Wastewater is water used for household, technical or other needs and contaminated with various impurities that have changed their initial chemical composition and physical properties, as well as water flowing from the territory of settlements and industrial enterprises as a result of precipitation or street watering.
Wastewater is divided into domestic, atmospheric (storm) and industrial. Domestic wastewater is formed as a result of human life, have a relatively constant composition (contain about 60% organic and about 40% minerals) and are usually sent to urban (district) treatment plants. Atmospheric wastewater is generated as a result of the flow of precipitation from certain territories directly into water bodies or into storm sewer systems. The composition of these waters can be extremely diverse. They may contain solid particles (sand, stone, shavings, dust, soot, plant debris, etc.), petroleum products (oils, gasoline, kerosene, etc.), fertilizers, etc. At some watercourses, atmospheric wastewater makes up about 30% and more than all wastewater entering them. Industrial wastewater is generated during various technological processes. At the same time, about 90% of the water taken for production needs is returned back to water bodies with various degrees of pollution. The main pollutants are mechanical suspensions (sand, scale, metal shavings, dust, fluxes, cotton fibers, etc.), mineral oils and other petroleum products, inorganic acids and their salts, alkalis and inorganic salts of heavy metals.
Wastewater poses a particular risk to human health, as it is sometimes contaminated with heavy metals (mercury, lead, cadmium, copper, zinc), as well as nitrogen, phosphorus and potassium compounds, which can cause severe poisoning. Often these waters are a source of the spread of serious infectious diseases (typhoid fever, cholera, dysentery, Botkin’s disease, polio, etc.). In addition to dangerous microorganisms, they can contain eggs and worm larvae. Wastewater containing radioactive substances is very dangerous.