Comparative performance evaluation of conventional and two‐phase hydrophobic stirred tank reactors for methane abatement: Mass transfer and biological considerations

Sánchez‐Andrea

et al. 2018

Bioresource Technology

This study constitutes the first-proof-of-concept of a methane biorefinery based on the multi-production of high profit margin substances (ectoine, hydroxyectoine, polyhydroxyalkanoates (PHAs) and exopolysaccharides (EPS)) using methane as the sole carbon and energy source. Two bubble column bioreactors were operated under different magnesium concentrations (0.2, 0.02 and 0.002 g L) to validate and optimize this innovative strategy for valorization of CH emissions. High Mg concentrations promoted the accumulation of ectoine (79.7-94.2 mg g biomass), together with high hydroxyectoine yields (up to 13 mg g biomass) and EPS concentrations (up to 2.6 g L culture broth). Unfortunately, PHA synthesis was almost negligible (14.3 mg L) and only found at the lowest Mg concentration tested. Halomonas, Marinobacter, Methylophaga and Methylomicrobium, previously described as ectoine producers, were dominant in both bioreactors, Methylomicrobium being the only described methanotroph. This study encourages further research on CH biorefineries capable of creating value out of GHG mitigation.

Section: Influence Of Mg 2+ Concentration On Eps Productionsupporting

confidence: 55%

Multi-production of high added market value metabolites from diluted methane emissions via methanotrophic extremophiles

Sánchez‐Andrea

et al. 2018

Bioresource Technology

“…Hence, the CH 4 -ECs recorded at 600 rpm (CH 4 -ECs of 10.1 ± 1.1 g CH 4 m -3 h -1 at 3 % NaCl and 5.0 ± 1.0 g CH 4 m -3 h -1 at 6 % NaCl) were significantly lower than those achieved at 300 rpm ( Figure 5). Higher agitation rates often support a better mass transfer of methane from the gas to the microbial community, thus enhancing CH -EC (Estrada et al, 2014;Cantera et al 2015). However, higher agitation rates in our study promoted an unexpected cell disruption as a result of a high shear stress on M. alcaliphilum 20Z ( Figure S2).…”

Section: <Figure 5>mentioning

confidence: 60%

“…In the case of the experimental run 4 (6 % NaCl and 600 rpm) the accumulation of intra-cellular ectoine decreased by a factor of 1.5 (23.8 ± 1.1 mg ectoine (g biomass) -1 ) compared to the experimental runs at 6% NaCl and 300 rpm. Although higher agitation rates can enhance the mass transfer of methane from the emission to the aqueous microbial community (Cantera et al, 2015), they can also induce a pernicious cellular stress, which resulted in a severe damage of the Methylomicrobium alcaliphilum 20Z culture.…”

Section: < Figure 1>mentioning

confidence: 99%

Continuous abatement of methane coupled with ectoine production by Methylomicrobium alcaliphilum 20Z in stirred tank reactors: A step further towards greenhouse gas biorefineries

Journal of Cleaner Production

Rodriguéz

et al. 2017

Self Cite

Abstract:This study demonstrates for the first time the feasibility of producing ectoine (a high added value osmoprotectant intensively used in the cosmetic industry) during the continuous abatement of diluted emissions of methane by Methylomicrobium alcaliphilum 20Z in stirred tank reactors under non-sterile conditions. An increase in NaCl concentration in the cultivation broth from 3 to 6 % increased the intra-cellular ectoine yield by a factor of 2 (from 16.5 to 37.4 mg ectoine (g biomass) -1 ), while high stirring rates (600 rpm) entailed a detrimental cellular stress and 3 times lower ectoine yields (5.6 mg ectoine (g biomass) -1 ) compared to process operation at 300 rpm. An increase in Cu 2+ concentration from 0.05 to 25 µM enhanced methane abatement by a factor of 2 (up to elimination capacities of 24.5 g m -3 h -1 ), did not enhance intra-cellular ectoine production but promoted the excretion to the cultivation broth of 20 % of the total ectoine synthesized regardless of the NaCl concentration and stirring rate. The results obtained by culture hybridization with the specific probe Mγ1004 showed that Methylomicrobium alcaliphilum 20Zaccounted for more than 80 % of the total bacterial population in most experimental runs. This work confirmed the technical feasibility of a new generation of biorefineries based on the abatement of diluted CH 4 emissions using extremophile methanotrophs.

“…Current biotechnological processes could be the best solution for methane abatement due to their cost-effectiveness and their low environmental impact; however the implementation of bio-reactors for CH4 treatment is still limited. This limitation is mainly based on the low water solubility of CH4, which hampers the transport of this GHG to the microbial community and increases the cost of CH4 treatment biotechnologies [1]. In this context, the development of a CH4 biorefinery based on using CH4-laden emissions as raw materials to bio-synthesize high added value products represents a cost-effective solution for the mitigation of this GHG [2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Technologies for the bioconversion of methane into more valuable products

Muñoz

Current Opinion in Biotechnology

et al. 2018

Self Cite

Methane, with a global warming potential twenty five times higher than that of CO is the second most important greenhouse gas emitted nowadays. Its bioconversion into microbial molecules with a high retail value in the industry offers a potential cost-efficient and environmentally friendly solution for mitigating anthropogenic diluted CH-laden streams. Methane bio-refinery for the production of different compounds such as ectoine, feed proteins, biofuels, bioplastics and polysaccharides, apart from new bioproducts characteristic of methanotrophic bacteria, has been recently tested in discontinuous and continuous bioreactors with promising results. This review constitutes a critical discussion about the state-of-the-art of the potential and research niches of biotechnologies applied in a CH biorefinery approach.