Working Experiences

  • Present 2018

    Associate Professor

    Technical University of Denmark, Department of Environmental Engineering

  • 2018 2017

    Senior Researcher

    Technical University of Denmark, Department of Environmental Engineering

  • 2017 2015

    Researcher

    Technical University of Denmark, Department of Environmental Engineering

  • 2015 2011

    PostDoc Fellow

    Technical University of Denmark, Department of Environmental Engineering

Education & Training

  • External Research Stay 9-12/2016

    Visiting Researcher

    Dpt of Biology, Padova University

  • Ph.D. 2011

    Ph.D. in Agricultural Engineering

    Aristotle University of Thessaloniki

  • M.Sc.2007

    Master of Science in Agricultural Engineering

    Aristotle University of Thessaloniki

  • M.Eng.2005

    M.Eng. in Agricultural Engineering

    Aristotle University of Thessaloniki

Selected Research Projects

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    BioUpgrade- Ex-situ biogas upgrading through biologically mediated CO2 reduction

    Duration: 2017-2020 Current status: Ongoing

    This project aims to develop a novel and efficient technology for ex-situ biological biogas upgrade achieving methane concentration equivalent to natural gas (>95% CH4).

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    Integration of biomass and wind power for biogas enhancement and upgrading via hydrogen assisted anaerobic digestiont

    Duration: 2014-2019 Current status: Ongoing

    This project is proposing an innovative process in which hydrogen produced by water electrolysis using peak load/excess electricity from wind mills, will be biologically converted by binding CO2 to CH4. This biologically catalyzed reaction can be utilized within two main objectives, namely:

    1) biogas upgrading and enhancement

    2) decoupling biogas production from biomass availability.

    For more info visit the project's webite
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    New technology for an efficient utilization of meadow grass in biogas reactor

    Duration: 2014-2017 Current status: Ongoing

    This project aims to exploit different pretretment methods applied to lignocellulosic substrates in order to mximise the energy yield in the biogas plants. The anaerobic process is monitored and the microbial community populating the biogas reactors is characterised with advanced molecular methods.

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    Foaming problems in biogas plants

    Duration: 2009-2014 Current status: Expired

    The aim of the project was to identify the causes of foaming in biogas plants

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Converting mesophilic upflow sludge blanket (UASB) reactors to thermophilic by applying axenic methanogenic culture bioaugmentation

Zhu, X., Treu, L., Kougias, P.G., Campanaro, S. and Angelidaki, I.
Journal Paper Chemical Engineering Journal, 332, 508-516 (2018)

Abstract

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 community to a new environment or condition can be accelerated by a process known as “bioaugmentation” or “microbial community manipulation”, during which exogenous microorganisms harbouring specific metabolic activities are introduced to the reactor. The aim of the current study was to rapidly convert the operational temperature of up-flow anaerobic sludge blanket (UASB) reactors from mesophilic to thermophilic conditions by applying microbial community manipulation techniques. Three different bioaugmentation strategies were compared and it was proven that the injection of axenic methanogenic culture was the most efficient approach leading to improved biomethanation process with 40% higher methane production rate compared to the control reactor. Microbial community analyses revealed that during bioaugmentation, the exogenous hydrogenotrophic methanogen could be encapsulated in granular structures and concomitantly promote the growth of syntrophic fatty acid oxidizing bacteria. The results derived from the current study indicated that microbial community manipulation is an efficient alternative method to speed up transition of UASB reactors from mesophilic to thermophilic conditions.

A novel archaeal species belonging to Methanoculleus genus identified via de-novo assembly and metagenomic binning process in biogas reactors

Kougias, P.G., Campanaro, S., Treu, L., Zhu, X., and Angelidaki, I.
Journal Paper Anaerobe, 46, 23-32 (2017)

Abstract

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 this reason it was provisionally named Methanoculleus sp. DTU006. Its full length 16S rRNA sequence is 97% similar to Methanoculleus marisnigri JR1 and to Methanoculleus palmolei DSM 4273. Despite the high similarity of the 16S gene sequence, Average Nucleotide Identity calculation (ANI) calculated on all protein encoding genes indicated that the two most similar species, Methanoculleus bourgensis MS2T and Methanoculleus sp. MAB1, are divergent enough to define Methanoculleus sp. DTU006 as new archaeal species. Its genome (2.15 Mbp) has an estimated completeness around 93%. Analysis of the metabolic pathways using KEGG confirmed that it is a hydrogenotrophic methanogen and therefore it is proposed the Candidatus status by naming it as “Candidatus Methanoculleus thermohydrogenotrophicum”.

Characterization of the planktonic microbiome in upflow anaerobic sludge blanket reactors during adaptation of mesophilic methanogenic granules to thermophilic operational conditions

Zhu, X., Treu, L., Kougias, P.G., Campanaro, S. and Angelidaki, I.
Journal Paper Anaerobe, 46, 69-77 (2017)

Abstract

Upflow anaerobic sludge blanket (UASB) technology refers to reactor technology where granules, i.e. self-immobilised microbial associations, are the biological catalysts involved in the anaerobic digestion process. During the start-up period, UASB reactors operate at relatively long HRT and therefore the liquid phase of the reactor becomes a favourable environment for microbial growth. The current study aimed to elucidate the dynamicity of the suspended microbial community in UASB reactors, during the transition from mesophilic to thermophilic conditions. High throughput 16S rRNA amplicon sequencing was used to characterize the taxonomic composition of the microbiome. The results showed that the microbial community was mainly composed by hydrolytic and fermentative bacteria. Results revealed relevant shifts in the microbial community composition, which is mainly determined by the operational conditions and the reactor performance. Finally, shared OTUs between the microbial consortia of the suspended and the granular sludge showed that planktonic microbiota is significantly influencing the granule microbial community composition.

Improving the energy balance of grass-based anaerobic digestion through combined harvesting and pretreatment

Tsapekos, P., Kougias, P.G., Egelund, H., Larsen, U., Pedersen, J., Trénel, P. and Angelidaki, I.
Journal Paper Anaerobe, 14, 131-137 (2017)

Abstract

An important challenge that has to be addressed to achieve sustainable anaerobic digestion of lignocellulosic substrates is the development of energy and cost efficient pretreatment methods. Technologies orientated to simultaneously harvest and mechanically pretreat the biomass at the field could meet these criteria as they can potentially reduce the energy losses. The objective of this study was to elucidate the effect of two full-scale harvesting machines to enhance the biogas production and subsequently, improve energy balance. The performances of Disc-mower and Excoriator were assessed on meadow and cultivated grass silages. The results showed that relatively high methane production can be achieved from meadow and cultivated grass harvested in different seasons. The findings indicated that the bioenergy production can be improved based on the selection of the appropriate harvesting technology. More specifically, Excoriator, which cuts and subsequently applies shearing forces on harvested biomass, enhanced the methane production up to 10% and the overall energy budget was improved proportionally to the driving speed increase.

