污水的生物处理过程外文文献翻译、中英文翻译

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附录Ⅰ：

Wastewater Biological Treatment Processes

The objective of wastewater treatment is to reduce the concentration of specific

pollutants

to the level at which the discharge of the effluent will not adversely affect the

environment or pose a health threat. Moreover , reduction of these constituents need

only be to some required level.

For any given wastewater in a specific location , the degree and type of treatment

are variables that require engineering decisions . often the degree of treatment

depends on the assimilative capacity of the receiving water . DO sag curves can

indicate how much BOD must be removed from wastewater so that the DO of

receiving water is not depressed too far . The amount of BOD that must be removed is

an effluent standard and dictates in large part the type of wastewater treatment

required .

To facilitate the discussion of wastewater , assume a “ typical wastewater ”and

assume further that the effluent from this wastewater treatment must meet the

following effluent standards :

BOD≤15mg/L

SS≤15mg/L

P≤1mg/L

Additional effluent standard could have been established , but for illustrative

purposes we consider only these three . The treatment system selected to achieve

these effluent standards includes

1. Primary treatment : physical processes that nonhomogenizable solids and

homogenize the remaining effluent .

2. Secondary treatment : biological process that remove most of the biochemical

demand for oxyen .

3. Tertiary treatment : physical , biological , and chemical processes to remove

nutrients like phosphorus and inorganic pollutants , to deodorize and decolorize

effluent water , and to carry out further oxidation .

Primary treatment

The most objectionable aspect of discharging raw sewage into watercourses is

the floating material . Thus screen were the first form of wastewater treatment used by

communities , and they are used today as the first step in treatment plants .Typical

screens consist of a series bars that might be about 2.5 cm apart . A screen in a modern

treatment plant removes might damage equipment or hinder further treatment . in

some older treatment plants are cleaned by hand , but mechanical cleaning equipment

is used in almost all new plants . The cleaning rakes are activated when screens get

sufficiently clogged to raise the water level in front of the bars .

In many plants , the second treatment step is a comminutor , a circular grinder

designed to grind the solids coming through the screen into pieces about 0.3 cm or

less in diameter .

The third treatment step is the removal of grit or sand from the wastewater . Grit

and sand can damage equipment like pumps and flow meters and must be removed .

The most common grit chamber is a wide place in the channel where the flow is

slowed enough to allow the dense grit to settle out . Sand is about 2.5 times dense

than most organic solids and thus settles much faster . The objective of a grit chamber

is to remove sang and grit without removing organic material .Organic material must

be treated further in the plant , but the separated sand may be used as fill without

additional treatment .

Most wastewater treatment plants have a settling tank after the grit chamber , to

settle out as much material as possible . Accordingly , the retention time is long and

turbulence is kept to a minimum .

The solids settle to the bottom of the tank and are removed though a pipe , while

the clarified liquid escapes over a V-notch weir that distributes the liquid discharge

equally all the way around a tank . Settling tanks are also called sedimentation tank or

clarifiers . The settling tank that immediately follows screening and grit removal is

called the primary clarifier . The solids that drop to the bottom of a primary clarifier

are removed as raw sludge .

Raw sludge generally has a powerfully unpleasant odor , is full of pathogenic ,

and is wet , three characteristics that make its disposal difficult . It must be stabilized

to retard further decomposition and dewatered for ease of disposal .

The objective of primary treatment is the removal of solids , although some BOD

is removed as a consequence of the removal of decomposable solids .

A substantial fraction of the solids has been removed , as well as some BOD is a

little P , as a consequence of the removal of raw sludge . After primary treatment the

wastewater may move on to secondary treatment .

Secondary Treatment

Water leaving the primary clarifier has not lose much of the solid organic matter

but still contains high-energy molecules that decompose by microbial action , creating

BOD . The demand for oxygen must be reduce (energy wasted ) or else the discharge

may create unacceptable condition in the receiving waters . The objective of

secondary treatment is to remove BOD , where the objective of primary treatment is

to remove solids .

The trickling filter consists of a filter bed of fist-sized rocks or corrugated plastic

blocks over which the waste is trickled . The name is something of a misnomer since

no filtration takes place . A very active biological growth forms on the rocks , and

these organisms obtain their food from the waste stream dipping through the rock

bed . Air either is forced through the rocks or circulates automatically because of the

difference between the air temperature in the bed and ambient temperatures . Trickling

filters use a rotating arm that moves under its own power , like a lawn sprinkler ,

distributing the waste evenly over the entire bed . often the flow is recirculated and a

higher degree of treatment attained .

Trickling filtration was a well-established treatment system at the beginning of

the twentieth century . in 1914 , a pilot plant was built for a different system that

bubbled air through free-floating aerobic microorganisms , a process which became

known as the activated sludge system . The activated sludge process differs from

trickling filtration in that the microorganisms are suspended in the liquid .

An activated sludge system includes a tank full of waste liquid from the primary

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摘要：

附录Ⅰ：WastewaterBiologicalTreatmentProcessesTheobjectiveofwastewatertreatmentistoreducetheconcentrationofspecificpollutantstothelevelatwhichthedischargeoftheeffluentwillnotadverselyaffecttheenvironmentorposeahealththreat.Moreover,reductionoftheseconstituentsneedonlybetosomerequiredlevel.Foranygivenwas...

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