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UF technology contributes to the recycling of dye salt solutions
casestudy
UF Technology Contributes to the Recycling of Dye Salt Solutions Working in conjunction with an Indian textile manufacturer situated in the state of Tamil Nadu, the membrane filtration specialist Hydranautics has devised a new system that enables the recycling of the salt solution used in its dyes. The system was successfully tested in July of this year and is now in full operation at the processing plant, where it is helping to cut costs and save unnecessary waste. Hydranautics’ role in the project involved designing an ultrafiltration (UF) system for the recycling process. The company selected its HYDRAcap® capillary membranes for the duty, which offers particulate removal down to 0.1 microns in size. he aim of the recycling sstem set up at the Tamil Nadu textile processing facility was to reuse the NaCl solution for dye bath preparations, without adversely affecting the dyeing quality. Spent dyes, colour, suspended solids and hard salts were the contaminants targeted for removal. Hydranautics was responsible for the UF technology part of the project. The treatment plant comprises a three-step process. The first step involves colour removal, using lime, ferrous sulfate and anionic polyelectrolyte. This was achieved in a lamella separator, followed by a media filter. Next, the filtered effluent was processed in an UF system using Hydranautics’ HYDRAcap capillary membrane. This module contains fibres made from low fouling hydrophilic polyethersulphone material. Each fibre measures 0.8 mm (inside diameter) and over 13 000 such fibres are bundled into the module. The fibres have a dense microporous structure on the inside surface that removes all colloidal and particulate solids larger than 0.1 microns. The HYDRAcap UF membranes remove coloured colloidal particles that slip through upstream equipment. These particles are so small they cannot be seen with the naked eye, but they do give a light colour to the effluent. After the UF stage the effluent becomes colourless. If these particles were not removed, they would pass through the downstream ion exchange units into the treated NaCl solution and would affect the colour balance and characteristics of the dyed cloth. These colloids would also foul the ion exchange resins and affect their performance. The third step in the recycling process comprises of a twin-bed ion exchange (IX) system containing cation and anion resins. The cation
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20 December 2003
resin removes multivalent hardness ions, while the anion resin removes any residual colour from the solution. The resins are regenerated with hydrochloric acid and sodium hydroxide solutions. The system is designed to treat spent dye baths at a flow rate of 5.3 gpm. An equalization tank, 9.99 m3 in size, is used to collect and equalize the dye baths when they are drained.
Ultrafiltration system Table 1 shows the system design and operational details of the UF system. The skid mounted UF system uses one of Hydranautics’ HydraCap 40 ” (102 cm) modules. Furthermore, provision has been made for installing another module in the near future. The feed and backwash pumps, piping and flow measuring instruments were selected to cope with this eventuality. The flow rate can be doubled by simply by adding one module. Table 1.0: UF System Details Parameter Module Quantity Operation Mode Feed Flow Permeate Flow Feed Pressure Concentrate Pressure Permeate Pressure Permeate Flux Specific Flux Feed Temperature Backwash Sequence CEB - Hypochlorite - HCl CIP
Units gpm gpm psi psi psi gfd gfd/psi °C -
-
Description/Value HYDRAcap 40" One Dead end without bleed 5.3 5.3 ~3.5 ~3.0 ~1.0 ~24.0 10-11 25-32 every 30 minutes every 8 backwashes every 16 backwases Not done
ISSN 0015-1882/03 © 2003 Elsevier Ltd. All rights reserved
casestudy The backwash system consists of a UF permeate tank, with a capacity of 4.92 m3, and a backwash pump with a flow rate of 80 gpm. The backwash effluents are returned to the equalization tank for the recovery of the salt solution, so no service water is used during the normal operation of the UF system. Prior to start-up, the UF module is flushed with tap water to remove any preservatives and then disinfected by soaking it with 150 mg/l of hypochlorite solution for three hours. The module is then flushed to remove any hypochlorite solution before it begins filtering the salt solution. During continuous operation of the plant the UF system is backwashed every 30 minutes, for 30 seconds, to remove accumulated coloured solids. After three months of operation at the Indian facility, the effluent is still perfectly clear during the forward flush step. During the top and bottom wash operation, however, the effluent is yellowish and turbid, but this only lasts for 5 seconds before the discolouration disappears. Following installation, the UF system began life with a specific flux of 11.3 gfd/psi at a water temperature of 28 °C. It has since stabilized between 10-11 gfd/psi. Furthermore, the transmembrane pressure (TMP) and pressure drop across the module have remained low and constant throughout.
