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.

An Improved Chemical Dose Controller

On Wednesday of last week, our Chemical Dose Controller team finished preparing a package to be sent out to India. The chemical dose controller is the part of our plant that administers coagulant and chlorine and it's an incredibly intricate piece of technology. The mechanism regulates the dosing of the desired chemical, adjusting dosages accordingly to complement the flow rate of the water through the plant. It's important to note that it achieves this without pumps or meters or anything other than gravity and some clever techniques. The team has also just finished adjusting the system to accommodate for lower flow rates for deployment in India.

The kit to India contained some new components for the CDC mechanism to be implemented there; there's even an instruction manual to be sent along with the parts, keeping with our goal of distributing technology that works well without the need for specialized knowledge or resources.

Next stop: India!

There was a problem concerning the lackluster performance of one component: it was found that one of the parts inside the valve slowly deteriorated from constant contact with chlorine, which jams the valve and prevents it from being properly maintained. 

The white part doesn't work well with chlorine in the long-run.

Luckily, Saugat and Zeyu, the two that make up the Chemical Dose Controller subteam, discovered what was happening and replaced the old valve with a new one that looks virtually identical in every respect, except that the knob is red. In the newer and much better model, what used to be EPDM rubber ring is now rendered in fluoroelastomer, a popular alternative to Teflon, the bulletproof material.

Bonus picture: a representation of the chemical dose controller mechanism. The actual mechanism doesn't look like this at all.

You can actually see the old valves with the blue knobs still attached; the newer ones have red knobs. This model, like the actual thing, is operated by gravity.