Dual-conditioning of sludge using chitosan and metal cations

Sludge dewatering is important in sludge management and disposal. In practice, chemical conditioners are often introduced to aid sludge dewatering. This study investigated the simultaneous application of chitosan and metal cations as dual-conditioners to improve sludge dewaterability. The dewatering performance of sludge was evaluated using three common measurements, i.e. capillary suction time, specific resistance to filtration, and moisture content of the filtered sludge cake. The effectiveness of metal cations in sludge conditioning and dewatering was found, in ascending order, to be Na⁺ < K⁺ ≈ Mg²⁺ < Ca²⁺ < Al³⁺ < Fe³⁺. Dual-conditioning using chitosan and metal cations further enhanced dewaterability. Cations may have significant effects on sludge conditioning by neutralization of negative surface charges, bridging of floc components, and the salting out effect, leading to improved dewaterability when used in conjunction with chitosan.