Low-cost Distillation/Desalination For Solving Most Of The World’s Water Problems

Summary:

Low-cost distillation/desalination can solve most of the world’s water problems, feed the world, stop a mass extinction, and stop global warming. With low-cost distillation coastal areas and cities can desalinate all the water they need, inland areas get to keep their water, and we can also irrigate the deserts. This can produce enough food to feed the world while also restoring natural habitat displacing farmland back to natural habitat. This stops a mass extinction and removes enough carbon to stop global warming. With low-cost distillation we can treat and recycle wastewater at source, avoiding the need for the collection of wastewater and greatly reducing the need for water utilities. With low-cost distillation we can clean up and recycle contaminated water, greatly reducing the water use of industrial processes and mitigating environmental impacts. We can also concentrate brines, including lithium brines, greatly reducing the cost and increasing the effectiveness of many industrial chemical processes.

Mechanical vapor compression distillation using very large surface area polymer film heat exchangers has a much lower capital cost than reverse osmosis, making it compatible with intermittent low-cost solar energy. It is similarly efficient and is far more tolerant to contaminants, $0.10/m3 is possible. It can be used for direct residential water recycling. With desalination it can produce salt directly, eliminating salt evaporation ponds and avoiding problematic and expensive brine discharge.

Mechanical vapor compression distillation using large polymer film heat exchangers:

Mechanical vapor compression is a distillation system that uses a single heat exchanger that evaporates on one side and condenses on the other. A gas compressor compresses the evaporated gas to a higher pressure and temperature so that it can condense on the other side of the heat exchanger. This is a very efficient system with efficiency primarily limited by the size of the heat exchanger. If distilling water at ambient temperature it also needs to operate far below atmospheric pressure at pressures corresponding to the vapor pressure of steam at that temperature - it must operate in a vacuum chamber. The primary weakness of mechanical vapor compression is that it generally needs very large and expensive titanium heat exchangers that do not corrode. The new insight is that polymer films can be very effective heat exchangers under these specific conditions. Plastic generally has very low thermal conductivity and so is not normally considered for heat exchangers, however the rate of heat transfer is also proportional to the thickness of the material and under these conditions the plastic film can be very thin, on the order of 0.5mil or 0.0127mm, which is comparable to a thin plastic shopping bag. At such small thicknesses the low thermal conductivity of the plastic is not limiting. Under near vacuum conditions the relative pressure on the plastic film is also very low, on the order of a thousand times less than atmospheric pressure, and these are effectively inflatable heat exchangers. Further, the plastic film is not subject to the same corrosion as a metallic heat exchanger meaning it is also resistant to saltwater and contaminants, and being in a vacuum chamber it is shielded from ultraviolet radiation - it can be long-lived. Plastic films enable extremely large areas at low-cost, enabling very efficient heat transfer and distillation. For example, a thousand square meter plastic film heat exchanger might cost a few hundred dollars and desalinate a metric ton of water per hour at efficiencies that surpass reverse osmosis - for around 2kWhs of electricity. A large vacuum chamber is needed but there are some relatively lightweight and low-cost ways of making these. The capital cost of the system is relatively low, longevity is high, and unlike reverse osmosis pre and post water treatment is not generally needed. The system is highly tolerant to contaminants and can likely distill all the way to a saturated salt solution. Variants of this system can be used for drying of solids, for example, fully drying out salt, but the efficiency for this stage is significantly lower as secondary heat transfer is required.

With mass production, the distillation system would be targeting a capital cost of around $1,000/m3/h. Rooftop solar in Australia now costs as little as $0.03/kWh. Grid scale solar can cost even less. The low capital cost of the distillation system means that it can be used intermittently in a manner that can take advantage of low-cost solar energy directly. While it will depend on the specific application and energy source, a desalination/distillation cost of around $0.10/m3 should be possible in the U.S. This cost enables:

Effectively unlimited low-cost desalinated water for coastal areas.
In home/business/industrial plant water recycling for lower cost water and wastewater treatment and increased water security.
Large scale desert farming solving food, biodiversity, and global warming.
Contaminated water clean-up, greatly reducing environmental impact.
Low-cost brine concentration, including lithium brines, which reduces the cost of many materials and eliminates the need for large and slow evaporation ponds.
Produced water purification for oil wells which also greatly extends oil well life.

Coastal desalination:

Many coastal cities are running out of water while being next to the ocean. Reverse osmosis desalination can cost as little as $0.41/m3 and use 2.79kWh/m3, yet residential water in California might average around $4.5/m3, over ten times higher. Although the Carlsbad desalination plant in San Diego likely costs well over $1/m3.This tells us that water distribution costs are often the larger problem and that low-cost desalination is not necessarily a substantial cost driver for many coastal cities. Brine discharge from desalination plants can also be a substantial cost, often entailing pipelines that go far out to sea, but there are some potential ways around this. Transporting desalinated water long distances inland, especially up to any significant altitude like a high desert, is often cost prohibitive. So this is only economically viable for lower elevation coastal areas. However, irrigation in coastal regions often leads to a significant increase in rainfall further inland. This occurs because irrigation boosts evaporation, and the resulting water vapor is carried inland by prevailing anabatic winds. For example, irrigation in California’s Central Valley leads to around a 15% increase in rainfall in neighboring inland states. Use of desalinated water in coastal areas provides drought independent water security, avoids expensive long distance water distribution, allows inland areas to keep their water, and further increases rainfall inland. This seems like a worthy objective for water stressed locations, and is especially beneficial to neighboring dry inland areas which receive a very high water benefit at almost no direct cost. This can greatly reduce water conflict and increase prosperity. Another interesting high value use case is supplying evaporative cooling water for thermal power stations and data centers. Gigawatt scale data centers are now being proposed. One gigawatt of evaporative cooling nominally requires around 1,500m3/h of water, which at 2kWh/m3 and $0.10/m3 would require around 3MW of electricity and only cost around $150/h.

