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

As of Fall 2013, the team has spent this semester redesigning the foam filtration unit to fit all into one 55gallon drum. The apparatus consists of a roughing filter that utilizes 30 ppi* foam and a finishing filter with 90 ppi foam approximately 23 inches in diameter. The filter unit was designed on the premise of providing for a community of 100 families at approximately 1 L/s. In order to clean this unit, a hoist supporting approximately 500 pounds of concrete will be used to compress the foam. Then a flexible piece of tubing acting as a siphon will drain the dirty water that pools on the surface. Towards the beginning of the semester and on the Summer 2013 team, the amount of time until the foam needed to be cleaned was investigated. These times should serve as an approximation of time until cleaning, instead of previous semesters suggestions of a Secchi disk. However, more research needs to be done to investigate the effectiveness of a wholly constructed apparatus including flow control with coagulant and post-filtration chlorination. The effectiveness of the foam and the times until cleaning will probably vary with the presence of coagulant. 

Future teams will  need to redesign an emergency filtration unit with the new one column design in mind to ensure easy transportability, preferably with all pieces fitting into the single column. Additionally, future teams should investigate easier to construct cleaning mechanisms.