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See detailProduction of bio-hydrogen and methane during semi-continuous digestion of maize silage in a two-stage system
Benito Martin, Patricia C.; Greger, Manfred UL; Schlienz, Markus UL

in International Journal of Hydrogen Energy (2017), 42

The feasibility and performance of applying a two-stage configuration for co-production of hydrogen and methane from maize silage in continuously stirred reactors was investigated under mesophilic ... [more ▼]

The feasibility and performance of applying a two-stage configuration for co-production of hydrogen and methane from maize silage in continuously stirred reactors was investigated under mesophilic conditions. The high organic loading used in the first-stage hydrogen producing reactor (e.g. load shock treatment) was effective at ensuring hydrogen-producing conditions, with no methanogenic activity observed for more than 60 days. A hydrogen yield of up to 53.8 NlH2/kg volatile solid (VS) was measured in the first reactor, with a hydrogen content of 33.1%. The methane yield in the second stage reactor was 133.9 NlCH4/kgVS, with a methane content of 65%. Abnormally low concentration of acetic acid and high concentrations of caproic acid were measured in the first reactor in the pH range 5–5.5, which could be explained by the presence of strains such as Clostridium kluyveri. Of the estimated total energy yield in the two-stage system, only 4% was from hydrogen production. The mixture of hydrogen and methane produced in the system (after carbon dioxide removal) is in the range recommended for use as vehicle fuel. [less ▲]

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See detail2-stage process for a higher flexibility of biogas-plants
Greger, Manfred UL; Benito-Martins, Patricia; Schlienz, Markus UL

Scientific Conference (2016, September 21)

The increasing part of renewable energy in the electricity production mix with its known fluctuations of wind and photovoltaic plants is leading to an enlarged discrepancy of production and consumption ... [more ▼]

The increasing part of renewable energy in the electricity production mix with its known fluctuations of wind and photovoltaic plants is leading to an enlarged discrepancy of production and consumption. Up to now the electricity production of biogas plants is more or less constant but could be used in future more to balance the energy production by using higher biogas storage capacity. An interesting alternative could be a 2 stage process. The 1st stage is operated at higher loadings and low pH where mainly substrate hydrolysis takes place and relatively small quantities of H2/CO2 gas are produced. The effluent shows high concentrations (total > 10 g FA/l) of mainly butyric and caproic acid which could easily and stable be temporarily stored in liquid-tanks. The transformation of the acidic intermediates from hydrolysis to biogas (and finally electricity) in the 2nd stage is faster compared to the traditional fermentation. The storage capacity for the acidic intermediates is more than 10 times smaller compared to the temporary storage of biogas. [less ▲]

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See detailStauverlust von Feinrechenanlagen - Vergleich verschiedener Berechnungsmethoden mit Messergebnissen
Uckschies, Thomas; Hansen, Joachim UL; Greger, Manfred UL et al

in Korrespondenz Abwasser Abfall (2016)

Zur Bestimmung des Stauverlustes von Rechenanlagen werden in der Praxis verschiedene Berechnungsmethoden genutzt. Die Ergebnisse dieser Berechnungen bilden z.B. die Grundlage für die Festlegung der ... [more ▼]

Zur Bestimmung des Stauverlustes von Rechenanlagen werden in der Praxis verschiedene Berechnungsmethoden genutzt. Die Ergebnisse dieser Berechnungen bilden z.B. die Grundlage für die Festlegung der Parameter der Steuerung von Feinrechenanlagen, d.h. Wasserspiegel absolut und Wasserspiegeldifferenz. Zugleich sind sie Basis für Festlegungen die Gerinnehydraulik betreffend, beispielsweise bei der Definition der Höhe von Schwellen und Sturzpunkten von Schneckenpumpen. Beobachtungen in der betrieblichen Praxis ergeben jedoch z.T. erhebliche Differenzen zu den Berechnungsergebnissen, selbst für unbelegte Feinrechen. Dies ist Anlass für weitere Untersuchungen, die hier angeregt werden sollen. Nachfolgend werden gängige Methoden zur Berechnung des Stauverlustes von Rechenanlagen vorgestellt und bewertet. Weiterhin werden exemplarisch für einige Kläranlagen die mit diesen Methoden errechneten Werte mit den vor Ort ermittelten Messwerten verglichen. [less ▲]

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See detailÜberarbeitete Methode zur hydraulischen Berechnung von Stabrechen
Hansen, Joachim UL; Greger, Manfred UL; Kimmerle, Klaus et al

in Wasser und Abfall (2015), 17(3), 39-43

Der hydraulische Verlust von Feinrechenanlagen im Rahmen der Berechnung der Hydraulik von Kläranlagen wird sehr oft über die Berechnungsmethode nach KIRSCHMER ermittelt. Aktuell durchgeführte Vergleiche ... [more ▼]

