Polluted Fracking Water

Cleaning Up Pennsylvania's Polluted Fracking Water

Forty of Pennsylvania’s sixty-seven counties are involved in the production of natural gas through the controversial practice of hydraulic fracking, the process in which a mixture of water and chemicals is driven at high pressure into deep wells to make horizontal fractures in shale rock, releasing trapped gas.

Andrew Zydney is Distinguished Professor of Chemical Engineering and an expert in membrane science, membrane transport phenomena, and membrane technologies for the purification of therapeutic molecules. He is co-PI, with his chemical engineering colleague Manish Kumar, on a project to assess the possibility of using membranes to clean up the water that results from hydraulic fracturing in the natural gas drilling operations in Pennsylvania’s Marcellus shale play.

“We’re trying to establish if membranes are a feasible solution,” Zydney remarked about the fracking wastewater, which is a complex mixture of the chemicals added to the water and the organic and even radioactive material that is brought up from underground. “Could we do this in a way that the membranes last long enough and have enough capacity to filter billions of gallons of fracking wastewater? The reality is that unless regulations are in place, companies are going to take the lowest cost approach, which is often just trucking the water and disposing of it in deep injection wells.”

Each natural gas well uses between 2 billion and 7 billion gallons of water. A portion of that water comes back to the surface, contaminated with high levels of salt, as well as some of the 700 chemicals listed as being used by fracking companies. The first step in cleaning the water is to remove the particulate matter. If the particles are not removed first, they will interfere with subsequent purification processes, for example by fouling the pores of filtering membranes. Zydney’s team has been studying the behavior of microfiltration membranes with pores sizes around 200 nanometers as a way to remove much of the particulate matter from frack water.

Each natural gas well uses between 2 billion and 7 billion gallons of water. A portion of that water comes back to the surface, contaminated with high levels of salt, as well as some of the 700 chemicals listed as being used by fracking companies. The first step in cleaning the water is to remove the particulate matter. If the particles are not removed first, they will interfere with subsequent purification processes, for example by fouling the pores of filtering membranes. Zydney’s team has been studying the behavior of microfiltration membranes with pores sizes around 200 nanometers as a way to remove much of the particulate matter from frack water.  

“We are looking to understand the interactions between the membranes and the different chemicals in fracking wastewater.  We are also examining surface modifications of the membrane that might enable them to be less sticky, as well as different geometries and different flow patterns that might let you wash the membranes periodically,” he said. 

Membranes separate primarily on the basis of the size of their pores. For water treatment, there are multiple stages of filtration using multiple size pores. Membranes with large pores in the 1/10 micron to one micron range are used to remove bacteria such as Giardia from water. To remove viruses, a much smaller pore size is required, on the order of tens of nanometers to a single nanometer. Even smaller pore size membranes can remove small organic molecules and salts.   

Why are membranes so expensive? 

“There is a lot that goes into making these membranes. They are very thin films and you have to control the pore size very carefully. The base material is a commercial polymer and is not that expensive. But it does require relatively expensive processing,” said Zydney. 

If the pore sizes are not uniform, the water and whatever is being filtered will tend to migrate through the largest (and least selective) pores. And because the membranes need to be thin in order for large volumes of water to be filtered, they have to be supported mechanically and carefully sealed in a module. All of this adds to their cost. 

Membranes for desalination 

In the Middle East, much of the water used for drinking and irrigation comes from the desalination of sea water. Even in the U.S., in San Diego, a new $1 billion membrane desalination facility opened in December 2015 to provide a drought-proof supply of drinking water to residents of San Diego County. 

But it is expensive to make potable water in this way, 100 to 1,000 times more expensive than the water that comes out of our taps in Pennsylvania. In desalination membranes, the pore sizes are much smaller than the microfiltration pores that Zydney typically studies. Consequently, it requires much more power to push water through these pores, with operating pressures around 500 psi. Pressurizing large quantities of water to 500 psi requires large amounts of energy.  

“If you live in an area with insufficient clean water, the cost of desalination is a problem,” Zydney said. “If we could make the membranes less expensive, and if the energy costs were more manageable, we could use membrane desalination anywhere in the world.” 

Because water is generally available in the U.S., we tend to be wasteful. Take the design of a typical water fountain. Only a small fraction of the water is drunk, with most going down the drain. But only around 3 percent of the world’s water is drinkable, and a time may come when a growing population and increasing pollution make water too valuable to waste. The water crisis in Flint, Michigan, and other municipalities with lead contamination highlights the crucial importance of clean water. 

“We have membranes today that can pull the lead out of the Flint water,” Zydney noted. “It just comes down to cost. The cost of water is typically so low that we don’t even think of the water we waste.”  

Zydney’s group doesn’t make the membranes that they study. Instead they let people in industry supply them and work with those membranes to see if they can improve their performance. He has also begun working with Mike Hickner’s group at Penn State, which does make membranes, on the fracking water problem.  

Zydney’s group also has an emphasis in bioprocessing, with a focus on the purification of therapeutic molecules used to treat cancer and many genetic disorders. Drugs that are produced in some type of genetically modified organism have to be purified to incredibly high levels before they can be used safely. 

“If there is any foreign protein, bacteria, viruses, any of those impurities, the drug can potentially cause side-effects that are worse than the benefits the therapeutic molecule provides,” he said. “A lot of our work is at the interface of membrane science and the application of that technology to the production of high value biological molecules.” 

What’s next? 

Zydney will continue working on frack water treatment. They began their work with a tremendous number of unanswered questions about what kinds of pollutants the water contained and which were most important or problematic in terms of treatment. “We began this work only about a year ago with very little information available about what in this mix was important for water treatment,” he said. “We wanted a fundamental understanding of what were the characteristics that made this water unique in terms of membrane processing.” 

A key insight they have developed is that looking at the individual components in membrane filtration is not sufficient. It is essential to look at interactions between the various components in order to truly understand the behavior of the water in the filtration process.  

Now, with a reasonable understanding of the complex system, the next step is to use that knowledge to design better membranes and membrane processes that can be used in the field. 

“We think we are getting closer to a position where we could say that if we had a membrane with this type of surface properties and this pore size, it would perform better than what is currently being tried,” Zydney said.  

With some 1.4 billion gallons of wastewater produced in just the Marcellus gas fields, a lot of precious water is simply going down the drain. 

Faculty/Research Experts: 
Zydney, Andrew