Atmospheric Water Harvesting Techniques and Technologies
- sort: News
- pubDate:2023-01-06 22:20
Atmospheric Water Harvesting Techniques and Technologies
- sort: News
- pubDate:2023-01-06 22:20
Many areas are water challenged today, yet there is enough water in the air to quench our thirst – if only we knew how to tap this ubiquitous source. This report by Mallika Naguran describes solutions, techniques and technologies that are commercially available and applicable in varied scenarios and settings around the world. From atmospheric water harvesters, desalination of seawater, compact reverse osmosis to thermo-ionic flow, innovators have presented to us newer applications of getting pure drinking water at low environmental impact.
Water is essential for the healthy functioning of the human body. Without food, human beings can live for 14 days or more, but the human body can only survive a few days without water. Having access to safe and sufficient water and sanitation are now recognized as a basic human right.
Freshwater scarcity and stress are increasing in tropical regions as a result of expanding populations, tourism, climate change and pollution, states the United Nations Environment Program.
According to Water & Sanitation for the Urban Poor, one billion people worldwide live without clean, safe drinking water, and two billion live without basic sanitation. The UN Joint Monitoring Programme in 2006 reported that the number of the world’s urban population without access to an improved source of drinking water will increase from 137 million (2006) to 296 million (2015).
In most cases, the problem is not a lack of available water but rather the inability to obtain it in a cost-effective, reliable manner. Population growth and rising standards of living in many developing countries are increasing demand for clean, safe drinking water.
Access to water can also be the critical difference in business continuity and adverse situations. An island or remote location where water infrastructure is not available will do well with a mobile machine that delivers water on site according to the capacity required, without fail, rain or shine.
This paper presents atmospheric water harvesters as viable alternatives to existing water supply systems. Atmospheric water harvesters producing varying water capacity can also be considered as supplementary resources and logistical assets for consumers and industries that have limited access to water.
2. Fog Harvesting - Age-old Practices That Still Work
Water treatment systems are rapidly seeing changes, from days of conventional filtration systems to top of the range desalination plants with sophisticated membrane systems.
The various sources of water are being tapped – rivers, lakes, springs, mountain streams and where these aren’t readily accessible, seawater and even humidity in the air are being harvested.
But collecting water from the air is not new. It has been in use for at least 2,000 years with air wells in the Middle Eastern deserts and in Europe. Dewponds in the 1400s collected water, and later fog fences.
Fog fences use a technique called fog harvesting or fog collection or even cloud stripping, to collect water from the humidity in the fog. It can be used in coastal areas where inland wind bring in the fog, and high altitude areas (if water is present in stratocumulus clouds), from 400m to 1,200 m (UNEP, 1997).
How does it work? It uses a mesh material strung tightly on poles, supported by gutter to collect droplets, fed into pipes, and then stored in tanks. The size of the mesh can be as small as a metre in length or nearly 100m long, depending on the lay of the land, space available, and the quantity of water needed.
According to non-profit organisation Fog Quest, fog collectors can harvest a range of water quantities, from 200 to 1,000 litres per day, factoring in daily and seasonal variables. Efficiency of harvesting is increased with larger fog droplets, higher wind speeds, and narrower collection fibres/mesh width.
A fog collection system in eastern Nepal produces on average 500 liters of water daily and about half the quantity in the dry season (see video).[i] A study has shown that in Eritrea (East Africa), 1,600 square metres of mesh produced an average of 12,000 litres of water a day.[ii]
Remote places in Peru, Ecuador and Chile rely on this technique to draw much needed water for consumption and irrigation. Other areas that can potentially benefit from this technique, according to the International Development Research Centre (1995), include the Atlantic coast of southern Africa (Angola, Namibia), South Africa, Cape Verde, China, Eastern Yemen, Oman, Mexico, Kenya, and Sri Lanka.[iii]
Scientists are still testing and innovating better quality meshes and configurations that will maximize water production under different conditions.
