There are so many ways to bring fresh water to every state.
If congress can give $5.7 trillion for Covid and PPP Loans, we can do the same to finally provide unlimited water for everyone in this country.
We need Roman type Aqueducts to move water from flooded areas to areas that don't have enough water. Someone needs to convince the Mayors of cities in Arizona, California (West Coast).
Didn't we have a dust bowl era in the early 1900's when all crops couldn't grow due to the lack for fresh water. https://drought.unl.edu/dustbowl/
Maybe every stupid realtor, and person in LAs Vegas need to boycott all the Casinos until they take their billions and make high--tech Desalination, and Solar/water extraction plants in the state. The Reservoirs' are drying up, time has run out, but our politicians and all the people and corporations in the state are in a state of denial.
Here are some of the technologies we can use today. Humans need Water, Food, and Shelter. Our congress and corporations have done a piss poor job in all the areas. They are so obsessed with money, and power they forgot why the heck they were elected in the first place.
Desalination Methods for Producing Drinking Water by
Justin K. Mechell and Bruce Lesikar
Source waters
Several factors influence the selection of source waters to feed desalination plants: the location of the
plant in relation to water sources available, the delivery destination of the treated water, the quality of
the source water, the pretreatment options available, and the ecological impacts of the concentrate discharge.
Seawater Seawater is taken into a desalination plant either from the water’s surface or from below the sea
floor. In the past, large-capacity seawater desalination plants have used surface intakes on the open
sea.
Although surface water intake can affect and be affected by organisms in the ocean, the issues related
to this method can be minimized or resolved by proper intake design, operation, and maintenance of
technologies. The technologies include passive screens, fine mesh screens, filter net barriers, and
behavioral systems. They are designed to prevent or minimize the environmental impact to the surrounding intake area and to minimize the amount of pretreatment needed before the feed water reaches the primary treatment systems.
Subsurface intakes are sometimes feasible if the geology of the intake site permits. When the water is
taken in from below the surface, the process causes less damage to marine life. However, if the geology
Desalination Methods for Producing Drinking Water
As quality fresh drinking water decrease, many communities have considered using desalina- populations increase and sources of hightion processes to provide fresh water when other
sources and treatment procedures are uneconomical
or not environmentally responsible.
Desalination is any process that removes excess salts and other minerals from water. In most desalination processes, feed water is treated and two streams of water are produced:
plant in relation to water sources available, the delivery destination of the treated water, the quality of
the source water, the pretreatment options available, and the ecological impacts of the concentrate discharge.
Seawater Seawater is taken into a desalination plant either from the water’s surface or from below the sea
floor. In the past, large-capacity seawater desalination plants have used surface intakes on the open
sea.
Although surface water intake can affect and be affected by organisms in the ocean, the issues related
to this method can be minimized or resolved by proper intake design, operation, and maintenance of
technologies. The technologies include passive screens, fine mesh screens, filter net barriers, and
behavioral systems. They are designed to prevent or minimize the environmental impact to the surrounding intake area and to minimize the amount of pretreatment needed before the feed water reaches the primary treatment systems.
Subsurface intakes are sometimes feasible if the geology of the intake site permits. When the water is
taken in from below the surface, the process causes less damage to marine life. However, if the geology
Desalination Methods for Producing Drinking Water
As quality fresh drinking water decrease, many communities have considered using desalina- populations increase and sources of hightion processes to provide fresh water when other
sources and treatment procedures are uneconomical
or not environmentally responsible.
Desalination is any process that removes excess salts and other minerals from water. In most desalination processes, feed water is treated and two streams of water are produced:
• Treated fresh water that has low concentrations of salts and minerals
• Concentrate or brine, which has salt and mineral concentrations higher than that of
the feed water The feed water for desalination processes can be seawater or brackish water. Brackish water contains more salt than does fresh water and less than salt water. It is commonly found in estuaries, which
are the lower courses of rivers where they meet the sea, and aquifers, which are stores of water underground.
