Comparative assessment of two biotrickling filters for siloxanes removal: Effect of the addition of an organic phase
Pascual, Celia ; Cantera, Sara ; Muñoz, Raúl ; Lebrero, Raquel - \ 2020
Chemosphere 251 (2020). - ISSN 0045-6535
Biogas upgrading - Biotrickling filter - Silicone oil - Siloxanes - Two-phase partitioning bioreactor
Biogas produced at wastewater treatment plants and landfills contains trace levels of volatile methyl siloxanes (VMS) that are responsible for abrasion, corrosion and erosion of equipment during biogas storage and combustion. This research comparatively evaluated the removal of the most common VMS (L2, L3, D4, and D5) under aerobic conditions in a conventional biotrickling filter (BTF) and a two-phase partitioning BTF (TP-BTF) with silicone oil (at 30%) as organic phase. The TP-BTF showed a superior performance compared to the conventional BTF, increasing the total VMS removal from <30% in the BTF up to ∼70% in the TP-BTF. The highest REs in the TP-BTF were recorded for D4 and D5, reaching values of 80–90%, corresponding to ECs between 0.12 and 0.17 g m−3.h−1. Slightly lower values were obtained for L3 (70–80%), and the lowest performance was recorded for L2 (20–60%) due to the high vapor pressure of this siloxane and therefore its lower affinity by the organic phase. Surprisingly, despite the different inocula used, a similar microbial community was found by the end of operation of both BTFs, with KMBC-112, Reynarella and Chitinophaga as the dominant genera.
A systematic comparison of ectoine production from upgraded biogas using Methylomicrobium alcaliphilum and a mixed haloalkaliphilic consortium
Cantera, Sara ; Phandanouvong-Lozano, Vienvilay ; Pascual, Celia ; García-Encina, Pedro A. ; Lebrero, Raquel ; Hay, Anthony ; Muñoz, Raúl - \ 2020
Waste Management 102 (2020). - ISSN 0956-053X - p. 773 - 781.
Biogas-biorefinery - Ectoine - Haloalkaliphilic methanotrophs - Methane treatment
Biogas is the byproduct of anaerobic digestion with the highest valorization potential, however its full exploitation is limited by the lack of tax incentives and the inherent presence of pollutants. The development of technologies for biogas conversion into added-value products is crucial in order to ensure the competitiveness of this bioresource. This study constitutes the first proof of concept of upgraded biogas bioconversion into the high profit margin product ectoine. Ectoine represents the most expensive product synthesized by microorganisms with a retail value of 1000 $ kg-1 and a yearly increasing demand that currently entails a total market opportunity of 15000 M€. First, the production of ectoine from upgraded biogas was assessed in batch bioreactors. The presence of H2S did not exert a negative effect on the growth of the haloalkaliphilic ectoine producers, and ectoine yields up to 49 mg g biomass-1 were obtained. A second experiment conducted in continuous bubble column bioreactors confirmed the feasibility of the process under continuous mode (with ectoine yields of 109 mg g biomass-1). Finally, this study revealed that the removal of toxic compounds (i.e. medium dilution rate of 0.5 day-1) and process operation with a consortium composed of methylotrophic/non-methylotrophic ectoine producers enhanced upgraded biogas bioconversion. This research discloses the basis for the application of this innovative technology and could boost the economic performance of anaerobic digestion.
