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

Basic Flow Diagram and Water Balance…

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)

Preliminary Conclusions…

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

storage?– Reservoir capacity?