In vitro fermentation of key dietary compounds with rumen fluid: A genome-centric perspective

Campanaro, S., Treu, L., Cattani, M., Kougias, P.G., Vendramin, V., Schiavon, S., Tagliapietra, F., Giacomini, A., Corich, V.
Journal Paper Science of the Total Environment, 584-585, 683-691 (2017)

Abstract

The anaerobic decomposition of organic substrates leads to the generation of gases, such as methane, which can either be a valuable energy carrier in industrial applications or can be considered as a main greenhouse gas when it is naturally emitted. In this study we investigated in vitro the effect of dietary compounds, such as starch and proteins, on the microbial community present in the rumen fluid. High throughput shotgun sequencing, followed by metagenomic assembly and binning allowed the extraction of 18 genome bins. A composite bioinformatic analysis led to the prediction of metabolic pathways involved in the degradation of dietary compounds and in the biosynthesis of crucial products like propionate, methane and ammonia. The identification of genomes belonging to poorly characterized phyla such as Thermoplasmata and Elusimicrobia shed light on their putative role. The high abundance of methylotrophic archaea in the inoculum suggests a relevant role in methane production.

Effect of micro-aeration and inoculum type on the biodegradation of lignocellulosic substrate

Tsapekos, P., Kougias, P.G., Vasileiou, S.A., Lyberatos, G. and Angelidaki
Journal Paper Bioresource Technology, 225, 246-253 (2017)

Abstract

The effect of various micro-aeration strategies on the anaerobic digestion (AD) of wheat straw was thoroughly examined using a mixture of inocula, containing compost and well digested sludge from biogas plant. The aim was to determine the most efficient oxygen load, pulse repetition and treatment duration, resulting in the highest methane production. The oxygen load had the largest impact on the biodegradability of straw, among the examined variables. More specifically, a micro-aeration intensity of 10 mL O2/g VS was identified as the critical threshold above which the AD performance was more susceptible to instability. The highest enhancement in biogas production was achieved by injecting 5 mL O2/g VS for a consecutive 3-day treatment period, presenting a 7.2% increase compared to the untreated wheat straw. Nevertheless, the results from optimisation case study indicated a higher increase of 9% by injecting 7.3 mL O2/g VS, distributed in 2 pulses during a slightly shorter treatment period (i.e. 47 h).

Microbial community changes in methanogenic granules during the transition from mesophilic to thermophilic conditions

Zhu, X., Kougias, P.G., Treu, L., Benavente, D.P., Boe, K., Campanaro, S. and Angelidaki, I.
Journal Paper Applied Microbiology and Biotechnology, 101 (3), 1313-1322 (2017)

Abstract

Upflow anaerobic sludge blanket (UASB) reactor is one of the most applied technologies for various high-strength wastewater treatments. The present study analysed the microbial community changes in UASB granules during the transition from mesophilic to thermophilic conditions. Dynamicity of microbial community in granules was analysed using high-throughput sequencing of 16S ribosomal RNA gene amplicons, and the results showed that the temperature strictly determines the diversity of the microbial consortium. It was demonstrated that most of the microbes which were present in the initial mesophilic community were not found in the granules after the transition to thermophilic conditions. More specifically, only members from family Anaerolinaceae managed to tolerate the temperature change and contributed in maintaining the physical integrity of granular structure. On the contrary, new hydrolytic and fermentative bacteria were quickly replacing the old members in the community. A direct result from this abrupt change in the microbial diversity was the accumulation of volatile fatty acids and the concomitant pH drop in the reactor inhibiting the overall anaerobic digestion process. Nevertheless, by maintaining deliberately the pH levels at values higher than 6.5, a methanogen belonging to Methanoculleus genus emerged in the community enhancing the methane production.

Ex-situ biogas upgrading and enhancement in different reactor systems

Kougias, P.G., Treu, L., Benavente, D.P., Boe, K., Campanaro, S. and Angelidaki, I.
Journal Paper Bioresource Technology, 225, 429-437 (2017)

Abstract

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 methane content in the output gas of the most efficient configuration was >98%, allowing its exploitation as substitute to natural gas. Additionally, use of digestate from biogas plants as a cost efficient method to provide all the necessary nutrients for microbial growth was successful. High-throughput 16S rRNA sequencing revealed that the microbial community was resided by novel phylotypes belonging to the uncultured order MBA08 and to Bacteroidales. Moreover, only hydrogenotrophic methanogens were identified belonging to Methanothermobacter and Methanoculleus genera. Methanothermobacter thermautotrophicus was the predominant methanogen in the biofilm formed on top of the diffuser surface in the bubble column reactor.

Process performance and comparative metagenomic analysis during co-digestion of manure and lignocellulosic biomass for biogas production

Tsapekos, P., Kougias, P.G., Treu, L., Campanaro, S. and Angelidaki, I.
Journal Paper Applied Energy, 185, 126-135 (2017)

Abstract

Mechanical pretreatment is considered to be a fast and easily applicable method to prepare the biomass for anaerobic digestion. In the present study, the effect of mechanical pretreatment on lignocellulosic silages biodegradability was elucidated in batch reactors. Moreover, co-digestion of the silages with pig manure in continuously fed biogas reactors was examined. Metagenomic analysis for determining the microbial communities in the pig manure digestion system was performed by analysing unassembled shotgun genomic sequences. A comparative analysis allowed to identify the microbial species firmly attached to the digested grass particles and to distinguish them from the planktonic microbes floating in the liquid medium. It was shown that the methane yield of ensiled grass was significantly increased by 12.3% due to mechanical pretreatment in batch experiments. Similarly, the increment of the methane yield in the co-digestion system reached 6.4%. Regarding the metagenomic study, species similar to Coprothermobacter proteolyticus and to Clostridium thermocellum, known for high proteolytic and cellulolytic activity respectively, were found firmly attached to the solid fraction of digested feedstock. Results from liquid samples revealed clear differences in microbial community composition, mainly dominated by Proteobacteria. The archaeal community was found in higher relative abundance in the liquid fraction of co-digestion experiment compared to the solid fraction. Finally, an unclassified Alkaliphilus sp. was found in high relative abundance in all samples.

Optimization of hydrogen dispersion in thermophilic up-flow reactors for ex situ biogas upgrading

Bassani, I., Kougias, P.G., Treu, L., Porté, H., Campanaro, S. and Angelidaki, I.
Journal Paper Bioresource Technology, 234, 310-319 (2017)

Abstract

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 gas recirculation flow rate were modulated to optimize gas-liquid mass transfer, and thus methanation efficiency. Results showed that larger pore size diffusion devices achieved the best kinetics and output-gas quality converting all the injected H2 and CO2, up to 3.6 L/LREACTOR·d H2 loading rate. Specifically, reactors’ CH4 content increased from 23 to 96% and the CH4 yield reached 0.25 LCH4/LH2. High throughput 16S rRNA gene sequencing revealed predominance of bacteria belonging to Anaerobaculum genus and to uncultured order MBA08. Additionally, the massive increase of hydrogenotrophic methanogens, such as Methanothermobacter thermautotrophicus, and syntrophic bacteria demonstrates the selection-effect of H2 on community composition.