Plant performance Table 2 provides a summary of complete plant performance, including that of the UF system. The bulk of the dye is removed by coagulation and clarification in the lamella clarifier and filter. There is close to a 50% reduction in COD and an 80% reduction in hardness during this first step. The UF system essentially removes coloured colloidal particles that slip through the previous treatment step. The effluent after the UF and ion exchange system is extremely clear. It contains only NaCl, water and some dissolved organics, making it ready for recycling.
the dyed cloth created with the recycled salt solution was 2% lower than the cloth that had been made in the traditional manner, i.e. using fresh NaCl and tap water. However, this change was acceptable to the manufacturer because it is possible to adjust the bath composition and dyeing conditions to compensate for the loss. Any manufacturer involved in the textile industry can make this simple alteration so that the validity of the system is not affected. Hydranautics’ HydraCap The Indian plant is now in module removes operation every day for particulate material down between 8-10 hours. It has to 0.1 microns in size. successfully treated spent dye baths of different colours and different compositions and produced clear recyclable NaCl solution for preparing fresh dye baths. The chemical dosing mix for some fast colours required adjusting, but the flexibility built into the clarification stage has enabled these alterations to be easily made. This flexibility should prove to be invaluable as the system is rolled out industry wide. Authors: Makhan Jhawar, Hydranautics’ regional sales manager, India & Australia Craig Bartels, Hydranautics’ VP of R&D and Applications Technology Satish Chilekar, director of Environmental Solutions Inc
Contact: Hydranautics, 401 Jones Road, Oceanside, CA 92054, USA. Tel: +1 760 901 2500; Fax: +1 760 901 2578; E-mail: [email protected]; Website: www.membranes.com
Conclusions Initial tests at the Tamil Nadu textile processing plant in India revealed that the colour fastness of Table 2: Plant performance summary Parameter
Units
NaCl concentration Total suspended solids COD Colour pH Total hardness
g/l mg/l mg/l O2 mg/l CaCO3
Filtration+Separation
Spent bath 50-70 150-200 2000-2400 dark 6.5-7.5 220-250
After colour removal 50-70 5-15 1100-1216 light 7.5-8.5 <50
After UF 50-70 <1 1000-1150 colourless 7.5-8.5 <50
After IX 45-65 <1 850-960 colourless 7.0-7.5 <=5
December 2003
21
UF Technology Contributes to the Recycling of Dye Salt Solutions Working in conjunction with an Indian textile manufacturer situated in the state of Tamil Nadu, the membrane filtration specialist Hydranautics has devised a new system that enables the recycling of the salt solution used in its dyes. The system was successfully tested in July of this year and is now in full operation at the processing plant, where it is helping to cut costs and save unnecessary waste. Hydranautics’ role in the project involved designing an ultrafiltration (UF) system for the recycling process. The company selected its HYDRAcap® capillary membranes for the duty, which offers particulate removal down to 0.1 microns in size. he aim of the recycling sstem set up at the Tamil Nadu textile processing facility was to reuse the NaCl solution for dye bath preparations, without adversely affecting the dyeing quality. Spent dyes, colour, suspended solids and hard salts were the contaminants targeted for removal. Hydranautics was responsible for the UF technology part of the project. The treatment plant comprises a three-step process. The first step involves colour removal, using lime, ferrous sulfate and anionic polyelectrolyte. This was achieved in a lamella separator, followed by a media filter. Next, the filtered effluent was processed in an UF system using Hydranautics’ HYDRAcap capillary membrane. This module contains fibres made from low fouling hydrophilic polyethersulphone material. Each fibre measures 0.8 mm (inside diameter) and over 13 000 such fibres are bundled into the module. The fibres have a dense microporous structure on the inside surface that removes all colloidal and particulate solids larger than 0.1 microns. The HYDRAcap UF membranes remove coloured colloidal particles that slip through upstream equipment. These particles are so small they cannot be seen with the naked eye, but they do give a light colour to the effluent. After the UF stage the effluent becomes colourless. If these particles were not removed, they would pass through the downstream ion exchange units into the treated NaCl solution and would affect the colour balance and characteristics of the dyed cloth. These colloids would also foul the ion exchange resins and affect their performance. The third step in the recycling process comprises of a twin-bed ion exchange (IX) system containing cation and anion resins. The cation
T
20 December 2003
resin removes multivalent hardness ions, while the anion resin removes any residual colour from the solution. The resins are regenerated with hydrochloric acid and sodium hydroxide solutions. The system is designed to treat spent dye baths at a flow rate of 5.3 gpm. An equalization tank, 9.99 m3 in size, is used to collect and equalize the dye baths when they are drained.
