Plumbing a new subdivision, four restaurants and several businesses into the Breitling Elementary School Waste Water Treatment Plant in Grand Bay, Ala., threatened to overwhelm its 30,000- gpd onsite system, sized to handle the school and a truck stop.
The Grand Bay Water Works Board Inc. decided to double the facility’s capacity, and Preston Hughes, owner of Hughes Plumbing & Utility Contractors Inc. in Mobile, Ala., won the bid. He also installed Phase 1.
Paul Coletta, applications engineer for J.H. Wright, a Quanics distributor in Daphne, Ala., incorporated elements of Phase 1 into the expansion. Phase 2 combined septic tanks, low-pressure sanitary sewers, recirculation tanks, open-cell foam fixed-film filters, and a pump station discharging to chambers. The upgrade was completed when classes began last fall.
Site conditions
Soils are sandy with the water table 8 feet below grade. The site, a flat field, is part of the wastewater treatment plant.
System components
Coletta designed Phase 2 to handle 30,000 gpd. The major components of the entire system are:
Phase 1
• 20,000-gallon fiberglass septic tank. All tanks from Xerxes Corp.
• 20,000-gallon recirculating tank.
• Nine AX100 AdvanTex textile treatment modules from Orenco Systems Inc.
• Quick4 chambers from Infil-tration Systems Inc.
• ProSTEP effluent pumping station, Orenco: Biotube pump vault; effluent pump; and riser, lid and control panel.
Phase 2
• 35,000-gallon fiberglass recirculating tank.
• Six 5,000-gallon ATS-AC-5000 AeroCell fixed-film modules with a 30-inch ATS-GRD-100/ 80/20 4-inch gravity recirculation device, Quanics.
• 1,400 Hi-capacity Enviro-chambers, Hancor Inc.
• Three duplex STEP systems, Quanics; 30-inch filtered pump vault; 50-gpm high-head turbine pump; and riser, lid and control panel.
System operation
At first, only the school was connected to Phase 1. A pump station at the school pumps wastewater to the septic tank at the plant. Settled wastewater gravity feeds to the recirculating tank, then to the AdvanTex modules in series.
As liquid trickles through synthetic textile sheets in the treatment units, microorganisms remove impur-ities. A gravity-flow collection system at the bottom of the last unit sends 80 percent of the effluent to the recirculation tank and 20 percent to the ProSTEP pump station.
Effluent flows on demand from the pump station through a 4-inch PVC Schedule 40 pipe to a distribution box in the drainfield. The absorption bed has three zones of 18 rows, 108 feet long on 8-foot centers. Operators dose the zones via manual gate valves and determine when to switch zones by looking into the inspection ports at the end of each lateral. “The amount of rain we get ruled out time-dosing the beds,” says Hughes.
Until Phase 2, each parcel in Grand Bay had its own conventional onsite system. Settled wastewater from those septic tanks now flows through a 6-inch PVC low-pressure force main to a splitter box at the plant. By opening gate valves, operators direct the flow through 6-inch lines to Phase 1, Phase 2 or both to check BOD, TSS and evaluate which treatment system is doing better.
Phase 2 wastewater from the plant flows to the 35,000-gallon recirculating tank, where on-demand P-TE-50 pumps dose dedicated AeroCell modules in series. Spray nozzles inside the pre-engineered unit evenly distribute wastewater over the open-cell foam media to the desired treatment level. The porous cubes have a large surface area for microbial attachment, allowing high loading rates.
A gravity recirculation device at the bottom of the last module sends 80 percent of the effluent to the recirculation tank and 20 percent to the Phase 1 pump station. A second distribution box on a 4-inch outflow line lets operators direct the flow to either treatment system. Phase 2 has a 2-inch pipe tying into a distribution box at the drainfield. Its three zones of 18 rows, 100 feet long on 8-foot centers, also are dosed with manual gate valves.
Installation
Grand Bay Water Works installed the low-pressure force main. Hughes’ crew used Komatsu PC 200 and PC 300 excavators to dig pits 15 feet deep, then bed them with 12 inches of pea gravel. “The tanks had to sit that deep if we were to plumb the components into the 24-inch-high risers,” says Hughes. “However, groundwater threatened to float the tanks out of their holes.”
The men drove wellpoints to combat the inflow, but the wellpoints could not keep up. “For Phase 1, I ran a centrifugal pump around the clock to dry the holes enough to install forms and pour concrete around the bottom of the tanks for ballast,” says Hughes. “The Phase 2 recirculating tank came with straps and concrete deadmen.”
Installing the drainfields was just time-consuming. “The only thing that happened was I had to buy 50 more chambers to make the zones uniform in length,” says Hughes.
Workers then positioned the treatment modules on the surface next to the Phase 1 units. Once they were plumbed, the men built a berm around the AeroCell modules and covered them to the service access openings just as they had done with the AdvanTex units. “Phase 2 blended seamlessly with Phase 1,” says Hughes.
Maintenance
Grand Bay Water Works services the low-maintenance system. Twice a year, a technician checks the condition of the media, vents, air supply and covers. The technician removes and cleans the spray nozzles and inspects the pumps and controls, and the effluent filter in the pump vault. He also evaluates the presence of odors within a 10-foot perimeter and the effluent quality. Buddy McGregor, utility manager, says the board was pleased with the system’s performance and ease of service.
