Solar-powered desalination is a sustainable method to convert seawater or brackish water into fresh, potable water using solar energy. This process is especially useful in regions with limited freshwater resources but abundant sunlight, providing a viable alternative to traditional, energy-intensive desalination methods. Here’s how it works:
Key Components and Processes in Solar-Powered Desalination
Solar Energy Collection The system starts with collecting solar energy, which can be harnessed through:
Solar Photovoltaic (PV) Panels: Convert sunlight directly into electricity, which powers a desalination unit (often using reverse osmosis).
Solar Thermal Collectors: Use sunlight to generate heat, which is then used in thermal desalination methods like multi-effect distillation or solar stills.
Desalination Methods Using Solar Power Several desalination techniques can be driven by solar energy, each suitable for different applications and scales:
Solar-Powered Reverse Osmosis (RO): Solar PV panels generate electricity that powers high-pressure pumps to push seawater through a semi-permeable membrane. The membrane filters out salts and impurities, leaving fresh water on one side and a concentrated brine on the other.
Solar Distillation: Also known as solar stills, this method mimics the natural water cycle. In a solar still, seawater is heated by solar energy, causing it to evaporate. The vapor rises, leaving salts and impurities behind, and condenses on a cooler surface, where it’s collected as fresh water.
Multi-Effect Distillation (MED) with Solar Thermal Energy: Uses solar heat to evaporate seawater in multiple stages (effects). The heat generated in one stage powers the next, maximizing energy efficiency. MED works well in large-scale plants combined with concentrated solar power (CSP).
Concentration of Salts and Brine Disposal Most desalination processes produce brine (a concentrated salt byproduct). Responsible disposal or brine management is essential to reduce environmental impacts. Some systems integrate brine management solutions or minimize brine by further utilizing it in salt extraction or other applications.
Benefits of Solar-Powered Desalination
Sustainability: Solar energy is renewable and clean, reducing greenhouse gas emissions compared to fossil-fuel-powered desalination.
Energy Efficiency: Solar desalination is cost-effective over the long term, especially in sunny regions where it can operate without ongoing fuel costs.
Scalability: Solar-powered desalination can be implemented on a small scale for rural and remote communities or expanded to larger systems for urban needs.
Applications and Challenges
Applications include remote or arid coastal areas, island communities, and disaster relief situations where conventional energy sources are limited. The primary challenges involve high initial setup costs, dependence on sunlight availability, and potential brine disposal impacts on marine ecosystems.
Solar-powered desalination is an evolving technology with promising advancements, offering a sustainable solution to the growing global water scarcity issue.
Project
Proposal: Sustainable Reverse Osmosis Water Purification System for Small
Islands in the Maldives
Project
Title:
Sustainable Water Purification for
Small Islands in the Maldives Using Renewable Tidal and Solar Energy
Project
Overview:
The project aims to provide small
islands in the Maldives (with populations under 6,000) with a sustainable and
reliable source of potable water through a reverse osmosis (RO) water
purification system powered by renewable energy sources. These systems will harness
tidal and solar energy, creating a resilient, environmentally friendly solution
to water scarcity and addressing the region's vulnerability to climate change.
Project
Objectives:
Ensure Access to Safe Drinking Water: Install RO desalination systems to convert seawater
into potable water, meeting the daily water needs of local populations.
Harness Renewable Energy: Use a hybrid system of tidal wave energy and solar
power to operate the RO plants sustainably, reducing reliance on fossil
fuels.
Promote Environmental Sustainability: Minimize environmental impacts by utilizing clean,
renewable energy, contributing to the Maldives' climate change mitigation
goals.
Create a Scalable Model: Develop a replicable model for water purification
that can be expanded to other islands across the Maldives.
Target
Population:
Small islands in the Maldives with
populations under 6,000 people, with a focus on islands with water scarcity
issues or those relying heavily on rainwater or expensive imports of bottled
water.
Project
Components:
Water Purification Technology:
Reverse Osmosis (RO) System: Desalination plants will be installed to purify
seawater and remove salts and impurities to produce safe drinking water.
