Imagine pleasantly strolling through beautiful, serene, breathtaking botanical gardens when suddenly you stumble upon a wastewater treatment plant. The sweet aroma and sights of various types of flowers and plants are suddenly replaced by an unsightly treatment tank, blower noise and distinct odors. This is a scene that Powell Gardens, a privately owned botanical garden attraction outside of Kansas City, Mo., did not want for its thousands of annual visitors. When the 915-acre facility constructed a new visitor center and cafeteria to accommodate its patronage, it required a cost-effective, onsite wastewater treatment system that could handle variable flow conditions while remaining aesthetically discrete. Daily patronage can vary from 100 to 3,000 depending on the weekday and scheduled special events.
Taking all of these factors into consideration, the unique, below-grade Modular FAST aerobic process by Smith & Loveless was selected and designed. The system design was based on an average daily attendance of 500 visitors—40 lb BOD per day at 7,500 gal per day. Following a primary septic sized for 24-hour detention, the wastewater encounters the Modular FAST System for up to 90% BOD removal. Equally as important for this application, the system installs underground, making it virtually out of sight yet still accessible at grade.
The fixed-film Modular FAST system provides a high surface area to volume ratio with its completely submerged media while air distribution provides sufficient oxygen and mixing. Bacteria exist in both the suspended and attached growth phases, providing the benefits of both a CMAS process and an attached growth system. The benefit of attached growth is key to countering the flow variation experienced on a day-to-day basis, including preventing solids washout after surges in the flow and maintaining sustained biological activity during the low flow periods. The higher level of bacterial concentration produces a longer sludge age, making nitrification and denitrification much easier to achieve should it ever become necessary under its permitting guidelines.
Modular FAST media provides a stable environment for the bacteria to grow, eliminating the need for return activated sludge. Instead of requiring a clarifier, a zone underneath the media provides a settling area for biological solids that slough off the media. Consequently, this zone has as much surface area as the aeration zone, which allows for a conservative settling rate of the biological solids that slough off. The settling sludge anaerobically decomposes in the underneath zone. This results in high quality effluent as seen in the post-installation testing. BOD and TSS effluent data remained consistently less than 10 mg/L.
Powell Gardens is a private facility, which relies on membership fees, merchandising and concession revenue and fundraising to maintain operation. Thus, minimizing operation and maintenance concerns was another important factor in selecting the FAST process. Modular FAST system contains no filters to clean or replace, and has only one moving part—the remote air blower. No daily or weekly adjustments are required on the actual biological process or sludge return calculations. The only operational control is the periodic maintenance of the blower (the system's only mechanized part) and an occasional measuring of the sludge level within the tank. The only sludge wasting is handled by a septic tank pumper truck on a quarterly or semi-annual basis. Powell Gardens does not have to allocate extensive dollars toward staffing, servicing or maintenance and can instead preserve precious funds for the betterment of the gardens and their patrons.
Modular FAST is often applied as pretreatment prior to leach fields, drip irrigation or city sewers, but in the Powell Gardens case, the desired aesthetics and system proficiency made it ideal for draining into a constructed wetland and ultimately to a nearby stream. With the Modular FAST system in place, Powell Gardens' visitors can fully enjoy the sights and scents of the natural surroundings while staff can focus on the garden's development.
For more information, contact Darby Ritter at [email protected] .