Anaerobic granular sludge for simultaneous biomethanation of synthetic wastewater and CO with focus on the identification of CO-converting microorganisms

Jing, Y., Campanaro, S., Kougias, P.G., Treu, L., Angelidaki, I., Zhang, S., Luo, G.
Journal Paper Water Research, 126, 19-28 (2017)

Abstract

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) was used for the simultaneous biomethanation of wastewater and CO. Batch experiments showed that AGS tolerated CO partial pressure as high as 0.5 atm without affecting its ability for synthetic wastewater degradation, which had higher tolerance of CO compared to suspended sludge (less than 0.25 atm) as previously reported. Continuous experiments in upflow anaerobic sludge blanket (UASB) reactors showed AGS could efficiently convert synthetic wastewater and CO into methane by applying gas-recirculation. The addition of CO to UASB reactor enhanced the hydrogenotrophic CO-oxidizing pathway, resulted in the increase of extracellular polymeric substances, changed the morphology of AGS and significantly altered the microbial community compositions of AGS. The microbial species relating with CO conversion and their functions were revealed by metagenomic analysis. It showed that 23 of the 70 reconstructed genome bins (GBs), most of which were not previously characterized at genomic level, were enriched and contained genes involved in CO conversion upon CO addition. CO-converting microorganisms might be taxonomically more diverse than previously known and have multi-functions in the AD process. The reductive tricarboxylic acid (TCA) cycle in combination with the oxidation of the CO was probably crucial for CO utilization by the majority of the GBs in the present study.

Bioaugmentation with hydrolytic microbes to improve the anaerobic biodegradability of lignocellulosic agricultural residues

Tsapekos, P., Kougias, P.G., Vasileiou, S.A., Treu, L., Campanaro, S., Lyberatos, G. and Angelidaki, I.
Journal Paper Bioresource technology, 234, 9350-359 (2017)

Abstract

Bioaugmentation with hydrolytic microbes was applied to improve the methane yield of bioreactors fed with agricultural wastes. The efficiency of Clostridium thermocellum and Melioribacter roseus to degrade lignocellulosic matter was evaluated in batch and continuously stirred tank reactors (CSTRs). Results from batch assays showed that C. thermocellum enhanced the methane yield by 34%. A similar increase was recorded in CSTR during the bioaugmentation period; however, at steady-state the effect was noticeably lower (7.5%). In contrast, the bioaugmentation with M. roseus did not promote markedly the anaerobic biodegradability, as the methane yield was increased up to 10% in batch and no effect was shown in CSTR. High-throughput 16S rRNA amplicon sequencing was used to assess the effect of bioaugmentation strategies on bacterial and archaeal populations. The microbial analysis revealed that both strains were not markedly resided into biogas microbiome. Additionally, the applied strategies did not alter significantly the microbial communities.

Mechanical pretreatment at harvesting increases the bioenergy output from marginal land grasses

Tsapekos, P., Kougias, P.G., Egelund, H., Larsen, U., Pedersen, J., Trénel, P. and Angelidaki, I.
Journal Paper Bioresource technology, 111, 914-921 (2017)

Abstract

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 used to define the most appropriate machinery in order to improve the energy output per hectare for full-scale biogas plants. Among the harvesters, Excoriator, a novel simultaneous harvest and mechanical treatment, was found to significantly increase the methane yield of meadow grass by 20% compared to a classical Disc-mower. The positive effect was also validated by three kinetic model equations. The modified Gompertz model was the most capable of determining the kinetics of anaerobic digestion process, pointing out also the superiority of Excoriator. The usage of the novel harvester was associated with increased energy output, either for electrical/thermal energy generation or for transport fuel production, compared to the alternative machineries. Moreover, it was shown that the co-digestion of harvested biomass with different types of manure can enhance the bioenergy output of a full-scale biogas plant in a range of 12%–23%.

In-situ biogas upgrading process: Modeling and simulations aspects

Lovato, G., Alvarado-Morales, M., Kovalovszki, A., Peprah, M., Kougias, P.G., Rodrigues, J.A.D. and Angelidaki, I.
Journal Paper Bioresource technology, 245, 332-341 (2017)

Abstract

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 these processes. This was done by including hydrogenotrophic methanogen kinetics for H2 consumption and inhibition effect on the acetogenic steps. Special attention was paid to gas to liquid transfer of H2. The final model was successfully validated considering a set of Case Studies. Biogas composition and H2 utilization were correctly predicted, with overall deviation below 10% compared to experimental measurements. Parameter sensitivity analysis revealed that the model is highly sensitive to the H2 injection rate and mass transfer coefficient. The model developed is an effective tool for predicting process performance in scenarios with biogas upgrading.

In-situ biogas upgrading in thermophilic granular UASB reactor: key factors affecting the hydrogen mass transfer rate

Bassani, I., Kougias, P. G. and Angelidaki, I.
Journal Paper Bioresource technology, 221, 485-491 (2016)

Abstract

Biological biogas upgrading coupling CO2 with external H2 to form biomethane opens new avenues for sustainable biofuel production. For developing this technology, efficient H2 to liquid transfer is fundamental. This study proposes an innovative setup for in-situ biogas upgrading converting the CO2 in the biogas into CH4, via hydrogenotrophic methanogenesis. The setup consisted of a granular reactor connected to a separate chamber, where H2 was injected. Different packing materials (rashig rings and alumina ceramic sponge) were tested to increase gas-liquid mass transfer. This aspect was optimized by liquid and gas recirculation and chamber configuration. It was shown that by distributing H2 through a metallic diffuser followed by ceramic sponge in a separate chamber, having a volume of 25% of the reactor, and by applying a mild gas recirculation, CO2 content in the biogas dropped from 42 to 10% and the final biogas was upgraded from 58 to 82% CH4 content.

Improving methane production from digested manure biofibers by mechanical and thermal alkaline pretreatment

Tsapekos, P., Kougias, P. G., Frison, A., Raga, R. and Angelidaki, I.
Journal Paper Bioresource technology, 216, 545-552 (2016)

Abstract

Animal manure digestion is associated with limited methane production, due to the high content in fibers, which are hardly degradable lignocellulosic compounds. In this study, different mechanical and thermal alkaline pretreatment methods were applied to partially degradable fibers, separated from the effluent stream of biogas reactors. Batch and continuous experiments were conducted to evaluate the efficiency of these pretreatments. In batch experiments, the mechanical pretreatment improved the degradability up to 45%. Even higher efficiency was shown by applying thermal alkaline pretreatments, enhancing fibers degradability by more than 4-fold. In continuous experiments, the thermal alkaline pretreatment, using 6% NaOH at 55 °C was proven to be the most efficient pretreatment method as the methane production was increased by 26%. The findings demonstrated that the methane production of the biogas plants can be increased by further exploiting the fraction of the digested manure fibers which are discarded in the post-storage tank.

Dynamic functional characterization and phylogenetic changes due to Long Chain Fatty Acids pulses in biogas reactors

Kougias, P. G.§, Treu, L.§, Campanaro, S.§, Zhu, X., Angelidaki, I.
Journal Paper Scientific Reports. 6: 28810 (2016)

Abstract

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 limited number of reference genomes in public databases prevented the comprehension of specific functional roles characterizing these microorganisms. The present study is the first research which deciphers by means of high throughput shotgun sequencing the dynamics of the microbial community during an inhibitory shock load induced by single pulses of unsaturated LCFA at two different concentrations (i.e. 2 g/L-reactor and 3 g/L-reactor). The metagenomic analysis showed that only the microbes associated with LCFA degradation could encode proteins related to “chemotaxis” and “flagellar assembly”, which promoted the ability to move towards the LCFA sources so as to degrade them. Moreover, the syntrophic interactions found between Syntrophomonas sp. together with Methanosarcina sp. were possibly assigned to the menaquinone-electron transfer. Finally, it was proven that a previously exposed to LCFA inoculum is more efficient in the degradation process of LCFA due to the specialization of the microbial consortium.

