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

the pre- aeration structure. Minor " roping" of material around the diffusers is occurring that is likely due to the fibrous material passing the screening. Wastewater discharges from the pre- aeration basin to the primary clarifiers. Stationary weirs control the wastewater flow from the aeration basin to pre'- the individual primary clarifiers. It appears the flow from the pre- aeration basin is not equally split causing " dead zones" of unequal flows to the primary clarifiers. The IIiI strong presence of hydrogen sulfide ( H2S) at this location reinforced the idea that a portion of the flow is stagnant. H2S is also known to be generated due to the long length of pipe run from the pump stations to the headworks. Minor concrete corrosion was noticeable at the air wastewater interface in the aerated grit chamber and the pre- aeration basin. Figures 2- 6 and 2- 7 include photographs of the aerated grit chamber and the pre- aeration basin. I F:\2001\ Ol.0387. 000\Report\ R-4\041403 FINAL\ SEC 2. doc HAI#01.0387. 000 2- 9 04/ 14/ 03  Figure 2- 4 City of Fort WaltQn Beach Wastewater Treatment Plant Facilities Plan Mechanical Bar Screen Photos MechanicalBar Screen Mechanical Bar Screen - Side View F:\2001\ 01.0387. 000\Report\ R-4\ 041403 FINAL\SEC 2. doc HAI#01.0387. 000 2- 10 04/14/ 03  Figure 2- 5 City of Fort Walton Beach Wastewater Treatment Plant Facilities Plan Grit Cyclone and Classifier Photos Grit Cyclone Facing West Grit Cyclone and Classifier Facing North F:\2001\ 01.0387. 000\Report\ R-4\ 041403 FINAL\ SEC 2. doc HAI#01. 0387. 000 2- 11 04/ 14/ 03  Figure 2- 6 City of Fort Walton Beach Wastewater Treatment Plant Facilities Plan Pre- Aeration Basin Photos Aerated Grit Chamber and Pre- Aeration Basin Facing West Pre- Aeration Basin Facing South F:\2001\ Ol.0387. 000\Report\ R-4\ 041403 FINAL\ SEC 2. doc HAI#01.0387. 000 2- 12 04/14/ 03  Figure 2- 7 City of Fort Walton Beach Wastewater Treatment Plant Facilities Plan Pre- Aeration Basin Photos Aerated Grifc;hambef(}3ackground) and Pre- Aeration Basin ( For~ grol.nd) FacingNorth with Blow~rs On Pre- Aeration Basin Facing South With Blowers Off F:\2001\ 01.0387. 000\Report\ R-4\ 041403 FINAL\SEC 2. doc HAI#01.0387. 000 2- 13 04/ 14/ 03 III III 2. 3. 2.2 Primary Clarifiers ill The purpose of the primary clarifiers is to provide a quiescent zone for settling of heavier organic solids not removed in the screening, thus reducing the downstream 5- day carbonaceous biochemical oxygen demand ( CBODs) and total suspended solids TSS) load of the raw wastewater. ta I The City' s WWTP has two ( 2) 65- feet diameter circular primary clarifiers, with I operating sidewater depths of 12- feet. The concrete appears to be in good condition, however, the bridges to the clarifier drives are corroded. The primary clarifiers have a i total surface area of 6, 636 square feet, and have a design overflow rate at average daily flow of approximately 678 gpd/sf. Typical overflow rates for primary clarifiers range between 600 and 1, 000 gpd/sf. The primary criteria used when evaluating the I primary clarifiers are configuration, hydraulic loading rates, and the detention times of f! III these units. Based on the design flow of 4. 50 MGD and the configuration of the primary clarifiers, the following were determined: FWB WWTP Parameter At Desi n Flow 678 600 to 1, 000 Detention Time, minutes 191 90 to 150 ill till!! Based on the information provided above, both of these performance- limiting ill parameters are generally within the typical design standards used for sizing these types of facilities. However, it should be noted that historic problems associated with II the infiltration and inflow ( III) in the City's wastewater collection system may limit the treatment efficiency of the primary clarifiers during high rainfall periods. During periods of heavy rainfall, the III entering the City' s wastewater system could significantly increase the influent flow to the City' s WWTP, thus hydraulically i' overloading these units. Over the past few years, the City has been identifying II problem areas in their wastewater collection system, and has developed a program to reduce the III entering the system. The City' s on- going III program is addressing I these issues, such as minimizing inflow coming from the cross connections by private F:\2001\ 01.0387. 000\Report\ R-4\041403 FINAL\SEC 2. doc filii HAI#01.0387. 000 2- 14 04/ 14/ 03 IiIIi III individuals and infiltration through existing deteriorating manholes, and gravity sewer mams. filii The expected CBOD5 removal through the primary clarifiers should range between 30- and 45- percent. While no infonnation is maintained at the City' s WWTP to detennine the effectiveness of these units, there is no reason to expect that these units are not perfonning within these limits. it. Each unit can be bypassed to route the flow to the other clarifier during times of I required maintenance. I"';'. 1,;'. Sludge from the primary clarifiers is pumped to a gravity thickener, which in turn The pumping directs the sludge to the anaerobic digesters for further treatment. facilities consist of two ( 2) sets of two ( 2) piston pumps, four ( 4) total, for the I removal of primary sludge and scum from the two ( 2) primary clarifiers. The two ( 2) piston pumps were installed in 1999 to replace two ( 2) problematic centrifugal III pumps. The two ( 2) scum pumps are non- clog centrifugal type pumps. Both sets of till pumps are in good operating condition. Figure 2- 8 contains photographs of the primary clarifiers and Figure 2- 9 shows photos of the primary sludge pumps. It III II Ii F:\2001\ 01.0387. 000\Report\ R-4\041403 FINAL\ SEC 2. doc HAI#01.0387. 000 2- 15 04/ 14/ 03  Figure 2- 8 City of Fort Walton Beach Wastewater Treatment Plant Facilities Plan Primary Clarifiers Photos North Primary Clarifier South Primary Clarifier F:\2001 \ Ol.0387. 000\Report\ R-4\ 041403 FINAL\SEC 2. doc HAI#01.0387. 000 2- 16 04/14/ 03  Figure 2- 9 City of Fort Walton Beach Wastewater TreatmentPlant Facilities Plan Primary Sludge Pumps Primary Sludge Pumps F:\2001\ 01.0387. 000\Report\ R-4\ 041403 FINAL\ SEC 2. doc HAI#O 1.0387. 000 2- 17 04/ 14/ 03 I'll III 2.3.2.3 Rotating Biological Contactors ( RBCs) From the primary clarifiers, the wastewater flows by gravity to the RBCs. The system is made up of four ( 4) trains of five ( 5) rotating units. Each drum- shaped unit is 25 feet long and 10 feet in diameter fitted with eight ( 8) sectors of plastic media for the treatment of organic waste streams. A total of 18 of the 20 units have four ( 4) quadrants of plastic media; and the other two ( 2) units are a newer design having a six I 6) quadrant configuration. Each unit rotates the media through the wastewater on a horizontal shaft in a basin filled with wastewater that has undergone primary I treatment. The units are powered at one