Bio-conversion of methane into high profit margin compounds : an innovative, environmentally friendly and cost-effective platform for methane abatement
Cantera, Sara ; Bordel, Sergio ; Lebrero, Raquel ; Gancedo, Juan ; García-Encina, Pedro A. ; Muñoz, Raúl - \ 2019
World Journal of Microbiology and Biotechnology 35 (2019)1. - ISSN 0959-3993
Bio-transformation - Ectoine - Market-value products - Methane abatement - Methanotrophs
Despite the environmental relevance of CH4 and forthcoming stricter regulations, the development of cost-efficient and environmentally friendly technologies for CH4 abatement is still limited. To date, one of the most promising solutions for the mitigation of this important GHG consists of the bioconversion of CH4 into bioproducts with a high profit margin. In this context, methanotrophs have been already proven as cell-factories of some of the most expensive products synthesized by microorganisms. In the case of ectoine (1000 $ kg−1), already described methanotrophic genera such as Methylomicrobium can accumulate up to 20% (ectoine wt−1) using methane as the only carbon source. Moreover, α-methanotrophs, such as Methylosynus and Methylocystis, are able to store bioplastic concentrations up to 50–60% of their total cell content. More than that, methanotrophs are one of the greatest potential producers of methanol and exopolysaccharides. Although this methanotrophic factory could be enhanced throughout metabolic engineering, the valorization of CH4 into valuable metabolites has been already consistently demonstrated under continuous and discontinuous mode, producing more than one compound in the same bioprocess, and using both, single strains and specific consortia. This review states the state-of-the-art of this innovative biotechnological platform by assessing its potential and current limitations.
Biological treatment of gas pollutants in partitioning bioreactors
Lebrero, Raquel ; Frutos Osvaldo, David ; Pérez, Victor ; Cantera, Sara ; Estrada, José Manuel ; Muñoz, Raúl - \ 2019
In: Advances in Chemical Engineering / Huerta-Ochoa, Sergio, Castillo-Araiza, Carlos O., Quijano, Guillermo, Academic Press Inc. (Advances in Chemical Engineering ) - ISBN 9780128149966 - p. 239 - 274.
Gas treatment - Gas-liquid mass transfer - Hydrophobic pollutants - NAP - Robustness
The off-gas treatment of hydrophobic pollutants in conventional biotechnologies is typically limited by the gas-liquid mass transfer as a result of the low-concentration gradient imposed by their high partitioning coefficients. The addition of a non-aqueous-phase (NAP) with a high affinity for the gas pollutant to packed bed or suspended-growth bioreactor configurations has resulted in enhanced elimination capacities and process robustness. Despite recent research has just added more desired characteristics to the selection criteria of the optimum NAP in gas treatment applications, silicone oil continues being the most popular mass transfer vector. This technology has been successfully applied to the treatment of hexane, methane, styrene, alpha-pinene and BTEX in biofilters, biotrickling filters, stirred tank and airlift bioreactors. The maximum potential of two-phase partitioning bioreactors (TPPBs) during off-gas treatment is achieved when the microbial community is confined inside the NAP. TPPB modeling has also experienced significant advances, the most advanced platforms being able to describe the recent findings in the field. This chapter will compile and critically discuss the fundamentals and most recent breakthroughs in the field of TPPBs for gas treatment applications.
Technologies for the bioconversion of methane into more valuable products
Cantera, Sara ; Muñoz, Raúl ; Lebrero, Raquel ; López, Juan Carlos ; Rodríguez, Yadira ; García-Encina, Pedro Antonio - \ 2018
Current Opinion in Biotechnology 50 (2018). - ISSN 0958-1669 - p. 128 - 135.
Methane, with a global warming potential twenty five times higher than that of CO 2 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 4 -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 4 biorefinery approach.
Multi-production of high added market value metabolites from diluted methane emissions via methanotrophic extremophiles
Cantera, S. ; Sánchez-Andrea, I. ; Lebrero, R. ; García-Encina, P.A. ; Stams, Alfons J.M. ; Muñoz, R. - \ 2018
Bioresource Technology 267 (2018). - ISSN 0960-8524 - p. 401 - 407.
CH-biorefinery - Ectoine - Exopolysaccharides - Hydroxyectoine - Methane abatement
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−1) to validate and optimize this innovative strategy for valorization of CH4 emissions. High Mg2+ concentrations promoted the accumulation of ectoine (79.7–94.2 mg g biomass−1), together with high hydroxyectoine yields (up to 13 mg g biomass−1) and EPS concentrations (up to 2.6 g L culture broth−1). Unfortunately, PHA synthesis was almost negligible (14.3 mg L−1) and only found at the lowest Mg2+ 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 CH4 biorefineries capable of creating value out of GHG mitigation.
