Abstract
Problem statement: The role of aeration in activated sludge process is to provide oxygen to microorganisms as they assimilate the organic carbon compounds and digest a portion of them to carbon dioxide and water, sulfate and nitrate compounds. The water aeration equipment used in this process consumes as much as 60-80% of total power requirements in modern wastewater treatment plants. Approach: The objective of this study is to enhance the oxygen transfer in aeration tank in activated sludge process by increasing pressure inside the part of aeration tank to increase the saturation level of dissolved oxygen in wastewater. The diffuser cap model is the experimental model which was used to show the effect of increasing pressure on oxygen transfer level. Three cases were considered, the first used without diffuser cap, the second with diffuser cap and the third with diffuser cap and plastic strips. Results: Obtained results show that in case of using the model with diffuser cap enhanced the oxygen level by about 5% than in case of without diffuser cap while that of adding plastic strips enhanced the oxygen level by about 7%. The variation of water flow showed that increasing water flow rate from 1-2 L min-1 decreased the oxygen saturation level by about 6%. Furthermore, increasing water depth from 15-60 cm increased the oxygen level by about 40%. Conclusion: The diffuser cap model showed that the increase of pressure and water depth increased the dissolved oxygen level while increasing water flow rate decreased the dissolved oxygen level.
Highlights
Activated sludge is the most widely used biological treatment process
The dissolved oxygen level increased with increasing depth the range of increase was about 40%
From this research study it is shown that the diffuser cap model shows that increasing pressure by about 4% causes an increase in oxygen level by about 5% at water flow rate 1 L min−1 and water depth 60 cm over diffuser cap
Summary
Activated sludge is the most widely used biological treatment process. In an activated sludge process, oxygen is usually supplied to the wastewater by diffused aeration or mechanical aeration (Reynolds and Richards, 1996). A diffuser is used to introduce small air bubbles near the bottom of the tank. The air bubble size is kept small for an efficient oxygen transfer to water. The efficiency of oxygen transfer depends on many factors, including the type, size and shape of the diffuser; the air flow rate; the depth of submersion; tank geometry; and wastewater characteristics (Tchobanoglous et al, 2004). In bubble diffused aeration systems the coefficient of oxygen transfer K increases with the airflow rate and water temperature, but decreases with the water depth
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