Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/58—Multistep processes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
  • B01D61/025—Reverse osmosis; Hyperfiltration
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
  • B01D61/027—Nanofiltration
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
  • B01D61/04—Feed pretreatment
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F9/00—Multistage treatment of water, waste water or sewage
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2311/00—Details relating to membrane separation process operations and control
  • B01D2311/04—Specific process operations in the feed stream; Feed pretreatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2311/00—Details relating to membrane separation process operations and control
  • B01D2311/12—Addition of chemical agents
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/001—Processes for the treatment of water whereby the filtration technique is of importance
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
  • C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
  • C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/30—Organic compounds
  • C02F2101/308—Dyes; Colorants; Fluorescent agents
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/30—Nature of the water, waste water, sewage or sludge to be treated from the textile industry
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2209/00—Controlling or monitoring parameters in water treatment
  • C02F2209/02—Temperature
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2209/00—Controlling or monitoring parameters in water treatment
  • C02F2209/03—Pressure
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2209/00—Controlling or monitoring parameters in water treatment
  • C02F2209/05—Conductivity or salinity
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2209/00—Controlling or monitoring parameters in water treatment
  • C02F2209/40—Liquid flow rate

Definitions

• the present invention relates to a process for the treatment of baths for the dyeing of cellulose fibres with reactive dyes comprising a prefiltration, then a neutralization, then a nanofiltration and then a reverse osmosis.
• hydrolysed dye not fixed to the material. This residual amount is responsible for the unacceptable colouring of the effluents.
• the standards relating to the salinity of waste water are today becoming increasingly strict.
• the invention consists in isolating the dye bath and in then filtering, neutralizing and treating it by nanofiltration (NF)/reverse osmosis (RO) coupling, separately, for the purpose of recovering most of the water of the bath devoid of dyes and of chemical products but with most of the salt introduced at the start of the dyeing, on the one hand, and, on the other hand, a minimum volume of an aqueous solution comprising the other compounds and in particular the hydrolysed reactive dyes.
• the water thus obtained is reused in a new dyeing.
• the aim of the process is to recover in value and to treat a dyeing effluent not in order to be allowed to discharge it but in order to reuse it.
• membrane filtration has the advantage of being efficient in terms of separation, of consuming little energy, of being able to be used continuously and to be easily automated, of offering a very low dead volume and a very high specific surface area, and, finally, of carrying out the desired separation in a single stage with the addition of a third substance.
• Membrane filtration can therefore advantageously replace more conventional biological or physicochemical operations used essentially for effluent treatment.
• RO reverse osmosis
• NF size of the solutes: 0.5-1.5 nm
• ultrafiltration size of the solutes: 1.2-500 nm
• microfiltration size of the solutes: 500-10 000 nm
• retentate The feed stream which has not passed through the membrane is known as the "retentate".
• the retentate can be collected directly but, in this case, to obtain a satisfactory effectiveness, it is necessary to use large membrane surface areas (or to repeat the operation over several successive filtration devices).
• the retentate can also be recycled to the main tank, which is the most common and most economical procedure, and that which will be described in this invention.
• Permeate flux flow rate of the material passing through the membrane / surface area of the membrane. This flux, given for a given transmembrane pressure (tmp), is generally corrected to 20°C by taking into account the variation in the viscosity of the solution as a function of the temperature.
• Filtration membranes are chemically aromatic polymers of crosslinked polyamide type which are deposited as a thin layer ("skin"), providing the selectivity, above a layer of microporous polymer (support), providing the mechanical strength, to provide a composite membrane structure.
• a membrane structure is commonly denoted TFC (thin film composite).
• Nanofiltration and reverse osmosis membranes are available from known suppliers of reverse osmosis membranes and of other membranes which operate in pressurized processes. Mention may be made, for example, of the companies: Osmonics, Millipore, Pall or Filmtec.
• Nanofiltration and reverse osmosis membranes are typically packaged in modular form.
