Characterization and treatment of textile chemical processing

effluents

R.B.ChavanDepartment of Textile Technology

Indian Institute of TechnologyHauz-Khas, New Delhi 110016E-mail rbchavan@hotmail.com

Environment pollution in India

• Environment pollution was not a serious threat until recently

• Scattered industries• Small scale industrial production• Lack of awareness for environment protection

Environment pollution in India

• Present trend• Large scale industries• Industry concentration in specialized industrial

areas and technology parks• International pressure for clean production

technologies.• Environment is not a local concern but global

concern • Environment protection involves minimization of • Air• Noise• Water pollution • Water pollution is highest In case of textile industry.

Water consumption in textile industry

• Water consumption for chemical processing 50-300 l/kg of fibre

• Depends on nature of fibre and processing steps. • 1-2 million litres per day for 50000 metres daily

production• Large quantity of water gets polluted with various

dyes, chemicals and textile auxiliries • Discarded in the form of effluents in river, lake, sea,

sippage in ground water stream• Pollution of surface and ground water• Increase in salinity affecting agriculture produce

Characteristics of textile effluents

• Diverse in nature• Contain large variety of organic and inorganic

materials used in degumming, desizing, scouring, bleaching, dyeing, printing and finishing.

• Inorganic substances• Oxidizing and reducing agents• Salts • Acids• Alkalis

Characteristics of textile effluents

• Organic substances• Dyes,• Organic acids• Thickeners• Finishig agents• Detergents• Textile auxiliaries

Methods resolving effluent problems

• Discharge to local authority sewer so that the wastes can be purified in admixture with domestic sewage.

• The consent of the local authority is essential • This method of disposal is often the most

satisfactory provided • the charges and the standards led down by the

sewage authority are not excessive. • It is in fact the method most commonly adopted.

Methods resolving effluent problems2. pre-treat the effluents to make them acceptable for discharge to

the sewer. 3. carry out full purification treatment at the factory and then

discharge either to river or stream. The standards of quality for discharge to stream are more stringent than for discharge to sewer.

4. make attempts to minimize pollution right from the beginning of each process.

• This approach is known as waste reduction at source or waste minimization technique.

• The treatment of the effluent is known as end of pipe treatment.

• Between the two approaches i.e. waste minimization and end of pipe treatment, the waste minimization techniques have been considered to be most important for pollution control and environment protection.

Characteristics Into inland surface water

Into public sewer

On land for irrigation

Into marine Coastal areas

Colour and odour Colourless Colourless Colourless Colourless

Suspended solids (mg/l ) 100 600 200 -

Dissolved solids (TDS, mg/l m 2100 2100 2100 -

pH 5.5-9 5.5-9 5.5-9 5.5-9

Temperature 0C Max. 40 45 - 45

Oil and grease mg/l 10 20 10 20

BOD (5 days ) 30 350 100 100

COD 250 - - 250

Hexavalent chromium mg/l 0.1 2 - 1.0

Copper mg/l 3 3 - 3

Zinc mg/l 5 15 - 15

Sulphides mg/l 2 - - 5

Pesticides mg/l Absent Absent Absent Absent

Tolerance limits for industrial effluents

Effects of effluent disposal

Effect on water courses

• Colour Psychologically coloured water gives the impression of high pollution.

• Suspended solids The colloidal and suspended impurities produce turbidity in the receiving water. Turbidity together and colour cause unsightly appearance.

• pH The extreme acidity or alkalinity makes the effluent dangerous to aquatic life and it becomes unsuitable for any other purpose.

• Oil and grease They interfere with oxygenation of streams as they form blanket on the surface and prevents the entry of oxygen at air/water interface.

Effects of effluent disposal

• Total dissolved solids The dissolved inorganic matter mainly sodium salts (NaCl, Na2SO4) increase the salinity of water and consequently it becomes unfit for irrigation.

• Toxic substances Chromium, sulphide, chlorine and dyes (particularly azo dyes) present in textile effluents are toxic to fish and organisms which carry out water purification in the stream. Thus the self purification of the water body is affected.

• Depletion of dissolved oxygen Substances present in the textile effluents (such as starch, dextrin, sulphide, etc. ) exert an oxygen demand. The stream then will be devoid of oxygen and the aquatic life are affected adversely.

Effects of effluent disposal

• Effect on land

• The excess sodium content in textile effluents is harmful to crops.

• The high alkalinity combined with salinity impair the growth of plants.

Steps involved in effluent treatment Primary treatment

• Screening Separation of coarse suspended matter such as pieces of rags, fabric, yarn, lints etc.

• Equalization The water from various textile processing operations is discharged at different time intervals. This is likely to cause variations in terms of pH, temperature, It is essential to equalize effluent to a certain pH and temperature otherwise the subsequent biological process based on purification with the help of microorganisms is severely affected.

Primary treatment

• Neutralization The secondary biological process is effective under pH 6-9. It is therefore essential to bring the effluent within this pH range.

• Chemical coagulation To remove colour, suspended solids, some of the decomposed products the effluents after neutralization are treated with coagulants like alum, ferrous salts or synthetic polyelectrolytes. In this process some of the impurities settle at the bottom of the effluents and disposed off as sludge.

Secondary treatment

Biological treatments

• Trickling filtration

• Activated sludge process

• Aerated lagoons

• Oxidation ponds

Common effluent treatment plants

• For small units installation and maintenance of secondary treatment plants is not economical.

