Resumen de Producción de salmuera saturada a partir de rechazo de desaladora o residuo de actividad minera
Access to drinking water is one of the challenges of the 21st century for an increasing number of countries in the world. In Spain, a desalination plant providing between 20% and 30% of Barcelona¿s drinking water has been in operation since summer 2009. The desalination plant¿s Reverse-Osmosis (RO) system processes sea water to produce drinking water and a waste product, concentrated brine, which has a negative impact on the flora and fauna (coral) around the plant outlet pipe. It would be a shame for this waste product with such a high salt concentration (60 g to 80 g of salt per litre, compared to about 30 g per litre in the sea) to go unused. This research explores the possibility to reduce the amount of brine discharged into the sea by the desalination plants by using it in an industrial process. By means of an Electrodialysis (ED) process, the concentration of the discharge from the Reverse- Osmosis process can be increased up to 250 g per litre so the brine can then be purified and used as a raw material in the chlor-alkali industry. Taking these challenges into account, an ED pilot plant using CIMS and ACS Neosepta membranes was built in Barcelona to test concentration of RO brine solutions. The ED pilot was dimensioned to concentrate 500L/h of brine coming from two different configured RO pilot plants. As the ED plant had unlimited access to the feed brine and it did not pretend to desalt this brine, the circuits of diluate and electrolyte were designed in one-single pass. This allowed operating the plant with high current densities, as limiting current density was never achieved. Consequently, higher NaCl concentrations on the concentrate stream were obtained. The results obtained during the start-up and preliminary operation of the pilot plant aredescribed in the current thesis. These experiences showed the concentration feasibility of this technology when reaching 258 g NaCl/L after 35h of operation at 0.4kA/m2 with a power consumption of 0.24 kWh/kg NaCl at 10ºC. Moreover, as the membranes used (Neosepta CIMS and ACS) were mainly selective for univalent ions, polyvalent ions such as calcium and magnesium were partially removed from the brine which represented an advantage for its final reuse in the chlor-alkali industry. However further treatments would be needed to meet the electrolysis requirements. A mathematical model was also developed based on Nernst-Planck equations to predict NaCl concentration performance of the ED pilot plant. Several of the model parameters were obtained experimentally and others were taken from the literature. The model was able to accurately predict the NaCl concentration reached in the concentrate tank along the experiment, as well as the time required to reach maximum concentration and production overflow as a function of the operation conditions such as electrical current intensity and NaCl feed concentration. In this work, the results of the mathematical model are compared with the preliminary experimental results obtained at the pilot plant in order to validate the model. Finally, this pHd aims at evaluating the possibility to use an alternative source of brine in a cost effective way compared to current sources of salt. At the same time it provides a technical solution for the optimal use of natural resources since it minimizes environmental impact of the desalinization process. To meet this challenge, our brine and electrolysis specialists in Italy are collaborating on the project with the Barcelona water company (Aguas de Barcelona - AGBAR) and the Universitat Politècnica de Catalunya (UPC). Finally this thesis brings an interesting step forward in reducing environmental impact of the desalinization process transforming the RO waste into raw material for the Chlor- Alkali Industry. Besides, it helps develop future applications for existing Technologies as the Electrodyalisis.
