New profile posted: Tate Rogers, an environmental engineering grad student at North Carolina State University, designed a novel device for emptying pit latrines in developing countries

Tate Rogers

Solving a neglected problem

By Tom Gibson

During his sophomore year at North Carolina State University, Tate Rogers went on a mission trip to Honduras with his church delivering food to villages in remote locations. He didn’t realize it at the time, but this would set the stage for a unique career path that lay ahead.

Fast-forwarding to his senior year in the environmental engineering department at NC State, the 23-year-old Rogers found himself taking a senior design course taught by Dr. Robert Borden. He had gotten an RFP (request for proposals) from the Bill and Melinda Gates Foundation for devices in several areas of sanitation, seeking ideas to improve the lives of the billions of people worldwide who live without proper facilities. The innovations they sought included improving current pit latrine design, re-use of the waste for agriculture and energy, and cheaper waste extraction methods from the pit latrines. Borden put this challenge to his class, and Rogers decided to focus on a new waste extraction method.

For eons, people have commonly removed sludge from latrines with buckets and shovels. They often dump it in the first convenient location they find, and it gets tracked through the neighborhood and into homes or washed into nearby streams, spreading disease. After several days of puzzling over possible ideas, Rogers came up with an answer. Growing up on a small farm, he had helped dig fence-post holes with power augers. A form of the ancient Archimedean screw, which has been used for more than 2,000 years to lift water, augers simply screw into the ground and lift the material to the surface. Rogers thought of placing a stationary pipe around the auger to control the lifting of the waste up the flights of the auger and out through a tee fitting. A gasoline motor would drive the auger, and a hose from the top of the pipe would direct the sludge to a truck or 55-gallon drum on a dolly that could be wheeled away.

After making sure this technology didn’t already exist, Rogers ran his idea past Borden, who immediately liked its simplicity and cost-effectiveness. Rogers set out to develop his design, and as a result, he now finds himself immersed in a career involving mission work to developing countries. “I’ve always had a passion for mission work,” he relates. “You see poverty, and you want to develop solutions, and I want to couple that with engineering.”

Rogers grew up on a 40-acre horse farm that specializes in barrel racing in Lawsonville, North Carolina, a small town in the country north of Winston-Salem. For his last two years of high school, he attended the North Carolina School of Science and Math, a boarding school in Durham. This not only prepared him for college, “it pointed me in the environmental engineering direction,” he recalls.

When Rogers started his design project, he didn’t have a clue about the extent of sanitation problems. Now he can spell out the facts: “You hear in the news all the time about water -- water treatment and getting clean water in Africa and the developing world. It is an issue, but 90 percent of the world now has access to clean water. Sanitation is way, way behind. Only about 63 percent of the world’s population has access to proper sanitation. That means 2.5 billion people out there don’t have access to proper sanitation, and there are still over a billion people that use open defecation, meaning they have no toilet and throw their waste wherever they can. It’s a big global problem that doesn’t get as much attention as it should.”

Project continues into grad school
As Rogers roughed out his design in class, he learned he had been accepted into graduate school at NC State, and he would pursue his Master’s in environmental engineering. This gave him the opportunity to continue the project as part of his Master’s work, and it would become the subject of his thesis. He worked on the project with Dr. Borden through that summer and submitted his proposal to the Gates Foundation in May 2011 knowing it was a long shot – more than 2,000 proposals were submitted. Then, a few days before he started grad school, they learned the project had been selected and would be awarded the $100,000 Phase I grant to design, produce, and test their technology.

“After we got funding, we built a prototype in the lab,” Rogers recalls. “There were several variations before we got it working decently, and we tested it on bentonite clay,” which is similar to human waste. After testing in the lab, they went to the NC State dairy farm and tested it on dairy waste. They used an electric motor to drive the auger. “We tested different flowrates and pressures produced for varying viscosities of the simulated waste.”

Rogers shows an original prototype of his design with other members of the team, including (left to right) Tarek Aziz, Dr. Francis de los Reyes, Stewart Farling, and Robert Borden, who taught the design class that started the project.

They did that for a year as they came up with the final version. It uses a gasoline engine to power a hydraulic pump, which in turn drives a hydraulic motor, which can rotate up to over 400 rpm. This arrangement is capable of higher rotational speeds and torque, yielding higher flowrate and lift and allowing them to empty less-viscous waste faster. They originally used a 2-horsepower engine, but it wasn’t powerful enough to lift waste 8 or 10 feet as required in many situations; most pits are 1.5-2 meters deep. The prototype has produced flowrates up to 13 gallons per minute. It costs less than $750 to produce, and they estimate the cost per pit latrine emptied at less than $5 compared to $30-$80 for current technologies.

In describing the final design, Rogers says, “It’s actually less cumbersome because there’s a big gasoline engine on wheels that doesn’t have to be right next to the pit to power the hydraulic pump. The only thing the user holds onto is the handlebars attached to the hydraulic motor that turns the auger. It’s not a very complicated design, which I think is the best part about it.”

Then in August 2012, Rogers traveled with Dr. Borden to the Reinvent the Toilet Fair on the Bill and Melinda Gates Foundation campus in Seattle to exhibit their prototype. The fair brings together innovators, design experts, investors, advocates, and potential customers to showcase the progress in the reinvention of the toilet and related technologies such as theirs. They received helpful feedback on the design and problems they might encounter in the field from people who have actually been on the ground in the developing world and dealt with pit latrine emptying first hand.

“That was a really good experience because I got to meet a lot of people working in the field. The water and sanitation in developing countries field is pretty small, so it was nice to meet some actual people that have been out in the field working on this. We made a lot of connections,” Rogers says.

