Stacked Rapid Sand Filtration for India

In October of 2011, a water treatment plant with a stacked rapid sand filter was completed in Tamara, Honduras.

Stacked rapid sand filtration is an idea that was realized by AguaClara students. Whereas systems using traditional rapid sand filtration might require pumps or elevated tanks in order to clean the filter, our stacked version is self-sufficient. Its innovation lies primarily in the hydraulics, and when the Tamara stacked rapid sand filtration system was implemented in 2011, it was the first of its kind in the world.

As we prepare for India, AguaClara students have started working on optimizing the processes of the stacked rapid sand filter for flows less than three liters per second. The LFSRSF (Low Flow Stacked Rapid Sand Filtration) subteam have split the work between two projects: a LFSRSF model four inches in diameter, and a model twelve inches in diameter.

Sarah, Chenxi, and Lishan have been working with machinists to create the parts needed to build the model twelve inches in diameter, which is close to the scale of what will be built in India. They're also in the process of implementing and testing a new method for joining the pieces of the filter column.

Sarah and Lishan measuring a section of the filter column.

Alex and Jeanette are working on the four-inch model you see below. During backwash—the process that cleans the filter—water is run through the filter column from the bottom and up through the top, and ideally what happens is that unwanted sediment will be broken up and moved out of the filter column. However, that doesn't always happen; the sand will sometimes move along with the sediment, forming a "plug," which is something we don't want. The filter model in the picture below comes installed with a "backwash initiator," which helps with the backwashing process. Alex and Jeanette's current goal is to build an instrument to gauge the amount of pressure needed for a successful backwash with and without the aid of the initiator, in an attempt to precisely quantity the effects of the backwash initiator.

Alex holding up a tube that will later become a manometer.
You can see the model filter on the left-hand side. The backwash initiator
is the metal rod that's partly visible through the translucent filter column.