Mechanism investigations into the effect of rice husk and wood sawdust conditioning on sewage sludge thermal drying

Abstract

This study attempts to employ wood sawdust and rice husk as biorenewable conditioners to improve the efficiency and energy consumption of sewage sludge thermal drying, besides revealing the mechanism of drying. Response surface methodology (RSM) approach has been used to optimize the operational parameters (drying temperature and dose of conditioners). Investigations into the thermal performance, water distribution and morphological of sludge have been used to explain the improvements obtained in the properties of drying with the addition of biomass. The optimal conditions found out were: 10% rice husk and 10% wood sawdust at 120 °C, which resulted in drying time to reduce by 17.64% with the energy consumption savings by 46.37% for the conditioned sludge. Also, the mechanism on the roles of these additives has been found out as follows: (1) Addition of biomass enhances the thermal conductivity of the conditioned sludge, leading to improvements in its heat transfer capacity; (2) Bound water → free water and strongly bonding water → weakly bonding water, due to cationic osmotic effects; (3) Structures with rigidity and porosity provide sufficient passages for the vapors to escape.

Keywords: Biomass; Drying mechanism; Environmental challenge; Response surface methodology; Sewage sludge.