Main design components
Unloading bays. Drivers connect their truck’s discharge pipe to a 4-inch OPW Engineered Systems Kamlok Quik Disconnect, located in the sump adjacent to the drain gate, which is depressed to allow for a full tanker drain. Both the bay drain grate and the pipe connection sump are drained to the structure drain sump-and-pump station, which returns flow to the headworks area.
Automated flow control and recordkeeping. The driver swipes a Dallas key and enters the load type (septage or grease) and location information. Upon receiving input on the load type, a three-way selection plug valve, driven by an electric actuator, selects the corresponding pipe position to either septage or grease. Load flow is delivered once the hauler manually opens the truck valve. The flow is then locked out until the appropriate sequence and identification are obtained.
Flow is measured by a bullet-nosed mag meter upstream of the three-way plug valve, which is elevated above the Quik Disconnect vault to ensure a full pipe for appropriate measurement. The controls software can print load information for the hauler and track actual gallons delivered for further analysis. The hauler also receives a printed receipt.
Controls/rebate integration. In the past, when a hauler delivered a load, he gave the location address to Spartanburg Water, which verified the address by hand against a map at the plant to confirm a residence was eligible for the rebate. A letter was then generated manually and forwarded to the resident with hard-copy reports provided to the accounts payable department to generate the rebate.
Developed by Avid Solutions Inc., the new system is fully automated with touch screens and easy-to-use features. County tax information is integrated into the programming, eliminating the need to verify the address against a hard-copy map. Letters are generated automatically to residents who are qualified for the rebate, and the system communicates directly with the finance department. The system also generates reports for review and management purposes.
Discharge routing. The hauler indicates the type of discharge he is delivering at the bay. The automated three-way plug valve directs the flow to either grease or septage piping, where it flows by gravity to the appropriate screening area. The septage is screened before continuing to the septage wet well, which is sized to handle about 3,000 gallons (just over one truckload).
Flow is pumped into the septage holding area of the storage tank. At the completion of the septage dump cycle, a solenoid valve opens and delivers hot water to flush the open line following load delivery. The parallel system for grease operates in the same manner.
Screening. The screening station handles septage and grease independently. A Hydro-Dyne Engineering Inc. Model # HF26-18-117-6L was selected. The flow passes into the screen and is diverted through a grid on each side of the unit. The unit has stainless steel elements that separate solids and convey screenings out of the channel.
At the top of the unit, a hot-water spray washes the solids into the screenings washer and compactor. Organics and wash water are returned to the channel, while solids are conveyed to the dumpster area.
Although both the septage and grease screens are equipped with their own wash system and compactor, there’s a common conveyor to the dumpster. All screenings are bagged before dropping into a full-length, roll-off dumpster.
Holding tank. A 600,000-gallon (344,000 for septage; 66,000 for grease) Crom Corp. prestressed concrete tank with a dome cover prevents odors from developing.
Septage tank mixing. The tank is equipped with appropriate inlet and outlet connection points constructed for the septage and grease storage tanks. A plug valve controls flow from the septage holding area back to the wet well for recycle into the tank. This recycle is augmented by submersible mixers. All piping is routed beneath the tank floor.
Grease tank mixing. Grease also is mixed through recycle using the pumping system with augmented mixing. Grease flows back to the grease wet well and is controlled by a plug or pinch valve. Flow and piping is arranged from the wet well to provide complete wet well drainage and recirculation for cleaning.
Grease treatment and disposal. A separate hot-water recirculation system located at the exit end of the grease screening chamber engages after load delivery begins. Hot water liquefies any solidified grease and flushes the lines. The ultimate fate of the grease is delivery to: the plant digester; the load station for loading and delivery for beneficial reuse; the plant headworks.
Canopy footing. The extent of the canopies’ footing was underestimated. At the shop drawing stage, it was learned they were 4 feet by 4 feet by 4 feet to accommodate wind load, etc. An adjustment was made during the course of the submittal and shop drawing process to modify to a cantilevered canopy that would be accommodated more easily in the bay area.
Lighting. Restrike sequence was evaluated closely during construction, and it was determined that the amount of time between haulers entering the facility and lights moving to full luminosity should be minimized. Higher-efficiency lighting with lower restrike times was selected during the shop drawing and submittal process.
Moving the tank. During the pre-bid meeting, it was determined that 10 to 14 working feet were needed circumferentially around the tank. The tank was moved for the appropriate adjustment and ease of construction while the project was still out for bids.
pH probe. Once construction began it was determined that the maintenance and the harsh environment for probes that had been designed for the facility weren’t the right application, and they were deleted from the overall process.
Timing matters. The construction schedule was very aggressive. Weather delays and delivery schedules must be managed proactively; flexibility for unforeseen conditions at a brownfield site (buried concrete, unsuitable material, etc.) should have been expected.
Team/inspector competence. Our strongest asset was the relationship between the contractor, engineer, owner, and the owner’s representatives. This partnership was a model of how to work through inclement weather conditions and changes in the field to produce cost-effective results.
—M. Steve Cavanaugh (email@example.com) is founder of engineering firm Cavanaugh & Associates (www.cavanaughsolutions.com). Hurley Cann (firstname.lastname@example.org) is a project manager with Spartanburg Water (www.sws-sssd.org), which provides water and sewer services to upstate South Carolina via Spartanburg Water System and the Spartanburg Sanitary Sewer District. A slightly different version of this article appeared in the June 2011 issue of Florida Water Resources Journal. Reprinted with permission.