Chemical precipitation using alkaline solution is one of the most popular methods to remove heavy metals from industrial wastewaters in Taiwan. The resultant metal hydroxide precipitates are separated from wastewaters by gravity settling. To design continuous clarifiers, the settling characteristics of heavy metal sludge must be known. A series of batch settling tests were performed to gain design information for heavy metal sludge settling tank. The classic Kynch sedimentation theory and the nonlinear wave propagation theory were employed to depict the sludge band movement in batch settling tests. The variation of sludge concentration within the settling tank was viewed as a wave, and its wave velocity was calculated by the wave theory. The batch settling curves at varying initial solid concentrations were measured and satisfactorily predicted by the wave theory.