Presentation on theme: "What is greywater? All non-toilet domestic wastewater: Bath / shower / handbasin Laundry Kitchen Toilet wastewater (blackwater) NOT included. Some definitions."— Presentation transcript:
What is greywater? All non-toilet domestic wastewater: Bath / shower / handbasin Laundry Kitchen Toilet wastewater (blackwater) NOT included. Some definitions also exclude kitchen wastewater. Sewered areas: greywater represents about 75% of total wastewater. Unsewered areas: greywater represents up to 100% of total wastewater.
Uncontrolled greywater is an environmental and health hazard. Photos K. Carden, UCT
Why use greywater for irrigation? Water scarcity. Pressure on freshwater sources. Potential benefit of greywater use for irrigation environmental. water, nutrients. food security, informal employment.
Concerns about the use of greywater for irrigation Human health. Plant growth and yield. Ability of soil to support plant growth.
Guidance for greywater irrigation Guide to Managing Uncertainty and Risk Greywater Quality: Guide to Greywater Constituents Greywater Quality: Mitigation of Greywater Quality Greywater Quantity: Guide to Irrigation Volumes
Guide to Managing Uncertainty and Risk A hazard becomes a risk only when people, plants or soil come in contact with it (exposure). For example: Hazard may be harmful microbes (‘germs’). Risk of illness exists if microbes are ingested by people. To prevent the risk (illness) - remove microbes from greywater. - prevent microbes from coming into contact with hands or crops. - make sure that microbes on hands or crops are removed or killed.
Guide to Managing Uncertainty and Risk So risk can be managed by: Removing hazards in greywater (improve quality). Preventing people/plants/soil from coming into contact with hazards in greywater (exposure barriers).
Guide to Managing Uncertainty and Risk Three categories, depending on how risk is managed. Category 1: No greywater analysis or treatment; Strict barriers to exposure. Category 2: Minimum greywater analysis so that greywater quality is controlled; Slightly less strict barriers. Category 3: Full greywater analysis; Least strict barriers.
Household level irrigation use No analysis; No treatment Kitchen greywaterLaundry greywaterBath/shower/basin greywater Wash waterRinse water Not recommended for irrigation use Can be used for irrigation in accordance with restrictions R1, Table 7.1 Category 1: No analysis or treatment
Restrictions relating to health impact Do: Wash hands and arms well with soap after handling greywater. Use bathwater water and laundry rinse water only. Use all greywater within 24 hours of collection. Grow only non-food plants or food plants with crops that will be cooked before consumption. Use irrigation methods that minimise contact of greywater with above- ground plant parts. If using on lawns, avoid direct human contact for 8 hours after irrigation. If using on crops, stop irrigating with greywater 2 weeks before harvesting. Reduce volume of greywater per application if ponding occurs on surface of irrigated ground, or if water runs off the surface. Wash all crops well in soapy water after harvest and dry in sunlight. Peel and cook crops prior to consumption.. Restrictions for Category 1
Restrictions relating to health impact Do not: Do not use greywater falling in this category of use restrictions for any form of communal gardening. Do not use greywater if someone in the household has an infectious disease.
Restrictions relating to impacts on plant growth and yield Restrictions relating to soil and environmental deterioration Restrictions for Category 1
Greywater irrigation by a single household Communal greywater irrigation Is greywater irrigation feasible according to greywater generation rate? Does greywater comply with quality guidance for minimum analysis? Is greywater going to be treated? Does greywater after treatment comply with quality guidance for minimum analysis? Kitchen greywaterLaundry greywater Bath/shower/basin greywater Minimum of mulch filter to reduce levels of solids and of oil and grease ? Can be used for irrigation in accordance with restrictions R2, Table 7.2 Not recommended for irrigation use NY N Y Y N N Y N Y Minimum analysis of greywater to be performed Category 2: Minimum analysis
Category 2: Minimum analysis Same groups of restrictions as for Category 1, but less strict. For example: This greywater can be used for communal gardens
Greywater Quality: Guide to Greywater Constituents Minimum analysis Electrical Conductivity (EC) Sodium Adsorption Ratio (SAR) E. coli pH Full analysis Minimum analysis plus Boron Chemical Oxygen Demand (COD) Oil and grease Suspended solids Total inorganic nitrogen Total phosphorus
Greywater Quality: Mitigation of Greywater Quality Integrated mitigation practices (part of irrigation). Greywater treatment systems.
Greywater Quality: Mitigation of Greywater Quality Integrated mitigation practices: Irrigation method. Improvement of soil. Leaching (rinsing with water). Planting tolerant plants. Accepting smaller/fewer crops. Using greywater only when there is no rain.
Rural / semi- rural small plots eThekwini Municipality
Tower gardens - Rural villages From Crosby C. (2005). The Water Wheel, January/February 2005, 10-13. Greywater treatment systems: Examples
Greywater treatment: Mulch tower Buffalo City Municipality; UKZN pilot study
Greywater treatment: Resorption bed, infiltration zone Buffalo City Municipality; UKZN pilot study
The importance of people!! Greywater use works only if the people using it are committed to making it work. Commitment means: Greywater use holds value for the users. Users are involved from the beginning. Users are given the information and training to use the system properly. Users have somewhere to go with questions and problems.
Acknowledgements Funding Water Research Commission eThekwini Municipality National Research Foundation Stockholm Environment Institute Research partners Prof Neil Armitage and Mrs Kirsty Carden, UCT Students of School of Biological and Conservation Sciences (Life Sciences), UKZN Lumka Salukazana, Siobhan Jackson, Preshanthie Naicker, Graham Taylor