Low Flow Stacked Rapid Sand Filtration

Low Flow Stacked Rapid Sand Filtration

Low Flow Stacked Rapid Sand Filters are an adaptation of rapid sand filters optimized for flows less than 3 L/s that don't require any flow control or backwash. SRSF is a "game changing" technology invented by the AguaClara team that is significantly simpler to operate than conventional rapid sand filters. 

Fall 2012

This semester we were responsible for analyzing and optimizing the Low Flow Stacked Rapid Sand filter.  Work for the semester began with an existing filtration unit which did not contain sand, due to predicted failure from large head losses in filtration and backwash. The existing design was modeled in AutoCAD 2013 to provide an illustration of the system. Updates to this drawing were completed and will continue to be as fabrication phases occur. One of the primary tasks was to develop a mathematical model in MathCAD to calculate the flows and head losses throughout the system. The model was completed for filtration and backwash, and includes calculations for both cycles with and without sand present.

Hydraulic testing was completed to determine the head losses in filtration and backwash, risk of sand transport through the backwash pipe, and flow rates. These measurements and observations were compared with the mathematical model to determine its validity. According to head loss values obtained from the mathematical model, several changes were made to the filter prototype. Such fabrications included complete reconstruction of the backwash pipe, changing of valve types, and installation of NPT fittings and ball valves. Finally performance testing was completed to determine the effectiveness of the prototype in regards to decreasing effluent turbidity. Overall, it was determined that the filter prototype is highly effective at decreasing turbidity for several influent concentrations at the designed flow rate.

This system was tested in Honduras in January 2013.

Spring 2013

In January 2013, the Low Flow Stacked Rapid Sand Filter was tested in Honduras. Although the filter worked, it quickly failed due to structural weaknesses. The primary tasks this year included improving the durability of the filter and increasing the ease of operation. New manifold and sand drain designs are in the process of being implemented. Additionally, the stacked rapid sand filter went to Washington, D.C. in April for the EPA P3 competition. A written approval for the P3 grant was written and submitted. To demonstrate the design and effectiveness of the LFSRSF, a fully operational unit was designed. The prototype underwent hydraulic and performance testing and operated well at the competition.