Panagiotis G. Kougias

• PhD
• Senior Researcher at Hellenic Agricultural Organization - DIMITRA

Recently, a first comprehensive catalogue of microbial genomes populating biogas reactors treating manure and agro-industrial residues was determined by sequencing samples collected from 22 biogas reactors including laboratory and full scale. Among the archaeal community, one of the most abundant methanogens belongs to Methanoculleus genus and for...

Biogas upgrading is envisioned as a key process for clean energy production. The current study evaluates the efficiency of different reactor configurations for ex-situ biogas upgrading and enhancement, in which externally provided hydrogen and carbon dioxide were biologically converted to methane by the action of hydrogenotrophic methanogens. The m...

The process stability of biogas plants is often deteriorated by the accumulation of Long Chain Fatty Acids (LCFA). The microbial community shifts due to LCFA disturbances have been poorly understood as the molecular techniques used were not able to identify the genome characteristics of uncultured microorganisms, and additionally, the presence of l...

Background Biogas production is an economically attractive technology that has gained momentum worldwide over the past years. Biogas is produced by a biologically mediated process, widely known as “anaerobic digestion.” This process is performed by a specialized and complex microbial community, in which different members have distinct roles in the...

This research aimed to better characterize the biogas microbiome by means of high throughput metagenomic sequencing and to elucidate the core microbial consortium existing in biogas reactors independently from the operational conditions. Assembly of shotgun reads followed by an established binning strategy resulted in the highest, up to now, extrac...

The European biofuel and bioenergy industry faces increasing challenges in achieving sustainable energy production while meeting carbon neutrality targets. This study provides a detailed analysis of biogenic emissions from biofuel and bioenergy production, with a focus on key sectors such as biogas, biomethane, bioethanol, syngas, biomass combustio...

Biomethanation is a crucial process occurring in natural and engineered systems which can reduce carbon dioxide to methane impacting the global carbon cycle. However, little is known about the effect of on-and-off gaseous provision and micronutrients on bioconversion. Here, anaerobic microbiomes underwent intermittent feeding with incremental starv...

A combination of membrane processes was applied to treat the digestate produced after the anaerobic treatment of pig manure in a biogas plant, aiming towards the recovery of nutrients and effective water treatment for potential reuse. Initially, coarse filtration (sieving and microfiltration) was used to remove particles larger than 1 µm, followed...

The presence of elevated ammonia levels is widely recognized as a significant contributor to process inhibition in biogas production, posing a common challenge for biogas plant operators. The present study employed a combination of biochemical, genome-centric metagenomic and metatranscriptomic data to investigate the response of the biogas microbio...

It is known that the presence of sulfate decreases the methane yield in the anaerobic digestion systems. Sulfate-reducing bacteria can convert sulfate to hydrogen sulfide competing with methanogens for substrates such as H2 and acetate. The present work aims to elucidate the microbial interactions in biogas production and assess the effectiveness o...

Minimizing food wastes and finding a second life use for industrial residuals have become some of the top priorities of modern society. This work considers the use of spent eggs and mussels shells, as well as marble dust, as raw sources to develop nanoparticles involving renewable resources in both their preparation and adoption in technological ap...

Packing materials improve biological methanation efficiency in Trickle Bed Reactors. The present study, which lies in the field of energy production and biotechnology, entailed the evaluation of commercial pelletized activated carbon and Raschig rings as packing materials. The evaluation focused on monitoring process indicators and examining the co...

This study reviews the major biogas upgrading technologies, with specific regard to recent progress in the field of membrane technology. More specifically, the objective of the present work is to provide the state-of-the-art of membrane-based processes for biogas upgrading, focusing primarily on the latest advances in membrane configurations/materi...

Application of mathematical models as tools and early warning indicators for the prediction of the overall performance of biogas reactors can contribute to the optimization of the anaerobic digestion. The present study aimed to simulate frequently found cases in biogas reactors during which the bioprocess is perturbated by common stressors (i.e., f...

