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Effect of Multiple Compartments on Oxygen Transfer in Postaeration Tanks
Author(s) -
Pincince Albert B.
Publication year - 1999
Publication title -
water environment research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.356
H-Index - 73
eISSN - 1554-7531
pISSN - 1061-4303
DOI - 10.2175/106143096x122438
Subject(s) - aeration , effluent , diffuser (optics) , environmental science , environmental engineering , wastewater , oxygen , saturation (graph theory) , limiting oxygen concentration , chemistry , waste management , engineering , light source , physics , mathematics , optics , organic chemistry , combinatorics
National Pollution Discharge Elimination System permits for approximately 5900 wastewater treatment plants in the U.S. include a minimum dissolved oxygen requirement. Of these plants, approximately 2300 have an average flow exceeding 3900 m 3 /d (1 mgd). To achieve these dissolved oxygen standards, final effluent from some plants is aerated before discharge using cascades or postaeration tanks. Postaeration tanks are typically designed as completely mixed tanks with effluent concentration equal to concentration throughout the tank. The concentration difference that determines rate of oxygen transfer is the saturation concentration minus the effluent concentration.
Oxygen transfer can be made more efficient by dividing the tank into two or more compartments. Because the difference between oxygen deficit in the compartments before the last one is greater than the deficit in the last compartment, the standard oxygen‐transfer rate (SOTR) required with multiple compartments is less than with one compartment. A decrease in SOTR causes the same percent decrease in number of diffusers and diffuser capacity (for diffused‐air systems) or capacity of mechanical aerators. Also, the basin itself can be made smaller. Optimum configuration is obtained when the SOTR for each tank is equal. The most efficient system is a plug‐flow regime, which can be achieved by means of multiple compartments or use of a tank with a high length‐to‐width ratio.