To understand the difference between sewage treatment and greywater treatment plants, we first have to understand what greywater actually is. Greywater can be defined as domestic water produced, excluding the sewage. Sewage water, also known as Blackwater, has a high organic loading which means it is rich in organic matter. But greywater, on the other hand, doesn’t contain any organic matter. Both greywater and Blackwater have different levels of contamination and are supposed to be kept separately in different tanks as the treatment methods of both are different.
Greywater is the wastewater that comes from sinks, washing machines, bathtubs, etc. These contain lower levels of organic contamination and can be treated easily. People are now slowly waking up to the benefits of greywater re-use. Greywater can be directly used to water plants in the garden as long as it doesn’t contain harmful chemicals from soaps and detergents. Recycled greywater can be used for irrigation in farms or in constructed wetlands. Greywater from the sink is a great source of nutrients as it contains food particles. This can be used to water plants and can provide them the necessary nourishment. Use of greywater can help in reducing the need for freshwater as the greywater can be used for laundry and toilet flushing. This helps in reducing the water bills of the households.
Greywater Treatment Plant
Greywater contains lower levels of contamination than blackwater so, its treatment is quite easy when compared to the treatment of sewage. The untreated greywater can be directly used to water the flower beds in the gardens. If left untreated for too long, there will be bacterial growth that can harm the plants. It is not recommended to water trees or shrubs that bear fruits and vegetables with untreated greywater as it can contain harmful chemicals from soaps and detergents.
There are various processes of treating greywater depending on what you want to use it for:
Sand filter method
Sand filter method is pretty basic and is used to remove any large particles in the water. The greywater enters through the top portion of a sand filter and then gravity does the work. The water comes out of the bottom with all the large particles removed. It then passes through a soil-box that has four layers. The four layers consist of humus rich top-soil, building sand, coarse sand, and finally pea shingles. The water is pushed down the top layer and most of the filtration takes place in the first layer itself. It travels down via gravity and comes down the last layer, purified.
Greywater which contains food debris is supposed to be treated anaerobically in septic tanks. Septic tanks clear the contamination and then the water that comes out of the septic tanks can be treated with soilbox as mentioned above.
Recycled water can meet a variety of water supply needs and can make an enormous impact in water sensitive areas.
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