Central Pollution Control Board

Technologies for Pollution Control Industry

AGRO-BASED INDUSTRIES

Textile Industry

The textile industry encompasses a range of industrial units, which use a wide variety of natural and synthetic fibres to produce fabrics. The textile industry can be broadly classified in two groups, namely cotton industry and woollen industry.

The effluent generated from textile industry contains various dyes, chemicals, auxiliary chemicals, sizing materials etc. The effluent is usually treated by physico-chemical treatment followed by biological treatment process. However, such treatment systems are not effective for removal of colour, dissolved solids, trace metals etc. In-plant control measures such as process change, recovery/reuse of chemicals, chemical substitutes can significantly reduce pollution from this sector. There are described below:

(a) Process Change/ Recovery

Area	Technologies/Current Practices	Requirements
Sizing	Starch is most commonly used as sizing material for cotton textiles. During sizing, the starch eliminates the possibility of its recovery. It also contributes high BOD.	Recovery of Sizing material: The other types of sizing material, such as carboxymethyl cellulose (CWC), polyvinyl acetate (PVA) are comparatively more expensive but are recoverable.
Mercerising	Mercerising waste contains about 4% caustic. Few textile industries have provision for its recovery.	Recovery of Caustic: Spent caustic from mercerising as well as other units can be recovered and reused either by membrane separation technology or by most commonly used evaporation method.
Dyeing	The textile industry uses various types of dyes to impart the desired quality in the fabrics, which generates coloured effluent. No specific treatment is given before it is discharged.	Reuse of dye bath: Instead of discharging the exhausted dyebath, it can be reconstituted by adding appropriate amount of make-up dyes and auxiliary chemicals. The reconstituted dyebath can be reused for dyeing successive batches.
Printing	The conventional printing involves colour paste application to fabric and subsequent dye fixation. After this, all chemicals other than the dye need to be removed from fabric. This increases effluent generation.	Transfer Printing: The transfer printing transfers dyestuff, previously printed on paper, on the fabric. Only the dyestuff and other chemicals are transferred on the fabric thus eliminating the after-washing.
Wastewater Treatment	The wastewater is treated by physico-chemical and/or biological treatment process. Some industry uses filtration alongwith physico-chemical treatment to reuse the specific effluent streams.	Recycling of Treated Wastewater: The effluent can be further treated by activated carbon adsorption process or other advanced treatment process so that the treated effluent can be recycled/reused.

(b) Chemical substitute

Area/Process	Chemical in Use	Substitute Required
Sizing/Process	Conventional Starch based size	Synthetic wrap sizes (PVA) Acrylates)
Desizing	Enzymes	Acids
Soaping	Conventional Soap	Synthetic Detergents
Good Scouring	Soda Ash	Sodium Acetate
Disperse Dyeing & Pigment Printing	Acetic Acid	Ammonium Sulphate
Printing	Gum	Emulsion
Oxidation of vat dye	Acetic Acid	Sodium Bicarbonate
Screen Printing machines	Conventional Gums	Permanent Adhesives
Finishing starch based	Temporary Finishes	Durable Finishes
Dyeing	Two stages dye (Disperse, vat. etc.)	Single stage dyes (Tindigosol)
Dyeing	Solvent Pthalogen blue	All aqueous Pthalogen blue
Dacron Dyeing	Conventional Carriers	Monochlorobenzene
Dye bath	Acetic acid	Formic Acid
Lubricants used in textile machinery	Carding oils anti-state lube	Non-ionic emulsifiers

Index

Tanneries

Tanning is an integral part of leather making process, which converts the raw hides and skins to finished leather, which is used for manufacturing various leather goods.

Tanning industries can be classified into two categories with respect to the kind of tanning practised: vegetable or EI tanning and chrome tanning. Further these processes can be classified into different processes each depending upon the level of tanning a particular industry adopts.

For vegetable tanning:

(a) Raw hide to vegetable tanned semi-finished leather

(b) Vegetable tanned semi-finished leather into finished leather.

For Chrome tanning:

(a) Raw hide to chrome tanned semifinished leather

(b) Raw hide to finished leather by chrome tanning

In India, mostly chrome tanning is practised.

The effluent generated from tanning process contains very high TDS, chromium (where chrome tanning is practised), high BOD & COD. So far, the practice to reduce TDS in effluent has been to segregate soak liquor and to minimise the total volume by solar evaporation. The chromium can be reduced by two ways i.e. chemical precipitation or chrome recovery. The biological treatment (anaerobic followed by aerobic) is practised to reduce BOD & COD.

