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

since 1992 and there has been a continued successful commitment on the City' s part to minimize III impacts to the system. II' Ii Based on the data review for the period beginning in January 1998 and ending in June 2002, the City's WWTP produces an effluent quality that consistently meets the permit c requirements for effluent disposal. There were times when the effluent total suspended solids ( TSS) directed to the sprayfield at the golf course exceeded the daily maximum 1 11.: F:\2001 \ 01.0387.000\ \ -4\041403 FINAL\ Excecutive Summary 041503. doc ReportR HAI# 01.0387. 000 ES- 3 04/ 14/ 03 C' J III requirement of 5 mg/l. For the period beginning on October 30, 1998 and ending on June 30, 2002, the permit condition for this parameter was exceeded six ( 6) times. Effluent I.',"'.. II pumped from the City' s WWTP to the restricted access sprayfield site met the effluent criteria on a consistent basis, however there were times the levels exceeded the permitted I requirements. The sludge wasted from the wastewater treatment process is treated using a series of I processes, which include anaerobic digestion and dewatering. The residuals produced from these processes are considered a Class B sludge under the provisions of the sludge I rule Chapter 62- 640, Domestic Wastewater Residuals, FAC, and the Federal Sludge Rule Title 40, Code of Federal Regulations ( CFR), Part 503. Since the City currently disposes I its residuals at the current agricultural use site ( Earl King Fanus in Freeport, Florida) quarterly sludge analyses are prepared. All have been within standards as outlined in the I current state and federal regulations. To address the future requirements of the system, the analyzed data consisted of historical I population and wastewater customer billing data provided by the City, historical plant flow data as reported in the FDEP DMR' s, and a land use analysis of the service area. m Utilizing this data, conclusions regarding the population and wastewater flow projections fIIIII were developed for this system in order to characterize future trends within the City of I Fort Walton Beach wastewater service area. Based on this infonnation, the projected flow rates were adjusted using new infonnation regarding development growth and trends within the City' s wastewater service area and the on- going III reduction program. As a result, the influent wastewater flow to the City' s WWTP is anticipated to remain generally at the present annual monthly average flow of 2.421 MGD to a maximum 5- iIIII percent increase in 10 years to 2. 542 MGD in 2012. ES.5 ALTERNATIVE SECONDARY TREATMENT UPGRADE OPTIONS II The City' s existing WWTP has been experiencing mechanical failure with the aging RBC' s over the past several years and the City is investigating treatment alternatives to I replace the fixed film process with the same type of process or a suspended growth activated sludge process. A survey determined that there are only two ( 2) WWTP' s with including the City of Fort Walton Beach, out of I capacities greater than 1. 0 MGD, approximately 283 WWTP' s in the State of Florida that utilize RBC' s as their primary means of wastewater treatment. Furthennore, it should be noted that of that total there I F:\2001\ 01.0387.000\ Report\ R-4\ 041403 FINAL\Excecutive Summary 041503. doc HAI# 01.0387. 000 ES- 4 04/14/ 03 Ii I are only five ( 5) facilities that use the fixed film technology ( trickling filter, RBC' s, etc.) and the remaining 278 facilities use the activated sludge technology as the primary means M.. of wastewater treatment. I There are three ( 3) primary alternatives available to the City to correct the City' s WWTP' s RBC operational issues and improve the overall treatment capabilities of this I facility including the following: 1. Rehabilitating the existing RBCs and replacing damaged units. I 2. Retrofitting the RBC basins with an advanced fixed film process, such as I the WesTech STM- Aerotor TM system. I 3. Abandoning the RBC process and replacing it with a conventional suspended growth activated sludge process, such as an oxidation ditch. The above three ( 3) treatment alternatives are being presented to the City and the Florida Department of Environmental Protection ( FDEP) for planning, design and construction of either a new treatment process or rehabilitated facility, which will provide reliable wastewater treatment to the customers within the City' s service area. A 10- year planning period was selected for this evaluation. till till Utilizing historical flow data from 1998 to the present and influent CBODs and TSS concentrations expected to remain around 200 mg/l, the City will maintain the existing III capacity of 4. 50 MGD, which will accommodate future flows beyond the planning period iii discussed in this report. Sizing the facilities for this influent flow should provide sufficient treatment capacity well beyond the year 2012, assuming a flow rate increase of h$i 5- percent over the 1 O- year planning period. ES. 5. 1 Rehabilitating Existing RBC Process I To utilize the existing RBC process, several items were addressed to determine the feasibility of this alternative. This alternative requires replacement of the i failing RBC shafts, mechanical drive units, media, and rehabilitation of the concrete structure to bring the existing facilities to an acceptable level of service. F-~~ In addition, this alternative includes the installation of torque sensing devices for J'.. J iii F: 2001 \ \ 0 1.03 87 .000\ Report\ R-4\ 041403 FINAL Excecut \ ive Summary 041503. doc lilt HAI# 01.0387.000 ES- 5 04/ 14/ 03 ill II!!! 1:>:\ the individual RBC shafts to signal shaft rotation stress when a malfunction occurs within the assembly. It is anticipated that the installation of a torque- I sensing device should reduce damage to the units by disrupting power to the motors and subsequently stopping rotation when a malfunction occurs. I Costs for rehabilitating the existing RBCs and replacing damaged units are based I on unit prices obtained from recent bid experience as well as information obtained from manufacturers of the equipment to be supplied. Prices reflect the anticipated costs if the project were currently bid. The total probable opinion of cost for the I upgrades to the City' s WWTP RBC process is estimated to be approximately 2, 650,000. Based on the proposed plan described above it is anticipated that the I overall program would be completed within 26- months from inception of the project. I ES. 5. 2 Retrofitting RBC' s to WesTech STM- AeratorTM I The second alternative is the WesTech STM- AerotorTM assembly which consists of P- 24 cylindrical polypropylene segmented pipe media bundles surrounding a steel i. center shaft and galvanized steel support framework. This system is similar to the City' s existing RBC system. The center shaft consists of a steel pipe with solid steel ends of hardened stainless steel bushings. As with the RBC process, the WesTech STM- AerotorTM unit utilizes a gear reduction drive, which is powered by a 5 horsepower ( HP) motor. The assembly measures approximately 10 feet in ill diameter and 15 feet in length and requires a minimum wall height of 11.5 feet. lflii! III The WesTech system operates with the media 75- percent to 85- percent submerged, and similar to the RBC process, the WesTech system utilizes several basins to accommodate the rotating assemblies. The existing concrete basins have a water depth of approximately 6. 0 feet and, in addition to the basin rehabilitation discussed in Alternative 1; the existing basins would require substantial modifications to increase the water depth to the required level. The existing basin 1'"+ 0' walls would require an extension of approximately 4. 5 feet to accommodate the WesTech STM- AerotorTM components, which would provide 2 feet of freeboard I and a one ( 1) foot clearance between the assembly and the bottom of the basin. Extending the existing walls would substantially increase the moment transferred to the tank base slabs, which would necessitate lateral support of the walls, which I I F:\2001\ 01.0387. 000\ \ -4\041403 FINAL\ Excecutive Summary 041503. doc ReportR HAI# 01.0387. 000 ES- 6 04/ 14/ 03 i. III r is difficult and expensive. Considering the cost to rehabilitate and modify the existing basin structure it is assumed that a new structure would be constructed to I accommodate the WesTech system for this alternative. The conversion to this activated sludge process will also require recycle pumping from the secondary I clarifiers. This return activated sludge ( RAS) is a necessary component for this option, and will require the addition of recycle pumps, recycle wet well, yard piping, and