In municipal and industrial wastewater treatment plants, sludge clarifiers are often used to separate solids from the effluent system by introducing air and flocculants. The process causes the sludge to rise to the top of the pond or tank, then spill over a weir into a separate collection area. The amounts of air and flocculants are controlled by measuring the liquid level interface between the sludge and water (Figure 1).Many types of flocculant chemicals treat municipal and industrial wastewaters. They cause suspended solids in wastewater to float to the top or sink to the bottom for removal. Flocculants also are