• It is therefore suggested to install common effluent treatment plant

• small units in the proximity can discharge their effluents

• cost involved may be shared among the units depending upon the volume of effluents let out and their pollution load

Tertiary treatment

• most common tertiary treatment is adsorption on activated carbon.

• Reverse osmosis

• filtration of the effluents through a membrane

• reject virtually all dissolved substances.

• The water thus available will be better than raw water

• suitable for recycling.

Criticism of Reverse osmosis

• it is one of the most efficient technology for the removal of salt or in general total dissolved solids (TDS).

• However it is capital intensive technology both in terms of initial cost and maintenance cost.

• The membranes are very expensive and prone to chocking.

• The technology is more suitable for handling small volumes of less polluted effluent.

• The volumes of effluents from textile mills are large and more complex in nature.

Circumstances under which reverse osmosis

can be used economically and efficiently • Reverse osmosis never becomes economical for the treatment of

raw effluent. • suggestions for economical and efficient use of reverse osmosis • Separately collect reasonably clean wash waters• Subject to flocculation

• used for RO. • In this way the load on RO plant will be reduced• chances of membrane chocking are minimized.• The water is suitable for recycling • 40-60% water may be recycled. • This would reduce considerable quantity of fresh

water consumption • less volume of effluent water.

RO of Rinsed water from dyeing

Other alternatives for RO

Option 1

• Subject effluent to

• Biological treatment

• Adsorption on carbon bed

• RO

Option 2

• Rinsed water

• Adsorption on carbon bed

• RO

Adsorption on activated carbon bed

Waste minimization

• Benefits• Reduction in consumption of raw materials

and energy• Reduce generation of waste• Reduction in cost of effluent treatment• Improvement in production efficiency and

product quality.

Cleaner production options

Advantages of cleaner production

• Improvements in products and processes • Increased competitiveness through the use

of new and improved technologies,• Generation of less waste, savings in

treatment costs,• Reuse or recycling of wastes,

• Green products image,

• Energy efficiency, conservation of resources,

Advantages of cleaner production

• Reduced liability associated with the treatment, storage and disposal of hazardous wastes,

• Improved health , safety and morale of employees,

• Compliance with governmental regulations and enhanced public acceptance,

• Compliance in attaining sustainable development

Trade prospects

Pollution prevention

• conventional waste treatment often causes only a transfer of waste from one phase to another.

• Treatment usually results in the generation of solids, sometimes hazardous, which are buried in a landfill.

• Disposal of waste in a landfill can result in• groundwater contamination, • gas formation and • problems with odors. • In other words,• waste treatment is not necessarily a cure.

Pollution prevention

As regulations become more stringent,• companies are forced toward more

technologically sophisticated treatment methods.

• This results in an increased cost for waste management and sometimes

• forces companies to go out of business. • More and more companies realize that

reducing the waste at the source is necessary to reduce the cost of treatment.

Pollution prevention

• Pollution prevention is defined as • those measures that eliminate or reduce

pollution prior to effluent treatment. • Pollution prevention does not only• reduce water pollution, but also • minimizes the release of pollutants to • land and • air. • Source reduction should be top priority of

the management policy

Pollution prevention Strategy

• Best way to reduce pollution to prevent it in the first place.

• Managing waste through source reduction

• Effluent treatment as a last alternative.

Pollution prevention Strategy

• Quality control of raw materials.• Perform tests on raw materials shortly after receipt.• Purchase raw materials in returnable containers.• Chemical Substitution• Replace chemicals with less-polluting ones.

• Process Modification

• Use low-liquor ratio dyeing machines.

• Use countercurrent washing to reduce water use.

Pollution prevention Strategy

Pollution prevention Strategy

• Optimize process conditions.

• Combine processes.

• Process Water Reuse and Recycle

• Reuse dyebaths.

• Reuse rinse baths.

• Install automated dosing systems and dye machine controllers.

Pollution prevention Strategy

• Good Operating Practices

• Schedule dyeing operations to minimize machine cleaning.

• Optimize housekeeping practices.

• Adopt worker training programs.

Reducing Chemical Consumption

• Recipe Optimisation• Chemical Substitution• Review chemicals used in the factory and

replace those hazardous to the environment with those that have less of an impact.

• Use dyes that have high exhaustion rates and require less salt.

• replace metal-containing dyes• use bi-reactive dyes in place of mono-reactive• avoid the use of APEO detergents and replace

with more biodegradable alternatives• replace stilbene optical brighteners with

alternatives, or eliminate altogether

Water conservation in silk processing

• Degumming

• Dyeing

• Printing

• Finishing

Degumming Methods

• Boiling with soap• Boiling with alkali• Enzyme degumming• Treatment with water at high temperature • Sequence• Treatment • Wash• Wash • Recycle second wash liquor for washing

after degumming

Dyeing

• Acid

• Metal complex

• Reactive

• Direct

Polluting agents

Salt

Colour

Acid

detergents

• Use low liquor dyeing machines for reduced salt consumption

• Use dyes with high exhaustion properties

Reduction of water consumption

Wash

Wash

Degumming

Reduction of water consumption

• Exhaust dyeing

Rinse

Rinse

RinseRecycle for rinsing subsequent dyeing