Floating Flocs

Abstract

Floating floc in the sedimentation tanks of AguaClara plants in Tamara, Ojojona, and Marcala results in polluted effluent water. The cause of the problem is thought to be bubbles forming on floc particles due to supersaturation of influent water. The Floating Floc team is conducting research with a back-washed sand filter to remove excess gas from the water in the grit chamber before it reaches the sedimentation tank. The sand provides a surface area on which bubbles can form to leave the water. The goal is to remove enough excess gas, so that the water entering the sedimentation tank has a lower bubble forming potential. Currently, research is being conducted with different sand grain sizes to observe and quantify the effectiveness of the method for removing the excess gas from supersaturated water. Our main objective is to find an optimal sand size and flow rate to maximize gas removal and minimize the amount of sand carried away by bubbles.

Introduction and Objectives

Introduce your approach to solving the problem you were working on by explaining what needs to be done to meet your goal. What did you hope to learn? How did you expect your work to guide the construction of water treatment plants or to improve drinking water quality in the Global South?

The goal of AguaClara is to provide safe drinking water through sustainable, replicable water treatment systems. Currently, Floating flocs caused by supersaturation of influent water into many treatment plants are polluting the effluent water. 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. Excess gas in the water causes bubbles to form on floc particles in the sedimentation tank, floating them to the surface. The goal of the Floating Floc team is to find an efficient and cost-effective approach to remove excess gas from water and to implement that method in current and future AguaClara plants to improve the sedimentation process.

The Floating Floc team is currently experimenting with a back-washed sand filter column. In the actual plants, a layer of sand would be suspended in the grit chamber to provide a surface area for gas bubbles to form and leave the solution.

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.