The capacity will be designed based on the population size and water
demand, approximately 30-50 liters per person per day.
Energy Supply:
Tidal Energy:
Small-scale tidal turbines will be installed to harness the natural ebb
and flow of tidal currents, generating electricity to power the RO plant.
Solar Energy:
Solar photovoltaic (PV) panels will be installed to supplement energy
needs, especially during daylight hours, ensuring continuous operation.
Battery storage systems will store excess energy for use during low
energy production times.
Hybrid Integration:
A smart grid system will integrate both energy sources, automatically
switching between tidal and solar energy depending on availability.
Infrastructure:
Water Storage Tanks:
Large tanks will be constructed to store treated water, ensuring a steady
supply even during maintenance or power outages.
Distribution Network:
A local water distribution system will deliver clean water to households
and communal water stations.
Capacity Building and Maintenance:
Training for Local Operators: Technical training programs will be provided to
local operators to manage and maintain the RO system and the energy
generation units.
Community Engagement:
Awareness programs will be conducted to educate the local community on
water conservation, system maintenance, and the benefits of renewable
energy.
Renewable
Energy Feasibility:
Tidal Energy:
The Maldives is well-positioned to exploit tidal energy due to its oceanic
location and predictable tidal patterns. Low-impact turbines will be
designed to minimize environmental disruption.
Solar Energy:
With abundant sunshine throughout the year, solar PV systems are highly
viable for consistent energy production. Solar power complements tidal
energy, especially during low tidal activity.
Estimated
Timeline:
Phase 1: Feasibility Studies and Site Selection (3-6 months)
Conduct detailed assessments of water needs, tidal and
solar potential, and environmental impact on each island.
Phase 2: System Design and Procurement (4-6 months)
Design the RO system and energy components, procure
equipment, and prepare construction materials.
Phase 3: Construction and Installation (6-9 months)
Build the RO plants, install solar PV systems, tidal
turbines, storage tanks, and distribution systems.
Phase 4: Testing and Commissioning (2-3 months)
Test the system for efficiency, address any
operational issues, and train local staff.
Phase 5: Operation and Monitoring (Ongoing)
Operate the system, monitor energy efficiency, and
ensure water quality standards are met.
Estimated
Budget:
Total Estimated Budget: $2,500,000 - $4,000,000 (depending on island size and
specific energy requirements)
Key
Cost Breakdown:
Reverse Osmosis System: $500,000 - $1,000,000
Solar Power System (PV Panels + Batteries): $800,000 -
$1,200,000
Tidal Energy System: $700,000 - $1,000,000
Installation, Infrastructure, and Distribution
Network: $300,000 - $500,000
Training and Capacity Building: $200,000 - $300,000
Sustainability
and Impact:
Environmental Benefits: By using tidal and solar energy, the project will
reduce CO₂ emissions and dependence on diesel-powered generators.
Economic Benefits:
Lower long-term operational costs as renewable energy will reduce the need
for fuel imports. The system will provide consistent water access, decreasing
dependency on costly bottled water imports.
Social Impact:
Clean water availability will improve public health, reduce waterborne
diseases, and improve overall quality of life for island communities.
Potential
Funding Sources:
Government of the Maldives: National initiatives for water security and renewable
energy.
International Aid Organizations: Such as the World Bank, Asian Development Bank (ADB),
or Green Climate Fund.
Private Investors/Corporate Social Responsibility (CSR): Partnerships with renewable energy companies and
impact investors.
Grants and Development Agencies: From entities focused on climate resilience, such as
the UNDP and other NGOs.
Conclusion:
This project offers a sustainable,
scalable solution to water scarcity in the Maldives' small island communities.
By integrating tidal and solar energy into a reverse osmosis system, the
project addresses both water security and environmental sustainability, making
it a model for similar island nations facing climate challenges.
Source: https://water.usgs.gov/edu/pesticidesgw.html Pesticides are chemicals used to kill or control pests such as insects, weeds, fungus, bacteria, rodents, fish or any other type of organism that poses a problem. Pesticides are most often applied to farmland, gardens and lawns. Pesticides are also applied to water bodies (for example, rivers, canals or lakes) to control pests such as mosquitoes, weeds or invasive fish species.
