Contaminant Concentration Reduction

8/2/2019 Contaminant Concentration Reduction

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CONTAMINANTCONCENTRATION

REDUCTION


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INTRODUCTION

Contaminant concentration reduction refers to reductionof pollutants in wastewater stream.

Contaminant concentration reduction

reduces requirements for waste treatment system

will be well rewarded by the savings, on account of lowerrequirements of land, equipment and energy.


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INTRODUCTION

The strength of wastes can be reduced by:

Process Changes;

Equipment Modifications;

Segregation of Wastes;

Equalization of Wastes;

By-product Recovery;

Proportioning Wastes; and Monitoring Waste Streams.


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PROCESS CHANGES

Process changes may result in reducedenvironmental pollution load

Textile Industry

Starch had been traditionally used as a sizing agentbefore weaving.

This starch, after removal from the finished cloth, is thesource of 3050% of the mills total oxygen-demandingmatter.

The cellulosic sizing agents, exhibits little or nobiochemical oxygen demand (BOD) or toxic effect instreams.


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PROCESS CHANGES

Coal Mining Waste

Acid mine waste (Mine drainage waste)

Waste from coal washeries

wash raw coal with acid mine waste rather than apublic or private water supply.

The mine drainage waste is neutralized while thecoal is washed clean of impurities.

The initial mine water had a pH of 3, and an iron contentof 551 ppm.

The wastewater finally discharged from the process hada pH of 6.77.1 and an iron content of less than 1 ppm.


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EQUIPMENT MODIFICATIONS

Changes in equipment can reduce the strength ofthe waste, by reducing the amount of pollutantsentering the waste stream.

Pickle factories screens placed over drain lines prevent the escape of

seeds and pieces of vegetables, which adds to thestrength and density of the waste.

Poultry plants traps on the discharge pipeline prevent emission of

feathers and pieces of fat. change the production procedure to dry-collect as

much waste material as possible from manufacturingmachines and operating floors rather than hosingdown the same matter into drains.


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EQUIPMENT MODIFICATIONS

Dairy industry.

Trebler (1944) redesigned the milk cans with smooth necksso that they could be drained faster and completely.

This prevented a large amount of milk waste from entering

streams and sewage plants.

Dairy farmers also installed drip pans to collect milk thatdrains from the cans after they have been emptied


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SEGREGATIONOF WASTES

Segregation of wastes reduces the strength of thefinal waste from an industrial plant. It usually resultsin two wastes: one strong and small in volume, can then be handled

with methods specific to the problem it presents; the other weaker, with large volume.

The two stream can then be treated collectively.

Another type of segregation is the removal of oneparticular process waste from the other processwastes of an industrial plant, which renders themajor part of the waste more amenable totreatment


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Textile Industry

The combined waste of a textile mill would be quite strong,difficult and expensive to treat.

However, when the kiering waste was segregated from the

other wastes, chemically neutralized, precipitated, andsettled.

The supernatant could be treated along with the other threewastes, because the strength of the resulting mixture wasconsiderably less than that of the original combined waste.

GrayWater

WhiteWater

Dye Waste Kier Waste

OxygenConsumedin ppm

1560 31 556 4900


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Metal-finishing plants

The wastes contains both chromium and cyanide, aswell as other metals.

It is necessary to segregate the cyanide-bearing

wastes, make them alkaline, and oxidize them. The chromium wastes, have to be acidified and

reduced.

The two effluents can then be combined andprecipitated in an alkaline solution to remove the metals.

Without segregation, poisonous hydrogen cyanide gaswould develop as a result of acidification.


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Poultry plant

the blood from the killing room floor interfere with thetreatment of the remainder of the chicken waste.

Nemerow and Dasgupta (1991) recommended

the blood be scraped, swept, and disposed of with thescreenings.

In this way, a high BOD waste was segregated from theremaining plant process waste and treated separately.


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EQUALIZATIONOFWASTES

It is dangerous, to arrive at a blanket conclusionthat segregation of strong or dangerous wastes isalways desirable.

Just the reverse technique

Complete Equalization

may be necessary in certain circumstances.


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Equalization requires holding wastes for a certainperiod, depending on the time taken for the repetitiveprocesses in the plant.

The effluent from an equalization basin is much more

consistent in its characteristics than each separateinfluent to that same basin.

Equalization offers

Stabilization of pH and BOD and settling of solids and heavy

metals

Stable effluents are treated easily and efficiently.

Sometimes equalization may produce an effluent thatwarrants no further treatment.


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Salt in large quantities is used to cure cucumbers

into pickles.

The large volume of salt brine waste can causedisproportionate objectionable effects whendischarged into a receiving water.

Holding the brine wastes in large vats for slowdischarge with the remaining plant waste over longperiods would minimize the salt effect.


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A textile-finishing mill that discharges its waste intoa domestic secondary sewage-treatment plantwould upset the efficiency of the plant due tofluctuations, primarily in pH and BOD.

An equalization basin capable of detaining thewaste long enough to reduce the fluctuations in pHand BOD.


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In addition, the equalized waste can be delivered tothe treatment plant at three different rates of flow:

the highest flow rate corresponded to the time when thegreatest amount of sewage was reaching the plant, and

vice versa.

This will give a more constant dilution of the mills

waste with domestic sewage.


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BY-PRODUCT RECOVERY

By-product recovery is the idealistic aspect of industrial-wastetreatment, that may lead to economic gain.

The low percentage of successful by-products developed fromwaste salvage may dissuade management. However, any use of

waste materials obviously eliminates at least some of the waste some wastes are very difficult to treat at low cost, Under such

circumstances, possibility of building a recovery plant will producea marketable by-product while solving a troublesome wasteproblem.

Both economic considerations and compliance with therequirements of pollution abatement play a major role in anydecisions involving by-product recovery.


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BY-PRODUCT RECOVERY

Metal-plating industries use ion exchangers torecover phosphoric acid, copper, nickel, andchromium from plating solutions. The de-ionizedwater, without any further treatment, is ideal for

boiler-feed requirements.

Paper mills, with the aid of multiple-effectevaporators, recover caustic soda from cookingliquors.

Chemical plants spray dilute waste acids into hot,brick-faced towers to concentrate the acids forreuse.


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BY-PRODUCT RECOVERY

Once a by-product is developed and put intoproduction, it is difficult to identify the new productwith a waste-treatment process.

For example, when sugar is extracted from sugar cane, a

thick syrupy liquid known as blackstrap molasses is left.

This molasses used to be so cheap that it was almostgiven away.

Today, it has many uses, with one of the best-known being

in the production of commercial alcohol.


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PROPORTIONING WASTES

By proportioning its discharge of concentrated wastesinto the main sewer, a plant can often reduce thestrength of its total waste to the point at which it willneed a minimum of final treatment or will cause the

least damage to the stream or treatment plant.

It may prove less costly to proportion one small butconcentrated waste into the main flow, according tothe rate of the main flow, than to equalize the entire

waste of the plant in order to reduce the strength.

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Contaminant Concentration Reduction

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