An early U.S. desalination plant was built in 1961 in Freeport, Texas. It produced 1 million gallons per day (mgd) using a long vertical tube distillation (LVT) process to produce water for the City of Freeport, Texas. As technology rapidly improves, two other processes—thermal and membrane—are becoming viable options to convert saline water to drinkable fresh water.
the feed water The feed water for desalination processes can be seawater or brackish water. Brackish water contains more salt than does fresh water and less than salt water. It is commonly found in estuaries, which
are the lower courses of rivers where they meet the sea, and aquifers, which are stores of water underground.
An early U.S. desalination plant was built in 1961 in Freeport, Texas. It produced 1 million gallons per day (mgd) using a long vertical tube distillation (LVT) process to produce water for the City of Freeport, Texas. As technology rapidly improves, two other processes—thermal and membrane—are becoming viable options to convert saline water to drinkable fresh water.
*Justin K. Mechell and Bruce Lesikar
* Extension Program Specialist, and Professor and Extension
Agricultural Engineer, The Texas A&M University System
E-249
04-10
2
of the site is unfavorable, a subsurface intake can harm nearby freshwater aquifers. Methods of subsurface intake include vertical beach wells, radial wells, and infiltration galleries. A major advantage to using a subsurface intake
is that the water is filtered naturally as it passes through the soil profile to the intake. This filtration
improves the quality of feed water, decreasing the need for pretreatment.
Brackish water
Brackish water is commonly used as a source for desalination facilities. It is usually pulled from
local estuaries or brackish inland water wells. Because it typically has less salt and a lower concentration of suspended solids than does seawater, brackish water needs less pretreatment, which decreases overall production costs. However, a disadvantage is that disposing of the brine from an inland desalination location increases the cost and can raise environmental concerns.
Desalination technologies
Two distillation technologies are used primarily
around the world for desalination: thermal distillation and membrane distillation.
Thermal distillation technologies are widely
used in the Middle East, primarily because the region’s petroleum reserves keep energy costs low. The
three major, large-scale thermal processes are multistage flash distillation (MSF), multi-effect distillation (MED), and vapor compression distillation
(VCD). Another thermal method, solar distillation,
is typically used for very small production rates.
Membrane distillation technologies are primarily used in the United States. These systems treat
the feed water by using a pressure gradient to forcefeed the water through membranes. The three major
membrane processes are electrodialysis (ED), electrodialysis reversal (EDR), and reverse osmosis
(RO).
Thermal technologies
Multi-stage flash distillation
Multi-stage flash distillation is a process that
sends the saline feed water through multiple chambers (Fig. 1). In these chambers, the water is heated
and compressed to a high temperature and high pressure. As the water progressively passes through
the chambers, the pressure is reduced, causing the water to rapidly boil. The vapor, which is fresh
water, is produced in each chamber from boiling and then is condensed and collected.
Multi-effect distillation
Multi-effect distillation employs the same principals as the multi-stage flash distillation process except that instead of using multiple chambers of a single vessel, MED uses successive vessels (Fig. 2).
The water vapor that is formed when the water boils is condensed and collected. The multiple vessels
make the MED process more efficient.
The water vapor that is formed when the water boils is condensed and collected. The multiple vessels
make the MED process more efficient.
Figure 1. Example of a multi-stage flash distillation (MSF) process (Source: Buros, 1990).
Vapor compression distillation
Vapor compression distillation can function independently or be used in combination with another thermal distillation process. VCD uses heatfrom the compression of vapor to evaporate the feed
water (Fig. 3). VCD units are commonly used to
produce fresh water for small- to medium-scale purposes such as resorts, industries, and petroleum
drilling sites.
Solar distillation
Solar desalination is generally used for small scale operations (Fig. 4). Although the designs ofsolar distillation units vary greatly, the basic principals are the same. The sun provides the energy to
evaporate the saline water. The water vapor formed from the evaporation process then condenses on
the clear glass or plastic covering and is collected as fresh water in the condensate trough. The covering
is used to both transmit radiant energy and allow water vapor to condense on its interior surface. The
salt and un-evaporated water left behind in the still basin forms the brine solution that must be discarded appropriately. This practice is often used in arid regions
where safe fresh water is not available. Solar distil
Figure 2. Example of a multi-effect distillation (MED) process (Source: Buros, 1990).
