Environment

Electrodialysis identified as potential way to remove salt from fracking waste water

Electrodialysis identified as ...
Waste water from fracking is over five times saltier than seawater (Photo: Christopher Halloran / Shutterstock.com)
Waste water from fracking is over five times saltier than seawater (Photo: Christopher Halloran / Shutterstock.com)
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Diagram of the MIT desalinating process (Image: Jose-Luis Olivares/MIT)
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Diagram of the MIT desalinating process (Image: Jose-Luis Olivares/MIT)
The MIT process may allow fracking waste water to be recycled and reused (Image: Shutterstock)
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The MIT process may allow fracking waste water to be recycled and reused (Image: Shutterstock)
Waste water from fracking is over five times saltier than seawater (Photo: Christopher Halloran / Shutterstock.com)
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Waste water from fracking is over five times saltier than seawater (Photo: Christopher Halloran / Shutterstock.com)

Fracking is a highly controversial and divisive issue. Proponents argue that it could be the biggest energy boom since the Arabian oil fields were opened almost 80 years ago, but this comes at a serious cost to the environment. Among the detrimental effects of the process is that the waste water it produces is over five times saltier than seawater, which is, to put it mildly, not good. A research team led by MIT that has found an economical way of removing salt from fracking waste water that promises to not only reduce pollution, but conserve water as well.

Hydraulic fracturing, or fracking uses water pressure to shatter oil shale formations, releasing oil and natural gas from deposits that would otherwise be uneconomical to exploit. One of the major problems with this process is that as the water is pumped through the oil shale, it picks up salt, and by the time it’s pumped back to the surface, it’s extremely salty – in the order of 192,000 parts per million (ppm). In contrast, seawater is only 35,000 ppm. This makes it not only too salty to be disposed of without reprocessing, but it’s also too salty to be reused in fracking.

The MIT research team sought to find the most cost effective means of desalinating fracking water. They found that electrodialysis is not only a promising way of cleaning up fracking waste water, but could also provide oil explorers with a closed-loop system that places less demand on local water supplies.

Diagram of the MIT desalinating process (Image: Jose-Luis Olivares/MIT)
Diagram of the MIT desalinating process (Image: Jose-Luis Olivares/MIT)

Electrodialysis is not a new technology. It was developed half a century ago and is currently used to desalinate brackish water and seawater, for small-scale drinking water plants, in food processing, greenhouses, hydroponics, and desalinating various chemicals.

In electrodialysis, a series of membranes divide streams of water of different salinity into stacks. An electric current on either side of the stack draws the sodium and chlorine ions of the salt across the membranes, leaving the water behind. The end result is a very salty stream of water, and a relatively pure stream.

According to MIT, electrodialysis has been overlooked as a way of treating fracking waste water until now because the process was thought to only be effective on water that wasn't of such high salinity. However, the team’s research found that electrodialysis is not only practical, but economically viable – not the least because water conducts electricity better as it gets saltier, therefore the electrodialysis process works better.

The team found that the key was to desalinate the water in stages and rather than making the water potable, it only had to be cleaned up enough to be pumped back into a fracking well and used again. This not only has the potential to reduce the costs, but also alleviate pressure on local water supplies and minimize the need for disposal of contaminated water.

In addition, the process described by MIT is extremely flexible, allowing engineers to "dial" the saline output. This is important, because reusing the water will mean finding the most effective level of salinity for fracking, which is a question still to be answered.

According to the team, there’s still a lot of work to be done before the process is practical. In addition to tweaking the electrodialysis design, laboratory work needs to be done on removing oil, gas, and mineral contaminants that may clog the membranes, and new equipment needs to be designed, built, and tested to apply the new technology.

The MIT team results were published in Applied Energy.

