paper n pulp

8/2/2019 Paper n Pulp

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REPORT

ON

PULP AND PAPER INDUSTRYWASTES AND ITS TREATMENT

SUBMITTED TO SUBMITTED BYMr. PAWAN KUMAR MANDAPAKA PRAMOD J (R080210023)

JIMMY ABU SAJAN (R080210015)RAJALESHMI SUBBIAH (R080210024)

ARPIT KHANNA (R080210007)


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S.N0. CONTENTS PAGE NO.

1 INTRODUCTION 3

2 SOURCES OF WASTE 5

3 PULPING PROCESSES 7

4 PULP PROCESSING 10

5 PAPER MAKING 11

6 AIR POLLUTION 13

7 WATER POLLUTION 16

8 SOLID WASTES 23

9 TREATMENT 28

10 COLOUR REMOVAL 40

11 MINAS 42

12 REFERENCES 43


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PULP AND PAPER INDUSTRY

INTRODUCTION :

Today pulp and paper industry in India is one of the largest industries due to tremendous

expansion during the last few decades.

Manfacture of paper from pulp is a water-intensive industry.

It involves:

(a)Conversion of raw material into pulp by digestion with various chemicals(b)Conversion of pulp into paper

A mill which carries out these functions under the same roof is called an Integrated mill.

Raw material used in this industry is mainly cellulose, which is obtained from wood, rags,old

paper,hemp,wheat and rice stalks, bamboo,esparto grass,bagasse etc.

Chemicals used in the pulpjng process are sodium hydroxide, sodium sulphate,calcium

bisulphite and sodium sulphite etc.

On the basis of the nature of the raw material, different pulping processes are used such as

mechanical, chemical ,semichemical etc.

Large and Small Paper Mills : There are small and big paper mills producing varieties of

paper for a number of uses from different types of raw materials. Printing, writing, kraft ,tissue,

currency, newsprint, packaging and wrapping straw and paperboards as well as bleached paper

are produced by this industry.

Primarily because of the constraints of large investments necessary for setting up of large

integrated pulp and paper mills, and the reduced availability of bamboo which is main raw

material for the paper industry in India, small scale paper mills have come up in recent years

utilisting agricultural residues besides waste paper, as raw material.


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This renewable resource which is claimed to be in abundance in several parts of the country,

stimulated the growth of small paper mills with capacities ranging between 3 and 3o tone per day

spread all over the country.All mills making upto 10,000 tonne per annum of paper,boards etc

are classified under small paper mills.

Based on the installed capacity, the paper mills are classified into 5 categories as shown below:

Category Capacity (TPA)

I 20000 +

II 1000020000

III 500010000

IV 20005000

V upto 2000

Categories I and II fall under large mills while the other three categories are termed small mills.

The Government of India is also encouraging entrepreneurs for setting up small paper mills

primarily based on agricultural residues. In turn, it saves the primary forest resources and

encourages regional development. In view of the small scale production and the inherent nature

of agricultural residues being poor in quality compared to forest wood or bamboo, there is a risk

of small paper mills not being competitive with the existing or new integrated large mills. To

promote unhindered growth of small paper mills, import of second hand machinery is permitted

and several concessions are given to the mills by the Government.


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SOURCES OF WASTES AND POLLUTION

Process of Manufacture :

Raw Materials: Conventional raw material for small paper industry is constituted of rice andwheat straw, bagasse, jute, cotton rags, different types of grasses, waste paper, purchased pulp

and occasionally gunny and hessian. All these have proved to be good for paper making and are

used by almost all the mills in various combinations. Composition of raw materials used in paper

industry is given in Table.

Composition of raw materials used in paper industry

Raw materials Cellulose Pentosan Lignin Alcohol

benzene

extractables

Ash Silica

(SiO2)

Bamboo 57.0 14.0 25 2.0 2.0 1-1.5

Rice straw 51.0 22.0 12 4.0 11.0 4-8

Bhutang grass 39.3 28.4 22.5 2.1 33.0 1.6

Khagre grass 36.5 29.0 23.3 4.4 2.7 0.9

Jute S tick) 56.0 20.0 21.0 1.0 2.0

Jute 70.0 15.0 11.0 1.0 3.0

Sial hemp 77.0 13.0 6.0 1.0 3.0

Bagasse 50.0 25.0 18.0 3.0 4.0 1-15

Sal 56.0 13.4 24.9 6.0 1.0

Salai 50.7 13.0 27.3 4.3 1.8 0.29

Casuarina 56.7 19.2 23.2 3.4 0.8

Pine 61.0 11.0 26.0 1.0 1.0 1-0.3

Eucalyptus 54.0 14.1 30.9 0.4 0.03


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Chemical Requirements :

Sodium hydroxide, lime chlorine, hypochlorite and sulphites are the normally used

chemicals in paper industry. Sodium hydroxide requirement essentially for agricultural residue

based industry varies with raw materials. About 5-10% of NaOH is required per tonne of raw

material. However when bagasse is used, the requirement for alkali would be as high as 12% of

the raw material used. Lime is used as supplement to NaOH. In board mills, only lime is used as

cooking chemical, Chlorine and calcium hypochlorinte are bleaching chemicals and are required

only when bleached products are made. The quantity used is highly varying and depends not

only on the raw material used but also on the final product made. Sizing chemicals such as alum,

starch, talc, rosin and acid are also used. Dyes are used for making coloured paper.

