This month we sat down with Dr. Matthew Stuber, co-founder of WaterFX and HydroRevolution and Head of Process Systems Engineering to tell us more about how solar thermal desalination technology actually works. The new HydroRevolution plant will utilize the Aqua4 technology developed by WaterFX and their partners, ATSI engineering, to create a green solution to the problem of water scarcity in the Central Valley. The technology not only outperforms traditional desalination in water recovery efficiency, it’s also better for the environment because of its renewable source of energy: the sun.
Comparing Solar Thermal Desalination to Traditional Desalination:
- How is the solar thermal desalination system employed by WaterFX and HydroRevolution different from traditional desalination plants? Is there a demand and need for both types in California?
When integrated with solar, MED systems– like the one used in HydroRevolution—are more efficient than RO [ed. Reverse osmosis] desalination. Distillation is different because it can be used onsite at a small or large scale, and is much more environmentally friendly than current reverse osmosis. The Aqua4 (the technology used in HydroRevolution) uses solar thermal energy as the primary energy source, limiting or eliminating the use of electricity and fuel. The technology is also modular for distributed deployment to sites with water treatment needs and isn’t limited to just treating seawater.
Additionally, Aqua4 treats a wide range of water sources – distillation is an extremely robust treatment process that separates freshwater from almost any source. RO desalination is limited in its capabilities due to the propensity for membrane scaling to occur. Distillation is a reliable way to ensure that no matter what kind of saltwater chemistry, the water that’s produced will be pure H2O. The advanced technology ensures that land requirements are minimized.
- Are systems that utilize MED always more efficient than membrane-dependent desalination technologies? Is this method particularly conducive to a certain type of impaired water?
Efficiency varies depending on the kinds of energy being used. We are using thermal energy which is thermodynamically different than electrical energy. When integrated with solar energy, MED is more energy efficient than RO, and therefore more cost effective.
It’s important to note that this system is also more robust to handling various qualities of water and is not tailored to one application. It is even effective for difficult to treat waters such as those with high scaling potential or that fluctuate in quality and composition. Industrial water and brackish groundwater are a few examples of these sources.
In particular, MED excels above traditional RO desalination in the treatment of drainage or brackish groundwater. Some people argue that RO desal is applicable here because these types of water have low salinity levels but the problem is that the sources become more difficult to handle when you want to get to high recovery rates with almost no liquid waste and these other systems can’t manage that.
- Aside from agriculture, does solar-thermal desalination have any other practical applications? How would the technology need to adapt to accommodate these industries?
The short answer is that Aqua4 is capable of treating any impaired water source with zero liquid discharge. The system can handle any salt impaired source such as seawater or groundwater, as well as produced water and gray water [ed. Municipal wastewater] But both produced water and gray water would be contaminated by more than just salt and, at that point, treating the water is not just about distillation. The system would have to go further with different treatments steps to remove contaminants such as oils and other organic compounds.
For delivering water, what we can produce with Aqua4 is already the purest water that you can buy so it’s suitable for any application, including pharmaceutical or semiconductor manufacturing.
- Aside from lower energy costs and cleaner fuel supply, the Aqua4™ system also has a greater recovery rate than membrane desalination, why is that?
When comparing results from the same water source, you can recover more water with distillation compared to RO because, as you begin to approach the saturation point of the dissolved salts, they pop out of the solution and form crystals. This isn’t a big deal for distillation, which essentially boils off the freshwater, but the crystals can form on the membranes of RO desalination systems and plug up the pores rendering it unusable over time.
In distillation, when crystals form, they form in the liquid mixture that is consistently flowing and preventing them from being deposited anywhere. In the event that they are deposited in the equipment, they can be swept or washed away without any mechanical cleaning. In the end, we want the salts to crystalize as we use our technology to separate out a solid co-product from the freshwater.
How the HydroRevolutionSM plant will benefit agriculture:
- Why hasn’t agricultural drainage been treated before now? How have other technologies failed where the WaterFX demonstration plant succeeded?
There hasn’t been any formal treatment of agricultural drainage aside from some pilot plants, most of which have been RO plants. The difficulty with this is that this water has a high scaling propensity that causes the membranes to fail and incurs high maintenance costs. Our system is also able to reach 100% water recovery rates (RO desal usually only hits about 50%) with zero discharge which is important because the agricultural industry doesn’t have brine disposal like you see in municipalities. Instead, we need to integrate this into the overall system which is what we’ve done by recycling the drainage water into freshwater and separating out the solid co-products.
