MIT tests new wastewater purification process

Modern urban wastewater treatment plant
Source: DollarPhotoClub

A new and inexpensive method of recycling highly contaminated, saline, produced water for reuse in fracking operations has been developed by MIT and its spinout company Gradiant.

The new process, which takes highly contaminated water that flows back from shale wells after they’ve been hydraulically fractured, and purifies it so that it can be reused in fracking, is more economical than the existing strategy of deep disposal.

Deep disposal is by far the most common way of disposing of wastewater produced during fracking. It is EPA-approved and is considered to be the best, and the cheapest, method of frac water disposal. The process involves injecting the water into the ground to be trapped under layers of impermeable rock that will prevent the wastewater from polluting aquifers.

The problem with deep disposal, however, is its ability to cause tremors and small-scale earthquakes, sometimes as far as tens of kilometres from the wellbore.

By contrast, the new technology – currently used in an unnamed water purification plant in Midland Texas – seems to be safe and relatively cheaper than deep well injections. The MIT blog reports that by the end of next month the technology is expected to be chugging 500,000 gallons per day, furnishing water that’s sufficiently clean to use in hydraulic fracturing, or fracking, for oil and natural gas production.

“This is far and away the largest such plant anyone has ever built. Past prototypes have done 200 gallons a day; this is vastly larger, modular, and scalable; if they wanted to double it, they could,” says John Lienhard, a professor of mechanical engineering at MIT who heads MIT’s Center for Clean Water and Clean Energy, where the technology was developed.

In the new process — which the company calls carrier gas extraction — pre-treated water, with oil and grease residue and solid particles removed, gets heated and sprayed into a porous material with a large surface area, saturating air with water vapour.

This water-saturated air is then pumped up through tiny holes in a series of shallow, water-filled trays. As bubbles pass through the water in the trays, the water vapour in the bubbles condenses and joins the water it is passing through, creating more fresh water. This so-called “bubble column” allows the company to condense water vapour without needing expensive metal heat exchangers.

The process recycles up to 85 percent of the heat needed to keep the system running. The remaining waste is then disposed as sludge in landfills. The project is being done with Pioneer Natural Resources, an oil company in Texas.

Anurag Bajpayee, president and CEO of Gradiant who co-developed the technology with the company’s CTO, Prakash Govindan, says the initial focus is on the booming petroleum and natural gas industry in the United States and elsewhere. “Water issues have been a point of a lot of controversy for the industry,” he says.

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