This page has only limited features, please log in for full access.

Unclaimed
Hariklia N. Gavala
Department of Chemical and Biochemical Engineering, Technical University of Denmark, Søltofts Plads 228A, 2800 Kgs, Lyngby, Denmark

Honors and Awards

The user has no records in this section


Career Timeline

The user has no records in this section.


Short Biography

The user biography is not available.
Following
Followers
Co Authors
The list of users this user is following is empty.
Following: 0 users

Feed

Journal article
Published: 31 May 2021 in Journal of CO2 Utilization
Reads 0
Downloads 0

Gas fermentation processes have attracted considerable attention in recent years as they hold high potential for capturing and converting C1 waste gases into a range of biofuels and commodity chemicals. The production of solvents in gas fermentation is typically achieved by exploiting the solventogenic metabolism of acetogenic cultures, which is generally triggered upon exposure to stressful conditions, e.g. low pH. Although the oxidoreduction potential (ORP) is a well-known trigger of the cellular stress response, it has been scarcely investigated as a process control parameter in gas fermentation. Thus, this study focused on evaluating the potential of ORP control strategies for boosting the productivity of ethanol by exploiting the metabolic response to oxidative stress of acetogenic cultures. The dynamics of the redox cofactor pool and ratio as a function of the extracellular ORP and other operational parameters were also studied by monitoring the intracellular levels of the redox cofactor NADH/NAD+. The results showed that increasing the ORP to oxidizing conditions using dilute H2O2 triggered a 3.7-fold increase in the specific ethanol productivity, from 0.63 ± 0.04 mmol∙gCDW−1 h−1 at an ORP of -210 mV to 2.32 ± 0.19 mmol∙gCDW−1 h−1 at 160 mV. Additionally, the concentration and product selectivity towards ethanol also increased considerably due to the partial inhibition of the chain elongation under oxidative stress. Boost in ethanol productivity and inhibition of the chain elongation were both found to be driven by the presence of H2O2 rather than by the ORP per se. Studying the profile of the redox cofactors revealed a highly dynamic nature in the pool and ratio of NADH/NAD+ as a function of the specific uptake rate and the ratio of acetate-to-ethanol, respectively. The latter was explained by analyzing the thermodynamics of the aldehyde:ferredoxin oxidoreductase (AOR) pathway, which showed that the intrinsic thermodynamic limitation of this pathway imposes a high Fdred/Fdox ratio (>88 % of reduced ferredoxin) while forcing a highly dynamic NADH/NAD+ ratio in order to maintain the thermodynamic drive in the forward direction. The dynamics of the NADH/NAD+ ratio were also found to be significantly affected by the oxidative stress triggered by dilute H2O2, which confirmed the involvement of the AOR pathway in the detoxification of reactive oxygen species.

ACS Style

Antonio Grimalt-Alemany; Christina Etler; Konstantinos Asimakopoulos; Ioannis V. Skiadas; Hariklia N. Gavala. ORP control for boosting ethanol productivity in gas fermentation systems and dynamics of redox cofactor NADH/NAD+ under oxidative stress. Journal of CO2 Utilization 2021, 50, 101589 .

AMA Style

Antonio Grimalt-Alemany, Christina Etler, Konstantinos Asimakopoulos, Ioannis V. Skiadas, Hariklia N. Gavala. ORP control for boosting ethanol productivity in gas fermentation systems and dynamics of redox cofactor NADH/NAD+ under oxidative stress. Journal of CO2 Utilization. 2021; 50 ():101589.

Chicago/Turabian Style

Antonio Grimalt-Alemany; Christina Etler; Konstantinos Asimakopoulos; Ioannis V. Skiadas; Hariklia N. Gavala. 2021. "ORP control for boosting ethanol productivity in gas fermentation systems and dynamics of redox cofactor NADH/NAD+ under oxidative stress." Journal of CO2 Utilization 50, no. : 101589.

Journal article
Published: 02 February 2021 in Energies
Reads 0
Downloads 0

Swine manure mono-digestion results in relatively low methane productivity due to the low degradation rate of its solid fraction (manure fibers), and due to the high ammonia and water content. The aqueous ammonia soaking (AAS) pretreatment of manure fibers has been proposed for overcoming these limitations. In this study, continuous anaerobic digestion (AD) of manure mixed with optimally AAS-treated manure fibers was compared to the AD of manure mixed with untreated manure fibers. Due to lab-scale pumping restrictions, the ratio of AAS-optimally treated manure fibers to manure was only 1/3 on a total solids (TS) basis. However, the biogas productivity and methane yield were improved by 17% and 38%, respectively, also confirming the predictions from a simplified 1st order hydrolysis model based on batch experiments. Furthermore, an improved reduction efficiency of major organic components was observed for the digester processing AAS-treated manure fibers compared to the non-treated one (e.g., 42% increased reduction for cellulose fraction). A preliminary techno-economic analysis of the proposed process showed that mixing raw manure with AAS manure fibers in large-scale digesters could result in a 72% increase of revenue compared to the AD of manure mixed with untreated fibers and 135% increase compared to that of solely manure.

ACS Style

Anna Lymperatou; Niels B. Rasmussen; Hariklia N. Gavala; Ioannis V. Skiadas. Improving the Anaerobic Digestion of Swine Manure through an Optimized Ammonia Treatment: Process Performance, Digestate and Techno-Economic Aspects. Energies 2021, 14, 787 .

AMA Style

Anna Lymperatou, Niels B. Rasmussen, Hariklia N. Gavala, Ioannis V. Skiadas. Improving the Anaerobic Digestion of Swine Manure through an Optimized Ammonia Treatment: Process Performance, Digestate and Techno-Economic Aspects. Energies. 2021; 14 (3):787.

Chicago/Turabian Style

Anna Lymperatou; Niels B. Rasmussen; Hariklia N. Gavala; Ioannis V. Skiadas. 2021. "Improving the Anaerobic Digestion of Swine Manure through an Optimized Ammonia Treatment: Process Performance, Digestate and Techno-Economic Aspects." Energies 14, no. 3: 787.