• a module of "spiral-wound" type is very often employed as this type of module exhibits the advantages of being compact, of having a low pressure drop and a low dead volume, and of being reasonably priced. It is this type of module which will be used in the description of this invention. However, modules of another type, with a different configuration, such as flat membranes, can also be employed.
• the main applications of nanofiltration are the production of softened water or of ultrapure water and the selective removal of multivalent ions with respect to monovalent ions.
• the removal of silica and of sulphate in brines is very important industrially. This is because the silica dissolved or in suspension in the brine which feeds the process for the manufacture of chlorine by electrolysis (in particular the membrane cell process) presents a problem because it forms a coating on the surface of or inside the ion-exchange membrane separator.
• the silica if it is present in the feed brine, also results in insoluble deposits on the anode, which result in an increase in the cell voltage and in premature wear of the coating of the anode.
• sulphate is a common component of commercial brine and, when specific operations are not carried out to remove it, it enters the electrolytic system, where it accumulates. With time, the concentration of sulphate increases and disrupts the electrolysis by causing operational problems due to localized precipitation in the electrolysis cells. It is therefore desirable for the concentration of sulphate or of silica in the concentrated brine to be reduced as much as possible. This is why nanofiltration methods have been described for replacing conventional methods for the precipitation of the harmful salts.
• Patent WO 96/33005 discloses a nanofiltration process for removing sulphate, silica and dichromate from a brine solution.
• Patent US 5 858 240 discloses a nanofiltration process for reducing the concentration of sulphate, of silica, of dichromate or of phosphate in the feed brine of the process for the manufacture of chlorine or of the chlorate process.
• K. Linde et al. describe the nanofiltration of saline solutions originating from landfill sites (leachate) which makes it possible to retain the heavy metals, which are polyvalent cations, such as Cd, Zn, Pb or Cr, and to discharge the monovalent cations, such as Na or K, which are substances of low toxicity (Desalination, No. 103 (1995) 223).
• Foster et al. remove chlorinated organic derivatives and pesticides from drinking water by nanofiltration (J. Inst. Water Environ. 5 (1991) 466-477).
• Garema et al. describe the standardization of the quality of milk by nanofiltration of amino acids over an organic membrane (Ie lait [Milk], 76 (1996), 267-281 ).
• Trebouet et al. describe the treatment of leachates from landfill sites by nanofiltration and ultrafiltration, in order to bring about the passage of organic molecules of moderate size at the expense of large organic molecules (not necessarily biodegradable molecules) (Rev. Sc. Eau [Sci. Rev. Water]; No. 3 (1993), 365-381).
• Object of the present invention is therefore a process for the treatment of baths for the exhaustion dyeing of cellulose fibres with reactive dyes comprising a prefiltration, then a neutralization, then a nanofiltration and then a reverse osmosis.
• the instant process is characterized in that the dye baths are industrial baths and in that they comprise hydrolysed reactive dyes which preferably belong to the trichloropyrimidine, difluoropyrimidine, difluoromonochloropyrimidine, monochlorotriazine and vinyl sulphone families.
• the prefiltration is carried out with a filter with a membrane having a preferred cutoff threshold of between 80 and 120 microns.
• the neutralization is carried out with acid, preferably hydrochloric acid, in the presence or absence of bubbling of air.
• the separation is carried out in an aqueous solution, on the one hand, of inorganic salts present at high concentrations, on the other hand, of hydrolysed reactive dyes having masses close to those of the cutoff threshold of the membrane.
• the feed liquor is continuously introduced into a filtration module comprising a nanofiltration membrane under a positive pressure to provide a liquor which has passed through the membrane (permeate) and a liquor which has transited without passing through the membrane (retentate), the retentate being continuously directed to the feed tank.
• hydrolysed reactive dyes are concentrated upstream of the membrane and inorganic salts are removed through the membrane via a concentration step.
