Sustainable processing of dairy wastewater: Long-term pilot application of a bio-electrochemical system

Demographic growth, increasing food demand and non-renewable fuels depletion require new sustainable industrial approaches in all areas of the agro-farming sector. Microbial fuel cells (MFCs) could represent an eco-innovative technology for energy and resources recovery from agrofood processes wastewaters. This study was conducted to: (i) assess the bioelectrochemical treatability of dairy wastewater by means of MFCs; (ii) determine the effects of the organic loading rate (OLR) on MFCs performance; (iii) evaluate the reactors' overpotentials, and identify possible strategies oriented to their reduction. For this purpose, two replicate MFCs were built and continuously operated for 65 days. The anode chamber was fed with undiluted dairy wastewater at 1 L d−1. An aerated mineral medium was fed to the cathode chamber with the same flow-rate. The study demonstrated that these types of industrial effluents can be treated by MFCs with 82% (average) organic matter removal, recovering a maximum power density of 26.5 W m−3. Coulombic efficiency (CE) of the lab-scale reactors decreased by increasing the OLR (organic loading rate). The highest CE was found to be 24% at a OLR of 3.7 kg COD m−3 d−1. MFCs energy losses were mainly due to cathode reaction (34-39% of total loss) and ionic transport through the membrane (27-33%). Achieved results were better than previously reported MFC-experiences dealing with dairy (or similar) wastewater treatment.