37 Effluent Treatment Plants for Textile Dyeing and Finishing Houses

M. Saravanan

epgp books

 

 

 

 

Introduction:

 

Textile manufacturing industry is one of the biggest and most confounded industrial chains in manufacturing industry. The processes of production of textiles materials or wet treatments and finishing processes of textiles are tremendous consumers of water and also that is of very high quality. Because of these kinds of different industrial processes, significant measures of contaminated water are discharged. The strategies for pre-treatment or cleansing of waste waters in the textile industries summarized as: Primary (screening, sedimentation, homogenization, neutralization, mechanical flocculation, chemical coagulation), Secondary (aerobic and anaerobic treatment, circulated air through lagoons, enacted sludge process, trickling filtration, oxidation dump and lake) and Tertiary (membrane technologies, adsorption, oxidation system, electrolytic precipitation and foam fractionation, electrochemical procedures, ion exchange technique, photo catalytic degradation, thermal evaporation).

 

The choice of the purging strategy relies upon the composition and kind of waste waters. Textile materials production encompasses wet treatments like sizing, desizing, scouring, dying, mercerizing, dyeing, printing and finishing operations, however there is a solid interrelation between dry processes and back to back wet treatments in textile chemical processing industries. The textile industry emits a wide assortment of contaminations from all phases in the fibre manufacturing, fabric and garment production units. Waste water, solid wastes, emissions to air and noise contamination. The main environmental worry in the textile industry is about the measure of water released and the chemical load it conveys. The textile industry is exceptionally water serious. Water is utilized for cleaning the raw material and for many flushing steps during the entire process of production. Almost 200 L of water are utilized to create 1 kg of textile material. Water is basically utilized for: (a) the transfer of chemicals onto fabric materials and (b) rinsing the manufactured textiles.

 

Objective:

 

Module aims to discuss the following core points and elaborate them in detail for clear understanding and appreciate the importance of waste water and different ways to treat waste water and, converting unused water stage to reusable water for normal Textile production.

  1. ETP (Effluent Treatment Plant) is a process design for treating the industrial waste water for its reuse or safe disposal to the environment which is covered elaborately.
  2. Various methods to control and Standards for emission or discharge of environmental pollutants from various Industries set by the Government and avoid hefty penalties.
  3. Role of industries: Quantity and quality of the industries discharge effluent. Land availability is discussed to support the Effluent Treatment process.
  4. Mechanism/principle on which these ETP works in Industries, Quality of wastewater to be treated and biological treatment t are also discussed in this module.

ETP:

 

The Effluent Treatment Plant (ETP) is having following in and out process activities as shown in Figure 1 and are quickly summarized as below:

  1. Influent: Untreated industrial waste water.
  2. Effluent: Treated industrial waste water.
  3. Sludge: Solid part separated from waste water by ETP.

Need of ETP:

  • Textile wastewater includes a huge assortment of colors and chemicals increases that make the Environmental challenge for textile industry as fluid waste as well as in its chemical synthesis which sometimes becomes toxic.
  • Main contamination in textile wastewater originated from dyeing and finishing processes.
  • Cleaning the industry effluent and recycle it for further use.
  • Diminish the usage of fresh/potable water in Industries.
  • Economical on the procurement of water for manufacturing processes.
  • Meeting the norms for emission or expulsion of environmental pollutants from various manufacturing units set by the Government and avoids hefty penalties.
  • Protecting the environment against pollution and contribute in sustainable development.
  • These processing textile units require the contribution of an extensive variety of chemicals and dyestuffs, which by and large are organic compounds of complex structure.
  • Because every one of them are not contained in the final product, became waste and caused disposal problems.
  • Major contaminations in textile wastewaters are high suspended solids, chemical oxygen demand, warm, shading, corrosiveness, and other solvent substances.
  • The expulsion of shading from textile industry and dyestuff producing industry waste waters speaks to a noteworthy natural concern.
  • In expansion, just 47% of 87 of dyestuff are biodegradable.
  • It has been recorded that residual colour is more often than not because of insoluble dyes which have low biodegradability as reactive blue.
  • Direct blue 80 and vat violet with COD/BOD proportion of 59.0, 17.7, and 10.8, separately.
  • Conventional oxidation treatment have discovered trouble to oxidize dyestuffs and complex structure of organic compounds at low concentration or on the off chance that they are particularly obstinate to the oxidants. Advanced oxidation processes (AOPS) have been emerged to produce hydroxyl free radicals by various methods.
  • AOPS forms are blend of ozone (O3), hydrogen peroxide (H2O2) and UV light.

