Graphic of Solution

Solutions Document

Subsurface Intakes

            Subsurface intakes’ water is naturally pretreated by passing through the sandy ocean floor. This water traveling through the bottom sediment contains low levels of solids, silt, and contaminants that are filtered by the sediment. However, because of the location, subsurface, these intakes are not only invasive in the marine environment because of the requirement that the bottom sediment be dredged, but also pose a large threat of entrainment. Therefore, subsurface intakes should be used in areas with a low risk of entrainment and are a solution to areas with a high level of impingement. Some methods of intake offer a simple solution to this problem, depending on the size of the treatment plant.

Vertical and Horizontal Wells

            Vertical wells can be implemented to supply water for small desalination plants of 1 million gallons per day or less. For larger plants, horizontal wells that have a higher capacity can be used. Radial Ranney wells of this type have intake pipes radiating out of a center point to intake maximum amounts of water. The wells also implement directionally drilled collectors that fan out under the seabed. The method of using wells can effectively alleviate the risk of impingement and lower the effects subsurface intakes have on marine organisms.

Offshore Intakes

            More economically feasible and less environmentally invasive than subsurface intakes are offshore intakes, which contain an inlet structure, placed underwater offshore, connected to a submerged pipe, which extends to the onshore concrete structure. While a more economically savvy than subsurface intakes, offshore intakes have a much greater risk for entrapment and impingement. However, several solutions to these problems are plausible.

Passive Wedge-Wire Screens

            Passive wedge-wire screens minimize impingement and entrainment because of their unique shape and eliminate the need for coarse and fine screens on the onshore concrete structure. The wedge-wire screens use cylindrical screens with trapezoidal shaped slots with openings from 0.5 mm to 10 mm, following data that states that the openings should be 3/8 inch or less to prevent entrapment of adult and juvenile fish. The screens also form low flow-through velocities to minimize impingement and entrainment. In addition, passive wedge-wire screens can be placed in locations where high natural cross flow in the current exists; the natural flow of water will prevent aquatic life from being impinged on the screen.

Active Traveling Screens

            To reduce the intake force on the surrounding organisms, active traveling screens can be implemented. They are placed after course bar screens, and the screens’ segments move in a rotational pattern. This rotating motion aids in preventing the impingement of fish by creating a cross flow that lessens the pull on the organisms around the area of intake.

Collocated Intakes

            In situations where desalination plants are located near power plants, collocated intakes can be used, reducing the number of intake valves needed for both plant. Because existing power plants require water intake for cooling purposes, new desalination plants can connect to the discharge water from these plants to use in the treatment process. This allows two plants to use one intake valve, therefore minimizing the amount of entrapment and impingement.

Graphics of Causes

Causes Document

Impingement

            Many shortcomings are evident in the large-scale process of converting seawater into fresh, clean water. Specifically, a detrimental outcome of the process is that marine organisms can be killed during the process. Through one cause, impingement, fish get stuck to the intake screen due to a high intake velocity. Impingement affects large aquatic and benthic organisms that are large enough to be caught by the intake screens, such as adult fish, crabs, and marine birds. Surface intake valves often have 150 mm outer layer bar screens followed by an inner fine screen with openings ranging from 1 mm to 20 mm. Although the majority of fish are prevented from entering and are removed by the screening and downstream filtration, many can get trapped against these screens due to the speed of the water being pulled inward.

Entrainment

            Another cause of harm to marine organisms is entrainment, through which organisms that are smaller than the screen are drawn into the intake, and end up going through the treatment process. This inevitably results in the organisms’ deaths. Entrainment affects smaller aquatic and benthic organisms that are not removed by the finer screens. When treatment processes utilize subsurface intake valves and intake wells, the water is filtered by ocean sediments above the intake, and organisms living in bottom sediment can be affected.

Entrapment

            Organisms can also be harmed during entrapment. Certain intake valves have an offshore pumping station that is connected to an onshore intake valve. The intake water is pumped from offshore stations through conveyance pipelines. If an organism travels through the pipeline to the onshore intake valve, it can be entrained into or impinged on the onshore intake valve’s retention screen.

Influences

            Ultimately, three factors largely influence whether or not impingement and entrainment will occur: intake velocity, screen opening sizes, and intake flow. If the speed of the intake is too fast, organisms will become caught against the screens meant to filter them out. Depending on the size of the screens, especially the finer ones used in the process, organisms may be able to pass through and killed during the treatment process. Finally, the larger the amount of water volume collected continuously, the greater the chance is that organisms will be negatively affected by the water treatment process.