3. Modern Atmospheric Water Harvesting
The artisanal method of fog harvesting, however, is not always suitable or practical, especially in dry and arid areas. This is where more modern techniques can be considered. An atmospheric water harvester or atmospheric water generator (AWG) is a electricity-powered device that uses the dehumidification principle to make drinking water out of the moisture in the air. With the amount of renewable water in the earth's atmosphere estimated to be around 12,504 cubic kilometres[iv], there is certainly an unlimited source of water to harvest from.
While AWG can be used virtually anywhere where potable water is needed, it is most applicable in places with higher humidity. The ideal place for this is the band around the equator (40° North Latitude to 40° South Latitude). That also happens to be where most of the people are in the world. Interestingly, this band is also where most of the water shortage problems have been identified.
AWG devices are specified to generate water at relatively moderate temperatures but high relative humidity. They tend to produce more water in places with higher temperatures and humid climates, and less water in colder or drier regions.
Absolutely no conventional or secondary water source is needed in an AWG. The only resource needed for AWG to work is the air with its trapped moisture, as the process mimics how rain is formed. Electricity powers the device, which can be obtained from the main power grid or from clean energy sources such as solar panels, wind turbine, wave converter and more.
The technology is a decentralized system of harvesting of atmospheric water that has not been previously considered as a potable water supply for the masses. It is sustainable, reliable, and produces potable water without massive, complicated installation.
4. How Does AWG Work?
Water vapor in the air is condensed by cooling the air below its dew point, exposing the air to desiccants, or pressurizing the air. The two primary techniques in use are cooling and desiccants.
The AWG operates by way of distillation. It captures water vapor from the air and channels it towards an evaporation system in a sanitary environment before it liquefies and is exposed to pollution. Figure 1 demonstrates the process behind AirQua products, manufactured by AridTec (http://www.aridtec.com).
Figure 1. AirQua systematic purification systemAirQua creates a clean air environment. Its technology extracts the distilled water vapor and converts it into crystal clear drinking water. Air is drawn through a double-layered anti bacteria air filter and ionised before being ‘captured’ into pure water. Collected water is then scientifically purified through pre-and-post charcoal filtration, chemical-free nano-membrane filtration and ultraviolet light sterilization to remove harmful organic substances.
A significant quantity of clean water is produced before it has been exposed to earthly contaminants. This sets AWGs apart from other water systems (municipalities, filtering and bottled water suppliers) that provide drinkable variations of polluted water by removing or neutralizing the hundreds of chemicals, micro-organisms and particulate in ground water.
The AirQua Sano model can produce up to 48 litres of pristine drink water per day, depending on the humidity, the volume of air passing through the coils, and the size of the machine. These units can operate 24 hours/day as water generators and also serve as water purifiers, air purifiers, hot and cold-water dispensers and dehumidifiers.
Depending upon local electricity costs, a litre of water from an AirQua unit can cost between 5 - 15 cents to produce. This is much less than the cost of purchasing bottled water, which currently averages around $1.00 - $2.00 per litre.
5. Tapping Clean Energy Sources
Electricity is needed to run certain water harvesters, and this can pose a challenge in areas where access to the power grid is limited or non-existent. Certain water harvesters even guzzle energy to produce copious amounts of clean drinking water. A certain AWG model uses 480W/hr to produce a litre of water an hour with intermittent heating for hot water output.
One inventor has gotten around that issue by tapping into clean and renewal energy sources. The Air to Water Harvest or A2WH (http://www.A2WH.com) uses solar power to extract the humidity in the air and convert it into drinking water. The patent pending technology makes use of a photo voltaic (PV) solar panel that requires full sun exposure at all times to power up the micro-controller, sensors, valves and so on. As it can condense at ambient temperatures, there is no need for refrigeration, which in other AWG systems can be a major cost item.
A2WH with built-in filtration can produce up to several thousand litres of water a day depending on the size of the machinery involved without the need for drawing any extra power from the grid and risk of polluting the ground with chemicals or concentrated salt deposits. Over five pounds of carbon per gallon is reduced in this process compared to electric systems, which works out to significant carbon emission reduction over time.