Pesticides have the potential to contaminate drinking water supplies in both agricultural and urban settings. Under the Safe Drinking Water Act (1974), the U.S. EPA and other federal agencies monitor and regulate drinking water supplies. Many contaminants of drinking water occur at very low concentrations. Whether the contaminants pose health risk depends on how toxic the pesticides are, how much is in the water, and how much exposure occurs on a daily basis.
Pesticide contamination of drinking water is very common, especially in agricultural areas. Accidental or illegal spilling or dumping of pesticides can lead to contamination of drinking water, and even proper application of pesticides can lead to contamination of drinking water through leaching into groundwater or runoff into surface water bodies. Concentrations of pesticides tend to be highest in streams adjacent to agricultural areas.
Pesticides can sometimes first appear in drinking water wells decades after the pesticides were applied or spilled, depending on the chemical properties of the pesticide and the geologic conditions.”
In a study published in 2006 by the U.S. Geological Survey, atrazine (a pesticide banned in the European Union but still widely used in the U.S.) was found 90% of the time in streams in agricultural areas and 70% of the time in streams in urban areas, and it was also frequently detected in groundwater [1]. Because groundwater can move very slowly, pesticides can sometimes first appear in drinking water wells decades after the pesticides were applied or spilt, depending on the chemical properties of the pesticide and the geologic conditions. Because of this, even pesticides that are no longer in use can still contaminate water supplies.
PESTICIDE FACTS
Pesticides are potentially toxic to humans and can have both acute and chronic health effects, depending on the quantity and the ways in which a person is exposed.
Some of the older, cheaper pesticides can remain in the soil and water for years. They have been banned in developed countries for agricultural use but are still used in many developing countries.
There are more than 1,000 pesticides used around the world to ensure food is not damaged or destroyed by pests. Each pesticide has different properties and toxicological effects (and the toxicological effects of multiple pesticides can be greater than the sum of their parts).
When using pesticides that may contaminate water supplies, the risk of contamination may be minimized by 1) using short-lived pesticides that biodegrade easily, 2) using pesticides that tend to stick to soil and not move easily, and 3) avoiding disposal of pesticides where they may contaminate water resources, such as near a well or spring or down a storm sewer.
Interesting fact: The pesticide DDT is so persistent in the environment that it is still found in fish more than 40 years after it was banned in the U.S. in 1972.
Health Effects Associated with Pesticides in Drinking Water
There are many different pesticides, each with a different level of toxicity. The health risks associated with pesticides in drinking water are related to how toxic the compound is, how much is in the water, and how much exposure a human gets to the contaminated water. In large doses, which could come from direct exposure to pesticides, they can cause health problems such as cancer, organ damage, reproductive effects, birth defects, or nervous system damage. In drinking water, concentrations are usually low, but some pesticides are toxic even at very low levels.
“High levels of nitrate from chemical fertilizers in the water supply may indicate possible contamination by pesticides.”
Many pesticides are not regulated as contaminants in drinking water, but the U.S. Environmental Protection Agency (USEPA) has set maximum contaminant levels (MCLs) for several pesticides. A MCL is the maximum concentration of a contaminant that is legally allowed in public drinking water systems under the Safe Drinking Water Act. The long-term health risks associated with concentrations above the MCL are considered to be unacceptable. The MCLs for individual pesticides are based on their toxicity, with more toxic pesticides having lower MCLs. Their values range from 0.00005 to 4 milligrams per liter (mg/L or parts per million). For example, the MCL for atrazine, which is the most commonly detected pesticide in drinking water in the U.S., is 0.003 milligrams per litre.
High levels of nitrate from chemical fertilizers in the water supply may indicate possible contamination by pesticides. Because these tests are the expensive and only test for specific compounds, it is best to only test for pesticides that you think may be contaminating your water.
How to Treat Drinking Water for Pesticides
Pesticides can be removed from drinking water by reverse osmosis or granulated activated carbon (GAC) filters. Reverse osmosis works by forcing the water through a membrane that allows water molecules to pass through but blocks larger ions or molecules, such as ones associated with iron, lead or pesticides. In homes, reverse osmosis systems are usually small systems (called point-of-use systems) located near the kitchen sink.