Influence of the gas-liquid flow configuration in the absorption column on photosynthetic biogas upgrading in algal-bacterial photobioreactors
Toledo-Cervantes, Alma ; Madrid-Chirinos, Cindy ; Cantera, Sara ; Lebrero, Raquel ; Muñoz, Raúl - \ 2017
Bioresource Technology 225 (2017). - ISSN 0960-8524 - p. 336 - 342.
Algal-bacterial photobioreactor - Bio-methane - Biogas upgrading - Digestate - Nutrients recovery
The potential of an algal-bacterial system consisting of a high rate algal pond (HRAP) interconnected to an absorption column (AC) via recirculation of the cultivation broth for the upgrading of biogas and digestate was investigated. The influence of the gas-liquid flow configuration in the AC on the photosynthetic biogas upgrading process was assessed. AC operation in a co-current configuration enabled to maintain a biomass productivity of 15 g m−2 d−1, while during counter-current operation biomass productivity decreased to 8.7 ± 0.5 g m−2 d−1 as a result of trace metal limitation. A bio-methane composition complying with most international regulatory limits for injection into natural gas grids was obtained regardless of the gas-liquid flow configuration. Furthermore, the influence of the recycling liquid to biogas flowrate (L/G) ratio on bio-methane quality was assessed under both operational configurations obtaining the best composition at an L/G ratio of 0.5 and co-current flow operation.
Continuous abatement of methane coupled with ectoine production by Methylomicrobium alcaliphilum 20Z in stirred tank reactors : A step further towards greenhouse gas biorefineries
Cantera, Sara ; Lebrero, Raquel ; Rodríguez, Elisa ; García-Encina, Pedro A. ; Muñoz, Raúl - \ 2017
Journal of Cleaner Production 152 (2017). - ISSN 0959-6526 - p. 134 - 141.
Climate change - Ectoine - Methane abatement - Methane biorefinery - Methylomicrobium
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 Cu2+ 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 20Z accounted 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 CH4 emissions using extremophile methanotrophs.
Technologies for the bio-conversion of GHGs into high added value products : Current state and future prospects
Cantera, Sara ; Frutos, Osvaldo D. ; López, Juan Carlos ; Lebrero, Raquel ; Torre, Raúl Muñoz - \ 2017
In: Carbon Footprint and the Industrial Life Cycle / Alvarez Fernandez, Roberto, Zubelzu, Sergio, Martinez, Rodrigo, Springer Verlag (Green Energy and Technology 9783319549835) - ISBN 9783319549835 - p. 359 - 388.
Today, methane (CH4) and nitrous oxide (N2O) emissions represent 20% of the total greenhouse gas (GHG) inventory worldwide. CH4 is the second most important GHG emitted nowadays based on both its global warming potential (25 times higher than that of CO2) and its emission rates, while N2O is the main O3-depleting substance emitted in this 21st century. However, despite their environmental relevance and the forthcoming stricter legislation on atmospheric GHG emissions, the development of cost-efficient and environmentally friendly GHG treatment technologies is still limited. In this context, an active bio-technological abatement of CH4 and N2O emissions combined with the production of high added value products can become a profitable alternative to mitigate GHGs emissions. The feasible revalorization of diluted CH4 emissions from landfills has been recently tested in bioreactors with the production of ectoine, a microbial molecule with a high retail value in the cosmetic industry (approximately $1300 kg−1), as well as with the generation of polyhydroxyalkanoates (PHAs), a commodity with potential to replace conventional petroleum-derived polymers. This CH4 bio-refinery approach can be also based on the biogas produced from anaerobic digestion, therefore improving the economic viability of this waste management technology. The N2O contained in emissions from nitric acid production processes can be also considered as a potential substrate for the production of PHAs, with the subsequent increase in the cost-effectiveness of the abatement strategies of this GHG. On the other hand, the off-gas N2O abatement from diluted wastewater treatment plant emissions has been recently confirmed, although at the expense of a high input of electron donor due to the need to first deplete the O2 transferred from the emission. This chapter constitutes a critical review of the state-of-the-art of the potential and research niches of bio-technologies applied in a CH4 and N2O bio-refinery approach.
