"The Namib Desert Beetle generates water from water vapor via its shell,
which has alternating hydrophilic and hydrophobic bumps which channel
water droplets into its mouth. Scientists at MIT developed a
self-filling water bottle using this technology, and have announced a
contest for the best design of a countertop water-from-air generator."
Written by Mike Awada on November 22, 2012. Posted in Gadgets, Science,
Social, Technology
namib-beetle-harvests-water-from-air
There are nearly four quadrillion gallons of water in the air, yet
people all over the world are still thirsty. Scientists have been
working to break into this untapped resource for over a decade, and are
making some incredible breakthroughs.
Progress in this field has been made by studying the survival mechanisms
of an insect living in one of the most hostile regions on the planet.
The Namib Desert, located on the Southwest African coast, has sands
reaching temperatures upwards of 140 °F. Here, there is less than 1/2″
of rainfall per year, yet the Namib Desert Beetle manages to survive
each and every year.
Stenocara Solution
National Geographic describes the Namib Desert Beetle, also known as the
stenocara, as a desert MacGyver. The stenocara is equipped with an armor
like shell covered with bumps. The peak of each bump is hydrophilic,
meaning that it attracts water. The slopes and valleys in between bumps
are hydrophobic, meaning they repel water.
The Namib Desert Beetle climbs atop a desert hill in the morning as a
fog sweeps over the land. The stenocara angles its body into the wind
and miniscule water droplets from the fog stick to the hydrophilic peaks
and gradually form droplets. Once enough water has accumulated, the
droplets roll effortlessly down the hydrophobic slopes directly into the
insect’s mouth, sustaining its life in the normally inhospitable
environment.
Researchers are mimicking this natural trait to develop a bevy of
important water harvesting platforms, including tent covers and roof
tiles several times more effective at capturing H2O than the next most
effective method. In the near future, it looks as if we’ll have water
bottles that can capture drinkable water from the air as well.
NBD Nano: Self-Refilling Water Bottle
A company called NBD Nano is implementing this technology originally
found only in nature into water bottles, with the hope that they’ll
continually fill themselves while you’re on the go. In an interview with
Public Radio International, we learn that the conceptual self-filling
bottle can operate using a rechargeable battery or solar cell to
speed-up accumulation and filter the water.
NBD Nano co-founder Deckard Sorensen wants this green technology
available in all walks of life; installing it on people, cars, homes and
anything else you can imagine. Sorensen believes that in a climate with
75% humidity, his device can harvest “three liters per square meter per
hour”.
“We see this being applicable to anything from marathon runners to
people in third-world countries, because we realize that water is such a
large issue in the world today, and we want to try to alleviate those
problems with a cost-efficient solution.”
Global Implications
While the invention is certainly fascinating for the first world
consumer, perhaps the most important use of this technology will be for
the billion plus people who live without access to clean, drinkable
water everyday.
NBD Nano hopes to have the self-refilling water bottle to market in
2014. How do you think we should use the technology?
<>
Comment:
This is not new technology. This solution is wrapped into a different
format, and uses slightly more advanced materials than what is already
in use:
This innovative technology is based on the fact that water can be
collected from fogs under favorable climatic conditions. Fogs are
defined as a mass of water vapor condensed into small water droplets at,
or just above, the Earth's surface. The small water droplets present in
the fog precipitate when they come in contact with objects. The frequent
fogs that occur in the arid coastal areas of Peru and Chile are
traditionally known as camanchacas. These fogs have the potential to
provide an alternative source of freshwater in this otherwise dry region
if harvested through the use of simple and low-cost collection systems
known as fog collectors. Present research suggests that fog collectors
work best in coastal areas where the water can be harvested as the fog
moves inland driven by the wind. However, the technology could also
potentially supply water for multiple uses in mountainous areas should
the water present in stratocumulus clouds, at altitudes of approximately
400 m to 1 200 m, be harvested.
Technical Description
Full-scale fog collectors are simple, flat, rectangular nets of nylon
supported by a post at either end and arranged perpendicular to the
direction of the prevailing wind. The one used in a pilot-scale project
in the El Tofo region of Chile consisted of a single 2 m by 24 m panel
with a surface area of 48 m2. Alternatively, the collectors may be more
complex structures, made up of a series of such collection panels joined
together. The number and size of the modules chosen will depend on local
topography and the quality of the materials used in the panels.
