NDUSTRIAL WASTEWATER TREATMENT AND ENERGY PRODUCTION BY MICROBIAL FUEL CELLS: NOVEL MEMBRANES, CONFIGURATIONS FOR CONTINUOUS FLOW AND MICROALGAE APPLICATION

Abstract

Climate change is a complex and cross-cutting problem that needs an integrated and transformative systems approach to respond to the challenge. The complex interdependencies between climate change, water, energy and other social and environmental factors present a challenge for researchers and policy makers. MFCs (microbial fuel cells) are an emerging biotechnology that could contribute to overcome the current energy crisis and meet water needs in developing world countries. Thus, this technology has become the focus of many research studies trying to improve its performance by investigating alternative materials and determining optimal operating conditions. In this work, a new single-chamber air-cathode microbial fuel cell configuration has been used to operate in continuous mode with vertical and horizontal up-flow. This design incorporates a novel embedded ionic liquid-based membrane-cathode assembly working as separator. The ionic liquid selected for the present work is triisobutyl (methyl) phosphoniumtosylate, [PI4;I4;I4;1+][TOS-]. MFC performance is investigated in terms of electricity production and wastewater treatment for various feed flow rates. It has been concluded, that the effectiveness of treatment is directly dependent to the HRT, pH, T° operated in continuous mode, and the highest performance of wastewater treatment was reached for the flow of 0.25 ml.min-1. Nutrients transport through polymer inclusion membranes based on different concentrations of methyltrioctylammonium chloride, was also investigated in this work, in order to broaden the application range of these kinds of membranes. Calcium chloride (CaCl2) and sodium hydrogen phosphate (Na2HPO4) nutrients were used at the concentration of 1 g.L-1 in the feeding phase. The evolution of the concentration in the receiving phase over time (168 h) was monitored and the experimental data fitted to a diffusion-solution transport model. The results show very low permeation values for CaCl2. By contrast, in the case of Na2HPO4 the permeation values were higher and increase as the amount of ionic liquid in the membrane also increases. The surface of the membranes was characterized before and after being used in the separation process by scanning electron microscopy coupled to energy dispersive X-Ray spectroscopy (SEM–EDX) and elemental mapping analysis. The SEM–EDX images show that the polymer inclusion membranes studied2 are stable to aqueous solution contacting phases and therefore, they might be used for the selective transport of nutrients in separation processes. Microalgae have been identified as one of the newest bio-material due to its use in microbial fuel cells (MFCs). The resulting microalgae-MFC systems can produce electricity using the electrons released to the anode during microalgae degradation. Furthermore, microalgae can be grown in the cathode chamber, capturing the CO2 therein and using light as power source.