Textile Wastewater Characteristics:

  • Composite textile wastewater is characterized mainly by measurements of biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS) and dissolved solids (DS).
  • COD values of composite wastewater are extremely high compare to other parameter.
  • In most cases BOD/COD ratio of the composite textile wastewater is around 0.25 that implies that the wastewater contains large amount of non biodegradable organic matter.

Advanced Oxidation Process (AOPS):

  • The goal of any AOPs design is to generate and use hydroxyl free radical (HO) as strong oxidant to destroy compound that cannot be oxidized by conventional oxidant. Generation of HO is commonly accelerated by combining O3, H2O2, TiO2, UV radiation, electron-beam irradiation and ultrasound.
  • Of these, O3/H2O2, O3/UV and H2O2/UV hold the greatest promise to oxidize textile wastewater.
  • About, 99% and 95% of colour removal was achieved when COD initial was 160 and 203 mg/L, respectively.
  • In addition, colour removal efficiency increased with increasing the temperature from 25 to 50°c.
  • That the rate of dye oxidation increased slightly with increasing solution pH.
  • Documented that high colour removal of simulated reactive dye bath effluent was achieved at pH 7 when using ozone concentration of 2970 mg/L and remained unchanged at pH 11.
  • The reaction pH had to be at least 7 to enhance ozone decomposition and high colour removal.

Categorization of Waste Generated in Textile Industry:

  • Textile waste is broadly classified into four categories, each of having characteristics that demand different pollution prevention and treatment approaches. Such categories are discussed in the following sections:
  1. Hard to Treat Wastes
  • This class of waste incorporates those that are persistent, resist treatment, or interfere with the task of waste treatment facilities.
  • Non-biodegradable organic or inorganic materials are the central wellsprings of wastes, which contain colour, metals, phenols, certain surfactants, toxic organic compounds, pesticides and phosphates.
  • Non-biodegradable organic materials surfactants.
  • Since these kinds of textile wastes are hard to treat, the distinguishing proof and disposal of their sources are the most ideal approaches to handle the issue.
  • Some of the techniques for anticipation are chemical or process substitution, process control and improvement, reuse/reuse and better work rehearses.
  1. Hazardous or Toxic Wastes
  • These wastes are a subgroup of hard to treat wastes. But, owing to their substantial impact on the environment, they are treated as a separate class.
  • In textiles, hazardous or toxic wastes include metals, chlorinated solvents, non-biodegradable or volatile organic materials. Some of these materials often are used for non-process applications such as machine cleaning.
  1. High Volume Wastes
  • Wash water from preparation and continuous dyeing processes and alkaline wastes from preparatory processes Batch dye waste containing large amounts of salt, acid or alkali.
  • These wastes sometimes can be reduced by recycle or reuse as well as by process and equipment modification.
  1. Dispersible Wastes
  • The following tasks in textile industry produce very dispersible waste:
  • Waste stream from continuous operation (e.g. preparatory, dyeing, printing and finishing)
  • Print paste (printing screen, crush and drum cleaning)
  • Lint (preparatory, dyeing and washing operations)
  • Foam from coating operations, Solvents from machine cleaning still bottoms from solvent recovery (dry cleaning operation)

Classification of waste water treatment process:

 

Treatment Operations

 

Preliminary Treatment level

  • Primary Screening – A screen with openings of uniform size is used to remove large solids such as plastics, cloth etc. Generally maximum 10mm is used.
  • Sedimentation – Physical water treatment process utilizing gravity to expel suspended solids from water. The suspended matters in textile effluent can be expelled productively and economically by sedimentation. This process is especially valuable for treatment of wastes containing high level of settable solids or when the waste is subjected to joined treatment with sewage. The sedimentation tanks are intended to empower littler and lighter particles to settle under gravity. The most widely recognized equipment utilized horizontal flow sedimentation tanks and focus centre-feed circular clarifiers. The settled sludge is expelled from the sedimentation tanks by mechanical rejecting into hoppers and directing it out in this way subsequently.
  • Equalization – Utilized for partition of solids from liquids. Effluent streams are gathered into sump pit. Sometimes mixed effluents are stirred by rotating agitators or by blowing compacted air from beneath. The pit has a funnel shaped base for improving the settling of solid particles.
  • Neutralisation – Typically, pH estimations of cotton finishing effluents are on the alkaline side. Thus, pH estimation of equalized effluent ought to be balanced. Utilization of dilute sulphuric acid and boiler flue gas rich in carbon dioxide are regularly used ones. Since the greater part of the secondary biological treatments is compelling in the pH 5 to 9, balance step is an essential procedure to encourage.
  • pH Control:   To adjust the pH in the treatment process to make wastewater pH neutral.Ø For acidic wastes (low pH): NaOH, Na2CO3Ø , CaCO3or Ca(OH)2.  For alkali wastes (high pH): H2SO4Ø , HCl.
  • Mechanical flocculation – the textile waste water is gone through a tank under gentle stirring; the finely isolated suspended solids mix into bigger particles and settle out. Specific equipment, for example, clariflocculator is likewise accessible, wherein flocculation chamber is a part of a sedimentation tank.
  • Chemical coagulation: Coagulation aims to gathering the minute strong particles scattered in a fluid into a higher mass. Chemical coagulants like Al2 (SO4)3 {also called alum} or Fe2 (SO4)3 are added to wastewater to enhance the fascination among fine particles with the goal that they meet up and shape bigger particles called flocs. A chemical flocculent (typically a polyelectrolyte) improves the flocculation procedure by uniting particles to frame bigger flocs, which settle out more rapidly. Flocculation is supported by delicate blending which makes the particles impact.