Direct water recycling:

Water distribution and wastewater collection and treatment involve substantial costs for local governments necessitating taxation. Done poorly this can also result in negative health outcomes, and water systems are vulnerable to natural disasters. 1.4 million people die each year as a result of inadequate drinking-water, sanitation and hygiene. Replacing centralized wastewater treatment and recycling with residential, commercial, and industrial consumer distillation appliances that are subject to cost reduction curves can substantially avoid water and wastewater distribution systems. This can greatly increase water and wastewater security, reduce costs, and reduce the dependency on high functioning local government. Makeup water that compensates for water that is lost, likely primarily by way of irrigation, for example, lawn and garden watering, is still needed, but the amount required is greatly reduced. Such a recycling system can also use rainwater, wellwater, seawater, and stormwater runoff as primary water sources, even if they are contaminated, by distilling prior to use. This might also be combined with some local water tank storage. Tanker trucks that transport water from other locations, which might even include seawater, can also be used if local supplies run out. Noting that makeup water requirements are likely far less than daily water use.

Food, biodiversity, and global warming:

We are in the middle of a mass extinction primarily caused by farming displacing around half of productive natural habitat. Around two thirds of the world’s land is productive with the remaining third roughly half covered in ice and half covered in tropical and temperate desert. Farming the deserts and restoring productive farmland to natural habitat could stop global warming and avert a mass extinction. The additional carbon absorbed by desert farming, and associated rain cycles, can largely offset fossil fuel emissions. Temperate and tropical deserts tend to have high sunshine hours and can produce high yields with irrigation. Desert farming can scale to feed the world without substantial natural habitat displacement. Irrigation with desalinated water is becoming viable for high value crops and is starting to be used in many countries. As noted earlier, coastal irrigation can significantly increase rainfall inland, further helping to increase higher productivity natural habitat and reduce global warming. Use of greenhouses can also dramatically increase yield and reduce water consumption and is often a high value first use for desalinated water. Initially desalinated water might be used for the irrigation of high value crops, but as costs come down with increasing production scale, it will be increasingly used for lower value crops. Irrigation water costs in California's Central Valley might typically be in the $0.10/m3 range but can exceed $1/m3 during times of drought. Low-cost desalinated water for irrigation could be economically viable now for California’s Central Valley, which is seriously impacted by water stress. It is at low elevation and already has extensive water distribution infrastructure. This would greatly increase yield and economic output, and make it much more consistent and secure. Many other water stressed locations around the world would be similarly benefitted. The food security benefits are substantial, especially with respect to drought and climate change.

Contaminated water purification:

Low-cost distillation would allow for the direct purification and onsite recycling of contaminated water. This would be hugely advantageous for contaminated sites, mining tailing ponds, many chemical industrial processes that use large quantities of water, and even the oil and gas industry. Interestingly, oil well life is often limited by increased produced water production. The water to oil ratio increases to a point where the separation of the oil stops being economic. Much lower cost distillation would greatly increase the economically viable water to oil ratio and could significantly increase the effective life of many existing oil wells. This could also serve as a source of critical minerals including rare earth metals. Onsite low-cost water purification and recycling would allow for much more extensive use of water for cleaning purposes.

Brine concentration:

Dewatering and concentration of chemicals is another energy intensive and expensive process that would be greatly aided. Desalination via mechanical vapor compression using plastic film heat exchangers can potentially produce a near saturated solution of salt that can be further dried into salt. It requires significantly more power and energy to produce saturated salt rather than desalinated water, but it does not actually require a larger desalination unit, the heat exchanger size remains approximately the same. Seawater boils at 100.6℃ where the salt content is around 3.5% whereas saturated seawater boils at 108.7℃ where the salt content is around 27%. Compressing water vapor to this higher temperature and pressure takes more power and energy; however the total energy required per metric ton of desalinated water is only approximately doubled. $0.20/m3 should still be possible while producing solid salt that does not require brine discharge. Alternatively, this equates to around $6/metric ton for salt assuming that the desalinated water produced is free. The total global market for salt is around $26 billion and the average value might be around $120/metric ton. This market would expect to get saturated, however this presents a very profitable first initial market for this technology and would allow large evaporating ponds to be returned to natural habitat. This also applies to brines with more valuable salts including lithium brines. This technology could dramatically reduce the cost of lithium and enable much faster scaling rates. Lithium brine evaporation ponds are very large and slow to scale, they can take eighteen months to produce salt. The lithium brines could effectively be concentrated for the value of the water with a much smaller footprint of colocated solar power. Brine can be a useful source of critical minerals and metals and it can have a much lower environmental impact than other mining approaches.

Current status:

We have prototyped mechanical vapor compression distillation using plastic film heat exchangers and distillation has recently been demonstrated. The project is not currently being actively worked on, although this might change. Further work is needed to prove high yields. We possess patent protection for this technology and technology advising and licensing is an option. We would actively encourage others to develop, manufacture, and scale this technology.