Der hydraulische Verlust von Feinrechenanlagen im Rahmen der Berechnung der Hydraulik von Kläranlagen wird sehr oft über die Berechnungsmethode nach KIRSCHMER ermittelt. Aktuell durchgeführte Vergleiche der Berechnungsergebnisse nach KIRSCHMER mit in realen Feinrechengerinnen erfassten Messwerten ergaben jedoch erhebliche Differenzen. Basierend auf diesem Vergleich wurde die bekannte Formel erweitert und evaluiert. [less ▲]

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See detailDigestion of grass silage in a semi-continuously fed reactor at increasing loading rates - Process stability and kinetics evaluatio
Benito Martin, Patricia UL; Greger, Manfred UL; Schlienz, Markus UL

in Venice 2014 5th International Symposium on Energy from Biomass and Waste Proceedings (2014, December 01)

Grass is a popular substrate in agricultural biogas plants in Central and Northern Europe. There is currently limited information about the impact of the organic loading rates (OLR) on methane yields ... [more ▼]

Grass is a popular substrate in agricultural biogas plants in Central and Northern Europe. There is currently limited information about the impact of the organic loading rates (OLR) on methane yields, process stability and kinetics for continuous systems digesting grass silage. Anaerobic mono-digestion of grass silage was evaluated in semi-continuously fed laboratory continuously stirred tank reactors (CSTRs) at increasing loading rates between 1.9 and 4.7gVS/l/d. Results show that digestion of grass silage in one-stage CSTR is feasible and do not present any loading-induced inhibition for the tested OLR range. While the volumetric methane production experienced an increase of 61%, the methane yield only decreased by 13% for the highest OLR. On the other hand, the estimated first-order hydrolysis constant decreased by 24% when increasing the loading from 1.9 to 4.7gVS/l/d, which related with an accumulation of the organic material in the reactor. It was also found that the composition of the grass silage affected the digester performance significantly. [less ▲]

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See detailBiodegradability of Cellulose in a Continuous Reactor with Increasing Feeding Rates
Benito Martin, Patricia UL; Greger, Manfred UL; Beierlein, Nomathamsanqa Nonjabulo UL

in Hoffmann, C.; Maniatis, K.; Grassi, A. (Eds.) et al 22nd European Biomass Conference Proceedings - Setting the course for a biobased economy (2014, July)

Cellulose is significantly present during the anaerobic digestion of energy crops and agricultural waste for biogas production. Nevertheless, its degradation poses some challenges due to its structure and ... [more ▼]

Cellulose is significantly present during the anaerobic digestion of energy crops and agricultural waste for biogas production. Nevertheless, its degradation poses some challenges due to its structure and resulting slow hydrolysis. The purpose of the current research was to analyse the response of a continuous anaerobic system digesting cellulose to increasing loading rates, in terms of the impact on the specific methane yield and biogas composition as well as on the process dynamics. To this end, a continuously stirred tank reactor with a working volume of 10 litres was operated under mesophilic conditions for over 60 days. Cellulose was added in the reactor daily as the sole carbon source at different organic loading rates (1gVS/l/d and 1.5 gVS/l/d). An increase in the OLR up to 1.5gVS/l/d resulted in an important decrease of the degree of solubilisation, thus creating an accumulation of the cellulose in the reactor and fluctuating methane production, below potential values. In particular, the results suggest that an acetate concentration of 1.3g/l in the medium, which was reached after increasing the loading, could have an effect on the enzymatic cellulose hydrolysis. This work contributes to the limited knowledge of cellulose solubilisation in continuous systems under anaerobic conditions. [less ▲]

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See detailAuslegung von Feinrechen auf kommunalen Kläranlagen
Hansen, Joachim UL; Greger, Manfred UL; Kimmerle, Klaus et al

in Korrespondenz Abwasser Abfall (2014)

Zur Bestimmung des Stauverlustes von Rechenanlagen werden in der Praxis verschiedene Berechnungsmethoden genutzt. Die Ergebnisse dieser Berechnungen bilden z.B. die Grundlage für die Festlegung der ... [more ▼]

