Co-pelletization of sewage sludge and biomass: The energy input and properties of pellets

• Energy input is affected by applied pressure, die temperature and water content.
• Protein denaturation and the content of lignocellulose affect moisture adsorption.
• 55 MPa, 90 °C and a water content of 10–15% are recommended for co-pelletization.
• Lignin, protein and carbohydrate can be activated as the natural binders.

Presently, most pellets are made of lignocellulose biomass. However, the rocketing development of demands and fierce competition of feedstock between biomass industries have resulted in local biomass supply insufficiency and rising prices of the raw material. Therefore, other kinds of raw materials should be involved in the production of pellets to improve the stable supply of feedstock. In this study, the pelletization of biomass materials mixed with sewage sludge (SS) was investigated. The effects of process parameters on energy consumption and pellet properties were studied. It was shown that the compression energy consumption was affected by applied pressure, die temperature and water content. Both temperature and water content had an influence on the above pellet properties to a different extent, which was found to be independent of pressure. Optimal parameters (55 MPa for pressure, 90 °C for temperature and 10–15% for water content) were recommended for co-pelletization.