DOMESTIC WATERS: WHERE THEY COME FROM, COMPOSITION AND EXAMPLES - ENVIRONMENT - 2024

Domestic waters are those that are used in the home or family dwelling site and then discarded as waste or waste. As waste they are called sewage, sewage or domestic sewage.

The use of domestic water includes its direct intake or as part of food and beverages, as well as its use in personal hygiene. In the same way it is used in the laundry, cleaning of the household goods and infrastructure.

Domestic water. Source: Photo taken by de: Benutzer: Alex Anlicker using a Nikon Coolpix 950.

On average, more than 150 L / inhabitant-day are consumed, although according to the World Health Organization 50 L / inhabitant-day of domestic water is required. It is used for personal bathing, washing utensils, cleaning the floors, washing the car, watering the garden or diluting body waste.

Once used, it must be discarded and transformed into domestic wastewater, which carries a large amount of impurities. These domestic wastewaters are classified according to their origin as black water and gray water.

Sewage comes from toilet flushes and is made up of organic matter, especially feces, urine, and microorganisms. While gray water comes from personal hygiene, laundry and household hygiene.

Where does the domestic water come from?

Drinking water source. Source: Débora Samara

Domestic waters originally consist of raw water from natural sources such as deep wells, rivers, or lakes. They are subjected to purification that includes filtering, disinfection and the addition of certain substances to adapt it to the standards established for human consumption.

Of the water consumed, around 70 or 80% of the water consumed in the home is transformed into domestic wastewater. They are classified into two types according to their origin, which are black water and gray water.

The former are those generated in the evacuation of human physiological waste (feces, urine), while the latter cover the rest of wastewater.

- Black water

The largest volume of domestic water is used in the evacuation of human organic waste. On average 10,800 liters / person per year are spent on the toilet drain and the most efficient consume up to 6 liters while others use an average of 26 liters.

- Grey waters

Personal hygiene

Gray water from the shower. Source:

Another important source of domestic wastewater is personal hygiene operations, such as daily showering or washing, shaving, and hand washing. According to the World Health Organization, an average of 95 liters / person of water is consumed in a 5-minute shower.

Laundry

Doing laundry or washing clothes in a 7 kg capacity washing machine consumes between 42 and 62 liters of water.

Scrubbing household items

Scrubbing kitchen utensils generates a water consumption of between 50 and 100 liters per day, although if a dishwasher is used this consumption can be reduced to 10 or 18 liters per wash.

Washing of domestic infrastructure

Although it is difficult to quantify maintaining the hygiene of floors, windows and other parts of the home, it also generates significant water consumption.

Wash the car

Washing the car with a hose causes an enormous consumption of water, close to 500 liters. Whereas if it is carried out in a car wash it can be reduced from 100 to 300 liters.

Watering plants

Watering plants also generates domestic wastewater, but in a garden on land it is absorbed by the soil. In the case of potted plants, the surplus can become wastewater that ends up in the drain.

Composition

As an inflow, domestic water is drinkable, previously subjected to filtering processes, the application of ozone, ultraviolet radiation or the addition of chlorine. Once used, domestic water becomes contaminated with a large number of substances.

- Composition of drinking water

The composition of water for domestic consumption depends both on the source of the water and on the previous treatment it receives. In general, the water from underground sources have high mineral content, especially calcium.

Parameters to be met by domestic drinking water

Taking Spanish legislation as a reference, in drinking water there should be no presence of any type of microorganism. While in relation to present chemical components certain levels are accepted depending on the case.

For example, water can contain up to 10 µg / l of arsenic or 2 mg / L of copper and be safe for consumption. In general, water for human consumption can contain traces of numerous chemical elements, including nitrates, heavy metals and even traces of pesticides.

- Composition of domestic wastewater

Organic material

Black Waters. Source: Gonzalo De La Rosa

Faeces are the main organic component of domestic wastewater and they contain 90% carbohydrates as well as fatty acids, proteins and hydrocarbons. Human urine has urea as its main component, however, it decomposes quickly when discarded.

The toilet paper used, when it is flushed down the toilet, incorporates large amounts of cellulose and various chemicals. On the other hand, domestic drains also carry organic waste from food preparation.

These wastes incorporate plant and animal tissues and exudates into domestic wastewater. Washing floors and other parts of the house carries dust that incorporates remains of epidermal cells and hair.

