generation, reduction, and reuse of effluents and flue gases in textile industry
TRANSCRIPT
DANISH [email protected]
Mehran University of Enginneering & Technology Jamshoro, Sindh
TEXTILE
ENGINEERING
DEPARTMENT
TOPIC:-Generation, Reduction, and Reuse
of effluents and flue gases in Textile Industry.
DANISH [email protected]
Generation of effluents in textile industryThe textile dyeing industry consumes large quantities of water and produces large volumes of wastewater from different steps in the dyeing and finishing processes. Wastewater from printing and dyeing units is often rich in color, containing residues of reactive dyes and chemicals, and requires proper treatment before being released into the environment. The toxic effects of dyestuffs and other organic compounds, as well as acidic and alkaline contaminants, from industrial establishments on the general public are widely accepted. Increasing public concern about environmental issues has led to closure of several small-scale industries.
Dyeing effluents
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Effluent Generation and CharacteristicsWet processing of textiles involves to extensive amounts of water and dyes, a number of inorganic and organic chemicals, detergents, soaps and finishing chemicals to aid in the dyeing process to impart the desired properties to dyed textile products. Residual chemicals often remain in the effluent from these processes. In addition, natural impurities such as waxes, proteins and pigment, and other impurities used in processing such as spinning oils, sizing chemicals and oil stains present in cotton textiles, are removed during de sizing, scouring and bleaching operations. This results in an effluent of poor quality, which is high in BOD and COD load.
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Nature of Effluent:Waste generated in textile industry is essentially based on water- based effluent generated in the various processes. Textile industry originates a complex huge volume of waste water containing various chemical used in dyeing, printing and finishing processes. Many dyes which causes intensive color in the waste water. The effluent generated in different step or processes is well beyond the standard and thus it is highly polluted and dangerous.Water Consumption in Textile ProcessingThe production of textile goods involves spinning (fiber to yarn), weaving / knitting (yarn to fabric), chemical (wet) processing, and garment manufacturing. The majority of the water consumption (72%) takes place in the chemical (wet) processing of textiles. The water is required for preparing the fabric for dyeing, printing and finishing operations, Intermediate washing / rinsing operations and machine cleaning.
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Other major uses of water in the textile industrySteam generation (boiler feed water) Water treatment plant (reject stream, periodic cleaning of reverse osmosis plant, regeneration and washing of demineralization, softener plant, back wash of media filters); Cooling (processing machines, cooling tower); Humidification (spinning process); and Domestic purposes (irrigation of lawn and garden, sanitation, cleaning, drinking and miscellaneous uses).
Generation and reducti0n of effluents in desizingIn general, about 50% of the water pollution is due to waste water from desizing, which has a high BOD that renders it unusable. The problem can bemitigated by using enzymes that degrade starch into ethanol rather to anhydroglucose. The ethanol can be recovered by distillation for use as a solvent or fuel, thereby reducing the BOD load. Alternatively, an oxidative system like H2O2 can be used to fully degrade starch to CO2 and H2O.
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Generation and reduction of effluents in bleachingHypochlorite is one of the oldest industrial bleaching agents. Over the last few years, hypochlorite is being replaced by other bleaching agents. Recently, a one-step preparatory process for desizing, scouring, and bleaching has helped to reduce the volume of water. There is an economical and pollution-free process for electrochemical mercerization (scouring) and bleaching of textiles. The process does not require conventional caustic soda, acids, and bleaching agents. The treatment is carried out in a low-voltage electrochemical cell. The base required for mercerization (scouring) is produced in the cathode chamber, while an equivalent amount of acid is produced in the anode chamber, which is used for neutralizing the fabric. Gas diffusion electrodes simultaneously generate hydrogen peroxide for bleaching. With a bipolar stack of electrodes, diffusion electrodes can be used as anode or cathode or both. The process does not produce hydrogen bubbles at the cathode, thereby avoiding hazardsinvolving the gas.
