the need to quantify the loss of marine life in desalination plants
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The need to quantify the loss of marine life in desalination plants. K.P. Manikandan, Mohammad A. Qurban, T.V . Joydas, M. Wafar and P.K . Krishnakumar. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
110th April 2012 Slide # 1
The need to quantify the loss of marine life in
desalination plantsK.P. Manikandan, Mohammad A.
Qurban, T.V. Joydas, M. Wafar and P.K.
Krishnakumar
210th April 2012 Slide # 2
Introduction
• Desalination is being used in 150 countries around the world, providing some or all the daily water needs of an estimated 300 million people
• There are now 16,000 desalination plants worldwide
• Total production = 77.4 million cubic meters per day (m3/d) (24th IDA Worldwide Desalting Plant Inventory, 2012)
60%
34%
4% 2%
ProductionROThermalEDOther
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Introduction
Red Sea
14%
Arabian Gulf
45%Mediterranea
n Sea
17%
76% from three Seas
76%
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Production in Arabian Gulf
45% of the global capacity
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Production in Red sea
14% of the global capacity
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• Most desalination plants draw/pump water from the coastal waters
• Coastal waters are the biologically productive zone
• This is the zone where most marine animals prefer to lay eggs
• As most marine larvae are passive swimmers (at the mercy of water currents) they are vulnerable to suction during the intake
• Every year there is a huge loss of billions of aquatic organisms, including fishes, fish larvae and eggs, crustaceans, shellfish, and many other forms of aquatic life from the coastal ecosystems.
• This huge loss will reflect on the declining fish landing and ultimately to the revenues generated by Fishery.
Introduction
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Definitions
Impingement:
Potential injuries or loss of marine organisms retained on the intake screens. (as per USEPA > 9.5mm)
Entrainment:
Loss of marine organisms which enter the desalination plant with the sourceSeawater (as per USEPA < 9.5mm)
Entrapment:impacts associated with offshore intakestructures connected to an on-shore intake screen and pump station via long conveyance pipeline – Trapped
Adult fishes
Fish and invertebrate
larvae
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Typical Larval Cycle
One Female 100,000
larvae100
juveniles
2 ADULTS
99.9%
98%
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An example from Florida
• Florida’s - Tampa Electric Company (TECO) Big Bend station, situated on Tampa Bay, at Apollo Beach.
• Annually, impingement resulted in the loss of 419,286 “age 1” equivalent fish, and 11,113 pounds of fishery yield
• Entrainment was far more lethal: 7.71 billion-age 1 equivalent fish were being decimated; 22.8 million pounds of lost fishery yield.
• Most heavily hit were bay anchovies
• Stone crabs, pink shrimp, sea trout, herring and black drum were also affected.
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Region-wise losses
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Loss due to Impingement &
Entrainment in Arabian Gulf & Red Sea –
Unknown ?
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• To identify the methodology for quantifying the loss of marine organisms due to entrainment and impingement
• To recommend mitigation measures by way of alternative modes of seawater intake
Objectives
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Assessment- Methodology
• What to sample?• Limited to only large and late stage larvae (Fish & Crabs)• Phytoplankton to be ignored
Short generation times Overly Abundant (bloom) can be a problem in quantification
• Small Invertebrate Larvae & Fish Eggs ignored – Cannot be Enumerated
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Assessment- Methodology
• Sampling Locations:• From the Intake Screens (for
Impingement) • In front of the Intake and at
Water Body Locations using 300-μ mesh Plankton net (for Entrainment)
• Two replicate tows were taken with a minimum target sample volume of 30 to 40 m3 for each net on the bongo frame.
• Sampling Frequency:• 12 to 18 Consecutive Months• Weekly – i.e., minimum of 52
Samples• 24-hr Sample Collection for
Impingement• Day/Night Samples for
Entrainment.• Four times per 24-hr period—
once every six hours.
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• For Impingement Assessment - Adult & Juvenile Species trapped on the plant Screens are:
• Identified/Classified• Counted and•Weighed
• For Entrainment Assessment – Larval Species Collected on the 300-μ nets in front of the screens & in various areas of the Potential Impact Zone are:• Identified to the lowest taxonomic classification possible (e.g., genus
or family level) and• Counted
• Data Sets to be collected:• For Each sample day, Larval Counts & densities (No. per Unit Volume)
at the Intake & in Water Body.