There have been other thermal methods tested, one in the late 70’s at a drainage research center in Los Banos. This was also a failure because it used a mechanical vapor compression system that was electrically driven making the process extremely energy intensive and limited in size with expensive moving parts which resulted in the need for costly regular maintenance. In our system, we get rid of the compressor for fewer electrical components, couple the solar energy on and create an overall cost efficient system with low maintenance and operating costs
- What is the potential for treating agricultural drainage in California? If we were to use solar-thermal desalination plants like HydroRevolutionSM to treat all of this water, how much closer would we be to closing the gap caused by the current drought?
If we could do a wide scale implementation of Aqua4, we estimate there are about 1 million acre-feet per year of drainage water available on the west side of the Central Valley that can be treated. California as a whole experienced a deficit of 6.6 million acre-feet of water in 2014. Californians tried to close this gap, which we now know is drought driven by climate change, by drilling wells and pumping 5 million acre-feet of water out of the ground. So that left agricultural users at a deficit of about 1.5 million acre-feet. Returning the 1 million acre-feet available in the Central Valley alone would nearly close this gap or at least offset groundwater pumping by 20% not to mention the various other saltwater sources that are abundant in California.
- Climate change and current drought aside, why is it imperative that farmers develop a method of treating irrigation water? What other benefits are provided by HydroRevolutionSM and the Aqua4™ technology?
As we go on, salt impairment of land becomes a larger and larger issue. If we don’t start removing the salts now, at least a 10% of all current farmland in production in California will have to be retired and in many scenarios, this number could be up to 30-40% especially on the west side of the Valley where the salinity is very high. And these predictions are only for the next 15 years, the situation will continue to get worse and worse.
If we continue irrigating and pushing drainage into the retired land surrounding crops, that water in the drainage areas will contaminate groundwater and natural surface waterways at an accelerated pace, eventually polluting sources of drinking water and the natural environment. Once that is released into the environment, you severely damage the natural habitat and wildlife. We see solar desalination systems as the future norm for sustainable farming in water scarce regions like California.
- Based on the results from the Panoche demonstration plant, would scaling the system down be as effective as scaling up? Will this technology one day be available to individual farmers who want to recycle their own irrigation water
Our vision right now is in scaling up; our scaled up version is still very very small compared to what’s been implemented for seawater systems. We want to continue doing distributed desalination across the nation instead of in one central location that has to connect to various resources.
We think we can make the biggest impact right now with the larger agribusinesses which tend to use a lot of water and are economically viable at this scale. The potential for water reuse in this industry is enormous. We think we could achieve large-scale adoption by going to a smaller scale and we hope our Gen II product, that will be coming out sometime next year, will demonstrate this.
A Closer Look at the Distillation:
- What are the leftovers after the distillation process, and what specifically will happen to them at the HydroRevolution plant?
The HydroRevolution plant is aiming to produce two products: water and solid salt. The water will be transferred to Panoche and the solid salt will be further processed by WaterFX and industrial partners into various downstream by-products that can be sold into the industrial and chemicals markets. Examples of these by-product materials are building components (gypsum), metals, selenium, and recovered fertilizers.
- How much energy is needed to power the the HydroRveolution plant at it’s first stage (producing 2,200 acre-feet of water per year)? How much of this energy can be derived from the sun?
We need 12 megawatts of thermal power to operate the system. Power is measured as energy per unit of time so 100% of this is coming from the sun when it is available. We will need roughly 50 of the large-aperture parabolic troughs similar to what we have at our pilot demonstration in order to collect solar energy to operate the HydroRevolution plant. Throughout the year we will use a natural gas backup if solar conditions are poor temporarily but we will maximize our use of solar power when conditions permit.
- Will the plant be able to store energy? How long will it be able to run on cloudy or rainy days with no solar input?
We are going to store as much as we can. The solar array for HydroRevolution is going to be sized much larger than can be used at any instant during the day. All of that excess (8-12 hours of energy) will be stored while the sun is up to power the system through the night. We want to operate at all times but there are times when you might have poor solar performance due to weather patterns and may need a back-up source.
- Can the water produced by the upcoming HydroRevolution plant be used for anything besides irrigation? Is it clean enough to drink?
Yes, if anything I’d say it’s too clean, the purest water you can ever get. To drink, you may even want to add some minerals back to it. But pure water, the quality of water produced by Aqua4, is needed for heavily regulated applications, such as pharmaceutical manufacturing and the high-tech semiconductor industry. Further, we’ve eliminated discharge of any salts back into the environment. It’s interesting that we can go from such a harsh waste product to the cleanest quality of water ever.