This would lead to the next stage of the project. In October 2012, Rogers attended the 2nd Fecal Sludge Management Conference in Durban, South Africa with Dr. Francis de los Reyes, another NC State researcher on the project. Here they spoke with people who have developed and tested several pit latrine-emptying devices, but the greatest experience was the field trip on the final day. They visited latrines and watched them being emptied with different mechanisms, allowing them to finally see the conditions where their machine will eventually be used. In addition, they met people their technology would ultimately benefit, which proved an inspiration.

From this experience, they determined that South Africa would make an ideal testing ground with its variety of pits. Rogers returned there recently with Walter Beckwith from NC State, another student working on the project, and they worked with an organization called Partners in Development. Here they would get a clear picture of the challenge in front of them, Rogers relates. “The problem with pit latrines, especially in this area, is that there are so many variations of the waste characteristics within the pit. Some are really dense; some are more water like. Some have different layers. Our device worked pretty well on semi-solid waste, but we ran into problems with the really dense sludge.”

A hydraulic motor drives an auger in Rogers’ design for a pit latrine-emptying device.

“There are probably 100 different pit latrine configurations,” Rogers continues. “As we learn more and more, there’s not one solution for every problem. One pit 30 meters away from another one could have a completely different configuration, and the waste inside could be completely different depending on how much water is infiltrating, where the water table’s at, how much trash is going in the pit. There’s just so much variability, it’s going to take multiple technologies to answer all the problems.” Their pit-emptying device would need to be adaptable to as many situations as possible to be a viable solution in the developing world.

Currently, some 20 variations of vacuum pumps are typically used to pump latrines, some powered by electric motor and generator and others by gasoline motor. Others are hand-powered and use a long PVC pipe. “The problem with these technologies is that they’re not very good at getting the solids that collect at the bottom of the pit. They’re good for real watery wastes, but nothing out there worked well for that,” Rogers adds too that “A conventional vacuum tanker is really expensive to use. Most of the people using these pit latrines are on a really small budget.”

One part of a big challenge
In working on this project, Rogers has developed a keen sense of where it fits in the big picture of the developing world’s sanitation problems. “Pit latrine emptying is just one aspect of it. You also have to find ways to transport the waste and then treat it and dispose of it,” Rogers explains. “The current pit emptying technologies are a Band-Aid solution for an overall problem. Right now, it’s a good solution, and it’s needed to maintain good sanitation, but the overall goal would be to have something that treats the waste from start to finish right there. Most of these developing countries are a long, long way from being able to have the infrastructure we have in the U.S., where you’re piping all the way to a treatment plant. That’s a lot of water and a lot of infrastructure that’s impossible for these countries to afford.”

The Reinvent the Toilet Fair is trying to achieve this with the long-term goal of turning waste into energy. The Gates Foundation, along with the sanitation community, is trying to change the stigma of human waste as something “nasty” that we want to magically disappear into our toilets. Instead, human waste should be looked at as a valuable resource with many uses, including fertilizer and energy. According to Rogers, “There are already technologies that transform waste into energy like anaerobic digestion; you can create methane gas and use it for heating and cooking.”

As one form of alternative technology already being used, Rogers notes the existence of composting toilets. “In rural areas, where you have plenty of room and time, composting toilets is a great idea. You can build multiple pits, and then while one’s composting, fill up another one. Then just go back and forth. The problem is, you get into these dense areas where you don’t have that space.” Most of them are dual pits, and you seal a full one for 2 to 3 years to let it compost while you fill the other one. Then you empty it and use it for fertilizer.

Workers use the device to empty a latrine in South Africa.

Rogers likes to talk about other, more exotic, designs he and Dr. Borden saw at the Reinvent the Toilet Fair. The Caltech design uses a solar-powered electrochemical reactor to convert human waste to fertilizer and hydrogen. A team based in Kenya provides low-cost kilns made from 55-gallon drums to local farmers that act as a waste disposal method through pyrolysis, which converts the waste to biochar by heating the waste to extreme temperatures. The biochar can be used as wood charcoal or chemical fertilizers. The Sanitation Ventures team is working on two designs: one uses tiger worms in a biofilter to digest the waste, and another uses black soldier fly larvae that digest the waste and are then harvested at their pre-pupae stage to be used for animal feed or biodiesel.

On to Phase II
The team’s initial 18-month grant ends in this spring, after which they hope to get a Phase II, two-year grant from the Gates Foundation for up to $1 million. They hope to find partners that will enable them to implement the technology in a suitable country for field testing. And they hope to build several of their machines for use in developing countries worldwide. “That’s the overall goal, continuing developing our technology and melding it into a comprehensive package that answers all the pit emptying problems,” Rogers says. “That includes educating the people using the pits and the local labor that will do the emptying, so you minimize the amount of waste that gets in places it shouldn’t. The idea is that the technology you develop should completely isolate humans from the waste.” Ultimately, the team’s goal is not to start a giant manufacturing operation and make millions of dollars, but rather to distribute enough of their devices that local people would see it and begin to copy it, starting their own businesses.

“For me, It’s been an amazing experience,” Rogers say in reflecting on his journey into third-world sanitation. “It’s really cool that I’ve gotten to work on this project from its conception all the way through to prototype development and field testing in South Africa. I got to go to Seattle for the Reinventing the Toilet Fair and twice to Africa, getting all kinds of knowledge and experience. It’s been a really awesome project.”

“Once I get done here, I want to continue working in the developing world focusing on water and sanitation,” Rogers adds. “There are tons of NGOs out there, and I think I can fit in with them. I want to be on the ground out there, not sitting in an office. I like bringing the message out about sanitation in the developing world.”