A thesis submitted-in partial fulfillment of the requirements for the degree of Master of Engineering in the Asian Institute of Technology, Bangkok, Thailand.

Thesis (M.Eng.) - Asian Institute of Technology, 1974

The research was conducted at. Pilot-.Plant scale to investigate the performance of tube-settlers and develop design criteria for treatment of tropical turbid waters. The evaluation of horizontal tube-settler was carried out using the "Neptune Microfloc" 10 gpm Pilot-Plant (5 degree inclination). ,-The tubes were of 1-in depth and 2 ft in length Inclined tube settler, with tubes 2 x 2 in. cross- v section, 3 ft in length and 60 degrees angle of inclination, was specially designed for this study It was found that horizontal tube-settlers were efficient devices in turbidity removal but sludge storage capacity was a limitation on the system. At flow rates of 2.45 m3 /m2-hr (1.0 gpm/ft2 ) and above and with raw turbidities 50-80 Jackson units tubes were filled in about one hour. Flow-rates of 0.98 m3 /m2-hr (0.4 gpm/ft2 ) and 1.96 m3 /m2-hr (0.8 gpm/ft2 ) "with average raw turbidities of 60 JTU, gave run lengths of 24 and 8 hours respectively for 70-percent removal efficiency~ The corresponding detention times were 37.5 and 18.9 minutes. Thus, under these conditions the advantages of short detention times were lost due to limitation of sludge storage capacity. Dual-media (Anthracite-Sand) filter did not perform satisfactorily when influent turbidities were 10 JTU and above. The inclined tube settlers performed very well at flow rates- as high as 10_._Q_m3 /m2-hr (4.0 gpm/ft2 ) and detention time 5.5 minutes, giving about 80 percent' turbidity removal operating at influent turbidities of 95 Jackson units. Thus, the high-rate capabilities of the tube-settling system were clearly demonstrated. ' The use of tube settlers in treatment plants affords substantial savings in space requirements and capital costs.