The reuse of nutrient-rich waste in order to create green fertilizers in a sustainable and efficient way is a new strategy for the transition to a circular economy. Digestate is produced as a by-product from anaerobic digestion plants in large amounts creating a major management issue both for storage, utilization or disposal. The current work focu...

The challenge of handling the enormous amount of bio-waste that is globally produced on an annual basis can become an opportunity by exploiting such residues for bioenergy production in the form of biogas or biomethane. The application of anaerobic digestion to bio-waste is still limited due to their specific characteristics (e.g., recalcitrant mat...

The treatment of municipal wastewater is considered a cornerstone for the protection of public health and environment. However, a major issue derived from this process is the large quantities of produced sewage sludge. Although anaerobic digestion is a widely applied method in Wastewater Treatment Plants (WWTPs) aiming to stabilize the sludge and t...

Background The viral community has the potential to influence the structure of the microbiome and thus the yield of the anaerobic digestion process. However, the virome composition in anaerobic digestion is still under-investigated. A viral induction experiment was conducted on separate batches undergoing a series of DNA-damaging stresses, in order...

Nitrification has been widely applied in wastewater treatment, however gaining more insight into the nitrifiers’ physiology and stress response is necessary for the optimization of nutrient removal and design of advanced processes. Since nitrification initiates with ammonia oxidation performed by ammonia-oxidizing bacteria (AOB), the purpose of thi...

Background Carbon fixation through biological methanation has emerged as a promising technology to produce renewable energy in the context of the circular economy. The anaerobic digestion microbiome is the fundamental biological system operating biogas upgrading and is paramount in power-to-gas conversion. Carbon dioxide (CO 2 ) methanation is freq...

The concerns over food security and protein scarcity, driven by population increase and higher standards of living, have pushed scientists toward finding new protein sources. A considerable proportion of resources and agricultural lands are currently dedicated to proteinaceous feed production to raise livestock and poultry for human consumption. Th...

Lactic acid is a valuable compound used in several industrial processes such as polymers, emulsifiers manufacturing, pharmaceutical, and cosmetic formulations. The present study aims to evaluate the potential use of food waste to produce lactic acid through fermentation, both by indigenous microbiota and by the bio-augmentation with two lactic acid...

Two thermophilic trickle bed reactors (TBRs) were packed with different packing densities with polyurethane foam (PUF) and their performance under different retention times were evaluated during ex-situ biogas upgrading process. The results showed that the TBR more tightly packed i.e. containing more layers of PUF achieved higher H2 utilization eff...

The present work was conducted to assess whether the implementation of Supercritical Carbon dioxide Explosion (SCE) is an efficient approach for sewage sludge pre-treatment. In this context, SCE was optimized with the aim to develop a method attempting to increase the biodegradability of sewage sludge's organic matter content, and thus, to enhance...

In this study, the effects of bioaugmentation of typically dominant hydrogenotrophic methanogens to CSTR co-digesting cheese whey and manure, under in-situ biomethanation operations were investigated. Reactors working at mesophilic (37°C) and thermophilic (55°C) conditions were independently treated and examined in terms of microbial composition an...

Olive mill wastewater, a by-product of olive oil production after the operation of three-phase decanters, was used in a thermophilic anaerobic digester targeting efficient bioconversion of its organic load into biogas. An active anaerobic inoculum originating from a mesophilic reactor, was acclimatized under thermophilic conditions and was filled i...

Biogas plants treating agricultural residues are associated with limited bioenergy output due to the high content of hardly degradable lignocellulosic fibers in the feedstock. Hence, effective treatment techniques are needed to enhance holocellulose deconstruction, and thus, increase the energy budget of anaerobic digestion (AD) process. In the pre...

Sustainable agriculture relies on replacing fossil-based mineral fertilizers, which are highly cost-energetic to produce, and demand extensive use of scarce natural resources. Today, agronomic practices within the concept of circular economy are emerging and, as such, the exploitation of digestate as a biofertilizer and soil amender is extensively...

