Abstract
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.
Highlights
The amount of wastewater treated by wastewater treatment plants in China exceeds 125,000,000 m3 per day
Crucial data on the influence of molecular weight (MW) and charge density (CD) on optimum cationic polyacrylamide (CPAM) dosage or sludge moisture evaporation behavior at optimal dewatering points with different types of CPAM at optimum dosages is lacking, which strongly limits the accurate evaluation of additional CPAM in optimal sludge dewatering. In view of this information, this study aims to: (1) determine the optimum CPAM dosage for sludge conditioning at different MWs and CDs; and (2) explore the sludge moisture evaporation behavior at optimal dewatering points with different types of CPAM at optimum dosages
The specific resistance to filtration (SRF) of the original sludge is 2.0561013 m kg21, and this value was initially reduced by the additions of all types of CPAM
Summary
The amount of wastewater treated by wastewater treatment plants in China exceeds 125,000,000 m3 per day. Approximately 6,000,000 dry tons of sewage sludge is generated each year [1] This amount increases substantially with the development of wastewater treatment facilities. The maximum moisture content in sewage sludge often reaches ,99% after secondary sedimentation and 95% to 98% after thickening in wastewater treatment plants [4,5]. This high moisture content is a major issue in sludge disposal because it increases transport and storage costs, decreases energy efficiency during incineration, requires increased amounts of supplemental bulking agents during composting, and increases leachate concentrations in sludge landfill [6,7]. The reduction of the moisture content in sludge by either dewatering or evaporation is a critical issue in sludge disposal
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