Efficient (tube) settling tanks

Abstract

This paper discusses design principles and theoretical results for a new type of settling tank. Within the settling zone of the tank, sedimentation takes place in tube, as in a quiescent container of equal (3-5 cm) depth. The inlet, sludge and outlet zone are arranged for a continuous-flow rectangular (or circular) basin. A particle that enters the sludge zone is and stays removed, and the sludge can be removed by gravity or pumped from the sludge zone. Hydraulically, the process can be formulated in terms of horizontal-vertical flow without short-circuiting. Tank loadings are 0.5 L/s per m2 to 1.5 L/s per m2 of tank surface area. The detention period of 15-20 minutes offers the same overall removal efficiency as 4-5 hours for classical one. Variations in flow are of little concern, provided that the maximum design flow is not exceeded. Scum is removed without difficulty from the tank as well as the sludge, and the sludge removal device will also act as a flocculator. This type of settling basin is suitable where sludge volumes are large or where putrefaction of sludge in contact with the flowing water is to be avoided.