1. Summary

The constructive and successful collaboration between textile finisher (Van Clewe GmbH/Dingden; Germany), textile machine manufacturer (BENNINGER AG/Uzwil; Switzerland) and process and waste technologist (MDS/Moers; Germany) has enabled the actual amount of washing water used in a complete textile finishing process (pre-treatment, CPB dyeing, re-washing and chemical finishing) to be reduced to 2.5 - 3.5 l/kg of fabric. This is presently the equivalent of 1/7 of the norm.

In so doing, highly concentrated wastewater flows are produced in selected areas of the installation, which makes thermal disposal of pre-treatment wastewater economically justifiable. This can reduce the wastewater load by up to 90%. The coloured wastewater produced when washing out reactive dyes is purified using a multistage membrane plant, which allows the water to be reintroduced into circulation and used in all areas of the textile finishing process. Highly concentrated reactive dye liquor, which accumulates as residual liquor in the padder chassis or as concentrate in the membrane plant, can be decolourised completely using an electro-chemical reduction process. Decolourising the concentrate by between 70 - 90 % can be achieved utilising a minimum of energy. This process does not produce any chlorine gases or sludge, which needs to be disposed.

BENNINGER AG Uzwil and MDS/Moers have agreed to co-operate in this future orientated area of environmental conservation in the textile field. The integrated competences of both companies put them in a position to fulfil individual customer requirements and offer effective problem solving.

2. Introduction
Increasing demands and more rigid sewage restrictions and general conditions, such as addendum 38, are progressively forcing the textile finisher to production integrated environmental conservation. Of great importance here is also the well-known and currently often quoted principle of sustainability, a principle, which satisfies current needs, without denying future generations their existence. This is characterised by long-term orientated thinking and handling in order to achieve a dynamic equilibrium of natural resources, reason enough to reflect on innovative ideas and solutions which take into account both ecology and economy.

3. Objectives of the washing concept and recycling systems
The most important objectives during the realisation of the new washing concept are reduction of the wastewater load (COD) and simultaneously lowering washing water and steam consumption. Referred to here is the water consumption of the entire system and not that of the washing machine alone. In spite of the latest washing machine technology and already extremely low water consumption values, further significant reduction of the effective water consumption can be still achieved by wastewater circulation. Recycling the wastewater is therefore an important derivative of the main objectives. A further objective of this project, originating from the fact that re-using the wastewater requires the impurities to be separated from the water, was to produce concentrates. Concentrates can be produced either directly at the place of origin (washing machine) or indirectly on the membrane plant. The concentrate quantities formed should be small and thermal disposal should be possible. Large quantities of effluent sludge are undesirable.

4. The machine concept
The installation referred to is a BENNINGER high-efficiency washing machine, operating with the counter flow principle. This means that the fabric and the washing water flow in opposite directions. The machine concept includes the following standard modules:

· High humidity impregnation (with variable liquor application)
· Bi-functional Reacta roller-steamer, used as either a washing compartment for pre-washing the dyed fabric or as a steamer for pre-treatment processes
· 6 vertical roller vat washing compartments with Extracta lay-on rollers
· 2 Hydrovac vacuum suction stations

The special features of this technology lie in the combination and operation of the components and the design of the washing liquor guidance. (fig. 1).

The BENNINGER EXTRACTA roller vat high-efficiency washing machine is especially suitable for counter flow washing since each washing compartment contains up to 7 additional washing chambers (fig. 2). The fabric is squeezed through pneumatically loaded lay-on rollers situated between each washing chamber. The washing liquor meanders within the compartment according to the counter flow principle, meaning that the liquor flow is guided in the opposite direction to the fabric run. This method of processing results in a high concentration of wastewater ingredients accumulating contrary to the fabric run. Other well known washing system such as horizontal or diagonal washing machines, which circulate the liquor, are not suitable for this application because there are only a max. of 2 chambers per washing compartment. The concentration variations in the washing water are therefore considerably less.

Fig. 1: High-efficiency washing machine with bi-functional steamer

The parameters of the washing machine can be set at will and are maintained thanks to the modern control system. This enables the various tasks in respect of water, counter flow and process guidance to be realised.

