A Florida Batch Plant Exceeds Design Performance Through Study, Observation And Testing

Extensive study, careful observation and diligent testing enable the operator of a small Florida batch plant to exceed design performance expectations.
A Florida Batch Plant Exceeds Design Performance Through Study, Observation And Testing
Kanahou Alana uses instrumentation (Hach DR 900 colorimeter shown here) and microbiological observation to help keep the plant process in control.

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Kanahou Alana admits he knew nothing about wastewater when he became the operator of the Layton Wastewater Treatment Plant on Florida’s Long Key five years ago.

He didn’t let that stand in the way of achieving excellent performance. Today, the 66,000 gpd (design) sequencing batch reactor (SBR) plant produces effluent of significantly higher quality than its permit requires. That includes, on an annual average, 95 percent removal of total nitrogen (to 3.01 mg/L in the effluent) and 92 percent removal of total phosphorus (to 0.69 mg/L).

Alana notes that the plant, designed to meet Florida’s best available technology standards, now meets advanced waste treatment standards. It does so in part with an innovative simultaneous nitrification-denitrification process for biological nutrient removal.

“I’m not interested in doing only what’s required to meet the permit,” says Alana, whose plant won the 2013 Plant Operations Excellence Award from the Florida Department of Environmental Protection. “From the day I came here, my goal has been to produce the best water I possibly can. That’s the only way I know how to operate.”

Seasonal challenges

The Layton plant is one of five operated by the Florida Keys Aqueduct Authority (FKAA), formed in 1937. The authority’s original mission was to supply drinking water to all residents of the Florida Keys, but it later took on wastewater treatment for certain areas of the Keys.

Alana joined the FKAA in 2006, working on the 130-mile transmission pipeline that brings water to the Keys from an aquifer on the Florida mainland. A year later he went to work as a trainee at the Layton plant; two years after that he became the lead operator. He’s assisted by part-timers Danny Price and Branson Bruce, who handle permit-required weekend plant checks and testing. “If there’s a problem, they’ll call me,” says Alana. “I make all the operational decisions, and I have for the past five years.”

The Layton plant faces challenges in seasonal changes in influent volume and strength. The plant serves mainly the community of Long Key and its 150 residences, but tourists boost the population, especially in winter. About 142,000 visitors a year pass through Long Key State Park, which has 60 campsites often occupied by recreational vehicles that empty their wastewater tanks at the park dump station.

“The strength of the influent that comes in from there is very high,” Alana says. “The visitors may come from hundreds of miles away, and the wastewater has been sitting in the tanks for days. They dump it, and it comes right to the plant. I deal with a lot of very septic conditions.”

The SBR plant (Fluidyne Corp.) has two basins that together handle average flows of 29,000 gpd in summer and 31,000 gpd in winter. Influent passes through a fine bar screen (Vulcan Industries) and enters a settling basin. When the water reaches a preset level, pumps deliver a batch to whichever SBR is filling at the time. Mixing and aeration occurs in each SBR through jet aeration manifolds.

Treated water from the SBRs is delivered to a storage basin through a fixed wall mounted decanter in each SBR and then to two upflow sand filters (also Fluidyne). Final effluent passes through a chlorine contact chamber before injection down a 90-foot-deep well. Biosolids are transferred to the authority’s Big Coppitt treatment plant, where they are dewatered with centrifuges. The material ultimately is landfilled.

Close-up learning

Steadily fine-tuning that process has been a mission for Alana, who holds a Class C (third highest) wastewater operator license. Upon being hired, he received basic training through the authority’s wastewater division. After that, he says, “By looking outside the box I began discovering new ideas about how wastewater treatment could be practiced. I started down the road to improving upon the already well-established process of operating SBRs.”

His journey has included mentoring from Tom Pfiester, FKAA wastewater division manager; Theodore Knowles, operator at the authority’s Big Coppitt Wastewater Treatment Plant; Tracie Finnegan at the Environmental Leverage consulting firm; and Tom Stirtzinger of the Florida Rural Water Association.

He also learned from books, from prowling on the Internet, from trial and error and, perhaps most important, from babysitting the plant. “I’m talking 24 to 48 hours at a time on site, testing all day long, every single cycle, to find out what was going on,” he says. “When are the peak flows? When is the influent the strongest? When is the plant converting nutrients the most effectively?

“Spending that amount of time gave me intimacy with the plant and knowledge of what goes on in the tanks. Before, the plant had to be run with an operator who had to be there seven days a week, eight hours a day, because it was so hard to control. Weekend flows would come in and demolish the process.”