Deeper insight into the structure of the anaerobic digestion microbial community; the biogas microbiome database is expanded with 157 new genomes

Treu, L., Kougias, P. G., Campanaro, S., Bassani, I., Angelidaki, I.
Journal Paper Bioresource Technology. 176, 260-266 (2016)

Abstract

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, extraction of microbial genomes involved in biogas producing systems. From the 236 extracted genome bins, it was remarkably found that the vast majority of them could only be characterized at high taxonomic levels. This result confirms that the biogas microbiome is comprised by a consortium of unknown species. A comparative analysis between the genome bins of the current study and those extracted from a previous metagenomic assembly demonstrated a similar phylogenetic distribution of the main taxa. Finally, this analysis led to the identification of a subset of common microbes that could be considered as the core essential group in biogas production.

Untangling the Effect of Fatty Acid Addition at Species Level Revealed Different Transcriptional Responses of the Biogas Microbial Community Member

Treu, L.§, Campanaro, S.§, Kougias, P. G.§, Zhu, X., Angelidaki, I.
Journal Paper Environmental Science & Technology. 50 (11), 6079–6090 (2016)

Abstract

In the present study, RNA-sequencing was used to elucidate the change of anaerobic digestion metatranscriptome after long chain fatty acids (oleate) exposure. To explore the general transcriptional behavior of the microbiome, the analysis was first performed on shotgun reads without considering a reference metagenome. As a second step, RNA reads were aligned on the genes encoded by the microbial community, revealing the expression of more than 51000 different transcripts. The present study is the first research which was able to dissect the transcriptional behavior at a single species level by considering the 106 microbial genomes previously identified. The exploration of the metabolic pathways confirmed the importance of Syntrophomonas species in fatty acids degradation, and also highlighted the presence of protective mechanisms toward the long chain fatty acid effects in bacteria belonging to Clostridiales, Rykenellaceae, and in species of the genera Halothermothrix and Anaerobaculum. Additionally, an interesting transcriptional activation of the chemotaxis genes was evidenced in seven species belonging to Clostridia, Halothermothrix, and Tepidanaerobacter. Surprisingly, methanogens revealed a very versatile behavior different from each other, even among similar species of the Methanoculleus genus, while a strong increase of the expression level in Methanosarcina sp. was evidenced after oleate addition.

Metagenomic analysis and functional characterization of the biogas microbiome using high throughput shotgun sequencing and a novel binning strategy

Campanaro, S.§, Treu, L.§, Kougias, P. G.§, De Francisci, D.§, Valle, G., Angelidaki, I.
Journal Paper Biotechnology for Biofuels. 9:26 (2016)

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 establishment of a collective organization. Deciphering the complex microbial community engaged in this process is interesting both for unraveling the network of bacterial interactions and for applicability potential to the derived knowledge.

Results

In this study, we dissect the bioma involved in anaerobic digestion by means of high throughput Illumina sequencing (~51 gigabases of sequence data), disclosing nearly one million genes and extracting 106 microbial genomes by a novel strategy combining two binning processes. Microbial phylogeny and putative taxonomy performed using >400 proteins revealed that the biogas community is a trove of new species. A new approach based on functional properties as per network representation was developed to assign roles to the microbial species. The organization of the anaerobic digestion microbiome is resembled by a funnel concept, in which the microbial consortium presents a progressive functional specialization while reaching the final step of the process (i.e., methanogenesis). Key microbial genomes encoding enzymes involved in specific metabolic pathways, such as carbohydrates utilization, fatty acids degradation, amino acids fermentation, and syntrophic acetate oxidation, were identified. Additionally, the analysis identified a new uncultured archaeon that was putatively related to Methanomassiliicoccales but surprisingly having a methylotrophic methanogenic pathway.

Conclusion

This study is a pioneer research on the phylogenetic and functional characterization of the microbial community populating biogas reactors. By applying for the first time high-throughput sequencing and a novel binning strategy, the identified genes were anchored to single genomes providing a clear understanding of their metabolic pathways and highlighting their involvement in anaerobic digestion. The overall research established a reference catalog of biogas microbial genomes that will greatly simplify future genomic studies.

Biogas upgrading via hydrogenotrophic methanogenesis in two-stage Continuous Stirred Tank Reactors at mesophilic and thermophilic conditions

Bassani, I., Kougias, P. G., Treu, L., Angelidaki, I.
Journal Paper Environmental Science & Technology. 49(20), 12585-12593 (2015)

Abstract

This study proposes an innovative setup composed by two stage reactors to achieve biogas upgrading coupling the CO2 in the biogas with external H2 and subsequent conversion into CH4 by hydrogenotrophic methanogenesis. In this configuration, the biogas produced in the first reactor was transferred to the second one, where H2 was injected. This configuration was tested at both mesophilic and thermophilic conditions. After H2 addition, the produced biogas was upgraded to average CH4 content of 89% in the mesophilic reactor and 85% in the thermophilic. At thermophilic conditions, a higher efficiency of CH4 production and CO2 conversion was recorded. The consequent increase of pH did not inhibit the process indicating adaptation of microorganisms to higher pH levels. The effects of H2 on the microbial community were studied using high-throughput Illumina random sequences and full-length 16S rRNA genes extracted from the total sequences. The relative abundance of archaeal community markedly increased upon H2 addition with Methanoculleus as dominant genus. The increase of hydrogenotrophic methanogens and syntrophic Desulfovibrio and the decrease of aceticlastic methanogens indicate a H2-mediated shift towards the hydrogenotrophic pathway enhancing biogas upgrading. Moreover, Thermoanaerobacteraceae were likely involved in syntrophic acetate oxidation with hydrogenotrophic methanogen in absence of aceticlastic methanogenesis.

Counteracting foaming caused by lipids or proteins in biogas reactors using rapeseed oil or oleic acid as antifoaming agents

Kougias, P. G., Boe, K., Einarsdottir, E.S., Angelidaki, I.
Journal Paper Water Research. 79, 119-127 (2015)

Abstract

Foaming is one of the major operational problems in biogas plants, and dealing with foaming incidents is still based on empirical practices. Various types of antifoams are used arbitrarily to combat foaming in biogas plants, but without any scientific support this action can lead to serious deterioration of the methanogenic process. Many commercial antifoams are derivatives of fatty acids or oils. However, it is well known that lipids can induce foaming in manure based biogas plants. This study aimed to elucidate the effect of rapeseed oil and oleic acid on foam reduction and process performance in biogas reactors fed with protein or lipid rich substrates. The results showed that both antifoams efficiently suppressed foaming. Moreover rapeseed oil resulted in stimulation of the biogas production. Finally, it was reckoned that the chemical structure of lipids, and more specifically their carboxylic ends, is responsible for their foam promoting or foam counteracting behaviour. Thus, it was concluded that the fatty acids and oils could suppress foaming, while salt of fatty acids could generate foam.