Nitrous Oxide Abatement Coupled with Biopolymer Production As a Model GHG Biorefinery for Cost-Effective Climate Change Mitigation
Frutos, Osvaldo D. ; Cortes, Irene ; Cantera, Sara ; Arnaiz, Esther ; Lebrero, Raquel ; Muñoz, Raúl - \ 2017
Environmental Science and Technology 51 (2017)11. - ISSN 0013-936X - p. 6319 - 6325.
N2O represents ∼6% of the global greenhouse gas emission inventory and the most important O3-depleting substance emitted in this 21st century. Despite its environmental relevance, little attention has been given to cost-effective and environmentally friendly N2O abatement methods. Here we examined, the potential of a bubble column (BCR) and an internal loop airlift (ALR) bioreactors of 2.3 L for the abatement of N2O from a nitric acid plant emission. The process was based on the biological reduction of N2O by Paracoccus denitrificans using methanol as a carbon/electron source. Two nitrogen limiting strategies were also tested for the coproduction of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) coupled with N2O reduction. High N2O removal efficiencies (REs) (≈87%) together with a low PHBV cell accumulation were observed in both bioreactors in excess of nitrogen. However, PHBV contents of 38-64% were recorded under N limiting conditions along with N2O-REs of ≈57% and ≈84% in the ALR and BCR, respectively. Fluorescence in situ hybridization analyses showed that P. denitrificans was dominant (>50%) after 6 months of experimentation. The successful abatement of N2O concomitant with PHBV accumulation confirmed the potential of integrating biorefinery concepts into biological gas treatment for a cost-effective GHG mitigation.
Ectoine bio-milking in methanotrophs : A step further towards methane-based bio-refineries into high added-value products
Cantera, Sara ; Lebrero, Raquel ; Rodríguez, Suní ; García-Encina, Pedro A. ; Muñoz, Raúl - \ 2017
Chemical Engineering Journal 328 (2017). - ISSN 1385-8947 - p. 44 - 48.
Bio-milking - Ectoine - Methane abatement - Methylomicrobium
This communication showed for the first time that the methanotrophic strain Methylomicrobium alcaliphilum 20Z (M. alcaliphilum 20Z) can efficiently synthesize and excrete (through a tailored bio-milking process) ectoine under continuous mode using methane (CH4) as the sole energy and carbon source. First, three consecutive 50 h fed batch fermentations consisting of alternating high salinity (6% NaCl for 24 h) and low salinity (0% NaCl for 24 h) cultivation stages were carried out in triplicate to determine the influence of sudden modifications in media salinity on ectoine synthesis and excretion. The results demonstrated that M. alcaliphilum 20Z exhibited a rapid response to osmotic shocks, which resulted in the release of the accumulated ectoine under hyposmotic shocks and the immediate uptake of the previously excreted ectoine during hyperosmotic shocks. A second experiment was carried out under continuous cultivation mode in two sequential stirred tank reactors operated at NaCl concentrations of 0 and 6%. Cells exhibited a constant intra-cellular ectoine concentration of 70.4 ± 14.3 mg g biomass−1 along the entire operation period when cultivated at a NaCl concentration of 6%. The centrifugation of the cultivation broth followed by a hyposmotic shock resulted in the excretion of ∼70% of the total intra-cellular ectoine. In brief, this research shows the feasibility of the continuous bioconversion of diluted CH4 emissions into high added-value products such as ectoine, which can turn greenhouse gas (GHG) abatement into a sustainable and profitable process.
Comparative performance evaluation of conventional and two-phase hydrophobic stirred tank reactors for methane abatement : Mass transfer and biological considerations
Cantera, Sara ; Estrada, José M. ; Lebrero, Raquel ; García-Encina, Pedro A. ; Muñoz, Raúl - \ 2016
Biotechnology and Bioengineering 113 (2016)6. - ISSN 0006-3592 - p. 1203 - 1212.
