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battling the brackish water Can desalination quench agricultures thirst? Some say its a costly pipe dream; others say its part of the future. Lela Nargi, Knowable Magazine Dec 2, 2024 7:41 pm | 7 Rows of dried out almond trees alongside green healthy trees growing in an orchard. Droughts have led farmers to consider new water sources. Credit: David Paul Morris/Bloomberg via Getty Images Rows of dried out almond trees alongside green healthy trees growing in an orchard. Droughts have led farmers to consider new water sources. Credit: David Paul Morris/Bloomberg via Getty Images Story textSizeSmallStandardLargeWidth *StandardWideLinksStandardOrange* Subscribers only Learn moreRalph Loya was pretty sure he was going to lose the corn. His farm had been scorched by El Pasos hottest-ever June and second-hottest August; the West Texas county saw 53 days soar over 100 Fahrenheit in the summer of 2024. The region was also experiencing an ongoing drought, which meant that crops on Loyas eight-plus acres of melons, okra, cucumbers, and other produce had to be watered more often than normal.Loya had been irrigating his corn with somewhat salty, or brackish, water pumped from his well, as much as the salt-sensitive crop could tolerate. It wasnt enough, and the municipal water was expensive; he was using it in moderation, and the corn ears were desiccating where they stood.Ensuring the survival of agriculture under an increasingly erratic climate is approaching a crisis in the sere and sweltering Western and Southwestern United States, an area that supplies much of our beef and dairy, alfalfa, tree nuts, and produce. Contending with too little water to support their plants and animals, farmers have tilled under crops, pulled out trees, fallowed fields, and sold off herds. Theyve also used drip irrigation to inject smaller doses of water closer to a plants roots and installed sensors in soil that tell more precisely when and how much to water.In the last five years, researchers have begun to puzzle out how brackish water, pulled from underground aquifers, might be de-salted cheaply enough to offer farmers another water resilience tool. Loyas property, which draws its slightly salty water from the Hueco Bolson aquifer, is about to become a pilot site to test how efficiently desalinated groundwater can be used to grow crops in otherwise water-scarce places.Desalination renders salty water less so. Its usually applied to water sucked from the ocean, generally in arid lands with few options; some Gulf, African, and island countries rely heavily or entirely on desalinated seawater. Inland desalination happens away from coasts, with aquifer waters that are brackishcontaining between 1,000 and 10,000 milligrams of salt per liter, versus around 35,000 milligrams per liter for seawater. Texas has more than three dozen centralized brackish groundwater desalination plants, California more than 20.Such technology has long been considered too costly for farming. Some experts still think its a pipe dream. We see it as a nice solution thats appropriate in some contexts, but for agriculture, its hard to justify, frankly, says Brad Franklin, an agricultural and environmental economist at the Public Policy Institute of California. Desalting an acre-foot (almost 326,000 gallons) of brackish groundwater for crops now costs about $800, while farmers can pay a lot lessas little as $3 an acre-foot for some senior rights holders in some placesfor fresh municipal water. As a result, desalination has largely been reserved to make liquid thats fit for people to drink. In some instances, too, inland desalination can be environmentally risky, endangering nearby plants and animals and reducing stream flows.But the US Bureau of Reclamation, along with a research operation called the National Alliance for Water Innovation (NAWI) thats been granted $185 million from the Department of Energy, have recently invested in projects that could turn that paradigm on its head. Recognizing the urgent need for fresh water for farmswhich in the US are mostly inlandcombined with the ample if salty water beneath our feet, these entities have funded projects that could help advance small, decentralized desalination systems that can be placed right on farms where theyre needed. Loyas is one of them.US farms consume over 83 million acre-feet (more than 27 trillion gallons) of irrigation water every yearthe second most water-intensive industry in the country, after thermoelectric power. Not all aquifers are brackish, but most that are exist in the countrys West, and theyre usually more saline the deeper you dig. With fresh water everywhere in the world becoming saltier due to human activity, we have to solve inland desal for ag in order to grow as much food as we need, says Susan Amrose, a research scientist at MIT who studies inland desalination in the Middle East and North Africa. Brackish (slightly salty) groundwater is found mostly in the western United States. Credit: CREDIT: J.S. STANTON ET AL / BRACKISH GROUNDWATER IN THE UNITED STATES: USGS PROFESSIONAL PAPER 1833. 