Water Requirements :

Paper industrys existence lies on water supply. All the process in paper making require

constant supply of water. Though paper machine water is recyled to a varying extent, total intake

of water per tonne of paper is very large. It is estimated that for an agricultural residue based

paper mill, for processing, the requirement is 200 to 350 cubic metre per tonne of paper made.

However, for units using waste paper, it varies from 100 to 150 cubic metre per tonne. Besides

water consumption for steam generation and domestic purpose is also to be accounted for

Quality tolerance for water in paper mills is given in Table.


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Quality tolerance for water in paper industry

Kraft

unbleached

paper

Kraft

bleached

paper

ISI Nordell TAPPI NCASI SIS Nordelt TAPPI

Colour 100@ 15 100 10-80 15 5 5

Turbidity 100@ 15 100 5-25 25 5 25

pH 6.5-8.0

Total Alkalinity

(CaCO3)

150 20-150 75

Hardness

(CaCO3)

200 200 5-200 100 100

Dissolved solids 500 50-500 250

Chloride 200 10-150 75

Iron 1.0 0.2 1.0 0.5 0.25 0.1 0.1

Manganese 0.5 0.1 0.5 0.3 0.1 0.05 0.05

COD 0-12

BOD 0-5

Total residual

chlorine

2.0

@ Colour as Hazen units and turbidity on silica scale. In other cases,these two are expressed

as units, standard colour units and mg/l, respectively.


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Pulping process in paper industry :

The main pulping processes that are normally employed in paper industry include :

(i) Chemical process

(ii) Chemo mechanical process

(iii) Mechanical process (hydro-pulping)

Chemical Process :

This involves digestion of raw material like agricultural residues gunny, jute etc at high

temperature and pressure in the presence of chemicals like sodium hydroxide and/ or lime.

Specially designed spherical digesters with capacity argound 25 cu m are employed for this

purpose. The rotary digester provides necessary mixing and efficient heating of the raw material.

Steam is used for heating. Steam pressure is maintained between 5 and 6 kg/cm 2. The

temperature of the digesting material will be around 1500C. About 1.21.5 tonne of steam are

required for each tonne of raw material digested. Chemicals are added in solution along with raw

material prior to cooking. Digestion time of 2.5 to 5 hours is provided for proper cooking. A ratio

of raw material to water of 1 to 3.3-4.0 is maintained before digestion starts.

Two processes are used :

(a)Kraft or Sulphate Process: The cellulosic materials after chipping to proper size arecooked in caustic soda, sodium sulphide mixture under temperature and pressure. This

process dissolves the fibre binding materials such as the lignins and loosens the cellulosic

fibres. The spent liquor known as black liquor is recovered for chemicals and the pulp is

washed and bleached before it is made into paper

(b) Sulphite Process: In the sulphite process the cooker liquor consists of calcium or

magnesium bisulphite and sulphurous acid. Where calcium salt is used the spent cooker

liquor is not utilised for recovery of chemicals.


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Chemo-mechanical pulping :

As the name suggests, the process makes use of both chemical and mechanical processes

in series. The raw material is soaked in 3-5% caustic soda solution at 900C for 15 to 30 minutes.

Acid sulphites are also employed as pulping chemical in a few cases. The soaked material is then

subjected to drastic mechanical treatment to separate fibres.

Mechanical Process :

For waste paper and recycled paper and recycled paper hydro-pulping is adopted

Hydropulping unit comprises of a high speed rotating disc which chops the paper to fibre in

presence of steam and moisture. The pulp yield is estimated to be 70-80%. Size of the hydro

pulper varies with the plant size.


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Pulp Processing

Pulp washing: Chemically digested pulp is discharged into a blow pit or on a perforated

floor where part of the black liquor (BL) also known as spent liquor drains out. In some mills thecooked materials is directly taken for washing in pouchers where washing is done by vacuum

rotary drum. The washing continues for 2-3 hours and is in series if more than one poucher is

used. The pulp wash is one of the major sources of wastewater besides black liquor. The drained

out black liquor joins the pulp wash water before leaving the unit. The wastewater leaving this

section is very strong initially and weak in final stages of washing.

Beater, centri-cleaner, thickener: Pulp from poucher is dumped to beater either directly

or through storing chest depending on the operation schedule. Pulp is beaten to separate fibres

and remove adhering dirt, chemicals and colour. Some mills employ washing along with beating

thus creating a source of wastewater. From beater, the pulp is screened and then taken to centri

cleaner for removal of heavy inorganic particles (mostly sand) It is then pumped to thickener

where water is sucked by rotary drums and discharged as wastewater. The pulp in this section

still contains some colour but can be used to make boards and unbleached paper.

Bleaching: The process is adopted in mills where bleached paper is produced. After

thickening the pulp is subjected to chlorination. Chlorine requirement is reported to be 120

kg/day, in a 2000 TPA plant but it generally varies with the type of raw material used. If straw is

the major raw material, the chlorine requirement will be high. After chlorination the pulp is

subjected to alkali extraction, only under special circumstances popularly known as caustic

extraction. This is followed by calcium hypochlorite treatment. Hypochlorite required is about

half the quantity of chlorine. The pulp is white and the yield is about 30-35% of raw material

used. These three steps together contribute bleach plant wastewater . In small mills, only calcium

hypochlorite or bleaching powder is used and the conventional steps are not usually followed.


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Paper Making:

Blending conditioning and stock preparation: Blending provides required pulp to

water ratio before sending it to the paper machine. Further conditioning by chemicals such asalum, rosin talc and acid to suit the requirements of final paper quality and addition of dyes to

make coloured paper are also adopted.

