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Floating Toilets That Clean Themselves Grow On A Lake

During the dry season, human waste makes the water putrid along the floating village of Prek Toal on Tonle Sap Lake.

Imagine you live on a floating lake house. Open air. Chirping crickets. Clear, starry nights. Everything seems great until you need to use the bathroom.

The natural instinct might be to make a deposit in the water. But that wouldn't be safe. Microbes in your feces would contaminate the water and could cause outbreaks of deadly diseases, like cholera.

A group of engineers in Cambodia wants to solve that problem for the floating villages of Tonle Sap Lake, the largest freshwater lake in Southeast Asia. Over a million people live on or around it. Exposure to wastewater spawns diarrhea outbreaks each year. In Cambodia, diarrheal diseases cause 1 in 5 deaths of children under age 5.

To help clean the lake's water, engineers at the company Wetlands Work! in Phnom Penh are developing plant-based purifiers, called Handy Pods. The pods are essentially little kayaks filled with plants. They float under the latrine of a river house and decontaminate the water that flows out.

Here's how it works. When a person uses the latrine, the wastewater flows into an expandable bag, called a digester. A microbial soup of bacteria and fungi inside the digester breaks down the organic sludge into gases, such as carbon dioxide, ammonia and hydrogen.

Some microbes in the waste survive that first step, but then they're washed into a pod filled with water hyacinth. The hyacinth roots have a large surface area to which the remaining bacteria stick. The water that runs off the roots into the lake is clean enough to play and swim in, Wetlands Work! founder Taber Hand says. But the water is still not safe enough to drink.

During a pilot project in 2013, Hand and his team gave pods to 35 houses in a village on Tonle Sap Lake. "The pods reduced E. coli in the ambient water by 50 percent," Hand says.

That wasn't as good as the pods performed in lab tests, where they cut levels of E. coli by more than 99 percent. Hand thinks that's because real lakes have other sources of contamination besides latrines.

At the top of that list? Pigs. Pigsties around Tonle Sap Lake produce a tremendous amount of waste, Hand says.

"The floating communities of Tonle Sap Lake are one of the most challenging contexts for sanitation in the world," says environmental engineer Joe Brown of Georgia Tech, who isn't involved with the project. "Handy Pods are potentially a useful way for processing human excrement in this context."

But the floating toilets still have a ways to go before they are widely distributed.

For starters, Brown says, it's unknown whether the pods filter out viruses and parasites that cause diseases. Manmade wetlands remove these pathogens, he says, so there's a possibility the hyacinth roots could also do it.

Another roadblock may be cost. Each Handy Pod costs about $30. Most villagers on the lake make less than $1,000 each year.

Hand thinks solving the pig problem is crucial to the overall success of the pods. Grand Challenges Canada recently gave Wetlands Work! a $100,000 grant to adapt Handy Pods for pigsties. The company will also use the money to distribute the pods to 10 more villages.

Hand isn't stopping there. His ultimate goal? "Total world domination of floating village sanitation," he jokes.

But he does hope that, one day, the pods could be used for overcrowded floating communities in places like Bangladesh, India and Nigeria.

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