Greywater Reuse Options 
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GRS: Greywater Reuse Systems
There are three main systems which have been developed to enable people to re-direct greywater into reuse situations. The first system (Standard) allows greywater dispersal and reuse from the complete household, the second (Watersave Trench) permits wastewater from limited sources, such as from the laundry and/or bathroom, to be re-directed onto garden areas. These first two use trench systems and subsurface irrigation. Now there is also a third option, one of which is a Dripper system (Watersave Dripper). All these three systems are detailed below. GRS Standard System A typical trench is about 400 mm deep and 300 mm wide. It is filled with stone and capped with a layer of sand as shown in the diagram below. Other configurations are also possible. For example, the trench can be shallower, but this would mean that the trench system would be longer. Water is dispersed via draincoil, which is a flexible, perforated pipe. 
Figure 1. Typical layout of trench.
The total length of drain is calculated by the number of bedrooms/people in the house, the type of soil present on site and the drain configuration. Generally, clay soils require longer trenches, alternating drain systems only need half the length of non-alternating drains, and the drain length is proportional to the number of bedrooms. The length of the drain system is typically 40 to 50 m for an alternating system.
The greywater is initially passed into a settling (sedimentation) tank. This enables larger particles such as hair, lint, soap flakes and sand to settle at the bottom of the tank, thus preventing blockage of the pipe and/or soil as the greywater is dispersed through the infiltration field. GRS Watersave Trench System The Watersave Trench System is used for partial greywater reuse situations. Greywater from the laundry and/or bathroom is re-diverted into a settling tank (or through a filter) and then into a subsurface drain system. The length of the drains is typically 20 m. The drain shape and style are the same as before (Figure 1). Often, a greywater diverter is installed to enable wastewater to be directed into the existing sewer or septic pipe system should this be required. Watersave Dripper System The GRS Watersave Dripper System comprises four parts. Initially, greywater is diverted from the normal waste stream, then it passes through either a sedimentation tank or GRS Filter, into a pump chamber, and finally the wastewater is dispersed throughout an interconnecting subsurface dripper system. The sizing of the system is calculated from the expected daily greywater volume as listed in table 1.
Table 1. Daily Domestic Greywater Volumes
(Source: Public Health Department. Note: * A 1800L sedimentation tank is required for Greywater systems that include kitchen greywater unless otherwise approved by the Executive Director, Public Health)
Dripper System
(a) Pump tank After the greywater has been filtered or allowed to settle for a day or so in a concrete or polyethylene tank, it passes into a pump chamber or tank. This has to have at least 250 L capacity, but GRS suggests a larger tank to enable 400 to 600 L of wastewater to be pumped at any one time. This is the preferred watering regime for most plants; the garden beds get watered every few days rather than a small volume every day. A sump (submersible) pump with float switch, such as those produced by Davey, Onga, KWT or Grunfos, will be used. A water level warning device will be fitted to enable an audible signal to be heard if the pump should fail. A 240V power source may need to be installed nearby to operate the pump. 
Figure 1. Typical sump or submersible pump.
(b) Irrigation System
The recycled greywater will then be pumped to areas of the garden through standard irrigation pipe to a network of subsurface drippers. A standard in-line irrigation filter is also placed before the dripper system to remove any sand which may be inadvertently pumped from the tank. Drippers at typically set at 300 mm spacing and deliver 8 - 10 L/h. The typical area required for dripper irrigation is calculated by dividing the greywater volume by 10 L/m2/day. e.g. 100 L = 10 m2 of irrigation area. It is anticipated that several different garden beds can be watered by this method. A distribution valve can be used to shift water to different irrigation zones. A 100 mm layer of mulch is placed on top of the irrigation dripper pipe (see Figure 2). 
Figure 2. An example of dripper irrigation in a garden bed.
Dripline and Tank Setback Distances for Installation
Below ground greywater tanks must be a minimum of 1.2 metres from any boundary or building or structure. The setbacks for the dripper irrigation line is found in Table 2. All greywater irrigation systems (i.e. the dripper line) must achieve a minimum of 500 mm clearance above the highest seasonal groundwater level. The “Perth Groundwater Atlas” is available on the Waters and Rivers Commission website at www.wrc.wa.gov.au. The atlas enables an estimate to be made of the depth to groundwater beneath a property.
Table 2. Minimum Setback Distance
Source: Public Health Department. Note: Drip distance measured from pipework.
* Greywater may contain chemicals that can damage your house if discharged against the foundations.
** Only EDPH may vary this setback requirement. *** For description of Public Drinking Water Supply Areas (PDWSA) or wetland positioning contact WRC. Greywater systems within 100 metres of a Priority 1 Drinking Water Source Protection Areas must be approved by the WRC. |
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