2017 That means lowering energy and other operational costs, making systems simple for farmers to run; and figuring out how to slash residual brine, which requires disposal and is considered the processs Achilles heel, according to one researcher.The last half-decade of scientific tinkering is now yielding tangible results, says Peter Fiske, NAWIs executive director. We think we have a clear line of sight for agricultural-quality water.Swallowing the high costFiske believes farm-based mini-plants can be cost-effective for producing high-value crops like broccoli, berries and nuts, some of which need a lot of irrigation. That $800 per acre-foot has been achieved by cutting energy use, reducing brine and revolutionizing certain parts and materials. Its still expensive but arguably worth it for a farmer growing almonds or pistachios in Californiaas opposed to farmers growing lesser-value commodity crops like wheat and soybeans, for whom desalination will likely never prove affordable. As a nut farmer, I would sign up to 800 bucks per acre-foot of water till the cows come home, Fiske says.Loyas pilot is being built with Bureau of Reclamation funding and will use a common process called reverse osmosis. Pressure pushes salty water through a semi-permeable membrane; fresh water comes out the other side, leaving salts behind as concentrated brine. Loya figures he can make good money using desalinated water to grow not just fussy corn, but even fussier grapes he might be able to sell at a premium to local wineries.Such a tiny system shares some of the problems of its large-scale cousinschiefly, brine disposal. El Paso, for example, boasts the biggest inland desalination plant in the world, which makes 27.5 million gallons of fresh drinking water a day. There, every gallon of brackish water gets split into two streams: fresh water and residual brine, at a ratio of 83 percent to 17 percent. Since theres no ocean to dump brine into, as with seawater desalination, this plant injects it into deep, porous rock formationsa process too pricey and complicated for farmers.But what if desalination could create 90 or 95 percent fresh water and 5 to 10 percent brine? What if you could get 100 percent fresh water, with just a bag of dry salts leftover? Handling those solids is a lot safer and easier, because super-salty water brine is really corrosive so you have to truck it around in stainless steel trucks, Fiske says.Finally, what if those salts could be broken into componentslithium, essential for batteries; magnesium, used to create alloys; gypsum, turned into drywall; as well as gold, platinum, and other rare-earth elements that can be sold to manufacturers? Already, the El Paso plant participates in mining gypsum and hydrochloric acid for industrial customers.Loyas brine will be piped into an evaporation pond. Eventually, hell have to pay to landfill the dried-out solids, says Quantum Wei, founder and CEO of Harmony Desalting, which is building Loyas plant. There are other expenses: drilling a well (Loya, fortuitously, already has one to serve the project); building the physical plant; and supplying the electricity to pump water up day after day. These are bitter financial pills for a farmer. Were not getting rich; by no means, Loya says.More cost comes from the desalination itself. The energy needed for reverse osmosis is a lot, and the saltier the water, the higher the need. Additionally, the membranes that catch salt are gossamer-thin, and all that pressure destroys them; they also get gunked up and need to be treated with chemicals.Reverse osmosis presents another problem for farmers. It doesnt just remove salt ions from water but the ions of beneficial minerals, too, such as calcium, magnesium and sulfate. According to Amrose, this means farmers have to add fertilizer or mix in pretreated water to replace essential ions that the process took out.To circumvent such challenges, one NAWI-funded team is experimenting with ultra-high-pressure membranes, fashioned out of stiffer plastic, that can withstand a much harder push. The results so far look quite encouraging, Fiske says. Another is looking into a system in which a chemical solvent dropped into water isolates the salt without a membrane, like the polymer inside a diaper absorbs urine. The solvent, in this case the common food-processing compound dimethyl ether, would be used over and over to avoid potentially toxic waste. It has proved cheap enough to be considered for agricultural use.Amrose is testing a system that uses electrodialysis instead of reverse osmosis. This sends a steady surge of voltage across water to pull salt ions through an alternating stack of positively charged and negatively charged membranes. Explains Amrose, You get the negative ions going toward their respective electrode until they cant pass through the membranes and get stuck, and the same happens with the positive ions. The process gets much higher fresh water recovery in small systems than reverse osmosis, and is twice as energy efficient at lower salinities. The membranes last longer, too10 years versus three to five years, Amrose saysand can allow essential minerals to pass through.Data-based designAt Loyas farm, Wei paces the property on a sweltering summer morning with a local engineering company hes tapped to design the brine storage pond. Loya is anxious that the pond be as small as possible to keep arable land in production; Wei is more concerned that it be big and deep enough. To factor this, hell look at average weather conditions since 1954 as well as worst-case data from the last 25 years pertaining to monthly evaporation and rainfall rates. Hell also divide the space into two sections so