Blog

Aqua4™: achieving zero discharge desalination

With phase I of the WaterFX demonstration plant with the Panoche Water and Drainage District complete, we are now moving into Phase II, which will prove that solar desalination can achieve zero discharge.

Zero discharge desalination (ZDD) using Aqua4™ overcomes two hurdles that have consistently plagued conventional seawater desalination: low water recovery and high brine disposal costs. Unlike conventional seawater desalination, the Aqua4™ process does not generate waste brine and instead utilizes ZDD to produce only freshwater and solid salt as co-products. Reverse osmosis (RO), the leading seawater desalination process, operates at only 50% recovery and requires the discharge of the remaining 50% brine back into the ocean, resulting in one of the primary hurdles to broad adoption of desalination. In contrast, ZDD operates at greater than 90% recovery and utilizes post processing to convert the remaining high concentration brine into salt crystals. High recovery desalination allows the brine to be sent to a salt crystallizer at concentrations of > 20% dissolved solids, making it economical to recover valuable compounds for resale. Once recovered and separated, these salt compounds are used for a variety of chemical and industrial applications, such as building products, fertilizers, health supplements and metals recovery. Eliminating the cost of brine disposal and capturing the value of recoverable compounds has a significant impact on the economics and potential for desalination to serve as a primary source of freshwater.

In the past, ZDD has been prohibitively expensive due to the low recovery of RO and the high cost of crystallization. However, by driving up the overall recovery using solar thermal desalination (multi-effect distillation) the volume of brine that needs to be processed is reduced to 7% of the overall process flow (Aqua4™ operates at 93% recovery) and brine concentrations exceed 210,000 ppm TDS; thus significantly reducing the size and cost of the crystallizer. Commercially available crystallization equipment can be utilized for this purpose and the overall ZDD process adds less than 5% to the total energy requirements of solar desalination. Further, when solar desalination is used to clean up a discharge stream rather than desalinate seawater, ZDD is critical for achieving full treatment.

If you have any questions about the Aqua4™ process, we encourage you to leave a comment or contact us. Our mission is to build a growing community that is working together to solve water scarcity.

- Aaron

WaterFX Aqua4 SaltsComposition of solid salt samples produced at the WaterFX demonstration plant: Sodium Sulfate, Sodium Chloride, Calcium Sulfate, Calcium Chloride, Magnesium Sulfate, Sodium Carbonate, Calcium Carbonate, Sodium Nitrate, Magnesium Chloride, Calcium Borate, Silica, various trace minerals (< 0.005%)  

 

Embracing Renewable Desalination

There has been a lot of discussion on the topic of desalination in California lately as a source of water to combat drought (see News10 ABC “drought buster”) and it’s apropos to the ongoing dialogue about the environmental consequences typically associated with desalination, namely what to do with the salt?

It’s important to first point out the recent technology advances at play for desalination, as well as the growing opportunity to handle and even monetize the salt and mineral byproducts, between conventional seawater desalination and the type of solar desalination being demonstrated by WaterFX at the Panoche Water & Drainage District. Seawater desalination most commonly relies on reverse osmosis (RO), which requires high pressure to drive freshwater through a membrane. Up to 1,000 psi of driving force is required to overcome the natural osmotic pressure of ocean water. Because of this, the practical limit for RO seawater desalination is 50% water recovery – for every 100 gallons of water processed, 50 gallons of freshwater are recovered and 50 gallons of brine are disposed. To exceed 50% recovery requires increasing the pressure of the system, which from a practical standpoint makes the equipment too costly and substantially increases the electricity consumption. The result is a large volume of high salinity brine that must be sent back to the ocean and as many environmentalists correctly point out, this can have negative consequences to the local marine ecosystem.

Solar desalination, like the Aqua4™ Concentrated Solar Still in use today at California’s Panoche Water District, does not use RO to desalinate seawater and instead uses evaporation (referred to as multi-effect distillation) to clean brackish drainage water. As a result, rather than only 50% recovery, the process achieves greater than 93% recovery. This means that for 100 gallons of water treated, only 7 gallons of salt brine are produced. In addition, the concentration of this brine is greater than 200,000 ppm of total dissolved solids (20% salt by weight). With this high concentration, solids can then be precipitated out of solution using salt separators and processed for a variety of uses. This is something that is not economically feasible with RO seawater desalination due to the high volume of brine. It is also important to note that agricultural drainage water has an inherent disposal cost, so there is substantially more economic incentive to treat this water in its entirety.

