Namwater Desalination Plant: Mile 6 (Swakopmund)
EIA: Water & Wastewater Management
21-04-2009
Philip de Souza
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
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)
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
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
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)
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)
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?
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 o Construction period: 22 months (~660 days)o 300 peopleo 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)
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)o 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)
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?
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
Stormwater Management…• Swakopmund area rainfall
– < 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
Treatment Chemicals…Environmental
aspectsChemicals 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
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?
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)
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?
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
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?
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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