Original paper
Published: 07 January 2021 in Waste and Biomass Valorization
Reads 0
Downloads 0

Contemporary challenges in decreasing Green House Gas emissions and finding alternative carbon and energy sources for fueling our society brought in the forefront processes based on biological conversions of gaseous substrates, such as syngas and carbon dioxide. Generation of synthesis gas or syngas (a gaseous mixture mainly of CO, H2 and CO2 generated during thermal decomposition of carbonaceous material in the presence of limited amount of an oxidizing agent) is known since the beginning of the 17th century and discovery of Fischer–Tropsch synthetic route in the beginning of the 20th century allowed the development of various routes for chemical catalytic synthesis of fuels and chemicals from syngas. Biological processing of syngas came in the forefront much later, following important advances within Microbiology and Biochemistry disciplines. This thermo-biochemical route for production of low-value products like fuels is considered competitive and advantageous compared to the thermochemical route when small-scale installations are concerned. Production of higher value products via the carboxylate platform is also a promising, and certainly worth-investigating route. Biological conversion of syngas and valorization of CO2 via biological means, besides contributing in greening our world, come with similar product portfolio and share the same technological challenges. Therefore, the target of the current study is to provide an overview of the latest scientific advances within syngas and CO2 valorization to fuels and chemicals and industrial applications and propose a way forward taking into account contemporary challenges and needs.

ACS Style

Hariklia N. Gavala; Antonio Grimalt-Alemany; Konstantinos Asimakopoulos; Ioannis V. Skiadas. Gas Biological Conversions: The Potential of Syngas and Carbon Dioxide as Production Platforms. Waste and Biomass Valorization 2021, 1 -26.

AMA Style

Hariklia N. Gavala, Antonio Grimalt-Alemany, Konstantinos Asimakopoulos, Ioannis V. Skiadas. Gas Biological Conversions: The Potential of Syngas and Carbon Dioxide as Production Platforms. Waste and Biomass Valorization. 2021; ():1-26.

Chicago/Turabian Style

Hariklia N. Gavala; Antonio Grimalt-Alemany; Konstantinos Asimakopoulos; Ioannis V. Skiadas. 2021. "Gas Biological Conversions: The Potential of Syngas and Carbon Dioxide as Production Platforms." Waste and Biomass Valorization , no. : 1-26.

Journal article
Published: 27 October 2020 in Membranes
Reads 0
Downloads 0

Forward Osmosis (FO) is a promising technology that can offer sustainable solutions in the biorefinery wastewater and desalination fields, via low energy water recovery. However, microbial biomass and organic matter accumulation on membrane surfaces can hinder the water recovery and potentially lead to total membrane blockage. Biofouling development is a rather complex process and can be affected by several factors such as nutrient availability, chemical composition of the solutions, and hydrodynamic conditions. Therefore, operational parameters like cross-flow velocity and pH of the filtration solution have been proposed as effective biofouling mitigation strategies. Nevertheless, most of the studies have been conducted with the use of rather simple solutions. As a result, biofouling mitigation practices based on such studies might not be as effective when applying complex industrial mixtures. In the present study, the effect of cross-flow velocity, pH, and cell concentration of the feed solution was investigated, with the use of complex solutions during FO separation. Specifically, fermentation effluent and crude glycerol were used as a feed and draw solution, respectively, with the purpose of recirculating water by using FO alone. The effect of the abovementioned parameters on (i) ATP accumulation, (ii) organic foulant deposition, (iii) total water recovery, (iv) reverse glycerol flux, and (v) process butanol rejection has been studied. The main findings of the present study suggest that significant reduction of biofouling can be achieved as a combined effect of high-cross flow velocity and low feed solution pH. Furthermore, cell removal from the feed solution prior filtration may further assist the reduction of membrane blockage. These results may shed light on the challenging, but promising field of FO process dealing with complex industrial solutions.

ACS Style

Stavros Kalafatakis; Agata Zarebska; Lene Lange; Claus Hélix-Nielsen; Ioannis V. Skiadas; Hariklia N. Gavala. Biofouling Mitigation Approaches during Water Recovery from Fermented Broth via Forward Osmosis. Membranes 2020, 10, 307 .

AMA Style

Stavros Kalafatakis, Agata Zarebska, Lene Lange, Claus Hélix-Nielsen, Ioannis V. Skiadas, Hariklia N. Gavala. Biofouling Mitigation Approaches during Water Recovery from Fermented Broth via Forward Osmosis. Membranes. 2020; 10 (11):307.

Chicago/Turabian Style

Stavros Kalafatakis; Agata Zarebska; Lene Lange; Claus Hélix-Nielsen; Ioannis V. Skiadas; Hariklia N. Gavala. 2020. "Biofouling Mitigation Approaches during Water Recovery from Fermented Broth via Forward Osmosis." Membranes 10, no. 11: 307.

Modeling and analysis
Published: 12 October 2020 in Biofuels, Bioproducts and Biorefining
Reads 0
Downloads 0

The unique characteristics and composition of macroalgae offer new possibilities for the production of bio‐based products such as biofuels and commodity chemicals. The technologies required for processing macroalgae are not currently mature enough, and those that exist are primarily oriented towards the production of biofuels. This study explores a production process to produce lactic acid (LA) from brown algae, designed with a capacity of 11 t h−1 of product. Four scenarios are simulated in Aspen Plus, for the production of polymer‐grade LA, utilizing Laminaria macroalgae as a feedstock. Techno‐economic models are established to investigate the feasibility of these new technologies. Configurations for heat recovery are suggested to maximize productivity, and a minimum viable selling price (MVSP) is calculated for LA to predict an optimal design configuration. The process does not recover investment, when using a composition represented by an avarage value for all the Laminaria sp. Moreover, the percentage difference between the MVSP and the current selling price (SP) is 34%. Nonetheless, when using Laminaria digitata, which comprises of higher carbohydrates, compared to other Laminaria sp, the percentage difference between the MVSP and the SP is estimated to be 28%. If the hypothetical fermentation of alginate is considered, the invested capital is recovered by the 11th year. These results also highlight the need for research into the valorization of the alginate fraction, improving the microorganisms’ ability to metabolize alginate to LA or other relevant products. The development of the respective processes would be a step that the scientific community would be justified in examining. © 2020 Society of Industrial Chemistry and John Wiley & Sons Ltd

ACS Style

Elena T Grasa; Ólafur Ögmundarson; Hariklia N Gavala; Sumesh Sukumara. Commodity chemical production from third‐generation biomass: a techno‐economic assessment of lactic acid production. Biofuels, Bioproducts and Biorefining 2020, 15, 257 -281.