In phase two of the solar desalination project with Panoche (to be completed in September 2014), we plan to demonstrate the types of solid byproducts that can be produced and sold into the market without harming the environment. For instance, gypsum (a calcium based salt) is one example of a valuable compound that can be recovered. It is used to make drywall and plaster, so with a concerted effort, the Central Valley could use a portion of the salts as locally sourced raw material for the built environment. Magnesium salts are also present in the drainage water and compounds such as magnesium sulfate (epsom salt) are used in the medical industry to treat pain and complications during pregnancy. It is also true there are naturally occurring materials like selenium that in high concentration are toxic, but if dried and separated, selenium is a highly valuable commodity. It is a health supplement (critical for life in animals), it is a semiconductor for photo-sensors and it is also a key ingredient for glass making. There are nitrates present in drainage water that can be recycled back into fertilizer for growers and calcium compounds that can be used to make cement. Boron is another highly valuable material present at 50 mg/L in drainage water and if extracted sells for $5,000/kg. For a small solar desalination plant this could generate $2.1M per day of revenue. As for motor oil and antifreeze, we have not observed these compounds in the drainage water specifically, but many natural water bodies will contain trace amounts of a variety of these commonly used chemicals.

While the Central Valley is not currently a source of these raw materials, there is no reason to think it can’t be. In Canada, potash (potassium carbonate) and soda-ash (sodium carbonate) salts are refined directly from naturally occurring brines and sold into the fertilizer and chemical industries, which support over $7B per year of exports to countries like China. In Israel, over 2 million tons of salts are produced every year from the Dead Sea. A new industry can be created in the Central Valley that not only removes salt from some of the most pristine farmland in the world, but also creates thousands of new jobs.

Solar desalination, if implemented thoughtfully, serves as a new source of water in California, and can alleviate the salt accumulation that is causing thousands of acres of valuable farmland to be fallowed every year. But why hasn’t this “feature” of desalination been implemented before? The answer lies in the electricity consumption required to separate salt from water. Electricity is a costly source of energy for desalination and even more costly if salts are to be fully processed into solid form. Running a desalination plant at high recovery (> 90%), reliably and in a way that doesn’t require significant upfront pretreatment is the key to unlocking the salt removal. By removing all of the recoverable water the cost of post-processing salts is economical. But it is uneconomical if the cost of the energy source is expensive and this is where solar desalination (pun) shines. Using solar energy as the primary fuel source relaxes the total energy requirements for desalination and enables robust, high recovery thermal technologies like distillation to be used. Without tapping into widely available solar energy, scaling up desalination as a solution to the water problem in California could require over 5,000 MW of additional electric power. Conversely, by efficiently harnessing solar energy, we can return hundreds if not thousands of megawatts back to the grid by displacing freshwater imports delivered through energy-intensive pumping stations. As solar desalination scales up, the cost will continue to fall with improvements in process technology and manufacturing.

This transformation won’t happen overnight and it is not without its challenges. But Californians don’t need to look very far to find incredible examples of industries that have sprung up seemingly overnight. In the midst of the worst drought in recorded history we should give renewable desalination a chance and apply the same innovative thinking to our water shortage that has produced so many disruptive industries throughout California’s history.

- Aaron

Looking Back on 2013

DSC_0551Looking back on 2013 marks a turning point in the sustainable use of water in California’s agricultural industry. In partnership with the Panoche Drainage District, we demonstrated that drainage water is not an unusable byproduct of irrigation in the Central Valley, but rather an important water resource that should be valued. For many years Panoche has taken a leadership position in the utilization of dedicated reuse regions for managing drainage water in a sustainable way. But to grow the farming industry, Panoche has also recognized that treatment and desalination is vital for both reducing drainage water and recovering freshwater. The demonstration project proved just this; that drainage water can be treated to provide a reliable source of potable quality water, sustainably and economically.

We have been running the pilot consistently now for over 6 months and the results have been extremely positive. A concept that just a year ago existed on paper is now generating data and proof of the potential for renewable desalination. It is important to point out that at WaterFX we believe there are many ways to deploy desalination and water reuse in a sustainable way and what we have demonstrated in Firebaugh, California is simply our take on the most efficient, most cost effective core process design that can be deployed at scale in the near term. We draw on an open source philosophy at WaterFX; the concept that an open exchange of ideas is the best way to aggressively build a broad-based, sustainable water platform. 2014 will be an important year for California water users; despite the consistent headlines proclaiming water crisis, we view this moment as the most opportune time for disruptive change.

- Aaron