Zero Discharge In Textile Processing Through TDS ControlBy B.D. Thakur, M. Joshi, M. Chakraborty, S. Pathak, Northern India Text. Research Assns., Ghaziabad, India Abstract The requirement of a high concentration of soluble inorganic salts in the dyebath recipe in cotton reactive reactive dyeing causes the eventual discharge of intensely colored dye effluent that contains a high level of total dissolved solids (TDS). The limitation of a conventional treatment scheme in removing the inorganic TDS has restricted the recovery and reuse of water from the resultant combined stream in other processing. Also, the repeated recirculation of conventionally treated water causes a further enhancement of inorganic TDS during the process recirculation and treatment stage. This article explores an appropriate treatment scheme for removing the dyestuff and other impurities from the segregated dye effluent by adopting physico-chemical and tertiary polishing treatments. This process helps in achieving commercial zero hardness and low level of metal content in the recovered water, providing an excellent scope for its reuse in the dyeing process itself. The waste inorganic chemicals were also recovered in the concentrated form or in pure crystalline form and were reused in the dyeing operation. The fastness properties such as light, washing and rubbing of the yarn after dyeing with recovered water and salt have been found comparable to the original samples dyed using fresh chemicals and soft water. The repeated recirculation does not cause any significant enhancement of TDS or metal content in the recirculated water. This helps in the indirect control of TDS limit for the remaining major segregated water as prescribed by the concerned pollution boards in its disposal into the outside environment, after repeated recycling. Table I: Dye removal from colored effluent using three different coagulant systems. System-l % Dye Removal Metal ion System-Ii % Dye Removal System-Ill % Dye Removal Metal ion (Fe +3 ) (ppm) 21 41 83 129 259 388 517 647 776 Before After Polishing Polishing Before After Metal ion (Al + 3) (ppm) 21 32 43 53 107 214 428 - Polishing Polishing After Before Polishing Polishing (Fe +2 ) (ppm) 50 100 151 202 252 302 352 403 504 605 80.7 83.4 84.9 86.0 87.0 89.0 91.5 92.4 93.7 94.4 99.76 99.69 99.81 99.55 99.56 99.58 99.63 99.68 99.83 99.89 83.5 84.6 86.5 87.7 88.5 89.8 90.6 - 99.90 99.89 99.85 99.86 99.88 99.81 99.87 - - 83.8 85.1 86.8 88.2 89.0 89.5 90.9 91.6 92.7 - 99.8 99.8 99.8 99.8 99.8 99.8 39.8 99.8 99.8 - lntroductlon The increasing cost and non-availa- bility of good quality water, especially in the arid regions of the developing countries, have magnified the already existing water crisis in the industrial sector. This has made it an imperative for the industry to try to adopt such waste water treatment schemes where recovery and reuse of the treated water is envisaged. Textile wet processing is a highly water intensive operation. The various chemicals like starch, dye-stuff, auxiliaries, alkalies, acids, detergents etc., that are used in the processing contaminate the water and cause pollution in terms of BOD, COD, pH, TDS, color, hardness etc., in the discharged effluent. Unexhausted soluble reactive dyes present in the textile dyeing effluent exhibit their color which is highly objectionable from the environmental and aesthetic point of view. Particularly, the reactive dyes or their hydrolyzed form hardly undergo biodegradation and thus pass through the treatment plant, causing serious contamination of natural water. Moreover, an increased use of cotton in textile products has significantly increased the use of direct, vat, sulphur and, especially, reactive dyes. These dyeing processes require large quantity of salts to achieve good exhaustion of the dye bath. As a result, the content of total dissolved salts (TDS) in these textile effluents is very high. Hence, reactive dyebaths are not amenable for reuse due to the presence of unabsorbed dye along with other contaminants and high TDS present in the bath at the end of the cycle. Several techniques investigated by earlier workers have been reported in review papers1-4 on handling such effluents, especially for the removal of color from the dyeing effluent. These are as under: i) activated charcoal (adsorption technique) ii) membrane technology iii) ozone treatments iv) coagulation/flocculation. not techno-economically viable for the textile industry. used were of analytical Experimental