Solutions for foaming problems in biogas reactors using natural oils or fatty acids as defoamers

Kougias, P. G., Boe, K., Angelidaki, I.
Journal Paper Energy and Fuels. 29(7), 4046-4051 (2015)

Abstract

Foaming is one of the most common and important problems in biogas plants, leading to severe operational, economical, and environmental drawbacks. Because addition of easily degradable co-substrates for boosting the biogas production can suddenly raise the foaming problem, the full-scale biogas plants face an increasing necessity in finding efficient and cost-effective antifoaming solutions to avoid the dramatic consequences of foaming incidents. One of the most common solutions to suppress foaming is the use of chemical defoamers. The present work is a mini-review summarizing the aggregated results from our previous extensive research along with some unpublished data on defoaming by rapeseed oil and oleic acid in manure-based biogas reactors. It was found that both compounds exhibited remarkable defoaming efficiency ranging from 30 to 57% in biogas reactors suffering from foaming problems promoted by the addition of protein, lipid, or carbohydrate co-substrates. However, in most cases, the defoaming efficiency of rapeseed oil was greater than that of oleic acid, and therefore, rapeseed oil is recommended to be used in biogas reactors to solve foaming problems.

Microbial diversity and dynamicity of biogas reactors due to radical changes of feedstock composition

De Francisci, D., Kougias, P. G., Treu, L., Campanaro, S., Angelidaki, I.
Journal Paper Bioresource Technology. 176, 56-64 (2015)

Abstract

The anaerobic digestion process is often inhibited by alteration of substrates and/or organic overload. This study aimed to elucidate changes of microbial ecology in biogas reactors upon radical changes of substrates and to determine their importance to process imbalance. For this reason, continuously fed reactors were disturbed with pulses of proteins, lipids and carbohydrates and the microbial ecology of the reactors were characterized by 16S rRNA gene sequencing before and after the imposed changes. The microbial composition of the three reactors, initially similar, diverged greatly after substrate change. The greatest increase in diversity was observed in the reactor supplemented with carbohydrates and the microbial community became dominated by lactobacilli, while the lowest corresponded to the reactor overfed with proteins, where only Desulfotomaculum showed significant increase. The overall results suggest that feed composition has a decisive impact on the microbial composition of the reactors, and thereby on their performance.

New steady-state microbial community compositions and process performances in biogas reactors induced by temperature disturbances

Luo, G., De Francisci, D., Kougias, P. G., Treu, L., Zhu, X., Angelidaki, I.
Journal Paper Biotechnology for Biofuels. 8:3 (2015)

Abstract

In the present study, three replicate biogas reactors treating cattle manure were run to examine the role of stochastic factors and disturbance in shaping microbial communities. In the triplicate biogas reactors with the same inoculum and operational conditions, similar process performances and microbial community profiles were observed under steady-state conditions. This indicated that stochastic factors had a minor role in shaping the profile of the microbial community composition and activity in biogas reactors. On the contrary, temperature disturbance was found to play an important role in the microbial community composition as well as process performance for biogas reactors. Although three different temperature disturbances were applied to each biogas reactor, the increased methane yields (around 10% higher) and decreased volatile fatty acids (VFAs) concentrations at steady state were found in all three reactors after the temperature disturbances. After the temperature disturbance, the biogas reactors were brought back to the original operational conditions; however, new steady-state microbial community profiles were observed in all the biogas reactors.

Assessment of beef cattle manure remained at ambient conditions for methane production by anaerobic digestion

Kalamaras, S., Firfiris, V., Kougias, P.G., Martzopoulou, A., Kotsopoulos, T.
Conference Proceedings1st International Conference on Agrifood SCM & Green Logistics, May 27-30, 2015, Porto Carras, Greece (2015)

Abstract

Cattle manure is one of the most common substances for methane production after anaerobic digestion. Manure is transported to anaerobic digestion plants for the production of energy and organic fertiliser. The daily collection of manure from farms to treatment plants is not economical viable due the need for many man-hours and it is also energy and time consuming. On the other hand, natural decomposition of manure that remains in the farm is leading to greenhouse gases emissions, mainly consisting of carbon dioxide and methane, which directly affect the environment. On top of that, a long standing of manure leads to the decrease of its potential for methane production. In this study, the effect of cattle manure dwelling time in the farm upon the methane production was evaluated. Beef cattle manure remained at ambient conditions in the farm under four different time periods: 1, 5, 10 and 15 days. Anaerobic digestion experiments were conducted at mesophilic conditions (37°C) in batch reactors. The results of this study indicate that it is economic viable, in terms of methane potential, to maintain cattle manure in the farm for a period up to 10 days. The latter is based on the fact that a significant lower methane production was observed in the time period of 15 days in comparison with the other three shorter time periods.

Biogas Upgrading By Injection Of Hydrogen In A Two-stage Continuous Stirred-Tank Reactor System

Bassani, I., Kougias, P.G., Treu, L., De Francisci, D., Angelidaki, I.
Conference Proceedings14th World Congress on Anaerobic Digestion, November 15-18, Vina del Mar, Chile (2015)

Abstract

An innovative method to upgrade the biogas combines the H2 produced by water electrolysis by surplus electricity from wind mills, with the CO2 in the biogas. CO2 is converted to CH4 by hydrogenotrophic methanogens. Here, a novel serial biogas reactor is presented, in which the produced biogas from the first stage reactor was introduced in the second, where also H2 was injected. The effects of the H2 on the process performance and on the microbial community were investigated. It was shown that after the H2 addition, the CH4 rate increased by 45%, resulting in an average CH4 content of 85.1%, with a maximum of 93.9%. The increase of the pH to 8.5, due to the CO2 conversion, was not inhibitory, demonstrating the adaptation of microorganisms to these pH levels. The composition of the microbial community changed upon the H2 addition, shifting the methanogenic pathway from aceticlastic to hydrogenotrophic.

Deciphering Foaming Phenomena In Manure-based Biogas Reactors

Kougias, P.G., Boe, K., Angelidaki, I.
Conference Proceedings14th World Congress on Anaerobic Digestion, November 15-18, Vina del Mar, Chile (2015)

Abstract

This work represents a synopsis of our previous studies on causes and solutions for foaming in manure-based biogas reactors. It was found that foaming was a common problem in 15 Danish full-scale biogas plants. Foaming was recorded either in the main reactor or in the pre-storage tank, resulting in most of the cases to 20-50% biogas production loss. In laboratory experiments, the chemical composition of the feedstock and the organic overload were identified as the main causes for foaming. Bacteria that were previously associated with foaming in sludge digesters were not present in the foaming manure-based reactors. Regarding the antifoaming strategies, it was shown that minimum specific amounts of rapeseed oil and oleic acid could efficiently suppress foam up to 57%. However, rapeseed oil was found to be more suitable as antifoam due to its high antifoaming efficiency, lower cost and synergistic effects resulting in higher obtained methane yield.

Metagenomic Analysis On Thermophilic Biogas Reactors Fed With High Load Of Long Chain Fatty Acids

Zhu, X., De Francisci, D., Kougias, P.G., Treu, L., Angelidaki, I.
Conference Proceedings14th World Congress on Anaerobic Digestion, November 15-18, Vina del Mar, Chile (2015)

Abstract

Accumulation of long chain fatty acids (LCFA) in biogas reactors leads to process imbalance. This detrimental condition is known to be reversible depending on the concentration of the accumulated LCFAs and on the microbial profile of the biogas reactors. Therefore, the understanding of how the microbial communities change in response to LCFA pulses is essential to process optimization. This study investigated the microbial shifts of biogas reactors due to LCFA increase in the feedstock composition via 16s rRNA gene analysis. The results showed that the addition of LCFA caused reversible inhibition. The correlation between the microbial community's profile and the reactors performance indicated that Syntrophomonas was the genus most likely involved in LCFA degradation. Methanoculleus was the main methanogen that was found prior and after the LCFA exposure. Its relative abundance was not significantly changed indicating that the main methanogenic pathway was not shifted due to the addition of LCFA.

