Gray water recovery systems
Introduction
Gray water or used water is the term used for water that comes from domestic use, such as washing utensils and clothes, as well as bathing people.
They differ from sewage that results from human intervention, where its natural composition is altered, for example, with excrement, organic or chemical materials that are usually discharged through the sewage system and that cannot be reused due to their content of bacteria, such as Escherichia coli, Campylobacter jejuni, Shigella, among others.
Currently, gray water is acquiring great importance because it can be very useful if it is reused for toilet flushing, washing patios, vehicles or others that do not involve direct consumption by people or animals. Its use is also becoming common in ecologically irrigated fields, especially in those locations affected by drought or resource shortages.
They generally decompose more quickly and have less nitrogen and phosphorus. However, it is not ruled out that the mixtures may contain some percentage of sewage, including pathogenic biological agents of various kinds.
The pioneers in its purification were the Israelis, who have been researching reuse systems for more than 20 years.
It should be noted that if they are not treated in some way, it is not recommended to reuse them, not even for flushing toilets, since they generate bad odors due to decomposition or stains if left for more than a day.[1].
Definition
Gray water owes its name to its cloudy appearance and its condition of being between fresh and potable water (known as white water) and wastewater (black water). In a family context, gray water is only the water left over from bathrooms, showers, sinks and washing machines. Some definitions of gray water include water from the kitchen sink. Any water that contains human feces is considered black water.
Gray water disposal
Domestic wastewater is often combined in sewers, so black and gray water are disposed of through a shared sewer system in a process called sewage drains.
Water coming from homes can then be treated to limit pollution and health risks, before being returned to the wider environment. Most gray water ends up as effluent in lagoons, rivers and oceans.