Avaluació de l’ús de l’osmosi directa per a la concentració de l’aigua residual urbana

Abstract

The growing need for the reuse of water and recovery of resources has awoken interest in the regeneration of wastewater through new processes of membrane treatment that generate high quality water. Forward osmosis is one of the promising technologies for wastewater treatment due to lower energy requirements, higher permeate purity and lower fouling tendency compared to the technologies that work at higher pressures. This system is based on the natural phenomenon of osmosis: water is transported via a difference in concentrations of solutes through a membrane that allows for the passage of water, but rejects most molecules and ions. The application of forward osmosis also allows concentrate the content of organic matter from wastewater and facilitates subsequent application of anaerobic digestion for energy recovery. In this study, the feasibility of using forward osmosis to concentrate a sample of urban wastewater was investigated and the composition of the concentrate was evaluated for its recovery as an influent in anaerobic digestion. Two modules have been compared with different membrane configurations: a submerged flat plate (Toray) and a hollow fiber (Aquaporin). In order to do it, the capacity of membrane modules has been quantified to concentrate in a pilot plant the organic matter of the wastewater from Quart’s WWTP under different operating conditions, as well as its performance (water and reverse solute fluxes), its fouling, the efficiency of various methods of cleaning and the influence of ionic species. Studies have shown that forward osmosis technology allows the concentration of organic matter from urban wastewater. The comparative analysis has shown that the Toray module allows concentrate more effectively the organic matter, especially in those situations where gas sparging was not used. However, this condition implies a lower water flux and a higher fouling degree. Regarding the Aquaporin module, the reverse solute flux has been lower, which implies a lower inhibition of the methanogenic activity in the subsequent anaerobic digestion. On the other hand, the results of the characterization of ionic species have shown that the sulphate concentration was higher in the experiments carried out with Aquaporin module and with the Toray module when gas sparging was applied. This fact causes the deterioration of the quality and the amount of the biogas produced by anaerobic digester