EFFECTS OF INCLINED PLATES AND POLYELECTROLYTE ON THE PERFORMANCE OF SETTLING TANKS

The effects of inserting inclined plates and using a polyelectrolyte on the improvement of the turbidity removal efficiency (TRE) in an upflow settling tank treating raw water from a river have been examined experimentally in a laboratory-scale setup. The inclined plates in the upper zone of the conventional upflow settling tank increased the hydraulic capacity and simultaneously improved the TRE. The maximum increase in the hydraulic capacity was 330% and it was combined by a 7.4% improvement in the TRE. In comparison with the polyelectrolyte, the inclined plates decreased the variability in the TRE despite the increase in the surface overflow rate (SOR). The inclined plates enabled the operation at a higher upflow velocity and increased the TRE of the alum with polyelectrolyte-treated water by 6.0 and 3.0% at SOR of 1.0 and 3.3 m3 m2 h-1, respectively. The results indicated that the TRE of alum with inclined plates was almost identical to that of alum with polyelectrolyte though the numerical values were statistically different based on Tukey's multiple comparisons test at a 95% confidence interval. The inclined plates are economically- and environmentally-competitive alternative to the polyelectrolyte chemicals currently used to improve settling tanks performance.