ILP Institute InsiderJanuary 9, 2013
Taking Action for Clean Water
Developing technology strategies as diverse as the oceans to provide clean water for the planet.
For John Lienhard, the issue of water availability comes down to a simple equation. There’s a fixed supply of renewable fresh water from precipitation over land. The world’s population will continue to grow. The result is that available resources will be increasingly strained.
Cleaning up a Natural Resource
The world does not lack for seawater. The problem, as Lienhard says, is that it is undrinkable. His group is working on technology to convert seawater to drinking water through a humidification-dehumidification desalination process. In it, Lienhard’s group, together with collaborators at King Fahd University of Petroleum and Minerals, has essentially engineered a version of the rain cycle. Seawater comes into the humidifier and a fraction of it is evaporated, creating a stream of warm, humid air. The moisture is then condensed out in a dehumidifier and the result is fresh water. While the system recycles the salt and water, with both eventually returning to the sea, energy is consumed in the process. Lienhard is now tackling the overall efficiency of the technology.
The challenge, he says, involves figuring out several variables, such as: the best configuration for circulating the air and water; where in the cycle to add heat; and the best temperatures and flow rates of the air and water. There have never been systematic studies of these factors, but Lienhard’s group has developed a thermodynamic methodology to explore various alternatives, such as using closed air loops, or closed water loops, or turbochargers, or solar energy, or even cross-injection of air and water between components. His findings have increased system performance and provided new ways of operating the system. Much of the scientific infrastructure that the group has developed can be used to analyze other types of desalination technologies. “We feel really good about the direction we’re taking,” he says.
Making the System Work at the Local Level
Apart from the thermal performance, Lienhard is looking at making the desalination process more robust and accessible. For that, he and his students have developed new components for the cycles which are smaller and require less upkeep.
One example is the dehumidifier. Traditionally, these tend to be bulky and involve a lot of internal surface area, usually in the form of metal plates. The plates take up space, and uncondensable air builds up near them, reducing the overall effectiveness of the system.
Lienhard’s students have invented a new dehumidifier that uses trays of water instead of plates. Warm, moist air is bubbled through cooler water, and the vapor condenses out of the bubbles into the water. Gone are the metal plates and air buildup, and the result is a system that is one-fifth the volume of a standard dehumidifier, Lienhard says.
The new device is also easier to clean and transport. Coastal villages that have a scarcity of drinkable water can desalinate seawater and can easily maintain the system without the need for a trained engineer to be on hand. That’s an essential element, Lienhard says, because if a technology is going to work it has to do so in the context of the community. Otherwise, it’ll become nothing more than an abandoned curiosity, he says.
Using technology like this, the local population can become more productive. In many parts of the developing world, clean water needs to be collected with buckets from a distant well or delivery truck. The chore of water hauling is often the responsibility of women and children, and it can take hours per day, Lienhard says. With self-contained desalination units, time can be saved and the population that was out getting water can instead be in school or earning money. “We have great hope that this technology will make a real difference to the lives of the people who receive it,” he says.
Unifying the Campus’s Effort
Outside of his lab, Lienhard has worked with colleagues on the Environmental Research Council to assess the full scope of MIT’s water-related research, which encompasses a host of questions in science, engineering, urban planning, policy and the humanities. They have talked to dozens of faculty members, soliciting their ideas, all in an effort to help coordinate the university’s efforts on challenges of water. The process has helped to draw attention to the range of work being done around campus.
There’s work on novel membranes for water purification, and on coatings to prevent bacteria from growing on them. New materials and nanofabrication technology are being used to create entirely new classes of water filters. There’s various work on leak detection in water distribution lines. As Lienhard notes, 20-30 percent of municipal water is lost due to leaks in small pipes buried under cities, which are difficult to locate and fix. MIT faculty are developing sensor arrays that can detect pressure variations in water lines and pinpoint the problematic segment. Other faculty are using self-propelled robots that can snoop out the location of a leak. The hope is that the new technology will not only be able to locate leaks, but also eventually repair them without excavation, Lienhard says.
MIT faculty are using satellites to assess water resources on land and the circulation of the oceans themselves. They are designing wetlands to retain water and control discharge into the oceans. They are developing biotechnology to screen for bacterial contamination of watersheds. And they are leading projects to provide sustainable water supplies in the developing world. Whatever the specific problem, the solution has to be crafted with the local social and economic situation in mind. There’s no one best approach, and the solutions are seldom based on technology alone. The key is flexibility. “You need a broad set of tools in your toolbox to address each problem,” Lienhard says.
It’s all part of the overall challenge of sustaining the environment while continuing human progress; and the science, technology, design, and policies involved can be wide-ranging. Lienhard and other faculty aim to see these diverse efforts connected into an effective framework for problem solving. As he says, “MIT has the capacity and the vision to make an enormous contribution to the provision of clean water to all humanity.”
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