Paper Machine : This consists of a moving wire mesh and rotary driers. Steam is used in

driers to drive away moisture from the sheet of paper formed on the wire mesh and picked up by

the driers. The wastewater generated in this section is known as white water and is recycled in

the process to the extent of 80% for pulp washing in the poucher in most of the mills. Finished

product is cut to size and ready for marketing.

The moisture content of finished paper varies from 2-8% by weight with an average value

of 4.5%.

A generalized flow sheet adopted for making paper in small mills depicting sources of

wastes is given in Fig on next page.


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GENERALISED FLOW SHEET ADOPTED FOR MAKING PAPER IN SMALL MILLS

DEPICTING SOURCESD OF WASTES


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AIR POLLTION :

Air Pollution from Paper Plants;

Particulates: Predominantly chipper house pulp washing paper machine, caustic

extraction Chemical recovery power plant coal handling and disposal sections have various sizes

of particulate pollution to a considerable degree.

Apart from this certain mills have cyclones and electrostatics precipitator in the recovery

sections which reduces air pollution to the desired level.

Large sized particles are removed by setting as solid wastes and some times reused in the

process i.e. coal dust fine fibre etc.

Sulphur Dioxide: Sulphur compounds are used for working wood material for

manufacture of paper hence major pulping processes emit sulphur dioxide. Sulphur dioxide is

emitted at the blow tank, evaporators recovery furnance lime kiln sulphitation tower etc. In

addition sulpur dioxide emission stake place at the power boilers either under normal operation

or during periods of auxillary fuel operation.

It is estimated that about 35 to 50 ibs of sulphur bearing compounds are emitted per tonne

of pulp.

Sulphur dioxide pollution is mostly controlled by scrubbing sulphur dioxide through thesolution of alkali. Some items such as sulphur compounds are converted into sulphur and

recovered in developed countries.

Carbon Monoxide : Power plants in India are mostly based on coal. Coal-based power

plants invariably emit carbon monoxide. However carbon monoxide emissions depend upon type

of coal used and firing time required for the carbon monoxide. The pollution restricted to initial

firing hence generally no controlled by using bnetter quality of coal.

Methyl mercaptans, hydrogen sulphides, methyl sulphides, methyl suylphides methyl

disulphides are emitted in the recovery and evaporating and cooking sections. To a greater extent

these can be controlled by process control and control of gugitive emissions. Whereever air

pollution control equipments like scrubber or electrostatic precipitators are used most of these air

pollutants are kept at a low level. However much depends on good housekeeping.


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Chlorine. : Chlorine, chlorine dioxide and various compounds of chlorine are used for

bleaching pulp. During process of bleaching chlorine, always finds its way into the environment.

Wherever control equipment like exhaust and vacum cleaners are used considerable reduction of

chlorine pollution is achieved. Most of the mills do not have any control equipment for this.

However some mills have blowers which reduce chlorine level in the work room environment.

Chlorine control is also achieved by scrubbing chlorine through alkaline solution.

Cause : Air pollution is due to release of gaseous omissions into atmosphere, which occurs

mainly from two sources in small paper mills viz.

(i) Digesters.

(ii) Steam boilers.

The third source could be the captive power generation facilities provided in the mills.

In agricultural residue-based mills, after the raw material digestion with caustic soda and/or

lime is completed, the pressure in the digester is released after the digester attains a temperature

of about 900C. During the process about 1.4 tonnes of steam per tonne of pulp escape containing

volatile organics released during digestion process. The escaping gases have characteristics

odour and cause aesthetic pollution problemsThe pollution is mostly confined to the

sorroundings of the mill, intermittent due to batch process adopted and can be felt at the time of

digester gas release.

Coal is the commonly used fuel for generating steam required in all the small paper mills,

it is reported that about 3.4 tonnes of coal is required per tonne of paper made in agricultural

residue based mills and the corresponding coal requirement in waste paper based mills is 1.5

tonne per tonne of paper. In all these boilers coal lumps of 2.5-5.0 cm diameter are fired. Very

few boilers use powdered coal. Besides coal, paddy husk diesel oil, etc. are also used in a very

few mills. Indian coals are reported to contain 0.5-0.8% sulphur. Since the quantity of steam

generation is small the steam boilers are not provided with any air cleaning equipment in these

mills.


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WATER POLLUTION FROM PAPER MILLS

Wastewater Generation :

Sources of Wastewater : As identified earlier, in agricultural residue based units, the

wastewater is released from the following sections :

(i) Black liquor from cooking section.

(ii) Pulp wash water from pouchers.

(iii) Beater section specially when rags are used.

(iv) Bleaching section

(v) Thickener

(vi) Paper machine.

Waste paper based mills generate wastewaters from section iv, v, and vi only as no chemical

pulping adopted.

Blacking liquor is the most polluting among the different streams. Black liquor is not

segregated, and it ends up in pulp washing wastewater.

Thus pulp washing section contributes nearly 80% of the total pollution load.Further flow

and composition of pulp wash wastewater will be highly varying because the operations are

carried out in batches.

Only in a very few mills counter current washing using two stages is adopted. Paper machine

wastewater is least polluting among all the sections but contributes appreciable amounts of

suspended solids. In most of the mills, paper machine wastewater either as such or after fibre

recovery, is used in pulp washing beaters, etc..


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Water Pollution

Big Paper Mills : Considerable work has been carried out by the CPHERI on the characteristics

of various pulp and paper mill effluents. Extensive work on the volumes and characteristics ofeffluents from the different sections of a large pulp and paper mill has been worked out and the

flow and characteristics are given in table.

