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Water management is an increasingly relevant topic. Climate change brings more frequent droughts and the need to use alternative water sources. Utilising wastewater is one way to reduce the consumption of drinking water as well as the production of wastewater. Additionally, thermal energy can be extracted from wastewater.
Grey water is wastewater that does not contain faeces or urine, i.e., water from sinks, showers, washing machines, etc. This water is only slightly contaminated, making its treatment neither complicated nor expensive. Grey water can be recycled within family or apartment buildings. Recycled grey water is called white water and has a wide range of uses not only in households. Recycling grey water can save up to 50% of total water consumption in a household, which is approximately 70 cubic meters of water annually, representing a financial saving of up to 7000 CZK.
So-called black water, or sewage wastewater from toilets, on the other hand, is not suitable for recycling and needs to be treated in wastewater treatment plants. Kitchen water, i.e., water from sinks and dishwashers, is considered borderline – its treatment is possible but more demanding than bathroom water.
There are many reasons to recycle grey water. Reusing wastewater will bring significant financial savings, with the return on investment estimated at 5-10 years. Recently, however, ecological motivation has taken precedence.
By recycling grey water, you conserve precious drinking water resources and reduce the amount of wastewater discharged, which is laboriously treated in already overburdened wastewater treatment plants. Using wastewater can also prevent supply issues and provide a source of utility water even in drought-affected regions, where water consumption is often strictly regulated.
Treated grey water can be used for garden irrigation.
Many new buildings already incorporate the use of wastewater and rainwater, and their treatment system is part of the project. However, recycling grey water can also be implemented in existing buildings and family homes, although additional costs should be anticipated. Environmental standards in construction are constantly rising, and the relevant regulations are becoming stricter, so it is expected that this will soon become a legal requirement.
Previously, state grants called Dešťovka were available for acquiring systems for collecting and using rainwater, as well as wastewater. Combined systems for treating rainwater and grey water were very common. This grant program has been discontinued and replaced by the New Green Savings grant program.
Grey water, after appropriate treatment (known as white water), can be used as utility water, particularly for flushing toilets, irrigation, and cleaning. Recycled water is not suitable for direct consumption, washing food, or dishes.
Extracting thermal energy from wastewater is not yet common in the Czech Republic, but the first existing projects demonstrate the effectiveness of this solution. Thermal energy can be extracted directly from the sewer network or locally within a building (including family homes).
Wastewater is naturally warmer and can, using a heat exchanger, preheat water in a hot water tank. Additionally, a heat pump can extract energy for heating buildings from wastewater.
The filtration and treatment system for grey water depends primarily on the source of the wastewater and the intended use of the recycled water. Water from personal hygiene and laundry is the least contaminated and therefore does not require such thorough treatment.
Kitchen water (from sinks and dishwashers) is contaminated with organic food residues and fats, leading to a higher risk of biological contamination and bacterial growth. In this case, it is necessary to choose more effective water treatment methods.
Wastewater from the bathroom is minimally contaminated.
Grey water from personal hygiene can be used without filtration and treatment, but only for garden irrigation and within 24 hours. You need not worry about cosmetic product residues, as they must not contain anything harmful to the environment or health.
Grey water treatment involves its disinfection and filtration. Biological cleaning, which filters and disinfects grey water, is very common. Water treated in this way can be stored and used in the household, for example, for flushing toilets and cleaning.
Grey water filtration: depending on the desired quality of the resulting white water, a filter with varying mesh fineness can be chosen. If the water is only to be used for irrigation or flushing, using a very fine mesh is unnecessary – this would unnecessarily lead to more frequent maintenance of the water filter.
Disinfection: water can be disinfected chemically using chlorine, ozone, or a UV lamp.
Biological cleaning using a membrane bioreactor: is the most effective; in this case, no home water filtration or disinfection is necessary, as the membrane bioreactor removes mechanical and biological contamination. This system, also known as a grey water treatment plant, is more expensive, but the water quality meets the requirements for personal hygiene, making its use much broader.
After treatment, white water is pumped from the tank into the utility water pipes using a pump. According to the law, this piping must not be connected in any way to the drinking water pipes, otherwise, you risk significant penalties. Connecting the pipes would endanger the entire drinking water source.
Using grey water is a highly effective way to reduce financial costs and the environmental burden of your home or business. Consider both nature and your wallet.
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