Fort Walton Beach Council agenda — 04-29-03 workshop agenda — reading text

end of the shaft by a 7. 5 horse- power, 460 volt, 1180 rpm, 10 amp, three- phase motor. Figure 2- 10 shows the RBC basin with covered and uncovered RBCs and Figure 2- 11 shows individual RBC units outside of Ii the RBC basin. Figure 2- 12 shows an example of the end of drum shaft and motor in operation. In each of the City' s four ( 4) treatment trains there are three ( 3) standard density ill media units, with a surface area of 112,480 square feet each, and two ( 2) high density media unit at 157, 000 square feet each. Two ( 2) standard density units are the first r units in the process stream, followed by a baffle, then one (1) standard density unit, followed by a another baffle, which are followed by the two ( 2) high- density units. The total media area in the RBC system of the four ( 4) trains of five ( 5) units is 2, 606, 000 square feet. Originally, RBC systems in the United States were designed pi! based on hydraulic loading. However, the design approach shifted and focused more on total BOD per unit of surface area ( pounds of BOD per square feet) and more fill specifically, soluble BOD per unit of surface area (pounds of soluble BOD per square j feet). Based on the design flow of 4. 50 MGD, the following hydraulic loading rate infonnation was calculated: FWB WWTP t Parameter At Desi Hydraulic Loading Rate, gallons per day per 1.7 0. 75 to 2. 0 III! square foot ( gpd/st) fill At a 4.50 MGD design flow, the allowable BOD loading for the City' s RBCs range i; from 104 mglL to 208 mglL. These values were calculated based on a typical total BOD per day per 1, 000 square feet range of 1.5 to 3. 0. I F:\2001\ Ol.0387. 000\Report\ R-4\041403 FINAL\SEC 2. doc P! HAI#01.0387. 000 2- 18 04/ 14/ 03  Figure2~10 City of Fort Walton Beach Wastewater TreatmentPlant Facilities Plan RBC Basin RBC Unit without Covers during Maintenance F:\2001\ Ol.0387. 000\Report\ R-4\ 041403 FINAL\ SEC 2. doc HAI#01.0387. 000 2~19 04/ 14/ 03  Figur~ 2- 11 City of Fort Walton Beach Wastewater Treatment Plant Facilities Plan Individual RBC Units Individual RBC Unit Individual RBC Unit F:\2001\ 01.0387. 000\Report\ R-4\ 041403 FINAL\SEC 2. doc HAI#01. 0387. 000 2- 20 04/ 14/03  Figure 2- 12 City of Fort Walton Beach Wastewater TreatmentPlant Facilities Plan RBC Drum Shaft and Motor RBC End Drum Shaft RBC Motor F:\2001\ Ol.0387. 000\Report\ R-4\ 041403 FINAL\ SEC 2. doc HAI#01.0387. 000 2- 21 04/ 14/ 03  to the media In the RBC process, the primary treated/ screened wastewater is applied becomes coated I through which the flow percolates. The surface of the media quickly The with a viscous, jelly-like, slimy substance containing bacteria and other biota. biota remove organics by adsorption and assimilation of soluble and suspended constituents. J The The quantity of biomass produced is controlled by the available organic load. W amount of biomass on the media surface increases as the organic load and strength is increase until a maximum effective thickness is reached. This maximum thickness 2 controlled by physical factors, including hydraulic dosage rate, type of media, type of and the nature of organic matter, amount of essential nutrients present, temperature, IJI!I I biological growth. fill As previously noted, there are 20 total RBC units with a plastic type media at the I the unit by gravity feed. No City's WWTP, and the influent wastewater is applied to Based the historical flit forced air ventilation is provided into the RBC basins. on i is not required, which is ill performance of the City' s RBC units, forced air ventilation normally installed to improve treatment efficiency. II Since the Effluent from the RBC basin is split between two ( 2) final clarifiers. fill effluent from the RBC discharges into two ( 2) pipes installed at each of the RBC for the WWTP basin, similar to the flow from the pre- aeration basin, it is difficult staff to adjust effluent discharges to ensure equal flow to each final clarifier. III maintenance The RBCs have proven to be labor intensive from an operation and and maintenance issues with the perspective. The City experiences routine operation motor/ drive media sectors separating from units, RBC units becoming unbalanced, the basin. The Ii unit operation difficulties, and problems with the concrete joints of 15 years for RBC repair and City has spent in excess of $1, 000, 000 over the past 000 in media replacement. The City' s capital improvement plan includes $ 590, iii funding over the next five ( 5) years starting in fiscal year 2002- 2003 for media shows photographs of a failed RBC repair/replacement for the RBCs. Figure 2- 13 Ii unit following the displacement of the media sector from the unit. I I F:\2001\ 01.0387. 000\Report\ R-4\041403 FINAL\ SEC 2. doc 2- 22 04/ 14/ 03 HAI#01.0387. 000 l. i  Figure 2- 13 City ofFQrt Walton Beach Wastewater Treatment Plant Facilities Plan Failed RBC Unit Photos RBC Drum with Missing Media Sector Failed RBC Media F:\200 1 \ 0 1. 0387 . 000\Report\ R-4\ 041403 FINAL\ SEC 2. doc 2- 23 04/ 14/ 03 HAI#01.0387. 000  lJj' lin 1 r", II fill i' I' 2. 3.2.4 Final/ Secondary Clarification From the RBC basin, the effluent flows by gravity to the final clarifiers. Similar to Ii the primary clarifiers, the final clarifiers provide a quiescent zone for settling of the effluent from the RBC process. The clarified effluent from these units then flows by solids in gravity to the chlorine contact basin for disinfection. A portion of the settled the final clarifiers are periodically wasted to the digestion units. It There are two ( 2) circular final clarifier basins at the City's WWTP. Each of the basins is 70- feet in diameter with an operating side- water depth of 12 feet. The final clarifiers have a total surface area of 7, 696 square feet, and have a design overflow II rate at average daily flow of approximately 585 gpd/ sf. Typical overflow rates for