Characteristics of wastewater from pulp and paper mills

Chipper*

house

Digester

house

Pulp

washing

Chemical

recovery

Pulp

Bleaching

Paper

machine

Combine-

d waste

Flow

m3/tonne

20-60 5-10 20-40 @ 140-180 40-90 240-30

colour Muddy Dark

Brown

Dark

brown

Light

brown

Brown Whitish Brown

pH 6.4-8.0 9.0-10.0 8.5-9.6 7.0-9.0 6.0-9.0 5.3-8.1 6.5

Total

solids

540-900 1000-2500 1400-

2500

1270-

2800

2100-

2900

850-

1250

1200-

2000

Suspended

solids

240-520 140-190 350- 400-760 140-220 490- 350-

COD 175-450 1850- 220 900-

1700

320-610 550-790 520-

780

600-750

BOD 30-50 300-360 230-480 90-180 125-155 100-

160

110

* This represents conditions where bamboos are carried by water before chipping. Water is

sprinkled on the bamboo stacks before chipping the quantity of wastewater will be very

low (2-8 m3/tonne of paper) and the wastewater characteristics will be fairly high.


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Water Pollutants: The main pollution constituents in pulp and paper mill wastewater are

suspended solids, colour foam, inorganic such as sodium carbonate, bicarbonate chlorides and

sulphates toxic chemicals such as mercaptans and inorganic sulphides, mercury if caustic

chlorine plant forms a part of pulp and paper mills, BOD and COD.

The wastewater when discharged untreated will damage the water course and the colour

in water persists for a long distance since lignin is not readly biologically degraded As paper

industry being scattered all over the country, it may be said that no river is spared from pollution

due to the discharge of these wastewater.

Another important pollutant (that is yet to be assessed) in pulp and paper industry is

mercury. This is so because some of the mills make their own caustic and chlorine in mercury

cells and it has been reported that about 0.25 kg of mercury is lost per tonne of caustic made.

Further some organic mercury compounds such as phenyl mercuric acetate (50-100 ppm of dry

weight of pulp) methoxy ethyl mercury and pyridyl mercury salts are being used as slimicides on

paper machines which finally find their way into the effluent. In sweden it is reported that about

25 tonnes of mercury salts are used per annum.


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Small Paper Mill : The data given in previous Table indicate that the combined wastewater will

have alkaline pH with high BOD and COD values. The BOD load contributed per tonne of

unbleached paper will be 1.56 kg and this may go up to 160 kg if bleached paper is made. The

BOD load from small mills will be 3 times the pollution load discharged from bigger mills with

chemical recovery systems.

Similarly, the suspended solid concentration is 2120 mg/l of which 40% will be inorganic

solids (848 mg/l). The combined wastewater will not be fit for irrigation in view of high sodium

and BOD (780 mg/l) content. The wastewater requires treatment before it can be discharged into

water course.

Another objectional constituent will be lignin as it imparts colours and COD to the

receiving body of water (derived from pulping of straw and gunny or ropes). Normally 90-95%

of the lignin present in the straw is removed during digestion with caustic and this quantity ends

up in the pulp washing wastes. Assuming that on an average 90% of the lignin present (in straw

pulping along will be of the order of 3090 mg/l. Gunny, ropes and rags contain lower percentage

of lignin as compared to straw. Therefore the combined wastewater will have lignin

concentration in the range of 750 to 850 mg/l. The quantity of lignin alone will exert a COD of

1350 to 1530 mg/l.


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Characteristics of Effluents :

Waste paper and/or purchased pulp based mills the flow and characteristics of combined

wastewater indicate that although there is variation in the flow of the combined wastewater the

minimum and maximum values respectively are 0.6 and 1.5 times the average flow. There is also

variation in the characteristics of the wastewater and is mainly due to the different practices

adopted for fibre recovery and extent of recycle of both recovered fibre and water. On an average

for each tonne of paper made 107 28.4 cu.m of wastewater is generated containing 58 + 10.7 kg

of suspended solids 20 + 10.5 kg of BOD and 70 + 15.2 kg of COD respectively.

The proportion of agricultural residue to waste paper used varies appreciably in all the

agricultural residue and waste paper based mills. Even in the same mill, depending on the raw

material availability season, type of paper made, the proportions vary even within a week. Hence

wastewater flow and characteristics are found to vary. It is not possible to generalise the flow

and pollution loads contributed per tonne of paper made from these mills.

Since most of the small paper mills are located in agricultural areas and some of them are

using the combined wastewater for crop irrigation the SAR and per cent sodium values in the

combined wastewater are high in mills where unbleached paper is made using soda pulping.

Leaving a few high values the SAR ranged between 3.5 and 7.6. If the ratio of calcium to sodiumcan be increased in the combined wastewater from small paper mills, then it can be used fro

irrigation after suitable dilution to keep the total dissolved solids and BOD in the ranges

recommended for irrigation waters.

BOD rate constant for black liquor and combined wastewater after settling compares with

that of domestic wastewater. The non biodogradable fraction of COD is high and is mainly due

to the lignin in black liquor. In case of combined settled wastewater 70% of the

nonbiodegradable COD is due to lignin and the remaining due to suspended solids, etc. Hence it

can be concluded that the COD due to lignin cannot be removed even after biological treatment.

The only alternative method is to remove colour vis-a-vis lignin by chemical treatment.


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Standards for Discharge of Effluents : The choice of methods for treatment of wastewater

dpends on the quality requirements for final disposal. The treated effluent will have to be

discharged either into sewers, if available or surface waters. It can also be applied on land for

agricultural utilisation.

