Effect of adding wood chips on sewage sludge dewatering in a pilot-scale plate-and-frame filter press process

Abstract

The addition of wood chips combined with cationic polyacrylamide (CPAM) and polymeric aluminium chlorides (PACl) to sewage sludge was investigated to enhance the dewatering in a pilot-scale plate-and-frame filter press. The results indicated that the chemical coagulation significantly affected the moisture content (MC) and specific resistance to filtration (SRF) of the sludge in bench-scale tests. The lowest MC and SRF were 87.93% and 0.31 × 10¹¹ m kg⁻¹, respectively, for CPAM and PACl dosages of 0.04% and 4%, respectively. However, when the wood chips were combined with chemical coagulation conditioning, minimal improvements were noted in the sludge dewatering ability compared to the coagulation conditioning alone. Moreover, the addition of wood chips was effective for the subsequent plate-and-frame filter press dewatering process. The wood chips acted as skeleton builders during this high-pressure dewatering (1.0 MPa). The lowest MC was 50.3% when the dosages of CPAM, PACl and wood chips were 0.05%, 4% and 100%, respectively. Furthermore, a wood chip dosage of 100% increased the high heat value (HV) and low HV of the products by 20% and 150%, respectively, compared to the control. Several subsequent disposal options, such as landfilling, incineration and bio-composting, are proposed as a result of the low MC and high low HV of the products.