Traditional wastewater treatment plants, designed to deal with sewage or storm water runoff, cannot cope with these kinds and levels of contaminants. That's where a company like Veolia comes in, which partners with the oil or gas company to assume the liability for the water. "Give us your wastewater and we'll get it where it needs to be," argues geologist Ed Pinero, Veolia's chief sustainability officer.
In California Veolia has partnered with PXP Plains Exploration & Production, an energy company, to design, build and operate a 45,000 barrel-per-day water treatment facility employing ceramic membranes and reverse osmosis to recycle water produced from the Arroyo Grande oilfield near San Luis Obispo. (A barrel of water or oil is 159 liters, or 42 gallons.) Much of the cleansed water would be turned to steam to scour yet more oil out of the ground, and the rest would be clean enough to discharge into local waterways. "We have the technology to meet those requirements," Veolia's Hopper says.
The technologies include membranes, filtration and even selective ion precipitation, where specific chemicals are added to cause particular contaminants, such as heavy metals, to precipitate, or fall out of the water. In certain cases Veolia employs a suite of technologies in a row—bubbling out gas; chemically reducing acidity; filtering; and employing pressure and membranes to extract salts and other contaminants—to deal with a wide variety of contaminated waters, such as that produced from oil and gas wells.
Complications can arise, however: Membranes, for example, often do not stand up to the harsh conditions created by such tainted waters. High acidity or alkalinity, or even just high salinity levels, can quickly foul membranes or simply render them ineffective. Boiling can cost as much as $8.50 per barrel of water, and the residue can quickly wear down even an industrial boiler. So scientists are working on new alternatives.
One option is to cut down on water use in the first place: so-called waterless fracking. A technique offered by the company GASFRAC Energy Services employs high-pressure propane—another hydrocarbon—as a gel in place of water to frack wells. The propane then mixes with the oil or natural gas coming back to the surface and can be used as a fuel, avoiding any of the contamination that leaches out of the rock when water is used. The process is being tested by a variety of companies, including Chevron and Shell.
Another alternative is to use what those who invented it have dubbed a "directional solvent"—liquids that molecularly bind to water but not the other contaminants in it. For example, soybean oil will absorb pure water by bonding to it with heat, leaving any contaminants behind. The water can then be recovered from the solvent by simply cooling it down so that the water flows back out, like cooling air releasing water vapor as rain. "This is the first molecular approach to water treatment," explains engineer Anurag Bajpayee, a PhD candidate at the Massachusetts Institute of Technology working on the new solution. The trick "is finding a solvent that will dissolve water, not dissolve other contaminants and not dissolve itself in water. It is rare."
Soybean oil is not the ultimate solution, of course, because too much oil is required to recover even a little bit of clean water. But the M.I.T. team is working on new alternatives and seeking new solvents with the same properties. At the same time Bajpayee and his colleagues are testing solvents they have already found on produced water from six different wells, including brines eight times saltier than seawater. "It's early, we're not in the field yet," Bajpayee says of the new option for water treatment, which likely will not be commercially available for years. "This is still work in the lab."