Effective and Responsible Grey Water Irrigation

EFFECTIVE AND RESPONSIBLE GREY WATER IRRIGATION

Dr Wendy van Dok 23rd November 2013

Garden irrigation is where significant improvements can still be made in terms of water use. For example by:

using plant stress sensing technology to schedule irrigation understanding soil permeability and applying water at a rate that enables the wetting front to reach the required depth using alternatives to mains water like grey, storm and tank water.

What is grey water and can you access it?

Domestic grey water is basically any used household water not contaminated by sewage. Sewage from the toilet is known as black water. Sometimes kitchen effluent is classed as black water because of the high grease and oil content and because dishwasher detergents are generally quite caustic and the effluent quite hot, all of which makes it unsuitable for garden irrigation.

Table 1 provides a very general comparison of the quality of wastewater from different rooms. It will vary widely from house to house.

To irrigate the garden with grey water, first you need to be able to access it from the drains outside. If you can’t, it will most likely be very difficult and cost prohibitive.

There are several different approaches you can take depending on whether the dwelling is sewered or not, how large an area of garden you wish to irrigate, how much grey water you generate, how much you want to spend on equipment, whether the grey water drains are higher than the garden so you can use gravity and the soil type and landscape features.

Effective and responsible grey water irrigation © Dr Wendy van Dok November 2013 1

Table 1 A relative comparison of wastewater quality from different rooms Grey water Black water

Washing mach. Bathroom Kitchen Toilet Nutrients eg nitrogen low-med low unless high very high & phosphorus urine included Pathogens low low-med low very high Solid organic matter low-med low-med high very high eg hair and lint Salt eg sodium low-very high low low low Fats, oils and grease low low-med high low Chemicals eg bleach, low-med low-high low–high low-high pharmaceuticals Suitability for direct Good if suitable Good if coarse Unsuitable Unsuitable garden irrigation detergents are filter used for unless unless treated used hair and degreased through an suitable first and the onsite products are dishwasher treatment used effluent is not system eg included septic tank

Chemicals in grey water Everything, including us, is made of chemicals. So it is not ‘chemicals’ per se that is a potential problem when using grey water. It depends on which ones are in the greywater, and that depends on habits, the products you use and medications people take. It is much easier to avoid problems by choosing appropriate products rather than trying to remove them by treating grey water. Of course some things can’t be avoided and so sometimes it is useful to keep at least one drain connected to the sewer so you can dispose of unsuitable grey water there.

In terms of grey water quality and its suitability for the garden, salinity is perhaps one of the most important and easiest problems to avoid.

Salinity is a measure of the total dissolved salts in a solution. It can be expressed as a concentration of salts e.g. milligram/litre (mg/L) or parts per million (ppm) or as conductivity i.e. salt solutions conduct electricity, which is expressed as micro Siemens/cm (µS/cm), deci Siemens/m (dS/m) or EC units.

1 dS/m = 1000 µS/cm = 1,000 EC units = 640ppm = 640 mg/L

The main salt in ‘salty’ grey water coming from the washing machine is sodium. Sodium is needed by plants and soil organisms but too much can cause problems, particularly in clay soil where an excess can reduce soil drainage. Powdered detergents generally have more salt than liquid detergents, partly because of the sodium based fillers that are used to keep powders flowing freely. An excellent resource for information about the salinity, or more specifically the sodium concentration of a wide range of laundry detergents can be found at www.lanfaxlabs.com.au.

The tolerance of soil and plants to sodium will vary widely and so the best strategy is to use a detergent with as little sodium as possible. Actually, the ratio of sodium to calcium and

Effective and responsible grey water irrigation © Dr Wendy van Dok November 2013 2 magnesium is more important than the concentration of sodium alone. The laboratory test for determining this is known as the sodium absorption ratio or SAR.

Table 2 Salinity of different types of water Salinity pH Alkalinity Phosphorus µS/cm mg CaCO3/L mg P/L Taste threshold for salty water 500 Powder detergents 350-1,900 8-10 110-1,190 0.3-29 (range of 3) wash cycle only Soap detergent 100 8 82 < 0.05 wash cycle only Liquid detergent 140 7.1 24 0 Wash cycle only Melb. tap water 50 6.5 12 < 0.05 River Murray at Murray Bridge 580-1,230 in SA-1997 Sea water 50,000-70,000 6-8 Recycled water, ex Eastern 938-1,053 7.6 Treatment Plant 2006 Levels in grey water 300-800 # 6-7.5 0-120# Depends recommended for irrigation on plants

# these ranges are based on the following publications 1. 1995 Farm water supplies-planning and installation. Neil Southorn, Inkata Press 2. 1991 Guidelines for wastewater irrigation. EPA Publication 168. 3. 1995 Physical and chemical quality of drinking water. Vic’n Dep’t of Cons. & Nat. Res. 4. 1999 Growing media for ornamental plants and turf. K. Handreck & N. Black. UNSW Press.

Of course some plants will tolerate more salt but higher levels would need to be flushed from the soil regularly to avoid residual problems like sodicity, especially with clay soil.