Zur Bestimmung des Stauverlustes von Rechenanlagen werden in der Praxis verschiedene Berechnungsmethoden genutzt. Die Ergebnisse dieser Berechnungen bilden z.B. die Grundlage für die Festlegung der Parameter der Steuerung von Feinrechenanlagen, d.h. Wasserspiegel absolut und Wasserspiegeldifferenz. Zugleich sind sie Basis für Festlegungen die Gerinnehydraulik betreffend, beispielsweise bei der Definition der Höhe von Schwellen und Sturzpunkten von Schneckenpumpen. Beobachtungen in der betrieblichen Praxis ergeben jedoch z.T. erhebliche Differenzen zu den Berechnungsergebnissen, selbst für unbelegte Feinrechen. Dies ist Anlass für weitere Untersuchungen, die hier angeregt werden sollen. Nachfolgend werden gängige Methoden zur Berechnung des Stauverlustes von Rechenanlagen vorgestellt und bewertet. Weiterhin werden exemplarisch für einige Kläranlagen die mit diesen Methoden errechneten Werte mit den vor Ort ermittelten Messwerten verglichen. [less ▲]

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See detailThermal and electrical aging of laser braze-welded aluminum–copper interconnects
Solchenbach, Tobias UL; Plapper, Peter UL; Greger, Manfred UL et al

in Translational Materials Research (2014), 1(1), 015001

Aluminum–copper (Al–Cu) interconnects are of great interest for a variety of electrical applications, such as lithium-ion batteries. In this paper, the effects of thermal and electrical aging on the ... [more ▼]

Aluminum–copper (Al–Cu) interconnects are of great interest for a variety of electrical applications, such as lithium-ion batteries. In this paper, the effects of thermal and electrical aging on the intermetallic compound growth of laser braze-welded Al–Cu interconnects are reported. Thermal aging was studied in a temperature range from 200 to 500 °C for durations between 1 and 120 h. Electrical aging was studied with 200 A direct current application with different polarities and durations between 1 and 24 h. The formation of intermetallic compounds was found to be dependent on the type of aging and, for electrical aging, on the polarity of the current. The growth of intermetallic compounds under the influence of the electric current was distinctly higher than for thermal annealing conditions. The formation of voids at the transition between intermetallic compounds indicates that electromigration may be the main driving force for the accelerated intermetallic growth. [less ▲]

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See detailOptimisation of the Co-Digestion of Maize and Grass Silage Influence of the Substrate Mixture on the Biogas Yield
Benito Martin, Patricia UL; Sibisi-Beierlein, Nonjabulo N.; Greger, Manfred UL

in Bilitewski, B.; Clarke, W. P.; Cossu, R. (Eds.) et al Venice 2012 Fourth International Symposium on Energy from Biomass and Waste Proceedings (2012, November)

In recent years, energy crops have been increasingly introduced as co-substrates in biogas plants due to their high biogas yield potential. The purpose of the current research was to investigate the ... [more ▼]

In recent years, energy crops have been increasingly introduced as co-substrates in biogas plants due to their high biogas yield potential. The purpose of the current research was to investigate the influence of the mixture of maize and grass silages, added as feedstock, on the specific methane production (SMP) and on the process dynamics. To this end, biological methane potential (BMP) tests were carried out in 500ml reactors with grass and maize silage in mono-digestion and 3 different co-digestion mixtures. For selected mixtures, process dynamics were further investigated in batch anaerobic experiments in 1 litre reactors by measuring different control parameters. A positive correlation was observed between the proportion of grass in the mixture and the specific methane yield due to the higher protein content (a yield up to 6% higher in comparison with mono-digestion of maize). Nevertheless, increasing amounts of grass were also related with slower degradation (lower hydrolysis rate constants) and higher instability during the first days of digestion. [less ▲]

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See detailMonitoring biodegradability of lignocellulosic biomass during anaerobic digestion
Benito Martin, Patricia UL; Sibisi-Beierlein, Nonjabulo N.; Greger, Manfred UL

in Book of abstracts of the 8th International Conference ORBIT2012 (2012, June)

Energy crops and crop residues can be digested anaerobically either alone or as co-substrate to produce biogas, a versatile renewable energy source. In the agricultural sector, this biomass is often co ... [more ▼]

