To improve the application of surfactants in methane hydrate formation, sodium dodecyl sulfate (SDS) was fixed on the surface of polystyrene nanospheres (named as SDS@PSNS). SDS@PSNS resulted in a shorter induction period of hydrate formation compared to SDS. With SDS@PSNS as a promoter, hydrates formed mainly at the bottom of the reactor with a much higher apparent density and higher methane consumption, and during the hydrate dissociation period, less foam was generated. In addition, the recycling experiments showed high stability and good recycling performance of SDS@PSNS in seven methane hydrate formation-dissociation cycles.

Biogas produced by anaerobic digestion is an important renewable energy carrier. Nevertheless, the high CO2 content in biogas limits its utilization to mainly heat and electricity generation. Upgrading biogas into biomethane broadens its potential as vehicle fuel or substitute for natural gas. CO2-to-CH4 bioconversion represents one cutting-edge solution for biogas upgrading. In-situ bioconversion can capture endogenous CO2 directly from the biogas reactor, is easy to operate, and provides an infrastructure for renewable electricity storage. Despite these advantages, several intrinsic challenges need to be addressed to move in-situ upgrading technologies closer to applications at scale. This opinion article reviews the state-of-art of this technology and identifies some obstacles and opportunities of biological in-situ upgrading technologies for future development.