Water Environment Federation (WEF) Discussion ForumsWater Environment Federation (WEF) Discussion Forumshttp://www.wef.org/TechnicalDiscussions/jfuller@wef.orgMon, 08 Sep 2008 02:27:37 GMT20http://www.wef.org/TechnicalDiscussions/Topic1658-16-1.aspxWhat 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.Thu, 10 Apr 2008 20:24:39 GMTBill Hhttp://www.wef.org/TechnicalDiscussions/Topic1658-16-1.aspxmay i know what is the formula for calculating detention time for settling? is it volume/flow rate?<br>i'm currently studying it, but not really understand, anyone has any webpage which contain useful information in this?Sun, 06 Apr 2008 13:05:26 GMTshlrenehttp://www.wef.org/TechnicalDiscussions/Topic1658-16-1.aspxSorry I misinterpeted. Listen to Dr.J.Fri, 05 May 2006 21:20:30 GMTJerryhttp://www.wef.org/TechnicalDiscussions/Topic1658-16-1.aspxNow 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 <STRONG>the aeration basin only</STRONG> 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.Fri, 05 May 2006 16:16:02 GMTdavid jenkinshttp://www.wef.org/TechnicalDiscussions/Topic1658-16-1.aspxDon'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.<P>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.Thu, 04 May 2006 14:52:51 GMTJerryhttp://www.wef.org/TechnicalDiscussions/Topic1658-16-1.aspxI 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.<P>How do you mathematically prove that the average detention time is the same with or without recirculation flow?</P><P>Thank you for your help,Thu, 04 May 2006 13:03:58 GMTLyle Milbyhttp://www.wef.org/TechnicalDiscussions/Topic1658-16-1.aspxThe 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!Thu, 04 May 2006 11:48:11 GMTdavid jenkinshttp://www.wef.org/TechnicalDiscussions/Topic1658-16-1.aspxI 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.<P>Thank you,Thu, 04 May 2006 10:55:03 GMTLyle Milby