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The re-use of grey water

With the correct recycling procedure, water can be used more than onceGrey water in use sign

In order to recycle it's necessary to treat the dirty water to replace:

  • Dissolved oxygen, to make it 'fresh'
  • Natural water bacteria, to stop it smelling

Note: To comply with the health regulations several authorities require that grey water be sterilized before it is discharged for re-use. Sewage water should never (domestically) be re-used as it will cause a health hazard.

What is grey water?

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Grey water is that which comes from the bath, shower, basins, laundry and/or kitchen sink. It is not to be confused with black water, which is sewage that comes from the toilet. Unlike black water, which is toxic and must be discarded and never treated for re-use, grey water can be recycled and used safely to:

  1. Irrigate your garden;
  2. Flush your toilets;
  3. Wash your yard; and
  4. Dampen down dusty approach roads near the house in country districts.

With the world's population exploding on the one hand and our access to water diminishing on the other, recycling water at home so you can use it again makes good common sense. In fact, with global weather patterns changing as a result of carbon emissions it's fast becoming a necessity. With our help you can recycle most of your 'dirty' water, enhance your garden and save on your water bill, too.

The BIO-SYSTEMS solution

BIO-SYSTEMS has developed the technology and a selection of products to effectively store and re-use grey water secure in the knowledge that it's safe for family and flowers.

1. Filtration. We supply a stainless steel filter that utilises re-usable/replaceable textile elements to remove hair, food particles and grit. These impurities can cause endless (and costly) trouble if they get into the irrigation jets or the valve seats of toilet cisterns. Conventional 'swimming pool' type filters are inadequate for this task.

GWA2. The BIO-SYSTEMS Grey Water Additive (GWA) is a blend of selected, natural, water-cleaning microbes supplied as a dry powder in a customized domestic pack. GWA is applied at a rate of a few grams per week to your grey water treatment tank where they build up a viable 'bio-mass' to degrade and remove most of the dissolved organic waste and emulsified fatty substances carried by and in the water. They also prevent anaerobic conditions, putrefaction and rotting; thereby controlling the formation of odour. The result is re-usable water that is relatively clean and does not smell.

Mazzei Airmix3. An AirMix Aeration Injector runs (almost silently) on either a submersible, or a surface-mounted 'well point' pump. The device, which is fitted to the delivery side of the pump, replaces the oxygen that is lost by heating. It does this by circulating the water over a pressure gradient, drawing in atmospheric air and entraining it into the effluent in micro-fine bubbles. These bubbles stimulate aerobic microbes and bacteria to proliferate, building the bio-mass. The AirMix Injector is usually fitted with a multi-valved manifold so that the device can be used as a transfer pump to move the treated water on to either a storage container or an irrigation spider.

Grey Water System4. Grey Water Bio-Aqua Kit. There is no one-size-fits-all with grey water system installations. This is because no two houses are identical. Most practical handymen or a local plumbing contractor can install Bio-Aqua kits, which are packed into a compact carton and usually posted for customer convenience. Bio-Aqua kits comprise of a stainless steel filter, a year's supply of GWA , microbial product, and a comprehensive manual. The client supplies his own pump, tanks, piping and fittings.


The processes involved

When water is heated, as about half of most wastewater has been (in the hot water cylinder, kettle or pan), the naturally dissolved oxygen is driven out. Gas expands faster than water when heated (note the bubbles on the inside of a saucepan before it starts to boil on the stove), so it follows that most wastewater is low in oxygen.

Due to natural phenomena, oxygen-deficient water is largely anaerobic and becomes 'stale' when stored. Although water from your cold taps contains dissolved oxygen, it is usually mixed with hot water that has gone through a heating process or has been boiled during food preparation. Sterility is caused by elevated temperatures, which destroy the latent benign bacteria essential for the degradation of organic wastes. This dirty water becomes stale and stinks.

Old laundry water is an ideal medium in which anaerobic bacteria flourish. With its depleted oxygen and typically high phosphate content (largely from incompletely expended washing detergents – especially sodium tri-poly-phosphate), it can have a high concentration of dissolved 'nutrients' and organic wastes – food for the microorganisms.

Grey water sign with tap

Anaerobic bacteria generate sulphide gasses, which are a principal cause of the infamous 'rotten egg', dirty drain odour that ultimately leads to acidic conditions and corrosion. When dissolved in water, sulphide gas forms sulphuric acid that will eventually eat away the internal walls of metal drain pipes, fittings, manhole covers, concrete benching and masonry. When irrigated onto vegetation, water in this state will progressively destroy plants as surely as industrially-generated acid rain. As a result, it is essential to ensure that stored wash water is treated so that it doesn't become damaging, stale and stinky.

Common grey water problems

  • Wash water that is stored becomes progressively anaerobic (due to residual aerobic bacterial activity that exponentionally depletes the dissolved oxygen). It is an ideal breeding medium for pathogenic bacteria that produce sulphide gasses.
  • Grey water that is not treated properly is 'fatty' and gives off an offensive odour (from the build up of dissolved anaerobic and sulphide gasses), especially when stored for a few days. It can smell really badly when irrigated out over vegetation.
  • Laundry, bath and kitchen sink wash water typically has a high fat content (from soaps, body and cooking fats), causing grey water to become slimy – not good for the grass!

Fast fact: The typical suburban family uses in the region of 140 litres of fresh, clean drinking water per person per day, a family of four uses 560 litres and with a guest or two, car wash etc. 600 litres of water per per day.

The good news is that it doesn’t all have to go to waste.
You can re-use most of this water in your garden without breaking the bank.


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