Effect of Inoculum Microbial Diversity in Ex Situ Biomethanation of Hydrogen

Abstract

The effects of the inoculum origin, temperature or operational changes on ex situ biomethanation by complex microbial communities have been investigated; however, it remains unclear how the diversity of the inoculum influences the process and its stability. We explored the effect of microbial diversity of four inocula (coded as PF, WW, S37 and Nrich) on methane production, process stability and the formation of volatile fatty acids as by-products. The highest methane amounts produced were 3.38 ± 0.37 mmol, 3.20 ± 0.07 mmol, 3.07 ± 0.27 mmol and 3.14 ± 0.06 mmol for PF, WW, S37 and Nrich, respectively. The highest acetate concentration was found in less diverse cultures (1679 mg L−1 and 1397 mg L−1 for S37 and Nrich, respectively), whereas the acetate concentrations remained below 30 mg L−1 in the more diverse cultures. The maximum concentration of propionate was observed in less diverse cultures (240 mg L−1 and 37 mg L−1 for S37 and Nrich cultures, respectively). The highly diverse cultures outperformed the medium and low diversity cultures in the long-term operation. Methanogenic communities were mainly composed of hydrogenotrophic methanogens in all cultures. Aceticlastic methanogenesis was only active in the highly diverse sludge community throughout the experiment. The more diverse the inocula, the more methane was produced and the less volatile fatty acids accumulated, which could be attributed to the high number of microbial functions working together to keep a stable and balanced process. It is concluded that the inoculum origin and its diversity are very important factors to consider when the biomethanation process is performed with complex microbial communities.

Biological Hydrogen Methanation with Carbon Dioxide Utilization: Methanation Acting as Mediator in the Hydrogen Economy

“…The microflora diversity is relevant when testing ex situ biomethanation since these cultures can degrade acetate whenever a process perturbation is observed. Logroño et al [139] corroborated these findings when testing the behavior of a mesophilic reactor for an extended period, using different inoculum sources. These authors reported that highly diverse cultures showed better performance because acetoclastic methanogenesis was active throughout the whole experimental period, reducing the tendency to acetate accumulation.…”

The microbiology of Power-to-X applications

“…Most effective biomethanation was observed when inocula dominated by hydrogenotrophic methanogens and the versatile Methanosarcina was also present. The role of the inoculum microbial diversity was also highlighted by Logroño et al (Logroño et al 2022) showing that highly diverse cultures, including acetoclastic methanogens, besides the predominant hydrogenotrophic ones outperformed the medium and low diversity cultures in the long-term operation of ex situ biomethanation. Tsapekos et al (Tsapekos et al 2022) found that an inoculum adapted to hydrogen utilization was able to convert H 2 /CO 2 mixtures at various initial pressures to methane, while acetate accumulation and predominance of homoacetogenesis was observed in the case of a non-adapted inoculum.…”

Enrichment of Microbial Consortium with Hydrogenotrophic Methanogens for Biological Biogas Upgrade to Biomethane in a Bubble Reactor under Mesophilic Conditions

“…The high microbial diversity in the initial inoculum cannot be sustained during the operation of biomethanation reactors since they are fed only on CO 2 and H 2 [30,32,33]. Generally, it has been pointed out that the rich microbial diversion in the inoculum can enhance methane productivity, minimizing acetate accumulation [34].…”