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

in the treatment process train, each having a diameter of 70- feet each with an operating I side- water depth of 12- feet. The waste sludge from the clarifiers is pumped to the gravity thickener and the first- stage anaerobic digestion basin. As with the primary clarifiers, each final clarifier can operate independently during times of required maintenance. I The City has budgeted to perfonn maintenance to the secondary clarifiers, which would be I relevant for both processes. Based on our inspection of the final clarifiers, no additional capital expenditures are necessary to accommodate either of the treatment process alternatives evaluated. I 5. 6 DISINFECTION E From the secondary clarifiers, the effluent flows by gravity to the chlorine contact chamber. The chlorine contact chamber consists of a single baffled chlorine contact basin. The basin is cast- in- place concrete with baffles constructed of concrete filled CMUs. The chlorine contact chamber basin is approximately 40 feet long by 40 feet wide with a maximum operating sidewater depth I,; i:i.,,~... f,$ of approximately 9 feet. The basin has a total working volume of approximately 16, 000 gallons. The chlorine residual sampling for R001, the onsite sprayfield, is taken at the chlorine contact I.", chamber. The sample location for R002, the sprayfield at the golf course, is 100 feet north prior to the golf course' s above ground storage tank and after the after the chlorine injector box in the I effluent discharge pipe. However, a primary concern with this basin is that it cannot be taken off-line to maintain and clean the tankage. III F:\2001\ 01.0387. 000\Report\ R-4\ 041403 FINAL\SEC 5. doc HAI#01- 387. 00 5- 5 041403 if ill f' c:.': The chlorination facilities at the City' s WWTP consist of two ( 2) 500 pounds per day (lbs./ day) filii! gas chlorinators. During nonnal operation there are two ( 2) cylinders on- line connected to a single 500 day chlorinator and an automatic switchover at each tank, which is activated when lbs./ operating pressure reaches a minimum value. Feed water for the chlorine solution is provided at I! II the facility by drawing off the effluent supply. In addition, the chlorine storage building is equipped with a chlorine leak detector. The chlorination unit is equipped with a remote injector I!."..' that is located immediately downstream of the Parshall flume. The chlorine feed rate is I automatically controlled for the flowmeter transmitter located at the Parshall flume. I At this time, the existing disinfection facilities are adequate to meet the City' s wastewater disinfection requirements although the chlorine contact chamber requires rehabilitation. An I estimated cost of $ 125, 000 has been allocated to rehabilitate the existing chlorine contact chamber. This cost includes sealing the perimeter walls with epoxy and reconstructing the I interior CMU walls; however, the improvements do not include costs for constructing an additional basin to accommodate the ability to bypass the structure. II 5. 7 EFFLUENT FILTERS I A sidestream of effluent from the City' s WWTP is used to irrigate the City public golf course. The WWTP effluent is passed through a denitrification filter prior to transmission to the golf i." E.'. J i:') course to reduce nitrogen levels prior to application. The denitrification filter consists of four (4) Parkson Dynasand trains each with three ( 3) units. Originally, methanol was to be added to C iii flows entering the filter for nitrogen removal, however, this chemical was never used. Polyaluminate chlorate is currently added to the effluent prior to the filters as a coagulant to aid III in suspended solids and turbidity control. Effluent from the filters is chlorinated prior to gravity feeding to the golf course storage tank. Additional filter capacity is necessary to treat the entire wastewater flow regardless of which alternative is chosen. The existing filters have a capacity of approximately 2. 1 MGD and approximately 2.4 MGD of additional capacity is required to treat the average daily flow through the effluent filters, if operated in the denitrification mode, which would be required if the RBC H,;~ option is used. However, for the MLE alternative nitrogen is removed in the MLE process, the existing filters can treat approximately 3. 1 MGD. Therefore, approximately 1.4 MGD of additional capacity would be required. lilt F:\2001\ 01.0387. 000\ \ - 4\ 041403 FINAL\ SEC 5. doc ReportR HAI#01- 387.00 5- 6 041403  The cost to construct additional denitrification filtration facilities to treat 4. 