Four different types of ceramic gas distributors (Al2O3 of 1.2 μm and SiC of 0.5, 7 and 14 μm) were evaluated to increase biomethane formation during ex-situ biogas upgrading process. Each type of gas diffuser was tested independently at three different gas retention times of 10, 5 and 2.5 h, at thermophilic conditions. CH4 production rate increase...

Biogas upgrading is an emerging technology offering unique opportunities for further exploitation of biomethane as fuel for vehicles or direct injection into the gas grid, expanding the conventional use of biogas for combined heat and electricity generation. Up to date, most of the studies exploring the potential of biological carbon dioxide hydrog...

Anaerobic fermentation of various organic wastes to produce valuable intermediate products and generate a mixture of combustible gases has been researched actively in the past decades. For one, marine biomass as an abundant organic residue of water-locked countries has recently gained increasing popularity. However, such biomass is known to contain...

This work presents an integrated biorefinery concept combining two biological platforms for the valorization of palm oil mill effluents and for simultaneous production of high market value products, such as microbial oils and bioenergy. Palm oil mill effluents were aerobically fermented to produce lipids and subsequently the effluent from the ferme...

Co-digestion with lipid-rich substrates is a likely strategy in biogas plants, due to their high energy content. However, the process stability is vulnerable to inhibition due to the sudden increase of fatty-acid concentration. Therefore, techniques that promote the adaptation of the microorganisms to the presence of lipids have been proposed. In t...

The aim of this work was to provide solid proofs regarding the achievement of “steady-state conditions”, which means that the performance of the anaerobic digester is representative of the applied environmental conditions. For this reason, we investigated how, starting from different inoculum sources (i.e., municipal wastewater treatment, bio-waste...

Gas fermentation for the production of building block molecules and biofuels is lately gaining attention as a means to eliminate the greenhouse gases emissions. Especially CO2 capture and recycling are in focus. Thus, the biological coupling of CO2 and H2 is of high interest. Therefore, the focus of the present work was to evaluate the performances...

Methane production by microbes is a hot topic - Literally. Because of the potential to cause global warming, increased methane production is of great concern, but if properly controlled, it can also boost energy generation. Unfortunately, the basic mechanisms through which microbes generate methane remain unclear. To provide some clarity, researche...

Background: Microorganisms in biogas reactors are essential for degradation of organic matter and methane production. However, a comprehensive genome-centric comparison, including relevant metadata for each sample, is still needed to identify the globally distributed biogas community members and serve as a reliable repository. Results: Here, 134...

Methanogenesis, a biological process mediated by complex microbial communities, has attracted great attention due to its contribution to global warming and potential in biotechnological applications. The current study unveiled the core microbial methanogenic metabolisms in anaerobic vessel ecosystems by applying combined genome-centric metagenomics...

Human waste (HW) poses environmental and public health risk, thereby its sustainable management is becoming a serious growing challenge. Anaerobic digestion (AD) has long been introduced as an environmental-friendly and sustainable waste management technology with bio-methane as final product. Energy production via AD of HW would significantly cont...

Background Microorganisms in biogas reactors are essential for degradation of organic matter and methane production. However, a comprehensive genome-centric comparison, including relevant metadata for each sample, is still needed to identify the globally distributed biogas community members and serve as a reliable repository. Results Here, 134 publ...

Background Microorganisms in biogas reactors are essential for degradation of organic matter and methane production. However, a comprehensive genome-centric comparison, including relevant metadata for each sample, is still needed to identify the globally distributed biogas community members and serve as a reliable repository. Results Here, 134 publ...

The lipolytic oleaginous yeast Yarrowia lipolytica was used in the bioaugmentation and biovalorization of oily industrial wastes during successive‐batch fermentation. Five cycles of non‐sterile successive‐batch fermentation with 70 % medium replacement achieved the highest oil removal of 68.1±5.60 % and produced biomass and lipid yields of 0.213±0....

Background: Microorganisms in biogas reactors are essential for degradation of organic matter and methane production.. However, a comprehensive genome-centric comparison, including relevant metadata for each sample, is still needed to identify the globally distributed biogas community members and serve as a reliable repository. Results: Here, 134 p...

