Automatic Sludge Blanket Level Detector: Monitor & control for effective, efficient processing


Courtesy of Markland Specialty Engineering Ltd.

Reducing energy consumption at municipal and industrial plants is, increasingly, a priority. Markland Specialty Engineering Ltd., designing and manufacturing process control instrumentation since 1967, helps achieve this important goal with its Automatic Sludge Blanket Level Detector. By helping facilities reduce waste - reducing unnecessary water, chemical or energy use, and unnecessary equipment operation that requires costly maintenance - Markland instruments enable increased efficiency and effectiveness.

This Detector uses high-intensity infrared light beams to help monitor interface levels in clarifiers (including lamellas, dissolved air flotation thickeners, decanting tanks and sequencing batch reactors), when clarifying incoming process water or wastewater. It measures primary, secondary and return-activated sludge, as well as backwash sludge from sand/membrane filters.

This detector allows users to program sludge removal pumps to operate only when necessary: preventing carryover; warning of process problems, such as inefficient flocculent dosing; avoiding pumping thin sludge or large volumes of water (when a core hole is pulled); and, optimizing sludge density before subsequent processing (such as feeding to belt presses, digesters and centrifuges), and improving the quality and quantity of water available for reuse. In addition, features are uniquely suited for specific applications. For example, in DAF units, the detector can adjust the speed of the surface skimmer to match the varying thicknesses of the floating sludge layer; in SBRs, it can control the decant valve, enabling cycle time to be kept to a minimum. Eliminating unnecessary pumping reduces wear-and-tear on pumps, downtime for maintenance, and energy usage.

The detector (4- and 8-foot models are available) uses a vertical probe submerged in the tank. Sixty-four LEDs are placed within a gap running along the length of the probe. Each shines across this gap to a matching phototransistor sensor. These pairs are sequentially scanned to locate the sludge bed. Beam power intensity automatically adjusts to accommodate different sludge and overlying liquid concentrations. The slim profile, with lights and sensors contained within the probe gap, make it well suited for obstructed or constricted areas; for example, readings are not affected by the curved walls of lamellas. The probe is placed at a height that enables the operator to maintain a desired sludge bed depth. When the sludge level reaches the preferred maximum height, the detector sends a signal to the control system or computer to trigger the desludge pump. Once the ideal minimum sludge level is met, an output signal turns the pumps off. The all-PVC probe is corrosion-free. Analog and relay outputs are available. No calibration is required with this simple-to-install detector. A wireless data link is available as an optional feature or upgrade.

Reducing energy usage, without sacrificing process effectiveness and/or production quality, results in benefits that extend well beyond the specific municipal or industrial application to benefit the broader environmental setting.

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