6. Applications for Use and Likely Scenarios
The AWG has distinct uses and applications in specific locations, circumstances and immediate needs. It can be considered a logistical asset due to the nature of its mobility and durability. Its reliability, due to the fact that it needs only two factors to produce drinking water - air and electricity, makes it a worthwhile investment.
Restaurants, bars, and hotels that need copious amounts of clean water and ice will find the AWG essential in the kitchen or lobby premises. Office environments that are using bottled water units can do away with plastics when replaced by AWG. AWG can be considered at remote locations, island resorts, mining sites, and instances where water scaling is an issue.
In cases of natural disasters and epidemics, the availability of AWGs can be timely in saving lives and improving sanitary conditions. Disaster management organisations specify drinking water as a top priority to maintain good health; the portability, reliability of AWGs in generating pure drinking water will prove to be a vital technological intervention in sustaining lives and health.
7. Advantages and Benefits of AWG
Water-from-air is an environmentally, sustainable and responsible water supply solution in tropical regions that have high moisture content in the ambient air.
AWG machines can be placed virtually anywhere, opening the door to otherwise impossible land development. Places that would benefit greatly from such machines are under developed sites where the water infrastructure is yet to be stabilized. Schools, hospitals, places of worship, police and fire stations stand to gain the most from the deployment of such machines.
Applications can also include larger housing developments – at a cost – as well as greenhouse irrigation and light industrial use. Some models are scalable while others are not. The volume of pure water generated can even go up to a few thousand litres of water a day.
There are distinct benefits associated with a typical AWG system:
Highly portable, economical and easy to maintain
No expensive piping infrastructure investment is needed
Quick flexible deployment
No conventional water source required
Needs only to plug into electrical socket to generate fresh, pure water
Convenient, dependable, and safe
Gives you total control over your water needs
8. Comparing AWG with Desalination
The water produced from AWG is purer than some other water treatment systems. Due to the rigorous filtration methods employed, a few AWG models generate water with virtually no inorganic minerals (e.g. sodium and chloride), impurities and contaminants. The “dew” water is clean, natural and free from chemicals.
Figure 2 lists the comparisons of AWG with the reverse osmosis (RO) process as documented by AridTec. Desalination is used widely around the world, in particular with the RO process, especially in dry countries, on maritime vessels and small islands.
The Middle East is still the largest user of desalination and seawater desalination plants of capacity over 300 ML/d are being constructed there(e.g. Ashkelon plant in
Figure 2. Product Comparison – Atmospheric Water Generator vs Conventional Reverse Osmosis (Source: AridTec)Israel). There is increasing use in Europe in countries such as Spain and in North America with plants of over 100 Ml/d of water per day capacity in the Caribbean.[v]
The process of desalination is conventionally expensive and energy intensive, with high maintenance and operations. In typical water production and distribution cycles of any water treatment plant for that matter, copious amounts of energy are needed to extract, pump, transport, treat and distribute water to all users. It is estimated that 2-3% of the world energy consumption is used to pump and treat water for urban residents and industry.[vi]
Desalination also produces concentrated waste streams of brine, which have to be disposed of responsibly. For these reasons, it is generally a source of last resource, implemented when all others have failed. The most practical and attractive desalination options are for water that does not have much salt in it to start with, i.e. brackish water or recycled water. Still the quality of water can be less than what was hoped for.
The environmental impacts are significant. With high energy consumption comes high greenhouse gas production. A study by the Sydney Coastal Councils Group in 2005 suggested that the proposed Sydney Water desalination plant producing up to 500 Ml/d through reverse osmosis would require 906 GWh of energy per year. It would also produce 950,000 tonnes (using the existing energy grid) of greenhouse gasses per year.[vii]
There are threats to marine life with the high volume of brine discharge that may also contain pollutants that are toxic, primarily due to contact with metallic materials used in the construction of the plant facilities. According to the study, the environmental impacts may include increased turbidity, reduced oxygen levels and increased density of discharged wastewater.
Concerns cited by the Sydney Coastal Councils Group included significant environmental impact on delicate local ecosystems containing heritage listed sand dunes, sensitive wetlands and protected marine and intertidal areas. Other research has suggested that the greatest single ecological problem associated with desalination plants that use seawater is that organisms living with in the vicinity of the desalination plant are sucked into its equipment.