Pollution Control Boards have prescribed tolerance limits for industrial effluents for

discharge into the three above mentioned media. These are shown in table.

Tolerance limits for industrial effluent discharged

Inland surface

water

Municipal sewer Marine outfall

BOD 5 days at

200C

100(30) 500a 500

COD 250

pH 5.59.0 5.59.0 5.59.0

Suspended solids 100 600b

Total dissolved

solids (in organic)

2100* 2100

Temperature, 0C 48 45

Oil and grease 10 100 30

Phenolic

compounds

1.0 5.0

Cyanides 0.2 2.0

Sulphides 2.0

Fluorides 2.0

Total residual

chlorine

1.0

Insecticides Absent

Arsenic 0.2

Cadmium 2.0


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Chromium

(hexavalent)

0.1 2.0

Copper 3.6 3.0

Lead 0.1 1.0

Mercury 0.01

Nickel 3.00 2

Selenium 0.05

Zinc 5.0 15

Chlorides 600* 600

Boron 2* 2

Sulphates 1000* 1000

Per cent sodium 60 60

Ammoniacal

nitrogen (N)

50 50

Radioactive

materials

Alpha emitters/c 107 107 109

Beta emitters/c 106 106 108

a - Subject to relation or tightening by local authority.

b - Relaxable to 750 by the local authority.

* These requirements shall apply only where after treatment the sewage is disposed of land

for irrigation.


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SOLID WASTES :

Solid Waste : Tracing back to unit operations in paper manufacture following units have serious

problems of solid wastes disposal.

Chipper House : Wood is reduced in cutters to desirable size of 20mm to 23 mm here

during this process lot of floating settleable material results which can be easily recovered by

screening and grit chamber. Recovered material is dried and used as fuel/land filling.

Pulp Washing: During pulp washing in centri cleaners lot of undigested/digested pulp is

part of effluent. This can be recovered by inclined screen of suitable mesh size. This screen is

called side hill screen. Pulp thus recovered can be reused/redigested.

Flow Machine : Paper machine is the final stage of paper production where pulp along

with sizing material is dried and converted into desired shape, size and weight small fibres are

always escaping in paper machine effluent. Generally fibre is recovered by an all vibrating

screen. Recovered fibre is used for making paper and thus greater economy is achieved in paper

making.

Hypochlorite Preparation and Floor washing sludge, Caustic Chlorine : These threesections constitute a major solid waste problem for all paper mills. I am sludge has considerable

amount of silica hence burining of this lime sludge for recovery of lime is not techincally and

economically feasible. Moreover lime recovery is not practised because lime is cheap. Hence

lime is disposed off on land for filling up low lying areas. However efforts are being made for

economical burning of lime and alterantive use of lime as fertilizer etc.

Coal Ash : Indian coal contains 10 to 40% ash hence wherever coal is used as fule in the

power plants problem of coal ash disposal requires immediate attention. Some of the mills have

constructed type S shaped channels which carry coal ash along with treated effluent upto water

course where ultimately it is disposed off.


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Solid waste generation :

Solid wastes are generated from the following operations :

(i) Raw material handling

(ii) Rejects from screening and centri cleaners

(iii) Primary and secondary sludged from wastewater treatment system

(iv) Coal or boiler ash from steam generation.

Estimates for the solid waste generation are based on information given by the mills and the

data collected from various sources available.

Agricultural residue based mills :

(a) Raw material handling

(i) Rice and wheat straw @ 5-10% of raw material handled is lost as rejects.

Solid waste generated139278 kg/t paper

Average210 kg/t paper

(ii) Bagasse @ 1015% of raw material handled is lost as rejects.

Solid waste generated440660 kg/t paper

Average550 kg/t paper

(b) Primary and secondary treatment of wastewater

Suspended solids load in wastewater155 kg/t paper

BOD load in wastewater175 kg/t paper

(i) Primary setting @ 75% suspended solids removal

solids in Primary sludge 155 0.75

= 116.25 kgSay 116 kg/t paper

(ii) Biological solids generation @ 0.5 kg per kg BOD removed and 90% BOD

removal expected.

Excess biological solids 175 0-9 0.5

= 79 kg/t paper


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(iii) Suspended solids remaining in the primary clarified effluent going to secondary

biological treatment and assuming about 66% of them settle along with secondary

studge.

Solids in the sludge 39 0.66

= 25.7 kg/t paper

Sa 26 kg/t paper

Total primary and biological solids generation220 kg/t paper

(c) Steam generation

Ash content of Indian coal is approximately 40%

(i) Coal requirement for digesters for steam generation

1.82.0 t/t paper

(ii) Coal requirement for paper macine driers and also a small fraction for hydro

pulpers (for steam generation)

1.41.5 t/t paper

Total coal requirement 3.23.5 t/t paper

say 3.35 t/t paper

Coal or boiler ash generated 0.4 3.35 t/t paper

= 1.34 t/t paper

Say 1.3 t/t paper

Total solid waste generation

(i) Raw material handling

(a) Straw, jute, etc 210 kg/t paper

(b) Bagasse 550 kg/t paper

(ii) Primary clarification 116 kg/t paper

(iii) Secondary clarification including biological sludge

105 kg/t paper


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(iv) Coal or boiler ash 1300 kg/t paper

Total solid waste generated

(a) When straw, jute is used 1731 kg/t paper (25% organics)

(b) When bagasse is used 2071 kg/t paper (37% organics)

Waste paper Based Mills

(a) Raw Material handling

Waste paper @ 1-2% of raw material handled in lost as solid waste

Solid waste generated 46 kg/t paper

(b) Primary clarification

(i) Suspended solids in combined wastewater 58 kg/t paper

Primary setting80% suspended solids removal

58 0.8 = 46.4 kg/t paper say 46 kg/t paper

(ii) Secondary treatment utilises aerated lagoon or stabilisation pond and

hence there will be no sludge generation.