Research Document

 Causes

·       Background

o   Impingement

§  Definition: “Fish get stuck to intake screen due to high intake velocity”

§  Organisms get caught through screens and are trapped

§  Usually involves large aquatic and benthic organisms that are large enough to be caught by intake screens i.e. adult fish, crabs etc.

o   Entrainment

§  Definition: “Organisms that are smaller than the screen are drawn into the intake”

§  Organisms go through treatment process

§  Involves aquatic and benthic organisms that are too small to be caught by intake screens.

o   Entrapment

§  Certain intake valves have an offshore pumping station that is connected to an onshore intake valve. The onshore intake valve has the retention screen, and intake water is pumped from the offshore stations through conveyance pipelines

§  Describes incidents where organisms are trapped in an offshore intake valve and cannot fight the current and swim out.

§  If organism travels through pipeline to the onshore intake valve it can be then entrained or impinged

·       Causes of Impingement and Entrainment

o   Varies site to site, different methods of intake.

o   Surface intake (Impingement)

§  Openings on intake valve can range from outer layer bar screens containing 150mm followed by inner fine screens with openings from 1mm-20mm.

§  Prevent majority of fish population from entering

§  Coarse outer screens are stationary, inner screens can be rotating.

§  Most organisms removed by screening and downstream filtration.

o   Subsurface intake valves and intake wells

§  Water filtered by ocean sediments above intake.

§  Sediment barrier between organisms and intake valve

§  Organisms living in bottom sediment can be effected (Entrainment)

o   Factors that influence Impingement and Entrainment

§  High intake velocity – Speed of water entering intake valve

§  Large screen openings - How fine pre-intake screens are

§  High intake flow – Amount of water volume collected

Solutions

·       Subsurface Intakes

o   Overview

§  Intake water is naturally pretreated through passing through sandy ocean floor

§  Water passing through bottom sentiments contains low levels of solids, silt, and contaminants

§  Bottom sentiments filter water before reaching intake

§  Unknown whether organisms in bottom sentiment can be entrapped

§  Subsurface intakes offer a low yield, low intake flow, low debris and entrapment possibility

§  Invasive installment, requires bottom sentiment to be dredged where the intake valve will be placed

o   Solutions

§  Vertical wells

·       Can supply water for small desalination plants (1 MGD or less)

§  Horizontal wells

·       Higher capacity than vertical wells

·       Radial Ranney-type wells have intakes pipes radiating out of a center point

·       Directionally drilled collectors (HDD wells) fan out under the seabed

·       Off-shore intakes

o   Overview

§  Contain inlet structure, submerged pipe, onshore concrete structure

§  Inlet structure placed underwater offshore and is connected to the onshore concrete structure through pipe.

§  Passive screens are stationary while active screens are rotating

§  Greater risk for entrapment and impingement, however are more economically feasible and less invasive to the environment

o   Intake system solutions

§  Passive wedge-wire screens can be used

·        They eliminate the need for coarse and fine screens on the onshore concrete structure

·       Use cylindrical screens with trapezoidal shaped slots

·       Openings from .5 to 10mm

·       Form low through screen flow velocities that minimizes impingement and entrainment

·       Also can be placed in locations with high natural cross flow in the current exists.

·       High cross flow prevents organism to be impinged on intake

·       Natural flow of the water prevents aquatic life from being impinged

§  Active traveling screens can be used

·       Placed after course bar screens

·       Screen segments move in rotational pattern 

·       Rotating motion prevents impingement of fish

·       Creates cross flow which reduces the intake force on surrounding fish

§  Collocated Intakes

·       For desalination plants located near power plants

·       Existing power plants require water intake for cooling purposes

·       New Desalination plants can connect to the discharge water from these plants for use as drinking water

·       Minimizes entrapment and impingement by using one intake valve rather than two intake valves

·       Additional information

o   Most impingement and entrainment occurs in the Littoral Zone

o   US EPA advises extending intakes 410 feet out of the littoral zone, 1100 feet from shore

o   US EPA determines that low through-screen velocities should be minimized and lower or equal to .5 feet per second to meet impingement mortality performance standards

o   Coarse bar screen openings should be no larger than 9inches

o   Small fine screen openings should be 3/8 inch or less to prevent entrapment of adult and juvenile fish

Citations:

Brush B., Yager E., Rich F. (May 2011), Con Edison East River Generating Station Aquatic Life Preservation [PowerPoint Slides]. Retrieved April 10, 2012.

WaterReuse Association (March 2011), Desalination Plant Intakes: Impingement and Entrainment, Impacts and Solutions. Retrieved on April 1, 2012 from http://www.watereuse.org/sites/default/files/u8/IE_White_Paper.pdf.

