Development of Methane-Utilizing Mixed Cultures for Sustainable Biopolymers Production from Wastewater Treatment Streams

Methane is classified as the second major greenhouse gas with a global warming potential 25 times higher than carbon dioxide. Wastewater treatment plants are considered as one of the main anthropogenic sources for global methane emissions. As many of the existing wastewater treatment facilities flare the biogas produced during anaerobic digestion to the atmosphere, methanotrophs can offer a promising solution for methane mitigation and play an important role in the paradigm shift of considering wastewater streams as a proactive energy and value-added material resource. Methanotrophs can convert methane into intracellular biopolymers mainly in the form of polyhydroxybutyrate (PHB) under specific environmental conditions. These biopolymers can be extracted and transformed into products which can replace conventional polymers in a wide range of applications due to their competitive physical and thermal properties. However, PHB accumulation is mainly limited to type II methanotrophs only. Moreover, enrichment of type II from mixed cultures is one of the challenges facing the scaling up of this process due to other non-producing PHB methanotrophs invasion. Accordingly, this study aims to discuss the factors enhancing the enrichment of type II methanotrophs in mixed cultures and the selection parameters that can halt the growth of type I without affecting type II. In addition, to discuss the PHB accumulation potential of the enriched cultures and the conditions maximizing their capacity as an input for designing sustainable biotechnology for biopolymer recovery. Moreover, to examine the capability of integrating the accumulated biopolymers in other environmental processes as methanol production. Finally, to develop novel phosphorus-based PHB accumulation strategies using the methanotrophic strain Methylocystis hirsute which can be then used as a selective pressure for targeting PHB-accumulating methanotrophs in mixed cultures