Namwater Desalination Plant:

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21-04-2009
Namwater Desalination Plant Mile 6 (Swakopmund)
EIA Water Wastewater Management
Philip de Souza
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Specialist Study Components

• Literature review and interactions
• Brief consideration of water and groundwater
  environments
• Technology review
• Water use
• Wastewater treatment and associated
  discharges/disposal
• Stormwater impacts
• Preliminary water balance
• Identification of any opportunities for improving
  integrated water management/promoting water
  conservation
• North/South scenarios ? NO significant impact on
  the water wastewater management study

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Legislative Aspects

• Water Resources Management Act (Act 24 of 2004)
• Part VIII Licence To Abstract And Use Water
• Part XI Water Pollution Control
• Draft Pollution Control and Waste Management Bill
  (1999)
• Taking water from a water resource (e.g. from the
  sea)
• Storing water on-site (e.g. in a reservoir)
• Discharging waste or water containing waste into
  a water resource through a pipe, canal, sewer or
  other conduit (e.g. brine disposal to the sea,
  wash water disposal to sea, spillages of
  chemicals/oil?)
• Disposing of waste in a manner, which may be
  detrimental on the water resource (e.g. disposal
  of solid waste, oil, chemicals with subsequent
  pollution of groundwater resources)

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Potential Impacts

• Water use
• Construction (earthworks, etc)
• Operations (drinking-water, process water, etc)
• Wastewater discharge
• Domestic wastewater
• Process wastewaters (concentrated brine, wash
  waters)
• Contaminated stormwater (poor housekeeping
  spillages)
• Sludge handling/disposal

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Basic Flow Diagram and Water Balance
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Construction

• Water Use
• Preliminary earthworks
• Seawater intake and discharge construction
• Desalination Plant construction
• Pump station, reservoir and pipeline construction
  
• Hydrostatic testing (of tanks, pipes, etc)
• Potable water (drinking water)
• Fire fighting water
• Wastewater Discharge
• Domestic wastewater (sewage)
• Construction runoff and hydrostatic testing
  wastewater
• Stormwater runoff (if contaminated)
• Proposed construction site management must be
  enforced

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Operation

• Water Use
• Sea water (for desalination)
• Potable water (drinking water, safety showers,
  etc)
• Process water (wash waters, etc)
• Fire fighting water
• Wastewater and Related Discharges
• Domestic wastewater (sewage)
• Process wastewater
• Wash waters (membrane cleaning, etc)
• Concentrated brine from SWRO units (combined with
  wash waters ? sea)
• Sludge wastes (e.g. from DAF)
• Oil and chemical wastes (spillages)
• Stormwater runoff (if contaminated)

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Review of Proposed Systems

• Generally have proposed standard good practice
• Need to meet Namibian DWQ requirements
• Intake design key
• Higher sediment higher sludge volume
• Good process control
• PLC and SCADA, adequate monitoring, alarming,
  logging, etc
• Safety considerations
• Isolation valves, vents, drains, etc
• Appropriate materials of construction
• E.g. to minimise corrosion
• Identified need for adequate back-up equipment
• E.g. standby skids, standby dosing pumps, spare
  parts, special tools, etc
• Use of standard chemicals proposed (not finalised)

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Queries Review of Proposed Systems

• DWQ requirements
• Same as WHO
• For all determinants?
• Only a selection provided
• Fire protection water supply/storage
• From the sea / on-site reservoir?
• Reservoir capacity
• SA 48 hr supply (preferable) or 24 hr supply
  (min)
• Swakopmund base reservoir (20 000 m3) ? 44 hr
• New reservoir (20 000 m3) ? 10 hr (initial) 6
  hr (future)
• Do clients understand risk?

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Water Use
Phase Water Use
Preliminary Earthworks Water requirements surface area (10 ha) Difficult to estimate at this stage Water from Omdel Swakopmund Pipeline (NamWater)
Construction Total use (industrial/potable water) 50 000 m3 Construction period 22 months (660 days) 300 people 252 L/person/day (e.g. 25 L/person/day for domestic and balance for building, concrete, etc) System flushing, hydraulic checks, etc included?
Operation Domestic Drinking Water From sea water desalination 0.3 m3/day used for drinking water purposes (assuming water use equals domestic wastewater generated (conservative)) (Possible need for Municipal supply - emergency situations)
Operation Client Produced Drinking Water From sea water desalination 71 429 m3/day produced for client purposes
Fire Water Storage No data (sea water or desalinated water)
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Wastewater and Related Discharge
Phase Wastewater Discharges
Construction Domestic wastewater (sewage) Assuming 300 people use of 100 L/person/day potable water, and assuming water use equals domestic wastewater generated (conservative) Domestic wastewater 30 m3/day
Operation Domestic wastewater (sewage) To on-site septic tank system 0.3 m3/day (30 people 10 L/person/day)
Operation Wash Waters Discharge To sea 7 150 m3/day
Operation Brine Discharge To sea 108 571 m3/day
Stormwater 15 mm/annum, 100 collected 2 m3/day (not continuous/predictable
Construction sludge None
Operation sludge Appropriate disposal/re-use options to be considered 65 tons/day (or 65 m3/day if assume density of sludge 1000 kg/m3)
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Domestic Wastewater (Sewage)

• Construction
• On-site sanitation for 300 persons (porta-loos)
• Collection by honeysucker? (frequency?)
• To municipal wastewater treatment works?
• Agreements?
• Operation
• 30 persons
• Septic tank system
• Capacity?
• French drain system or collection by honeysucker?
  (frequency?)
• Agreements?

