the treated water was allowed to settle for 15 min, and the supernatant sample was withdrawn by a syringe from approximately 2 cm below the liquid level for analysis. The initial pH of the river turbid water was adjusted to a desired value with 1-M NaOH or 1-M HCl, and a further correction of the pH was not carried out during the experiments. The same coagulation test was conducted with no coagulant as a blank. The impact of water pH, initial turbidity concentration, coagulant quantity, and humic acid concentration as variable parameters was evaluated as different conditions in this research. Table 3 presents the details of the experimental runs and conditions. All the experiments were conducted in duplicate (the accuracy is considered to be ±4%) to ensure the reproducibility of the results; the mean of these two measurements are presented herein. The turbidity removal efficiency (TRE) was calculated using Eq.