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

include the following: ill 1. Screening and Pretreatment m 2. Primary Clarifiers 3. Secondary Treatment I 4. Secondary Clarifiers 5. Effluent Filtration 6. Disinfection L. 7. Recycle Pump Station F:\2001\ 01.0387. 000\Report\ R-4\ 041403 FINAL\ SEC 5. doc HAI#01- 387.00 5- 1 041403 i. II II I Each unit process is previously described in detail in Sections 3 and 4. Generally, the raw I wastewater passes through a mechanically cleaned bar screen to remove large inert solids. The screened wastewater enters an aerated grit chamber prior to flowing to the pre- aeration basin. I From pre- aeration the wastewater stream is directed to two ( 2) 65- foot primary clarifiers. The primary clarified wastewater is then biologically treated utilizing fixed film RBC units. After biological treatment, the mixed liquor is settled to remove TSS in the two ( 2) 70- foot secondary I clarifiers. After final clarification the secondary effluent is chlorinated for disinfection. The disinfected effluent either flows to a reclaimed water holding pond or through a denitrification I filter prior to a golf course for irrigation. The sludge withdrawn from the primary and final clarifiers is pumped to a gravity thickener prior to entering the anaerobic digesters. From the I anaerobic digesters the solids are pumped to a dewatering station after the addition of lime for stabilization. Supernatant from the digesters is pumped back to the headworks of the facility for I treatment. 5. 2 SCREENING AND PRETREATMENT I Wastewater is pumped from the collection system and enters the City' s WWTP through a force I main that discharges into a common channel at the aerated grit chamber. Prior to entering the aerated grit chamber, the influent passes through a mechanically cleaned bar screen. Due to the E City' s use of comminutors in the their wastewater collection system, the majority of the influent has been ground or shredded to very fine material prior to reaching the WWTP. As a result, C some of the fine material passes through the screen and has entered the wastewater treatment process causing roping problems in the aerated grit chamber and pre- aeration basin. To reduce f"" the fine material that enter the wastewater treatment process a cost of $25, 000 has been allocated I. to replace the components of the existing bar screen with screening mesh that has smaller opemngs. Solids from the aerated grit chamber are directed to a grit cyclone and screw classifier prior to disposal. The City' s WWTP staff has experienced significant clogging in the grit feed line to the cyclone and classifier. The problem appears to be associated with the inability to flush the lines II prior to withdrawal of the grit, which becomes compacted in the lines during operation. To address the existing clogging problem associated with the grit feed line $ 18, 750 has been III allocated to install a high pressure flushing line. II F:\2001\ 01.0387.000\ \ -4\041403 FINAL\ SEC 5. doc ReportR HAI#01- 387. 00 5- 2 041403 III' IiII I I From the aerated grit chamber, the wastewater flow enters the pre- aeration basin. To be able to hydraulically split the wastewater flows between the two ( 2) primary clarifiers a total of $25, 000 I has been allocated for the installation of weir gates. I Concrete corrosion is evident at the air wastewater interface in the aerated grit chamber and the In addition, the epoxy coated steel support structure of the grit cyclone is pre- aeration basin. severely corroded. The deteriorated pretreatment structures require rehabilitation due to I corrosion to the concrete structures and the grit cyclone support structure. The rehabilitation process will include approximately 1, 000 square feet of epoxy coating to resurface the concrete I surfaces of the preaeration basin as well as resurfacing the support structure. A cost of $62, 500 has been allocated to resurfacing the pre- treatment structures, which includes surface preparation, I coating and any bypass pumping required. I The screening and pretreatment facilities are common to both the RBC process and MLE and pretreatment process. The total capital cost associated with the screening facility rehabilitation including engineering, contingency, and pennitting is estimated to be $ 131, 250. I 5. 