Multiple-unit systems have the advantage of a lower cost per unit of
water produced, and the number of panels in use can be changed as
climatic conditions and demand for water vary.
The surface of fog collectors is usually made of fine-mesh nylon or
polypropylene netting, e.g., "shade cloth," locally available in Chile
under the brand name Raschel. Raschel netting (made of flat, black
polypropylene filaments, 1.0 mm wide and 0.1 mm thick, in a triangular
weave) can be produced in varying mesh densities. After testing the
efficiency of various mesh densities, the fog collectors used at El Tofo
were equipped with Raschel netting providing 35% coverage, mounted in
double layers. This proportion of polypropylene-surface-to-opening
extracts about 30% of the water from the fog passing through the nets.
As water collects on the net, the droplets join to form larger drops
that fall under the influence of gravity into a trough or gutter at the
bottom of the panel, from which it is conveyed to a storage tank or
cistern. The collector itself is completely passive, and the water is
conveyed to the storage system by gravity. If site topography permits,
the stored water can also be conveyed by gravity to the point of use.
The storage and distribution system usually consists of a plastic
channel or PVC pipe approximately 110 mm in diameter which can be
connected to a 20 nun to 25 nun diameter water hose for conveyance to
the storage site/point of use. Storage is usually in a closed concrete
cistern. A 30 m3 underground cistern is used in the zone of Antofagasta
in northern Chile. The most common type of fog collector is shown in
Figure 6.
Storage facilities should be provided for at least 50% of the expected
maximum daily volume of water consumed. However, because the fog
phenomenon is not perfectly regular from day to day, it may be necessary
to store additional water to meet demands on days when no fog water is
collected. Chlorination of storage tanks may be necessary if the water
is used for drinking or cooking purposes.
Extent of Use
Fog harvesting has been investigated for more than thirty years and has
been implemented successfully in the mountainous coastal areas of Chile
(see case study in Part C, Chapter 5), Ecuador, Mexico, and Peru.
Because of a similar climate and mountainous conditions, this technology
also can be implemented in other regions as shown in Figure 7.
Figure 6: Section of a Typical Flat, Rectangular Nylon Mesh Fog
Collector. The water is collected in a 200 l drum.
Source: G. Soto Alvarez, National Forestry Corporation (CONAF),
Antofagasta, Chile.
In Chile, the National Forestry Corporation (CONAF), the Catholic
University of the North, and the Catholic University of Chile are
implementing the technology in several regions, including El Toro, Los
Nidos, Cerro Moreno, Travesía, San Jorge, and Pan de Azúcar. The results
of the several experiments conducted in the northern coastal mountain
region indicate the feasibility and applicability of this technology for
supplying good-quality water for a variety of purposes, including
potable water and water for commercial, industrial, agricultural, and
environmental uses. These experiments were conducted between 1967 and
1988 at altitudes ranging from 530 m to 948 m using different types of
fog water collectors. The different types of neblinometers and fog
collectors resulted in different water yields under the same climatic
conditions and geographic location. A neblinometer or fog collector with
a screen containing a double Raschel (30%) mesh was the most successful
and the one that is currently recommended.
In Peru, the National Meteorological and Hydrological Service (SENAMHI)
has been cooperating with the Estratus Company since the 1960s in
implementing the technology in the following areas: Lachay, Pasamayo,
Cerro Campana, Atiquipa, Cerro Orara (Ventinilla-Ancón), Cerro Colorado
(Villa María de Triunfo), and Cahuide Recreational Park (Ate-Vitarte),
and in southern Ecuador the Center for Alternative Social Research
(CISA) is beginning to work in the National Park of Machalilla on Cerro
La Gotera using the Chilean installations as models.
Operation and Maintenance
Operating this technology is very simple after once the fog collection
system and associated facilities are properly installed. Training of
personnel to operate the system might not be necessary if the users
participate in the development and installation of the required
equipment. A very important factor in the successful use of this
technology is the establishment of a routine quality control program.
This program should address both the fog collection system and the
possible contamination of the harvested water, and include the following
tasks:
· Inspection of cable tensions. Loss of proper cable tension can
result in water loss by failing to capture the harvested water in the
receiving system. It can also cause structural damage to the collector
panels.
· Inspection of cable fasteners. Loose fasteners in the collection
structure can cause the system to collapse and/or be destroyed.
· Inspection of horizontal mesh net tensions. Loose nets will lead
to a loss of harvesting efficiency and can also break easily.