The technologies available and the requirements are described below:

Technologies/Current Practices	Requirements
(I) CHROME RECOVERY Adoption of chrome recovery in case of raw hide to finished processes especially is practised by some of the medium and large-scale tanneries. It comprises collection of spent chrome liquor after basification and recovery of chrome from the same. This results in substantial saving besides reducing the concentration of chrome in the trade effluent. The supernatant liquor after recovery of chrome can be used for soaking. The recovered chrome can be used alongwith regular basic chrome sulphate for chrome tanning.	Large and medium units should provide individual chrome recovery system barring those which are practising semi-chrome finished to finished leather. The small-scale units need to adopt the chrome recovery system in a group of 4 to 5 units.
(ii) SOAKING (a) Reuse of main soak for dirt soak Soaking consists of dirt soak and main soak. The main soak is retained and used for dirt soak for the next batch.	(a) Addition of soaking enzymes Soaking enzymes @ 0.4% of w/s wt. can be added to achieve uniform and thorough soaking.
(b) Drum soaking instead of pit soaking Drum soaking instead of pits soaking which reduces the water consumption besides bringing down the soaking time from 12 hrs. To 3 hrs.	(a) Reuse of dirt soak Possibilities of collection of dirt soak liquor and adding polyelectrolyte to flocculate and settle the suspended solids need to be explored. Soak liquor after treatment and filtration can be reused partially in liming/deliming washes and picking. Modern plants are providing these facilities.
(iii) LIMING (a) Substitution of paste lime by 85% pure calcium oxide (CaO) This can bring down the quantity of consumption of powered lime to one third of its original quantity. It can also reduce the frequency of cleaning the primary settling containing the lime sludge. (b) Provision of slight slope in the pasting area By providing a slight slope in the pasting area, the excess liming paste can be effectively collected and used, which is otherwise washed away in the drain by lime yard workers. (c) Reuse of relime liquor 50% of relime liquor can be retained and reused for liming of subsequent batches. This also reduces water consumption. Other than optimisation of chemical consumption in this section, fleshing can be used for production of high-grade protein. This, if achieved, will solve the problem of solid waste disposal from the liming section.	(a) Use of Liming Enzymes Use of liming enzymes @ 0.4% can reduce Sodium Sulphide (Na₂S) Consumption by 40%. Use of soaking and liming enzymes can improve liming quality resulting in cleaner and flatter pelts. The marginal increase in cost is more than offset by increase in yield achieved in Wet Blue as well as reduction in Na₂S consumption. At higher enzyme levels, hair can be shaved off without burning which can be screened and used as a fertiliser. Some tanneries are practising; however, others should be encouraged to do so.
(iv) DELIMING Efforts can be made to reduce water consumption in this section by implementing the following measures: a. Use of deliming agents. b. Use of first delimes wash for liming.	Proper deliming agents need to be identified.
(v) PICKLING Use of drained float for next batch Normally after desired pH is obtained in pickling, 1/3rd float is drained to ensure better chrome exhaustion at lower floats. This liquor can be collected and used for next batch to reduce consumption of salt and acids.	Such facilities need to be installed in selected units for demonstration purposes.

Technologies for waste minimization in tanneries

Manual/mechanical desalting prior to soaking

Reducing hydraulic load in soaking
Counter current recycling of soak liquors
Lime-free Beam house operations
Enzyme assisted less-sulfide unhairing
Recycling of lime liquor/washings
Ammonia-free deliming process
Salt-less picking
Pickle-free chrome tanning
Closed loop pickle-chrome recycling methods involving high exhaust chrome tanning
Less chrome and chrome-free tanning methods
Full chrome tanning methods
Use of Eco-benign post tanning auxiliaries
Optimization of float volumes in processing
Formaldehyde-free finishing techniques
Use of newer finish application systems
Use of Roller Coater for improved transfer efficiency
Split finishing

Index

Distillery

The main source of pollution from distilleries is the spentwash, which is produced as a result of fermentation and distillation of the molasses. The spentwash is acidic in character having very high BOD (40,000 - 50,000 mg/l) and COD (10,000-125,000 mg/l). The different treatment technologies for treatment of distillery effluent have been adopted depending upon the availability of land; filler material for compost and mode of disposal of treated effluent. The existing technologies and technologies required are given below:

Technologies/Current Practices	Requirements
Bio-methanation followed by Secondary Biological treatment system Large number of industries have provided the system wherein methane gas produced can be used into boilers which saves the fuel to the tune of 60%, besides removing BOD in the order of 80-90%. The secondary biological treatment such as activated sludge process or extended aeration system after bio-methanation brings down the BOD in the range of 300-500 mg/l. The final effluent after mixing with the other wastewater can be used on land for irrigation.	Two stage secondary biological treatment system is needed preferably using diffused aeration system for better efficiency and saving in power. The treated effluent when utilised on land for irrigation should meet the requirement of TDS by mixing with the irrigation water from other sources.
Composting In this process, press mud generated from sugar mill is utilised to produce compost by mixing distillery effluent. Both anaerobic and aerobic composting systems are practised. In some plants composting with treated effluent treated through bio-methanation plant is also practised. This system can achieve zero effluent if the press mud quantity matches with the effluent generated.	Adequate capacity of composting facility is needed and the compost quality is required to be checked periodically. There should be adequate holding capacity of effluent so that at no time effluent finds way into the drain or in the ground water. Ground water monitoring is also necessary to ensure that there is no seepage from the composting site.
Incineration Following drying of spentwash and using dried material in the boiler for steam generation.	Use of the spent wash alongwith baggasse/biomass for generation of power.

Index

Pulp & Paper Industry

The pulp & paper industries can be classified into three-category i.e. large-scale pulp & paper mills, agro based pulp & paper mills and waste paper based mills having installed capacity of 4.25 million tonnes. Environmental problems associated with pulp & paper industries vary with the size and category of the mill. Although all the large-scale pulp & paper mills have adequate treatment systems but still some of the problems like colour in the effluent and solid waste disposal problem still persists. The colour problem is basically due to spillage of black liquor during its handling which ultimately joins the effluent stream. The effluent that emanates from the bleaching section of the mill also contributes the colour. The toxicity is another problem, which is mainly due to use of elemental chlorine during the bleaching.

In small scale agro-based pulp and paper mills, major cause of pollution is discharge of black liquor which is otherwise taken to chemical recovery plant by large scale pulp and paper mills. The absence of chemical recovery plant in small-scale pulp & paper mills is due to their smaller size and high cost involved in its installation.

In waste paper based mills, zero discharge is possible through recycling of wastewater after suitable treatment. But due to poor waste treatment and old fibre recovery technologies, the industries are unable to recycle the effluent.

In the following table, the present practices adopted by the pulp and paper mills alongwith the technology requirements are outlined.

Technologies/Current Practices	Requirements
Use of elemental chlorine in bleaching of pulp which is resulting in generation of toxic effluent containing chloro compounds of lignin. It results in generation of AOX, which is highly toxic and carcinogenic.	Bleaching techniques, which avoid the use of elemental chlorine, should be adopted. Use of chlorine dioxide and use of oxygen at alkali extraction stage should be preferred. It reduces generation of AOX by about 70%. The use of oxygen/ozone as bleaching agents makes the effluent recyclable from this section with no colour
Use of kraft pulping process for delignification of wood/bamboo raw material in large-scale mills.	Use of modern pulping process like RDH pulping, Oxygen delignification should be practised. These processes produce pulp of low kappa number and high brightness, which require low bleach chemicals. Low steam requirement with high pulping yield are the attempted benefits.
Land disposal of lime sludge by the mills having chemical recovery plant	Most of the large-scale mills dispose lime sludge on land. Lime kiln should be used for recalcination of lime sludge so that it can be reused in the process.
Discharge of black liquor by the small scale agro-based pulp & paper mills	Chemical Recovery Plant (CRP) is required to be installed by such mills. The black liquor can be taken to CRP for recovery of pulping chemicals. Some agro-based pulp & paper mills have installed CRP and running it successfully. The installation of CRP by all units is necessary to control pollution and colour.
Removal of colour through lignin precipitation by adding poly-electrolyte	For the industry where chemical recovery is not feasible economically and problem of colour persists, the removal of lignin through precipitation and its conversion into useful and marketable product e.g. binders should be practised.
Use of obsolete technologies like conical save-all etc. as fibre recovery system	Dissolved air floatation based fibre recovery systems and micro-filters. Use of micro-filters improves the recycling of wastewater significantly.

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