Diluted methane mitigation by a co-culture of alkaliphilic methanotrophs and the microalgae Scenedesmus obtusiusculus towards carbon neutrality

• Published in: Biochemical engineering journal 2024-03, Vol.203, p.109211, Article 109211
• Main Authors: Ruiz-Ruiz, Patricia, Gómez-Borraz, Tania L., Saldivar, Alexis, Hernández, Sergio, Morales-Ibarría, Marcia, Revah, Sergio
• Format: Article
• Language: English
• Subjects: biomass production; carbon; Carbon capture; carbon dioxide; coculture; Diluted methane; lighting; methane; Methanotrophic bacteria; methanotrophs; Microalgae; Microbial co-culture; nitrates; nitrogen; photobioreactors; Photonic pH control; photons; protein sources; salinity; Scenedesmus
• ISSN: 1369-703X; 1873-295X
• DOI: 10.1016/j.bej.2023.109211

A co-culture of an alkaliphilic methanotrophic consortium and the microalga Scenedesmus obtusiusculus was designed to consume CH4 and CO2 from diluted CH4 streams under alkaline conditions to favor CO2 retention. The highest CH4 consumption rate in batch assays was 318 mgCH4 gbiomass−1 d−1 with 8 % initial CH4 and nitrate as the nitrogen source. Subsequently, the co-culture was evaluated in a photobioreactor with batch and fed-batch CH4 feeds. Under continuous illumination, the CH4 consumption rate reached 258 mgCH4 gbiomass−1 d−1, but the pH increased to 9.8. After a photonic pH control implementation, the pH remained at 9.1 ± 0.05 with a consumption rate of 196 mgCH4 gbiomass−1 d−1. The co-culture exhibited continuous activity, synchronized growth, and long-term stability, effectively removing both gases in a single reactor. Moreover, the co-culture's biomass showed an increase in reserve molecules, including carbohydrates and lipids, with protein as the primary product (40–52 % DCW), offering potential as a microbial protein source. The photonic pH control exhibited a rapid response, substituting the traditional acid/alkali addition method, which increases salinity, medium volume, and operational costs. The methanotroph-microalgae co-culture is a successful, robust, and stable alternative for diluted methane mitigation, resulting in nearly zero carbon emissions and valuable biomass production. [Display omitted] ●Alkaliphilic methanotrophs-microalgae consume CH4 and CO2 from diluted CH4 streams.●Alkaline conditions retained the produced CO2 allowing sustained microalgal growth.●O2 production by microalgae supported bacterial CH4 oxidation.●Photonic pH control substituted the conventional acid/alkali addition.●The co-culture allowed almost complete carbon capture reducing GHG net impact.