%. Heating values of sludge mixed pellets were found higher than sewage sludge pellets. Compression models had well evaluated the compaction behavior of FR, SS, CS and their corresponding mixture with R2 ≥ 0.9. Using SS in lower proportion (e.g. 20%) could reduce the odor during pelletization or even in the pellets. The results showed that co-pelletization of SS with FR and CS could be feasible approach to enhance the characteristics of pellets and reduced the energy consumption.