AMA Style

Elena T Grasa, Ólafur Ögmundarson, Hariklia N Gavala, Sumesh Sukumara. Commodity chemical production from third‐generation biomass: a techno‐economic assessment of lactic acid production. Biofuels, Bioproducts and Biorefining. 2020; 15 (1):257-281.

Chicago/Turabian Style

Elena T Grasa; Ólafur Ögmundarson; Hariklia N Gavala; Sumesh Sukumara. 2020. "Commodity chemical production from third‐generation biomass: a techno‐economic assessment of lactic acid production." Biofuels, Bioproducts and Biorefining 15, no. 1: 257-281.

Journal article
Published: 16 June 2020 in Biochemical Engineering Journal
Reads 0
Downloads 0

One of the factors limiting the economic viability of polyhydroxyalkanoates (PHA) is the low volumetric productivity obtained with second-generation feedstocks, resulting from their low carbon concentration. In the present study, the use of membrane bioreactors (MBRs) was evaluated as a strategy to retain the microbial cells in the reactor and to enable a repeated supply of substrate without increasing the reactor volume. Two immersed MBR systems were studied: classical pressure-driven MBRs (hollow fibers and ceramic filters), and a novel diffusion-based MBR. In the latter, the rate of volatile fatty acid (VFA) diffusion across the membranes was lower than the VFA consumption rate of the culture, and thus, not suitable to attain high productivities. Possible research directions to increase substrate diffusion are suggested. On the other hand, pressure-driven configurations led to high values of productivity (0.87–1.44 g/(L.h)) during a fed-batch PHA accumulation using mixed microbial consortia. No flux reduction was observed in a 24 h fed-batch process, which allowed for a reduction of up to 82 % of the reactor volume, demonstrating the potential of this strategy. Hollow fibers and ceramic filters offered similar results during the fed-batch, but they presented different limitations and advantages.

ACS Style

Anna Burniol-Figols; Manuel Pinelo; Ioannis V. Skiadas; Hariklia N. Gavala. Enhancing polyhydroxyalkanoate productivity with cell-retention membrane bioreactors. Biochemical Engineering Journal 2020, 161, 107687 .

AMA Style

Anna Burniol-Figols, Manuel Pinelo, Ioannis V. Skiadas, Hariklia N. Gavala. Enhancing polyhydroxyalkanoate productivity with cell-retention membrane bioreactors. Biochemical Engineering Journal. 2020; 161 ():107687.

Chicago/Turabian Style

Anna Burniol-Figols; Manuel Pinelo; Ioannis V. Skiadas; Hariklia N. Gavala. 2020. "Enhancing polyhydroxyalkanoate productivity with cell-retention membrane bioreactors." Biochemical Engineering Journal 161, no. : 107687.

Journal article
Published: 01 April 2020 in Water Research
Reads 0
Downloads 0

Over the last decades, the use of mixed microbial communities has attracted increasing scientific attention due to their potential biotechnological applications in several emerging technological platforms such as the carboxylate, bioplastic, syngas and bio-electrochemical synthesis platforms. However, this increasing interest has not been accompanied by a parallel development of suitable cryopreservation techniques for microbial communities. While cryopreservation methods for the long-term storage of axenic cultures are well established, their effectiveness in preserving the microbial diversity and functionality of microbial communities has rarely been studied. In this study, the effect of the addition of different cryopreservation agents on the long-term storage of microbial communities at −80 °C was studied using a stable enrichment culture converting syngas into acetate and ethanol. The cryopreservation agents considered in the study were glycerol, dimethylsulfoxide, polyvinylpyrrolidone, Tween 80 and yeast extract, as well as with no addition of cryopreservation agent. Their effectiveness was evaluated based on the microbial activity recovery and the maintenance of the microbial diversity and community structure upon revival of the microbial community. The results showed that the commonly used glycerol and no addition of cryopreservation agent were the least recommendable methods for the long-term frozen storage of microbial communities, while Tween 80 and polyvinylpyrrolidone were overall the most effective. Among the cryoprotectants studied, polyvinylpyrrolidone and especially Tween 80 were the only ones assuring reproducible results in terms of microbial activity recovery and microbial community structure preservation.

ACS Style

Antonio Grimalt-Alemany; Mateusz Łężyk; Konstantinos Asimakopoulos; Ioannis V. Skiadas; Hariklia N. Gavala. Cryopreservation and fast recovery of enriched syngas-converting microbial communities. Water Research 2020, 177, 115747 .

AMA Style

Antonio Grimalt-Alemany, Mateusz Łężyk, Konstantinos Asimakopoulos, Ioannis V. Skiadas, Hariklia N. Gavala. Cryopreservation and fast recovery of enriched syngas-converting microbial communities. Water Research. 2020; 177 ():115747.

Chicago/Turabian Style

Antonio Grimalt-Alemany; Mateusz Łężyk; Konstantinos Asimakopoulos; Ioannis V. Skiadas; Hariklia N. Gavala. 2020. "Cryopreservation and fast recovery of enriched syngas-converting microbial communities." Water Research 177, no. : 115747.

