Editor-in-Chief Elisabeth Lisican showcases a handful of features to read in the April 2017 issue of Water & Wastes Digest.
NAME: Englewood Water District Water Reclamation Facility (WRF)
LOCATION: Englewood, Fla.
PLANT SIZE: The district encompasses approximately 44.5 sq miles in Southern Sarasota County and Western Charlotte County on the western coast of Florida. The wastewater treatment facility has a current capacity of 3 mgd.
INFRASTRUCTURE: The district’s WRF is a 3-mgd extended aeration plant. The raw wastewater mixes with bacteria in the extended aeration process. The treated effluent goes through an aqua disc membrane filter or an activated carbon, sand and media filter, and the filtered effluent is chlorinated. After disinfection, the water is pumped to either the aquifer storage well or reclaimed water customers. Biosolids are pumped from the wastewater treatment plant to the centrifuge and de-watered. The biosolids are trucked to the N-Viro complex in Daytona Beach, Fla. for further treatment. The Class AA biosolids, produced from the dewatered sludge, may be used on farms, in parks and on playgrounds.
The Englewood Water District (EWD) was built in 1959 to oversee the operation and maintenance of water and wastewater services of the unincorporated area known as Englewood, Grove City, and Manasota Key. The district also provides wastewater collection and treatment for water customers who are connected to the sanitary sewer system.
With an annual growth rate of 3.3%, and the anticipated connection of all water customers to the sanitary sewer system, additional wastewater treatment was clearly needed.
The first expansion
District officials solicited Siemens Water Technologies to complete the first expansion project in 1996. The project consisted of screens, equalization basins, aeration tanks, clarifiers, aerobic digester tanks, traveling bridge filters, a chlorine contact chamber and wet weather storage pond. This 1.2 mgd treatment system was installed at a cost of $2.15 per gallon.
In 2000, the district awarded Siemens another contract—this time, worth $3.5 million—to expand the wastewater treatment plant installed in 1996. Siemens supplied a 1-mgd extended aeration process treatment plant to complement the existing 1.2-mgd facility. In addition, an existing concrete treatment plant was retrofitted into an influent wet well and surge tank. The expansion construction began in February 2001.
The district’s water reclamation facility has also recently been expanded to include a new control building that was built to withstand a Class 5 hurricane—obviously an important feature for a structure located on the Gulf of Mexico.
The total amount for both contracts given to Siemens in 1996 and 2000 was $5,615,674.
The district’s WRF is currently a complete mix activated sludge-based treatment facility. Three Siemens package treatment plants operate in complete mix mode at the plant. Because it operates either in extended aeration or in complete mix mode, the plant has the ability to meet all plant discharge limits.
The plant’s primary treatment facilities consist of an influent wet well that is fitted with a biofilter odor control system, static screens and a post-screening equalization tank that stores screened raw wastewater before it is pumped to the treatment units.
Each package treatment plant unit is equipped with a surge tank. The biological treatment process consists of complete mix aeration and secondary clarification. Settled effluent flows to a disk filter unit and the traveling bridge automatic backwash sand filter. Filtered effluent travels to a double-compartment chlorine contact basin where it undergoes high-level disinfection before moving on to a reclaimed water pumping station. The pumping station delivers reclaimed water into the EWD reclaimed water distribution system and then to customers for reuse.
Sludge generated by the treatment process is stored in two mixed or aerated sludge-holding basins. Sludge is de-watered on site in a centrifuge building. De-watered solids are transported by truck to a Florida Department of Environmental Protection (FDEP)-approved sludge processing plant where they become Class AA biosolids material.
The district is planning a three-phase expansion process, which will be carried out by the engineer CH2M Hill. Phase I will install a 1.2-mgd extended aeration treatment unit to provide backup capacity and additional unit process volume for future re-rating and expansion of overall treatment plant capacity. Phases II and III would involve expanding plant capacity by increasing the capacity of other plant unit processes and re-rating the treatment units to operate in the complete mix mode instead of the extended aeration mode.
Other current plans include the expansion of the reverse osmosis plant from 3 to 5 mgd capacity, ongoing testing of a recently built aquifer storage and recovery well and a general extension of the wastewater collection system throughout the district’s area.
Reclaimed water use
Water resources are becoming more limited in some areas of Florida, especially during certain periods of the year. To obtain a permit for expanded plant capacity, the EWD must show the FDEP they have attempted to expand the use of reclaimed water within their service area. Because of this stipulation, the water district continues to aggressively expand its reclaimed water customer base and continues to maintain long-term reclaimed water reuse agreements with many customers in its service area.