3 PRIMARY CLARIFIERS I From the pre- aeration basin wastewater discharges to the primary clarifiers. The City' s WWTP I utilizes two ( 2) 65- foot diameter circular primary clarifiers, with operating sidewater depths of 12- feet. The concrete appears to be in good condition, however the bridges to the clarifier drives fill corroded. It is estimated that it will cost approximately $ 312, 500 for rehabilitation of the I. are clarifiers drive units for these two ( 2) units. This capital expenditure is associated only with the RBC process since the MLE process does not require primary clarification. For both treatment alternatives, $ 12, 500 has been allocated for the removal and disposal of clarifier existing drive units. fill Sludge from the primary clarifiers is pumped to a gravity thickener, which in turn directs the sludge to the anaerobic digesters for further treatment. The pumping facilities consist of two ( 2) sets of pumps for a total of four ( 4) pumps. The pumps are used for the removal of primary u~ sludge and scum from the two ( 2) primary clarifiers. The pumping facilities were inspected and were detennined to be in good operating condition, and therefore, no improvements are f,:, ,'::; necessary. However, for the MLE process these pumps and the structure will be abandoned in place. The total capital expenditure including engineering, contingency, and pennitting to III F:\2001 \ 01.0387. 000\Report\ R-4\ 041403 FINAL\ SEC 5. doc HAI#01- 387. 00 5- 3 041403 III it II rehabilitate the primary clarifiers as related to the RBC process is estimated to be $ 325, 000. The total primary clarifier capital cost allocation including engineering, contingency, and pennitting I...'.'.'.. I for the MLE process alternative is estimated to be $ 12, 500. I 5.4 SECONDARY TREATMENT For the existing process, the wastewater stream discharges from the primary clarifiers by gravity I.. to the RBC process units. The RBC system is made up of four ( 4) trains with five ( 5) rotating units. Each unit is 25 feet long and 10 feet in diameter fitted with eight ( 8) sectors of four ( 4) I quadrants of plastic media for the treatment of organic waste streams. Each unit slowly rotates the media through the wastewater on a horizontal shaft in a basin filled with wastewater that has I undergone primary treatment on a continual mechanical basis. I In each of the WWTP' s four ( 4) treatment trains there are three ( 3) standard density media units and two ( 2) high density media units. As discussed previously, the RBCs have proven to be labor intensive from an O& M perspective. The City experiences routine O& M issues with the I media sectors separating from the RBC units which makes the assembly unbalanced, motor/ drive unit operation difficulties, and problems with the concrete joints of the basin end. Due to the I O& M problems associated with RBC' s a number of utilities in the State of Florida have converted their treatment process from RBC' s to an activated sludge process. Since 1995, of the I eight ( 8) facilities with capacities greater than 1. 0 MGD there are only two ( 2) remaining utilities that currently use RBC' s as their primary treatment process. To improve process perfonnance and reliability the replacement of the RBC units, drive systems, and weir gates is necessary. The M RBC process rehabilitation includes an aeration system, dissolved oxygen monitoring, and II rehabilitation of the RBC structure. These improvements are recommended to improve process efficiency. The total capital expenditure including engineering, contingency, and pennitting III allocated to RBC rehabilitation is estimated to be $ 2, 650,000. 1 For the MLE process alternative the primary clarifiers and RBC basin would be utilized for flow I equalization. The clarifiers and RBC basin would be equipped with mixers, rails, supports and related components to stir the contents prior to entering the oxidation ditches. To utilize the I RBC basin for flow equalization, a cost of $25, 000 has been allocated for RBC unit removal and disposal. A total capital cost of $187, 500 is allocated to converting the existing basins to flow fill equalization. j. F:\2001\ Ol.0387. 000\Report\ R-4\041403 FINAL\SEC 5. doc HAI#01- 387.00 5- 4 041403 I I The MLE process and sequencing to bring this process online is detailed in Section 4. This process would include the construction of a new secondary process facility, W AS/RAS pumping I facility, and associated yard piping. In addition, it is anticipated that the MLE anoxic/ oxidation ditch structure will require additional excavation to achieve the hydraulic profile necessary to I eliminate the need for additional pumping. A capital cost of $312, 500 has been allocated for the additional excavation necessary for the oxidation ditch construction. The total capital expenditure allocated to the construction of the oxidation ditch and associated equipment I including engineering, contingency, and pennitting is estimated to be $ 4,262, 500. I 5. 5 FINAL /SECONDARY CLARIFICATION I From the RBC basin, the effluent flows to the final clarifiers. There are two ( 2) circular final clarifiers