• the concentration of hydrolysed reactive dyes upstream of the membrane is kept constant by addition of pure water and inorganic salts are removed through the membrane via a diafiltration step.
• the nanofiltration stage can operate (i) in a single step (concentration), (ii) in two steps (diafiltration-concentration), or
• the initial concentration of inorganic salts is between 30 and 100 g/l.
• the feed liquor has an initial concentration of inorganic salts of between 5 and 70 g/l , preferably between 10 and 15 g/l.
• the retentate from the reverse osmosis is composed of pure water comprising inorganic salts concentrated to between 3 and 8% by weight, without coloured waste products, at a pH preferably of between 5.5 and 6, and in that it can be reused in dyeing.
• the object of the present invention is to provide an innovative process which makes it possible to separate several compounds present in an aqueous solution so as to carry out the most complete recycling possible of a compound with respect to the other compounds and to recycle the greatest possible amount of water. More specifically, the object of the invention consists in separating and concentrating inorganic salts, dyes and organic additives which are soluble in water.
• the dyes in question are reactive dyes which either become attached by virtue of a covalent bond to the cellulose or are hydrolysed and remain in the bath.
• the inorganic salts in question are compounds having the sodium cation and the Cl " , S0 4 2" or C0 3 2" anion.
• the organic additives in question are partially neutralized compounds based on polyacrylic acid, dispersions of polyethylene waxes, or sulphonated polymers.
• the aqueous solution comprising only concentrated inorganic salts without hydrolysed reactive dyes which is thus obtained can be reused for a new dyeing. This results in savings in water and in sea salt, in a simplification of the conventional treatment of the other baths and in a drastic reduction in the salinity of the effluents.
• the other separated part, which is low in volume and comprising the hydrolysed reactive dyes and the chemical products at high concentrations, will be readily treated conventionally (incineration or placing in a landfill site).
• the invention relates to a prefiltration-neutralization- nanofiltration-reverse osmosis process.
• the aim of this very important stage is to remove the cotton fibrils and other large compounds which may block the membranes downstream of the process.
• the formation of these fibrils is intrinsic to the exhaustion dyeing technique on modern dyeing machinery. It depends on the type of material (jersey, interlock, loop, and the like) and on the quality of the yarn, namely the mean length of the fibres and the degree of twist.
• the range of cutoff thresholds envisaged varies from 10 to 200 microns, preferably from 80 to 120 microns. Various prefilter tests have shown that the use of a mean cutoff threshold of 100 microns is sufficient to completely carry out this removal.
• NEUTRALIZATION STAGE 2
• the aim of this stage is to neutralize the alkali salts present in the form of carbonate essentially and of sodium hydroxide, with acid, preferably hydrochloric acid, in order to convert them to sodium chloride and to carbon dioxide gas.
• acid preferably hydrochloric acid
• hydrochloric acid we have shown that it is optimal to bubble air during the neutralization with hydrochloric acid in order to remove as rapidly and as completely as possible the carbon dioxide gas formed. If the pH of the water is insufficiently acidic and if C0 2 is present, sodium bicarbonate is reformed.
• a feed liquor is introduced into a filtration module comprising a membrane, under a positive pressure, to provide a liquor which has passed through the membrane (permeate) and a liquor which has passed over without passing through the membrane (retentate), and the retentate is recycled to the tank comprising the feed liquor.
• the aim of this nanofiltration is, first, to keep constant and then to increase as much as possible the concentration of dye in the retentate and reduce as much as possible the concentration therein of inorganic salts; and, secondly, to obtain the greatest possible concentration of inorganic salts, the lowest possible concentration of inorganic compounds (hydrolysed dyes, dye additives) and the maximum volume of water in the permeate.
• the initial concentrations of the inorganic salts in the feed liquor are between 30 and 100 g/l.
