There are several areas within a wastewater treatment facility where solids settle and are subsequently removed as sludge. These include hoppers, holding tanks, gravity thickeners, and other sludge collection systems. Sludge level is monitored to control against incomplete discharge or dilution of the sludge.
Non-contact measurement is often preferred since sensors are located above the process fluid and beyond direct contact with the sludge. Sensors of contact technologies should be single rod types to minimize material buildup - or bridging - that occurs in twin rods configurations.