Microbial conversion of methane into single cell protein in a dual-membrane biofilm reactor

Single cell protein (SCP, or microbial protein) is a promising alternative food source that could sustainably address the growing demand for proteins. Recently, methane, as the main component of biogas, has been explored as a carbon and energy source for SCP production due to its lower cost and renewability compared to traditional substrates such as carbohydrates. However, a major challenge is how to safely deliver methane and oxygen, and the explosion risk impedes the CH₄-based SCP production. This study designed a dual-membrane biofilm reactor (dMBfR) for SCP production from methane, incorporating hollow fiber membranes to enhance the delivery of methane and oxygen. Over a 240-day operation, methane utilization efficiency reached 100 %, achieving the SCP yield of up to 0.49 g SCP/g CH₄. The reactor also exhibited competitive protein content of 50.2 % and biomass productivity of 506 mg/L/d. Additionally, we evaluated the reactor performance in response to varying aeration modes (open-end versus dead-end) and weekly protein harvest ratios (20 % versus 50 %). Compared to the dead-end aeration mode, the open-end mode led to 1.5-fold higher SCP production rates, 3.5-fold higher nitrogen-based SCP yields, 3.7-fold higher carbon-based SCP yields, and 1.1-fold higher protein content. Moreover, we applied the freeze-drying approach to produce dry SCP products in the reactor. The final SCP products exhibited higher solubility (17.4 %), water holding capacity (5.0 %), and emulsifying stability (93.3 %, after 24 h incubation) compared to typical fish meals, jointly indicative of the high quality of the produced SCP. This work offers valuable insights into CH₄-based SCP production, offering a promising avenue for efficient microbial protein synthesis.