• the prior art does not indicate examples of a separation of hydrolysed reactive dye / inorganic salts at high concentrations present in real industrial solutions at high concentrations. This is because it has been shown that the flux decreases on average by a power of 10, while the retention of salt becomes very low, when the concentration of inorganic salt increases and reaches values of 10 to 20% by weight per volume (M. Nystrom et al.; J. Membrane Science, 98 (1995), 249-262).
• the dye is at a concentration of 0.01 to 4 g/l (with a preferred mean of 2 g/l); the inorganic salts are at a concentration of 1 to 100 g/l (with a preferred mean of 70 g/l).
• the third stage of the process according to the invention operates at pressures of 1 to 40 bar, preferably at 10 bar, and at circulation flow rates of 100 to 600 l/h, preferably between 250 and 350 l/h. They can be carried out at any desired temperature chosen between 0°C and the boiling point of the feed liquor. However, it is limited by the temperature range recommended for the membrane (5°C to 70°C), preferably between 45 and 55°C.
• This nanofiltration stage can be carried out in two or three stages depending on the concentration and the nature of the hydrolysed reactive dye but also on the concentration of salts. If the concentration of hydrolysed reactive dye alone is taken as basis, the following classification may be proposed:
• the stage of preconcentration of the dyes consists in recovering the maximum of the salts downstream of the membrane. In fact, the greater the concentration of salt upstream, the greater the amount of salts which passes through the membrane. When the concentration of hydrolysed reactive dye becomes too great upstream of the membrane, that is to say when the permeate flux becomes too low, the diafiltration stage is begun.
• the diafiltration stage consists in recovering the salts downstream of the membrane while operating at a constant concentration of hydrolysed reactive dye upstream.
• pure water is added to the main reactor at a flow rate equal to the value of the permeate flow rate.
• purified water is understood to mean water with a concentration of inorganic salts such that the conductivity does not exceed 1 mS.cm "1 and which is devoid of hydrolysed reactive dye.
• the concentration stage consists in concentrating the hydrolysed dyes as much as possible. This concentration stage is halted when the permeate flux becomes too low or the blinding too great, more specifically when the permeate flux is approximately less than 1 l.h “1 .m “2 .bar “1 (approximately 20% of the initial permeability of the membrane) in the case of the solutions described in this invention.
• This stage does not have to take place when the concentration of hydrolysed reactive dye at the beginning of stage 3 is very low. This is the case with colorations in light shades, whatever the category of reactive dyes used, or light, medium, indeed even dark, colorations produced with reactive dyes having a high degree of fixing. This is because a stage of preconcentrating the dyes is sufficient. On the other hand, from the point where diafiltration is necessary, it is necessary to recover, by reverse osmosis in the permeate, the pure water introduced during the diafiltration and, in the retentate, a brine comprising as much as possible salts originating from the dye bath.
• the aim of the reverse osmosis is therefore, on the one hand, to increase as much as possible the concentration of inorganic salts without decomposing them and, on the other hand, to obtain the purest possible water.
• the initial concentrations of the inorganic salts in the feed solution depend on the diafiltration stage and are between 5 and 70 g/l with a preferred mean of 10 - 15 g/l. We have found that it is possible to efficiently concentrate an inorganic salt (or several inorganic salts), even when their concentrations are greater than 1 % by weight.
• the fourth stage of the process according to the invention operates at pressures of 1 to 80 bar, preferably at 70 bar, and at circulation flow rates of 300 to 800 l/h, preferably at 600 l/h. It can be carried out at any desired temperature chosen between 0°C and the boiling point of the feed liquor. However, it is limited by the temperature range recommended for the membrane (5°C to 70°C).
• the pH used in the process according to the invention is between 5.5 and 6, a function in fact of the conditions of the second stage.
• the concentrations of the inorganic salts recovered in the retentate of the reverse osmosis are between 30 and 80 g/l with a mean of 60 g/l.
• FIG. 1 is a diagrammatic representation of the complete process described in this invention.