Similarly, discarded domestic water carries traces of synthetic organic substances such as phenols, detergents, soaps and organic disinfectants.

Living organisms

The most abundant are coliforms, especially fecal coliforms, the most frequent being the bacterium Escherichia coli. Other genera of bacteria that are part of coliforms are Klebsiella, Enterobacter, and Citrobacter.

Other bacteria such as Salmonella typhi, Leptospira sp., Yersinia sp., Vibrio cholerae and Shigella sp. Are also found. As well as fungi such as Aspergillus fumigatus and Candida albicans, or viruses from the group of adenoviruses and rotaviruses.

Helminths are also common, including Ascaris lumbricoides, Fasciola hepatica, Taenia saginata, and Trichuris trichiura.

Polluting chemicals

Domestic wastewater contains, to a greater or lesser extent, various polluting chemical elements. Among these are mainly nitrogen (ammonia, nitrites, nitrates), chlorides, sulfates and surfactants (soaps, detergents).

They may also contain aluminum, arsenic, barium, cadmium, cyanide, copper, chromium, iron, mercury, silver, lead, selenium, and zinc. Other relevant contaminants in domestic wastewater are drugs, disinfectants, antibiotics, analgesics and others.

Examples

Domestic wastewater in the State of Mexico

Only about 20% of the municipalities in the State of Mexico have a domestic wastewater treatment system.

Saint Michael Almaya

It is an Otomí-Nahua indigenous town located in the Capulhuac municipality in Mexico, which has drifted towards tourism and commercial activity. The Almaya lagoon is located here, which faces serious pollution problems, especially due to the discharge of domestic wastewater.

This contamination has generated eutrophication problems in the lagoon due to the contributions of nitrates and phosphates. Around the lagoon there are seven houses whose drains are not connected to the communal collector and therefore are a source of contamination.

To remedy the problem, a pilot project was implemented based on separating black and gray water. The gray water is led to a settling tank where air and ozone are injected.

These waters are reused for toilets, washing floors, cars and other purposes, to later be treated as sewage. For its part, the sewage is led to a solids trap, then to an anaerobic biodigester and air and ozone are injected.

Uncontrolled discharges of domestic wastewater

One of the biggest problems of contamination of bodies of water in Colombia is due to the uncontrolled discharges of domestic wastewater. In many cases, despite the existence of septic tanks, the sewage ends up leaking into rivers and groundwater.

Case of the La Macana creek

In the town of San Antonio de Prado in the municipality of Medellín is the La Macana stream basin. This basin presents problems of deterioration and environmental contamination, among these the contamination of the waters of the stream.

The main problem is the discharge of domestic wastewater into the stream, generating pollution, especially by total coliforms. The organic load supplied by domestic water discharges is 2,120 g / day, where 62% come from homes with a septic tank and 38% are direct discharges.

References

1. Birks, R. and Hills, S. (2007). Characterization of indicator organisms and pathogens in domestic graywater for recycling. Environmental Monitoring and Assessment.
2. Díaz-Cuenca, E., Alavarado-Granados, AR and Camacho-Calzada, KE (2012). Treatment of domestic wastewater for sustainable local development: the case of the unitary system of water, nutrient and energy treatment (SUTRANE) technique in San Miguel Almaya, Mexico. Quivera.
3. Hidalgo-Santana, M. and Mejía-Álvarez, E. (2010). Diagnosis of contamination by domestic wastewater, lower basin of the La Macana creek, San Antonio de Prado. Municipality of Medellín. Applied research monograph to qualify for the title of Specialists in Environmental Management. Faculty of Engineering, University of Antioquia.
4. Howard, G. And Bartram, J. (2003). Domestic Water Quantity, Service Level and Health. World Health Organization.
5. Ministry of Economic Development (2000). Technical regulation of the drinking water and basic sanitation sector RAS - 2000. Section II, title E. Wastewater treatment. Directorate of Drinking Water and Basic Sanitation. Colombia.
6. Nuñez, L., Molinari, C., Paz, M., Tornello, C., Mantovano, J. and Moretton, J. (2014). Analysis of sanitary risk in gray waters of the province of Buenos Aires, Argentina. International Journal of Environmental Pollution.
7. Raffo-Leca, E. and Ruiz-Lizama, E. (2014). Characterization of wastewater and biochemical oxygen demand. Journal of the Faculty of Industrial Engineering.