The rise of desalination plants, now almost 16,000 worldwide, has led to a glut of brine waste—much of which is dumped into oceans, which can raise salinity to dangerous levels and put toxic chemicals in the marine environment threatening ocean life, according to a new study.
(Credit: Bureau of Reclamation)<p>"Brine underflows deplete dissolved oxygen in the receiving waters," lead author Edward Jones, a researcher at Wageningen University in the Netherlands, said in a statement. "High salinity and reduced dissolved oxygen levels can have profound impacts on benthic organisms, which can translate into ecological effects observable throughout the food chain."</p><p>The study recognizes the important role desalination plays in getting people water.</p><p>"Around 1.5 to 2 billion people currently live in areas of physical water scarcity, where water resources are insufficient to meet water demands, at least during part of the year. Around half a billion people experience water scarcity year-round," Vladimir Smakhtin, the assistant director of United Nations University's Institute for Water, Environment and Health, said in a statement.</p><p>"There is an urgent need to make desalination technologies more affordable and extend them to low-income and lower-middle income countries."</p><p>Brine waste does not have to be all bad news — Smakhtin and colleagues point to potential economic opportunities in "mining" it. With bolstered technology, metals and salts—such as sodium, magnesium, calcium, potassium, bromine, boron, strontium, lithium, rubidium and uranium—could be extracted from the brine and sold for industrial and agricultural uses.</p><p>"There is a need to translate such research and convert an environmental problem into an economic opportunity," co-author Manzoor Qadir, assistant director of United Nations University's Institute for Water, Environment and Health, said in a statement.</p><p>"This is particularly important in countries producing large volumes of brine with relatively low efficiencies, such as Saudi Arabia, UAE, Kuwait and Qatar."</p>
Perchlorate decon<p>Perchlorate is mostly used in <a href="https://www.ncbi.nlm.nih.gov/pubmed/26868023" target="_blank">rocket fuels and munitions</a>. Improper <a href="https://onlinelibrary.wiley.com/doi/abs/10.1002/rem.20071" target="_blank">storage or disposal</a> of rockets or debris may contaminate the environment. Through <a href="https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.highlight/abstract/6065/report/F" target="_blank">leaks</a> or <a href="https://sma.nasa.gov/docs/default-source/safety-messages/safetymessage-2012-11-05-pepconexplosion.pdf?sfvrsn=ceae1ef8_6" target="_blank">explosions</a>, perchlorate can also pollute waterways near manufacturing plants. It's water soluble and chemically stable, so it can persist in ground and surface water for <a href="https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=23292" target="_blank">decades</a>.</p><p>And that's bad news for people whose drinking water comes from contaminated sources, especially pregnant women and children. Perchlorate has been shown to impair <a href="https://www.ncbi.nlm.nih.gov/pubmed/26485730" target="_blank">thyroid function</a>; proper thyroid function is essential for normal brain development during the <a href="https://www.ncbi.nlm.nih.gov/pubmed/29693263" target="_blank">prenatal period</a> and during <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2826.2004.01243.x" target="_blank">childhood</a>.</p><p>When Coates submitted his first academic paper on perchlorate-degrading bacteria in 1998 (it was published in <a href="https://www.ncbi.nlm.nih.gov/pubmed/11207750" target="_blank">1999</a>), there were only a few bacterial species known to be capable of performing this feat. Coates wanted to see if there were more.</p><p>"It turns out that the microorganisms that use perchlorate are essentially ubiquitous — they're not difficult to find. And you can culture them fairly readily. To remediate perchlorate, you just needed to create specific conditions," he says.</p><p>The way to do this is to use something called a bioreactor — a home for bacteria that provides all the nutrients and minerals they need to thrive. It's similar to a fermenting tank for beer, except instead of yeast converting sugars into alcohol and carbon dioxide, perchlorate-destroying bacteria turn dangerous perchlorate into harmless <a href="https://jplwater.nasa.gov/Docs/NAS710428.PDF" target="_blank">chloride and oxygen</a>. Contaminated ground or surface water gets pumped into the bioreactors, which are full of these bacteria. Once the bacteria have broken down the perchlorate, the water is filtered and sterilized to remove bacteria. The decontaminated water can then be sent to consumers or pumped back into the ground.