Reverse osmosis systems are cost-effective, but low-end systems can only produce a few gallons of treated water each day. Significant recent improvements in membrane elements allow for more expensive systems to produce 100 or more gallon per day. The taste of the water may be affected by the removal of the minerals.
Granulated activated carbon (GAC) filters are relatively inexpensive and are simple to use. They remove pesticides and other contaminants that stick to small particles of material such as coal or charcoal. These filters can take the form of point-of-use systems or pitchers manually filled with water. GAC filters must be replaced or regenerated periodically to maintain their effectiveness.
FACTORS AFFECTING PESTICIDE POLLUTION OF WATER
Drainage: Farmland is often well-drained and natural drainage is often enhanced by land drains. Water from excessive rainfall and irrigation cannot always be held within the soil structure. Therefore, pesticides and residues (also nitrates and phosphates) can be quickly transported to contaminate groundwater and freshwater supplies over a large geographical area.
The pesticide: Individual pesticides have unique properties, and many variable factors (including those below) determine the specific risk in terms of water pollution.
active ingredient(s) in the pesticide formulation
contaminants that exist as impurities in the active ingredient(s)
additives that are mixed with the active ingredient(s) (wetting agents, diluents or solvents, extenders, adhesives, buffers, preservatives, and emulsifiers)
degradate that is formed during chemical, microbial, or photochemical degradation of the active ingredient
Pesticide half-life: The more stable the pesticide, the longer it takes to break down. This can be measured in terms of its half-life, the longer it takes to break down, the higher its persistence. The half-life is unique to individual products but variable depending on specific environmental and application factors.
An active substance is any chemical, plant extract, pheromone, or microorganism (including viruses), that has an action against ‘pests’ or on plants, or parts of plants or plant products.
Mobility in soil: All pesticides have unique mobility properties, both vertically and horizontally through the soil structure. Residual herbicides applied directly to the soil are designed to bond to the soil structure.
Solubility in water: Many pesticides are soluble in the water out of necessity so that they can be applied with water and be absorbed by the target. The higher the solubility of the pesticide, the higher the risk of leaching. Residual herbicides are generally of lower solubility to aid soil binding but their persistence in the soil can cause other problems.
Microbial activity: Pesticides in the soil are primarily broken down by microbial activity. The greater the microbial activity, the faster the degradation. Loss of pesticide residues can also occur by evaporation and photodecomposition.
Soil temperature: Soil microbial activity and pesticide breakdown is largely linked to soil temperature.
Application rate: The more pesticide that is applied, the longer significant concentrations remain.
Irrigation Management: Irrigation increases the chance that pesticides will migrate to ground water and surface water. Irrigating saturated soils or irrigating at a rate that exceeds the infiltration rate of soil promotes runoff that can carry pesticides with it. Irrigation that promotes the frequent downward movement of water beyond the root zone of plants also promotes the leaching of substances including pesticides to ground water. This is of particular concern in areas where frequent irrigation is necessary because of coarse-textured soils. Proper irrigation management is critical to minimize the risk of pesticides infiltrating ground water.
How to Prevent Water Contamination
There are a variety of common management practices that provide multiple benefits.
Crop and Soil Management Strategies
Crop rotation keeps pests off-balance, especially those that prefer a particular crop with its associated cultural practices.
Cover crops provide crop residues, which enhance soil organic matter.
Careful crop variety selection ensures that the crop is well-adapted to local conditions and grower needs,
and often provides valuable disease or insect resistance, or tolerance to pesticides that will be used to control pests.
Proper seedbed preparation and planting allows the crop to emerge quickly, potentially reducing early-season disease and insect damage and weed competition.
Proper drainage and irrigation management promotes optimum plant growth, inhibits various root diseases, and reduces runoff.
Proper equipment use avoids soil compaction, which can slow crop growth and promote runoff.
