Talking Shop: Professor John H. Lienhard V

A resource in crisis.

What are some of the most important problems to solve when it comes to providing clean water globally?

Depending on where you are, the challenges around water are different. In some places where you have a good infrastructure but still have water shortages, you may want to look at the way water is being used and focus on conservation as the first step. California has made progress this way in dealing with the current drought. In other places, the challenge is a lack of infrastructure. For example, in many parts of Africa, there is no pipe distribution system or water treatment plant and there’s not much of an economy to build on. People use relatively little water because they lack easy access, and the approach is often to purify water at the point of use or to provide some very basic infrastructure to aid water collection and distribution. Costs for water have to be kept extremely low. In other cases, you may have dysfunctional governance and no effective regulation of pollutants that spoil fresh water resource: India and China both have problems of this sort. So, the challenges – and the solutions – are different in each situation.

The one problem that is universal is that rising population and higher standards of living are straining water supplies around the world. Fresh water resources that seemed adequate, or even abundant, 100 years ago are overtaxed all around the world. And our environment is suffering as we suck up rivers, lakes, and other supplies for human use.

These are big problems. How does MIT’s School of Engineering, and MechE in particular, fit in to solving them?

Great question! Technology has a big role to play in solving these problems. We can do a lot more to recycle and reuse water, by advanced membrane processes, by advanced biological processes, and by other separation and purification processes. We can find environmentally benign means to convert salt water to fresh water, by driving desalination with solar power and by safely designing the exchange of water with the coastal oceans. We can use information technology – data and sensors – to better manage water consumption and to prevent pollutants from reaching our fresh water resources. And we can make agricultural use of water far more efficient, for example with inexpensive soil moisture sensors and low-pressure drip irrigation. Amazing things are being done at MIT in all of these areas, and the Department of Mechanical Engineering in particular is working on almost every one of these issues.

How does your research fit in?

My own group’s work is focused on how we can reduce the energy consumption of desalination systems, and how we can make those systems robust. We’ve been interested in both drinking water production and wastewater treatment. We’ve developed a number of technologies, and in the last few years my former students have gone on to form two companies based on the developments. We’ve also done a lot of research on the theoretical underpinnings of energy efficiency in desalination.

Is energy efficiency the key to getting these technologies used?

No, not entirely. What determines the selection of a water treatment system is how much water costs in the end. Energy is part of the cost, but even for seawater desalination it’s only about one third. Capital and operating costs also matter a lot. And these trade off against one another in the engineering process. Usually if you have more area, bigger heat exchangers, more membrane area, larger humidifiers or dehumidifiers, you can raise the energy efficiency – but your capital costs go up proportionally. There’s a point beyond which the increase in capital cost adds so much to the price of water that the savings in energy just don’t make sense. That tradeoff is really intrinsic to the decision-making that happens in systems engineering.
You have a similar kind of tradeoff if you are looking at using renewable energy. Solar energy is not free energy: The sun comes up and irradiates your collector for free, but you pay for the collector. The more energy your system consumes, the more collector area you need. If you have high energy efficiency in the desalination plant, then you reduce the cost for solar collectors. But at some point, by getting the energy consumption down, you are making the desalination plant larger and larger, so you are paying less for a solar collector, but you are paying more for desalination equipment. Again, there’s a tradeoff between the two, and a lot of our focus is on finding the optimum.

In your role as director of MIT’s water and food initiative, J-WAFS, what do you see as the Institute’s contribution to world water security?

A key question is whether with today’s knowledge and technology, we can take another look at our means of obtaining water and come up with approaches that are not so negative environmentally. If we did more with recycling wastewater, for instance, that would reduce the amount of fresh water that needs to be transferred by aqueduct, or pumped out of an aquifer or river. If we could find alternative ways to make plants grow, other than using current chemical fertilizers, we could end the damage done to our waterways by the run-off of those chemicals. If we can find inexpensive and scalable technologies for rural water purification, we improve the health of millions of people in the developing world. If we can make desalination cheap and environmental neutral, we can provide coastal cities with the water they need and give them resilience against droughts, especially in the face of an increasing variable climate. And we can look at how to make agriculture as a whole more water efficient.

And all of these ideas are important in the US, but they all have a worldwide reach. What we’d like to do through J-WAFS is to take the things we’re uniquely good at here at MIT and pair up with people outside who can help us innovate in ways that are effective in and transferrable to other localities – whether overseas or here at home. Water is everybody’s problem.