Figure 3. Example of a vapor compression distillation (VCD) process (Source: Buros, 1990).
Distillation units produce differing amounts of fresh water, according to their design and geographic location. Recent tests on four solar still designs by the Texas AgriLife Extension Service in College Station, Texas, have shown that a solar still with as little as 7.5 square feet of surface area can produce enough water for a person to survive.
Membrane technologies
A membrane desalination process
uses a physical barrier—the membrane—and a driving force. The driving
force can be an electrical potential, which is used in electrodialysis or electrodialysis reversal, or a pressure gradient, which is used in reverse osmosis. Membrane technologies often require that the water undergo chemical
and physical pretreatment to limit blockage by debris and scale formation on the membrane surfaces. Table 1
(page 5) details the basic characteristics of membrane processes.
Electrodialysis
and electrodialysis reversal
The membranes used in electrodialysis and electrodialysis reversal are
built to allow passage of either positively or negatively
charged ions, but not both. Ions are atoms or molecules that have a net positive or net negative charge. Four
common ionic molecules in saline water are sodium, chloride, calcium, and carbonate.
Electrodialysis and electrodialysis reversal use the driving force of an electrical potential to attract
Figure 4. Example of a solar still desalination process desalination process (Source: Buros,1990). and move different cations |
anions (negatively charged ions) through a permeable membrane, producing fresh water on the other
side (Fig. 5).
The cations are attracted to the negative electrode, and the anions are attracted to the positive
electrode. When the membranes are placed so that
Figure 5. Example of an electrodialysis process showing the basic
movements of ions in the treatment process (Source: Buros, 1990).
| Membrane process | Membrane driving force | Typical separation mechanism | Operating structure (pore size) | Typical operating range, (µm) | Permeate description | Typical constituents removed |
| Microfiltration | Hydrostatic pressure difference or vacuum in open vessels | Sieve | Macropores (> 50 nm) | 0.08–2.0 | Water + dissolved solutes | TSS, turbidity, protozoan oocysts and cysts, some bacteria and viruses |
| Ultrafiltration | Hydrostatic pressure difference | Sieve | Mesopores (2–50 nm) | 0.005–0.2 | Water + small molecules | Macromolecules, colloids, most bacteria, some viruses, proteins |
| Nanofiltration | Hydrostatic pressure difference | Sieve + solution/ diffusion + exclusion | Micropores (< 2 nm) | 0.001–0.01 | Water + very small molecules, ionic solutes | Small molecules, some hardness, viruses |
| Reverse osmosis | Hydrostatic pressure difference | Solution/ diffusion + exclusion | Dense (< 2 nm) | 0.0001– 0.001 | Water + very small molecules, ionic solutes | Very small molecules, color, hardness, sulfates, nitrate, sodium, other ions |
| Dialysis | Concentration difference | Diffusion | Mesopores (2–50 nm) | -- | Water + small molecules | Macromolecules, colloids, most bacteria, some viruses, proteins |
| Electrodialysis | Electromotive force | Ion exchange with selective membranes | Micropores (< 2 nm) | -- | Water + ionic solutes | Ionized salt ions |
some allow only cations to pass and others allow
only anions to pass, the process can effectively remove the constituents from the feed water that make
it a saline solution.
The electrodialysis reversal process functions as
does the electrodialysis process; the only difference
is that in the reverse process, the polarity, or charge,
of the electrodes is switched periodically. This reversal in flow of ions helps remove scaling and other
debris from the membranes, which extends the system’s operating life.
Reverse osmosis
Reverse osmosis uses a pressure gradient as the driving force to move high-pressure saline feed
water through a membrane that prevents the salt ions from passing (Fig. 6).