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Generation and reduction of effluents in mercerizationIn order to impart luster, increase strength, and improve dye uptake, cotton fiber and fabric are mercerized in the gray state after bleaching. The large concentrations of NaOH in the wash water can be recovered by membrane techniques. Use of ZnCl2 as an alternative method leads to an increase in the weight of fabric and in dye uptake, and allows easy recovery of NaOH. Moreover, the process is ecologically friendly and does not require neutralization by acetic or formic acid.
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Generation and reduction of effluents in dyeingTreatment of fiber or fabric with chemical pigments to impart color is called dyeing. In the dyeing process, water is used to transfer dyes and in the form of steam to heat the treatment baths. Cotton, which is the world’s most widely used fiber, is a substrate that requires a large amount of water for processing. For example, to dye 1 kg of cotton with reactive dyes, 0.6–0.8kg of NaCl, 30–60 g of dyestuff, and 70–150 lit of water are required. Morethan 80,000 tones of reactive dyes are produced and consumed each year. Once the dyeing operation is over, the various treatment baths are drained,including the highly colored dye bath, which has high concentrations of salt and organic substances. The wastewater must be treated before reuse. Coagulation and membrane processes (nanofiltration or reverse osmosis) are among processes suggested for treatment of this water; however, these treatments are effective only with very dilute dye baths. Dye baths are generally heavily polluted. For example, wastewater produced by reactive dyeing contains hydrolyzed reactive dyes not fixed on the substrate (representing 20 to 30% of the reactive dyes applied on an average of 2 g/l). This residual amount is responsible for the coloration of the effluents, andcannot be recycled. Dyeing auxiliaries or organic substances are non-recyclable and contribute to the high BOD/COD of the effluents.Membrane technologies are increasingly being used in the treatment of textile wastewater for the recovery of valuable components from the waste stream, as well as for reusing the aqueous stream. A number of studies deal with application of various pressure-driven membrane filtration processes in the treatment wastewater from the dyeing and finishing process.
Generation and reduction of effluents in printingPrinting is a branch of dyeing. It is generally defined as ‘localized dyeing.’ Textile fabric printing produces hydrocarbon effluents that must be removed before they reach the atmosphere. Limits on emissions will become more restrictive in the future, which makes cleaning exhausts an environmental necessity. The most common chemical in reactive dye printing is urea, which leads to a high pollution load. A number of attempts have been made to limit or eliminate the use of urea in the print paste to reduce effluent load.Printing is mainly done by a flat or rotary screen, and after every lot of printing some residual paste is left in the wastewater. This can be reused for printing of similar shades by adding new stock. Recently, screen free printing methods, such as ink-jet printing and electrostatic printing, have been developed that make use of an electronic control of color distribution on fabric. Screen-free printing methods are attractive for pollution reduction.
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Generation and reduction of effluents in finishingThis is done to improve specific properties in the finished fabric and involves the use of a large number of finishing agents for softening, cross-linking, and waterproofing. All of the finishing processes contribute to water pollution. Among the products that are used in textile finishing, the most ecologically friendly ones are formaldehyde-based cross-linking agents that bestow desired properties.EFFLUENT TREATMENTSDyes in wastewater can be eliminated by various methods. The wastewater from the dye house is generally multi-colored. The dye effluent disposed into the land and river water reduces the depth of penetration of sunlight into the water environment, which in turn decreases photosynthetic activity anddissolved oxygen (DO).