Ultrafiltration system Table 1 shows the system design and operational details of the UF system. The skid mounted UF system uses one of Hydranautics’ HydraCap 40 ” (102 cm) modules. Furthermore, provision has been made for installing another module in the near future. The feed and backwash pumps, piping and flow measuring instruments were selected to cope with this eventuality. The flow rate can be doubled by simply by adding one module. Table 1.0: UF System Details Parameter Module Quantity Operation Mode Feed Flow Permeate Flow Feed Pressure Concentrate Pressure Permeate Pressure Permeate Flux Specific Flux Feed Temperature Backwash Sequence CEB - Hypochlorite - HCl CIP
Units gpm gpm psi psi psi gfd gfd/psi °C -
-
Description/Value HYDRAcap 40" One Dead end without bleed 5.3 5.3 ~3.5 ~3.0 ~1.0 ~24.0 10-11 25-32 every 30 minutes every 8 backwashes every 16 backwases Not done
ISSN 0015-1882/03 © 2003 Elsevier Ltd. All rights reserved
casestudy The backwash system consists of a UF permeate tank, with a capacity of 4.92 m3, and a backwash pump with a flow rate of 80 gpm. The backwash effluents are returned to the equalization tank for the recovery of the salt solution, so no service water is used during the normal operation of the UF system. Prior to start-up, the UF module is flushed with tap water to remove any preservatives and then disinfected by soaking it with 150 mg/l of hypochlorite solution for three hours. The module is then flushed to remove any hypochlorite solution before it begins filtering the salt solution. During continuous operation of the plant the UF system is backwashed every 30 minutes, for 30 seconds, to remove accumulated coloured solids. After three months of operation at the Indian facility, the effluent is still perfectly clear during the forward flush step. During the top and bottom wash operation, however, the effluent is yellowish and turbid, but this only lasts for 5 seconds before the discolouration disappears. Following installation, the UF system began life with a specific flux of 11.3 gfd/psi at a water temperature of 28 °C. It has since stabilized between 10-11 gfd/psi. Furthermore, the transmembrane pressure (TMP) and pressure drop across the module have remained low and constant throughout.
Plant performance Table 2 provides a summary of complete plant performance, including that of the UF system. The bulk of the dye is removed by coagulation and clarification in the lamella clarifier and filter. There is close to a 50% reduction in COD and an 80% reduction in hardness during this first step. The UF system essentially removes coloured colloidal particles that slip through the previous treatment step. The effluent after the UF and ion exchange system is extremely clear. It contains only NaCl, water and some dissolved organics, making it ready for recycling.
the dyed cloth created with the recycled salt solution was 2% lower than the cloth that had been made in the traditional manner, i.e. using fresh NaCl and tap water. However, this change was acceptable to the manufacturer because it is possible to adjust the bath composition and dyeing conditions to compensate for the loss. Any manufacturer involved in the textile industry can make this simple alteration so that the validity of the system is not affected. Hydranautics’ HydraCap The Indian plant is now in module removes operation every day for particulate material down between 8-10 hours. It has to 0.1 microns in size. successfully treated spent dye baths of different colours and different compositions and produced clear recyclable NaCl solution for preparing fresh dye baths. The chemical dosing mix for some fast colours required adjusting, but the flexibility built into the clarification stage has enabled these alterations to be easily made. This flexibility should prove to be invaluable as the system is rolled out industry wide. Authors: Makhan Jhawar, Hydranautics’ regional sales manager, India & Australia Craig Bartels, Hydranautics’ VP of R&D and Applications Technology Satish Chilekar, director of Environmental Solutions Inc
Contact: Hydranautics, 401 Jones Road, Oceanside, CA 92054, USA. Tel: +1 760 901 2500; Fax: +1 760 901 2578; E-mail: [email protected]; Website: www.membranes.com
Conclusions Initial tests at the Tamil Nadu textile processing plant in India revealed that the colour fastness of Table 2: Plant performance summary Parameter
Units
NaCl concentration Total suspended solids COD Colour pH Total hardness
g/l mg/l mg/l O2 mg/l CaCO3
Filtration+Separation
Spent bath 50-70 150-200 2000-2400 dark 6.5-7.5 220-250
After colour removal 50-70 5-15 1100-1216 light 7.5-8.5 <50
After UF 50-70 <1 1000-1150 colourless 7.5-8.5 <50
After IX 45-65 <1 850-960 colourless 7.0-7.5 <=5
December 2003
21