STUDIO DEI MECCANISMI DI SCAMBIO ELETTRONICO INTER-SPECIE NEL PROCESSO DI DIGESTIONE ANAEROBICA DI RIFIUTI ORGANICI

Anaerobic digestion is one of the most attractive technologies for the treatment of industrial wastewaters and organic wastes, because it requires less energy investments and generates less excess sludge than other treatment approaches such as the activated sludge system (Mata-Alvarez et al., 2000). Complete conversion of organic matter to CO2 and CH4 via anaerobic digestion typically requires the syntrophic cooperation between acetogenic bacteria (also referred to as syntrophs) and methanogenic archaea. Indeed, catabolic reactions catalysed by acetogenic bacteria become energetically favorable only when produced reducing equivalents are efficiently scavenged by their syntrophic partners, namely the methanogenic archaea. Typically, this interspecies electron transfer (IET) process is reported to occur via diffusive transport of soluble electron carriers (e.g., hydrogen and formate) from the acetogens to the methanogens (Morris et al., 2013; Stams and Plugge, 2009). Low concentrations of electron carriers however result in slow diffusion rates, causing IET to be often the bottleneck in the methanogenic conversion of organic substrates. Recently, direct interspecies electron transfer (DIET), in which two microbial species exchange electrons via electric currents flowing through conductive solid conduits (e.g., magnetite nanoparticles) or microbial pili, has been proposed as an alternative strategy to interspecies H2/formate transfer, through which microbial species in a community share reducing equivalents to drive the methanogenic degradation of organic substartes (Kouzuma et al., 2015; Shrestha and Rotaru, 2014).