DANISH RAJADanish_raja1@hot
mail.com
Discharge Quality Standard for Classified IndustriesTextile dyeing industries need huge quantity of water for textile dyeing, which they normally pump out repeatedly from the ground or natural water sources resulting in depletion of ground water level.There are various types of Efficient Treatment Plants (ETPs) and their design will vary depending on the quantity and quality of the effluent, amount of money available for construction, operation and maintenance, and the amount of land available. There are three mechanisms for treatment which are: Physical, Chemical and Biological. These mechanisms will often be used together in a single ETP.There are generally four levels of treatment, as described below:
ETP Plant
1) Preliminary: Removal of large solids such as rags, sticks, grit and grease that may result in damage to equipment or operational problems (Physical);
2) Primary: Removal of floating and settable materials, i.e. suspended solids and organic matter (Physical and Chemical);
3) Secondary: Removal of biodegradable organic matter and suspended solids (Biological and Chemical);
4) Tertiary: Removal of residual suspended solids / dissolved solids (Physical, Chemical and Biological).
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In dyeing textiles, ecological standards are strictly applied throughout processing from raw material selection to the final product. This has become more critical since the German environmental standards regarding dye effluents became effective (Robinson etal., 1997). The main challenge for the textile industry today is to modify production methods, so they are more ecologically friendly at a competitive price, by using safer dyes and chemicals and by reducing cost of effluent treatment/disposal. Recycling has become a necessary element, not because of the shortage of any item, but because of the need to control pollution. There are three ways to reduce pollution: (1) Use of new, less polluting technologies; (2) Effective treatment of effluent so that it conforms to specified discharge requirements; and (3) Recycling waste several times over before discharge (Sule and Bardhan, 1999), which is considered the most practical solution.
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Flue gases in textile industryFlue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produced at power plants. Its composition depends on what is being burned, but it will usually consist of mostly nitrogen (typically more than two thirds) derived from the combustion air, carbon dioxide (CO2), and water vapor as well as excess oxygen (also derived from thecombustion air). It further contains a small percentage of a number of pollutants, such as particulate matter (like soot), carbon monoxide, nitrogen oxides, and sulfur oxides.
DANISH RAJADanish_raja1@hotmail
.com
Scrubbing of flue gasesAt power plants, flue gas is often treated with a series of chemical processes and scrubbers, which remove pollutants. Electrostatic precipitators or fabric filters remove particulate matter and flue gas desulfurization captures the sulfur dioxide produced by burning fossil fuels, particularly coal. Nitrogen oxides are treated either by modifications to the combustion process to prevent their formation, or by high temperature or catalytic reaction with ammonia or urea. In either case, the aim is to produce nitrogen gas, rather than nitrogen oxides. In the United States, there is a rapid deployment of technologies to remove mercury from flue gas—typically by adsorption on sorbents or by capture in inert solids as part of the flue gas desulfurization product. Such scrubbing can lead to meaningful recovery of sulfur for further industrial use. There are number of proven technologies for removing pollutants emitted from power plants that are now available. There is also much ongoing research into technologies that will remove even more airpollutants.
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Iso 14001The ISO 14000 family of standards provides practical tools for companies and organizations of all kinds looking to manage their environmental responsibilities.ISO 14001:2015 and its supporting standards such as ISO 14006:2011 focus on environmental systems to achieve this. The other standards in the family focus on specific approaches such as audits, communications, labeling and life cycle analysis, as well as environmental challenges such as climate change.ISO 14001 is a family of standards related to environmental management that exists to help organizations: (a) Minimize how their operations (processes, etc.) negatively affect the environment (i.e., cause adverse changes to air, water, or land); (b) Comply with applicable laws, regulations, and other environmentally oriented requirements, and (c) Continually improve in the above.
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Environmental management system (EMS)Environmental management system (EMS) refers to the management of an organization's environmental programs in a comprehensive, systematic, planned and documented manner. It includes the organizational structure, planning and resources for developing, implementing and maintaining policy for environmental protection.More formally, EMS is "a system and database which integrates procedures and processes for training of personnel, monitoring, summarizing, and reporting of specialized environmental performance information to internal and external stakeholders of a firm." The most widely used standard on which an EMS is based is International Organization for Standardization (ISO) 14001. Alternatives include the EMAS.An environmental management information system (EMIS) is an information technology solution for tracking environmental data for a company as part of their overall environmental management system.
DANISH [email protected]
DANISH [email protected]