| Abstract | This experimental study on mechanical sludge dewatering, which consisted of laboratory tests for sludge conditioning and full scale dewatering trials, aimed to investigate the use of centrifuge dewatering four different types of sludges produced at Nongkaem nightsoil treatment plant, Sipraya sewage treatment plant, Bangkhen water treatment plant and Bangpra water treatment plant. Sludges collected from Nongkaem, Sipraya and Bangkhen, were conditioned with seven different types of organic powder polymers and tested for capillary suction time(CST) and specific resistance to filtration(SRF). The conditioning tests revealed that the range of optimum polymer dosages was 11.0-13.0kg/tDS of five cationic polymers, 5.0-7.0kg/tDS of five cationic polymers and 0.5-1.0kg/tDS of two anionic polymers for nightsoil, sewage and waterwork sludge, respectively. Full scale dewatering trials were conducted on four different plants using KHO CP 1.1-1 centripress mobile unit. The values of maximum cake solids concentration obtained from full scale dewatering trials were 28.0%, 29.3%, 49.5% and 38.6% for Nongkaem, Sipraya, Bangkhen and Bangpra, respectively. Also, 96.96%, 99.97%, 99.99% and 99.72% for maximum recovery were obtained, respectively. By the analysis of the experimental data, the high bowl speed, about 3,800-4,200rpm was suitable for Sipraya, Nongkaem and Bangpra, but for Bangkhen, the low bowl speed, about 2,800-3,000rpm was suitable. Lower differential speed with higher hydraulic pressure gave a higher cake solids concentration. Increasing pond depth increased the cake solids concentration with the expense of lower recovery values. The lower feed rate and solids loading rate produced the higher cake solids concentration and cleaner centrate. The optimum polymer dosages of full scale trials were well coincided with that of laboratory conditioning tests. Process control algorithm for optimizing the centripress dewatering process was developed using major process parameter, such as solids concentration in centrate, differential speed, hydraulic pressure, bowl speed, polymer dosage rate and solids loading rate. To achieve more effective process control, fuzzy set theory is recommended to be introduced. |