Valorization of methane from environmental engineering applications: A critical review.

Wastewater and waste management sectors alone account for 18% of the anthropogenic methane (CH) emissions. This study presents a critical overview of methanotrophs ("methane oxidizing microorganisms") for valorizing typically discarded CH from environmental engineering applications, focusing on wastewater treatment plants. Methanotrophs can convert CH into valuable bioproducts including chemicals, biodiesel, DC electricity, polymers, and S-layers, all under ambient conditions. As discarded CH and its oxidation products can also be used as a carbon source in nitrification and annamox processes. Here we discuss modes of CH assimilation by methanotrophs in both natural and engineered systems. We also highlight the technical challenges and technological breakthroughs needed to enable targeted CH oxidation in wastewater treatment plants.