In all the experiments the dye recipe used is presented in tabular form as: .4 Various techniques such as reverse osmosis.0 g/l 60.0 g/l 3.g. therefore.000 ppm) and the possibility of recirculation of treated water in the process house. involve high cost and are. It is. M:L = 1:30 Dyebath constituents Depsoluble ACA (ICI) Matexil PA-L (ICI) Calgon (ICI) Common salt Dye Reactofix Brill HE-8B Soda Ash Caustic soda 85°C 60 min 1.. Such water increases the tendency to form incrustations in sewers due to the high amount of dissolved salts. Matexil PA-L Anti-reducing agent Water softener + Calgon sequestrant All of the chemicals such as sodium chloride. except the coagulation technique. An attempt has also been made to critically evaluate the various problems encountered in the reuse of water and recovered salt. The remaining effluent can be treated using a simple technique at a comparatively low cost.5 Another such example is the use of cellulose based cation exchange composite for color removal of some basic dyes. This also reduces the calcium and magnesium contents of soil. and all of them. but it fails to control the total dissolved solids (TDS) level. Shade: Red. This article deals with an in-depth study of a physico-chemical treatment scheme of removing color from the reactive cotton dyeing effluent having a high level of TDS (60.2 g/l Note: Depsoluble ACA.6 The conventional treatment scheme generally employed in the textile industry though removes color and reduces the BOD/COD level to permissible limits. hardens the texture of soil. Recovery of salt from the segregated dye effluent which is only about 10% to 20% of the total combined effluent will make this process highly cost-effective.Although these treatments are effective in color removal. sodium hydroxide etc. polyamide -ipichlorohydrin-cellulose polymer have been used for acid dye removal.Fiber lubricant which also minimizes the risk of dye stains.0 g/l 1 . time to search for other techno-economically viable alternative devices in order to recover and reuse the waste inorganic chemicals so that the remaining water can be recovered and recirculated without any technical hurdles.000 to 80. Newer technologies have also been reported in recent literature where specific dye adsorbers-e. have also currently emerged to reduce the TDS level in such salt rich effluent streams. but limitations of such processes are exposed after attaining a certain concentration level. therefore.0 g/l 8% (owf) 5. prevents penetration of roots and affects the subsoil water.0 g/l 0.. demineralization etc. sodium carbonate. each technique has its associated problems. Inorganic Salts (a) The presence of inorganic salts like sodium chloride or sodium sulphate at a level varying from 2 % to 8 % i.8 125 100.88 93.5 'Using Navy Blue HE-2R special recipe formulation depending on the type of shade desired.71 99.99 92. The reactive dyes used in the experiments were as under: l-For red shade. Thalactive green HE-4BD (Goldpal Chem. model 121E) was used for measuring the pH.4370 After Polishing Treatment Dye cone (ppm) 0.91 100. The presence of additional chemicals like water softener.25 98.8 50.75 98. according to BIS specification for color fastness to light (IS: 2454:1967) and color fastness to washing. Such recipe has the special characteristics as mentioned below: order to maintain the desired pH range from 9 to 10.93 99.18 97.69 99.7856 0. A pH meter (Electronic India.8 50.95 99.8 50.61 99. Navy blue HE-2R (Serene Dyestuff Industries Ltd) 4-For green shade.585 10.1 201.4 100.82 98.74 94.9 93. color.000 to 20.1 201.52 93.2506 0.25 99. Industry) S-For navy blue shade.70 95.37 99.2282 6.93 99..75 88. and the actual effluent thereafter obtained was used.2336 0. hardness and iron content were determined using the respective BIS specifications. recovered water and chemicals and those using only recovered chemicals were subjected to light and wash fastness tests etc. The different dyed yarns using original dye solution.17 99.11 98. test no.4 100.89 96. COD.0% (5.41 97. HE-8 B (Jaysynth) Dyechem Pvt Ltd) 2-For golden yellow shade. The experimental recipe was used for dyeing scoured yarn with reactive dye HE-8B (red shade) in experiments.grade.70 99.8 50.93 99. For other shades. 