Health Aspects of Re-use of Household Wastewater (Greywater)

Transcription

1 Health Aspects of Re-use of Household Wastewater (Greywater) Jo M Barnes Division of Community Health Faculty of Health Sciences University of Stellenbosch TYGERBERG Envirowater Conference, 2009 Copyright reserved 1

2 WATER SITUATION Water demand increasingly outstrips supplies In South Africa 98% of all potential raw water sources are allocated for use Increasing urbanisation and demand for safe sanitation place heavy demands on water resources 2

3 NEED FOR RE-USE OF WATER Innovative solutions needed Accessing additional water supplies inherently costly and not without negative consequences Other water uses (agriculture, industry) compete with urban dwellers for water rights Water conservation and water demand management may delay shortages but need is inevitable Re-use of household wastewater increasingly viewed as a partial solution 3

4 HOUSEHOLD GREYWATER What is it? Domestic wastewater refers to all the wastewater produced in a household, including the wastewater from toilets Greywater refers to the water drained from baths, showers, washing machines, and sinks (i.e. household wastewater excluding toilet waste) USA and Australia - water drained from kitchen sinks, garbage disposal units and dishwashers also excluded from greywater because of high concentrations of organic waste 4

5 HOUSEHOLD GREYWATER - What is in it? Soaps and detergents Cleaning compounds Fabric softener Hair products (shampoo, hair conditioner) Toothpaste Medicines Disinfectants Pesticides Dyes Cosmetics Lint and other fibres Food particles as well as fats, oils, blood Human waste products: saliva, sweat, body oils, hair, blood, and some urine and faecal matter 5

6 RE-USE OF HOUSEHOLD GREYWATER Potential advantages May potentially replace expensive potable municipal water that would have been used for landscape irrigation May provide financial savings to already overburdened sewage treatment facilities because greywater use diminishes sewer flows, thereby lessening the need to expand such facilities May benefit plants because greywater contains some compounds beneficial to growth 6

7 RE-USE OF HOUSEHOLD GREYWATER Contrary to common belief, greywater is not a safe product Contains bacteria, viruses, parasites - potential pathogens able to cause disease in humans or animals Species and total counts vary widely according to climatic conditions, season, sanitation technology available, sanitation habits of the people living in the dwelling and the disease incidences in the area Potential re-use of greywater is as much a public health issue as it is a water conservation priority Implementation involves balancing risks 7

8 OVERSEAS RESTRICTIONS ON RE-USE (1) Water used to wash articles contaminated with faeces, etc should not be used Greywater should not be allowed to leave the boundaries of the property and should under no circumstances be allowed to enter the stormwater system Provision must be made for the safe disposal of excess greywater into the sewerage system during rain periods or when too much greywater is produced for the garden to absorb This should be a "fail-safe" disposal system Greywater should never be allowed to pond or pool where mosquitoes can breed or where it can develop foul smell 8

9 OVERSEAS RESTRICTIONS ON RE-USE (2) Should never be applied to edible crops Should be withheld from areas where children play, such as lawns. Children are the highest risk group for acquiring infection from greywater. Should be withheld if anybody living on the premises is suffering from diarrhoea, ear or skin infections, etc Warm water should be stored in a holding tank to cool down. Use within 24 hours; otherwise the bacterial load will rise too high for safety. Everybody living on the premises where gardens are irrigated with greywater should wash their hands without fail before eating or drinking 9

10 REALITIES IN DEVELOPING COUNTRIES Far larger proportion of population poverty-stricken Burdens of disease predominated by infectious diseases 40% of women aged HIV + in South Africa Very poor sanitation - high infection pressure Direct link between food and contaminated water Populations more inclined towards 'civil disobedience' due to lack of enforcement of regulations 10

11 Popular images in the media 11

12 Suburbia typical domain for greywater re-use studies 12

13 No place to discard washing water - runs into stormwater drains 13

14 Standpipe also serves as dirty water disposal site 14

15 Poor living conditions - high infectious pressure 15

16 40-60 persons per toilet 16

17 Poor solid waste removal causes contamination 17

18 Who is most at risk of water- related disease? Newborns, babies and children Pregnant women and their developing foetuses Old people Individuals with compromised immunity such as those with TB, HIV/AIDS Persons who are chronically malnourished Patients on long-term medication Persons with pre-existing chronic diseases such as diabetes, kidney failure, liver failure Persons who abuse alcohol or other drugs = Major proportion of SA population 18

19 ORGANISMS ISOLATED BELOW SETTLEMENT β haemolytic Streptococcus Group B Acinetobacter spp including A. lwoffii Bacillus spp including B.subtilis Citrobacter spp Coagulase negative staphylococci Enterobacter spp including E. cloacae Enterococcus faecalis E. coli (4 morphologically distinct colony types) Klebsiella spp including K. pneumoniae, K. oxytoca Mycobacterium intracellulare Proteus spp including P. mirabilis Viridans group of streptococci, including S. faecalis 19

20 Greywater applied to gardens Should be used for landscape garden watering Microbes in greywater have higher survival rates in topsoil. Always use subsurface irrigation or irrigation under a heavy mulch cover Irrigation lines clog more easily. These should be cleaned with due care - bioslimes are contaminated Keep children and pets away from areas that are irrigated with greywater and under no circumstances allow them to drink this water. 20

21 Risk to edible crops Should never be applied to edible crops - especially not to vegetables eaten raw or lightly cooked, such as in salads. Should also be avoided for root crops such as carrots, since the pathogens accumulate in the topsoil Garlic irrigated with wastewater only reached sanitary acceptability 90 days after harvest once the roots and soil were removed. Onions cleaned immediately after harvest reached sanitary acceptability 55 days after harvest. Some documents advise withholding irrigation with greywater for one week only before harvesting root crops - not safe advice! 21

22 Risk to edible crops Irrigation carried out under plastic sheeting or buried under the soil surface significantly reduced crop contamination Microbial contamination persisted in the irrigation pipes for at least 8 days and in the soil for at least 18 days. Survival of E. coli O157:H7 was greatest in soil under rooted grass - moderate decline occurred only after 130 days. Clumping of viruses on lettuce and carrots irrigated by contaminated water occurred - caused underestimation of risks. Edible crops should only be irrigated with greywater in time of such severe food shortage that the risk of disease becomes less than the risk of hunger. 22

23 "Irrigation with greywater happens anyway!" Irrigation with contaminated greywater occurs in subsistence farming and informal settlements Such irrigation for subsistence and market gardening encouraged by some NGO's Impact of such advice unassessed epidemiologically Different liability when officially sanctioned - when initiated by citizens themselves they carry the risk 23

24 Systems problems increase risks Needs high commitment and sophisticated understanding Needs strict supervision - luxury in developing countries Needs proper, safe systems (filters, directional valves, etc) During outbreaks or health hazards, how can use be stopped? (No 'undo button') What if subsequent owners do not comply with safety rules? Who will carry costs if health risks rise to unacceptable levels or outbreaks occur? If stopped, who will compensate the poor who make a living selling the produce grown with greywater? 24

25 Re-use may be feasible, but it imposes added public health risks that need to be accepted only as a last resort in developing countries or in impoverished areas. Pronouncements on feasibility, especially in engineering publications, should take this reality into account. 25

26 "In nature there are neither rewards nor punishments - there are consequences" R J Ingersoll 26