Measuring the salinity of a soil extract i.e. EC1:5 to ECe Soil samples can be measured by the '1:5' w/v method. That is, one part dried soil by weight (g) to five parts by volume (ml) distilled water. One mL of distilled water weighs 1 g. Shake the solution, allow to settle and measure the EC of the water not the sediment. ECe or saturated extract gives a more robust measure of salinity in relation to plant growth because it takes soil texture into account. Table 3 provides the estimated conversion figures.

Table 3 Conversion factors from EC1:5 (w/v) to ECe Source: http://vro.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/soil_mgmt_subsoil_pdf/$FILE/BCG_ subsoils_09_ch04.pdf Soil texture Multiply EC1:5 Example (w/v) by: sand 12.5 EC1:5 100, i.e. 100 µS/m = 120 ECe sandy loam 10 loam 8 clay loam 8 light/medium clay 7 heavy clay 6 EC1:5 100, i.e. 100 µS/m = 600 ECe

Other chemicals Other chemicals and products to be mindful of in grey water include aluminium in deodorants and some cleaners, fluoride in toothpaste, boron in cleaners, enzymes in cleaners, preservatives in some cleaners and personal hygiene products, surfactants in detergents and nutrients like nitrogen and phosphorus, the latter of which is often used in washing powders. Whether any of these chemicals cause harm in the garden is often only a matter of concentration so always use products sparingly and try to avoid them if possible. Especially try to avoid harsh caustic or acidic cleaning products, or at least dilute them.

Pathogens in grey water Pathogens are mostly microscopic organisms that cause disease and include viruses, bacteria, protozoa (e.g. Giardia) and Helminths (parsitic worms). Many diseases potentially can be transmitted in human waste, vomit and secretions, either as aerosol, by ingestion or by direct surface contact. Grey water generally contains some human excreta from clothes and body washing. The organisms of most concern come from faeces not urine. Urine from a healthy person is sterile.

Whether someone becomes infected by a pathogen though depends on many factors, like the amount of pathogen present, exposure time, how good the organism is at infecting humans i.e. how virulent, and how immune suppressed a person is. The presence of a pathogen only creates the potential for disease transmission it does not necessarily mean a disease will be transmitted.

Soil permeability Indicative soil permeability is the estimated rate at which clean water percolates through the soil. It will vary greatly and can range from 3 metres/day (m/d) for sand to 0.6 m/day for clay and so it is important to understand your soil texture before irrigating with grey water.

The most effective and efficient way to irrigate is to apply it at a rate that prevents runoff, does not waterlog the soil and allows the wetting front to go down far enough so that plant roots can actually use it. Quick bursts of water from a hose or bucket usually result in very shallow irrigation and shallow rooted plants as a consequence. Obviously the wetting front won’t need to go down as far for groundcovers as for large trees. You could invest in a simple wetting front detector like the Full Stop, or use the grey water for a day and see how far down it goes with a spade or post hole digger. Obviously the permeability rate will slow as the soil becomes wetter and wetter and as more grey water is used.

For more specific information about how to apply wastewater to land, e.g. design irrigation rates, refer to AS/NZS 1547:2012 On-site Domestic Wastewater Management.

Table 4 Summary of good grey water practices

Good grey water practices Why Laundry Choose low sodium and Reduces the potential damage to phosphorus-free detergents plant, soil and soil organisms Filter out course matter like hair and Prevents blockages in the irrigation lint. New washing machines may system have an inbuilt filter Recommended doses of detergent This will reduce the chemical load on packaging are sometimes higher and save money than necessary so try using less Avoid nappies, vomit or any other Faeces has a high concentration of wash water with a high faecal human pathogens and vomit may content also Bathroom Only use tepid water Hot water can damage plants and soil Avoid disinfectants, bleach, hair dye, Anything that can kill harmful acid, and drain cleaners. For any bacteria inside can potentially kill cleaning product, use it sparingly beneficial soil bacteria Kitchen Allow chlorinated water to stand Chlorine can damage plants overnight so that the chlorine can dissipate into air Avoid effluent from the dishwasher Detergents are usually very caustic (high pH) and the water hot, both of which can harm plants and soil If you want to use greasy kitchen Grease and oil can damage soil sink water, use a grease trap first. structure and make it water repellent Collect cleaner rinse water in a basin and allow greasy wash water to discharge to the sewer Grey water in Don’t store untreated grey water, Under warm stagnant conditions general and if a surge tank is used to microorganisms will proliferate and temporarily hold the water while it increase the risk of spreading flows out through a hose, allow air to disease as well as create a bad get into the tank, even aerate it with odour a simple aquarium pump if possible, and keep the tank out of the hot sun Leave at least one drain connected You will have somewhere to dispose to the sewer of any grey water not suitable for the garden Use liquid hand soaps rather than This will reduce the amount of fat in cakes of soap grey water which is better for the soil Avoid spraying the edible parts of Avoids the likelihood of ingesting fruit and vegetables with grey water pathogens Wear rubber gloves and wash your The reduces the risk of accidentally hands after handling grey water ingesting any pathogens Set up more than one distribution Moving grey water around the outlet e.g. aggie pipes garden will help minimise waterlogging and other potential soil problems from chemicals