</p><p>Thanks to discoveries made by Coates and a legion of other scientists, perchlorate-decontaminating bioreactors have been applied in the real world with great success. Large-scale perchlorate bioreactors are now at work cleaning contaminated water at several sites in <a href="https://apps.dtic.mil/dtic/tr/fulltext/u2/1055469.pdf" target="_blank">California</a>, <a href="https://jplwater.nasa.gov/Docs/NAS710428.PDF" target="_blank">Kansas</a>, <a href="https://clu-in.org/download/contaminantfocus/perchlorate/Bioreactors.pdf" target="_blank">Texas</a> and <a href="https://jplwater.nasa.gov/Docs/NAS710428.PDF" target="_blank">Utah</a>. These bioreactors are astonishingly efficient: The bioreactor-based groundwater treatment plant in Rialto, California, for example, is capable or decontaminating <a href="http://www.dtic.mil/dtic/tr/fulltext/u2/1055469.pdf" target="_blank">2,000 gallons (over 7,500 liters) of perchlorate-polluted water per minute</a> — that's more than a billion gallons (over 3.7 billion liters) a year. In fact, Coates says that the bacterial removal of perchlorate represents one of the largest-scale bioremediation projects in the world.</p>
Converting uranium<iframe src="https://player.vimeo.com/video/107101199" width="640" height="360" frameborder="0" allowfullscreen=""></iframe><p>Implementing bioreactor technologies isn't always so straightforward, even when the bioreactor performs well in the lab. A bioreactor designed by Bruce Rittmann, the director of the Swette Center for Environmental Biotechnology at Arizona State University's Biodesign Institute, was initially used to remove water contaminants like perchlorate and trichloroethene, but can also be used to remove uranium and other metals from water. This kind of contamination can occur around <a href="https://www.nrdc.org/sites/default/files/uranium-mining-report.pdf" target="_blank">uranium mines and mills</a>, especially older abandoned ones. In people, drinking water contaminated with uranium can cause <a href="https://ephtracking.cdc.gov/showUraniumHealth.action" target="_blank">kidney damage</a>; uranium is also toxic to fish, <a href="https://www.ncbi.nlm.nih.gov/pubmed/24846854" target="_blank">decreasing their reproductive success</a>.<br></p><p> The bacteria in the bioreactor can't destroy the uranium, but they can convert it to a form that separates from water. Once the uranium comes out of the solution, it's much easier to remove —think about the difference between taking a sugar cube out of a glass of water and trying to remove the sugar once it's dissolved. <a href="https://www.sciencedirect.com/science/article/abs/pii/S0043135414005090" target="_blank">In tests</a>, Rittmann's bioreactor removed about 95 percent of the uranium from a contaminated water supply. </p><p> Rittmann says it would be relatively straightforward to construct a bioreactor system in currently operational mines that already have some sort of water treatment system in place. However, cleaning up abandoned mines would be more difficult, since they have no such infrastructure. There are about <a href="https://www.nrdc.org/sites/default/files/uranium-mining-report.pdf" target="_blank">4,000 abandoned uranium mines</a> in America's western states. </p><p> This technology, Rittmann says, can be applied not just to water contaminated by uranium mines but also to wastewater from precious metal mines, including silver, gold and palladium. "In these cases, the materials that we produce — the solids these microbes remove from the water — are really valuable. We're working on the development of this technology not only to remove pollutants but to generate high value. It's a good deal," he says. </p>
