Automated Treatment, Monitoring System Keeps An Eye On Operations

Sept. 3, 2002
Products In Action

To make the most of its resources, including operator time and energy, Warrington Township Water and Sewer Department, located in Bucks County, Pennsylvania, installed a compact sequencing batch reactor (SBR) system when the facility was built fouryears ago. And an equally hardworking Hach OptiQuant (TM) SST Analyzer, installed two years ago, keeps a vigilant eye on the final product.

"We can't afford time lost to maintenance and monitoring," facility supervisor Sam Cramer explained. "The OptiQuant does exactly what we need: watch the operation when we have other jobs to attend to, which is most of the time."

Warrington Township found an efficient wastewater treatment solution with the SBR system that combines aeration and mix, react, decant, and settling functions in one 42 ft. x 36 ft. x 18 ft. deep basin. Operators program the duration of each phase, based on load. The plant uses two of these basins, each processing about five batches of wastewater daily on an alternating basis. This arrangement provides a 320,000 mgd capacity.

Even Mill Creek, receiving the plant's discharge, is modest, "sometimes non-existent," confessed Cramer, who added, "All the more reason to make certain effluent reflects proper treatment. The SST Analyzer serves as our eye on the operation after hours, during weekends, when we're taking care of our many other tasks."

In the open-channel installation at Warrington Township, the OptiQuant probe is positioned after the effluent weir and UV treatment but before the holding tank. Cramer usually sets the OptiQuant controller alarm level at 50 mg/L suspended solids (SS), and any excursion sends an analog signal directly to the PLC system, which in turn shuts off the post-equalization chamber valve and notifies an operator.

Operator-required attention of the probe is rare in this application because it is positioned with the probe face into sample flow --an arrangement that provides a cleaning effect on the probe. The probe also can be installed as a tank "dip" probe or within a pipeline. A distance of at least 30 cm between the probe end and nearest surface (which should be dark) helps eliminate error due to reflections.

Further, the probe uses an 880-nm light source--not in the visible range--so visible sample color does not interfere. If the Warrington Township effluent does present a component that absorbs at this wavelength, the instrument's unique, advanced color compensating technology minimizes interference effect.

"If the mixer doesn't shut off as we expect, if the float misses its activation level, if suspended solids concentration surpasses what we think represents complete treatment, we rely on the analyzer signal to initiate effluent hold," Cramer noted.

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