Applying organic polymer flocculants in conditioning and advanced dewatering of landfill sludge as a substitution of ferric trichloride and lime: Mechanism, optimization and pilot-scale study

In this study, poly dimethyl diallyl ammonium chloride (PDADMAC) and polyacrylamide (PAM) were applied to substitute ferric trichloride (FeCl₃) and lime conditioning for advanced dewatering of landfill sludge (LS). Four response surface methodology (RSM) models were constructed for FeCl₃-lime, FeCl₃-PAM, PDADMAC-lime and PDADMAC-PAM, and identical dosages, namely 29.86, 57.91, 5.73 and 2.99 mg/g dry solids (DS) for FeCl₃, lime, PDADMAC and PAM, were obtained by solving the system of four RSM equations at water content of 60% to investigate conditioning mechanisms. Compared to FeCl₃-lime, PDADMAC-PAM conditioning had strong charge neutralization and bridging performance, and obtained conditioned LS with large flocs size, strong network structure and rapid dewatering rate. By integrating RSM with nonlinear programming for optimization, the total cost of PDADMAC-PAM route was saved by 7.9% and close to FeCl₃-lime, and the optimized condition with dosages of 1.93 and 3.47 kg/t DS was further confirmed by pilot-scale experiments. The results indicated that PDADMAC-PAM was a feasible substitute for FeCl₃-lime in sludge conditioning, and showed more advantage if dewatered sludge was further treated by incineration.