Biogas production from anaerobic digestion of grass was evaluated in this study taking into account two harvesting machines, i.e., a Disc-mower and an Excoriator, under diverse operating conditions. In addition, the application of generated biogas either in a Combined Heat and Power (CHP) plant for thermal and electrical energy production or as tra...

This work investigated the thermophilic (55 °C) co-digestion performance both in batch and continuous mode operation. The biochemical methane potentials of L. digitata and cattle manure were 308 ± 24 and 203 ± 33 mL CH4/g VS, respectively. The optimum co-digestion feedstock ratio was found to be 80% macroalgae: 20% manure on a volatile solids basis...

Biogas production is a well-established process for energy generation, nutrient recovery, and valorization of organic residues. Typically, the biogas is composed of methane, carbon dioxide, and other impurities. The removal or transformation of carbon dioxide (biogas upgrading) and the purification from other contaminants (biogas cleaning) are esse...

This study investigates the efficiency in methane production of lab-scale mesophilic (37 °C) and thermophilic (54 °C) continuous stirred tank reactors fed with cheese whey at different operational conditions. Results showed that whey mono-digestion was feasible at mesophilic conditions, while at thermophilic conditions frequent acidification incide...

In typical anaerobic digestion (AD) systems, the microbial functional assertion is hampered by synchronised versatile metabolism required for heterogeneous substrates degradation. Thus, the intricate methanogenic process from organic compounds remains an enigma after decades of empirical operation. In this study, simplified AD microbial communities...

This work investigated the thermophilic (55 °C) co-digestion performance both in batch and continuous mode operation. The biochemical methane potentials of L. digitata and cattle manure were 308 ± 24 and 203 ± 33 mL CH4/g VS, respectively. The optimum co-digestion feedstock ratio was found to be 80% macroalgae: 20% manure on a volatile solids basis...

The anaerobic digestion (AD) of municipal biopulp with two macroalgal biomasses (i.e. Saccharina latissima and Fucus serratus) was investigated at batch and continuously fed digesters at thermophilic conditions (54 ± 1 °C). At batch mono-digestion tests, municipal biopulp was associated with significantly higher methane production (549 ± 9 mLCH 4 /...

This study evaluated the process performance and determined the microbial community structure of two lab-scale thermophilic trickling biofilter reactors used for biological methanation of hydrogen and carbon-dioxide for a total period of 94 days. Stable and robust operation was achieved by means of a single-pass gas flow. The quality of the output...

Background: The expansion of renewable energy produced by windmills and photovoltaic panels has generated a considerable electricity surplus, which can be utilized in water electrolysis systems for hydrogen production. The resulting hydrogen can then be funneled to anaerobic digesters for biogas upgrading (biomethanation) purposes (power-to-methan...

The mechanisms by which specific anaerobic microorganisms remain firmly attached to lignocellulosic material, allowing them to efficiently decompose organic matter, have yet to be elucidated. To circumvent this issue, microbiomes collected from anaerobic digesters treating pig manure and meadow grass were fractionated to separate the planktonic mic...

Lignocellulosic substrates are associated with limited biodegradability due to the structural complexity. For that reason, a pretreatment step is mandatory for efficient biomass transformation which will lead to increased bioenergy output. The aim of the present study was to assess the efficiency of two pretreatment machines to enhance the methane...

A mixture of piggery slurry and algal species (mainly composed of Nannochloropsis limnetica), grown in municipal wastewater, were used as substrates for biogas production. Mono- and co-digestion experiments were performed at batch and continuous reactor operation. The mono-digestion of wastewater microalgae led to the highest methane yield (408 ± 3...

The paper can be downloaded for free until June 22, 2018 from this link: https://authors.elsevier.com/c/1W~dvin8VSLJc---------------------------------------------------------------------------------------------------------------- The aim of this study is to propose a hybrid biogas upgrading configuration composed of two-stage thermophilic reactors...

Dilution is considered to be a fast and easily applicable pretreatment for anaerobic digestion (AD) of chicken manure (CM), however, dilution with fresh water is uneconomical because of the water consumption. The present investigation was targeted at evaluating the feasibility and process performance of AD of CM diluted with algal digestate water (...