Journal article
Published: 10 March 2020 in Chemical Engineering Journal
Reads 0
Downloads 0

Syngas, mainly consisting of CO, H2 and CO2, can be generated from the gasification of biomass and organic waste and constitutes an important energy and carbon source. However, its biological conversion is still challenging due to the low solubility and the toxic nature of its components. In this study, enriched mixed microbial consortia were inoculated in trickle bed reactors operated in continuous mode with the supply of artificial syngas (45% H2, 25% CO2, 20% CO and 10% N2) under mesophilic (37 °C) and thermophilic (60 °C) conditions. The results revealed a clear superiority of the thermophilic conditions exhibiting higher methane productivities, higher conversion efficiencies and lower yields of byproducts at all steady states tested compared to mesophilic temperature. The highest methane productivity achieved was 8.49 mmol∙lbed−1∙h−1. The microorganisms related to syngas biomethanation were investigated through metagenomic analysis of samples obtained from the inoculum, the liquid phase and the biofilm of the reactors. The continuous operation altered completely the dominant species in mesophilic conditions compared to the inoculum. Accumulation of volatile fatty acids (VFAs) under mesophilic conditions was attributed to the high relative abundance of the genus Sporomusa. A large quantity of acetogenic cell debris scavengers and potential acetogenic metabolism of the genus Thermincola could justify accumulation of VFAs under thermophilic conditions. Absence of aceticlastic methanogens in both reactors was also noticeable. The archaeal communities were enhanced in the biofilm compared to the liquid phase presenting a 6.2 fold and a 1.8 fold higher relative abundance at 37 °C and 60 °C, respectively.

ACS Style

Konstantinos Asimakopoulos; Mateusz Łężyk; Antonio Grimalt-Alemany; Antonios Melas; Zhiyou Wen; Hariklia N. Gavala; Ioannis V. Skiadas. Temperature effects on syngas biomethanation performed in a trickle bed reactor. Chemical Engineering Journal 2020, 393, 124739 .

AMA Style

Konstantinos Asimakopoulos, Mateusz Łężyk, Antonio Grimalt-Alemany, Antonios Melas, Zhiyou Wen, Hariklia N. Gavala, Ioannis V. Skiadas. Temperature effects on syngas biomethanation performed in a trickle bed reactor. Chemical Engineering Journal. 2020; 393 ():124739.

Chicago/Turabian Style

Konstantinos Asimakopoulos; Mateusz Łężyk; Antonio Grimalt-Alemany; Antonios Melas; Zhiyou Wen; Hariklia N. Gavala; Ioannis V. Skiadas. 2020. "Temperature effects on syngas biomethanation performed in a trickle bed reactor." Chemical Engineering Journal 393, no. : 124739.

Journal article
Published: 21 January 2020 in Applied Energy
Reads 0
Downloads 0

The syngas biomethanation process is a promising bioconversion route due to its high versatility, as it could be applied as a stand-alone technology, coupled to gasification plants, and integrated in anaerobic digestion or bioelectrochemical conversion systems. The biomethanation of syngas typically takes place through a rather complex network of interspecies metabolic interactions, which may vary significantly depending on the operating conditions applied and the diversity of microbial groups present. Despite there are several benefits derived from using microbial consortia, these also present challenges associated with limited process control and low product selectivity. To address the latter, the syngas biomethanation process carried out by mesophilic and thermophilic microbial consortia was modelled with the ultimate goal of studying possible catabolic route control strategies through the modulation of key operating parameters. The results showed that the thermophilic microbial consortium presented much higher apparent specific methane productivity (18.8 mmol/g VSS/d) than the mesophilic (4.6 mmol/g VSS/d) at an initial PCO of 0.2 atm, and that the difference increased with increasing initial PCO. This difference in productivity was found to derive from the catabolic routes used rather than the kinetic parameters of each microbial consortium. Additionally, the thermodynamic considerations included in the models revealed the possibility of controlling the catabolic routes used by each consortium through the modulation of the mass transfer and PCO2. Our results strongly indicate that modulating the PCO2 is a promising operational strategy for boosting the product selectivity towards CH4, the productivity of the system and the biomethane quality simultaneously.

ACS Style

Antonio Grimalt-Alemany; Konstantinos Asimakopoulos; Ioannis V. Skiadas; Hariklia N. Gavala. Modeling of syngas biomethanation and catabolic route control in mesophilic and thermophilic mixed microbial consortia. Applied Energy 2020, 262, 114502 .

AMA Style

Antonio Grimalt-Alemany, Konstantinos Asimakopoulos, Ioannis V. Skiadas, Hariklia N. Gavala. Modeling of syngas biomethanation and catabolic route control in mesophilic and thermophilic mixed microbial consortia. Applied Energy. 2020; 262 ():114502.

Chicago/Turabian Style

Antonio Grimalt-Alemany; Konstantinos Asimakopoulos; Ioannis V. Skiadas; Hariklia N. Gavala. 2020. "Modeling of syngas biomethanation and catabolic route control in mesophilic and thermophilic mixed microbial consortia." Applied Energy 262, no. : 114502.

Research article
Published: 09 January 2020 in Journal of Chemical Technology & Biotechnology
Reads 0
Downloads 0

BACKGROUND Purification of polyhydroxyalkanoates (PHA) is a challenging step, given the difficulty of achieving high PHA purity, while maintaining polymer integrity, in a sustainable and cost‐efficient manner. This study evaluated the potential of dilute ammonia digestion as a method to purify PHA from mixed microbial consortia. RESULTS Digestion temperatures were critical to the obtainable purity and the amount of recovered PHA. At temperatures below 75 °C (regardless of the incubation time and ammonia concentration), a low PHA recovery (down to 65%) and no increase in purity was observed. By increasing the temperature above 75 °C, a significantly higher PHA purity and higher recovery (above 90%) could be achieved. Temperatures maximizing the purity (140 °C) led to a detrimental reduction in the molar mass of the isolated PHA, but the use of a sonication pre‐treatment enabled to increase the purity at temperatures leading to limited molar mass loss (75–115 °C). The impurities still present in the recovered PHA did not compromise its thermal stability, and no significant degradation occurred during melting of PHA with 86% purity (comparably to pure chloroform‐extracted PHA). Conversely, PHA recovered through sulphuric acid (H2SO4) digestion underwent severe degradation during melting, despite presenting higher purity (98%). CONCLUSIONS High PHA purity, recovery and thermal stability can be obtained with dilute ammonia digestion. These observations, combined with the possibility of reusing ammonia within the process, make this method a promising approach for a more sustainable purification of PHA. © 2020 Society of Chemical Industry

ACS Style

Anna Burniol-Figols; Ioannis V. Skiadas; Anders E. Daugaard; Hariklia N. Gavala. Polyhydroxyalkanoate (PHA) purification through dilute aqueous ammonia digestion at elevated temperatures. Journal of Chemical Technology & Biotechnology 2020, 95, 1519 -1532.