Source: MIT

12 comments
asdf
Great! Now hopefully, companies can be motivated to implement this. As of now, why would they? They are exempt from many environmental regulations in the USA, which is to say the least, concerning.
RaVOLT
It's all a shoot boom! The environmental impact is not included in the triple bottom line. The reality is the Frackers are scavengers trying get a bite at the carcas before it becomes irreverent. Renewable sources are already cheaper than subsidised coal in some places and getting cheaper! While the fossil fuel industry turns to tobacco industry tactics their plight is only highlighted. Case in point, my electric car has done 15000km in 11 months all recharged from renewables. Oil and gas are too valuable to burn and too dirty for our increasing population. They have had their day, like coal house fires in industrial England of the 1800's
Daishi
Natural Gas itself produces 44% less carbon dioxide per joule delivered than oil and coal (s: wikipedia) but I saw a report recently that wells and pipes leak methane into the air that is a more potent greenhouse gas than CO2. The amount of methane may be small but scientific american says its 86 times as potent as carbon dioxide over 20 years so even a small amount of leaked methane can offset some or all of the savings that natural gas provides over burning coal. If methane(CH4) is really that much more potent as a greenhouse gas than CO2 it might also mean that it's possible to impact climate change with a successful effort to recapture it from the atmosphere. Another interesting algae have seen recently mentioned the potency of Algae in converting CO2 to oxygen. CO2 levels go down every year in the northern hemisphere summer because of the larger base of vegetation and then rise again in the winter. How hard would it be to fight global CO2 levels if we bio-engineer Algae or other vegetation to survive in harsher global climates?
Synchro
"promises to not only reduce pollution, but conserve water as well" This is somewhat disingenuous - it's trying to make it sound like "Fracking is good for you". It may well be an improvement, but it's still much worse than not fracking. The diagram is misleading too - that big blue arrow at the bottom suggests that only uncontaminated water is allowed to escape - quite a neat trick considering it's mixed with fresh water... @Daishi algal blooms have happened in the past - they do indeed eat up CO2, but they also bring problems of their own. There is much confusion about CO2 - in order to normalise much of the conversation, many things are talked about in terms of Global Warming Potential (GWP), which can be applied to all gases. GWP is time dependent (some gases break down naturally). Over 20 years, methane is indeed about 86 times CO2's GWP; nitrous oxide is about 268 times. When there is talk of CO2 reduction, it's often really GWP reduction, as it doesn't matter which kind of greenhouse gas is reduced, so long as overall GWP is reduced.
Freyr Gunnar
RaVOLT > Renewable sources are already cheaper than subsidised coal in some places and getting cheaper! How do you manage to produce electricity during windless nights? What about the TCO of switching to solar/wind? How much does the ultimate kWh cost?
owlbeyou
Hey, is this another soft-sell for fracking? All the literature I've read thus far have never mentioned this high level of salt, which is strange. Given that this might be true, what about the cocktail of other harmful chemicals used in the process? If MIT wants to do research on the process of fracking that is of benefit to us all, why don't they examine the potentially disastrous effects to the water table aquifers? Is this saltwater study being funded by the industry? This hunger-for-profit oil and gas industry will turn out to be a disaster to our eco-system. We could be spending valuable resources towards sustainable and renewable technologies that would benefit us all AND be profitable... But the oil and gas corps wouldn't be making any profits would they?
Synchro
@Freyr Gunnar Easy - by having lots of them spread around, and by them not being the only source of power. There have been some great studies done in the US on exactly this subject. It doesn't help that probably the best way of getting unpredictable weather is to burn lots of coal... The TCO figures you're looking for - are you including environmental and personal costs? Or don't you think they count? The Canadian dept of energy estimates that coal power costs the government about 4-5x its quoted price, so renewables have a fair amount of headroom to play with. Gas, even from fracking, is preferable to coal, but it's still a long way from being 'good' in any useful sense. "What if it's all a hoax and we made the world a better place for nothing?"
StWils
Where does the waste brine stream wind up? How long can this process be used in a given area before leakage and other side effects begin to have an impact on aquifers? As an earlier commentor noted what about the other toxic compounds used to enable fracking? Who recaptures and reuses that stuff? Renewable energy is a far better choice. Energy storage is still a legitimate concern but so was handling food and waste when horses were our only power choice. The problems changed when coal came. Storing energy from renewable sources is a completely surmountable challenge.
PuraVida
I am curious at understanding MIT's research promoting desalination by electrodialysis (energy input is proportional to salinity) considering thermal desalination energy input is independent on salinity (and there was no critical cost comparison between various processes). Zero liquid discharge (ZLD) processes for desalination don't include electrodialysis but utilize evaporators and crystallizers - costly process. Why not utilize the gas you are seeking to help you? Another viable alternative to desalinating the brine waste may be in clathrates (aka gas hydrates) more specifically utilizing the natural gas to form cage like structures that will form under low temps and moderate pressures (naturally occurring in sea beds). Gas hydrates form with pure water so separating them will desalinate the fracking brine. Electrodialysis membranes are costly and will require cleaning and maintenance. One last item: radon gas - ok it has a half-life of 3.8 days, but it is known issue for geothermal plants but they inject the water in deep wells to mitigate the effect. Radon is also used by hydrologists to measure the effect of groundwater into surface water since surface water has low levels and groundwater high levels of radon. I wonder how well this is being monitored - my suspicions are that it is being ignored or downplayed by the fracking companies.
PuraVida
MIT also has another process to clean up fracking waste water called carrier gas extraction (now this idea makes a hell of lot more sense). They initially separate oil and particles and then heat the water and blast it onto a porous wall creating water vapor. The water vapor is pumped to a location of many shallow filled trays of water initiating condensation creating more fresh water. Pro of this idea: no $$$ membranes, no $$$ stainless steel (duplex) heat exchangers or glass-lined pipes. My money is on this idea.