Conservation Buffers
Conservation buffers are areas designed to intercept and trap chemicals before they reach surface water. Often native grasses are planted alone or in combination with shrubs and trees along field borders between the crop and a waterway. Buffers trap pesticides, bacteria, fertilizers, and soil sediment, reducing the quantity of potential contaminants that move off the site. Buffers are one of the best management tools a landowner can install, as they offer multiple benefits, and often require little maintenance.
Choose these sites for more information on conservation buffers:
Conservation Buffers – Design Guidelines for Buffers, Corridors, and Greenways, National Agroforestry Center, USDA
Conservation buffers can improve water quality, University Extension, Iowa State University
Use conservation buffers to make dollars and sense, University Extension, Iowa State University
Buffer Strips: Common Sense Conservation, Natural Resources Conservation Service, USDA
For more on buffers, view or download The Value of Buffers For Pesticide Stewardship and Much More
Integrated Pest Management (IPM)
An IPM program combines the best techniques to prevent pests and to keep them below economically damaging threshold levels and ensure that pesticides are used appropriately. If a pesticide is prone to reach surface or groundwater, suitable IPM tactics can reduce or eliminate the risk of surface or groundwater contamination.
The IPM program also facilitates the selection of a pesticide to be delivered precisely on target and at the proper time. Crop scouting, or monitoring, correctly identifies the pest and collects information needed so that applications are made only when needed, and only when the pest is vulnerable, allowing for a more effective pesticide application. Reducing the need for multiple applications of pesticides reduces the chance that pesticides may reach and contaminate water. Visit the PES site Integrated Pest Management.
Best Management Practices (BMPs) are conservation practices, or systems of practices, and management measures that control soil loss and reduce water quality degradation caused by nutrients, animal wastes, toxics, and sediment. BMPs can improve the environment while also improving the farmer’s bottom line.
Visit any of these web sites to learn more about best management practices to protect water resources from agricultural pesticides:
Best Management Practices for Agricultural Pesticides to Protect Water Resources, Cooperative Extension, Institute of Agriculture and Natural Resources, University of Nebraska
Water Publications from Colorado State University,
Protecting water from contamination requires planning and records. Past pest scouting or monitoring records, along with past pesticide application records, help you select the best controls. Selecting the proper pesticide for the crop, the pest, and the site is important. When a site has groundwater near the surface and the soil is permeable, then the leaching potential of the pesticide must be considered during pesticide selection.
Applicators should read the label to find warnings that tell them that the pesticide may leach. Here is an example of language to look for in the Environmental Hazards section of the label: “This product has properties and characteristics associated with chemicals detected in groundwater. The use of this chemical in areas where soils are permeable, particularly where the water table is shallow, may result in groundwater contamination.” There may also be a “Groundwater Advisory” statement on the label. Many new labels have this statement, which is a critical aid in selecting the right pesticide for the job.
Proper Pesticide Mixing and Loading Procedures
More pesticide spills occur while the pesticide is being measured and mixed than during any other part of a pesticide application. Locate the mixing/loading site away from wells, streams and lakes. Maintain a distance of at least 100 feet (check the pesticide label for more specifics) between the mixing and loading site and wellheads, ditches, streams or other water sources.
Measure, mix and load over an impervious surface, such as a concrete pad, which prevents spills from soaking into the ground. Measure the product carefully to avoid spills. Using a closed transfer system to mix and load pesticides also helps reduce the risk of spills. If you are not using a pad, move the mixing and loading steps from place to place to avoid chemical buildup from accidental splashes or spills (see Pesticide Spills).
Be prepared for spills and have a “spill kit” readily available near the mixing loading area. Never leave a tank while it is being filled, and pay constant attention during filling to prevent overfilling and spilling of the pesticide on the ground. Be disciplined and patient.
Applicators should read the label carefully to find warnings regarding mixing/loading pesticides. Here is a statement found in the Environmental Hazards section of many labels: “Most cases of groundwater contamination involving this pesticide have been associated with mixing/loading and disposal sites. Caution should be exercised when handling this product at such sites to prevent contamination of groundwater supplies. Use of closed systems for mixing or transferring this pesticide will reduce the probability of spills. Placement of the mixing/loading equipment on an impervious pad to contain spills will help prevent groundwater contamination.”