(c) Steam generation

Coal requirement 1.41.5 t/t paper

Coal or boiler ash 1.45 0.4 = 58 kg/t paper

Total solid waste generation

(i) Raw material handling 46 kg/t paper

(ii) Primary setting 46 kg/t paper

(iii) Boiler ash 58 kg/t paper

150 kg/t paper

(61% organic solids)


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Pollutional Effects

The pollutional effects of discharging waste water from a paper mill are:

1. Oxygen depletion in the receiving body of water2. Presence of undesirable colour, odour and taste in the water3. Reduced photosynthesis4. Formation of blanket of suspended solids settling at the bottom of the

receiving body of water

5. The death of fish6. Toxicity added to the aquatic life due to the formation of

mercaptans,pentachlorophenol etc.


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TREATMENT FOR THE WASTE WATER

5 Various unit operations in seewage treatment plant and their appicability for pulp and paper

mill effluent treatment.

Unit Applicability for treatment of pulp and papermill effluent

Screens- coarse screens the floating and coarse materials from chipper house and

pulp mill can be removed in this operation.

Grit chamber Useful for grit removal from chipper houses, floor

washings etc.

Primary settling tanks For removal of readily settleable solids such as fibre. For

efficient removal of suspended matter mechanically

scrapped clarifiers with or without addition of chemicals

should be employed. This treatment is the minimum

essential requirement before discharge of the effluent.

The settled sludge requires only dewatering before

disposal.

Biological treatment in the form

of trickling filter or activated

sludge followed by secondary

setting tank.

For biological treatment will require addition of N and P

(30D : N.P. as 1995:1)

Sludge disester Secondary sludge requires digestion before disposal.

Since its volume will be much less compared to the

primary sludge, the primary and secondary sludges can

be mixed together and simply lagooned or dewatered

without digestion. The primary and secondary sludge can

be dried before disposal. The land requirements will be

very high and hence mechanically dewatering is

preferable.

Sludge drying beds For drying and dewatering primary and secondary

sludges.


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Treatment for Mills Using Agricultural Residues as Raw materials : The unit

process involved in the treatment of wastewater from agricultural residue based paper mills are:

(i) Equalisation of flow from pulp wash section.

(ii) Primary clarification for combined wastewater

(iii) Secondary biological treatment.

(iv) Sludge drying beds or lagoons for primary sludge depedning on the availability

of land

Equalisation for Pulp Wash Wastewater : Pulp washing section accounts for about 20-

25% of total wastewater and contributes around 70-80% of pollution load from small paper

mills using agricultural residues as raw materials. These wastewaters are discharged

intermittently since in most of the mills. washing of pulp is done in batches using pouchers.

Normally two pouchers are employed and operated in series and this generate two washes.

The period of washing is more or less same in both but the quantity of water used varies

appreciably and thus the first wash water is more concentrated than the second wash water.

The flow variation has been observed to be fairly wide since the minimum and maximum

values respectively are 0.15 and 2.3 times the average flow. Discharge of these washes to the

main wastewater stream (on an intermittent basis) as is being practised will alter the

composition of the combined wastewater appreciably. This necessitates provision ofequilisation to the pulp washes and discharge at a constant rate into the main sewer.

Two alternatives can be considered for this purpose-

Alternative 1 : It evisages flow equalisation for the first pulp wash wastewater. This

wastewater is generated at a rate of 12.5 cu.m/tonne of paper made and is discharged at a rate

of 1.56 cu m/batch in 8 batches of 2 hours each per day. The discharge rate is fairly uniform

during the 2 hours of washing period.

Capacity of equalisation tank to be provide works out to 1.0 cm m/t paper

Adding 25% extra volume including

free board to meet any sarge discharge 0.25 cm m/t paper


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Total volume of equalisation tank 1.25 cm m/t paper

Rate of pumping of wastewater from the

equalisation tank into sewer 0.52 cu m/t for 24 hours

Therefore two equalisation tanks are to be provided to facilitate cleaning and

maintenance.

Alternative 2 : It envisages flow equalisation of the entire pulp wash wastewater (2 washes).

The total pulp wash wastewater is generated at a rate of 50 cu m/tonne of paper and is

discharged at a rate of 6.25 cu m/batch in 8 batches of 2 hours each per day. As stated above,

the flow rate of wastewater is fairly uniform during the 2 hour washing period.

Capacity of equalisation tank to be provide works out to 4.0 cm m/t paper

Adding 25% extra volume including

free board to meet any sarge discharge 1.0 cm m/t paper

Total volume of equalisation tank 5.00 cm m/t paper

Rate of pumping of wastewater from the

equalisation tank into sewer 2.08 cu m/t for 24 hours

Therefore, two equalisation tanks are to be provided to facilitate cleaning and

maintenance. Pumps of suitable capacity have to be provided one each for the two tanks and

one as a stand-by.

Primary clarifier and sludge Drying : If secondary treatment like activated sludge,

oxidation ditch or rotating biological disc is used as suggested, the excess secondary

biological sludge should be added to the combined wastewater before primary settling such

that the settled sludge can be filtered on drying bed. The combined primary and secondary

sludges do not require biological stabilisation. The dried sludge can be disposed off by

burning in an incinerator or dumping in open pits in a controlled manner.