Secondary Aerated lagoon

  •  Trickling filtration – The trickling filters for the most part comprises of round or rectangular beds, 1 m to 3 m profound, made of well-graded media, (for example, broken stone, PVC, Coal, Synthetic tars, Gravel or Clinkers) of size 40 mm to 150 mm, over which wastewater is sprinkled consistently on the whole bed with the assistance of a gradually turning distributor, (for example, rotating sprinkler) outfitted with orifices or nozzles. Therefore, the waste water trickles through the media. The channel of filter is organized in such a form, to the point that air can enter at the base; counter current to the effluent flow and a natural draft is produced. A gelatinous film, including microbes and aerobic micro-organisms known as Zooglea, is shaped on the surface of the filter channel medium, which blossom with the nutrient supplements provided by the waste water. The organic pollutants in the waste water are adsorbed on the gelatinous film amid its entry and afterward are oxidized by the bacteria and the other small scale creatures show in that.
  • Activated sludge process – This is the most versatile biological oxidation strategy utilized for the treatment of waste water containing broke down solids, colloids and coarse strong organic matter. In this procedure, the waste water is circulated air through in a response tank in which some microbial floc is suspended. The aerobicbacterial flora achieve biological degradation of wastes into carbon dioxide and water molecule, while consuming some organic matter for synthesizing bacteria. The microbe’s verdure develops and stays suspended as a floc, which is called Activated Sludge. The effluent from the response tank is isolated from the sludge by settling and released. A piece of the sludge is reused to same tank to give a compelling microbial populace to a fresh treatment cycle. The surplus sludge is processed in a sludge digester, alongside the primary sludge acquired from preliminary sedimentation. An effective air circulation for 5 to 24 hours is required for industrial wastes. Biochemical Oxygen Demand (BOD) to the degree of 90-95 % discharge can be accomplished in this procedure.
  • Oxidation ditch & pond – An oxidation pond is a vast shallow pond wherein stabilization of organic matter in the waste is realized for the most part by microorganisms and to some degree by protozoa. The oxygen necessity for their metabolic digestion is given by algae in the pond. The algae, thus use the CO2 discharged by the microorganisms for their photosynthesis. Oxidation ponds are sometimes renamed as waste stabilization ponds.
  • Anaerobic digestion – Sludge is the watery deposit from the primary sedimentation tank and humus tank (from secondary treatment). The constituents of the sludge experience slow fermentation or digestion by anaerobic microscopic organisms in asludge digester, wherein the sludge is kept up at a temperature of 35°C at pH 7-8 for around 30 days. CH4, CO2 and some NH3 are liberated as the final results.

Tertiary Oxidation technique

 

An assortment of oxidizing agents can be utilized to decolorize wastes. Sodium hypochlorite decolourizes dye bath effectively. In spite of the fact that it is an ease and low cost method, however it frames absorbable toxic organic halides (AOX). Ozone on decay creates oxygen and free radicals and the later consolidates with colouring agents of effluent bringing about the destruction of colours. The fundamental drawback of these methods is it requires a successful sludge producing pre-treatment.

 

•    Electrolytic precipitation and Foam fractionation – Electrolytic precipitation of concentrated dye wastes by diminishment in the cathode space of an electrolytic bath been accounted for extremely to a great degree long contact times were required. Froth/Foam fractionation is test technique in light of the wonders that surface-active solutes collect at gas-fluid interfaces. In any case, the chemical costs make this treatment strategy excessively costly.

