waste water ppt by shilpa

8/3/2019 Waste Water Ppt by Shilpa

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Major identified sources of waste in pulp & paper industry are from:

a) Separator

b) Washing tank

c) Bleaching stages

d) Paper machine

a) From separator:

The loosened cellulosic fibres from digester are separated fromblack liquor which is a waste product containing lignin , resin, non-cellulosic materials & unutilized chemicals in the digester.

b) From washing tank:

The separated cellulosic fibres are washed which produce wastewater known as brown stock wash.


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c) From bleaching tanks:

The washed cellulosic fibres are sent for bleaching in 3 stages, wherechlorine,caustic & hypochlorite are used in successive stages.

The waste produced from the first & last stages is light yellow in colour wherefrom the second stage is highly coloured .

d) From paper machine:

The bleached pulp is then sent for the paper mill where the final productpaper is produced. The drained water from this mill section often called as

white water forms the waste water which contains fine fibres, alum, talc etc.

besides those mentioned above , a small volume of waste water is alsoproduced when the bark is removed from the raw water & later is reduced tochips by wet process.


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Item Small mill Large mill

Produce 20 tonnes ofpaper/day

Produce 2000 tonnesof paper/day

Flow per day 330 m/tonne 222 m/tonne

Colour 7800 units

Ph 8.28.5 8.59.5

Total solids, mg/l 4410

Suspended solids, mg/l 9002000 3300

C.O.D., mg/l 3400

5780 716

B.O.D., mg/l 6801250 155

COD/BOD ratio 3.95 4.6

CHARACTERISTICS OF COMBINED EFFLUENT OF PULP &PAPER MILLS


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The treatment of waste may consist of all or a combination of some of thefollowing processes:

a) Treatment for recovery

b) Physical treatment

c) Chemical treatmentd) Biological treatment

e) Lagooning

f) Land treatmant method

g) Disposal of the waste by irrigation


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Following are generally adoptedrecoveries:

(1) Chemical recovery (from black liquor)

(2) Lime recovery (from lime mud)

(3) Fine fibres recovery (from white liquor)


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(1)Chemical Recovery:

- The black liquor from the separator is concentrated by evaporation.

- Then its incinerated with addition of sodium sulphate.

- The organics like lignin, resin etc., are burnt out & the smelt is

dissolved in water.

- The resulting liquor is known as GREEN LIQUOR .

- Lime is now added ,resulting in the formation of WHITE LIQUOR

& LIME MUD .

-Thus, the obtained white liquor is sent for use in digester.


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(2) LIME RECOVERY:

- The lime mud obtained contains chiefly calcium

carbonate.

- It is then calcined to form calcium oxide , which

is reused to recaustic other green liquors into

white liquors.

-This is not practiced in INDIA due to undesirable

content of silica in it.


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(3) FIBRES RECOVERY:

- The fibres are recovered either by sedimentation or by floatation

using force in the tank.

-Some very toxic waste material are also generated during the

process.

Chemical recovery from black liquor toxicmaterial like dimethyl sulphide, methyl

mercaptan etc., also comes out with digesterrelief gases , & forms a colour-less waste waterafter condensation.


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It is required to separate the suspended matter by phsical operations like

# Sedimentation

# Floatation

-Mechanically cleaned circular clarifiers remove 70-80% of suspended

solids.

-About 95-99% removal of settleable solids can be accomplished in the

clarifiers.-BOD reduction is 25-40% only.

- The primary sludge produced in the clarifiers can be thickened to a

consistency that can be easily dewatered mechanically.


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- MASSIVE LIME TREATMENT process , developed by the nationalcouncil for stream improvement in USA is said to be capable ofremoving 90% of colour & 40 to 60% of BOD from waste.

-Entire quantity of lime is first reacted with the colour waste effluent.

-Colour is absorbed by lime & sludge after settling is used inrecausticising.

-This results in the formation of dark brown liquor containing lignin, etc.

-This liquor is used as digester liquid, & then is destroyed along with

fresh lignin in subsequent operations of concentration & incineration

in the process of chemical recovery.


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# Acidic activated carbon can remove 94% colourfrom the

pulp mill waste .(Observed by NEERI)

# pH of the waste required to be reduced to 3.0before the

treatment.


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Considerable reduction of BOD can be accomplished in bothconventional & low cost biological treatment.

Some are also effective in reduction of colour.

If sufficient area is available, the wastestabilization ponds offer the cheapest means.

Depth of pond-0.9-1.5m & Detention period -12to 30 days.

85% of BOD is removed with a loading rate

upto 56kg/hectare/day.


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These are the improved forms of the stabilization ponds,adopted to upgrade the performance.

The mechanical surface aerators are the mostsatisfactory oxygen transfer device.

BOD reduction of 50-95% can be achieved by varyingnutrients feed, air supply & detention time , at a loading rateof 670-1340 kg/hectare/day.

Nitrogen & Phosphorus are to be added into lagoons inthe form of urea or ammonia & phosphoric acid in BOD:N:Pratio of 100:5:1 as the pulp & paper mill waste does notcontain necessary nutrients.

Segregated strong waste or combined wastes may be

well treated in anaerobic lagoons with a loading rate of0.048 kg/m3/day & detention period of 20 days is adequateto remove 72.5% of BOD.

77.5% removal is reported at a detention time of 6-8 days& loading of 0.017kg BOD/m3/day.


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It is the most satisfactory & sophisticated process for effluenttreatment.

Instead of porous diffusers , the surface aerators are often

suggested.

80-90% removal is reported with a loading rate of 0.2-0.3 kg ofBOD / kg of MLSS at a detention time of 3-9 hrs, MLSSconcentration of 2000-4000 mg/l, recirculation ratio of 0.3-0.5.

Trickling filter has got a limited use in the treatment, due to

greater chances of clogging of media with fibrous material.

Trickling system is also incapable to provide a high degree oftreatment.


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When black liquor is not treated separately for chemicalrecovery ,it must

Be segregated from the other wastes & stored in alagoon .

The content may be discharged into stream under

favourable conditions inMonsoon.


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# Some type of soil is capable of removing colour from

the waste.

# The waste is stored & allowed to be absorbed in such

a soil.

# The capability of soil in removing depends on cation

exchange capacity of the soil.

# In addition, soil should be suuficiently permeable to

accept the entire volume of the waste.


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The pulp mill effluent may be utilized for irrigation.

No adverse effect on crops are reported for crops likemaize, paddy, jowar & kenaf.

Yield almost identical to that with conventional irrigation

practices is reported for wheat & sugarcane.


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waste water ppt by shilpa

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