Foam and Bag Filtration

Currently, the effluent water from an AguaClara plant has 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 the 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.

Foam Filtration Current Research

Flat Foam Sheet Experiments

Prior to considering the actual design of a proposed filtration unit, it is necessary to know the actual filtering capacity of the foam material we would like to use. Therefore, a number of experimental trials on foam with vary pore sizes and flow rates were conducted. 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, 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.

Flat Foam Sheet Experiments with larger 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 is not a realistic condition, and 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 tube flocculation to our system, in order to produce larger particles, which will then lead to, hopefully, higher levels of colloid removal.

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:http://www.wioa.org.au/conference_papers/06_vic/documents/StewartShipard.pdf