Waste water treatment

1.Memorise the following technical words:

activated sludge – активный ил

aerate – аэрировать

bar screen – грохот, решетка

clarifier – осветлитель, отстойник

digester – септиктенк,

effluent – выпуск, фильтрат

expose – подвергать воздействию

grit chamber – песколовка,

landfill – мусорная свалка, захоронение отходов

primary clarifier – первичный отстойник

rake –скребок, скребковый механизм отстойника

scum - пена, пленка

secondary clarifier – вторичный отстойник

solid processing facility – оборудование для переработки твердых отходов

2.Read and translate the text.

Before wastewater can be released into the environment, it is treated in a wastewater treatment plant.

Pumping. Wastewater treatment facilities are usually located on low ground so that gravity will move sewage from homes to the treatment plant. Usually, pumps are needed to lift the sewage as it enters the treatment facility. The treatment facility uses gravity to move the wastewater through the treatment process.

Bar screen. As it enters the treatment plant, wastewater may contain large items such as plastic bottles, cans, sticks, rocks, and even dead animals. These items are removed by the bar screen and sent to a landfill. If they are not removed, they will damage equipment in the treatment plant.

Grit chamber. After screening, wastewater enters the grit chamber in which larger particles (such as sand or dirt) settle out of the water. Often, the water is aerated (air is bubbled through it) to keep smaller particles from settling out. Aeration causes some of the gases that are dissolved in the water (e.g. hydrogen sulfide that smells like rotten eggs) to be released.

Sedimentation tank. In the sedimentation tank (also known as the primary clarifier), solids settle to the bottom as sludge and scum floats to the top. The sludge is pumped out of the primary clarifier and sent to the solids processing facility. The scum is composed of lighter materials such as grease, oil, soap, and so forth. Slow-moving rakes are used to collect the scum from the surface of the wastewater.

Secondary aeration and clarifier. The wastewater is exposed to air in an aerator, which provides oxygen for microorganisms that help break down contaminants in the water. This may be done by spraying the wastewater into the air or by bubbling air through the wastewater. The aerated effluent is passed into a secondary clarifier, which is a large tank or pond; in the clarifier, microorganisms decompose organic material and absorb nutrients such as nitrogen and phosphorus. The microorganisms and remaining solids settle out of the effluent as activated sludge. Most of the activated sludge is pumped to the solids processing facility, while the remaining sludge is pumped into the wastewater entering the aerator. This introduces additional microorganisms to the wastewater to hasten the breakdown of organic matter.

Filtration. Filtration may be used to further reduce the organic matter in the water. The water is filtered through a substance, usually sand and rocks. During this filtration process, most bacteria are removed, turbidity and color in the wastewater are reduced, odors are removed, the amount of iron content in the wastewater is reduced, and any other solids that may have remained in the water are also removed. This water may subsequently be filtered again through a carbon filter such as charcoal to remove organic particles.

Disinfection. To kill remaining harmful bacteria and other pathogens in the processed wastewater, chlorine and other chemicals are added in a disinfection tank. The chlorine can be harmful if added in excess quantities. Therefore, in some cases, the chlorine must be neutralized with other chemicals after it has killed the bacteria to protect marine organisms.

Solids processing. Solids include the sludge and scum removed in the sedimentation tank and the activated sludge removed from the secondary clarifier. These solids may be processed further in devices called digesters, which are heated and enclosed tanks. The solid wastes are kept in these tanks for 20–30 days to reduce the volume of the material, reduce odors, and also destroy any organisms that have the potential to cause disease. Depending on the source and composition of the wastewater, the digested solids are either sent to a landfill or used as fertilizer for crops. The use of the processed solid wastes as fertilizers is usually done only after careful testing for any potential dangerous contamination.

The treated water that is released by the plant is called effluent. The effluent is usually released into a local river or the ocean. In some places, this water may be used for landscaping (e.g. to water lawns or golf courses), but not for drinking purposes.

3.Answer the questions:

1. Wastewater treatment facilities are usually located on low ground. Why? 2. What is the function of a bar screen? 3. Why is wastewater aerated? 4. What can the processed solids be used for?

Text 4 (1900)