Costs associated with desalination include initial construction, sophisticated equipment and materials, maintenance and operations – these can run from hundreds of thousands of dollars to millions. As desalination plants have shorter lifespan than that of traditional water treatment plants, capital cost has to be amortized over a shorter time span – this piles on the cost.
According to the study, desalinated water from seawater by a large plant may cost slightly more than A$1 per kilolitre at 100 megalitres per day. For smaller plants and less favourable conditions, the cost could be $4 per kilolitres or more.
The Water Treatment Guide website provides a brief overview of the factors that affect the performance of RO membranes such as pressure, temperature, feedwater salt concentration, permeate recovery and system pH. http://www.watertreatmentguide.com/factors_affecting_membrane_performance.htm.
9. Desalination Advancements
Due to increasing population and water demands, there has been an exponential growth in desalination plants worldwide with the reduction in capital and operating costs and improvements in energy efficiency of RO systems. Prof Asit K Biswas of Third World Centre for Water Management noted that the use of new generation membranes and improved management practices have led to seawater desalination costs falling by almost a factor of three during the past decade.
“At the current cost of producing desalinated water (around $0.45–0.60 per m3) through reverse osmosis, the technique has become cost-effective for many cities where water availability is a constraint. The cost of treating brackish water has become even lower: $0.20–0.35 per m3, depending on its salt content.” Prof Biswas concludes that the technological and management breakthroughs achieved are making desalination a viable alternative for solving water quantity and quality problems for domestic and industrial uses, especially for coastal areas.[viii]
HelioAquaTech (www.helioaquatech.com) is able to provide drinking water via desalination that is powered by solar energy. The water source can be from the ground (wells, spring, river) or from the sea, hence suitable for homes, resorts and villages at remote places as well as coastal areas. A basic system comprises eight modules of solar panels (3 m² and 17 kg each) and a pump that works on the principle of evaporation. The company claims that a basic system operating at an average temperature of 20º C can produce 128 litres of water daily. On the high end, 184 modules operating at an annual temperature range of 30º C, is able produce up to 3,600 litres of drinking water a day.
According to HelioAquaTech, the performance of the system is dependent on: the latitude, sunlight hours, solar radiation, and season on the location of the operation.[ix] The company also offers another solution for drinking water treatment via reverse osmosis that is powered by solar and/or wind energy.
Another innovation hails from Vancouver, Canada. Saltworks Technologies (http://www.saltworkstech.com) introduced its Thermo-Ionic™ desalination technology that harnesses renewable energy sources – dryness in the atmosphere and heat from the sun – to reduce the huge amount of energy used in treating water. Neither distillation nor reverse osmosis is used in the treatment. Instead, the energy transfer system is driven by salt! The company claims that their patent pending technology uses up to 80% less electrical or mechanical energy than conventional desalination machines. It can also reuse waste heat and brine from other desalination plants to boost its performance.
Saltworks has put out its first mobile plant in June 2010 by building it into a portable shipping container. It produces 1,000 litres of water a day and is being tested in the Okanagan region of British Columbia at the company’s solar-thermal test facility. According to the company, the plant has a higher capacity when treating waste saltwater and will be used for pilot runs at customer sites.[x]
Its latest contract in March 2012 is to deliver a pilot unit to NASA, to test its feasibility for use at the International Space Station. "The NASA project is an example of how Saltworks' innovative technology could be used in diverse applications, both on - and off - the planet," said Joshua Zoshi, Saltworks' President.[xi]
10. Compact Reverse Osmosis Systems
The principle of reverse osmosis or RO is taking centre stage in various design patents of water treatment machines suitable for commercial and industrial uses from the USA to Taiwan. In fact, the variety of systems catering for different water sources in the market poses a challenge for the concerned user to decipher what is the most suitable machinery to procure, at what cost – both in the short and long term - and to what effect.
