Современные проблемы промышленного и гражданского строительства на занятиях английского языка. Кузьмина Е.В. - 50 стр.

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TEXT D. THE CONTINUOUS COUNTERCURRENT FILTRATION

SYSTEM

The continuous countercurrent filtration system includes chemical

precipitation and coagulation directly followed by filtration through a filter bed.

The basic principle involved is continuous countercurrent filtration through a

moving sand bed.

Chemicals are added directly to the influent wastewater line. Precipitation

and coagulation occur in the head tank. The dosage of chemicals can be varied

depending on the nature of the waste to be treated and the quality of effluent

desired.

The filter medium, which could be other than sand, is contained in a

tubular shell (called a bed) and is driven in one direction while the wastewater

being treated passes through the filter bed in the opposite direction. The

filtering action occurs through the depth of the bed as well as at its face.

Filtered water flows out of the bed through discharge screens located on the

side of the bed. The sand and solids filtered out of the water are pushed by a

hydraulic diaphragm toward the head tank countercurrent to the flow of water.

The solids are removed from the face of the filter bed by a mechanical face

cutter. After the diaphragm pushes the bed forward, it relaxes, thus allowing

clean sand to fall into the space vacated by the relaxing diaphragm. The

frequency with which the sand push-face cutting cycle occurs is varied to

optimize flow rate and effluent quality and is controlled automatically by the

level in the head tank.

The sludge-sand mixture mechanically removed from the filtering face

falls down into the hopper bottom of the head tank. This mixture is transferred

to a washing column for cleaning. The clean sand is then returned by gravity to

the hopper. The removal and washing of the sand may be intermittent or

continuous. Final washing of the sand is accomplished by means of filtered

effluent. Because the sand is removed, cleaned, and then returned to the system,

the filtration process is not interrupted for backwashing as it is in conventional

practice. The waste wash water flows into a settling tank where the sludge is