Foam Filtration

Foam Filtration

Numerous techniques of water filtration are in use today, most of which involve the use of sand as the porous media. A preliminary  literature review revealed a dearth of information on foam filtration. Our team has decided to focus on investigating the actual filtering capacity of a polyurethane foam material as opposed to the traditional method of sand filtration. With proper implementation, a foam filter could reduce the amount of water that is wasted during the backwash cycle of a traditional sand filter. A foam filter requires less surface area, and could potentially be less expensive to build than a traditional sand filter. However, a foam filtration unit will also require a tight seal with all of the edges of the tank, in order to avoid preferential flow paths which will result in unfiltered water. In addition, a foam filter will likely require manual maintenance by the plant operator.

Foam filtration has been ruled out for an AguaClara plant because the foam would be too difficult for an operator to clean. However, previous research has proven that foam is an effective method of filtration, therefore this team decided to focus on designing a point of use foam filtration unit. Due to chemical dosing and usability concerns, the point-of-use application was ruled out as a possibility for foam filtration. The team then focused on the design of an emergency filtration system that can be transported on the back of a pickup truck. After speaking with communities in Honduras, it was decided that foam filtration would be more useful in small communities. Research has been done to optimize the design such that it is as efficient as possible and provides the desired standard of 1 NTU effluent water turbidity. 

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Note: Turbidity is defined as the cloudiness of a fluid caused by suspended particles. Higher turbidities correlate to more opaque fluids.

Current & Future Research

The Fall 2012 team focused on improving the apparatus by making it run without electricity and more user friendly. As that  unit was deployed to Honduras over the January 2013 Winter Trip, the Spring 2013 Foam Filtration Team is focused on the fabrication techniques of a new foam filtration system. The Spring 2013 focused on designing, building and documenting a new foam filtration system, measuring flow and headloss, and additionally adapting a linear chemical dosing system. A key long-term goal will be to provide clear, concise documentation for this design as the goal will be easy assembly of this system in Honduras. As a result, a small scale filtration unit was designed to be deployed in Spring 2013. The design consists of a roughing filter that utilizes 30 ppi* foam and a finishing filter with 90 ppi foam. The filter unit, which consisted of the stand, filter casing, and pipes that transport water between the filters, was built using PVC pipes, of which the diameter can be selected based on the volume of clean water needed. Originally, the Spring 2013 team planned on utilizing AguaClara's design linear chemical dose controller to dose the influent with coagulant and effluent with chlorine.  Due to time constraints, this was not finished. A simple visual indicator for when the filter should be cleaned is necessary due to the fact that we are trying to minimize cost. The current visual indicator consists of a Secchi Disk that can detect turbidities at least 20 NTU. 

Additionally, experiments with the foam column and Secchi Disk will continue.  Other research areas will be explored as well. This will include the improving the method where the Secchi Disk is used as a visual indicator or finding an even more effective way to visually indicate when the filters need to be cleaned. Future teams will also need to adopt an effective way of implementing a linear chemical dosing system in the current foam filtration unit.