It’s not easy operating a wastewater treatmentplant when you can’t smell it or hear it, and most of it is out of sight. Yet that’s the task facing the staff at the 15 mgd treatment facility at the 43-acre Johns Creek Environmental Campus in Roswell, Ga.
Located just a few yards from well-to-do neighborhoods, the brand-new 90,000-square-foot treatment and recycling facility is designed to be odorless and noiseless. Most of the process equipment is located underground.
“It’s a highly technical operation,” says Kevin Miller, who manages the plant for Veolia Water North America, the operations firm under contract with the plant’s owner, the Fulton County Commission. “It’s much different from other plants, and that poses a challenge.”
Adding to the challenge, Johns Creek is the largest membrane bioreactor (MBR) plant in the United States. “We test for everything,” says Veolia project manager Doug Worsham. “There’s nothing in the plant that isn’t tracked and trended by our SCADA system.”
To keep pace with area growth and meet new standards for clean water, the Johns Creek Environmental Campus plant replaced a conventional activated sludge operation. The design-build team, led by Brown and Caldwell Engineers and Archer Western Contractors, developed acoustical models to ensure that the plant would not exceed pre-established noise levels at the fence line, and guaranteed the cost of the operation and treatment per million gallons. The costs were confirmed during a four-month period of startup.
The state-of-the-art operation is also designed with redundant process equipment at peak flows throughout the plant and can meet stringent effluent standards.
The uniqueness of the plant starts right at the influent station with a self-cleaning wet well. An “ogee” ramp causes the water to cascade, creating enough sweeping across the wet well bottom to keep any material suspended. The material is sluiced to the influent chopper pump (Vaughan), which discharges all of the accumulated material so the structure doesn’t have to be cleaned manually.
The flow then passes through 6-mm coarse screens (Ovivo) and a pair of 50 mgd vortex grit removal units. Screenings and grit are washed, removed and landfilled.
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Primary solids settle out in a battery of four rectangular clarifiers (one standby). Miller calls the tanks “activated clarifiers,” in that a portion of the primary solids can be returned to the influent line to increase the production of volatile fatty acids (VFAs). The rest goes to aerobic digestion. About 70 percent of the primary solids are recycled.
After the primaries, the flow moves on to 2-mm fine screens (Ovivo) positioned ahead of the MBR. The biological system is a hybrid Johannesburg UCT process, consisting of anaerobic, anoxic, and oxic zones for biological phosphorus removal. These are followed by aerobic treatment, driven by fine-bubble diffusers (Sanitaire – a Xylem brand).
“In the swing tank we can mix or aerate the contents, depending on the needs of the plant,” says Miller. “It follows the aerobic treatment step.”
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The submerged ultrafiltration membranes (GE Water & Process Technologies – Zenon) have a pore size of 0.4 microns. There are eight trains, with 11 cassettes per train, each containing 48 modules. A single train can produce about 2,600 gpm, but in actuality the flow is spread over four trains to take peak flow. “We have our plant currently set to add a train for every increase of 650 gpm,” Miller notes.
Membranes are cleaned in several ways. After producing water for about 12 minutes, a membrane train will either relax or backpulse for about two minutes. “During a relax cycle, the train stops producing water, and air is sequentially blown up between the membrane fibers to shake off solids that may have accumulated,” Miller says. “During a backpulse, the train stops producing water and water is pumped back through the membrane fibers to unplug any clogged fibers.” (Goulds Water Technology) supplied the permeate and return activated sludge pumps.)
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The membranes are controlled by a PLC program and are completely automated. When a membrane train is on standby or offline, a scheduled maintenance clean pulses chlorine or citric acid for a certain amount of time. A 1.5 percent hypochloride solution is used to eliminate organic fouling and citric acid for inorganic fouling.
Finally, recovery cleans soak the membranes for 12 hours in a hypochloride or citric acid solution after the tank is emptied of all solids. “We usually do these twice a year or as often as necessary based on train production and efficiency,” says Miller. After the membranes are cleaned, solids are returned either to the return activated sludge line, or directly to the digester.
Easier to control
Miller feels that the Johns Creek process allows for better control than a conventional plant. “It is definitely a lot easier to control a plant with inline equalization space and no secondary clarifiers, because most of a conventional wastewater treatment plant’s problems come from hydraulic overload or settling issues,” he says. “With an MBR, that isn’t a factor.”
The filtered effluent is UV-disinfected (WEDECO) and then cascades down a post-aeration channel to the Chattahoochee River and is reused for various uses around the plant. About 25 percent of the effluent is reused for washing, irrigation, flushing, and recharging the onsite pond. Recycled water is used for fire protection.
While water reuse is limited to in-plant use today, long-range plans allow for expanded use of the reclaimed water within the community. Paul Williams, Fulton County deputy director for Public Works – Water Division, says area golf courses might use the water for irrigation, and it could be made available to area industry and commercial users. “If a particular industry has an interest in using the water in the future, entering into a partnership is a possibility,” he says.
Biosolids are aerobically digested, then dewatered to about 20 percent solids in an Andritz centrifuge. The resulting cake is landfilled.
No sounds or smells
The Johns Creek campus includes a park and interpretive nature trail, a cascading stream and pond system, and an educational facility with a lecture hall, classroom and teaching lab so that the community can learn about water quality and the local environment. With this open invitation to the public to visit the plant, it’s not surprising that Johns Creek is designed to be both quiet and odor free. The noise control and odor abatement systems are state-of-the-art. “A lot of thought went into the odor and noise control systems,” says Williams.
To remain quiet, the plant employs a number of innovative noise control measures, including landscaping (see sidebar). And to eliminate odors, designers implanted several features, including enclosed processes and odor scrubbing.
“All tanks are covered, and negative pressures are maintained in all structures where odors could be an issue,” says Miller. Those measures essentially eliminate the release of odorous air to the atmosphere. In addition, Johns Creek uses both wet scrubbers (HEE Environmental) and granular activated carbon scrubbing (Calgon Carbon) of air from the preliminary and primary sections of the plant.
While much equipment is out of sight, it’s not out of mind, thanks to a sophisticated SCADA system (GE Proficy iFIX) that not only tracks and trends data but also maintains a historical account of all process operations. “All equipment is seen and operated from our control room,” says Miller. “There’s nothing in the plant that isn’t tracked and trended.”
Miller and his staff especially like the historical data. “We have a complete history on every piece of equipment and process step in the plant, from startup,” says Miller. In conjunction with the plant’s process control testing laboratory, the Johns Creek staff can closely monitor plant performance to assure that the stringent effluent and other parameters are being met.
“We run solids tests on MLSS, RAS, and WAS samples,” says Miller. “We also run PO4 (using a quick-check method with reagent and a spectrophotometer), NH3, and alkalinity tests on the permeate, MLSS and RAS.” In addition, the lab staff runs pH, turbidity, and DO tests to cross-check online meters.
All this technology, however, does not dismiss the human factor in plant operations. “Although a good majority of our systems are automated, operators must not rely on SCADA alone to tell the story,” says Miller. “You still have to double-check the actual conditions in the plant. After all, it’s only a machine, and operators are the actual brains behind the operation of it!”
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