Household Greywater Reuse for Garden Irrigation in Perth (2004)
Submitted by: May-Le NgSupervisor: Dr. Carolyn Oldham
Australians are one of the highest water consumers per capita in the world, and approximately a quarter of Australia’s surface water management areas are nearing, or have exceeded, sustainable extraction limits. As the Western Australian population continues to grow, so too does the demand for water and the resulting pressures on current water resources. Individual households can contribute towards reducing water consumption and wastewater volumes by installing small greywater reuse systems and reusing household greywater for non-potable uses such as garden irrigation. The impact of greywater reuse on plants and soils is highly dependent upon site-specific characteristics such as plant species, soil type, and climate. An improved understanding of the effects of greywater reuse on the environment is required. This dissertation focuses on a local system in Perth and uses a combination of experimentation and modelling to determine whether the nutrients supplied by greywater irrigation alone are sufficient to sustain the growth of a family lawn, and whether these nutrients are available for uptake by the turf. A mass balance was carried out to determine the amount of nutrients flowing into and out of the lawn. The results showed that the nutrients supplied by the greywater are beneficial to the irrigated lawn but are not sufficient to sustain its growth. Consequently, the lawn requires the addition of fertiliser to supplement growth. The dissertation examines why greywater reuse for garden irrigation is not a widespread practice in Perth. Six possible barriers were identified, the most influential of these being the cost of installing and maintaining a greywater reuse system.
NTRODUCTION AND LITERATURE REVIEW
1.1. What is Grey Water?
Domestic sewage or wastewater is the amalgamation of two distinct flows. The first flow is known as blackwater and consists of all wastewater that contains gross faecal coliform contamination. The majority of blackwater is sourced from toilets but can also come from bidets and laundry water used to wash soiled diapers.
The other, more dominant flow is known as greywater (graywater or sullage). Greywater is the term given to all untreated household wastewater that has not been contaminated with toilet water and includes water sourced from hand basins, bathtubs and showers.
For the purpose of this study, greywater includes all household wastewater other than toilet and kitchen wastewater.
1.1.2. Typical Characteristics and Composition of Greywater
Siegrist (1977) states that greywater constitutes the following percentages of the total household wastewater load (the balance is sourced from blackwater):
- 63% of the BOD5
- 39% of the suspended solids
- 18% of the nitrogen
- 70% of the phosphorus
- 65% of the flowThe chemical, physical and biological characteristics of greywater vary from household to household and depend on the number of occupants and their practices. There are typically three streams of greywater, sourced from the kitchen, from the bathroom and from the laundry.
Wastewater originating from the bathroom makes up approximately 55% of the total greywater volume produced by a typical household in Western Australia (Department of Health 2002). Personal cleaning products, hair, lint, body fats, hair dyes, and oils often contaminate bathroom wastewater. Also present are some faecal contamination, bacteria and viruses.
Wastewater originating from the laundry makes up approximately 34% of the total greywater volume produced by a typical household in Western Australia (Department of Health 2002). The quality of laundry water depends on the cleanliness of the items washed. The wastewater typically contains cleaning agents, chemicals, nutrients, lint, oils and greases. Some faecal contamination, bacteria and viruses may also be present, especially if the water has been used to clean soiled napkins.
Wastewater originating from the kitchen makes up approximately 11% of the total greywater volume produced in a typical household in Western Australia (Department of Health 2002). Kitchen wastewater is heavily contaminated with food particles, cooking oils, grease, and cleaning products. Food particles, cooking oils and grease place heavier loads on greywater reuse systems, increasing filter maintenance requirements, and the potential for blockages in the system (Jeppesen & Solley 1994). The particles and fats can also block soil pores and decrease the efficiency of irrigation, as the microorganisms living in the soil cannot break them down easily.
The relatively low flow contribution that contains high concentrations of organic particulates, cooking oils and greases, detergents, and other cleaning agents that are difficult to treat and potentially detrimental to irrigated soils are the grounds on which this study, along with a number of others, bases the decision to exclude kitchen wastewater from the greywater stream (Prillwitz & Farwell 1995; Emmerson 1998; Allen & Pezzaniti 2001).
1.2. Why Reuse Greywater For Irrigation?
Approximately 80% of Australia is classified as semi-arid, making it the driest inhabited continent on Earth (ABS 2002). The dry nature of the land results in a low population density, with the majority of the population situated in higher rainfall areas on the southern parts of the continent (Anderson 1996). Australia’s low population density accounts for the apparent high volumes of
Introduction and Literature Review
available water per capita relative to many other countries (World Bank 2002). However, Australians are also one of the highest water consumers per capita in the world (Gleick 2000), and approximately a quarter of Australia’s surface water management areas are nearing, or have exceeded, sustainable extraction limits (ABS 2002).
Approximately 241 GL of scheme water is consumed within the Perth region each year (Loh & Peter 2003). Approximately 70% of Perth’s total scheme water demand is consumed by private residences, and, on average, over half of this water is used to water lawns and gardens (Loh & Peter 2003). This means that watering lawns and gardens accounts for over 90 GL of potable water use per year.
As the Western Australian population continues to grow, so too does the demand for water and the resulting pressures on current water resources. Consequently, the disposal of increasing volumes of wastewater is also becoming a significant environmental challenge. The concept of wastewater reuse has been present since cities were first constructed downstream of one another along major rivers. The rivers were originally used to supply water to communities and to carry away their wastewater, causing one city’s waste to become another’s source. For example, it has been said that water in the Rhine River has passed through eight people’s kidneys by the time it reaches the North Seas (Denlay & Dowsett 1994). However, the reuse of wastewater has not yet been thoroughly investigated as a public policy in Australia (Emmerson 1998).
Although large-scale municipal wastewater reuse has not been realised to its full potential in Australia, individual households can contribute towards reducing water consumption and wastewater volumes by installing small de-centralised greywater reuse systems (although both household blackwater and greywater have the potential for reuse, greywater is easier, more convenient, safer and faster to reuse (Emmerson 1998)). If every household in Perth began reusing their greywater for the irrigation of lawns and gardens, potentially 35% less scheme water would be used and require treatment and disposal each year. Based on statistics presented by Loh and Peter (2003), these savings could be in the order of around 175 litres per person per day.
An obvious consideration that follows such savings in water use and corresponding decreases in sewage volumes is the effects of these reduced volumes on the sewerage transport and treatment system. The capacity of the sewerage system must necessarily remain unchanged for the following reasons:
- the system is designed to allow for increased wet weather flows as well as decreased dry weather flows (Jeppesen & Solley 1994);
- greywater that is reused for irrigative purposes will be diverted straight to the sewer during wet weather when the vegetation does not require additional watering; and
- realistically, not all residences will employ greywater reuse systems for practical, economic, psychological, or other reasons.
- The Brisbane City Council (1988) conducted trials to gauge the effects of low flush toilet volumes on the performance of a sewer system. The study concluded that the low volumes were sufficient to provide a transport medium for the toilet waste, and that the flow reduction had not detrimental effects on the sewer. In addition, informal conversations with a number of employees of the Water Corporation have established that a decrease in flow volume is more likely to benefit the sewage treatment process through savings in energy, and money that would otherwise be spent on dewatering processes. Therefore, lower flows as a result of the implementation of household greywater reuse systems are not an issue of concern.