Environmental Implications of Desalination: Concentrate Management

Report
Consultative Workshop on
Desalination and Renewable Energy
Environmental Implications of Desalination:
Concentrate Management
Dr. Fulya Verdier, Dr. Rudolf Baten
Fichtner GmbH & Co.KG
Muscat, Oman
22-23 February 2011
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Table of Contents
 Need for Concentrate Management
 Characteristics of Concentrate
 Potential Environmental Impacts
 Impact Mitigation Measures
 Concentrate Management Options
 Conclusions
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Concentrate Management
There is increasing need, because of:
Increasing number and size of desalination plants
Increasing accumulation of desalination plants in certain regions
Increasing concentrate volumes
Limited available disposal options
More strict environmental regulations (e.g. groundwater protection)
Increasing public awareness and environmental concerns
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Characteristics of Concentrate
Typically there are three types of desalination plant discharges:
Brackish water concentrate
Seawater concentrate
Process effluents
Salinity level of concentrate highly depends on feed water
salinity and recovery
Volume of concentrate is much greater than volume of
process effluents
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Characteristics of Concentrate
Overview on the relevant discharge flows
Desalination Technology
RO / MED / MSF
RO
Relevant Discharge Flow
Content
Seawater concentrate
Salt Content & Heat
Biocide (Chlorine)
Chemical
Anti-scalants
Chemical
Filter backwash waste water
Suspended Solids
Sodium bisulfite (SBS)
Chemical
Coagulants
Chemical
Flocculants
Chemical
Corrosion inhibitors
Chemical
Anti-foam agents
Chemical
MED / MSF
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Potential Impacts of Concentrate
Physio-chemical Impacts
Increased salinity, temperature and density of concentrate relative to
receiving environment
Contaminants
Biocides (e.g. NaOCl or Cl2)
Dechlorination using SBS (sodium bisulfite)
Antiscalants (polymeric substances)
Cleaning chemicals (acid, base, detergents)
Coagulants from RO plants (e.g.FeCl3) causing reddish color
Antifoaming agents from thermal plants (polyethylene, polypropylene)
Traces of heavy metals if there is corrosion of plant equipment
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Cause - Impact Assessment
“Cause Impact Assessment” is difficult to determine since
 there is no direct link
 the receiving eco-system is complex
 thorough investigations and analysis with adeaquate replication on annual basis
are required to establish
 statistical analysis of results
 comparative analysis of trends
 Even if some cause and effect relationships are not fully established
scientifically, “precautionary measures” should be considered
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Impact Mitigation
The approaches are two-fold:
Environmental Impact Mitigation of Concentrate
Process
Effluent
Treatment
Concentrate
Management
Options:
Concentrate Disposal
&
Volume Reduction
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Impact Mitigation Measures
Waste water treatment plant (WWTP) including sludge treatment
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Impact Mitigation Measures
Surface Water Discharge
 Measures to reduce the extent of impacts i.e. diffusers for enhanced mixing
and dispersion of concentrate
Source: Wilf (2007)
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Source: Bleninger (2007)
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Impact Mitigation Measures
 “Best practice” desalination plant
 Minimization of plant wastes (liquid, solid)
 Process optimization in order to minimize the discharge flow quantity and
contamination
 Involvement of waste water treatment plants (WWTP) including sludge
treatment
 Neutralization of chemicals prior to discharge (~ pH=7)
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Further Measures
Relevant Legislations and Guidelines
 Generally subject to national water framework
 MENA countries like Saudi Arabia, Oman, Israel and Egypt have introduced
discharge limits for selected effluent pollutants and mixing zone regulations
 e.g. Omani discharge requirements limit parameters in the concentrate
 Temperature, Suspended solids, Total chlorine, Copper, Nickel, Molybdenum, Iron
 Besides the discharge limits, a mixing zone of 300 m in diameter around the outfall is
specified. Within the mixing zone, no marine life at the seabed may be destroyed.
 Beyond the mixing zone
• the ambient water temperature must not be increased by
more than 1 °C (weekly average)
• the average ambient salinity must not be changed by
more than 2 g/l
• the average dissolved oxygen level should not be reduced
by more than 10%
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Further Measures
Appropriate Site Selection
 Data collection and evaluation including installed desalination plants in the
vicinity of plant
 Semi-closed areas such as Red Sea and Arabian Gulf can be more susceptiple
to cumulative impacts due to limited flushing
 Impact modeling and assessment (EIA) prior to environmental permit
Measures for Permit Granting
 Evaluation on case-by-case basis
 Establishment of discharge quality standards
 Definition of minimum requirements for outfall structure
 Prohibition of discharge at coast
Appropriate Monitoring
 Before-After/ Control-Impact Monitoring
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Further Measures
Additional (international) environmental requirements
 Equator Principles
 World Bank Standards
Measures for Institutional Water Authorities
 Preparation of master plans for water bodies
 Integrated, multi-scale water resources planning
 Development of local, regional, national water regulations
 Conducting studies to promote national water program
 Assessment of desalination guidelines
 Establishment of incentives, task forces
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Concentrate Management Options
There is no universal concentrate disposal solution for all plants and sites
 Surface water discharge (oceans, seas, rivers) is the most economic and common option for
large concentrate volumes
 Sewer disposal may require fees and permit by local sewage agency
 Deep well injection requires highly permeable, unusable saline aquifer nearby. Its feasibility
depends on hydro-geological conditions
 Evaporation pond is land intensive and thus rather applicable for smaller volumes
 Zero liquid discharge means no liquid discharge across plant boundary. It is more applied by
industry by using thermal evaporators and processing to solids
 Selective salt recovery needs market development in the long term
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Concentrate Management Options & Costs
Options & Benchmark
Indicative Costs (1) Critical factors
[US$/m³]
Concentrate disposal
options
Surface Water
0.03 - 0.30
Piping, pumping and outfall construction
Sewer
0.30 - 0.66
Disposal rate, salinity, sewer capacities, fees
Deep Well Injection
0.33 - 2.64
Tubing diameter and depth, injection rate, chemical
costs
Evaporation Pond
1.18 - 10.04
Pond size and depth, salt concentration,
evaporation rate, disposal rate, pond liner cost
Zero Liquid Discharge
0.66 - 26.41
Disposal rate, energy costs, salinity
Benchmark
Membrane replacement
Chemicals
(1) Costs
0.008 - 0.05
0.008 - 0.05
include CAPEX and OPEX costs after Greenlee et al., 2009
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Conclusions
 Pioneer installations are operated for backwash water treatment (e.g. Perth
SWRO, Sydney SWRO, planned for Raz Azzour hybrid plant), the related
costs are not significant
 Eco-toxicity and chemical dosing rates has been reduced
 Measures to mitigate concentrate impacts are state-of-the-art
 Concentrate minimization is not yet established. Currently limiting factors
are related to economics rather than technical feasibility
 Today’s best practice is expected to become minimum requirement for future
desalination plants
 MENA countries can provide a suitable platform to establish a common
consensus
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Concentrate Management
Thank you!
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