Slow Sand Filter Technology

Slow Sand Filter Technology

A Purdue-affiliated startup has developed a low-cost, low-maintenance slow sand water filter technology to better provide clean and safe drinking water to schools and communities in developing countries around the world. 

college-of-engineering.png Maji Safi International LLC, which means clean water in Swahili, was founded by John Maiyo, a doctoral student in Purdue’s College of Engineering; Chad Jafvert, a professor of civil engineering and environmental and ecological engineering; and John Howarter, assistant professor of materials engineering and environmental and ecological engineering.

The company currently installs groundwater wells, provides ceramic filters, and slow sand filters in Western Kenya where safe water is not readily accessible.

The unique Purdue technology used by Maji Safi is a slow sand filter that utilizes containers filled with sand and water. At the bottom of the container is a water collection plate, designed at Purdue. The sand provides a large surface area on which microbial growth occurs that metabolizes the dissolved and particulate organic material in the water. The point-of-use slow sand filters are made from readily available five-gallon plastic pails or 55-gallon drums.

“Typical slow sand filters use gravel layers at the bottom of the filter as the water collection zone, however, our filters does not use gravel. Instead we use a porous plastic plate enclosed within a mesh bag ,” Jafvert said. “We’ve found this method to be much simpler to use and maintain. There is only the sand to sieve and rinse, instead of sand and different gravel sizes. It provides easier maintenance and makes for easier filter transportation and final assembly.”

Once water is treated by a filter, a small amount of chlorine is added to the water for final disinfection, producing clear, colorless, drinkable water. 

Maiyo said that after 30 minutes of contact with the chlorine, the water is ready to drink.  “People and children in schools come up to the filter systems with a cup to get a drink, and the schools are able to use the water in their kitchens or for cleaning,” he said. “Because the filters are operated in ‘batch’ mode, water is generally added three times each day, providing for an eight hour contact time between the water and microorganisms in the filter. Each 55 gallon drum filter can process 200 liters of water each day. With five filters installed at one school, this meets the needs of over 400 children and teachers at the school every day.”

The filters are ideal for rural communities.   

“The materials needed for these filters are very basic and can be found in the countries we aim to serve. The idea is that the microorganisms do the work to remove organic materials from the water so the only energy demand is pouring water into the filter,” he said. “Our particular design allows for the filters to be easily transported, and does not require any particular expertise for final construction at the “point-of-use”.  As a disinfectant, chlorine is very inexpensive in the countries where we have installed filters, so there is no huge investment required by the communities to use the technology.”

Maji Safi has installed 10 large slow sand filters in rural schools in Kenya, and Jafvert and Howarter have installed similar filters in Colombia, Tanzania, and China.  

Maiyo said the company’s next steps involve marketing the filters to other schools.

The company also is seeking support from people who would like to sponsor one or more schools, which would enable Maji Safi to install filters and provide clean drinking water to the students, teachers, and community members. 

Source: Nasdaq