• Steps 1 and 2 are stages of pretreatment of the effluent which make it possible to carry out Stages 3 and 4 under the best possible conditions.
• the solution is conveyed to Stages 3 and 4, which constitute the core of this invention. All the tests were carried out on baths originating from industrial dyeing and not on reconstituted baths. All the membrane filtration (nanofiltration and reverse osmosis) tests were carried out with membrane surface areas of between 0.4 and 5 m 2 , preferably 2.5 m 2 .
• the dyeing plant effluent is first conveyed to prefiltration in Stage 1.
• the object is to stop the cotton fibrils present in order to avoid blinding of the membranes in Stages 3 and 4.
• Stage 2 is a stage of neutralization of the sodium carbonates present in the solution. This neutralization is carried out with concentrated hydrochloric acid until a pH of between 5.5 and 6.0 is obtained.
• the effluent, thus prefiltered and neutralized, is conveyed to Stage 3.
• the main aim of this stage is to separate the sodium chloride salts and to concentrate the dyes. This Stage 3 is divided into 2:
• a diafiltration stage where the inorganic salts are separated while keeping the concentration of dye constant by addition of purified water
• a concentration stage where the dye is concentrated as much as possible.
• purified water is understood to mean water with a concentration of inorganic salts such that the conductivity does not exceed 1 mS.cm "1 and which is devoid of hydrolysed reactive dye. In view of its very low volume, the concentrated dyeing solution is subsequently conveyed to a landfill site or is incinerated.
• the sodium chloride solution is conveyed to Stage 4, where it is concentrated.
• the concentrated sodium chloride solution is intended to be recycled at the head of the dyeing plant process.
• the solution of pure water obtained downstream of the reverse osmosis membrane is recycled either to Stage 3, to provide purified water necessary for the diafiltration step, or the head of the dyeing process, to provide softened water.
• Stage 1 is composed solely of a stainless steel prefilter, the characteristics of which are as follows: stainless steel material, cut off at 100 ⁇ m.
• the scheme of the prefilter is given by Figure 2. Tests on approximately 15 000 litres of industrial solutions of hydrolysed reactive dyes did not show any blinding of these prefilters and complete retention of the fibrils. This retention is demonstrated by the presence of a 70 micron safety prefilter placed downstream and comprising no cotton fibrils.
• the arrangement in Figure 3 relating to Stage 2 comprises a holding tank with a capacity of 100 litres, a stirring paddle, a pH-meter probe, a metering pump, a hydrochloric acid tank and an aeration system in the vessel bottom for conveying air.
• the pH of the dyeing solution is continuously measured and a metering pump makes it possible to adjust the pH of the solution to a value between 5.5 and 6.0.
• the amount of concentrated hydrochloric acid (9.05 N or 33%) is between 5 and 35 ml/1 (preferably 20 ml/1) depending on the type of effluent and on the concentration of carbonates.
• the arrangement of Figure 4 comprises a tank A made of polymethacrylate with a capacity of 25 litres which comprises the feed solution originating from Stage 2.
• This tank is connected to the filtration cartridge D via a feed circuit 2 made of stainless steel and is adjusted in temperature by a thermostatically controlled bath which makes it possible to keep the temperature constant between 20 and 60°C.
• the feed circuit 2 comprises a high-pressure pump B with a variable-speed drive unit and an emptying circuit 5 with a valve C which are situated before the pump B.
• the filtration cartridge D composed of a cylinder made of epoxy glass polymerized under hot conditions, comprises a membrane of spiral-wound geometry.
• the membrane is of organic type, made of polyamide/polysulphone, with an exchange surface area of 2.5 m 2 .
• This nanofiltration membrane is sold by Osmonics under the generic term Desal 5. The permeate which passes through the membrane is directed to receiver H.
• the retentate is recovered via the circuit 3 and passes through a control valve E to be recycled to the tank A.
• an amount of purified water equal to the volume of the permeate removed is optionally added (diafiltration stage) to the tank A.