Biogas upgrading via carbon dioxide hydrogenation is an emerging technology for electrofuel production. The biomethanation efficiency is strongly dependent on a balanced microbial consortium, whose high- resolution characterization along with their functional potential and interactions are pivotal for process optimization. The present work is the f...

A novel biological process to upgrade biogas was developed and optimised during the current study. In this process, CO2 in the biogas and externally provided H2 were fermented under mesophilic conditions to volatile fatty acids (VFAs), which are building blocks of higher-value biofuels. Meanwhile, the biogas was upgraded to biomethane (CH4 >95%), w...

The mechanisms by which specific anaerobic microorganisms remain firmly attached to lignocellulosic material allowing them to efficiently decompose the organic matter are far to be elucidated. To circumvent this issue, the microbiomes collected from anaerobic digesters treating pig manure and meadow grass were fractionated to separate the planktoni...

Microbial dynamics in an upgrading biogas reactor system undergoing a more than two years-period at stable operating conditions were explored. The carbon dioxide generated during biomass degradation in the first reactor of the system was converted to methane into the secondary reactor by addition of external hydrogen. Considering the overall effici...

Biogas production is a well-established technology primarily for the generation of renewable energy and also for the valorization of organic residues. Biogas is the end product of a biological mediated process, the so called anaerobic digestion, in which different microorganisms, follow diverse metabolic pathways to decompose the organic matter. Th...

The aim of this work was to elucidate the microbial ecology in twelve mesophilic and thermophilic full-scale biogas plants using a genome-centric metagenomic approach. In this study both biogas plants treating manure and those treating sludge from waste water treatment plants were considered. The identification of 132 Metagenome-Assembled Genomes (...

The present research is the first comprehensive study regarding the thermophilic anaerobic degradation of cheese wastewater, which combines the evaluation of different reactor configurations (i.e. single and two-stage continuous stirred tank reactors) on the process efficiency and the in-depth characterization of the microbial community structure u...

In the past few years, many studies investigated the anaerobic digestion microbiome by means of 16S rRNA amplicon sequencing. Results obtained from these studies were compared to each other without taking into consideration the followed procedure for amplicons preparation and data analysis. This negligence was mainly due to the lack of knowledge re...

Biogas production is an established sustainable process for simultaneous generation of renewable energy and treatment of organic wastes. The increasing interest of utilizing biogas as substitute to natural gas or its exploitation as transport fuel opened new avenues in the development of biogas upgrading techniques. The present work is a critical r...

Biogas upgrading processes by in-situ hydrogen (H2) injection are still challenging and could benefit from a mathematical model to predict system performance. Therefore, a previous model on anaerobic digestion was updated and expanded to include the effect of H2 injection into the liquid phase of a fermenter with the aim of modeling and simulating...

CO is a main component of syngas, which can be produced from the gasification of organic wastes and biomass. CO can be converted to methane by anaerobic digestion (AD), however, it is still challenging due to its toxicity to microorganisms and limited knowledge about CO converting microorganisms. In the present study, anaerobic granular sludge (AGS...

The application of thermophilic conditions in anaerobic digesters leads to higher methane production rates and better sanitation of the effluents compared to mesophilic operation. However, an increase in operational temperature is challenging due to the tremendous selective pressure imposed on the microbial consortium. The adaptation of microbial c...

Meadow grass has recently gained increased attention as a substrate for full-scale biogas reactors. However, to increase its biodegradability, pretreatment is needed. In the present work, different harvesting machines were compared in order to assess their effect on biogas production. Specifically, a Disc-mower, an Excoriator and a Chopper were use...

This study evaluates the efficiency of four novel up-flow reactors for ex-situ biogas upgrading converting externally provided CO2 and H2 to CH4, via hydrogenotrophic methanogenesis. The gases were injected through stainless steel diffusers combined with alumina ceramic sponge or through alumina ceramic membranes. Pore size, input gas loading and g...