Optimizing Coagulation of Municipal Wastewaters for Turbidity Removal

The objectives of this laboratory study were to determine the effect of types and dosages of coagulants on the removal of turbidity from municipal wastewaters. Wastewaters were collected from Southerly Wastewater Treatment Plant, Cleveland, Ohio and Central Wastewater Treatment Plant, Solon, Ohio. Wastewaters from the Southerly plant consisted only of samples taken after primary settling. Wastewaters from the Solon plant consisted of samples taken after four different stages of treatment, primary settling, secondary settling, tertiary filters and chlorination. Coagulants selected for investigation included earth materials (granite, basalt, shale and limestone), flyashes and two types of activated carbon. The coagulant dosages varied from 0.4 to 6.0 g/I. The turbidity of the wastewaters from the Southerly plant increased when powdered samples of granite, basalt, shale, limetsone and flyash were added with increasing dosage. Similar results were also noted in the samples of Solon plant, but the levels of increase decreased with increasing stages of treatment in the plant. The granulated activated carbon decreased the turbidity by 5.8% at a dosage of 4.0 g/l while the powdered activated carbon reduced the turbidity by 88% at a dosage of 1.0 g/1 in treating Southerly wastewaters. Similar results were also obtained with Solon wastewaters. However, the improvement in turbidity with addition of the powdered activated carbon was less drastic as the stages of the wastewater treatment in the plant increased. © 1989, Taylor & Francis Group, LLC. All rights reserved.