Grantee Research Project Results
Final Report: Point-of-Use Polyurethane Foam Filter
EPA Grant Number: SU836023Title: Point-of-Use Polyurethane Foam Filter
Investigators: Weber-Shirk, Monroe , Irish, Bradshaw , Edwards, Katie , Grimshaw, Walker , Shebaro, Nadia , McBride, Kelly
Institution: Cornell University
EPA Project Officer: Hahn, Intaek
Phase: I
Project Period: August 15, 2011 through August 14, 2012
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2011) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Safe and Sustainable Water Resources , P3 Awards , Sustainable and Healthy Communities
Objective:
Students from the AguaClara Program at Cornell University are designing and testing a filtration unit for drinking water treatment that uses reticulated polyurethane foam as its filtration media to produce safe drinking water. The final design will be scalable, easily constructed from locally available materials, require no electricity, and effectively filter turbid surface waters (< 100 NTU) to meet the EPA drinking water standard (< 0.3 NTU). The device is small and lightweight to ensure ease of use but also robust enough to sustain continuous operation for extended periods of time in extreme conditions. The filter could be built at different scales and used in a variety of scenarios, including during an emergency for treatment of water with a highly mobile unit, as a stationary unit for treatment of water with a water kiosk or a pipe network for very small communities (less than 1,000 people).
The primary motivation for this research, and the goal of AguaClara as a whole, is to provide safe, clean drinking water to those who need it through sustainable designs that are easy to operate and maintain, economically viable, and gravity-powered. As a complement to AguaClara’s existing municipal water filtration plants, this filter aims to target smaller communities that are simply too small for a municipal scale water treatment plant to be economically viable. Such communities are ideally suited to treat nearby surface water with the foam filtration unit and deliver it via a centralized water kiosk system or a pipe network. In both developed and developing nations that have been subject to a disaster, clean water can be even more difficult to deliver to those in need. Thus, a resilient, scalable technology would prove invaluable in disaster relief and for communities that lack access to safe drinking water. Ultimately, our team’s goal is that this effective foam filtration device be used widely to provide safe, clean drinking water to small communities that are currently unserved.
Summary/Accomplishments (Outputs/Outcomes):
The research team performed extensive testing of a bench-scale prototype with single-stage foam filters during Phase I and made several significant discoveries that influenced the current design of the filtration unit. Early trials demonstrated that a polyurethane foam filtration system can significantly decrease the turbidity of surface water, but its efficacy can be enhanced substantially by the addition of a chemical coagulant such as polyaluminium chloride (PACl) (Figure 1).
Figure 1: Performance of filter with and without chemical coagulant (alum).
Since the coagulant was deemed necessary, operation and maintenance of the filter was determined to be too complex for use on the household scale. Subsequently, the application for the research shifted to a larger scale. Paired with PACl, foam filtration has shown to provide clean, low turbidity water that meets the EPA standard of less than 0.3 NTU even with an influent turbidity of 100 NTU. Phase I trials also showed that foam filtration is a depth filtration process, with performance increasing with an increase in depth of filtration media. Trials were also conducted to determine the maximum head loss through the filter as the pores clog. Based on these design factors, our team designed a prototype filter to be used for a community water supply or emergency water supply system.
A prototype has been constructed based on the research performed in Phase I and will undergo extensive testing in Phase II followed by eventual deployment in the field. The updated system is designed to meet the UNHCR's (United Nations High Commissioner for Refugees) water recommendations for refugee situations. This standard suggests providing fifteen liters of “reasonably safe” water per day per individual as well as two liters per day of clean water specifically for drinking (Stafford, 1992). The current prototype can provide 15 L/person/day for 50 people with a 5 cm (2 in) diameter pipe or 1000 people with a 20 cm (8 in) diameter pipe. The design is also inexpensive to build and easy enough to operate that multiple units could be used to increase the total treatment capacity.
Figure 2: Filter performance of three depths of 30 ppi foam with 100 NTU influent turbidity | Figure 3: Filter performance of 25 cm of 90 ppi foam. Influent turbidity of 10 NTU. |
An important feature of the current design is the use of two stage filtration. Phase I studied the independent performance of roughing and finishing filters (Figures 2 and 3); Phase II will investigate improved performance through the use of a multi-stage system, both roughing and finishing filtration in series. First, a roughing filter consisting of 30 pores per inch (ppi) foam captures the majority of the suspended solids and extends the run time of the finishing filter. Next, a finishing filter made of 90 ppi foam further reduces turbidity to below EPA standards. Filtration theory predicts that the overall performance of these two filters in series will be the sum of the performance of the individual components. Thus, it is predicted that the full scale prototype will meet EPA standards of effluent turbidity of less than 0.3 NTU, even with influent turbidities as high as 100 NTU. Testing of the pilot-scale prototype in Phase II will confirm this hypothesis. Additionally, we will expand our investigation by testing influent water with turbidity that is greater than 100 NTU and explore the use of roughing filters in parallel and in series to see which configuration performs best.
During Phase I, the team analyzed the feasibility of the size and portability of the preliminary design. A review of development literature and consultation with our implementation partner, Agua Para el Pueblo (APP) informed our approach to designing the filtration unit. Previously implemented systems have shown success accessing remote or resource-deficient areas of the world with designs that can be transported and operated from the bed of a truck (Garsadi, 2009). The proposed designs are easily carried by a person and thus easily meet this objective.
Conclusions:
Based on the findings of the Phase I research, we have concluded that the best course of action is to develop a filter for a water kiosk or piped network distribution system first. These applications will provide an opportunity to gain extensive operating experience and refine the design. Our goal is to develop a technology that will have a pronounced impact on the market and maximize the benefits of the research and funding that has gone into the project. The current prototype design (Figure 4) was built to improve upon all aspects of our bench scale trials so the design can be optimized for use in the field. Phase I findings have already demonstrated the technical success and feasibility of the bench scale design; Phase II will not only focus on further improving technical performance, but will also focus on economic feasibility, ease of operation, and overall feasibility in the field.
Figure 4: Current Demonstration Prototype
Supplemental Keywords:
clean water, water filtration, foam filtrationRelevant Websites:
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.