20. Thalactive golden yellow HE-RB (Goldpal Chem.12 93.87 98.e. In reactive cotton dyeing. (b) The requirement of soda ash /caustic soda varying from 0.4 100.95 8 20 40 80 100 50. Effluent and treated water characteristics such as pH.7 89.4 87. the final treated water was directly employed in the experiments or salts were recovered from the treated water and reused in the dyeing operation.95 - - Colorless Table III: Dye removal from simulated effluent of varying concentrations.40 99.4 100. The reactive dye concentration varies from 2% to 8% (on the weight of fabric/yarn to be dyed).84 99.5 100.5 100.78 % Dye Removal 99.25 92. TDS. Auxiliary Chemicals Dye concentration and The concentration of reactive dye depends on the type and depth of product shade.98 91.1 201.021 16. etc. The effluent thus received was initially given physico-chemical treatment after which it was polished in order to ensure the removal of iron and hardness.5% to 2. 3 (IS: 764-l 979).000 ppm.8 151.000 ppm) in Results and Discussion The major bottleneck encountered in the recovery and recirculation of treated water from the segregated textile dye effluent is its high TDS content and the possible contamination by iron ions.20 98.8 151..1050 % Dye Removal 90. In the physico-chemical treatment commercial grade metallic salts and flocculating aids were used. simulated effluent was prepared to study the effectiveness of chemical treatment for all types of dye structures.5 98. Reactofix Brill Red. Original Dye* Cone (ppm) Metal ion Cone (ppm) Dye removal % in treated water % Dye Removal % Dye Removal After PhysicoAfter Polishing Chemical (ppm) Treatment 87. it requires the 34 American Dyestuff Reporter August I994 . Dye Used Characteristics of Treated Effluent After Physico-chemical Treatment Dye cone (ppm) Red ( HE-8B) Golden Yellow HE-RB) Green (HE-4BD) Navy Blue (HE-2R) Mixture of Dyes 18.72 99.87 99.71 94. fiber lubricant and antireducing agents are also present. Table II: Dye removal from simulated effluents of varying colors.000 to 80.88 99.4 90. Industry) Dye concentration in the effluent and treated water was measured using optical density method by UV/VIS spectrophotometer (Model-ShimadzuUV160A) and respective dye concentration evaluated using a calibration curve.4 89.8 150 200 151.87 99.44 96. Thus. . After further polishing of the treated water it is observed that dye removal could be achieved more than 99. Test Conducted Initial Dyeing sample Samples Redyelng After using treated water by Al3+ system 6/7 Dyeing with recovered salt Redyeing After using treated water by Fe2 + system 6/7 Treatment Scheme As per the scheme.Change in shade . Table IV shows the initial and final TDS values. the initial experiments deal with the critical evaluation of the dye effluent characteristics and the necessary treatments to be provided. formed is insoluble and can be removed easily. This implies the effect of chemical dosing is equally effective for most of the reactive dyes commonly employed in the dyeing. as shown in Table I. The reuse of such treated water and its further recirculation will lead to the gradual enhancement of TDS value.Although the undesirable properties of water containing aluminum are less serious. color. giving a major thrust to the recovery and reuse of spent waste inorganic chemicals following a suitable techno-economically viable process. 10 60 110 I60 210 260 310 3 6 0 410 4 6 0 510 560 610 EFFECTIVE ION CONCENTRATION (PPm) 660 710 750 Table V: Evaluation of fastness properties. This also indicates that the efficiency of dye removal increases as the original dye concentration in the effluent is enhanced. 2100 mg/l) as prescribed by concerned pollution control boards is a difficult task unless the problem is tackled by alternative ways and means. The dye concentration in the effluent has been found to vary from 16 ppm to 400 ppm.7 Excess iron [Fe( + 2)] removal was ensured in the experiments by maintaining a pH above 6 and providing proper aeration so that all iron in ( + 2) state is oxidized to Fe( + 3) and precipitates in the form of insoluble Fe(OH).5%. Table III shows the degree of chemical dosing to be maintained according to the initial level of dye concentration which varies from 8 to 200 ppm. strict maintenance of TDS level (e. Figure P-Effect of metal ion concentration on percentage of dye removal. the dye effluent is segregated from the other wash streams and subjected to the physicochemical treatment until final polishing as shown in the schematic flowdiagram in Figure 1. This shows the degree of chemical dosing and coagulant aid concentration required for complete removal of dye is directly proportional to the dye concentration present in untreated effluent. Excess iron in Fe( + 2) or reduced