5. Process concepts
The following process steps occur:

· Continuous desizing taking into account the aspects of the separation and utilisation of highly concentrated partial flows e.g. sizing agent recovery · Continuous and/or semi-continuous bleaching and scouring with the premise of the partial flow separation and efficient utilisation and recovery of wastewater · Extremely low water consumption when washing out dyes, separating concentrates and re-introducing washing water into circulation.

5.1 Pre-treatment process
The last three washing compartments in the pre-treatment process are operated in the classical form. The washing water flows through these three compartments in counter flow. A defined partial flow is taken from the overflow and fed into the washing compartments in the front area of the installation. This partial flow serves to re-concentrate and determines the amount of sizing concentrate produced during the pre-treatment. A counter flow of washing water passes through the front washing compartments again. Another part of this highly concentrated washing water is applied to the fabric at the intake of the machine using a high pick up application aggregate.

The fabric then reaches the steamer. The sizing agent swells in the steamer and the viscosity of the swollen sizing agent is reduced. Immediately after leaving the steamer, the fabric passes over the first suction bars where the size concentrate is extracted. The concentrate is fed into the water seal of the steamer, which operates on the overflow principle. The concentrate accumulated via the overflow represents the volume available for recycling or for re-use.
The amount is determined and controlled according to the portion taken out of the last three washing compartments. This ensures that the process conditions and parameters are maintained. The pre-treatment or de-sizing can be carried out in two different processes:
· Cold store bleaching with oxidative de-sizing.

· De-sizing with water soluble sizing agent: De-sizing takes place directly in the washing machine. The advantages of this process lie in the fact that the fabric is dry when it enters the machine and wet when it leaves the washing machine. This moisture is removed from the process and therefore reduces the accumulation of wastewater. In addition, the sizing agent has not been modified or degraded and can therefore be recycled.

The concentrate that accumulates during the pre-treatment is collected in a separate container and then fed into a specially developed evaporator (fig. 3). The concentrate is evaporated and the residual solids then removed. This is, in principle, a two-step roller dryer. A small part of a heated roller is immersed in the liquid and coated with a film of concentrate. The first step is to increase the concentration of the sizing concentrate. The second step is the complete evaporation of the water and the subsequent removal of the dried residual solids with a scraper. Thermal disposal is carried out on the residual solids.

5.2. Washing out reactive dyes
During the washing out process all compartments, as well as the steamer, operate as a washing compartment. The steamer operates with cold water flowing in counterflow in order to wash out the bulk of the unfixed dyes and residual alkalis from the fabric. The fabric is then passed over the first suction bars, extracting as much moisture as possible, in order to achieve a good bath separation. A second suction bar, situated after the first washing compartment, boosts this effect. The subsequent washing compartments operate with hot water.

The use of the Hydrovac vacuum results in a reduced water consumption because the highly concentrated hydrolyzates have already been extracted from the fibre core and removed in the pre-rinsing process.

Another option is a new electrochemical process in which the dye concentrate is decolourised and subsequently released into the communal sewage.

6. Results
De-sizing / Pre-treatment

Thanks to the partial liquor flow guidance on the BENNINGER washing machine, only 0.5 - 0.7 l of effluent per kg of textile is generated. This partial effluent flow contains up to 90% of the COD load from the pre-treatment process. (fig. 4). An even higher 95% COD retention was attained using water-soluble sizing agents.

The small volume facilitates evaporation directly at the place of origin. This suits VAN CLEWE, from an economical and ecological point of view, because it is cheaper than treatment at the

municipal sewage plant. Van Clewe increases the solvent concentration in the roller evaporator, as described above, and then recycles the residual solids in a thermal disposal. Table 1 lists the material balances and liquor flows.

The possibility of disposing of concentrate in a liquid form or reducing it to solids depends on the regional circumstances. Official regulations or the capacity and suitability of municipal sewage plants are of vital importance.

The regional environmental circumstances are taken into account early in the project phase. Only a specific adaptation of the concept and machine guarantees the expected success.

