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Greywater purification in your house and how to use energy from it

Water management is an increasingly discussed topic. Climate change brings growing periods of drought and the need to use alternative water sources. Reusing wastewater is one of the ways to reduce your drinking water, but also wastewater production. In addition, thermal energy can be produced from wastewater.

What even is "greywater"?

Grey water is water from waste that does not contain faeces and urine, for example water from washbasins, showers, washing machines, etc. This water is only slightly polluted and its treatment is not complicated or expensive at all. Grey water can also be recycled within family or apartment houses. Recycled grey water is called white water and is widely used not only in the home. Recycling gray water can save up to 50% of your water consumption in the house, or about 70 cubic meters of water per year, which represents a financial saving of up to 300 EUR.

Black water or sewage water from toilets on the other hand is not suitable for recycling and must be treated in wastewater treatment plants. Kitchen water from sinks and dishwashers, is considered marginal - its treatment is possible, but it is more demanding than water from your bathroom.

Reasons to reuse greywater

There are many reasons for recycling gray water. Wastewater reuse will result in significant financial savings, the ROI is estimated at 5-10 years. Recently, however, ecological motivation has been playing a leading role.

By recycling gray water, you save precious sources of drinking water and reduce the amount of drained wastewater, which must be treated in the already overloaded wastewater treatment plants. Reusing wastewater can also prevent supply problems and thus have a source of service water even in drought-affected regions, where water consumption is often strictly regulated.

You can use the purified greywater to water your garden.  

Many new buildings already use wastewater and rainwater. However, gray water recycling is also not a problem to introduce into existing buildings and family houses, but it is necessary to take into account the additional costs. Environmental standards in the construction sector are constantly becoming more demanding and the relevant standards are being tightened.

How to use recycled white water

Grey water after appropriate treatment (white water) will serve as service water, especially for flushing toilets, watering and cleaning. Recycled white water is not suitable for direct consumption, washing food and dishes.

How to use thermal energy from grey water

Obtaining thermal energy from wastewater is not yet common, but the first existing projects show promising effectiveness of this solution. Thermal energy can be gained directly from the sewer network or locally in the building (including family houses).

Waste water is naturally warmer and can preheat the water in the DHW tank using a heat exchanger. In addition, a heat pump can be used to produce energy for heating buildings from wastewater.

How to purify grey water

Fltration system and treatment of grey water depends mainly on the source of wastewater and intended use of recycled water. Water from personal hygiene and washing is the least polluted and therefore does not require such thorough treatment.

Kitchen water (sinks and dishwashers) is contaminated with organic food residues and fat, which leads to a higher risk of organic contamination and bacterial growth. In this case, it is necessary to choose more efficient methods of water treatment.

Bathroom wastewater is minimally polluted.

Greywater from personal hygiene can be used without filtration and treatment, but only for watering your garden and within 24 hours at the latest. You do not have to worry about cosmetic residue, because it must contain nothing that would harm the environment or health.

Greywater treatment consists of disinfection and filtration. The so-called biological treatment, which filters and disinfects this water, is very common. Water treated in this way can also be stored and used at home, for example for flushing toilets and cleaning.

  • Grey water filtration: depending on the required water quality, a filter with different screen densities can be used. If the water is only used for watering or flushing, it is not necessary to use a very fine mesh - this would unnecessarily lead to the need for more frequent maintenance of the water filter.
  • Disinfection: water can be chemically disinfected using chlorine, ozone or a UV lamp.
  • Microbiological cleaning with a membrane bioreactor: is the most efficient, in this case no water filtration or disinfection is required, as the membrane bioreactor removes both mechanical and microbiological pathogens. This system, also known as a grey water purifier, is more expensive, but the water quality also meets the requirements for personal hygiene and its use is therefore much wider.

How to use white water

After treatment, white water is drawed from the tank into the service water pipeline. According to the law, you must not connect this pipeline to the drinking water pipeline in any way, otherwise you would face significant sanctions. By connecting the pipes, you would endanger the entire source of drinking water.

Grey water reusage is a very effective way to reduce costs and environmental impact of your home or business. Think of nature and your wallet.