 

•  Reverse osmosis – Reverse osmosis and electrodialysis are the vital cases of membrane/layer process. The TDS from waste water can be evacuated by reverse osmosis. These kind of osmosis technique is reasonable for expelling ions and larger species from dye bath effluents with high effectiveness (upto > 90%), clogging of the membrane by dyes after long use and high capital cost are the primary downsides of this process. Reverse osmosis process is reasonable for expelling high salt concentrations with the goal that the treated effluent can be re-utilized again in Textile wet processing processes. The presence of electrolytes in the washing water causes an expansion in the hydrolyzed dye affinity (for reactive dyeing on cotton) making it hard to remove.

  • Electrochemical process – They have lower temperature requirement than those of other proportionate non-electrochemical treatment and there is no requirement for extra chemical. Its additionally can prevent the creation of undesirable side products. Be that as it may, if suspended or colloidal solids were high focus in the waste water, they hinder the electrochemical response. Along these lines, those materials should be adequately expelled before electrochemical oxidation.
  • Ion exchange method – This is utilized for the expulsion of unfortunate anions and cations from waste water. It includes the section of waste water through the beds of ion exchange resins where some unfortunate cations or anions of waste water get exchanged for sodium or hydrogen ions of the resin. Most ion exchange resins now being used are synthetic polymeric materials containing ion groups for example, sulphonyl, quarternary ammonium assemble and so on..
  • Photo catalytic degradation – Photograph reactant debasement – A propelled strategy to decolourize an extensive variety of dyes relying on their molecular structure. In this process, photoactive catalyst illuminates with UV light, creates exceedingly responsive radical, which can break down organic compounds.
  • Adsorption (Activated Carbon etc.) – It is the exchange of material at the interface between two immiscible stages in contact with each other. Adsorption seems to have significant potential for the expulsion of colour from industrial effluent.

Fig. 2: Industrial Model of ETP Two types of effluent treatment

 

•         Wash Liquor effluent

•         Dye-bath effluent

 

These are the practical industrial setup of effluent treatment plant (ETP) which will found in the industries that deals with processing of goods with the aid of chemicals and other synthetics which place its footprint in the waste water. It is depicted in the figure 2.

 

Conclusion:

 

Among numerous engineering disciplines Civil Engineering, Mechanical Engineering, Electrical Engineering and so forth. Textile Engineering has an immediate association with environmental aspects to be explicitly and richly considered. Out of different activities in textile industry, chemical processing contributes around 70 % of contamination. It is well known that cotton factories consume extensive volume of water for different processes namely sizing, desizing, scouring, bleaching, dying, mercerization, printing, finishing and at last washing. Because of the nature of various chemical processing of textile materials, huge volumes of waste water with various toxins are released. Since these surges of water influence the aquatic eco-system in number of ways for example, depleting the dissolved oxygen content or settlement of suspended substances in anaerobic condition, a unique consideration should be paid.

 

The quality of life relies upon the capacity to oversee accessible water in the more noteworthy enthusiasm of the general population. Water consumption of good quality water and ecological contamination has given huge significance to the water management. Joints efforts are required by water technologists and textile industry specialists to decrease water utilization in the business. While the consumer enterprises should endeavor to advance water utilization, water technologists ought to receive a coordinated way to deal with water treatments and re-usage of it in the business. Our general view is to spare living species and its welfare condition. The main cause of generation of these kind of contaminants is the utilization of enormous volume of water either actual chemical processing or during re-processing in preparatory, coloring, printing and finishing. Indeed, in a down to practical estimate, it has been discovered that 45% material in preparatory processing, 33% in coloring and 22% are re-processed in finishing. In this manner we should quit utilizing chemicals and dyes, which deliver destructive impact to the biotic and abiotic factors in our eco-frameworks. Diminishment of waste at the source is the favored methodology rather than the customary technique for end of pipe waste treatment. Aside from dangerous chemicals and colors, the principle toxin is, obviously, water. Along these lines, the new advancements, which intend to decrease or eliminate water, are to be considered.

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REFERENCES and URLs

 

  1. Harold R, Park Ridge. N.J, “Pollution Control in the Textile Industry”, Jones NoyesData Corp., 1973.
  2. Best Management Practices for Pollution Prevention in the Textile Industry –Manual by US Environmental Prevention Agency, 1996.
  3. Pollution Prevention in Textile Industry manual by U.S EPA/SEMARNAP Pollution prevention work group, 1996.
  4. S.C.Bhatia “Handbook of Industrial Pollution and Control (Vol. 1 & 2), CBS edition, 2002.
  5. http://mytextilenotes.blogspot.com
  6. http://www.textileschool.com/Home.aspx