Conversion of carbon dioxide in biogas into acetic acid by Clostridium thailandense immobilized on porous support materials.

This study aimed to convert CO2 in biogas into acetic acid using immobilized Clostridium thailandense cells on various support materials, including activated carbon, expanded clay, and coir. Immobilized cells and free cells were evaluated for their CO2 conversion ability into acetic acid using H2 as an electron donor at an H2 to CO2 in biogas ratio of 2:1 (v/v), 30 °C, 150 rpm. Results showed that immobilized cells on activated carbon increased CH4 content to 96.9% (v/v), and acetic acid production to 15.65 mmol/L within 96 h. These values outperformed free cells. The activated carbon-immobilized cells could be reused two times without losing efficacy in the purification of biogas and acetic acid production. This work indicates that using the immobilized cells offers a sustainable approach to biogas upgrading, reducing the environmental footprint of biogas production by increasing its energy content and purity.

Clostridium thailandense sp. nov., a novel CO2-reducing acetogenic bacterium isolated from peatland soil.

Some species of the genus Clostridium are efficient acetate producers and have been deemed useful for upgrading industrial biogas. An acetogenic, strictly anaerobic, Gram-stain-positive, subterminal endospore-forming bacterium designated strain PL3T was isolated from peatland soil enrichments with H2 and CO2. Cells of strain PL3T were 0.8-1.0×4.0-10.0 µm in size and rod-shaped. Growth of strain PL3T occurred at pH 6.0-7.5 (optimum, pH 7.0), at 20-40 °C (optimum, 30 °C) and with 0-1.5 % (w/v) NaCl (optimum, 0.5%). Biochemical analyses revealed that strain PL3T metabolized lactose, maltose, raffinose, rhamnose, lactic acid, sorbitol, arabinose and glycerol. Acetic acid was the predominant metabolite under anaerobic respiration with H2/CO2. The major cellular fatty acids were C16 : 0, C16 : 1 cis 9 and C17 : 0 cyc. The main polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, aminolipid and aminophospholipid. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain PL3T belongs to the genus Clostridium with the highest sequence similarity to Clostridium aciditolerans DSM 17425T (98.6 %) followed by Clostridium nitrophenolicum (97.8 %). The genomic DNA G+C content of strain PL3T was 31.1 mol%.The genomic in silico DNA-DNA hybridization value between strain PL3T and C. aciditolerans DSM 17425T was 25.1 %, with an average nucleotide identity of 80.2 %. Based on phenotypic, chemotaxonomic and phylogenetic differences, strain PL3T was suggested to represent a novel species of the genus Clostridium, for which the name Clostridium thailandense sp. nov. is proposed. The type strain is PL3T (=DSM 111812T=TISTR 2984T).