· Maintenance of mesh nets. After prolonged use, the nets may tear.
Tears should be repaired immediately to avoid having to replace the
entire panel. Algae can also grow on the surface of the mesh net after
one or two years of use, accumulating dust, which will cloud the
collected water and cause offensive taste and odor problems. The mesh
net should be cleaned with a soft plastic brush as soon as algal growth
is detected.
· Maintenance of collector drains. A screen should be installed at
the end of the receiving trough to trap undesirable materials (insects,
plants, and other debris) and prevent contamination of water in the
storage tank. This screen should be inspected and cleaned periodically.
· Maintenance of pipelines and pressure outlets. Pipelines should
be kept as clean as possible to prevent accumulation of sediments and
decomposition of organic matter. Openings along the pipes should be
built to facilitate flushing or partial cleaning of the system.
Likewise, pressure outlets should be inspected and cleaned frequently to
avoid accumulation of sediments. Openings in the system must be
protected against possible entry of insects and other contaminants.
· Maintenance of cisterns and storage tanks. Tanks must be cleaned
periodically with a solution of concentrated calcium chloride to prevent
the accumulation of fungi and bacteria on the walls.
· Monitoring of dissolved chlorine. A decrease in the concentration
of chlorine in potable water is a good indicator of possible growth of
microorganisms. Monitoring of the dissolved chlorine will help to
prevent the development of bacterial problems.
Figure 7: Locations Where Fog Harvesting Has Been or Can Be Implemented.
Source: W. Canto Vera, et al. 1993. Fog Water Collection System.
IDRC, Ottawa, Canada.
Level of Involvement
In applying this technology, it is strongly recommended that the end
users folly participate in the construction of the project. Community
participation will help to reduce the labor cost of building the fog
harvesting system, provide the community with operation and maintenance
experience, and develop a sense of community ownership and
responsibility for the success of the project. Government subsidies,
particularly in the initial stages, might be necessary to reduce the
cost of constructing and installing the facilities. A cost-sharing
approach could be adopted so that the end users will pay for the
pipeline and operating costs, with the government or an external agency
assuming the cost of providing storage and distribution to homes.
Costs
Actual costs of fog harvesting systems vary from location to location.
In a project in the region of Antofagasta, Chile, the installation cost
of a fog collector was estimated to be $90/m2 of mesh, while, in another
project in northern Chile, the cost of a 48 m2 fog collector was
approximately $378 ($225 in materials, $63 in labor, and $39 in
incidentals). This latter system produced a yield of 3.0 l/m2 of
mesh/day. The cost of a fog harvesting project constructed in the
village of Chungungo, Chile, is shown in Table 2. The most expensive
item in this system is the pipeline that carries the water from the fog
collection panel to the storage tank located in the village.
Maintenance and operating costs are relatively low compared to other
technologies. In the project in Antofagasta, the operation and
maintenance cost was estimated at $600/year. This cost is significantly
less than that of the Chungungo project: operating costs in that project
were estimated at $4 740, and maintenance costs at $7 590 (resulting in
a total cost of $12 330/year).
Both the capital costs and the operating and maintenance costs are
affected by the efficiency of the collection system, the length of the
pipeline that carries the water from the collection panels to the
storage areas, and the size of the storage tank. For example, the unit
cost for a system with an efficiency of 2.0 l/n^/day was estimated to be
$4.80/1 0001. If the efficiency was improved to 5.0 l/m2/day, then the
unit cost would be reduced to $1.90/1 0001. In the Antofagasta project,
the unit cost of production was estimated at $1.41/1000 l with a
production of 2.5 l/m2/day.
Table 2 Capital Investment Cost and Life Span of Fog Water Collection
System Components
Component
Cost ($)
%of Total Cost
Life Span (Years)
Collection
27680
22.7
12
Main pipeline
43787
35.9
20
Storage (100m3 tank)
15632
12.8
20
Treatment
2037
1.7
10
Distribution
32806
26.9
20
TOTAL
121 942
100.0
Source: Soto Alvarez, Q. National Forestry Corporation,
Antofagasta, Chile.
