POTENTIAL HEALTH RISKS FROM GREY WATER

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POTENTIAL HEALTH RISKS FROM GREY WATER

• David Cunliffe

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What is Grey Water ?

• Shower and bath water 33 of total wastewater
  generated
• Hand basins 5
• Laundry 23
• Kitchen 7
• Total - about 70 of wastewater is grey water

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Purpose of Grey Water

• Sanitation and cleaning
• Washing hands, skin, clothes, food etc to
  remove pathogenic microorganisms, oil, grease
  and dirt
• - higher loads from washing clothes/nappies
  from babies and young children
• Aim is to separate people from harmful
  microorganisms by carrying them away in grey
  water.
• Other uses
• Washing animals, cleaning tools, transporting
  urine, disposal of hazardous waste (chemical)

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What is in Grey Water

• BathroomPathogenic microorganisms (Thermotol
  coliforms lt10-106 per 100 mL), hair, skin, soaps,
  oil, grease (Sewage 106-1010 thermotol
  coliforms per 100 mL)
• LaundryPathogenic microorganisms (Thermotol
  coliforms lt10-107 per 100 mL), bleach, soap
  powders (boron, sodium, phosphate, ammonia,
  surfactants), lint
• KitchenPathogenic microorganisms (Thermotol
  coliforms lt10-106 per 100 mL), detergents, food
  particles and residues, oils, fats, hazardous
  wastes

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Unknowns

• Washing of nappies and other faecally-soiled
  clothing
• Washing of pets
• Disposal of hazardous liquids
• Washing of tools

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Health Risk

• Depends on hazards present in the source water
  and exposure ( mosquitoes)
• Exposure controlled by managing
• - method of application - public
  accessibility- use

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Heath risk by source

• Risk SourceLower Laundry rinse
• Laundry wash and rinse
• Bathroom
• Higher Kitchen
• Other risk factors - young children and pets

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Heath risk by application method

• Risk Method Lower Sub surface
• Drip
• Spray
• Higher Hose
• Other risks - ponding/storage can support
  mosquito
• breeding

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Heath risk by use

• Risk Method Lower Trees and shrubs
• Lawn
• Fruit trees
• Vegetables
• Higher In house (toilet flushing)
• Other risks - non-approved cross-connections

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Heath risk by accessibility

• Risk AccessibilityLower No access
• No access by young children
• Higher Unlimited access

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Conclusions

• Grey water usually contains fewer hazards than
  sewage but concentrations vary over a very wide
  range
• For on-site systems the concentration and range
  of hazards will depend on household management
• Restricting methods of application and types of
  use can reduce risk but for on-site systems this
  will rely on household management
• Systems need to be robust and designed to involve
  a minimum of maintenance. Centralised management
  systems are best.