Backflow occurs when a water supply loses pressure and starts flowing backwards toward the water source. The backward flow creates a siphon that draws some of the contents of the sprayer tank back toward the water source if a pipe or hose is below the water surface in the tank. If backflow occurs, the water supply pipes, pumps, and well become contaminated by pesticides from the tank. An anti-siphon device (check valve) prevents backflow and the resulting contamination from occurring. Proper anti-siphoning techniques include the use of a reduced pressure zone (anti-siphon) device or an air gap between the filler pipe and the tank.
Proper Application Procedures
Proper application of pesticides starts with calibration. Calibrating application equipment is the only way to be sure that the proper amount of pesticide is applied. Application of excess pesticide increases the risk of contaminating water by overloading the protective mechanisms of degradation and adsorption, making them ineffective. Over application is not only risky for the environment but is a violation of label directions and the law.
Knowledge of the application site is very important for preventing water contamination. You should know where wells are located, the depth to groundwater, and where surface water is located before making an application. After identifying these features, make plans to protect them. Decide in advance where to turn the application equipment on and off. Using buffer zones and setback areas creates safety zones by keeping applications away from sensitive areas, particularly surface waters. Pesticide applications should hit the target precisely. Applications that move off-target can contribute to water contamination.
Preventing drift is another important task of the applicator. Drifting pesticide can contaminate water and cause other problems. Monitoring the weather conditions, setting the boom height as close as possible to the target, and selecting the proper nozzle type are important activities that help reduce the chance of pesticide drift contaminating surface waters.
Irrigation Management
Irrigation increases the chance that pesticides will
migrate to groundwater and surface water. Irrigating saturated soils or irrigating at a rate that exceeds the infiltration rate of soil promotes runoff that can carry pesticides with it. Irrigation that promotes the frequent downward movement of water beyond the root zone of plants also promotes the leaching of substances, including pesticides, to groundwater. This is of particular concern in areas where frequent irrigation is necessary because of coarse-textured soils. Proper irrigation management is critical to minimize the risk of pesticides moving to groundwater.
Proper Pesticide Storage
Proper storage of pesticides is also important to prevent water contamination. Locking pesticides inside a fire-resistant, spill-proof facility is an excellent way to prevent accidental pesticide spills. Proper storage is very cheap compared with the expensive consequences of accidents, spills, or fires. Be prepared for spills, and have a “spill kit” readily available inside or near the storage area.
Proper Disposal of Pesticides and Containers
Pesticide containers that have not been triple rinsed pose a risk to water resources. Contaminated containers left outside, and exposed to rain, can leak pesticides into the environment. Triple rinsing pesticide containers prior to disposal remove pesticide residues. Water collected from cleaning and rinsing application equipment should be applied to the original site of the application. Be careful not to exceed label rates. Re-using this pesticide-containing water is an environmentally responsible way to dispose of this material. Collect rinsed containers in a dry, secure, and protected area for disposal. Dispose of the rinsed containers following label directions and local ordinances. Use pesticide container recycling programs where available.
Sedimentation basins have 4 zones
1. The Inlet zone,
2. The Settling zone,
3. The Sludge zone, and
4. The Outlet zone.
Each zone should provide a smooth transition between the zone before and the zone after.
Zones in Rectangular Sedimentation Basin
Each and every zone has its own unique purpose. All zones are in a rectangular sedimentation basin.
Zones in a Circular Sedimentation Basin
In a square or circular basin (clarifier), water typically enters the basin from the center rather than from one end and flows out to outlets located around the edges of the basin. But the four zones can still be found within the clarifier the above figure. Inlet Zone
The two primary purposes of the inlet zone of a sedimentation basin are to distribute the water and to control the water’s velocity as it enters the basin. In addition, inlet devices act to prevent turbulence of the water. The incoming flow in a sedimentation basin must be evenly distributed across the width of the basin to prevent short-circuiting. Short-circuiting is a problematic circumstance in which water bypasses the normal flow path through the basin and reaches the outlet in less than the normal detention time. In addition to preventing short-circuiting, inlets control the velocity of the incoming flow. If the water velocity is greater than 0.15 m/ see, then floes in the water will break up due to agitation of the water. Breakup of floes in the sedimentation basin will make settling much less efficient.
