An automatic sludge blanket detector from Markland Specialty Engineering helps wastewater treatment plants monitor sludge levels in clarifiers and other tanks and automate sludge removal.

The instrument uses high-intensity infrared light beams to monitor blanket interface levels in clarifiers, DAF units, decanting tanks and sequencing batch reactors. It allows users to program sludge removal pumps to operate only when necessary, preventing carryover, avoiding the pumping of large volumes of thin material, and allowing sludge density to be optimized before subsequent processing.

The detector (4- and 8-foot-long models available) uses a vertical probe submerged in the tank. Sixty-four high-intensity infrared LEDs are stacked vertically and shine across the probe gap to matching phototransistor detectors.

The 64 pairs are sequentially scanned, top to bottom, to locate the sludge bed. Beam power intensity is automatically adjusted to accommodate different sludge and overlying liquid concentrations. The lights and sensors are contained within the probe so that nothing external can affect them,” says Scott Langstaff, company general manager.

“The top LED is turned on, and we measure the light intensity going from the LED through the liquid in the tank to a photosensor on the other side,” Langstaff says. “Then we step down to the next LED, and ultimately we scan over the whole length of the probe. Based on the optical clarity of the liquid and the slurry, we determine where the sludge blanket begins.

“The device doesn’t have to sit right on the tank bottom. Suppose you want to carry 4 to 5 feet of sludge. You might locate a 4-foot probe 3 feet off the bottom, so that its measuring range would be 3 to 7 feet. The output signal goes to a computer or control system; when the blanket reached a thickness of 6 feet, it would trigger the sludge pumps. When the thickness reached 5 feet, the pumps would shut off. It’s designed to help maintain an optimum level of sludge in the tank.”

The light system has four power levels that automatically adjust for different particulate concentrations. The device is simple to install and it requires no calibration. A wireless data link is available as an option. 855/873-7791; www.sludgecontrols.com.