Biofilter uses dust to clean dirty water

Cocopeat, the dust from coconut husks, offers a cheap way to filter water in heavily populated urban areas.

The humble coconut can offer a quick-fix for the thirsty, but could it also provide a reliable source of clean water?

RTI International [RTI] believes it could. With funding from the Bill & Melinda Gates Foundation, it has been developing a cost-effective wastewater filtration system to tackle the problem of poor sanitation across the developing world. The new technology’s magic ingredient is cocopeat – the dust that remains after the husks are removed from coconuts, which can be used to separate and purify organic material in the water.

Wastewater is passed through a biofilter, made of cocopeat, which traps suspended solids. The organic matter is then consumed by microbes living in the dust. The process removes 90% of solids and pathogens found in domestic wastewater. The final product is an effluent safe enough to be used for crop irrigation or simply discharged back into the environment.

Cocopeat’s durability is a plus: it only needs replacing after six months of use and costs less than two US cents per day to filter enough water for one person. What’s more, the used cocopeat can be composted with tank sludge, creating a soil additive with nutrients which boost its water retention – a bonus for water conservation efforts. It is also compact, making it ideal for heavily populated urban areas.

The biggest obstacle to the implementation of this technology, however, is the willingness of poor communities to pay for it, explains David Robbins, water and sanitation specialist at RTI.

“Incomes are very low, and there are a lot of competing needs for things like food, shelter, water”, he says. “Convincing people to pay for wastewater treatment is always a challenge.”

However, Robbins thinks there’s a case for investment. The cocopeat biofilter is about 30% cheaper than other water-purifying methods such as constructed wetlands technology, he argues. It is due for commercialisation in 2013. – Maina Waruru and Kyla Mandel

Photo: David Robbins / RTI International Organization