Effectiveness of the Technology
Experimental projects conducted in Chile indicate that it is possible to
harvest between 5.3 l/m2/day and 13.4 l/m2/day depending on the
location, season, and type of collection system used. At El Tofo, Chile,
during the period between 1987 and 1990, an average fog harvest of 3.0
l/n^/day was obtained using 50 fog collectors made with Raschel mesh
netting. Fog harvesting efficiencies were found to be highest during the
spring and summer months, and lowest during the winter months. The
average water collection rates during the fog seasons in Chile and Peru
were 3.0 and 9.0 l/m2/day, respectively; the lengths of the fog seasons
were 365 and 210 days, respectively. While this seems to indicate that
higher rates are obtained during shorter fog seasons, the practical
implications are that a shorter fog season will require large storage
facilities in order to ensure a supply of water during non-fog periods.
Thus, a minimum fog season duration of half a year might serve as a
guideline when considering the feasibility of using this technology for
water supply purposes; however, a detailed economic analysis to
determine the minimum duration of the fog season that would make this
technology cost-effective should be made. In general, fog harvesting has
been found more efficient and more cost-effective in arid regions than
other conventional systems.
Suitability
In order to implement a fog harvesting program, the potential for
extracting water from fogs first must be investigated. The following
factors affect the volume of water that can be extracted from fogs and
the frequency with which the water can be harvested:
· Frequency of fog occurrence, which is a function of atmospheric
pressure and circulation, oceanic water temperature, and the presence of
thermal inversions.
· Fog water content, which is a function of altitude, seasons and
terrain features.
· Design of fog water collection system, which is a function of
wind velocity and direction, topographic conditions, and the materials
used in the construction of the fog collector.
The occurrence of fogs can be assessed from reports compiled by
government meteorological agencies. To be successful, this technology
should be located in regions where favorable climatic conditions exist.
Since fogs/clouds are carried to the harvesting site by the wind, the
interaction of the topography and the wind will be influential in
determining the success of the site chosen. The following factors should
be considered in selecting an appropriate site for fog harvesting:
Global Wind Patterns: Persistent winds from one direction are ideal
for fog collection. The high-pressure area in the eastern part of the
South Pacific Ocean produces onshore, southwest winds in northern Chile
for most of the year and southerly winds along the coast of Peru.
Topography: It is necessary to have sufficient topographic relief
to intercept the fogs/clouds; examples, on a continental scale, include
the coastal mountains of Chile, Peru, and Ecuador, and, on a local
scale, isolated hills or coastal dunes.
Relief in the surrounding areas: It is important that there be no
major obstacle to the wind within a few kilometers upwind of the site.
In arid coastal regions, the presence of an inland depression or basin
that heats up during the day can be advantageous, as the localized low
pressure area thus created can enhance the sea breeze and increase the
wind speed at which marine cloud decks flow over the collection devices.
Altitude: The thickness of the stratocumulus clouds and the height
of their bases will vary with location. A desirable working altitude is
at two-thirds of the cloud thickness above the base. This portion of the
cloud will normally have the highest liquid water content. In Chile and
Peru, the working altitudes range from 400 m to 1 000 m above sea level.
Orientation of the topographic features: It is important that the
longitudinal axis of the mountain range, hills, or dune system be
approximately perpendicular to the direction of the wind bringing the
clouds from the ocean. The clouds will flow over the ridge lines and
through passes, with the fog often dissipating on the downwind side.
Distance from the coastline: There are many high-elevation
continental locations with frequent fog cover resulting from either the
transport of upwind clouds or the formation of orographic clouds. In
these cases, the distance to the coastline is irrelevant. However, areas
of high relief near the coastline are generally preferred sites for fog
harvesting.
Space for collectors: Ridge lines and the upwind edges of
flat-topped mountains are good fog harvesting sites. When long fog water
collectors are used, they should be placed at intervals of about 4.0 m
to allow the wind to blow around the collectors.
Crestline and upwind locations: Slightly lower-altitude upwind
locations are acceptable, as are constant-altitude locations on a flat
terrain. But locations behind a ridge or hill, especially where the wind
is flowing downslope, should be avoided.
Prior to implementing a fog water harvesting program, a pilot-scale
assessment of the collection system proposed for use and the water
content of the fog at the proposed harvesting site should be undertaken.
