Direct ultrafiltration with membranes applied to the carbon recovery from municipal wastewater

Abstract

Wastewater treatment plants (WWTPs) are considered with relevant importance for the safe continuity of the water cycle, with a direct impact on the environment and human activities. In this sense, the increasing global demand for sustainable technologies should encourage the urban wastewater treatment sector to improve carbon and nutrient recovery combined with the high quality of treated water. In this context, direct filtration with membranes applied to the recovery of organic material from municipal wastewater, together with the ever-greater robustness and experience of ultrafiltration membranes, appears as a robust, flexible and reliable process. The organic material embedded in municipal wastewater could be converted into biogas with the potential to change the current scenario of WWTPs from huge energy consumers to energy producers. In the present thesis, the feasibility of direct filtration with membranes has been studied by carrying out both short and long-term experiments, considering that it is a relatively new process in which the membrane fouling is the greatest operational difficulty. The operations have been developed in two different WWTPs. Low cost and common techniques have been used to control membrane fouling. The results showed that between 10 and 45 g/L in total solids concentrations, and between 11 and 54 g/L in chemical oxygen demand can be conveyed directly to anaerobic digestion, thereby up taking a major part of the organic material from municipal wastewater, whereas the transmembrane pressures of filtration are maintained under 400 mbar by applying combined techniques such as gas agitation, permeate backwash and purging of solids concentrated in the membrane tank. This thesis contributes in a small extent to the development of knowledge by providing to the field of municipal wastewater treatment processes a novel technology that in the future could be sustainable.