AMA Style

Anna Burniol-Figols, Ioannis V. Skiadas, Anders E. Daugaard, Hariklia N. Gavala. Polyhydroxyalkanoate (PHA) purification through dilute aqueous ammonia digestion at elevated temperatures. Journal of Chemical Technology & Biotechnology. 2020; 95 (5):1519-1532.

Chicago/Turabian Style

Anna Burniol-Figols; Ioannis V. Skiadas; Anders E. Daugaard; Hariklia N. Gavala. 2020. "Polyhydroxyalkanoate (PHA) purification through dilute aqueous ammonia digestion at elevated temperatures." Journal of Chemical Technology & Biotechnology 95, no. 5: 1519-1532.

Journal article
Published: 05 July 2019 in Molecules
Reads 0
Downloads 0

(1) Background: The continuously increasing demand for renewable energy sources renders anaerobic digestion as one of the most promising technologies for renewable energy production. Due to the animal production intensification, manure is being used as the primary feedstock for most biogas plants. Their economical profitable operation, however, relies on increasing the methane yield from the solid fraction of manure, which is not so easily degradable. The solid fraction after anaerobic digestion, the so-called digested fibers, consists mainly of hardly biodegradable material and comes at a lower mass per unit volume of manure compared to the solid fraction before anaerobic digestion. Therefore, investigation on how to increase the biodegradability of digested fibers is very relevant. So far, Aqueous Ammonia Soaking (AAS), has been successfully applied on digested fibers separated from the effluent of a manure-fed, full-scale anaerobic digester to enhance their methane productivity in batch experiments. (2) Methods: In the present study, continuous experiments at a mesophilic (38 °C) CSTR-type anaerobic digester fed with swine manure first and a mixture of manure with AAS-treated digested fibers in the sequel, were performed. Anaerobic Digestion Model 1 (ADM1) previously fitted on manure fed digester was used in order to assess the effect of the addition of AAS-pre-treated digested manure fibers on the kinetics of anaerobic digestion process. (3) Results and Conclusions: The methane yield of AAS-treated digested fibers under continuous operation was 49-68% higher than that calculated in batch experiments in the past. It was found that AAS treatment had a profound effect mainly on the disintegration/hydrolysis rate of particulate carbohydrates. Comparison of the data obtained in the present study with the data obtained with AAS-pre-treated raw manure fibers in the past revealed that hydrolysis kinetics after AAS pre-treatment were similar for both types of biomasses.

ACS Style

Chrysoula Mirtsou-Xanthopoulou; Ioannis V. Skiadas; Hariklia N. Gavala. On the Effect of Aqueous Ammonia Soaking Pre-Treatment on Continuous Anaerobic Digestion of Digested Swine Manure Fibers. Molecules 2019, 24, 2469 .

AMA Style

Chrysoula Mirtsou-Xanthopoulou, Ioannis V. Skiadas, Hariklia N. Gavala. On the Effect of Aqueous Ammonia Soaking Pre-Treatment on Continuous Anaerobic Digestion of Digested Swine Manure Fibers. Molecules. 2019; 24 (13):2469.

Chicago/Turabian Style

Chrysoula Mirtsou-Xanthopoulou; Ioannis V. Skiadas; Hariklia N. Gavala. 2019. "On the Effect of Aqueous Ammonia Soaking Pre-Treatment on Continuous Anaerobic Digestion of Digested Swine Manure Fibers." Molecules 24, no. 13: 2469.

Original paper
Published: 19 March 2019 in Waste and Biomass Valorization
Reads 0
Downloads 0

Two identical trickle-bed reactor setups were designed and operated under mesophilic conditions and atmospheric pressure, without pH control, for the biomethanation of syngas consisted of 45% H2, 25% CO2, 20% CO and 10% CH4. The reactors were inoculated with mixed methanogenic microbial consortia formerly adapted to the gaseous mixture. During the start-up of the reactors acetic acid accumulation in the liquid broth resulted in a pH decrease to levels unfavorable for methanogenic activity. This was corrected by introducing a strong phosphate buffer in the medium (K2HPO4/KH2PO4 : 87 mM/13 mM). Channeling phenomena observed across the trickle bed were eliminated by setting a high liquid recirculation rate (1600 l/lbed/d). The reactors were operated for 294 days presenting minor deviations between them at the 24 extracted steady states and high cell retention even at a hydraulic retention time (HRT) of 3.7 days. At a gas residence time of 2.31 h and a HRT of 5.5 days the achieved CH4 productivity was 2 mmol/lbed/h with 93% H2 and 90% CO conversion efficiency and a 78% electron yield to CH4. The conducted study verified that an enriched methanogenic microbial consortium can effectively convert syngas to CH4 in a trickle bed reactor under appropriate operational conditions.

ACS Style

Konstantinos Asimakopoulos; Hariklia N. Gavala; Ioannis V. Skiadas. Biomethanation of Syngas by Enriched Mixed Anaerobic Consortia in Trickle Bed Reactors. Waste and Biomass Valorization 2019, 11, 495 -512.

AMA Style

Konstantinos Asimakopoulos, Hariklia N. Gavala, Ioannis V. Skiadas. Biomethanation of Syngas by Enriched Mixed Anaerobic Consortia in Trickle Bed Reactors. Waste and Biomass Valorization. 2019; 11 (2):495-512.

