Sand, sun and $60 = clean water
Combining a biosand filter and sunlight, Kettering's Engineers Without Borders A-Section engineered a solution to make contaminated water potable for a village in Mexico.
It took a year and a half from when they first heard about the plight of villagers in Estanque de Leon, Mexico, until Kettering’s Engineers Without Borders A-Section developed a solution to their potable water problem.
Between April 2007 and October 2008, the group visited the village three times: to assess the need and resources, to test a prototype and finally to install 45 biosand filters for the 300 people living in this rural northeastern village near the Texas border.
They group identified Estanque de Leon as their first international project after hearing that the lack of potable water caused frequent illness in the adults and threatened the long-term health of the children. They decided to take on the project and use their collective engineering education to design a water filtration system that was cheap, effective and culturally appropriate.
One of their biggest challenges was the lack of electricity in the village and a meager water supply that literally dried up for months during the year. In addition, they navigated difficult roads to reach the village and negotiated with local partners for materials, food, and lodging. “Despite the obstacles, we developed relationships with key community leaders and designed a way to bring potable water to Estanque de Leon,” said Mario Flores, former president of EWB A-Section and team member for the Mexico project.
The team engineered a simple, low-tech solution to the clean drinking water problem; biosand filters.
Biosand filters are a household-sized version of slow sand filters, which are usually large beds of sand that a continuous supply of unfiltered water runs through. The power of these filters is not in the mechanical removal of dirt by the sand, but from a biological process that develops on the top layer of sand. A layer called the “biolayer” or “smutzdecke” contains many “good” bacteria that get rid of harmful bacteria. This layer develops naturally in response to the presence of the harmful bacteria and is how a slow sand filter is able to achieve filtration rates of close to 99 percent.
The Kettering group based their design for a biosand filter on one developed by Dr. David H. Manz, P. Eng., P. Ag. (), whose biosand filter features a raised outlet pipe that rises above the sand level and keeps the biolayer alive.
The biolayer, or smutzdecke, is where the majority of filtration occurs. It has many organisms that create a threatening environment for pathogenic organisms. The smutzdecke also improves the absorption of water contaminants, or turbidity, on to the surface of the sand. The smutzdecke must be maintained by keeping it wet with approximately 5cm of water during periods of in-operation.
This allows the filter to remain effective even though it does not have a continuous supply of raw water flowing through it at all times. This design characteristic enables each family in Estanque de Leon to take ownership of their own filter, instead of having a communal slow sand filter.
The group slightly modified Manz’s filter for the Estanque de Leon project, according to Flores and Jeremy Bell, of Collingville, Ill., adapting it to the materials available in the region. The filtration system uses a combination of the biosand filter and solar disinfection (SODIS) to ensure very high filtration and disinfection rates. The filtration system is designed for personal home use in order to prevent ownership, maintenance and distribution conflicts in the community.
In addition to the filters, the team also designed, built and installed SODIS racks. The SODIS racks are the last step in the process. Ultraviolet (UV) radiation from the sun is actually an excellent disinfector, according to Flores, just as effective as chlorine in bacteria removal, but with a resource that is more renewable (chlorine has to be continually purchased).
After filtering the water through a sand filter it is put into one liter PET plastic bottles and placed on corrugated metal sheets in the sun. The UV radiation will fully disinfect the water within a few hours.
According to the World Health Organization (WHO), for high water consumers, consumption is estimated to be about two liters per day for a 60 kg person. Based on this metric, the minimum amount of water needed for the community would be 568 L per day[AW1] . The EWB team determined the bottles should be on the SODIS rack for a full day’s worth of sunlight for best results.
To ensure the sustainability of their solution to Estanque de Leon’s potable water problem, the students also designed and delivered one-on-one training sessions to community members.
Preliminary water testing showed that the biosand filters are successful in removing the majority of parasites and bacteria present in the water in the village. Subsequent solar disinfection should result in water that is 100 percent potable.
The low tech aspect of sand and sunlight to purify water is a good choice for remote areas without electricity, explained Dr. Laura Sullivan, professor of Mechanical Engineering at Kettering and EWB adviser. “It doesn’t require a lot of training or excessive translation of instruction,” she said, adding “it doesn’t need much to be sustainable, just minor maintenance.”
“Between initial trip EWB and final trip the government drilled a well in Estanque de Leon,” said Sullivan. “If there is enough water in the well the village won’t have to worry about surface water any more. The problem is that the well is 1,500 meters below ground level, whereas typical wells in Michigan are 20 meters below ground level,” she said.
Sullivan explained that it takes a lot of energy to bring water up 10000+ meters. “The village will need a significant source of energy to raise the water for daily use, they may have to a way to use wind or solar energy since there is no electrical service in the village.”
“We are now in a monitoring stage to make sure the filters are being used properly and see if it is having a positive impact on their health,” Sullivan said.
Many team members who were part of the initial group that chose the Estanque de Leon project, graduated before installation of the biosand filters. Throughout the project, the following people have been involved in bringing potable water to the village:
Erin Clancy ’04
Stacy Gardner ’06
Nadine Thor, director Environmental Health and Safety at Kettering University
Kettering’s EWB A-Section would like to acknowledge the generous support and assistance of:
General Motors Foundation
Engineers Without Borders USA
Banco de Alimentos de Saltillo A.C.
Universidad Autonoma de Coahuila
Diocesis de Saltillo Hospital Guadalupano,
Emerson Climate Technologies, and
Engineers Without Borders-Kettering University
Written by Dawn Hibbard