Simultaneous hydrogen utilization and biogas upgrading by anaerobic microorganisms

Angelidaki, I., Luo, G., Kougias, P.G.
Conference Proceedings14th World Congress on Anaerobic Digestion, November 15-18, Vina del Mar, Chile (2015)

Abstract

In this paper we give a collective synopsis of our previous studies on development of systems for biological upgrading of biogas with H2. These methods are based on conversion of CO2 to CH4 by the hydrogenotrophic methanogenesis. Two different concepts (in-situ and ex-situ biogas upgrading) were developed.

Microbial analysis in biogas reactors suffering by foaming incidents.

Kougias, P. G., De Francisci, D., Treu, L., Campanaro, S., Angelidaki, I.
Journal Paper Bioresource Technology. 167, 24-32 (2014)

Abstract

Foam formation can lead to total failure of digestion process in biogas plants. In the present study, possible correlation between foaming and the presence of specific microorganisms in biogas reactors was elucidated. The microbial ecology of continuous fed digesters overloaded with proteins, lipids and carbohydrates before and after foaming incidents was characterized using 16S rRNA gene sequencing. Moreover, the microbial diversity between the liquid and foaming layer was assessed. A number of genera that are known to produce biosurfactants, contain mycolic acid in their cell wall, or decrease the surface tension of the media, increased their relative abundance after foam formation. Finally, a microorganism similar to widely known foaming bacteria (Nocardia and Desulfotomaculum) was found to increase its relative abundance in all reactors once foam was observed, regardless of the used substrate. These findings suggest that foaming and specific microorganisms might have direct association which requires to be further investigated.

Foam suppression in overloaded manure-based biogas reactors using antifoaming agents.

Kougias, P. G., Boe, K., Tsapekos, P., Angelidaki, I.
Journal Paper Bioresource Technology. 153, 198-205 (2014)

Abstract

Foam control is an imperative need in biogas plants, as foaming is a major operational problem. In the present study, the effect of oils (rapeseed oil, oleic acid, and octanoic acid) and tributylphosphate on foam reduction and process performance in batch and continuous manure-based biogas reactors was investigated. The compounds were tested in dosages of 0.05%, 0.1% and 0.5% v/vfeed. The results showed that rapeseed oil was most efficient to suppress foam at the dosage of 0.05% and 0.1% v/vfeed, while octanoic acid was most efficient to suppress foam at dosage of 0.5% v/vfeed. Moreover, the addition of rapeseed oil also increased methane yield. In contrast, tributylphosphate, which was very efficient antifoam, was found to be inhibitory to the biogas process.

Effect of feedstock composition and organic loading rate during the mesophilic co-digestion of olive mill wastewater and swine manure.

Kougias, P. G., Kotsopoulos, T.A., Martzopoulos, G.G.
Journal Paper Renewable Energy. 69, 202-207 (2014)

Abstract

In the present study, the optimisation of the mesophilic anaerobic co-digestion process of olive mill wastewaters (OMW) together with swine manure (SM) was investigated. Batch and continuous mode experiments were performed in order to define the most efficient mixing ratio and to determine the performance of the reactors under different organic loading rates (OLR). In batch experiment, the most efficient mixing ratio consisted of 40% OMW and 60% SM, since it presented the highest methane production equal to 277 mL CH4/g COD, which corresponded to 79% of the theoretical yield. It was found that the effectiveness of this mixing ratio was not affected in the continuous operation of the reactors. The stepwise increase of the OLR did not affect negatively biomethanation, although the concentration of the inhibitory compounds of the OMW was higher. Under OLR of 4.4 g volatile solids/(L-feed·day) the methane yield of the reactors fed with 40% OMW reached 373 mL CH4/gVS (78% of the theoretical yield). The findings of the present study proved that the co-digestion of OMW together with SM is a sustainable solution, capable to efficiently treat simultaneously these residual residues.

Anaerobic digestion foaming in full-scale biogas plants: a survey on causes and solutions.

Kougias, P. G., Boe, K., O-Thong, S., Kristensen, L.A., Angelidaki, I.
Journal Paper Water Science and Technology. 69, 889-895 (2014)

Abstract

Anaerobic digestion foaming is a common operation problem in biogas plants with negative impacts on the biogas plants economy and environment. A survey of 16 Danish full-scale biogas plants on foaming problems revealed that most of them had experienced foaming in their processes up to three times per year. Foaming incidents often lasted from one day to three weeks, causing 20–50% biogas production loss. One foaming case at Lemvig biogas plant has been investigated and the results indicated that the combination of feedstock composition and mixing pattern of the reactor was the main cause of foaming in this case. Moreover, no difference in bacterial communities between the foaming and non-foaming reactors was observed, showing that filamentous bacteria were not the main reason for foaming in this case.

Inoculum and zeolite synergistic effect on anaerobic digestion of poultry manure.

Fotidis, I.A., Kougias, P. G., Zaganas, I.D., Kotsopoulos, T.A., Martzopoulos, G.G., I.
Journal Paper Environmental Technology (United Kingdom). 35, 1219-1225 (2014)

Abstract

Poultry manure is an ammonia-rich substrate due to its high content of proteins and amino acids. Ammonia is the major inhibitor of anaerobic digestion (AD) process, affecting biogas production and causing great economic losses to the biogas plants. In this study, the effect of different natural zeolite dosages on the mesophilic AD of poultry manure inoculated with a non-acclimatized to ammonia inoculum (dairy manure) was investigated. Additionally, a comparative analysis was performed between the data extracted from this study and the results of a previous study, which has been conducted under the same experimental conditions but with the use of ammonia acclimatized inoculum (swine manure). At 5 and 10 g zeolite L−1, the methane yield of poultry manure was 43.4% and 80.3% higher compared with the experimental set without zeolite addition. However, the ammonia non-acclimatized inoculum was not efficient in digesting poultry manure even in the presence of 10 g zeolite L−1, due to low methane production (only 39%) compared with the maximum theoretical yield. Finally, ammonia acclimatized inoculum and zeolite have demonstrated a possible ‘synergistic effect’, which led to a more efficient AD of poultry manure. The results of this study could potentially been used by the biogas plant operators to efficiently digest poultry manure.

