Abstract
Problem statement: The oxidation ditch system has been used to treat various types of wastewaters. Several types of aerators are used to supply the treatment process with oxygen. Among these devices, the disc aerator has certain advantages regarding foam generation over the brush and paddle type rotors, but the main disadvantages of this aerator is the limited oxygenation capacity. The main objectives of this study were to study the effects of various design parameters and system operation parameters on the oxygenation capacity of the system. Approach: A bench scale oxidation ditch system equipped with a disc aerator was used to gain better understanding of the phenomena of oxygen transfer and to study the effects of hole diameter, number of holes per disc, disc thickness, disc speed, immersion depth and number of discs on the oxygenation capacity of the system. The unsteady state method with sulphite oxidation was used to deoxygenate the water. The test involved chemical removal of dissolved oxygen from water followed by oxygenation. The power consumed was measured, the oxygen transfer coefficient was determined and both the oxygenation capacity and oxygenation efficiency were calculated. Results: The oxygen transfer coefficient was affected by the immersion depth, hole diameter, disc speed, disc thickness and number of discs, with the disc speed having the greatest effect. The results showed that three physical processes simultaneously contributed to oxygen transfer by the disc aerator: bubble aeration, eddy aeration and surface aeration. Conclusion: The use of sodium sulphite with cobalt chloride for deoxygenation of the water via the oxidation ditch was effective and the results were very consistent and repeatable. The aerator disc of 2.55 cm thickness, 1.92 cm diameter and 48 holes was found to achieve the highest oxygenation capacity. The system is anticipated to provide a broad range of oxygen transfer rates under actual conditions (23-164 mgO2/L-h) to meet varying process demands encountered in aerobic treatment systems.
Highlights
Process should be accomplished at the least cost per Wastewaters have been successfully treated using aerobic biological systems. (Pell and Worman, 2008; LaPara and Alleman, 1998; Groves et al, 1992; Fenlon and Mills, 1980)
The results showed that the drive system of the aerator disc was rather inefficient; only about 14-19% of the input power was apparently consumed in the aeration process
Oxygenation capacity: The oxygenation capacity of the system was a function of KLa and was affected by the immersion depth, hole diameter, disc thickness and disc speed with the disc speed having the greatest effect
Summary
Process should be accomplished at the least cost per Wastewaters have been successfully treated using aerobic biological systems. (Pell and Worman, 2008; LaPara and Alleman, 1998; Groves et al, 1992; Fenlon and Mills, 1980). Mass transfer occurs by sequential molecular diffusion through the two films as shown in Fig. 1 (Haut and Halloin, 2003) With this concept, equation 2 can be written in terms of a gas and liquid films as follows: Oxygen transfer: Aeration is used to transfer oxygen to a biological treatment process. Equation 2 can be written in terms of a gas and liquid films as follows: Oxygen transfer: Aeration is used to transfer oxygen to a biological treatment process It is a gas-liquid N = KLA(CS − CL ) = KGA(Pt − PG ). Assuming equilibrium at the gas-liquid interface, the mass transfer can be expressed as follows: The penetration theory: It is postulated that the contact between phases occurs in a series of intermittent steps and the mass transfer rate is a function of the contact time. The objective of aeration and agitation management in a wastewater treatment system is to achieve a value of KLa such that the oxygen supply meets the oxygen demand of the microorganisms at a value of CL sufficient for the microorganisms to exist
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
