1983-10-26 Workshop Meeting - Laserfiche WebLink

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.Ji.. '-'__II",71"t't'i;F~1t;;1;:r>t:,ti;1'f17-!'ij_'1H11i111111m11UJ_l~"tIlIII"'" ..'-'H____. Rf1IfIlmiU-liZ'J" .'!'!!!! e e Turner Collie (6Braden Inc. July 29, 1983 Mr. Jerry L. Hodge City of La Porte .,. Page Two At the peak flow rate of 9.375 mgd, the maximum water surface elevation in the headworks will be 25.52 under the bypass . condition. This will result in a freeboard of 1.48 feet, which we also consider acceptable. Our conclusion is that the l8-inch sluice gate in the bypass channel is adequate if the remaining gates are modified to a 3G-inch width. During periods when the grit chamber is out of service for cleaning or maintenance, the raw sewage pump station pumps should be controlled so that the flow rate from the station does not exceed the design peak flow of 9.375 mgd (G,500 gpm). The l8-inch sluice gate in the headworks bypass channel is adequate and we recommend that no modifications be made to that gate. 2. WASTE SLUDGE PIPING - check hydraulics of piping system for transfer of waste sludge between the digester and the thickener There have been a series of problems with clogging of the waste sludge transfer pipe between the digester and thickener. The pip~ is 8-inch diameter. There is over 200 feet of pipe bet.een the thickener and the digester, and over 350 feet of equivalent length including fittings. The waste sludge is not pumped from the digester to the thickener. The difference in water surface elevations between the digester and the thickener provides the head to overcome friction loss and cause the sludge to flow to the thickener. We have analyzed the hydraulics of this piping system for a wide range of possible operating conditions. Our analysis indicates that the probable waste sludge flow rate in this pipe is 150 to 200 gpm, with a corresponding range of velocity of 0.96 to 1.28 feet per second in the pipe during wasting periods. Since the wasting operation should not be continuous, ther~ should be no flow at times during the day. In fact, the wasting period should not exceed 2.5 hours at the current plant design rate and 3.8 hours at the future design rate. Under the -most favorable operating conditions, our analysis shows that the sludge flow rate will be approximately 300 gpm during wasting periods, with a corresponding velocity of 1.91 feet per second. "