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The treatment alternatives suggested are shown in Figs for agricultural based mills and

for waste paper based mills. The wastewater is practically devoid of nitrogen and

phosphorus. Hence, nutrients will have to be supplemented to biological treatment process.

For anaerobic system BOD : N.P. should be 100 : 2.5 : 0.5 and the corresponding ratio for

aerobic system is 100 : 5 : 1,

The treatment alternatives are detailed below.

Treatment Alternative 1 : The primary clarified effluent is proposed to be treated in an

anaerobic lagoon after proper seeding and acclimatisation. The lagoon will have a deterntion

time of 20 days. The anaerobic effluent will be subsequently treated in an aerated lagoon

with a detentiontime of 4 days. The effluent leaving the aerated lagoon will be passed

through a polishing pond with a detention time of 2-3 days before discharge or use on land

for agriculture. Anaerobic treatment prior to aerated lago in will reduce foaming problems

.

Treatment Alternative II ;Effluent from primary clarifier will be treated in an acrated

lagoon with a detention time of 6 days. The lagoon effluent will be taken through a polishing

pond with 3-5 days detention time before final discharge or use on land for irrigation after

suitable correction for SAR and total dissolved solids.

Surface aeration of pulp will washtes generate considerable foam which most often

covers the entire surface of the aeration tanks and thus prevents or reduce oxygenation of the

medium. It is observed that in square type of aeration basin or tank, the form formed is very

stable and does not dispense or break away easily. On the other hand, it is noticed that in

rectangular taks with length to breadth ratio equal to or greater than 2 to 1. although foam

formation takes place, the foam stability is less and breaks away at a faster rate, i.e. more

easily. Further spacing of aerators in the basin and the rotation in clockwise and anti

clockwise direction for alternate aerators will also help in reducing the foam accumulation as

well as breaking away of foam formed. With these arrangements and addition of anti forming

agents, it is likely that acrated lagon can be used as a method of treatment. However this

system is likely to create a problem of foam which should be kept in mind.


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Treatment Alternative III : Oxidation ditch operated on extended aeration principle

with high MLSS (4000-5000 mg/l) can be used to obtain high degree of BOD removal. High

MLSS in the system will help in destabilisation of foam. Although foam formation can not be

eliminated, it is observed in one of the mills, where this system is used, that foam breaks

away as the mixed liquid flows in the channel and the liquid surface is more or less free from

foam. The mixed liquor after secondary clarification will have low BOD.

In place of oxidation ditch a diffused aeration activated sludge system can also be used

on the same principle. In this system, foam does form but because of diffused aeration, the

oxygenation of the liquid in the tank will not be affected vis-a-vis biological purification.

However foam control from a physical point of view will be required. A secondary settling

tank is also necessary.

Treatment Alternative IV : Combined effluent without equalisation and primary settling

is proposed to be treated in anaerobic lagoon after proper seeding and acclanatisation. The

lagoon will have deterntion time of 25 days. The effluent from anaerobic lagoon will be

subsequently treated in aerated lagoon with a detention time of 4 days followed by polishing

pond with 4 days detention time.

Treatment Alternative V : Same as alternative II excepot that the polishing pond is

replaced by settling tank.

Treatment Alternative VI : Rotating biological contractor (RBC) can be successfully

used for the treatment of the settled combined wastewater from paper mills. This has been

domonstrated in the USA and other places. Actual design data used for treating pulp and

paper mill waste by RBC are not readily available. No foam problem will exist in RBC

treatment as there is no liquid and air mixing through agitation. Thus RBC may be

considered as a package plant for the treatment of the wastewater. A secondary clarifier is

required to remove the biological solids which can be collected and sent to the inlet of

primary clarifier and removed along with primary sludge. The design data available for


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domestic sewage treatment by RBC can be used for treatment plant design for pulp and

paper mill wastes. Over 90% BOD reduction can be expected.

TREATMENT 1 AND TREATMENT 2


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TREATMENT 3,4,5

WASTE WATER TREATMENT ALTERNATIVE FOR AGRICULTURAL RESIDUE

BASE3D PAPER MILLS


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Treatment For Mills Using waste paper and Purchased pulp as Raw Material

Treatment of wastewater from mills using waste paper and purchased pulp may be carried

out in the following processes :

1.Fibres should be recovered and recycle of recovered fibre and water to the maximum

possible extent to be adopted. The dissolved air floatation system is found suitable for

recovery of fibre from white water. After fibre recovery this water is recycled to the pulp

section for pump washing.

2.Primary clarification of the combined wastewater before or after fibre recovery is

essential for which rectangular or circular clarifiers can be used.

3.Primary sludge can be dried on sludge drying beds or lagooned depending on the

availability of land.

4.The effluent from primary clarifier needs to be further treated either in a stabilisation

pond or in an aerated lagoon (1/2 day detention time) if land is a limiting factor. The treated

effluent will then meet the permissible effluent standards.

5.Primary clarified effluent can be used on land for crop irrigation.


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WATEWATER TREATMENT ALTERNATIVES FOR WASTES PAPER AND PURCHASED

PULP-PAPER MILLS


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Treatment Methods for Small Mills

Treatment Alternative 1 : The suggested flow sheet for treatment alternative I, although

similar to alternative II, differs from it in two ways. In this case, it is proposed to segregate about

50% of black liquor from straw and 20% fromrag digesters. The segregated black liquor is

proposed to be stored in a lagoon and discharged into rivers during monsoon.