one can be cleaned while the other is in use. Loyas pond will likely be one-tenth of an acre, dug three to six feet deep.The desalination plant will pair reverse osmosis membranes with a batch process, pushing water through multiple times instead of once and gradually amping up the pressure. Regular reverse osmosis is energy-intensive because it constantly applies the highest pressures, Wei says, but Harmonys process saves energy by using lower pressures to start with. A backwash between cycles prevents scaling by dissolving mineral crystals and washing them away. You really get the benefit of the farmer not having to deal with dosing chemicals or replacing membranes, Wei says. Our goal is to make it as painless as possible.Another Harmony innovation concentrates leftover brine by running it through a nanofiltration membrane in their batch system; such membranes are usually used to pretreat water to cut back on scaling or to recover minerals, but Wei believes his system is the first to combine them with batch reverse osmosis. Thats whats really going to slash brine volumes, he says. The whole system will be hooked up to solar panels, keeping Loyas energy off-grid and essentially free. If all goes to plan, the system will be operational by early 2025 and produce seven gallons of fresh water a minute during the strongest sun of the day, with a goal of 90 to 95 percent fresh water recovery. Any water not immediately used for irrigation will be stored in a tank.Spreading out the researchNinety-eight miles north of Loyas farm, along a dead flat and endlessly beige expanse of road that skirts the White Sands Missile Range, more desalination projects burble away at the Brackish Groundwater National Desalination Research Facility in Alamogordo, New Mexico. The facility, run by the Bureau of Reclamation, offers scientists a lab and four wells of differing salinities to fiddle with.On some parched acreage at the foot of the Sacramento Mountains, a longstanding farming pilot project bakes in relentless sunlight. After some preemptive words about the three brine ponds on the property They have an interesting smell, in between zoo and ocean facility manager Malynda Cappelle drives a golf cart full of visitors past solar arrays and water tanks to a fenced-in parcel of dust and plants. Here, since 2019, a team from the University of North Texas, New Mexico State University and Colorado State University has tested sunflowers, fava beans and, currently, 16 plots of pinto beans. Some plots are bare dirt; others are topped with compost that boosts nutrients, keeps soil moist and provides a salt barrier. Some plots are drip-irrigated with brackish water straight from a well; some get a desalinated/brackish water mix.Eyeballing the plots even from a distance, the plants in the freshest-water plots look large and healthy. But those with compost are almost as vigorous, even when irrigated with brackish water. This could have significant implications for cash-conscious farmers. Maybe we do a lesser level of desalination, more blending, and this will reduce the cost, says Cappelle.Pei Xu has been co-investigator on this project since its start. Shes also the progenitor of a NAWI-funded pilot at the El Paso desalination plant. Later in the day, in a high-ceilinged space next to the plants treatment room, she shows off its consequential bits. Like Amroses system, hers uses electrodialysis. In this instance, though, Xu is aiming to squeeze a bit of additional freshat least freshishwater from the plants leftover brine. With suitably low levels of salinity, the plant could pipe it to farmers through the countys existing canal system, turning a waste product into a valuable resource.Xus pinto bean and El Paso work, and Amroses in the Middle East, are all relevant to Harmonys pilot and future projects. Ideally we can improve desalination to the point where its an option which is seriously considered, Wei says. But more importantly, I think our role now and in the future is as water stewardsto work with each farm to understand their situation and then to recommend their best path forward whether or not desalting is involved.Indeed, as water scarcity becomes ever more acute, desalination advances will help agriculture only so much; even researchers whove devoted years to solving its challenges say its no panacea. What we're trying to do is deliver as much water as cheaply as possible, but that doesn't really encourage smart water use, says NAWIs Fiske. In some cases, it encourages even the reverse. Why are we growing alfalfa in the middle of the desert?Franklin, of the California policy institute, highlights another extreme: Twenty-one of the states groundwater basins are already critically depleted, some due to agricultural overdrafting. Pumping brackish aquifers for desalination could aggravate environmental risks.There are an array of measures, say researchers, that farmers themselves must take in order to survive, with rainwater capture and the fixing of leaky infrastructure at the top of the list. Desalination is not the best, only or first solution, Wei says. But he believes that when used wisely in tandem with other smart partial fixes, it could prevent some of the worst water-related catastrophes for our food system.Lela Nargi, Knowable Magazine Knowable Magazine explores the real-world significance of scholarly work through a journalistic lens. 7 Comments Prev story