• This water is withdrawn from the tank G, maintained at the same temperture T as that of the fluid which circulates in 2, and is transferred to the tank A using the pump F via the circuit 4.
• the choice of this optional addition of water is explained by the presence or absence of a high concentration of hydrolysed reactive dyes (cf. summary and description of the invention).
• the diafiltration (the addition of water from G) is halted and the filtration operation is continued, which is reflected by the decrease in the weight of retentate in A.
• the weight of concentrated retentate in A is only 1/10 to 1/40 of the initial mass, the filtration operation is halted and the solutions are analysed. This range of final retentate weights makes it possible to operate with a permeate flux which is not too low, that is to say without significantly blinding the membrane. In view of its very low volume, the concentrated dye solution will be easily treated conventionally (incineration or placing in a landfill site).
• the NaCI solution recovered in the tank H is conveyed to Stage 4 of the process.
• FIG. 5 DESCRIPTIVE DIAGRAM OF STAGE 4: REVERSE OSMOSIS PROCESS
• the arrangement of Figure 5 comprises a tank A" made of polymethacrylate with a capacity of 20 litres which comprises the permeate originating from Stage 3.
• This tank is connected to the filtration cartridge D" via a feed circuit 2 made of stainless steel and is adjusted in temperature by a thermostatically controlled bath which makes it possible to keep the temperature constant between 20 and 60°C.
• the feed circuit 2 comprises a high-pressure pump P" and an emptying circuit 5 with a valve C" which are situated before the pump P".
• the filtration cartridge D composed of a cylinder made of stainless steel, comprises a membrane of spiral-wound geometry.
• the membrane is of organic type, made of polyamide/polysulphone, with an exchange surface area of 2.3 m 2 .
• This reverse osmosis membrane is sold by Osmonics under the generic term SC2540C.
• the permeate which passes through the membrane is recycled to the receiver G of the nanofiltration operation, to provide for the diafiltration or is used as production water in dyeing.
• the retentate is recovered via the circuit 3 and passes through a control valve E" to be recycled to the tank A".
• the concentrating is halted.
• the concentrated retentate solution is conveyed to the head of the process to carry out a new dyeing, with or without addition of topping-up salts.
• Stages 1 and 4 can operate continuously or noncontinuously. On the other hand, because of the bubbling step and the concentration step in Stages 2 and 3 respectively, the latter operate very well noncontinuously.
• a synthetic solution representing a dye bath comprises 50 g/l of sodium chloride and 5 g/l of sodium carbonate.
• a volume of 9.4 ml/l of hydrochloric acid (33%) has to be added to this solution to obtain a pH of 5 and a total alkalinity of 2.73, thus making it possible to have a concentration of HCO 3 " of 0.546 mmol/l and of free CO 2 of 2.903 mmol/l.
• Example 2 The same synthetic solution as in Example 1 is used but this time, after having added the same volume of hydrochloric acid, air is introduced using an aeration system.
• the pH of the solution is now 7.37 and the total alkalinity is 2.545, thus making it possible to have a concentration of HCO 3 " of 1.018 mmol/l and of free C0 2 of 0.032 mmol/l.
• a synthetic solution representing a dye bath comprises 80 g/l of sodium chloride and 12 g/l of sodium carbonate. It is necessary to add a volume of 22 ml/l of hydrochloric acid (33%) to this solution to obtain a pH of 5 and a total alkalinity of 7.86, thus making it possible to have a concentration of HCO 3 " of 1.5 mmol/l and of free C0 2 of 2.25 mmol/l.
• Example 5 The same synthetic solution as Example 5 is used but this time, after having added the same volume of hydrochloric acid, air is introduced using an aeration system.
• the pH of the solution is now 7.25 and the total alkalinity is 6.495, thus making it possible to have a concentration of HCO 3 " of 1.3 mmol/l and of free CO 2 of 0.3 mmol/l.
