Role and Potential of Direct Interspecies Electron Transfer in Anaerobic Digestion

Abstract

Anaerobic digestion (AD) is an effective biological treatment for stabilizing organic compounds in waste/wastewater and in simultaneously producing biogas. However, it is often limited by the slow reaction rates of different microorganisms' syntrophic biological metabolisms. Stable and fast interspecies electron transfer (IET) between volatile fatty acid-oxidizing bacteria and hydrogenotrophic methanogens is crucial for efficient methanogenesis. In this syntrophic interaction, electrons are exchanged via redox mediators such as hydrogen and formate. Recently, direct IET (DIET) has been revealed as an important IET route for AD. Microorganisms undergoing DIET form interspecies electrical connections via membrane-associated cytochromes and conductive pili; thus, redox mediators are not required for electron exchange. This indicates that DIET is more thermodynamically favorable than indirect IET. Recent studies have shown that conductive materials (e.g., iron oxides, activated carbon, biochar, and carbon fibers) can mediate direct electrical connections for DIET. Microorganisms attach to conductive materials' surfaces or vice versa according to particle size, and form conductive biofilms or aggregates. Different conductive materials promote DIET and improve AD performance in digesters treating different feedstocks, potentially suggesting a new approach to enhancing AD performance. This review discusses the role and potential of DIET in methanogenic systems, especially with conductive materials for promoting DIET.

Italian Biogas Plants: Trend, Subsidies, Cost, Biogas Composition and Engine Emissions

“…(a) Potential and role of biogas in rural development (see, e.g., [13][14][15]) or in developed countries (see, e.g., [16][17][18][19][20][21]). (b) Analysis and optimization of biogas feeding composition, carbon-nitrogen ratios and methane production during anaerobic digestion or co-digestion of different kinds of substrates (see, e.g., [22][23][24][25][26]).…”

A critical review: emerging bioeconomy and waste-to-energy technologies for sustainable municipal solid waste management

“…One common challenge in AD is the long time needed for the methanogenic reaction in biogas production, as it typically takes between 20 and 40 days for each batch cycle and an even longer duration for new system startup [106]. Recent research revealed that direct interspecies electron transfer exists within AD microbial communities and an appropriate dosage of conductive materials (e.g., activated carbon and biochar) in the digester can lead to reduced lag phase, improved organic degradation and enhanced biogas formation rate [107][108][109]. On the other hand, the presence of nitrogenous wastes and high salinity in the feedstock would pose inhibitory effects on the AD processes due to the elevated levels of ammonia and salt [110][111][112], sometimes leading to AD system failure.…”

A PESTLE Analysis of Biofuels Energy Industry in Europe

“…The scope of this research on commercially available production technologies limits the effect of innovation on long-term sustainability. It is, however, important to notice that the development of the third generation biofuels, produced from algae, is a future development that could render the biofuels considered in this research relatively less sustainable [108][109][110][111][112][113][114][115].…”