5 MGD is estimated to be $ 812, 500 including engineering, contingency, and pennitting. Denitrification filtration is 1J not required for the MLE process since this process achieves nitrogen removal to less than 5 mg/l. However, the MLE process requires additional filters to accommodate the additional flows to treat 4. 5 MGD at an estimated cost of $ 187, 500, which includes engineering, ill contingency, and pennitting. j II 5. 8 RESIDUALS MANAGEMENT FACILITIES I The City' s residuals management facilities consist of a conventional gravity thickener, a two- stage anaerobic digestion system and a vacuum drum dewatering system. These facilities are I utilized to stabilize and dewater the sludge generated in the treatment process. I Sludge from the primary and secondary clarifiers is pumped to the gravity thickener. From the gravity thickener, the thickened sludge is pumped to the primary or first stage of the anaerobic digestion tame The facility' s anaerobic digesters are circular concrete tanks, 60- feet in diameter I with a side water depth of approximately 22- feet. The total combined volume of both anaerobic digesters is approximately 125, 000 cubic feet. The digester supernatant is recovered and I returned to the headworks of the WWTP for treatment. I Two ( 2) vacuum drums are utilized to dewater the sludge prior to transport by the City. Filtrate drained from the sludge is collected and also pumped to the head works of the facility for I treatment. Dewatered sludge is removed from the vacuum filters and hauled to a permitted Agricultural Use Site, consisting of268 acres. The evaluation of the residuals management facilities, historical data, and the operation of the facilities indicate the system is adequate for the present design condition of 4. 50 MGD. As noted I in Section 2, the State of Florida is presently evaluating the treatment and disposal of Class B sludges, which includes the type of sludge that is treated and ultimately disposed by the City. I Based on recent workshop meetings, it appears that the State are leaning toward either banning the land application of Class B sludges or significantly restricting their uses by increased set- I backs, increased monitoring, site specific pennits and/or liability issues regarding the ultimate use being switched to the land owners. If Class B residuals are banned in the State of Florida, the City can either convert their treatment system to treat the sludges generated to meet Class A t requirements or dispose of their sludges in a landfill, similar to the disposal of grit and t fit F:\200 1\0 1.0387 . 000\Report\ R-4\ 041403 FINAL\SEC 5. doc HAI#01- 387. 00 5- 7 041403 I screenings. At the present time, Class A treatment options were not investigated further. One of the primary reasons that a conversion to a Class A treatment process would be needed is that it I may impact the land application practices presently used at the Earl King land application sites, based on the type of process used, and the agronomic requirements of the site. E 5. 9 PLANT RECYCLE PUMP STATION I The City' s WWTP pump station is adjacent to the grit cyclone and classifier which receives plant flow from the vacuum coil drums filtrate, anaerobic digesters, gravity thickener supernatant and I miscellaneous plant drains. The discharge from this station is pumped to the headworks for treatment and consists of a cast- in-place concrete wetwell with three ( 3) submersible pumps. I This pump station is severely corroded, specifically at the air/wastewater interface and freespace above the wastewater level in the wetwell. Moreover, the aboveground piping network at the I pump station exhibits severe corrosion. City operating staff has reported pump failures and subsequent repairs due to aggregate and debris from the deteriorating concrete walls entering the A new recycle pump station is currently being constructed and will not be included in I pumps. this cost analysis. The new pump station will include a new wetwell, submersible pumps, and piping and is common to both secondary treatment processes. I 5. 10 EFFLUENT DISPOSAL I The City' s WWTP is currently pennitted to discharge 4.50 MGD of treated wastewater. The I effluent from this facility is disposed of by reuse land application; restricted access sprayfield and public access golf course. The existing pennit conditions are as follows: Ii flow to restricted land 1. 3. 1 MGD maximum monthly average daily access application slow-rate sprayfield irrigation system ( ROO 1). Discharge is to a 400 acre site adjacent to the WWTP. 2. 1. 55 MGD maximum monthly average daily flow to public access land lilt application slow-rate sprayfield