Effects of cationic polyacrylamide characteristics on sewage sludge dewatering and moisture evaporation

The effects of the molecular weight (MW) and charge density (CD) of cationic polyacrylamide (CPAM) on sludge dewatering and moisture evaporation were investigated in this study. Results indicated that in sludge conditioning, the optimum dosages were 10, 6, 6, 4, and 4 mg g(-1) CPAM with 5 million MW and 20% CD, 5 million MW and 40% CD, 3 million MW and 40% CD, 8 million MW and 40% CD, and 5 million MW and 60% CD, respectively. The optimum dosage of CPAM was negatively correlated with its CD or MW if the CD or MW of CPAM was above 20% or 5 million. In the centrifugal dewatering of sludge, the moisture content in the conditioned sludge gradually decreased with the extension of centrifugation time, and the economical centrifugal force was 400×g. The moisture evaporation rates of the conditioned sludge were closely related to sludge dewaterability, which was in turn significantly correlated either positively with the solid content of sludge particles that were >2 mm in size or negatively with that of particles measuring 1 mm to 2 mm in diameter. During treatment, sludge moisture content was reduced from 80% to 20% by evaporation, and the moisture evaporation rates were 1.35, 1.49, 1.62, and 2.24 times faster in the sludge conditioned using 4 mg g(-1) CPAM with 5 million MW and 60% CD than in the sludge conditioned using 4 mg g(-1) CPAM with 8 million MW and 40% CD, 6 mg g(-1) CPAM with 5 million MW and 40% CD, 6 mg g(-1) CPAM with 3 million MW and 40% CD, and 10 mg g(-1) CPAM with 5 million MW and 20% CD, respectively. Hence, the CPAM with 5 million MW and 60% CD was ideal for sludge dewatering.