Chicago/Turabian Style

Konstantinos Asimakopoulos; Hariklia N. Gavala; Ioannis V. Skiadas. 2019. "Biomethanation of Syngas by Enriched Mixed Anaerobic Consortia in Trickle Bed Reactors." Waste and Biomass Valorization 11, no. 2: 495-512.

Original paper
Published: 06 February 2019 in Waste and Biomass Valorization
Reads 0
Downloads 0

Mixed culture-based syngas biomethanation is a robust bioconversion process with high versatility in terms of exploitable feedstocks and potential applications, as it could be operated independently, or coupled to anaerobic digestion systems and in-situ biogas upgrading processes. Typically, the syngas biomethanation consists in the stepwise conversion of syngas into methane through a number of catabolic routes, which may vary considerably depending on the operating conditions. In this study, two enrichments were performed at 37 °C and 60 °C to investigate the effect of the incubation temperature on the microbial selection process and the dominant catabolic routes followed. This was carried out through the characterization of the catabolic routes and the microbial composition of the enriched cultures, and a thermodynamic feasibility study on their metabolic networks. The enrichments resulted in two stable microbial consortia with different patterns of activity. The mesophilic enriched consortium presented a more intricate metabolic network composed by four microbial trophic groups, where aceticlastic methanogenesis contributed to 64.9 ± 8.3% of the CH4 production. The metabolic network of the thermophilic enriched consortium was much simpler, consisting in the syntrophic association of carboxydotrophic hydrogenogens and hydrogenotrophic methanogens. This led to significant differences in methane productivity, corresponding to 1.83 ± 0.27 and 33.48 ± 0.90 mmol CH4/g VSS/h for the mesophilic and the thermophilic enriched consortium, respectively, which would potentially make the thermophilic consortium more suited for industrial applications. 16S rRNA gene amplicon analysis indicated the presence of strains with similarity to Acetobacterium sp., Methanospirillum hungateii, Methanospirillum stamsii and Methanothrix sp. at mesophilic conditions, and Thermincola carboxydiphila and Methanothermobacter sp. at thermophilic conditions, implying a role in the conversion of syngas. The thermodynamic feasibility study demonstrated that the microbial selection was not driven solely by kinetic competition, since thermodynamic limitations also played a significant role defining the dominant catabolic routes.

ACS Style

Antonio Grimalt-Alemany; Mateusz Łężyk; David M. Kennes-Veiga; Ioannis V. Skiadas; Hariklia N. Gavala. Enrichment of Mesophilic and Thermophilic Mixed Microbial Consortia for Syngas Biomethanation: The Role of Kinetic and Thermodynamic Competition. Waste and Biomass Valorization 2019, 11, 465 -481.

AMA Style

Antonio Grimalt-Alemany, Mateusz Łężyk, David M. Kennes-Veiga, Ioannis V. Skiadas, Hariklia N. Gavala. Enrichment of Mesophilic and Thermophilic Mixed Microbial Consortia for Syngas Biomethanation: The Role of Kinetic and Thermodynamic Competition. Waste and Biomass Valorization. 2019; 11 (2):465-481.

Chicago/Turabian Style

Antonio Grimalt-Alemany; Mateusz Łężyk; David M. Kennes-Veiga; Ioannis V. Skiadas; Hariklia N. Gavala. 2019. "Enrichment of Mesophilic and Thermophilic Mixed Microbial Consortia for Syngas Biomethanation: The Role of Kinetic and Thermodynamic Competition." Waste and Biomass Valorization 11, no. 2: 465-481.

Research article
Published: 07 January 2019 in Journal of Chemical Technology & Biotechnology
Reads 0
Downloads 0

BACKGROUND Clostridium pasteurianum is a well described strain for the conversion of glycerol into butanol. In general, cell growth kinetics depends on the type of glycerol used and the concentration of butanol in the fermentation broth. However, despite the numerous studies existing on the subject, there is limited information in the literature regarding growth inhibition kinetics due to the cytotoxic effect of butanol on the cell growth. This can be attributed to the difficulty of growing cells at high butanol concentration which renders the determination of inhibition kinetics a rather challenging task. RESULTS During this study a new approach for the determination of the butanol inhibition kinetics on the growth of C. pasteurianum was tested. Specifically, pulses of crude glycerol were applied when steady state was reached during continuous fermentation experiments with increasing butanol concentration in the feed. Combining pulse experiments with batch fermentation at low substrate concentration allowed for accurate determination of the kinetic constants for inhibited growth. This approach also minimised the correlation of the growth constants which often leads to poor identifiability. CONCLUSION In overall, the proposed experimental approach showed good identifiability of the kinetic parameters for butanol inhibition of the microbial growth and can be proven valuable for the determination of inhibitory effects of highly toxic compounds. This article is protected by copyright. All rights reserved.

ACS Style

Stavros Kalafatakis; Ioannis V. Skiadas; Hariklia N. Gavala. Determining butanol inhibition kinetics on the growth ofClostridium pasteurianumbased on continuous operation and pulse substrate additions. Journal of Chemical Technology & Biotechnology 2019, 94, 1559 -1566.

AMA Style

Stavros Kalafatakis, Ioannis V. Skiadas, Hariklia N. Gavala. Determining butanol inhibition kinetics on the growth ofClostridium pasteurianumbased on continuous operation and pulse substrate additions. Journal of Chemical Technology & Biotechnology. 2019; 94 (5):1559-1566.

Chicago/Turabian Style

Stavros Kalafatakis; Ioannis V. Skiadas; Hariklia N. Gavala. 2019. "Determining butanol inhibition kinetics on the growth ofClostridium pasteurianumbased on continuous operation and pulse substrate additions." Journal of Chemical Technology & Biotechnology 94, no. 5: 1559-1566.