Inlet arrangement for a rectangular basin
The inlet of rectangular basin is shown in Fig. 13.9. The stilling wall, also known as a perforated baffle wall, spans the entire basin from top to bottom and from side to side. Water leaves the inlet and enters the settling zone of the sedimentation basin by flowing through the holes evenly spaced across the stilling wall.
The second type of inlet allows water to enter the basin by first flowing through the holes evenly spaced across the bottom of the channel and then by flowing under the baffle in front of the channel.
The combination of channel and baffle serves to evenly distribute the incoming water. Settling Zone
After passing through the inlet zone, water enters the settling zone where water velocity is greatly reduced. This is where the bulk of settling occurs and this zone will make up the largest volume of the sedimentation basin. For optimal performance, the settling zone requires a slow, even flow of water. The settling zone may be simply a large area of open water. Outlet Zone
The outlet zone controls the amount of water flowing out of the sedimentation basin. Like the inlet zone, the outlet zone is designed to prevent short-circuiting of water in the basin. In addition, a good outlet will ensure that only well-settled water leaves the basin and enters the filter. The outlet in the form of overflow weir can also be used to control the water level in the basin. The best quality water is usually found at the very top of the sedimentation basin, so outlets are usually designed to skim this water off the sedimentation basin.
Outlet arrangemenfin rectangular basin
A typical outlet zone begins with a baffle in front of the effluent. This baffle prevents floating material from escaping the sedimentation basin and clogging the filters. After the baffle, the effluent structure, which usually consists of a launder, weirs, and effluent piping, is located.A typical effluent structure is shown the figure.
The primary component of the effluent structure is the effluent launder, a trough which collects the water flowing out of the sedimentation basin and directs it to the effluent piping. The sides of a launder typically have weirs attached. Weirs are walls preventing water from flowing uncontrolled into the launder. The weirs serve to skim the water evenly off the tank.
Finger weirs in rectangular basin
A weir usually has notches, holes, or slits along its length. These holes allow water to flow into the weir. The most common type is the V -shaped notch shown on the picture above which allows only the top few centimeters of water to flow out of the sedimentation basin. Conversely, the weir may have slits cut vertically along its length, an arrangement which allows for more variation of operational water level in the sedimentation basin.
Water flows over or through the holes in the weirs and into the launder. Then the launder channels the water to the outlet pipe. This pipe carries water away from the sedimentation basin and to the next step in the treatment process. The effluent structure may be located at the end of a rectangular sedimentation basin or around the edges of a circular clarifier. Alternatively, the effluent may consist of finger weirs an arrangement of launders which extend out into the settling basin as shown below. Sludge Zone
The sludge zone is found across the bottom of the sedimentation basin where the sludge is collected temporarily . Velocity in this zone should be very slow to prevent resuspension of sludge.
A drain at the bottom of the basin allows the sludge to be easily removed from the tank. The tank bottom should slope toward the drains to further facilitate sludge removal. In some plants, sludge removal is achieved continuously using automated equipment. In other plants, sludge must be removed manually.
Thanks http://www.thewatertreatments.com
Science Daily — Engineers at Brown University have developed a system that cleanly and efficiently removes trace heavy metals from water. In experiments, the researchers showed the system reduced cadmium, copper, and nickel concentrations, returning contaminated water to near or below federally acceptable standards. The technique is scalable and has viable commercial applications, especially in the environmental remediation and metal recovery fields.
An unfortunate consequence of many industrial and manufacturing practices, from textile factories to metalworking operations, is the release of heavy metals in waterways. Those metals can remain for decades, even centuries, in low but still dangerous concentrations.Results appear in the Chemical Engineering Journal.
Ridding water of trace metals "is really hard to do," said Joseph Calo, professor emeritus of engineering who maintains an active laboratory at Brown. He noted the cost, inefficiency, and time needed for such efforts. "It's like trying to put the genie back in the bottle."
