a pilot study for the application of one- and two-stage tube settlers as a secondary clarifier for wastewater treatment

secondary clarifiers with large areas are widely applied in wastewater treatment plants. a pilot study was conducted to examine the possibility of applying one and two-stage inclined tube settlers instead of conventional secondary clarifiers. tube diameter in the first stage of the two-stage settler was wide as the conventional ones, but in the second stage, it was narrow to improve the efficiency. the results indicated that in short detention times, the tube settler was more effective in shorter detention time than the conventional secondary sedimentation basin, and its effluent of tss and turbidity was acceptable to discharge into the surface waters. the average removal of tss, bod5, and cod, in a 20-minute detention time in the tubes, in the one-stage tube settler pilot plants was 97.6%, 96.4%, and 96.36%, respectively, while in the conventional secondary sedimentation basin was 98.2%, 99%, and 98.6%, respectively. there was a good agreement between theoretical analyses and experimental results of the pilot plant. two-stage tube settlers in the series could improve hydraulic condition and removal efficiency of tss, in comparison with the one-stage tube settler. the average tss removal, in shorter detention times than that the one-stage, was 97.8%.