Beyond the bioreactor<p>What if we want to break down pollutants in places where building bioreactors isn't feasible, like in runoff from agricultural fields contaminated with pesticides? Colin Scott, head of the Biocatalysis & SynBio Team at Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO), may have an answer.</p><p>Bacteria make enzymes, and it's these enzymes that do the dirty work of actually breaking down pollutants. So, Scott and his team are experimenting with bacterial enzymes to decontaminate water systems polluted with pesticides and herbicides. Enzymes aren't alive, so they don't need nutrients, which means they can be used in places that bacteria won't survive. They can't reproduce or adapt, so won't multiply and disturb delicate ecosystems.</p><p>"Enzymes themselves are terrific because they're really specific for the thing that you want them to do, so they don't have any other effects. And they're also biodegradable, so they don't persist in the environment," says Scott.</p><p>Such enzymes are not yet used on a large scale, but they've been successful in field tests. For example, a bacterial enzyme called <a href="https://www.researchgate.net/publication/260060160_Free-Enzyme_Bioremediation_of_Pesticides_A_Case_Study_for_the_Enzymatic_Remediation_of_Organophosphorous_Insecticide_Residues" target="_blank">OP-A</a> is capable of breaking down organophosphate insecticides, which have been linked to deficits in <a href="https://www.ncbi.nlm.nih.gov/pubmed/30144465" target="_blank">attention, coordination and memory</a>, especially in agricultural workers. In <a href="https://www.researchgate.net/publication/260060160_Free-Enzyme_Bioremediation_of_Pesticides_A_Case_Study_for_the_Enzymatic_Remediation_of_Organophosphorous_Insecticide_Residues" target="_blank">field trials</a>, the OP-A enzyme reduced levels of the controversial pesticide chlorpyrifos — <a href="https://www.nejm.org/doi/full/10.1056/NEJMp1716809" target="_blank">linked to impaired brain development in children</a> — in contaminated field runoff by 99 percent in just eight hours. (Since these tests, the researchers say they have developed an improved version of OP-A, known as A900.)</p><p>The specificity of enzymes is both their brilliance and their downfall. On one hand, high specificity means that enzymes aren't likely to produce unwanted side effects, like harming plants or animals. On the other hand, there are thousands of different pollutants, which means we'll need a <em>lot </em>of different enzymes.</p><p>After an appropriate enzyme has been identified, scientists have to figure out how to cost-effectively mass produce it. Since enzymes usually biodegrade quickly, scientists have to make sure the enzyme stays intact long enough to do its job. They also have to run safety studies to make sure that whatever components the enzymes break the pollutant down into aren't also toxic.</p>
A long way to go<p>There's still a lot of work to be done. At the science level, we need to identify and characterize bacteria that can break down specific pollutants. Although bacteria for degrading or removing contaminants like perchlorate, uranium and certain pesticides are well understood, as-yet undiscovered bacteria may be important in dealing with emerging water pollutants such as <a href="https://www.sciencedirect.com/science/article/pii/S004896971834141X?via%3Dihub" target="_blank">PFAS</a>, which can cause <a href="https://www.atsdr.cdc.gov/pfas/health-effects.html" target="_blank">immune system dysfunction and cancer</a>, as well as <a href="https://www.sciencedirect.com/science/article/pii/S0048969716305551?via%3Dihub" target="_blank">pharmaceuticals</a>, the effects of which are not yet fully understood.</p><p>Other hurdles are policy based. It's often not a question of whether to use bioremediation or alternative techniques, but whether to do anything at all. Many contaminants — including several <a href="https://www.epa.gov/dwucmr/fourth-unregulated-contaminant-monitoring-rule" target="_blank">pesticides, cyanotoxins and solvents</a> — are monitored by the EPA, but not regulated. Without set limits for acceptable amounts of these chemicals in drinking water, there's no incentive for anyone to spend money to get rid of them. Even though bioremediation may be cheaper than the alternatives, in the short term, it's still more expensive than doing nothing. And for many pollutants — including many pesticides — there's currently a whole lot of nothing being done.</p><p>But with the continued work of scientists and stricter water quality standards, bacteria could be a public health game-changer.</p><p>"These bugs are amazing," says Coates. "What limits us is our imagination rather than the organisms' abilities." </p><p><em>Editor's note: Hannah Thomasy wrote this story as a participant in the <a href="https://ensia.com/about/mentor-program/" target="_blank">Ensia Mentor Program</a>. <em>The mentor for the project was EHN editor Brian Bienkowski.</em></em></p>
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