That may be changing. Calo and other engineers at Brown describe a novel method that collates trace heavy metals in water by increasing their concentration so that a proven metal-removal technique can take over. In a series of experiments, the engineers report the method, called the cyclic electrowinning/precipitation (CEP) system, removes up to 99 percent of copper, cadmium, and nickel, returning the contaminated water to federally accepted standards of cleanliness. The automated CEP system is scalable as well, Calo said, so it has viable commercial potential, especially in the environmental remediation and metal recovery fields. The system's mechanics and results are described in a paper published in the Chemical Engineering Journal.
A proven technique for removing heavy metals from water is through the reduction of heavy metal ions from an electrolyte. While the technique has various names, such as electrowinning, electrolytic removal/recovery or electroextraction, it all works the same way, by using an electrical current to transform positively charged metal ions (cations) into a stable, solid state where they can be easily separated from the water and removed. The main drawback to this technique is that there must be a high-enough concentration of metal cations in the water for it to be effective; if the cation concentration is too low -- roughly less than 100 parts per million -- the current efficiency becomes too low and the current acts on more than the heavy metal ions.
Another way to remove metals is through simple chemistry. The technique involves using hydroxides and sulfides to precipitate the metal ions from the water, so they form solids. The solids, however, constitute a toxic sludge, and there is no good way to deal with it. Landfills generally won't take it, and letting it sit in settling ponds is toxic and environmentally unsound. "Nobody wants it, because it's a huge liability," Calo said.
The dilemma, then, is how to remove the metals efficiently without creating an unhealthy byproduct. Calo and his co-authors, postdoctoral researcher Pengpeng Grimshaw and George Hradil, who earned his doctorate at Brown and is now an adjunct professor, combined the two techniques to form a closed-loop system. "We said, 'Let's use the attractive features of both methods by combining them in a cyclic process,'" Calo said.
It took a few years to build and develop the system. In the paper, the authors describe how it works. The CEP system involves two main units, one to concentrate the cations and another to turn them into stable, solid-state metals and remove them. In the first stage, the metal-laden water is fed into a tank in which an acid (sulfuric acid) or base (sodium hydroxide) is added to change the water's pH, effectively separating the water molecules from the metal precipitate, which settles at the bottom. The "clear" water is siphoned off, and more contaminated water is brought in. The pH swing is applied again, first redissolving the precipitate and then reprecipitating all the metal, increasing the metal concentration each time. This process is repeated until the concentration of the metal cations in the solution has reached a point at which electrowinning can be efficiently employed.
When that point is reached, the solution is sent to a second device, called a spouted particulate electrode (SPE). This is where the electrowinning takes place, and the metal cations are chemically changed to stable metal solids so they can be easily removed. The engineers used an SPE developed by Hradil, a senior research engineer at Technic Inc., located in Cranston, R.I. The cleaner water is returned to the precipitation tank, where metal ions can be precipitated once again. Further cleaned, the supernatant water is sent to another reservoir, where additional processes may be employed to further lower the metal ion concentration levels. These processes can be repeated in an automated, cyclic fashion as many times as necessary to achieve the desired performance, such as to federal drinking water standards.
In experiments, the engineers tested the CEP system with cadmium, copper, and nickel, individually and with water containing all three metals. The results showed cadmium, copper, and nickel were lowered to 1.50, 0.23 and 0.37 parts per million (ppm), respectively -- near or below maximum contaminant levels established by the Environmental Protection Agency. The sludge is continuously formed and redissolved within the system so that none is left as an environmental contaminant.
"This approach produces very large volume reductions from the original contaminated water by electrochemical reduction of the ions to zero-valent metal on the surfaces of the cathodic particles," the authors write. "For an initial 10 ppm ion concentration of the metals considered, the volume reduction is on the order of 106."
Calo said the approach can be used for other heavy metals, such as lead, mercury, and tin. The researchers are currently testing the system with samples contaminated with heavy metals and other substances, such as sediment, to confirm its operation.
The research was funded by the National Institute of Environmental Health Sciences, a branch of the National Institutes of Health, through the Brown University Superfund Research Program.
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