Floating Flocs

Abstract

Rising flocs in the sedimentation tanks have been polluting the effluent water at the plants in Tamara, Ojojona, and Marcala. Initially, Alum overdosing was thought to be the cause of the problem; however, the issue persisted even after the dosage was changed. The speed at which the flocs rise suggests that air bubbles are lifting them to the surface.

Gas bubbles form in water when the total dissolved gas pressure is greater than the local solution pressure (when the water is supersaturated with gas). Supersaturation of the water flowing into the plants may be caused by a pressure drop to below atmospheric pressure due to high rates of mixing caused by turbulence at the plant entrance and churning in the grit chamber. Cracks in the transmission lines combined with high pressure regions would also result in gas being infused into the influent water. Supersaturation of the water causes gas bubbles to form on dirt particles in the water, resulting in flocs floating to the surface and contaminating the effluent water.

A procedure is needed to either prevent supersaturation of influent water or remove excess gas prior to sedimentation to increase the effectiveness of the water treatment plant. Currently, research is being performed using a back-washed sand filter to remove excess gas from the plant influent water.

Introduction and Objectives

The goal of the Floating Floc Team is to find an efficient and cost-effective remedy to the floating floc problem and to implement that method in current and future AguaClara plants. We are currently looking into a back-washed sand filter approach, which involves decreasing the gas content of the water in the grit chamber before it enters the flocculation tank.

Floating Floc Team Semester Goals
Floating Floc Team Meeting Minutes

Current Research

[Floating Floc Sand Filter Method]

• The sand filter approach involves forcing water upward through a layer of sand, as if backwashing a sand filter. The sand filter method provides a substance besides the sediment in the water on which the bubbles can form. When the bubbles grow large enough, they will rapidly rise to the surface.

Additional Information

Floating Floc Aeration Method

• This page discusses past research on the aeration approach to dissolved oxygen removal. The aeration approach attempted to use bubbles as a catalyst to increase the rate of dissolved oxygen transfer out of solution by allowing dissolved oxygen to diffuse into the bubbles. This would increase the bubble size and cause the bubble to rise faster.

[Theoretical Modeling of Aeration Method]

• This page discusses the research into the floating floc phenomenon that is being conducted.

Floating Floc Team Annotated Bibliography

[Quiz]
This quiz checks that you have a basic understanding of the principles behind this research.