Background The dyeing processes developed in the finished textile industry use chemical reducing agents such as sodium sulphide, the so-called polysulphides, or, at best, a mixture of sodium hydrosulphide, glucose and caustic soda, in order to reduce the dye. All these chemicals lead to a high level of Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD) in the effluent from the dyeing bath and have a negative impact on the environment, especially for aquatic ecosystems. Objectives The project’s objective was to construct for demonstration purposes a prototype dyeing process with a system for electrolytic reduction of the dye. In this way, the chemical reducing agents that seriously affect the contaminant levels of the dyeing baths should be eliminated. The aim therefore, was to offer the textile finishing industry a clean technology that allowed low COD and BOD in the effluent discharge. It would also allow the reuse of dye baths, because the chemical breakdown products from the colorant- reducers would no longer be present in the water. Results The project had the initial aim of creating a technology that would enable the optimisation of the current costs of dyeing processes and operations (regarding the consumption of chemical reducing agents, water consumption, costs of the treatment/decontamination of effluents), and that would allow for shorter dyeing times, thus making it a more efficient process and adding value to the final product. With the aid of INTEXTER at UPC, who carried out important work at laboratory level, ATYC designed and constructed two trial prototypes for dyeing by electrolytic reduction, one a small scale version (50 kg) and the other on an industrial scale (300 kg); the former to work at pressure and the latter at 98ºC. These prototypes anticipated an electrolytic reduction tank connected to the dyeing equipment, with a system of electrolyte re-circulation, together with a preparation tank for introducing the products. A power supply allowed the voltage and intensity to be regulated in order to produce the electrolytic reduction of the dye between the two electrodes, which were of stainless steel. Trials and tests were carried out on these prototypes to determine their operating potential, together with trials where pulses of various lengths were applied to the electrodes. The results obtained were good in terms of dye uniformity and solidity, leading the project beneficiary to conclude that the system of electrolytic reduction was technically viable. However, the project so far cannot be considered as fully successful as it did not reach its main objective of developing an industrial prototype ready for large scale production. The beneficiary calculates that the objectives have been 75-80% achieved. The situation at the completion of the contract with Commission can be summarised as follows: - COD in the effluent has been decreased by up to 87.4% and BOD by 94%. - The reuse of dye baths has decreased water consumption by 10%. - Elimination of atmospheric pollution and noxious odours from H2S a by-product of the reactions of reducing agents. - Improvement of the ecological performance. However, the prototype needs further tests to calculate the reduction of costs in effluent treatment that this new system will produce. This project has a significant potential for replication, once the technical and economic feasibility of the proposed technology is demonstrated. Given the interest of the initiative, and the favourable reception that it is expected to receive on the market, it is envisaged that the response of other textile machinery manufacturers would be to incorporate systems that do not use chemicals within their equipment ranges. As a result, effective take up among the textile finishing sector is expected, owing to the market-oriented nature of the project. One factor that could restrain the European textile finishing industries from implementing such system is the high cost incurred in the treatment of effluent that would affect the competitiveness of the product. This factor has had a decisive influence in the shift of the sector of the textile industry with the highest levels of water contamination to other areas, for example, to North Africa and South America, where environmental legislation is more permissive. The collaboration agreement between ATYC and INTEXTER finished with the ending of the project. A new contract in order to continue the research and develop the final industrial model is being discussed. The continuation of the project will focus on the following: - Testing the current industrial model. An agreement with AUTOTEX (Mexico) has been signed in order to carry out the tests (supervised by INTEXTER) of the electrolytic system. AUTOTEX will perform the test in exchange of discount in the purchase of the equipment (the model can also be used conventionally if the electrolytic system is disconnected). - Construction of a model to scale (2 Kg) to be installed in the laboratory of INTEXTER (the current 50 Kg model is at ATYC) in order to carry out the optimisation tests more systematically.