Critical evidence for direct interspecies electron transfer with tungsten-based accelerants: An experimental and theoretical investigation.

Accelerants can significantly enhance the biodegradability in anaerobic digestion (AD), which can be attributed to the direct interspecies electron transfer (DIET) mechanism. However, critical evidence for DIET mechanism is absent. In this work, nano-scale tungsten (W)-based compounds (WC, W2N, and W18O49) are employed to clarify the roles of W-based accelerants in AD systems. A DIET mechanism based on the W-based accelerants is proposed, and three critical pieces of evidence are provided: (i) First-principle density functional theory calculations provide theoretical evidence, illustrating that W-based accelerants are of zero band gap. (ii) Electrical conductivity evaluation further elucidates that W-based accelerants have superior electronic transport. (iii) Pyrosequencing of 16S rRNA gene confirms the existence of acetogens and methanogens in AD systems, which can act as electron-donor bacteria and electron-acceptor archaea, respectively. Combining theoretical with experimental results, the critical evidence provides a general strategy for understanding the DIET mechanism of accelerant in AD systems.