CH abatement - Hydrophobic bacteria - Mass transfer limitation - Methanotrophs - Two-phase partitioning bioreactors
This study demonstrated for the first time the capability of methanotrophs to grow inside silicone oil (SO200) and identified the optimum cultivation conditions for enrichment of hydrophobic methanotrophs (high dilution rates (D) and low CH4 transfer rates). The potential of the hydrophobic methanotrophs enriched was assessed in a single-phase stirred tank reactor (1P-STR) and in a two-phase stirred tank reactor (2P-STR). Different operational conditions were systematically evaluated in both reactors (SO200 fractions of 30 and 60 %, stirring rates of 250 and 500rpm, and D of 0.1-0.35 day-1 with and without biomass retention). The results showed that the TPPB only supported a superior CH4 abatement performance compared to the 1P-STR (40% enhancement at 250rpm and 25% enhancement at 500rpm) at a D of 0.3 day-1 due to the retention of the biocatalytic activity inside the SO200, while the 1P-STR achieved higher elimination capacities (EC up to ≈3 times) than the TPPB under the rest of conditions tested (ECmax=91.1gm-3h-1). Furthermore, the microscopic examination and DGGE-sequencing of the communities showed that the presence of SO200 influenced the microbial population structure, impacting on bacterial biodiversity and favoring the growth of methanotrophs such as Methylosarcina.
Evaluation of the influence of methane and copper concentration and methane mass transport on the community structure and biodegradation kinetics of methanotrophic cultures
Cantera, Sara ; Lebrero, Raquel ; García-Encina, Pedro A. ; Muñoz, Raúl - \ 2016
Journal of Environmental Management 171 (2016). - ISSN 0301-4797 - p. 11 - 20.
Biodegradation kinetics - CH concentration - Cu concentration - Methanotrophs - Microbial population structure
The environmental conditions during culture enrichment, which ultimately determine its maximum specific biodegradation rate (qmax) and affinity for the target pollutant (Ks), play a key role in the performance of bioreactors devoted to the treatment of methane emissions. This study assessed the influence of Cu2+ and CH4 concentration and the effective CH4 supply rate during culture enrichment on the structure and biodegradation kinetics of methanotrophic communities. The results obtained demonstrated that an increase in Cu2+ concentration from 0.05 to 25 μM increased the qmax and Ks of the communities enriched by a factor of ≈3, even if the Cu2+ concentration did not seem to have an effect on the enzymatic "copper switch" and only pMMO was detected. In addition, high Cu2+ concentrations supported lower diversity coefficients (Hs ≈ 1.5× lower) and apparently promoted the growth of more adapted methanotrophs such as Methylomonas. Despite no clear effect of CH4 concentration on the population structure or on the biodegradation kinetics of the communities enriched was recorded at the two low CH4 concentrations studied (1 and 8%), a higher agitation rate increased the qmax by a factor of ≈2.3 and Ks by a factor of ≈3.1.
Valorization of CH4 emissions into high-added-value products : Assessing the production of ectoine coupled with CH4 abatement
Cantera, Sara ; Lebrero, Raquel ; Sadornil, Lidia ; García-Encina, Pedro A. ; Muñoz, Raúl - \ 2016
Journal of Environmental Management 182 (2016). - ISSN 0301-4797 - p. 160 - 165.
Ectoine - Greenhouse gas - Methane biorefinery - Methane treatment
This study assessed an innovative strategy for the valorization of dilute methane emissions based on the bio-conversion of CH4 (the second most important greenhouse gas (GHG)) into ectoine by the methanotrophic ectoine-producing strain Methylomicrobium alcaliphilum 20 Z. The influence of CH4 (2–20%), Cu2+ (0.05–50 μM) and NaCl (0–9%) concentration as well as temperature (25–35 °C) on ectoine synthesis and specific CH4 biodegradation rate was evaluated for the first time. Concentrations of 20% CH4 (at 3% NaCl, 0.05 μM Cu2+, 25 °C) and 6% NaCl (at 4% CH4, 0.05 μM Cu2+, 25 °C) supported the maximum intra-cellular ectoine production yield (31.0 ±1.7 and 66.9 ±4.2 mg g biomass−1, respectively). On the other hand, extra-cellular ectoine concentrations of up to 4.7 ± 0.1 mg L−1 were detected at high Cu2+concentrations (50 μM), despite this methanotroph has not been previously classified as an ectoine-excreting strain. This research demonstrated the feasibility of the bio-conversion of dilute emissions of methane into high-added value products in an attempt to develop a sustainable GHG bioeconomy.