There are several membrane treatment processes, including reverse osmosis, nanofiltration,
ultrafiltration, and microfiltration. The pore sizes of the membranes differ according to the type of
process
(Fig. 7).
Because the RO membrane has such small pores, the feed water must be pretreated adequately before being
passed through it. The water can be pretreated chemically, to prevent biological growth and scaling, and physically,
to remove any suspended solids. The high-pressure feed water flows through the individual membrane elements. The spiral RO membrane element is constructed in a concentric spiral pattern that allows alternating layers of feed water and brine spacing, RO membrane, and a porous product water carrier (Fig. 8). The porous product water carrier allows the fresh water to flow into the center of the membrane element to be collected in the product water tube. To enable each pressure vessel to treat more water, the individual membrane elements are connected in series (Fig. 9). After the water passes through the membrane elements within the pressure vessels, it goes through post treatment. Post treatment prepares the water for distribution to the public.
Concentrate management options
Both thermal and membrane desalination processes produce a stream of brine water that has a
high concentration of salt and other minerals or chemicals that were either removed during the desalination process or added to help pretreat the feed water. For all of the processes, the brine must be disposed of in an economical and environmentally friendly way.
Because the RO membrane has such small pores, the feed water must be pretreated adequately before being
passed through it. The water can be pretreated chemically, to prevent biological growth and scaling, and physically,
to remove any suspended solids. The high-pressure feed water flows through the individual membrane elements. The spiral RO membrane element is constructed in a concentric spiral pattern that allows alternating layers of feed water and brine spacing, RO membrane, and a porous product water carrier (Fig. 8). The porous product water carrier allows the fresh water to flow into the center of the membrane element to be collected in the product water tube. To enable each pressure vessel to treat more water, the individual membrane elements are connected in series (Fig. 9). After the water passes through the membrane elements within the pressure vessels, it goes through post treatment. Post treatment prepares the water for distribution to the public.
Concentrate management options
Both thermal and membrane desalination processes produce a stream of brine water that has a
high concentration of salt and other minerals or chemicals that were either removed during the desalination process or added to help pretreat the feed water. For all of the processes, the brine must be disposed of in an economical and environmentally friendly way.
Figure 6. Basic components of a membrane treatment process.
Figure 7. Range of nominal membrane pore sizes for reverse osmosis (RO),
nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) (Source: Metcalf
and Eddy, 2003).
saline aquifer, and evaporation. Each option has advantages and disadvantages. In all cases, the brine
water should have a minimal impact on the surrounding water bodies or aquifers. Specific considerations for the water quality include saline concentration, water temperature, dissolved oxygen concentrations, and any constituents added as pretreatment.
Summary
As high-quality freshwater resources decrease, more communities will consider desalination of
brackish and salt water to produce drinking water. All desalination technologies have advantages and
disadvantages based on site-specific limitations and requirements. Small-scale desalination of brackish
water using solar stills is a promising method in remote locations where good-quality water for drinking and cooking is unavailable. For more widespread
Figure 8. Cutaway view of a spiral reverse osmosis membrane element (Source: Buros, 1990).
Figure 9. Cross section of a pressure vessel with three membrane elements (Source: Buros, 1990).
implementation, desalination processes need technological improvements and increased energy
efficiency.
implementation, desalination processes need technological improvements and increased energy
efficiency.
References
Buros, O. K., The ABC’s of Desalting,
International Desalination Association.
Topsfield, Massachusetts. 1990.
Krishna, Hari J., Introduction to Desalination
Technologies, Texas Water Development
Board. 2004.
Metcalf and Eddy, Wastewater Engineering:
Treatment and Reuse. McGraw-Hill, Inc.,
New York. 2003.
Pankratz, Tom, Desalination Technology
Trends, CH2M Hill, Inc. 2004.
This material is based on work supported by the
National Institute of Food and Agriculture, U.S. Department of Agriculture,
under Agreement No. 2009-34461-19772 and Agreement No. 2009-45049-05492.
