Treatment of Wastewater in H-Type MFC with Protonic Exchange Membrane: Experimental Study of Organic Carbon and Ammonium Reduction with Electrochemical Characterization

Food processing industries produce large amount of organic high strength wastewater, thus requiring a treatment before their release in the environment. A serious environmental problem is the ammonium pollution related to nitrogen-rich effluents, such as zootechnical wastewater and anaerobic digestion supernatant. In more recent years, microbial fuel cells (MFC) have been successfully proposed to reduce both pollutants in sludge and wastewater. In this work, the effectiveness of carbon and ammonium removal was investigated in H-type mediator-less MFCs, aiming at evaluating the PEM membrane performances. Anaerobic digestion residue was used as a source of microorganisms. In a first series of tests, synthetic wastewater were prepared by adding sodium acetate or glucose at different ratios, and carbon cycle was investigated. Different ratios, in terms of sodium acetate and glucose (10 gL(-1)), were tested (100 % v/v Acetate; 50 % v/v Acetate and 50 % v/v Glucose; 75 % v/v Acetate and 25 % v/v Glucose). In the tests devoted to nitrogen cycle investigation, two different ratios in term of initial TOC/NH4+ (1 and 0.35, obtained by adding ammonium sulfate) were adopted. During the tests, pH, Total Organic Carbon (TOC), NH4+, NO2- and NO3- concentrations, and Open Circuit Voltage (OCV) were daily monitored. TOC values allowed to assess process kinetic and the optimal experimental conditions for carbon removal. Results showed a carbon reduction up to 78 % in the case of feeding with 75 % v/v Acetate and 25 % v/v Glucose, whilst, in the presence of higher amount of glucose, substrate degradation was found to be affected by pH decrease caused by membrane fouling. In the tests performed to investigate nitrogen cycle, an ammonium reduction to nitrite of 70 % was observed in the cell fed with TOC/NH4+ = 0.35 while at TOC/NH4+ = 1 the reduction was about 60 %, due to the occurrence of competitive carbon and ammonium degradation reactions. In such a systems, the PEM allowed to assess microaerobic conditions and a good proton transfer ensuring the maintenance of basic pH in the anodic chamber.