One invention arising from Illinois, USA addresses the water wastage issue that is common in RO systems, where for every volume of potable water produced, four volumes of used water is dumped in the sewage. See http://www.everpure.com/newspress/Pages/MRS-ENVI-RO-600.aspx
The Everpure MRS-600 HE uses patent-pending dual headed pump that eliminates membrane back pressure, ensuring consistent stream of permeate water production. This improvement by the company plus others reverses the conventional wastage of RO by producing only one volume of wastewater to four volumes of pure RO water. The system produces as much as 600 gallons of water a day and retails at $4,500, excluding cost of filter and cartridge replacements.
Applied Membrane Systems from California, USA has a range of systems producing RO water from as little as 300 gallons to as much as tens of hundreds of gallons a day depending on the concentration of total dissolved solids (TDS) in the feed water and output requirements. http://www.appliedmembranes.com/Product_Catalog/Reverse%20Osmosis%20Systems.pdf
Even smaller, for home or office use, Takada originating from Singapore/Malaysia sells its RO water dispenser online with a shopping cart facility. The ISB-ROI Pipe-In RO System has to be connected directly to the water source before a multi-stage filtration takes place to produce hot (above 95C) and cold (below 10C) water. It retails at around $415. http://www.mytakada.com/direct.htm
A 2007 Reddot design award winner, the Bonnie model of Taiwanese PurePro is a sleek addition to the office. The four-stage RO system has an invisible cup dispenser and direct chill system of up to 20 litres per hour capacity. It has the ability to produce up to 80 gallons of treated water a day. http://www.pure-pro.com/bonnie.htm
In considering an RO system, it pays well to enquire right at the beginning the cost of maintaining RO systems and the lifespan of the machinery. Water quality test for contaminants is recommended along with regular system maintenance. There also has to be caution on how the concentrated wastewater is disposed of without causing harm to the environment.
11. Addressing Bottled Water Issues
In many parts of the world, bottled water is viewed as a necessity due to unsafe locally produced water. This has been a key driver of bottled water sales in emerging markets.
Across the globe consumers have reached into their pockets to the tune of $50 billion dollars this year to purchase bottled water. Worldwide bottled water sales could be as high as 160 billion litres per year and consumption is increasing 7% to 10% annually.
Western Europeans remain the biggest bottled water consumers, guzzling a little more than a quarter of the world’s production. In some emerging markets such as India, water consumption has been tripling and more than doubling in China over the past five years. In fact, it is likely that over the next few years, up to and probably beyond 2010, the growth rate will accelerate, and that Asia Pacific will become the world's largest regional market for packaged water.
Only about 12 percent of "custom" plastic bottles, a category dominated by water, were recycled in 2003, according to industry consultant R.W. Beck, Inc. That's 40 million bottles (USA) a day that went into the trash or became litter. In contrast, the recycling rate for plastic soft drink bottles is around 30 percent. Millions of tons of greenhouse gases are generated in the manufacture and transport of plastic bottles.
Plastics should be recycled so that less petroleum — a finite commodity — is consumed. The use of AWG in commercial, tourism, hospitality and MICE sectors where most bottled water is consumed will reduce the supply of earth-choking plastic bottles.
Bottled water is a growing part of the beverage market. While the broader non-alcoholic beverage market is growing, bottled water is growing at a faster rate due to increasing awareness of health issues, as bottled water is perceived to have health benefits.
Bottled water has no calories and is perceived as healthier than sugar-laden and acidic CO² rich fizzy soft drinks. Global sales of bottled water may run as high as 160 billion litres annually and consumption is increasing 7-10% annually. Research shows that people want better tasting and healthier alternatives to many of the soft drinks and sports drinks currently available.
Plastic bottles also pose a health risk with leaching of volatile organic compounds. Harvard School of Public Health researchers traced the chemical bisphenol A (BPA) in the urine of college students who drank from polycarbonate bottles. BPA is known to interfere with the reproductive development of animas and might also be associated with heart disease and diabetes.[xii]
12. AWG Strengths and Weaknesses
Atmospheric water harvesting technology in comparison requires little infrastructure building as AWG equipment are portable and scalable. The equipment can serve large requirements by integrating them together to produce greater outputs. An advantage is to be able to take them apart depending on situational changes.