Review
Published: 01 September 2018 in Chemical Engineering Journal
Reads 0
Downloads 0

Implementation of biofuels as an alternative to fossil fuels has been established as an answer to climate change by limiting GHG emissions. Syngas fermentation has emerged as a promising process for the conversion of waste biomasses to valuable products with bioethanol being on the main focus. However, the bottleneck of the mass transfer of syngas compounds H2 and CO along with low production yields has set barriers to the development of an industrial scale plant. Recent research indicates that many different methodologies spring up in order to face this important challenge. The aim of this review is to assemble all these techniques applied in syngas fermentation, focusing on the different bioreactor configurations operated in continuous mode for the production of liquid and gas biofuels. This article also outlines the so far entrepreneurial initiatives and the progress made towards the commercialization of the process.

ACS Style

Konstantinos Asimakopoulos; Hariklia N. Gavala; Ioannis V. Skiadas. Reactor systems for syngas fermentation processes: A review. Chemical Engineering Journal 2018, 348, 732 -744.

AMA Style

Konstantinos Asimakopoulos, Hariklia N. Gavala, Ioannis V. Skiadas. Reactor systems for syngas fermentation processes: A review. Chemical Engineering Journal. 2018; 348 ():732-744.

Chicago/Turabian Style

Konstantinos Asimakopoulos; Hariklia N. Gavala; Ioannis V. Skiadas. 2018. "Reactor systems for syngas fermentation processes: A review." Chemical Engineering Journal 348, no. : 732-744.

Journal article
Published: 19 July 2018 in Biotechnology for Biofuels
Reads 0
Downloads 0

The production of ethanol through the biochemical conversion of syngas, a mixture of H2, CO and CO2, has been typically studied using pure cultures. However, mixed microbial consortia may offer a series of benefits such as higher resilience and adaptive capacity, and non-sterile operation, all of which contribute to reducing the utility consumption when compared to pure culture-based processes. This work focuses on the study of strategies for the enrichment of mixed microbial consortia with high ethanologenic potential, investigating the effect of the operational conditions (pH and yeast extract addition) on both the ethanol yield and evolution of the microbial community along the enrichment process. The pH was selected as the main driver of the enrichment as it was expected to be a crucial parameter for the selection of carboxydotrophic bacteria with high ethanologenic potential. Additionally, a thermodynamic analysis of the network of biochemical reactions carried out by syngas-converting microbial consortia was performed and the potential of using thermodynamics as a basis for the selection of operational parameters favoring a specific microbial activity was evaluated. All enriched consortia were dominated by the genus Clostridium with variable microbial diversity and species composition as a function of the enrichment conditions. The ethanologenic potential of the enriched consortia was observed to increase as the initial pH was lowered, achieving an ethanol yield of 59.2 ± 0.2% of the theoretical maximum in the enrichment at pH 5. On the other hand, yeast extract addition did not affect the ethanol yield, but triggered the production of medium-chain fatty acids and alcohols. The thermodynamic analysis of the occurring biochemical reactions allowed a qualitative prediction of the activity of microbial consortia, thus enabling a more rational design of the enrichment strategies targeting specific activities. Using this approach, an improvement of 22.5% over the maximum ethanol yield previously obtained was achieved, reaching an ethanol yield of 72.4 ± 2.1% of the theoretical maximum by increasing the initial acetate concentration in the fermentation broth. This study demonstrated high product selectivity towards ethanol using mixed microbial consortia. The thermodynamic analysis carried out proved to be a valuable tool for interpreting the metabolic network of microbial consortia-driven processes and designing microbial-enrichment strategies targeting specific biotransformations.

ACS Style

Antonio Grimalt-Alemany; Mateusz Łężyk; Lene Lange; Ioannis V. Skiadas; Hariklia N. Gavala. Enrichment of syngas-converting mixed microbial consortia for ethanol production and thermodynamics-based design of enrichment strategies. Biotechnology for Biofuels 2018, 11, 198 .

AMA Style

Antonio Grimalt-Alemany, Mateusz Łężyk, Lene Lange, Ioannis V. Skiadas, Hariklia N. Gavala. Enrichment of syngas-converting mixed microbial consortia for ethanol production and thermodynamics-based design of enrichment strategies. Biotechnology for Biofuels. 2018; 11 (1):198.

Chicago/Turabian Style

Antonio Grimalt-Alemany; Mateusz Łężyk; Lene Lange; Ioannis V. Skiadas; Hariklia N. Gavala. 2018. "Enrichment of syngas-converting mixed microbial consortia for ethanol production and thermodynamics-based design of enrichment strategies." Biotechnology for Biofuels 11, no. 1: 198.

Journal article
Published: 01 June 2018 in Water Research
Reads 0
Downloads 0

Crude glycerol is an important by-product of the biodiesel industry, which can be converted into volatile fatty acids (VFA) and/or 1,3-propanediol (1,3-PDO) by fermentation. In this study, a selective conversion of VFA to polyhydroxyalkanoates (PHA) was attained while leaving 1,3-PDO in the supernatant by means of mixed microbial consortia selection strategies. The process showed highly reproducible results in terms of PHA yield, 0.99 ± 0.07 Cmol PHA/Cmol S (0.84 g COD PHA/g COD S), PHA content (76 ± 3.1 g PHA/100 g TSS) and 1,3-PDO recovery (99 ± 2.1%). The combined process had an ultimate yield from crude glycerol of 0.19 g COD PHA and 0.42 g COD 1,3-PDO per g of input COD. The novel enrichment strategy applied for selectively transforming fermentation by-products into a high value product (PHA) demonstrates the significance of the enrichment process for targeting specific bio-transformations and could be potentially proved valuable for other biotechnological applications as well.

ACS Style

Anna Burniol-Figols; Cristiano Varrone; Simone Balzer Le; Anders Egede Daugaard; Ioannis V. Skiadas; Hariklia N. Gavala. Combined polyhydroxyalkanoates (PHA) and 1,3-propanediol production from crude glycerol: Selective conversion of volatile fatty acids into PHA by mixed microbial consortia. Water Research 2018, 136, 180 -191.

