Lesson 7

Water purification (II)

1. Mind the pronunciation of the words below.

flocculation ["flOkju'leiSn], coagulation [kqu"xgiu'leISn], anthracite ['xnTrqsait], agent ['eiGqnt], hydroxide ['haidrOksaid], hydroxychloride [haI'drOksI'klOraId], synthetic [sin'Tetik], molecular [mq'lekjulq], incident ['insidqnt].

2. Remember the following words and word combinations.

flock – хлопья

flocculation – флоккуляция, хлопьеобразование

coagulation – коагуляция (процесс осаждения взвешенных примесей с помощью химических веществ – коагулянтов)

clarify – осветлять, отстаивать

turbidity – мутность

precipitate – осадок

stir – взбалтывать, перемешивать

stick together – сцепляться, прилипать друг к другу

insoluble – нерастворимый

coarse – крупный (песок)

impact – воздействие

handle – пользоваться, иметь дело

sedimentation - basin = setting basin – отстойник

clarifier – отстойник

tank – танк, резервуар, ёмкость

exit – покидать

break up – распад, расщепление

outward – наружу, наружный, внешний

outflow – вытекание

weir – водослив

dispose of – удалять

sludge – ил

operating cost – эксплуатационные расходы

3. Watch out!

close to – близко, а не закрывать

ready – готовый, но: readily - легко

incident – случай, происшествие, не только инцидент.

4. Translate the following pairs of verbs. Remember the meaning of “mis” – «неправильно».

understand – misunderstand;

handle – mishandle;

inform – misinform;

judge – misjudge;

lead – mislead;

interpret – misinterpret;

hear – mishear;

use – misuse

5. Define the parts of speech:

coagulant – coagulation – coagulated; clarify –clarification – clarifier; precipitate – precipitation; absorb – absorption; soluble – insoluble – solution - solvent; treat – treatment – untreated; molecule – molecular; artificial – artificially; organic – inorganic; sediment – sedimentation; type – typical – typically; depend – dependent – dependence; remove – removal; clean – cleaned - cleaning.

6. Text.

Flocculation is a process which clarifies the water. Clarifying means removing any turbidity or colour so that the water is clear and colourless. Clarification is done by causing a precipitate to form in the water which can be removed using simple physical methods. Initially the precipitate forms as very small particles but as the water is gently stirred, these particles stick together to form bigger particles - this process is sometimes called flocculation. When a coagulant is added to the water the coagulated precipitate takes most of the suspended matter out of the water and is then filtered off, generally by passing the mixture through a coarse sand filter or sometimes through a mixture of sand and granulated anthracite Coagulants or flocculating agents that may be used include:

1. Iron hydroxide. This is formed by adding a solution of an iron compound such as iron chloride to pre-treated water with a pH of 7 or greater. Iron hydroxide is extremely insoluble and forms even at a pH as low as 7

2. Aluminium hydroxide is also widely used as the flocculating precipitate although there have been concerns about possible health impacts and mishandling led to a severe poisoning incident in 1988 at Camelford in south-west UK when the coagulant was introduced directly into the holding reservoir of treated water.

3. Aluminium hydroxychloride is an artificially produced polymer and is one of a class of synthetic polymers that are now widely used. These polymers have a high molecular weight and form very stable and readily removed flock but tend to be more expensive in use compared to inorganic materials.

Sedimentation. Water exiting the flocculation basin may enter the sedimentation basin, also called a clarifier or settling basin. It is a large tank with slow flow, allowing flock to settle to the bottom. The sedimentation basin is best located close to the flocculation basin so the transit between does not permit settlement or flock break up. Sedimentation basins can be in the shape of a rectangle, where water flows from end to end, or circular where flow is from the centre outward. Sedimentation basin outflow is typically over a weir so only a thin top layer - furthest from the sediment - exits. The amount of flock that settles out of the water is dependent on the time the water spends in the basin and the depth of the basin. The retention time of the water must therefore be balanced against the cost of a larger basin. The minimum clarifier retention time is normally 4 hours. A deep basin will allow more flock to settle out than a shallow basin. This is because large particles settle faster than smaller ones, so large particles bump into and integrate smaller particles as they settle. In effect, large particles sweep vertically though the basin and clean out smaller particles on their way to the bottom.
As particles settle to the bottom of the basin a layer of sludge is formed on the floor of the tank. This layer of sludge must be removed and treated. The amount of sludge that is generated is significant, often 3%-5% of the total volume of water that is treated. The cost of treating and disposing of the sludge can be a significant part of the operating cost of a water treatment plant. The tank may be equipped with mechanical cleaning devices that continually clean the bottom of the tank or the tank can be taken out of service when the bottom needs to be cleaned.

Notes:

1. the holding reservoir of treated water – резервуар чистой воды, (дословно: накопительный резервуар обработанной воды)

2. the retention time of the water – время пребывания воды (в отстойнике)

3. balance against – сопоставлять

4. sweep – зд. быстро двигаться

5. take out of service – приостановить эксплуатацию.

7. Match synonyms.

1. normally a. bottom

2. clarifier b. flocculating agent

3. floor c. very

4. remove d. sediment

5. coagulant e. untreated water

6. extremely f. generally

7. precipitate g. near

8. raw water h. settling basin

9. in effect i. dispose of

10. close to j. as a result

8. Make up a plan of the text and retell the text according to it.

9. Translate the text in the written form.

Suspended and dissolved impurities present in naturally occurring water make it unsuitable for many purposes. Objectionable organic and inorganic materials are removed by such methods as screening and sedimentation to eliminate suspended materials; treatment with such compounds as activated carbon to remove tastes and odours; filtration; and chlorination to kill infective microorganisms.

In aeration, or the saturation of water with air, water is brought into contact with air in such a manner as to produce maximum diffusion, usually by spraying water into the air in fountains. Aeration removes odours and taste caused by the decomposition of organic matter, and also industrial wastes such as phenols and volatile gases such as chlorine. It also converts dissolved iron and manganese compounds into insoluble hydrated oxides of the metals which may then be readily settled out.

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