• Actual Intake flows are measured at the time of sample collection.
Assessment- Methodology
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Assessment- Methodology• Once species are identified and enumerated – the population and
community levels effects caused by the removal needs to be estimated
• Long term data not typically available
• Models have to be used to estimate the potential effects of larval removal
• Estimating the Larval mortality due to entrainment
Calculate the volume of water entering the intake (V)Measure the concentration of larvae (no. per volume) that are entrained
(N)(assume 100% mortality)Estimate Entrainment mortality = N x V
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Assessment- Methodology
Demographic Models
•Adult Equivalent Loss (AEL)•Fecundity Hindcasting (FH)•Habitat Production Foregone (HPF)
Conditional Mortality Models
•Empirical Transport Model (ETM)
• Models – two categories • Those that require life history data and those that do not
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Assessment- Methodology• Requirements for demographic models
• Fecundity• Age at first maturity• Longevity• Survival data for eggs, larvae and other stages through adults
• Adult Equivalent Loss
• Uses entrainment mortality in conjunction with larval sizes ( proxies for age) and natural mortality rates and estimate the Adult Equivalent loss
• Fecundity Hindcasting
• Uses entrainment mortality and back calculates the number of adult females that were lost (assuming 1:1 sex ratio or any other from literature)
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Assessment- Methodology• In the absence of life history information, ETM models could be utilized
• The ETM estimates conditional probability of mortality (PM) associated with entrainment
• PM requires (PE - Proportional entrainment) as input which is calculated as :
• Source water has to be defined based on hydrodynamic and biological characteristics of the water body
• Calculation of No. of days when larvae are at risk (d):• Estimate the age of the fish based on the average size entrained –
for eg., 23 days• So, for 365 days = 365/23 = 16 days at risk(d)
• Calculation of proportion of larvae that will escape entrainment (Pesc) : (1- PE )d
• Proportional mortality (PM) = 1/d (1- Pesc)
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• Estimation of Habitat Production Foregone or Area Production Foregone
• HPF = Proportional mortality (PM) x Source water body (SWB)• An example from Carlsbad Desalination study
Assessment- Methodology
Entrained Species
Proportional mortality (PM)
Source water body (SWB)
HPF = Proportional mortality (PM) x Source water body (SWB)
Gobies 21.56 302 acres 65.11Blennies 8.63 302 acres 26.06Hypsopops 6.48 302 acres 19.57Average 12.22 302 36.93 (37 acres)• So, HPF = 37 acres for 304 Million gallons per day in Carlsburg
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• 37 acres of new bay habitat if restored to the system will reduce the impacts caused due to impingement and entrainment- assuming that new bay habitat was a comparable mixture of habitats to that in source water body
• Scale and context of HPF are very important
Two fishes have estimated entrainment losses (PM) of 1%
– Case 1: northern anchovy has estimated source water of 1,000 km2, results in
HPF =10 km2 – meaningless in a context as no habitat dependency for anchovy spawning
– Case 2: kelp bass occupying kelp habitat around intake of 1 km2, results in
HPF = 0.01 km2 – could be of greater concern if kelp habitat limited in area of intakes
• Mitigation could be by way of creating a coastal habitat similar to that of source water body, which will provide measurable long term environmental benefits
Assessment- Methodology
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Mitigation measures
Sand Filtration
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Mitigation measures
Wedge Screens
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Mitigation measuresSubsurface intakes
Vertical beach well
Radial intake well
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Mitigation measuresSlant wells
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Mitigation measuresHorizontally directed drains (HDD) wells
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Mitigation measuresMarine Life Exclusion System
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Conclusion
• The current US EPA standard requires that the best available technology should be used in order to achieve impingement reduction of 85-95% and entrainment reduction of 60-90%
• Middle east has the maximum number of desalination plants, but unfortunately, no estimate of loss due to entrainment and impingement in the Middle east
• There is an immediate need to assess the impacts of entrainment and impingement in the Middle east
• Only by quantifying the impact, measures could be taken to minimize the loss
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Thank You