AMA Style

Anna Burniol-Figols, Cristiano Varrone, Simone Balzer Le, Anders Egede Daugaard, Ioannis V. Skiadas, Hariklia N. Gavala. Combined polyhydroxyalkanoates (PHA) and 1,3-propanediol production from crude glycerol: Selective conversion of volatile fatty acids into PHA by mixed microbial consortia. Water Research. 2018; 136 ():180-191.

Chicago/Turabian Style

Anna Burniol-Figols; Cristiano Varrone; Simone Balzer Le; Anders Egede Daugaard; Ioannis V. Skiadas; Hariklia N. Gavala. 2018. "Combined polyhydroxyalkanoates (PHA) and 1,3-propanediol production from crude glycerol: Selective conversion of volatile fatty acids into PHA by mixed microbial consortia." Water Research 136, no. : 180-191.

Research paper
Published: 24 April 2018 in Bioprocess and Biosystems Engineering
Reads 0
Downloads 0

Forward osmosis (FO) is a low energy-intensive process since the driving force for water transport is the osmotic pressure difference, Δπ, between the feed and draw solutions, separated by the FO membrane, where πdraw > πfeed. The potential of FO in wastewater treatment and desalination have been extensively studied; however, regeneration of the draw solution (thereby generating clean water) requires application of an energy-intensive process step like reverse osmosis (RO). In this study, the potential of applying FO for direct water recirculation from diluted fermentation effluent to concentrated feedstock, without the need for an energy-intensive regeneration step (e.g. RO), has been investigated. Butanol production during crude glycerol fermentation by Clostridium pasteurianum, has been selected as a model process and the effect of cross-flow velocity and the dilution of draw solution on the water flux during short-term experiments (200 min), were investigated. Statistical analysis revealed that the dilution of the draw solution is the most influential factor for the water flux. Subsequent modelling of an integrated FO-fermentation process, showed that water recoveries could lead to substantial financial benefits, although the integrated FO-fermentation process demonstrated lower water flux than expected. FTIR analyses of the membrane surface implied that the decrease in water flux was due to the presence of proteins, polysaccharides and other extracellular polymeric substances on the membrane active layer, indicating the presence of a fouling layer. Based on these findings, possible fouling alleviation strategies and future research directions are discussed and proposed.

ACS Style

S. Kalafatakis; S. Braekevelt; Anna Lymperatou; A. Zarebska; Claus Hélix-Nielsen; L. Lange; Ioannis V. Skiadas; H. N. Gavala. Application of forward osmosis technology in crude glycerol fermentation biorefinery-potential and challenges. Bioprocess and Biosystems Engineering 2018, 41, 1089 -1101.

AMA Style

S. Kalafatakis, S. Braekevelt, Anna Lymperatou, A. Zarebska, Claus Hélix-Nielsen, L. Lange, Ioannis V. Skiadas, H. N. Gavala. Application of forward osmosis technology in crude glycerol fermentation biorefinery-potential and challenges. Bioprocess and Biosystems Engineering. 2018; 41 (8):1089-1101.

Chicago/Turabian Style

S. Kalafatakis; S. Braekevelt; Anna Lymperatou; A. Zarebska; Claus Hélix-Nielsen; L. Lange; Ioannis V. Skiadas; H. N. Gavala. 2018. "Application of forward osmosis technology in crude glycerol fermentation biorefinery-potential and challenges." Bioprocess and Biosystems Engineering 41, no. 8: 1089-1101.

Journal article
Published: 12 April 2018 in Chemical Engineering Journal
Reads 0
Downloads 0

This study investigated the possibility to perform statistical optimization of an enriched mixed microbial consortium, MMC, fed in continuous with a highly inhibiting 2G glycerol, for the joint production of 1,3 propanediol (1,3 PDO) and butyric acid (BuA). Key variables taken into consideration were HRT, pH and feed concentration. The optimized process reached a glycerol consumption rate of 137 g/L/d and a maximum predicted production rate of 82.61 g/L/d and 21.13 g/L/d for 1,3 PDO and BuA, respectively. This corresponded to a 2.2 and 1.9-fold increase compared to the non-optimized process. The model was able to satisfactorily predict the joint maximum production of 1,3 PDO and BuA (22.6 and 8.1 g/L respectively) of the steady state also in non-sterile conditions, implying thus that MMC can be a robust and reliable biological production platform.

ACS Style

Cristiano Varrone; Ioannis V. Skiadas; Hariklia N. Gavala. Effect of hydraulic retention time on the modelling and optimization of joint 1,3 PDO and BuA production from 2G glycerol in a chemostat process. Chemical Engineering Journal 2018, 347, 525 -534.

AMA Style

Cristiano Varrone, Ioannis V. Skiadas, Hariklia N. Gavala. Effect of hydraulic retention time on the modelling and optimization of joint 1,3 PDO and BuA production from 2G glycerol in a chemostat process. Chemical Engineering Journal. 2018; 347 ():525-534.

Chicago/Turabian Style

Cristiano Varrone; Ioannis V. Skiadas; Hariklia N. Gavala. 2018. "Effect of hydraulic retention time on the modelling and optimization of joint 1,3 PDO and BuA production from 2G glycerol in a chemostat process." Chemical Engineering Journal 347, no. : 525-534.

Journal article
Published: 01 January 2018 in AIMS Environmental Science
Reads 0
Downloads 0
ACS Style

Anna Lymperatou; Ioannis V. Skiadas; Hariklia N. Gavala. Anaerobic co-digestion of swine manure and crude glycerol derived from animal fat—Effect of hydraulic retention time. AIMS Environmental Science 2018, 5, 105 -116.

AMA Style

Anna Lymperatou, Ioannis V. Skiadas, Hariklia N. Gavala. Anaerobic co-digestion of swine manure and crude glycerol derived from animal fat—Effect of hydraulic retention time. AIMS Environmental Science. 2018; 5 (2):105-116.

Chicago/Turabian Style

Anna Lymperatou; Ioannis V. Skiadas; Hariklia N. Gavala. 2018. "Anaerobic co-digestion of swine manure and crude glycerol derived from animal fat—Effect of hydraulic retention time." AIMS Environmental Science 5, no. 2: 105-116.