• the bath to be treated originates from the industrial dyeing of 250 kilograms of pure cotton knitwear in a bath ratio of 1:6.5, i.e. a volume of 1625 litres.
• the starting format is as follows:
• Drimarene Blue K-2RL i.e. 0.076 g/l
• Additive based on ethoxylated fatty alcohol 1 g/l
• the resulting solution is placed in a tank and is maintained at a temperature of 50°C.
• the circulation flow rate of the retentate is adjusted to 300 l/h.
• the transmembrane pressure is brought to 10 bar.
• the permeate is collected continuously.
• a constantly identical flow rate of distilled water at 50°C is added to the tank in order to operate at a constant concentration of hydrolysed dyes: this stage is the diafiltration.
• the conductivity of the downstream and upstream solutions is measured continuously by a conductimeter.
• the membrane used is a spiral membrane made of polypropylene from Osmonics with a filtering surface area of 2.5 m 2 and with a cutoff threshold of between 200 and 300 Da.
• a concentration stage is carried out (the addition of distilled water is halted and the dyes remaining in the retentate were concentrated) with a total duration of 2 minutes.
• 39 800 g of permeate with a mean composition of 14 g/l of NaCI are recovered.
• 1400 g of retentate with a composition of 5.7 g/l of NaCI remain in the feed tank.
• the degree of instantaneous retention of NaCI varies from 0 to 27% within a concentration range from 61 to 5.7 g/l.
• the permeate recovered is colourless and transparent throughout the operation as the degree of retention of the hydrolysed reactive dyes is 99%. 91% of the sodium chloride is finally recovered with a material balance confirmed to within a relative accuracy of the measurements of less than 1 %.
• the permeate flux varies from 40 to 51 l/h.m "2 during the diafiltration phase and from 51 to 39 l/h.m "2 during the concentration phase.
• the membrane module is fully regenerated at the end of the handling by simple acid/base washing under hot conditions.
• a mass of 9477 g of a solution corresponding to the bath described above and comprising 61 g/l of sodium chloride is prefiltered with a 100- ⁇ m prefilter to remove the cotton fibrils.
• This solution is subsequently neutralized with a volume of hydrochloric acid (33%) of 4.9 ml/l.
• a filtration operation is carried out under conditions identical to those of Example 1 , apart from the fact that the transmembrane pressure is brought to 20 bar. At the end of the diafiltration operation, of a duration of 9 minutes, and the operation for concentration of the dyes, with a total duration of 1 minute, 35 509 g of permeate with a mean composition of 18 g/l of NaCI are recovered.
• a mass of 9220 g of a solution corresponding to the bath described above and comprising 61 g/l of sodium chloride is prefiltered with a 100- ⁇ m prefilter to remove the cotton fibrils.
• This solution is subsequently neutralized with a volume of hydrochloric acid (33%) of 4.9 ml/l.
• a filtration operation is carried out under conditions identical to those of Example 1 , apart from the fact that the transmembrane pressure is brought to 5 bar.
• 50 696 g of permeate with a mean composition of 11.5 g/l of NaCI are recovered.
• a mass of 9399 g of a solution corresponding to the bath described above and comprising 60 g/l of sodium chloride is prefiltered with a 100- ⁇ m prefilter to remove the cotton fibrils.
• This soluton is subsequently neutralized with a volume of hydrochloric acid (33%) of 4.9 ml/l.
• a filtration operation is carried out under conditions identical to those in Example 1 , apart from the fact that the circulation flow rate of the retentate is adjusted to 100 l/h.
• 54 418 g of permeate with a mean composition of 10.8 g/l of NaCI are recovered.
• a mass of 9467 g of a solution corresponding to the bath described above and comprising 61 g/l of sodium chloride is prefiltered with a 100- ⁇ m prefilter to remove the cotton fibrils.
• This solution is subsequently neutralized with a volume of hydrochloric acid (33%) of 4.9 ml/l.
