Sep 03, 2002

Automated Treatment, Monitoring System Keeps An Eye On Operations

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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