Antifoaming effect of rapeseed oil and oleic acid in biogas reactors

Kougias, P.G., Boe, K., Angelidaki, I.
Conference ProceedingsBiogas Science 2014 International conference on anaerobic digestion, October 26-30, 2014, Vienna, Austria (2014)

Abstract

To be inserted

Metagenomic analysis of foaming in biogas reactors

Kougias, P.G., De Francisci, D., Treu, L., Campanaro, S., Angelidaki, I.
Conference ProceedingsBiogas Science 2014 International conference on anaerobic digestion, October 26-30, 2014, Vienna, Austria (2014)

Abstract

To be inserted

Changes in the microbial profile of biogas reactors due to variations in the feedstock composition

De Francisci, D., Kougias, P.G., Treu, L., Campanaro, S., Angelidaki, I.
Conference ProceedingsBiogas Science 2014 International conference on anaerobic digestion, October 26-30, 2014, Vienna, Austria (2014)

Abstract

To be inserted

Anaerobic co-digestion of wastewater microalgae together with swine manure for biogas production

Kougias, P.G., De Francisci, Corbiere, M., Angelidaki, I.
Conference Proceedings2nd International Conference on Algal Biorefinery: A potential source of food, feed, biochemicals, biofuels and biofertilizers, August 27-29, 2014, Kgs. Lyngby, Denmark (2014)

Abstract

To be inserted

An integrated process of biogas upgrading and microalgae production for co-digestion in biogas reactor

Vasilaki, G., Kougias, P.G., Van Wagenen, J., De Francisci, Angelidaki, I.
Conference Proceedings2nd International Conference on Algal Biorefinery: A potential source of food, feed, biochemicals, biofuels and biofertilizers, August 27-29, 2014, Kgs. Lyngby, Denmark (2014)

Abstract

To be inserted

Microbial diversity and dynamicity of biogas reactors fed with different substrates

De Francisci, D., Kougias, P.G., Treu, L., Campanaro, S., Angelidaki, I.
Conference Proceedings2nd International Conference on Biogas Microbiology-ICBM, June 10-12, 2014, Uppsala, Sweden (2014)

Abstract

To be inserted

Comparative microbial analysis before and after foaming incidents in biogas reactors

Kougias, P.G., De Francisci, D., Treu, L., Campanaro, S., Angelidaki, I.
Conference Proceedings2nd International Conference on Biogas Microbiology-ICBM, June 10-12, 2014, Uppsala, Sweden (2014)

Abstract

To be inserted

Comparative analysis of the microbial diversity in liquid and foaming layer in biogas reactors

Campanaro, S., Treu, L., Kougias, P.G., De Francisci, D., Angelidaki, I.
Conference Proceedings2nd International Conference on Biogas Microbiology-ICBM, June 10-12, 2014, Uppsala, Sweden (2014)

Abstract

To be inserted

A novel bioinformatic strategy to characterise microbial communities in biogas reactors

Treu, L., Campanaro, S., De Francisci, D., Kougias, P.G., Angelidaki, I.
Conference Proceedings2nd International Conference on Biogas Microbiology-ICBM, June 10-12, 2014, Uppsala, Sweden (2014)

Abstract

To be inserted

Foaming in manure based digesters: Effect of overloading and foam suppression using antifoam agents

Kougias, P.G.,Tsapekos, P., Angelidaki, I.
Conference ProceedingsXXXV CIOSTA & CIGR V Conference 2013, 3-5 July 2013, Billund, Denmark (2014)

Abstract

To be inserted

Antifoaming effect of chemical compounds in manure biogas reactors

Kougias, P. G., Tsapekos, P., Boe, K., Angelidaki, I.
Journal Paper Water Research. 47, 6280-6288. (2013)

Abstract

A precise and efficient antifoaming control strategy in bioprocesses is a challenging task as foaming is a very complex phenomenon. Nevertheless, foam control is necessary, as foam is a major operational problem in biogas reactors. In the present study, the effect of 14 chemical compounds on foam reduction was evaluated at concentration of 0.05%, 0.1% and 0.5% v/vsample, in raw and digested manure. Moreover, two antifoam injection methods were compared for foam reduction efficiency. Natural oils (rapeseed and sunflower oil), fatty acids (oleic, octanoic and derivative of natural fatty acids), siloxanes (polydimethylsiloxane) and ester (tributylphosphate) were found to be the most efficient compounds to suppress foam. The efficiency of antifoamers was dependant on their physicochemical properties and greatly correlated to their chemical characteristics for dissolving foam. The antifoamers were more efficient in reducing foam when added directly into the liquid phase rather than added in the headspace of the reactor.

Effect of organic loading rate and feedstock composition on foaming in manure-based biogas reactors

Kougias, P. G., Boe, K., Angelidaki, I.
Journal Paper Bioresource Technology. 144, 1-7. (2013)

Abstract

Foaming is one of the major problems that occasionally occur in biogas plants, affecting negatively the overall digestion process. In the present study, the effect of organic loading rate (OLR) and feedstock composition on foaming was elucidated in continuous reactor experiments. By stepwise increasing the OLR and the concentration of proteins or lipids in the substrate, foaming in biogas reactors was investigated. No foam formation was observed at the OLR of 3.5 g volatile solids/(L-reactor·day). Organic loading was the main factor affecting foam formation in manure digester, while the organic composition, such as content of proteins or lipids were factors that in combination with the organic loading were triggering foaming. More specifically, gelatine could initiate foam formation at a lower OLR than sodium oleate. Moreover, the volume of foam produced by gelatine was relatively stable and was not increased when further increasing either OLR or gelatine concentration in the feed.

Zeolite and swine inoculum effect on poultry manure biomethanation

Kougias, P. G., Fotidis, I. A., Zaganas, I. D., Kotsopoulos, T. A., Martzopoulos, G. G.
Journal Paper International Agrophysics, 169-172 (2013)

Abstract

Poultry manure is an ammonia-rich substrate that inhibits methanogenesis, causing severe problems to the anaerobic digestion process. In this study, the effect of different natural zeolite concentrations on the mesophilic anaerobic digestion of poultry waste inoculated with well-digested swine manure was investigated. A significant increase in methane production was observed in treatments where zeolite was added, compared to the treatment without zeolite.Methane production in the treatment with 10 g dm-3 of natural zeolite was found to be 109.75% higher compared to the treatment without zeolite addition. The results appear to be influenced by the addition of zeolite, which reduces ammonia toxicity in anaerobic digestion and by the ammonia-tolerant swine inoculum.

Når biogasanlægget skummer over

Angelidaki I. and Kougias, P.G.,
Special Issue Journal FiB - Forskning i Bioenergi, (46), pp 21
image

Når biogasanlægget skummer over

Skum i biogasanlæg kan være et både økonomisk og miljømæssig problem for mange anlæg. Skum betyder faldende gasproduktion, overfyldte lagertanke og udslip af metangas. Høj organisk belastning er den vigtigste årsag til skum i reaktoren, men sammensætningen af biomassen har også en vis indflydelse..

Anaerobic digestion foaming in Danish full-scale biogas plants: a survey on causes and solutions

Kougias, P.G., Boe, K., O-Thong, S., Kristensen, L.A., Angelidaki, I.
Conference Proceedings13th World Congress on Anaerobic Digestion. 25-28 June 2013, Santiago de Compostela, Spain (2013)

Abstract

To be inserted

Effect of substrates and intermediate compounds on foaming in manure digestion systems

Boe, K., Kougias, P. G., Pacheco, F., O-Thong, S., Angelidaki, I.
Journal Paper Water Science & Technology. 66, 2146-2154 (2012)

Abstract

Manure contains several compounds that can potentially cause foaming during anaerobic digestion. Understanding the effect of substrates and intermediate compounds on foaming tendency and stability could facilitate strategies for foaming prevention and recovery of the process. In this study, the effect of physicochemical properties of substrates and intermediate compounds on liquid properties such as surface tension, surfactant property, and hydrophobicity were investigated and compared with the effect on foaming tendency and foam stability. The results showed that there was no consistent correlation between foaming potential and hydrophobicity, oil displacement area (ODA) or surface tension of the tested solutions, and the best way to determine the foaming property of the solution was to directly measure foaming tendency and foam stability. Na-oleate and acetic acid showed the highest potential to create foam in a manure digester. Moreover, high organic loading of lipids and protein, and high concentrations of acetic and butyric acids also showed a strong tendency to create foaming during anaerobic digestion. Due to their great ability to stabilize foam, high organic loadings of Na-oleate or gelatine were considered to be the main potential foaming problem.