state is soluble and thus must be converted to Fe( + 3) or an oxidized state.Staining on white cloth Color fastness to Rubbing Dry Wet 7 6/7 4/5 4 4/5 4 4 4 4 3/4 3 3/4 3 3/4 3 3/4 3 treatment at a constant level of chemical dosing. Consequently. pH. which ultimately makes it unfit for further recirculation and needs inevitable disposal into the outside drain. Figure 3 shows the variation of percent dye removal as a function of initial dye concentration. which may be removed easily.g. excess iron present in process water can lead to staining and is therefore objectionable. With this objective in view. Figure 2 shows the effect of metallic ion concentration on the percentage removal of reactive dye while dealing with the actual dyeing effluent with the dye concentration of 212 ppm where mare than 90% of dye could be removed. Table II shows the type of different reactive dyes used in the experiments and the percentage removal of dye from their simulated effluent having an initial dye concentration of 200 ppm before Color fastness to light Color fastness to washing (Test No 3) . as the Fe (OH). COD and iron content present in the effluent before and after the chemical and polAmerican Dyestuff reporter August 1994 . depending on the depth of the shade of the fabric being dyed and the type of dye used. hardness. The light. 24. pp. Acknowledgement The authors are high/y grateful to Dr. MR. (6) Abo-shosha. Tecoya Technical Update. but its reuse in concentrated form up to a certain level is very much techno-economically feasible. Textile Dyer & Printer. Seaborg. Figure i-Effect of dye concentration in the effluent on the percentage of dye removal. Sept. ing and rubbing fastness of dyed yarn using fresh and recovered water are shown in Table V. J. NlTRA for his constant encouragement and support in carrying out this work. February (1993) 41. But as dis cussed earlier. G. July (1993) 37. F?. Othmer. 397. (1993) 10.. and the recovered salts were reused in the subsequent dyeing operations using soft water. the reuse of such treated (recovered) water is limited to its application where the dye bath recipe is formulated for dyeing deeper shade: only. The salt recovery by this technique is expected to be quite economical and comparable to the cost of commercial salt of the same purity. N. American Dyestuff Reporter. However.. Soc. Perhaps the most prominent feature of this study is that the TDS level of discharged water is maintainable within pollution control board limits without any harmful effect on the environment with a scope of repeated recycling of recovered water. P.S. 3rd Ed. M. ed..F. such treated water containing a high amount of dissolved salts can be reused only when deeper shades need to be dyed. (1993) 23. Jai Prakash. A. Dyer and Co/.. Appl. The possible contamination of recovered salt by iron ions was crosschecked by an optical density method using a calorimetric method of iron determination. Aug. (1984) Vol. The salt was recovered from the highly salt rich treated water using a multiple vacuum evaporator..A. (7) Kirk-Othmer Encyclopedia of Chemical Technology.C.G. In the case of lighter shades.. quence of the addition of various salts Therefore. Overberger.M. M..00125% which is very much within the safe limit prescribed for salt water to be used in the process houses.. Yadav for their he/p in the experimental work.. (5) Hwang. Maheshwar Singh and Mr. K. References (1) Cooper. (4) Sharma. Director. the dyeing recipe formu lation also depends on the time se. H. wash. H. J. Colourage. M. Our thanks also to Mr. 49 (1993) 975. 109 (1993) 97. Conclusions The recovery and reuse of inorganic salts has significant importance as far as the water recovery and its reuse in the process is concerned. as in a case where the presence of a high quantity of salt in the initial dye ing water is acceptable. C. John Wiley &Sons.. and Chen..T. an alter. as available in the market.ishing treatment. D.H. native scheme was tried where the treated water is concentrated. As shown in Table IV. and Halwagi. August 1994 American Dyestuff Reporter . (3) Sharma. It is quite obvious that the recovery cost of the salt in crystalline form exceeds the cost of commercial salt. Such recovered water has been used in the dyeing operation. Iron content in the recovered salt was found to be in the range 0.. Polymer Sci.. Ibrahim. Mark.EI.F. (2) Sampath.. the final recovered water after treatment satisfactor ily meets the standards specified for it: use in the dyeing operation.