Other wastewaters (about m3/tonne of paper) after primary clarification are proposed to

be treated in an aerated lagoon instead of activated sludge. Nutrient addition is needed in this

case in the same proportion. Detention period in the lagoon will be 5 days. The aerated lagoon

will be provided with a silting chamber to prevent escape of solids in the effluent. Normally no

excess sludge is expected from aerated lagoon. Primary sludge will be disposed of into the

sludge lagoons. Effluent of aerated lagoon is expected to have a BOD of 30 mg/l and suspended

solids of 80 mg/l and is fit for discharge into inland surface waters except for COD and colour.

Treatment Alternative II : In this alternative, it is proposed to use the combined waste,

resulting after segregation of black liquor as suggested in alternatives I, on land for agricultural

utilisation.

The combined wastewater (about 200 m3/tonne of paper) will be taken through a clarifier

to remove the settleable solids. The clarified wastewater after mixing with calcium sulphate

(Gypsum) to bring down the per cent sodium below 60, will be used on land for irrigation.

Depending on the type of soil, crop grown and the climatic conmditions, a dose of 54 to 108 m3

of wastewater can be applied on land per hectare per day.

It is of importance to mention that the studies carried out so far by NEERI, on

agricultural utilisation of pulp mill wastes, have indicated that several kharif and rabi crops

(except 3 varieties of grass and groundnut) have responded favourably when irrigated with pulp

mill effluent as such or diluted with plain water.

Continued use of the wastewater on land is likely to create ground water pollution due to

percolation of the adsorbed colour. This is a drawback for this method of disposal.


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TREATMENT ALTERNATIVES 1 AND 2 For Small Paper Mills


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COLOUR REMOVAL

Presence of colour and its effect : Kraft pulp mills discharge dark brown coloured

wastes. The colour is due to lignin and its derivatives. Only a small fraction of the total lignin ofthe wood processed comes out in the waste. Although lignin and its derivatives present in the

waste are not toxic to human beings, animals and aquatic life, they create aesthetic pollution.

Since they are not readily biodegradable when present in water, they also reduce the utility of the

water and increase the cost of its treatment.

In the manufacture of 1 tonne of bleached paper from bamboo, as much as 40-50 kg of

lignin will be discharged into waste. In case of straw, used in small mills, as much at 225 kg of

lignin per tonne of paper will be discharged into the waste. The high value is because no

chemical recovery is adopted in small mills.

Studies on biological degradation of lignin revealed that :

1.There are only a limited number of micro organisms capable of degarding lignin-higher

organisms like fungi are more capable than bacteria.

2.Biological decomposition is extremely slow and incomplete.

3.There seems to be of not much scope for removal of lignin in the existing biological

waste treatment methods.

Methods for Colour Removal :

Lime treatment : Among the chemical methods employing precipitation or coagulation,

massive lime treatment for colour removal has been found to be technically and economically

feasible. This method besides achieving over 90% colour removal also result in 20-40% reductin

in BOD from the coloured pulp will wastes. In India, some mills are presently establishing the

massive lime treatment for colour removal.

Lime recovery is an essential part of this process. A modified lime treatment for colour

removal using only 1000 mg/l CaO for the total unclarified kraft pulp and paper mill waste with

lime recovery system has a great promise as this method also helps in the removal and disposal

of the suspended solids in the combind waste.


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Activated carbon treatment : Activated carbon treatment for colour removal from raw

waste water may not prove economcial. However activated carbon treatment preceded by

massive lime treatment will yield effluents that can be reused in the mill. Such a combination

will make activated carbon treatment an econoic proposition.

Microlime carbon sequence : A Microlime carbon sequence for removal of 90% colour and

40% TOC from clarified wastewater of unbleached kraft mill, has been shown to yield reuseable

water at a relatively low cost compared to massive or minilime activated carbon treatment.

Soils : Soils as a medium for colour removal can be used sussessfully provided the right

type of soil and adequate land are available. This method of disposal of coloured pulp mill

wastes will be most suited for Indian conditions. The land requirement will be high in most

cases. Colour removal in waste from small mills where black liquor is not recovered, will pose

serious problems and prove uneconomical. In such cases, it is desirable to segregate the small

volume of strong black liquor and store it in lagoons before discharge into weater courses in the

monsoon. The remaining coloured wastes can be used on land or treated by coagulation. This

aspect has to be given a serious consideration before locating the mills.


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Minimal National Standards (MINAS) :

The Minimal National Standards for pulp and paper mill effluent have been evolved after

looking into practical difficulties, limitations, techno-economic feasibility and economic impact

on the industry.

The basic considerations that went into the development of the minimal national standards were

therefore as follows :

Characteristics of effluent from small pulp and paper mills without chemical recovery

systems.

Achievability and techno-economic feasibility of various wastewater treatment

alternatives.

Maintained ratio of annualised cost to the turnover of the industry.

The MINAS limits for effluents from small pulp and paper industries after considering

the above mentioned aspects have been evolved as presented in Table

MINAS for small pulp and paper industry

Parameter Concentration

pH 6.09.0

Suspended solids 100 mg/1

Biochemical oxygen demand 50 mg/l

The implementation of above prescribed limits will be made in a phased manner. In the

first instance, the BOD and suspended solids of treated effluent should be reduced by 90% of the

total BOD and SS load in the effluent.


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REFERENCES

1. Chapter 20 of Environmental Pollution and Control in Chemical Process Industries ByS.C.Bhatia

2. Chapter 11 of Industrial Waste Water Treatment By A.D.Patwardhan3. www.cpcb.gov.in

paper n pulp

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