Low cost and low maintenance measurement devices to measure the liquid
water content of fog, called neblinometers, have been developed at the
Catholic University of Chile (Carvajal, 1982). Figure 8 illustrates four
different types of neblinometers: (a) a pluviograph with a perforated
cylinder; (b) a cylinder with a nylon mesh screen; (c) multiple mesh
screens made of nylon or polypropylene mesh; and (d) a single mesh
screen made of nylon or polypropylene mesh. The devices capture water
droplets present in the fog on nylon filaments that are mounted in an
iron frame. The original neblinometer had an area of 0.25 m2 made up of
a panel with a length and width of 0.5 m, and fitted with a screen
having a warp of 180 nylon threads 0.4 mm in diameter. The iron frame
was 1.0 cm in diameter and was supported on a 2.0 m iron pole. These
simple devices can be left in the field for more than a year without
maintenance and can be easily modified to collect fog water samples for
chemical analysis.
In pilot projects, use of a neblinometer with single or multiple panels
having a width and length of one meter, fitted with fine-mesh nylon or
polypropylene netting is recommended. It should be equipped with an
anemometer to measure wind velocity and a vane to measure wind
direction. The neblinometer can be connected to a data logger so that
data can be made available in computer-compatible formats.
Advantages
· A fog collection system can be easily built or assembled on site.
Installation and connection of the collection panels is quick and
simple. Assembly is not labor intensive and requires little skill.
· No energy is needed to operate the system or transport the water.
· Maintenance and repair requirements are generally minimal.
· Capital investment and other costs are low in comparison with
those of conventional sources of potable water supply used, especially
in mountainous regions.
· The technology can provide environmental benefits when used in
national parks in mountainous areas, or as an inexpensive source of
water supply for reforestation projects.
· It has the potential to create viable communities in inhospitable
environments and to improve the quality of life for people in
mountainous rural communities.
· The water quality is better than from existing water sources used
for agriculture and domestic purposes.
Disadvantages
· This technology might represent a significant investment risk
unless a pilot project is first carried out to quantify the potential
rate and yield that can be anticipated from the fog harvesting rate and
the seasonably of the fog of the area under consideration.
· Community participation in the process of developing and
operating the technology in order to reduce installation and operating
and maintenance costs is necessary.
· If the harvesting area is not close to the point of use, the
installation of the pipeline needed to deliver the water can be very
costly in areas of high topographic relief.
· The technology is very sensitive to changes in climatic
conditions which could affect the water content and frequency of
occurrence of fogs; a backup water supply to be used during periods of
unfavorable climatic conditions is recommended.
· In some coastal regions (e.g., in Paposo, Chile), fog water has
failed to meet drinking water quality standards because of
concentrations of chlorine, nitrate, and some minerals.
· Caution is required to minimize impacts on the landscape and the
flora and fauna of the region during the construction of the fog
harvesting equipment and the storage and distribution facilities.
Figure 8: Types of Neblinometers.
Source: G. Soto Alvarez, National Forestry Corporation,
Antofagasta, Chile.
Cultural Acceptability
This technology has been accepted by communities in the mountainous
areas of Chile and Peru. However, some skepticism has been expressed
regarding its applicability to other regions. It remains a localized
water supply option, dependent on local climatic conditions.
Future Development of the Technology
To improve fog harvesting technology, design improvements are necessary
to increase the efficiency of the fog collectors. New, more durable
materials should be developed. The storage and distribution systems
needs to be made more cost-effective. An information and community
education program should be established prior to the implementation of
this technology.
Information Sources
Contacts
Guido Soto A., Waldo Canto V., and Alejandro Cruzet, Corporación
Nacional Forestal (CONAF), IV Región, Cordovez 281, La Serena, Chile.
Tel. (56-51)22-6090/22-4306/21-3565. Fax (56-51)21-5073.
Roberta Espejo Guasp, Profesor, Departamento de Física, Facultad de
Ciencias, Universidad Católica del Norte, Av. Angamos 0610, Casilla de
Correo 1280, Antofagasta, Chile. Tel. (56-55)24-1148, anexos 211/287.
Fax (56-55)24-1724/24-1756, E-mail: respejo@ocompa.cecum.ucn.cl.
Pilar Cereceda T., Instituto de Geografia, Universidad Católica de
Chile, Casilla 306, Correo 22, Santiago, Chile. Tel./Fax (56-2)552-6028.
Derek Webb, Coordinador del Proyecto CIID/IDRC, Universidad Católica de
Chile, Casilla 106, Correo 22, Santiago, Chile. Tel/Fax (56-2)233-7414.
Christian Gischler, Consultant, Alvaro Casanova 294-B2A, La Reina,
Casilla 206, Correo 12, Santiago, Chile. Tel. (56-2)273-1433.
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