As there is no need to tap in to any existing of potential water infrastructure, the AWG can be considered as a stop-gap measure in the building of huge and large scale water treatment plants.
Environmental impacts of AWG are negligible as by-products are warm air and machine consumables – much smaller carbon footprint compared to desalination plants and bottled water factories. The energy consumption of AWG machines in general is said to be lower than any other water generation methods, however this remains unsubstantiated.
Clean energy sources should be considered for the reduction of costs of electrical power in the long run, like solar or wind power.
Where cost is concerned, the product price of an AWG is relatively higher compared to municipal water supplies, as the latter tends to enjoy government subsidies.
Climate plays an important factor for AWG machines to run efficiently. The best conditions would be places with relative humidity and cool.
AWGs face a challenge with sandy areas such as deserts – the air filters are susceptible to blockage by sand particles. This can be resolved by changing blocked air filters often while the machine continues to produce untainted drinking water. In arid areas such as Middle East winters, according to AridTec, water production by AWGs can be less efficient by 15% -20%.
Despite widespread water pollution and shortages of drinking water, there is an abundance of water around us – from the air that we breathe to the water in the sea. Several water treatment methods exist to tap these sources, from artisanal, traditional methods of atmospheric water generation to unconventional, modern techniques of desalination.
Water harvesting and treatment technologies that are solar or wind powered is the most environmentally friendly way to extract pure quality water from the air or sea at a low cost. The good news is that these technologies are now commercially available and mostly scaleable depending on need and location.
This report was contributed in April 2012 to The Green Disc: Innovative Technologies for Sustainable Development published by The UNCSD Small Island Developing States Partnership in New Sustainable Technologies. The First Edition of the Green Disc, released at the UN Climate Change Conference in Copenhagen in 2009, is now available on the web. The second edition was released at the UN Conference on Sustainable Development in Rio de Janeiro in June 2012.
About the author: Mallika Naguran is an environmental writer and founder of Gaia Discovery.
UNEP (1997) Sourcebook of Alternative Technologies for Freshwater Augmentation in Some Countries in Asia, UNEP, Unit of Sustainable Development and Environment General Secretariat, Organisation of American States, Washington, D.C.
Schemenauer, R.S., P. Osses, and M. Leibbrand (2004) Fog collection evaluation and operational projects in the Hajja Governorate, Yemen. In: Proceedings of the 3rd International Conference on Fog, Fog Collection and Dew, Cape Town, South Africa, 38.
Schemenauer, R.S. and P. Cereceda (1994). Fog collection's role in water planning for developing countries. Natural Resources Forum, 18, 91-100, United Nations, New York.
UNISA (University of South Africa) (2008) Research Report, UNISA. Cape Town.
International Desalination Association (IDA) http://www.idadesal.org
European Desalination Society (EDS) http://www.edsoc.com
Australian Water Association http://www.awa.asn.au
[i] Fog Quest website and video http://www.fogquest.org/index.php/home/
[iv] US Geological Survey http://ga.water.usgs.gov/edu/watercycleatmosphere.html
[v] Desalination article by Australian Water Association http://www.awa.asn.au/AM/Template.cfm?Section=Desalination
[vi] E & WR (2005) In: CSIS. Global water futures. Addressing our global water future. Center for
Strategic and International Studies, Sandia National Laboratories, California
[vii] Desalination Fact Sheet by Sydney Coastal Councils Group Inc.
[viii] Asit K. Biswas and Cecilia Tortajada, 2009 “Changing Global Water Management Landscape”
[ix] HelioAquaTech website http://www.helioaquatech.com/solarwatermaker.html
[x] SaltWorks website http://www.saltworkstech.com/press_20100630.php
[xi] SaltWorks website http://www.saltworkstech.com/news_20120316.php
[xii] Harvard School of Public Health Research on Polycarbonate Bottle Use and Urinary Bisphenol A Concentrations http://www.ehponline.org/members/2009/0900604/0900604.pdf