Foam Filtration

Currently, an AguaClara plant can produce effluent water after sedimentation with a turbidity of about 5 NTU. Our goal is to reduce the effluent turbidity to less than 1 NTU. One potential method of accomplishing this is adding a filtration unit to the AguaClara plants.

Numerous techniques of water filtration are in use today, most of which involve the use of sand as the porous media. After preliminary research revealed a lack 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 could also potentially require less area, and be less expensive to build than a traditional sand filter.

With these advantages in mind, we have considered a number of different designs which could provide the desired standard of 1 NTU effluent water turbidity.

(Include your disadvantages here too or include a separate section in your wiki to compare and contrast sand filter and filter foam including cleaning)

Foam Filtration Current Research

Flat Foam Sheet Experiments with coagulated particles

Currently, we are testing the filtering capacity of foam under the worst case lab conditions, which consists of filtering water containing unflocculated clay particles. This represents the worst case senario, because the particles are small and uncoagulated. We would like to test the filtering capacity of the foam under conditions that are more reflective of conditions in an AguaClara plant. This involves adding alum and a rapid mix tube to our system, in order to produce larger particles, which will then lead to, hopefully, higher levels of colloid removal.

Flat Foam Sheet Experiments

Prior to considering the actual design of a proposed filtration unit, it is necessary to test the filtering capacity of the foam material we would like to use. Therefore, a number of experimental trials on foam with varying pore sizes and flow rates were conducted. Pore sizes are measured in the units pores per inch, which is a linear measurement. A smaller pore size corresponds with a larger number of pores per inch, i.e. a pore size of 90 ppi will have smaller pores than foam with 60 ppi. Briefly, it was found that the flat foam sheets alone do not provide enough colloid removal, under the conditions tested, to be an implementable method of filtration for the AguaClara plants. However, under more realistic conditions, where particles would be flocculated, rather than the worst case lab conditions as tested, foam filtration may in fact be feasible. Please see the results and discussion of each experiment for further explanation.

Foam Filtration Future Research

Later this semester, we would like to further investigate a few different methods of achieving our goal of 1 NTU effluent turbidity, as outlined below.

Foam Media Upflow Design

An alternative to using the foam simply as a flat sheet which water is filtered through is to design a hybrid upflow filter, which uses small pieces of the foam as the filtering material, as opposed to the traditional upflow sand filter. This idea is based on the technique outlined in this article