• a filtration operation is carried out under conditions identical to those of Example 1 , apart from the fact that tap water is used instead of distilled water during the diafiltration (0.395 mS/cm).
• At the end of the diafiltration operation, with a duration of 22 minutes, and the operation of concentrating the dyes, with a total duration of 2 minutes 54 663 g of permeate with a mean composition of 11 g/l of NaCI are recovered.
• the bath to be treated originates from the dyeing of 200 kilos of pure cotton knitwear in a bath ratio of 1 :8, i.e. a volume of 1600 litres.
• the formula is as follows:
• Drimarene Blue HF-RL i.e. 1 g/l 0.312% Drimarene Red HF-G, i.e. 0.39 g/l 0.520% Drimarene Yellow HF-R, i.e. 0.65 g/l Sulphonated polymer 1 g/l
• a mass of 14 360 g of a concentration of 25.8 g/l of the permeate originating from the nanofiltration of this dye bath is introduced into a tank as retentate and is maintained at a temperature of 40°C.
• the circulation flow rate of the retentate is adjusted to 400 l/h.
• the transmembrane pressure is brought to 50 bar.
• the conductivity of the downstream and upstream solutions is measured continuously by a conductimeter.
• the membrane used is a spiral membrane from Osmonics with a filtering surface area of 2.5 m 2 .
• a stage of concentrating the salts is carried out with a duration of 15 minutes. 8178.2 g of permeate with a mean composition of 2.26 g/l of NaCI are recovered.
• a mass of 14 439 g of a concentration of 24.8 g/l of the permeate originating from the nanofiltration of the same dye bath mentioned in Example 1 is introduced into a tank as retentate and is maintained at a temperature of 40°C.
• the circulation flow rate of the retentate is adjusted to 400 l/h.
• the transmembrane pressure is brought to 50 bar.
• the conductivity of the downstream and upstream solutions is measured continuously by a conductimeter.
• the membrane used is a spiral membrane from Osmonics with a filtering surface area of 2.5 m 2 but tighter than the preceding one.
• a stage of concentrating the salts is carried out with a duration of 20 minutes.
• EXAMPLE 3 A mass of 14 161 g of a concentration of 26.3 g/l of the permeate originating from the nanofiltration of the dye bath mentioned in Example 1 is introduced into a tank as retentate and is maintained at a temperature of 40°C. The circulation flow rate of the retentate is adjusted this time to 600 l/h. The transmembrane pressure is brought to 50 bars. The conductivity of the downstream and upstream solutions is measured continuously by a conductimeter. The membrane used is the same as that in Example 2. A stage of concentrating the salts is carried out with a duration of 16 minutes. 7975 g of permeate with a mean composition of 1.046 g/l of NaCI are recovered.
• this recycled brine will be regarded as comprising 60 g/l of sodium chloride.
• the brine is colourless.
• the concentrated colorant is the aqueous solution comprising the hydrolysed reactive dyes, the additives and the inorganic salts which have not passed through the membrane.
• the concentration in g/l is the concentration of remaining inorganic salts.
• the concentrated brine is the aqueous solution comprising a VERY high concentration of inorganic salts which is obtained downstream of the membrane when a preconcentration stage (before a diafiltration-concentration stage) or a concentration stage alone is carried out.
• the brine is the aqueous solution comprising a high concentration of inorganic salts which is obtained downstream of the membrane when a diafiltration stage followed by a concentration stage is carried out.
• the brine is the aqueous solution which remains upstream of the membrane and the purified water is the aqueous solution which has passed through the membrane.
• the concentration is the concentration of inorganic salts.
• DFP difluoropyrimidine
• TCLP trichloropyrimidine
• MCT monochlorotriazine
• VS vinyl sulphone
• Drimagen E2R is a chemical dyeing product, an aromatic sulphonated derivative.
• Sandopur R3C is a chemical dyeing product, a copolymer of partially neutralized carboxylic acids

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