Text A. Sewage (wastewater). Types of sewage (wastewater).

UNIT 4

SEWAGE (WASTEWATER) TREATMENT AND SLUDGE DISPOSAL

READING MATERIAL

Ex. 1. Read the following international words and guess their meaning. Mind the stress. Prove that these words are international ones.

Model: Problem – проблема, задача, вопрос

Ex. 2. Match English and Russian equivalents.

Ex. 3. Read the text thoroughly and translate it into Russian in written form.

TEXT A. SEWAGE (WASTEWATER). TYPES OF SEWAGE (WASTEWATER).

Sewage is waste water that is created by residences, institutions, industrial enterprises and commercial establishments, and is conveyed and disposed of via sewers.

Wastewater is used water. Untreated wastewater in the underground pipes is badly contaminated and it can damage the environment and cause serious illnesses in humans. It needs to be made safe before sending it back into the environment. Wastewater is commonly treated at the sewage treatment plant (STP). Sewage treatment is essential to maintain clean aquatic environment, as well as people’s health and quality of life.

There are three types of wastewater (sewage): domestic sewage, industrial sewage, and storm sewage.

Domestic sewage carries used water from houses and apartments; it is also called sanitary sewage, residential sewage or household wastewater. Domestic sewage is slightly more than 99.9 percent pure water by weight. The rest, less than 0.1 percent, contains a wide variety of dissolved and suspended impurities. Although amounting to a very small fraction of the sewage by weight, the nature of these impurities and the large volumes of sewage in which they are carried make disposal of domestic wastewater a significant technical problem. The principal impurities are putrescible organic materials and plant nutrients, but domestic sewage is also very likely to contain pathogens (disease-causing microbes, bacteria, viruses) and parasitic worms. In addition to human wastes, raw sewage contains such substances as metals, dissolved gases, dirt particles, food fragments, oil and grease, soaps, detergents, bleaches, other cleaning agents, solvents, paint, pharmaceuticals, and cosmetics.

Sanitary sewage can be divided into two types: grey water (sullage, or wastewater from kitchen and bathroom sinks, baths, showers, washing machines, dishwashers, and laundry) and black water (wastewater from toilets). Black water is a health risk if not treated properly because it contains human waste. Grey water is a lesser health risk. The separation and draining of household waste into grey water and black water is becoming more common in the developed world (grey water is used for watering plants or recycled for flushing toilets).

Industrial sewage, also called industrialeffluent, is used water from manufacturing or chemical processes. Industrial wastewater usually contains specific and readily identifiable chemical compounds, depending on the nature of the industrial process. Process wastes from industries can include, for example, silver from photofinishing shops, solvents from dry-cleaning services, and inks and dyes from printing houses.

Pict. 1.

A Canadian harbor fouled with sewage

Storm sewage, or storm water, is runoff from precipitation that is collected in a system of pipes or open channels. As rainfall runs over rooftops, roads, parking lots and the surface of the ground, it may pick up various contaminants including suspended and dissolved solids, soil particles and other sediment, heavy metals, organic materials and compounds, animal waste, and oil and grease. Some level of treatment is required before storm water is discharged directly into waterways. Examples of treatment processes include sedimentation basins, wetlands, or vortex separators for removing coarse solids.