As EWB Valpo prepared for the upcoming trip to Africa, the Projects Team was hard at work researching different clean water alternatives. Of the alternatives, the Projects team decided to build a prototype of a bio-sand filter. It was the team’s belief that this filter was one of the most likely alternatives for the region and the team desired to better understand the process behind the construction of the filter. What makes a bio-sand filter different from other alternatives is that it both purifies and filters water, meaning that it kills bacteria while also removing dirt and debris.
The initial stage of the prototype consisted of the team scouring the internet and previous EWB-Valpo documents for the specifications of a bio-sand filter. The team also spoke with multiple Valparaiso University faculty who have had experience in water treatment and water testing. One resource that the team used as a guideline during the construction of the prototype filter was a purifier construction manual from Aqua Clara, a non-profit water treatment organization. However, the instructions provided had to be adapted to fit supplies and funding.
A basic bio-sand filter requires a large container filled from top to bottom with layers of large stones, small stones, pea gravel, coarse sand, and fine sand. At the base of this container is a pipe that allows water to flow outside of the container after having been filtered by the layers of media. The two layers of sand are the most important layer, and together these layers are required to have a minimum depth of 21 inches. A bio-sand filter works like multiple layers of netting that capture suspended particles as water flows through them. Also, over time, this process will eventually form a layer of bacteria at the top of the filter. This bio-layer kills the bacteria present in the water, purifying it.
The challenges that the team faced while building this prototype was finding an appropriately sized container to house the media and the flow rate of the filter. The container the team used was a 42 inch Rubbermaid rectangular trashcan. Although the container was plenty large enough, it was too thin, and distended as more and more sand was poured into the trashcan. In order to avoid a potential rupture, straps were tightened around the container for reinforcement. Also, the flow rate of the trashcan was initially 3 liters per minute. For most bio-sand filters, a target flow rate of 4 liters per minute is ideal. Upon noticing this, the projects team decided on two possible alternatives to increase the flow rate. The first would be to use more coarse sand as opposed to fine sand. This would allow the water to flow through the filter and reach the piping faster. Also, if the team were to create a larger network of pipes in the base of the container, the flow rate could have potentially increased.
The plan for the upcoming trip is to take all of this knowledge and present it to the villagers so that they can make an educated decision about which water treatment options are best for their community. Either way, the building of this prototype resulted in EWB-Valpo having a richer knowledge of bio-sand filter construction and operations.