Influence of microbial composition on foam formation in a manure-based digester

Kougias, P.G., Boe, K., O-Thong, S, Angelidaki, I.
Conference ProceedingsSymposium of The Danish Microbiological Society, Copenhagen, Denmark (2012)

Abstract

To be inserted

Foaming in manure based digesters- Causes and solutions

Kougias, P.G., Boe, K., Angelidaki, I.
Conference ProceedingsNordic Biogas Conference. 23-25 of April 2012, Copenhagen, Denmark (2012)

Abstract

To be inserted

Experimental performance of a hybrid solar energy saving system in greenhouses

Boe, K., Kougias, P. G., Pacheco, F., O-Thong, S., Angelidaki, I.
Journal Paper International Agrophysics 25(3), 257-264 (2011)

Abstract

The present study investigates the possibility of energy saving during the spring period in a conventionally heated greenhouse, using an innovating hybrid solar energy saving system. The greenhouse was divided in two equal parts (experimental and control), where tomato plants were cultivated hydroponically. The control part of the greenhouse covered the heating requirements exclusively by a conventional heating system. The experimental part used the conventional heating system only when the hybrid solar energy saving system could not maintain the greenhouse air temperature above 16°C. The hybrid solar energy saving system was consisted of a transparent cylindrical polyethylene sleeve filled with water and two perforated polyethylene tubes resting on the top of it. Through these tubes, air was pumped in order to inflate them and to be mixed with the greenhouse air. The use of hybrid solar energy saving system led to an energy saving portion capable of decreasing the greenhouse energy cost. Energy saving between the two parts of the greenhouse was recorded to be 36% from March to May. It has been also calculated that the oil consumption was significantly decreased in the experimental part and for the whole experimental period was 149.08 l, while in the control part reached 233.03 l. The application of this system contributed to smoother variation of the greenhouse air temperature and the rockwool slabs temperature, leading up to a better plant growth

The effect of different natural zeolite concentrations on the mesophilic anaerobic digestion of poultry manure

Kougias, P.G., Fotidis, I.A., Zaganas, D.I., Kotsopoulos, T.A., Martzopoulos, G.G.
Conference Proceedings16th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region-Mediterranean Scientific Association of Environmental Protection. Ioannina, Greece, 24-27 September 2011 (2011)

Abstract

To be inserted

Numerical study of a wind turbine and location used to produce energy for ventilation, heat pumps and water pumping systems in agricultural structures

Ntinas, G.K., Kougias, P.G., Fragos, V.P., Martzopoulos, G.G.
Conference Proceedings16th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region-Mediterranean Scientific Association of Environmental Protection. Ioannina, Greece, 24-27 September 2011 (2011)

Abstract

To be inserted

Performance and Techno-economic analysis of a covered closed loop geothermal heat pump for greenhouse heating

Firfiris V., Kougias, P.G., Nikita-Martzopoulou Ch., and Martzopoulos, G.G.
Conference ProceedingsAdvanced technologies and management towards sustainable greenhouse ecosystems-GreenSys2011. Halkidiki, Greece, 5-10 June 2011 (2011)

Abstract

To be inserted

Experimental study of improving the coefficient performance value of a ground source heat pump for greenhouse heating and cooling

Kougias, P.G., Firfiris V., and Martzopoulos, G.G.
Conference ProceedingsAdvanced technologies and management towards sustainable greenhouse ecosystems-GreenSys2011. Halkidiki, Greece, 5-10 June 2011 (2011)

Abstract

To be inserted

Effect of substrates and intermediate compounds on foaming in manure digestion systems

Boe, K., Kougias, P.G., Pacheco, F., O-Thong, S., Angelidaki, I.
Conference ProceedingsInternational Symposium on Anaerobic Digestion of Solid Waste and Energy Crops, Vienna, Austria, 28/8-1/9/2011 (2011)

Abstract

To be inserted

Anaerobic co-digestion of pig waste with olive mill wastewater under various mixing conditions

Kougias, P. G., Kotsopoulos, T. A., Martzopoulos, G. G.
Journal Paper Fresenius Environmental Bulletin. 19, 1682-1686 (2010)

Abstract

The influence of the waste ratio of olive mill wastewater (OMW) and pia waste (PW) on the anaerobic co-digestion, in batch experiments operated at 35 degrees C, was investigated. The experiments were carried out in duplicate using 900 cm(3) working volume batch reactors. Four PW/OMW ratios were applied in each experimental run. namely 100/0 (A), 80/20 (B), 60/40 (C), 30170 (D) in terms of volatile solids (VS), each treatment was carried out by duplicate. The VS content for each digester was 12g/L. The inoculum used in the experiment was a well digested mixture of OMW and PW at a ratio of 50% (v/v). The results obtained from the co-digestion of OMW and PW under mesophilic temperature showed that methane production as well as the VS removal increased significantly with the increase of OMW ratio up to 40%. Specifically. In the mixture C the methane production was 130% and the VS removal was 139% higher compared to the mixture A A further increase of OMW up to 70% in mixture D. caused instability of the anaerobic process and only some amounts of methane was detected in the gas mixture.

Anaerobic co-digestion of olive mill wastewater with pig waste: effect of waste ratio, impact of the co-digested inoculums on the anaerobic digestion of pig waste

Kougias, P.G., Kotsopoulos, T.A., Martzopoulos, G.G.
Conference Proceedings 15th Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region (MESEAP), Bari, Italy, 7-11 October (2009)

Abstract

The present study evaluates the energy efficiency of the anaerobic co-digestion of olive mill wastewater with diluted swine manure at mesophilic temperature. It was also an aim to investigate the effect of the inoculum used in the degradation of swine manure.

Energy saving in greenhouses using passive solar heating system combined with hydropony

Kougias, P.G., Ntinas, G.K., Nikita-Martzopoulou, Ch.
Conference Proceedings International Conference on Agricultural Engineering & Industry Exhibition (AgEng), Hersonissos-Crete, Greece 23-25 June (2009)

Abstract

Τhe present research investigates the possibility of energy saving using passive solar sleeves filled with water in a greenhouse, where tomato is cultivated hydroponically. The greenhouse is located in the Farm of Faculty of Agriculture. The passive solar sleeves exploit an important percentage of direct and indirect radiation and they act as deposits of heat. In the hydroponic installation, tomato (Optimum sp.) was cultivated in a chemical inert substrate “rockwool”, which was placed on film of polyethylene filled with water. The evaluation of the passive system has been done in comparison with a conventional system of heating, placed in a greenhouse where rockwool slabs were placed on plastic gutter.

At My Office

You can find me at my office (No. 170, 1st floor) located at Building 113 of Technical University of Denmark, Miljøvej, 2800 Kgs. Lyngby.

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You can find me at the Biotechnology Lab Building 113 of Technical University of Denmark, Miljøvej, 2800 Kgs. Lyngby.