Curren Hits the Bull's Eye Using Online Process Analyzers

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Courtesy of ASA Analytics

Howard F. Curren Advanced Wastewater Treatment Plant improved its efficiency by upgrading to online process monitoring and control.

The Howard F. Curren Advanced Wastewater Treatment Plant is one of the largest nitrification/denitrification filter plants in the world with a design capacity of 96 million gallons per day average daily flow. It serves about 110,000 accounts in the City of Tampa and portions of Hillsborough County, Fla. Over the years, the quality of its treated effluent has been frequently cited as the primary factor behind the dramatic improvements in Tampa Bay's water quality and the return of its sea grasses, turtle grasses and game fish.

The facility is Tampa's only wastewater treatment plant so the volume and characteristics of the influent flowing into the plant vary constantly, making access to reliable real-time information critical for optimal process control. Years ago, plant managers recognized that attempting to operate the plant without timely information was akin to trying to hit a target's bull's eye while blindfolded.

To better inform its operators about the nitrification and denitrification processes plant management invested in three ChemScan online process analyzers manufactured by ASA Analytics. For fifteen years the ChemScan Analyzers have provided operators with automated sampling and online, real-time results. At two points on the six stages in the plant's nitrification reactors, they automatically draw samples and then analyze them for nitrate and ammonia.

'Online monitoring has removed the guesswork from optimizing our nitrification and denitrification processes,' said Robert Decker, operations specialist. 'We've used ChemScan as a tool to inform our operators when it's appropriate to start and stop blowers in our nitrification reactors. If the ammonia is creeping up in Zone 6, it means we're not converting everything, so we need to start a blower. At one time, operators relied on their experience to adjust the process because they didn't have access to timely information. Now online realtime data enables them to adjust the process much more efficiently. We're soon going to connect our analyzers to a PLC via the SCADA, which will enable the PLC to automatically adjust the blowers and provide more precise control.'

Decker said by using the diffused aerators more efficiently they've saved energy and reduced operating costs. 'We found that sometimes we didn't need that extra blower. In fact, sometimes we could get the job done by turning them down and saving power.'

The ChemScan Online Analyzers use fully automated ultraviolet-visible spectrometry to measure absorbance levels across 256 wavelengths of light. A single process analyzer can monitor up to eight sample points, separately detecting ammonia, nitrite and nitrate from multiple process sample points or basins.

The plant's analyzers also are instrumental in controlling the denitrification process. Samples of the flow exiting the nitrification final tanks are taken and analyzed automatically for nitrates. The resulting value is used in a calculation sent through a PLC via the SCADA system to pace the methanol that feeds denitrification.

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