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| | | Forum Newbie
Group: Forum Members
Last Login: 5/30/2008 12:55:19 PM
Posts: 2, Visits: 26 |
| | I am trying to determine the proper way of calculating the treatment plant detention time. We are required to compensate for the detention time when doing some of our influent and effluent sampling. The question I have about doing this is whether or not to include recirculated flow in the calculations, specifically the return activated sludge flow from the secondary clarifiers to the activated sludge basins. I would really like to have a reference manual citation that addresses this calculation. Thank you,
Lyle Milby
City of Norman
Environmental Services
P.O. Box 370
Norman, OK 73070
lyle.milby@normanok.gov
Phone (405) 292-9731
Fax (405) 292-9731 |
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| | | Forum Guru
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Last Login: 7/19/2007 11:20:51 PM
Posts: 68, Visits: 239 |
| | The answer is "no". All recycles in a treatment plant are "internal", meaning that they take place after the influent enters the plant and before the effluent leaves the plant. When I was teaching one of my favorite questions was to ask the students to prove mathematically that the average detention time of plant with and without recycles was the same! |
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| | | Forum Newbie
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Last Login: 5/30/2008 12:55:19 PM
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| | I was taught - maybe incorrectly - that the volume of recirculated flow is displacing volume in the affected tank and so should be considered. For instance the calculations for the detention time through the aeration tank in question would be; basin volume divided by primary clarifier effluent plus RAS volume. I single this treatment unit out as an example because, in making our calculations, we were determining the detention time of each treatment unit, since they do not all receive an equal portion of flow, and then adding them together to arrive at the plant detention time. How do you mathematically prove that the average detention time is the same with or without recirculation flow? Thank you for your help,
Lyle Milby
City of Norman
Environmental Services
P.O. Box 370
Norman, OK 73070
lyle.milby@normanok.gov
Phone (405) 292-9731
Fax (405) 292-9731 |
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| | | Supreme Being
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Last Login: Yesterday @ 3:05:04 PM
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| | Don't use the existing formulas out there. There are to many of them and they conflict with one another. They will drive you nuts. Simply use a percentage of the flow. In the activated sluge process I have found that 100% of the influent flow works good. I have had the opportunity to work at 100's of different plants and found that they all seem to work best at that percentage. Balancing your clarifiers, if you have two seperate return pumps, is more difficult at some plants. You can use the sludge (most common method) or a D.O. Meter. |
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| | | Forum Guru
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Last Login: 7/19/2007 11:20:51 PM
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| | Now you are asking a different question I think. Your first post referred to estimating the detention time between plant influent and effluent...and that is the question that I tried to asnwer in my first response. Now it seem you are asking about the detention time in and aeration basin only (w/o the secondary clarifier included). In that case you draw the box around the aeration basin only and the average detention time of the aeration basin only is calculated, as you state, on the basis of the influent flow plus the recycle flow. If you draw the box around the aeration basin influent and the secondary clarifier effluent then the RAS flow is not counted. |
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| | | Supreme Being
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Last Login: Yesterday @ 3:05:04 PM
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| | Sorry I misinterpeted. Listen to Dr.J. |
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| | | Forum Newbie
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Last Login: 4/6/2008 1:00:44 PM
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| may i know what is the formula for calculating detention time for settling? is it volume/flow rate?
i'm currently studying it, but not really understand, anyone has any webpage which contain useful information in this? |
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| | | Supreme Being
Group: Forum Members
Last Login: 7/2/2008 12:01:02 AM
Posts: 86, Visits: 550 |
| | What goes in, must come out, so just use the effluent flow in your calculation and not worry about all the other side streams that do not make a difference, if and only if you are calculating the plant as a whole for detention time. |
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