Enhancement of biomethane recovery from batch anaerobic digestion by exogenously adding an N-acyl homoserine lactone cocktail

Biomethane recovered through anaerobic digestion (AD) is a renewable, sustainable, and cost-effective alternative energy source that has the potential to help address rising energy demands. Efficient bioconversion during AD depends on the symbiotic relationship between hydrolytic bacteria and methanogenic archaea. Interactions between microorganisms occur in every biological system via a phenomenon known as quorum sensing (QS), in which signaling molecules are simultaneously transmitted and detected as a mode of cell-to-cell communication. However, there's still a lack of understanding on how QS works in the AD system, where diverse bacteria and archaea interact in a complex manner. In this study, different concentrations (0.5 and 5 μM) of signaling molecules in the form of an N-acyl homoserine lactone cocktail (C6-, C8-, C10-, and 3-oxo-C6-HSL) were prepared and introduced into anaerobic batch reactors to clearly assess how QS affects AD systems. It was observed that the methane yield increased with the addition of AHLs: a 5 μM AHL cocktail improved the methane yield (341.9 mL/g-COD) compared to the control without AHLs addition (285.9 mL/g-COD). Meanwhile, evidence of improved microbial growth and cell aggregation was noticed in AHLs-supplemented systems. Our findings also show that exogenously adding AHLs alters the microbial community structure by increasing the overall bacterial and archaeal population counts while favoring the growth of the methanogenic archaea group, which is essential in biomethane synthesis.