He changed the operating protocols, making adjustments to account for specific influent characteristics. He also changed out the plant’s original programmable logic controller for a unit supplied by Aqua-Aerobic Systems: That changed the process from a level batch to time batch. This added flexibility to customize control of the plant.

“The original specifications said the plant should run at 2,500 mg/L mixed liquor suspended solids,” Alana says. “My research says it runs best at almost 3,500 mg/L. We average 80 percent mixed liquor volatile suspended solids, which means 80 percent of the sludge in there is bugs — is alive. At that rate, we’re able to treat heavy, heavy amounts of CBOD and ammonia. Having that big an army in there, nothing can stop it.

“Now I can walk away on the weekend and not even think twice. By understanding the different flows at different times of year, we can predict the heavier influent loadings during times of seasonal vacationing and foresee events that could wreak havoc on facility operation. The predictions enable process adjustments to be made before the loadings reach the facility and ensure a much smoother and well-maintained biology to handle those conditions.”

Monitoring and testing

The plant accomplishes nutrient removal with oxic and anoxic cycle times in the SBR basins. In-line monitoring includes dissolved oxygen (DO), oxidation reduction potential (ORP) and total solids meters in each SBR, regulated by a Hach sc1000 controller. “The DO meters allow us to ensure that we are not over-aerating the oxic process, and the ORP meters ensure that we are reaching anoxic and anaerobic conditions for denitrification and luxury uptake for biological phosphorus removal,” Alana says.

“The total solids meters are for quick measurements and help reduce labor when extra time is needed. Since a mixed liquor suspended solids [MLSS] sample can take well over an hour to run, the meters give us a quick look at the MLSS inventory.”

Meanwhile, the plant’s lab runs daily tests on influent, the oxic and anoxic cycles, and final effluent for ammonia, nitrate, phosphate, pH, alkalinity, salinity and chlorine residual. Daily settleometer tests are also conducted.

“We also test for COD and correlate that with CBOD5 results that come from contracted certified laboratory,” Alana says. “This correlation of two tests is needed because the CBOD5 takes sometimes seven to 10 days to get the results back, whereas we can run the COD in a little over two hours and have real-time results to make more proactive process decisions.

“The COD test lets me know the influent strength coming into plant — the loading. By knowing this and trending the numbers, we can increase or decrease air schemes proactively. So instead of getting hit with heavy loading and having a low air scheme, then spending days with the air cranked higher to catch up, we can trend when it is increasing and be ahead of the game.”

Process innovation

Pushing the plant’s performance took some added creativity. One thing Alana discovered was that batch processing time was limiting the capacity for nutrient removal. “Within any part of a wastewater system, time is of the essence,” he says. “More wastewater keeps coming in, and you have to put it back out. So time management in the process is very important.”

To lessen the time required for nutrient removal, Alana created an environment for simultaneous nitrification-denitrification — a condition in which DO in the aeration basin is maintained at just the right level so that the outer edges of bacterial floc remain aerobic, while the interior of the floc is kept anoxic. Nitrification occurs on the outside of the floc, and nitrate is then utilized (denitrified) within the floc. “Plants normally buy their nitrates,” Alana says. “AWT plants usually use a carbon source, which is very expensive, to achieve what this plant is doing just by creating the right environment.”

Making that process work meant overcoming low alkalinity that was limiting nitrification. “While the process is converting the ammonia, it’s also denitrifying while the air is on in the system,” Alana says. “Increased alkalinity will allow it to do that. The influent alkalinity was in the range of 200 to 250 mg/L, but going out the back in the effluent, it was 40 mg/L. So we spiked it with sodium hydroxide. We tripled the alkalinity at the beginning of the process so that the effluent alkalinity was 140 mg/L.

“It took months and months of testing. I have a stack of probably 10 legal pads of data on every single cycle. I would go out and test the full range — NH3, NO3, alkalinity, pH. I would watch where and when the nitrates started reducing. The more alkalinity we put in, the faster the nitrates would be gone.”

In the end it all comes down to a simple principle: “The more you know,” says Alana, “the more power you have.” It’s not a bad lesson to learn for someone who, just a few short years ago, by his own admission didn’t have a clue.  

More Information

Aqua-Aerobic Systems, Inc. - 877/271-9694 - www.aqua-aerobic.com

Fluidyne Corp. - 319/266-9967 - www.fluidynecorp.com

Hach Company - 800/227-4224 - www.hach.com

Vulcan Industries, Inc. - 712/642-2755 - www.vulcanindustries.com



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