Washing out dyes

The BENNINGER high-efficiency washing machine EXTRACTA, with integrated Hydrovac vacuum system, has been successful in washing light nuances with only 1, 5 l/kg (0,5 l/kg cold; 1,0 l/kg hot) instead of the previous 7 l/kg used in a conventional washing machine. Today, medium shades require 3,0 (1,0 + 2,0) l/kg and dark shade fabrics 4,5 (1,5 + 3,0) l/kg instead of 8 - 10 l/kg. Very dark shades, such as black and dark blue, which normally required 12 l/kg, are today washed with only 6 l/kg.

The water quantities were optimised by visually inspecting the washing water in each compartment (fig. 5). Simultaneously, extracted samples of the textile were analysed and a correlation of the fastness level established.

The impurities in the equation remain the same, however the considerably lower amount of washing water results in significant energy savings in the form of steam required for the washing process.

The washing water is fed into a multistage membrane plant. The smaller quantities of water also allow the utilisation of a smaller plant compared to that found in conventional washing systems. The result is a greatly reduced investment and a drop in electrical energy consumption of the membrane plant, leading to lower running costs of the entire processing system.

The multistage membrane plant consists primarily of an ultra-filtration (fig. 6) with an ensuing nanofiltration and/or reverse osmosis. The ultra-filtration is fitted with a special ceramic membrane. This membrane filters out particles and long-chain organic molecules from the wastewater up to a temperature 95°C. The ensuing nanofiltration and/or reverse osmosis remove almost all the dissolved dyes and salts from the water. The purified process wastewater can be reintroduced into all areas of textile finishing without negatively affecting the end product. The membrane plant has been in continuous, near to failure-free, operation with practically no personnel expenditure for more than 5 years.

Fig. 5: Sampling at the EXTRACTA open width washing machine (source: photo ex-works Van Clewe)

Using a combination of ultra-filtration and reversed osmosis can result in a recycling rate of more than 80% of the wastewater. The recycled process wastewater is decolourised after treatment with the membrane plant, has a COD value of approx. 100 to 300 mg/l and a conductibility of approx. 100 µS/cm.

7. Future prospects
The extent of the successful reduction of the flow volumes during pre-treatment and washing out dyes is impressive. The COD load in the wastewater has been reduced by 90 - 95 %. All the water from the washing out process can be re-introduced into circulation. This has allowed the effective water consumption needed to process one kg of fabric to be reduced to 1/7 of what is conventionally required.

Further economical and ecological optimisation accomplished was:
· Recycling the sizing agent
· Decolourising of dye concentrate from the padder chassis and the membrane plant

The recycling of the sizing agent is dependent upon the manner in which the company produces. Experience has shown that it is only viable for vertical companies (own weaving and textile finishing) to recycle the sizing agent. This is due to the fact that the sizing recipes of external weavers is not always known to remunerated finishers, whereas Van Clewe supplies weaving mills with sized warps. Recycling the sizing agent is therefore possible. Van Clewe is presently examining the circumstances with regard to their feasibility and cost. Initial trials have shown that in such cases, processing can be carried out with almost no wastewater. In one article, the accumulated sizing concentrate is increased by adding 10 % of fresh sizing agent and then re-introduced directly into their own sizing department. Today, decolourising dye concentrate from the dye liquor and the membrane plant by way of electrochemical reduction is a fully developed

Fig. 6: Ultra-filtration installation (Q = 10 m3/h)

and economically interesting process. The costs are approx. € 2.50,-- per m3 concentrate. Decolourising the concentrate can, depending on the dye combination, constitute 70 - 90 % of the initial dye value (DFZ). When considering a medium-sized textile finishing company with 2 CPB dye stations, which today accumulates between 0.8 - 1.0 m3 of concentrate from the padder chassis and the membrane plant each day, one finds that the decolourising costs are virtually negligible. This technology has been developed by the Textile Institute in Dornbirn (Austria), Dystar and BENNINGER Ltd as a solution to decolourise dye concentrate without producing any additional by-products such as effluent sludge and chlorine.