(a) Using 200 ml of sample on a magnetic stirrer, add coagulant in small increments at a pH of 6.0. After each addition, provide a 1-min rapid mix followed by a 3-min slow mix. Continue addition until a visible floc is formed.
(b) Using this dosage, place 1000 ml of sample in each of six beakers.
(c) Adjust the pH 4.0, 5.0, 6.0, 7.0, 8.0 and 9.0 with standard alkali.
(d) Rapid-mix each sample for 3 min; follow this with 12-min flocculation at slow speed.
(e) Measure the effluent concentration of each settled sample.
(f) Plot the percent removal of characteristic versus pH and select the optimum pH (Fig. 4.6).
(g) Using this pH repeat step (b). (d) and (e) varying the coagulant dasage.
(h) Plot the percent removal versus the coagulant dosage and select the optimum dosage (Fig. 4.6).
(i) If a polyelectrolyte is used, repeat the procedure, adding polyelectrolyte toward the end of a rapid mix.