Construction and use of coagulation diagrams as a tool for continuous monitoring of flocculation in water supply

Abstract

In this work coagulation diagrams were constructed from bench tests with the aid of jartest equipment in order to evaluate the remaining turbidity of water prepared by adding kaolin suspension (until reaching a turbidity of 25 ± 2 uT). The water was then subjected to coagulation, flocculation and sedimentation. Iron-free aluminum sulfate was used as a coagulant in dosages varying from 5 mg L-1 to 100 mg L-1 and coagulation pH varying from 3 to 9. Three different rates of sedimentation velocities were investigated (3.0; 1,5; and 0.5 cm min-1). Based upon the coagulation diagrams, satisfactory results for turbidity removal were observed with coagulation pH values between 6.5 and 7.5 and coagulant dosages greater than 15 mg L-1; high dosages of coagulant did not necessarily lead to lower remaining turbidity values. Turbidity removal efficiency was higher in lower rates of sedimentation velocities, reaching values less than 1 uT at the lowest sedimentation rate studied. The construction of coagulation diagrams using jartest equipment proved to be an effective tool for the optimization of the coagulation phases, flocculation and sedimentation in water treatment, producing flocs whose characteristics were more easily analyzed using techniques of continuous monitoring flocculation.