WaterReuse Association (June 2011), Overview of Desalination Plant Intake Alternatives. Retrieved on April 5, 2012 from http://www.watereuse.org/sites/default/files/u8/Intake_White_Paper.pdf

Original Research - Eutrophication

Two major marine related environmental issues are Eutrophication and Algal Blooms. Both of these issues negatively affect water bodies around the world, destroying ecosystems and harming humans. Eutrophication is the addition and overabundance of nutrients to a body of water. Algal Blooms are a population explosion of algae in a body of water. Both of these occurrences are major environmental problems in the world today

The main causes of eutrophication are runoff and inadequately treated wastewater. Runoff rich in fertilizer pollutants is a major cause of eutrophication. The major components of fertilizer, nitrates and phosphates, are designed to stimulate plant growth in farms and lawns. These chemicals, if introduced to a water system will also encourage algae growth. Runoff from agricultural and residential sources is the main contributing factors to the introduction of nutrients into the water column. A freshly fertilized farm field or house lawn will have some of its fertilizer washed away during a rain storm. The rainwater carries this fertilizer from the original source to a water source. This introduces the nutrients to the aquatic system, causing eutrophication. Another cause of eutrophication is the release of insufficiently treated waste water into a water system. The discharge of sewage, rich in nutrients, to the water system can cause eutrophication. 

The main cause of an Algal Bloom is Eutrophication. As stated before, Eutrophication is the overabundance of nutrients in the water column. Algae and other plankton use these nutrients to thrive, grow, and reproduce, causing rapid population growth. This population expansion is called an “Algal Bloom.” Algal Blooms are also known as “red tides.” Algal blooms have two major devastating environmental effects. After the nutrients in a water body are depleted by the algae, the algae can no longer survive. This causes a massive decline in the algae population because it can no longer be sustained. In the process of dying, the algae exhaust the dissolved oxygen in the water. Eventually, the dissolved oxygen in the water declines to such a level, that fish and other aquatic species can no longer survive in the ecosystems. This depletion of oxygen is known as a “dead zone.” A Harmful Algal Bloom is an algal bloom where the species of algae that has undergone a population expansion either is toxic, or unsafe to other organisms, including humans. Harmful Algal Blooms have been tied to shellfish poisonings and the death of endemic species to the ecosystems involved.

Many possible solutions have been developed to stop Eutrophication. The reduction of runoff and the instillation of Riparian buffer zones are two major preventative methods to curtail eutrophication. Governmental regulation of the type, amount, application, and timing of fertilization has helped reduce runoff pollution from agricultural and residential sources. The addition of Riparian buffer zones, the area between land and a river, help to reduce runoff into river sources. These zones act as a divider between land and water, and can trap pollutants in runoff before they reach the river. These solutions greatly reduce runoff containing pollutants and unwanted nutrients into the water column. The reduction of nutrients helps decline the rate of eutrophication. Without eutrophication, the occurrence of Algal Blooms declines. Each of these processes has consequences on other processes down the sequence of events. By eliminating pollution at its source, algal blooms can be brought to an end.

Original Research - Seawater Desalination

The lack of sufficient sources of fresh water may not seem like a crisis in New Jersey, but many parts of the world face this monumental issue. Approximately 1 in 6 people lack access to safe water, water that is necessary for cooking, farming, drinking. A way to combat the steadily growing deficiency of fresh water as the world’s population steadily increases is through a process known as desalination. To desalinate water is just as the word implies---to remove the salts from briny water. This conversion from saltwater/seawater to fresh water is accomplished through a couple of techniques and has eye-opening advantages over other solutions to the water crisis, but also has some outstanding shortcomings that need to be fixed.

            To begin, one technique to desalination is distillation. To distill salt water, large amounts are heated to evaporate pure water from the liquid. The large structure containing the process then separates the once saline water into two products: fresh, almost pure, water and very briny water. Another way to desalinate water, the most popular, is through membranes and filtration. Two processes under this category are reverse osmosis and electrodialysis. Basically, a semi-permeable membrane removes ions, the salts, selectively, after a filter has removed most of the impurities.

            Several advantages of desalination are that the supply of water from the ocean is unlimited, the water product is relatively pure, and it removes the need to destroy or infringe on other sources of freshwater. However, there are negative aspects to the workings of the many desalination plants throughout the world. Although the cost of desalination has decreased over past years, this method of purification is still expensive in comparison to others. Also, tons of energy is consumed in the process; it isn’t “green.” Additionally, it negatively impacts marine life and the environment. Larger animals are killed on the impact screen through impingement; small organisms are killed in the process through entrainment. The briny solution left over contains nitrates, iodine, lead, and lots of salt, and there is no useful or safe place for it to be disposed.

            Ultimately, while desalination has some major distinct advantages over other methods of obtaining safe water, problems are evident that need to be fixed: the cost, the excessive energy consumption, the death of marine organisms, and the harmful briny leftover.