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Brine Discharge

• Options
• Regulated discharge to the marine environment
• Discharge to municipal sewers (volumes, quality)
• Disposal via evaporation ponds (area, cost)
• Concentration of brine via evaporator /
  concentrator / crystallization treatment steps
  (cost, brine further concentrated)
• Zero Effluent Discharge facility (cost)
• Discharge to sea
• Wash waters co-disposal
• ? Dependant on Marine Discharges Impact Study
  findings

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Stormwater Management

• Swakopmund area rainfall
• lt 15 mm/annum ? very low rainfall
• Storm events are unlikely
• Air emissions from the NamWater Desalination
  Plant ? no impact on stormwater quality
  (electricity generated off-site)
• BUT how do we handle
• Stormwater?
• Wastewaters generated on-site from non-process
  activities that could pollute stormwater?
• E.g. washing of vehicles, chemical or oil
  spillages

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Treatment Chemicals
Environmental aspects Chemicals present Environmental impacts
Corrosion products Iron, copper, nickel, zinc and other heavy metals Toxicity to biological systems
Antiscaling additives Polycarbonc, polyphosphates Eutrophication (algal blooms) Increased biofouling
Antifouling additives Chlorine, hypochlorite Sterilization effect in organisms Can form compounds with carcinogenic and mutagenic properties
Antifoaming additives Alcylated polyglycols, fatty acids, fatty acid esters Interrupts intercellular membrane system of organisms Full extent of environmental impacts unknown (i.e. precautionary approach required)
Cleaning processes Acids (e.g. sulphuric acid) Damage organisms if pH too low
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Chemical/Oil Waste Management

• Construction chemicals cleaning/lubrication
• PVC glue, acetone, grease, lubricating oils
• Water treatment chemicals
• Lab chemicals for DWQ analysis
• Oils/fuels (e.g. diesel for generators)
• Spillage management structures?
• Secure buildings, impervious areas, containment
  dikes, bunded areas
• Spillage management protocol/plan
• Immediate spill response and cleanup measures
• Sorbent and other materials availability
• Empty chemical containers hazardous?

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Sludge Handling/Management

• Sludge utilization
• Nutrients
• Metals
• Odours (nuisance conditions, public attention)
• Pathogens
• Sludge classification (e.g. agriculture)
• Microbiological class (i.e. faecal coliforms,
  helminth ova)
• Stability class (i.e. stability of the sludge)
• Pollutant class (i.e. analysis of 8 potentially
  toxic metals and elements arsenic, cadmium,
  chromium, copper, lead, mercury, nickel and zinc)

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Sludge Handling/Management

• Sludge concentration ? dry solids
• Estimated 65 tons dry matter/day
• Assume density of sludge density of water
• Sludge concentration 20 solids
• Water 80 or 260 tons water/day
• Components
• Ferric hydroxide (coagulation)
• Suspended solids (sea water)
• Polymer (coagulant aid)
• Grit (backwashing of calcite beds)
• Calcium hydroxide?

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Sludge Handling/Management

• General waste (e.g. domestic waste, builders
  rubble)
• Hazardous waste (need a Hazardous Waste landfill)
• Bleaching powder, Calcium hypochlorite, Cyanuric
  chloride, Dichloroisocyanuric acid salts, EDTA,
  Ferric chloride, Ferrous chloride, Potassium
  permanganate, Sodium fluorosilicate, Sodium
  hypochlorite, Sodium phosphate tribasic,
  Trichloroisocyanuric acid
• mg/L and mass per area per time period

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Sludge Handling/Management Queries

• Classified as non-hazardous?
• Precautionary Principle ? always hazardous if
  doubt (unless proven)
• Determine properties, characteristics and
  components
• Classification and treatment
• Analysis and Hazard Rating
• Likely sludge quality (concentrations)?
• Equipment/processes (e.g. dewatering,
  stabilization)?
• Options
• Cannot dispose to ocean?
• Land disposal (quantity, transport)?
• Beneficial land use?

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Preliminary Summary of Impacts

• Water use ? low impact
• Domestic wastewater discharge ? low impact
• Construction wastewater discharge ? low impact
• Process wastewater (brine/wash waters) discharge
  to surface water/groundwater ? N/a
• Process wastewater (brine/wash waters) discharge
  to sea ? ?
• Stormwater contamination ? medium impact
  (precautionary)
• Sludge disposal ? high impact (precautionary)

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Preliminary Conclusions

• Main queries/concerns
• Desired drinking-water quality?
• Stormwater management?
• Spillages management?
• Sludge handling/management?
• Fire protection water supply
• storage?
• Reservoir capacity?