AERATION PROCESS Dr Abdul Haqi bin Ibrahim Water
AERATION PROCESS Dr. Abdul Haqi bin Ibrahim Water Research Group (WAREG) School of Environmental Engineering Universiti Malaysia Perlis.
METHOD • air and water are brought into intimate contact • contact time and the ratio of air to water must be sufficient for effective removal of the unwanted gas. • used for the following operations: • carbon dioxide reduction (decarbonation) • oxidation of iron and manganese found in many well waters (oxidation tower) • ammonia and hydrogen sulfide reduction (stripping)
EFFECIENCY OF AERATION • Depends on: • Amount of surface contact • Time of contact • Type of aerator
TYPE OF AERATORS • Water-into-air • - cascade aerator • - circular cascade aerator • - Spray aerator
TYPE OF AERATORS • Air-into-water • Venturi aerator • Draft tube aerator
CIRCULAR CASCADE AERATOR • Commonly used by JKR • Simple to operate n keep clean • Reliable and has long service life • Not the most efficient but acceptable • Consist of 3 circular tray. . stacked one above another. . with a central vertical feed pipe.
CIRCULAR CASCADE AERATOR • Total height of fall being calculated from Gameson’s formula: • r = 1 + 0. 5 (a x b x h) • Where: • r = the ratio of the oxygen deficit just before the aerator to that just after the aerator. The “oxygen deficit” is the difference between the actual oxygen content and the equilibrium oxygen content for the water at that temperature and pressure • a= 1. 25 in slightly polluted water, 1. 00 moderately polluted water, 0. 85 in sewage water. • b = 1. 00 for free fall weir, 1. 30 for a stepped weir • h = the total height of the fall in metres
CIRCULAR CASCADE AERATOR • Aeration occurs in splash area • The collecting basin area is sized according to the loading rate of 49 000 liter/hour/m 2 • A side wall is built around the collecting basin. • Generally the head required at a cascade aerator ranges from 1 m to 3 m
DESIGN EXAMPLE • Dissolved Oxygen (DO) of raw water sample is 4. 5 mg/l. At saturation point at average temperature 26 C and pressure of 755 mm Hg, the DO is 8. 2 mg/l. For treatment requirement, it is sufficient to raise the DO to 80% of that saturation condition. The raw water is slightly polluted and stepped weir is use • r = 1 + 0. 5 (a x b x h) • r = (8. 2 -4. 5)/(8. 2 -6. 56) = 2. 256 • a = 1. 25 • b = 1. 30 • h = fall required…? ?
DESIGN EXAMPLE • Taken the inflow to the aerator is 390 000 liter/hour • The area of collecting basin is ? ? ? • What is the diameter?
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