Towards cheaper water treatment

Towards cheaper water treatment

9:02 AM, 27th July 2015
Towards cheaper water treatment
Gradiant’s 12,000-barrel-per-day, carrier gas extraction plant (shown here), uses a humidification and dehumidification (HDH) technique. This yields freshwater and saturated brine, commonly used in drilling and completion processes. © Gradiant Corp

CAMBRIDGE, US: Hydraulic fracturing, or “fracking,” produces a lot of wastewater. Drilling one well requires millions of gallons of water that’s injected into the ground to loosen rocks and release oil. While some is reused, much of the produced water is discarded into deep injection wells, and clean water is purchased again and again.

But MIT spinout Gradiant Corporation is working toward making fracking a water-neutral process, by making water reuse more economical. Founded by Anurag Bajpayee SM ’08, PhD ’12 and Prakash Govindan PhD ’12, Gradiant has developed cost-effective systems to treat briny oilfield water for reuse, saving millions of gallons of water — and millions of dollars — annually.

Launched in 2012 with help from MIT’s industry-connected ecosystem, Gradiant has erected two 12,000-barrel-per-day plants in the Permian basin of Texas, partnering with two drilling clients who treat about 10,000 barrels daily there. “That’s 10,000 barrels a day they’re not disposing of and 10,000 they’re not buying from the city or taking off the public water supply,” said Bajpayee, now Gradiant’s CEO.

The plants each use separate technologies that treat varying infeed water. Carrier gas extraction (CGE), a humidification and dehumidification (HDH) technique developed by the Gradiant co-founders at MIT, heats produced water into vapour and condenses it back into water, without contaminants. This yields freshwater and saturated brine, commonly used in drilling and completion processes.

Selective chemical extraction (SCE) is a cost-effective version of standard chemical-precipitation techniques — where chemical reactions remove specific contaminants to produce clean brine.  

These systems can treat water with higher levels of contamination using less energy and at lower costs than competing treatment methods, according to Gradiant.

Reverse osmosis, for example, treats water with a maximum contamination level of around 7 percent, while legacy thermal desalination reaches about 20 to 22 percent. But Gradiant’s technology uses even less energy to treat water beyond 25 percent, broadening the range of water that can be treated, Bajpayee said.

Commercializing HDH

HDH is a decades-old concept: Water is vapourized and condensed on a cold metallic surface to remove salts. But commercial-scale systems have always been too energy-intensive, because water must be boiled while condensing surfaces must be kept very cold.

But Gradiant’s system — designed by Govindan and colleagues in the lab of Gradiant co-founder John Lienhard, the Abdul Latif Jameel world water and food security, professor at MIT — scaled well by using a readily available carrier gas (dry air) that vapourizes water below boiling temperatures, and incorporating a column with microbubbles that optimizes condensing surfaces.  

In the Gradiant system’s humidifier chamber, briny water drops through packing material and mixes with dry air to produce a hot and humid vapour stripped of contaminants — such as salts — that forms at the top of the chamber. “We creatively mimic nature’s rain cycle — we create the cloud and then we condense that water back out to create rain,” Bajpayee said.

Heated water is also reused to preheat incoming feed water. Instead of fully heating the incoming water to the desired temperature, Bajpayee said, “You only have to make up the little bit that you couldn’t recover,” which saves energy.  

Working alongside industry

Bajpayee and Govindan met in the late 2000s while working on separate water-treatment technologies in MIT’s Rohsenow Kendall heat transfer laboratory. The oil and gas industry were then heavily investing in fracking, leading to outcries about wastewater.

The solution was in Govindan’s PhD thesis, in which he fleshed out a CGE system with dry air and a bubble column. Based on this work, Govindan, MIT engineers, and collaborators at King Fahd University of Petroleum and Minerals built a 12-foot-high prototype, which produced about 700 litre of clean water per day. (The system’s design was described in papers published in the International Journal of Heat and Mass Transfer, Applied Energy, and the AIChE Journal.)

Soon, Bajpayee teamed with Govindan on the system, and they began reaching out to different industries — oil and gas, leather, and power plants — for feedback.

Through the MIT Deshpande Center for Technological Innovation, the team also began connecting with investors. This constant contact with industry, Bajpayee said, gradually helped refine the system for commercial use. In two years the startup has managed to build two plants and commercialize two product lines. It also has three additional water-treatment technologies — one based on Bajpayee’s PhD thesis — under development that could be commercialized in the next two years.

Although Gradiant’s first market is the oil industry, it plans to introduce its technologies to different industries across the globe.

Moving forward, said Govindan, Gradiant’s chief technology officer, the company will stay focused on making water treatment and recycling more energy efficient for the oilfield and other industries — an enduring philosophy from his alma mater.

© Massachusetts Institute of Technology News

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