Energy crops and crop residues can be digested anaerobically either alone or as co-substrate to produce biogas, a versatile renewable energy source. In the agricultural sector, this biomass is often co-digested with animal manure and slurry, one of the most significant agricultural waste streams. In spite of the growing number of agricultural biogas plants using agricultural waste and energy crops, the use of process simulation models for predicting and defining plant behaviour is still very limited, mainly due to the complexity of the process and the heterogeneity of the substrates. Also, the lack of standardized substrate characterisation methodology contributes to this issue. The chemical oxygen demand (COD), widely used as a mass balance term in modelling of wastewater treatment plants, could be applied in this field. However, COD is difficult to measure in the case of heterogeneous and solid substrates, including samples with high solids content. This, in turn, has limited its use to date to evaluate substrate biodegradability over time and methane production potential in the field of co-digestion of agricultural by-products. This research paper reports and analyses experimental results on the applicability of COD as a substrate characterisation and process monitoring parameter in the context of lignocellulosic biomass digestion, as collected from the research work currently being undertaken at the University of Luxembourg. The reliability of this parameter was investigated using different silages. Four sets of batch experiments were carried out using maize silage (12.17gVS/l), grass silage (14.58gVS/l), and two co-digestion mixtures of 40% maize and 60% grass (18.31 gVS/l) and 70% maize and 30% grass (12 gVS/l) in 1 litre reactors running under mesophilic conditions. The reactors were inoculated with pre-acclimatized inoculum from Beckerich agricultural biogas plant in Luxembourg. Soluble and particulate COD, volatile solids (VS), total solids (TS), volatile fatty acids (VFAs), and gas production, including composition, were monitored over a period of 24 days. A few adapted analytical procedures for measuring COD in solid and heterogeneous substrates and samples with high suspended solids concentration, in comparison to standard methods widely used for wastewater, have been proposed in recent years but these have rarely been applied and validated in the field of digestion of agricultural by-products. The COD methodology adopted in this study was developed by the process research group at the University of Luxembourg as a modification of the DIN 38414-S9 considering some suggestions from Raposo et al. (2008). The modified COD method was applied to different substrates (i.e. grass, maize silages, and cellulose) and also to monitor particulate COD (pCOD) evolution during anaerobic digestion of the different silages. The soluble COD (sCOD) method as established in the ISO 15705 standard method was modified for these experiments as the digestate has relatively high suspended solids concentration. First, the measured substrate COD concentration was compared with the theoretical oxygen demand for each substrate. COD recovery obtained was 96% for cellulose, 92.5% on average for the different maize silages tested and 91.5% on average for the grass silages tested. For all different batch series, the pCOD decreased overtime as a result of the hydrolysis of the particulate fraction of the substrate. The pCOD evolution along with the methane accumulative yield suggested that the solubilisation of the substrate was slower in the case of the co-digestion experiments. sCOD, on the other hand, initially increased sharply as a result of the solubilisation of the substrate and subsequent acidification and then decreased as digestion progressed. After 9 days of digestion, 77%, 71%, 69% and 48% substrate to methane conversion rates had been achieved for the experiments fed with grass silage, maize silage, the 70% maize/30% grass mixture and the 40% maize/60% grass mixture, respectively. Measuring the pCOD and sCOD together with biogas and VFAs concentration during digestion allows, not only to estimate the degradation advancement through COD mass balance, but also to obtain relevant information about the solubilisation of the particulate fraction (hydrolysis step). [less ▲]

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See detailKinetic Considerations on Thermophilic Digestion of Maize Silage at Different Feeding Modes
Golkowska, Katarzyna UL; Sibisi-Beierlein, Nonjabulo; Greger, Manfred UL

in Chemie Ingenieur Technik (2012), 84(9),

Digestion of maize silage in batch, semi-batch and continuous mode was investigated under similar experimental conditions with the aim to compare the degradation kinetics. The modeling with the 1st order ... [more ▼]

Digestion of maize silage in batch, semi-batch and continuous mode was investigated under similar experimental conditions with the aim to compare the degradation kinetics. The modeling with the 1st order equation shows that despite the ensiling pre-treatment the disintegration/hydrolysis step determines the total degradation rate of the substrate. The results confirmed an extremely high adatation capability of anaerobic biocenosis to increased feeding frequency, rather than to higher but less frequent loadings. 2-3 times higher degradation rates were observed for triple feeding frequency. On the other hand an increase in organic loading within the same feeding mode always resulted in reduction of digestion rate. [less ▲]

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See detailMonovergärung von Maissilage und Zellulose
Golkowska, Katarzyna; Greger, Manfred UL

in Cahiers scientifiques (2012), (1), 24-27

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See detailMonovergärung von Maissillage und Zellulose
Golkowska, Katarzyna UL; Greger, Manfred UL

in Cahiers scientifiques (2012), Vol. 1

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See detailStudying Microbial Dynamics in Anaerobic Monofermentation of Energy Crops – is FISH the right Technique
Beierlein-Sibisi, N. UL; Greger, Manfred UL

in Microbes in Wastewater and waste Treatment, Bioremediation, and Energy Production (2011)

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See detailInfluence of environmental conditions for the rheological properties of SCC
Weisheit, Sandro UL; Waldmann, Danièle UL; Greger, Manfred UL

in Professeur D. SC. A. Kamal H. Khayat (Ed.) CD-Proceedings, Paper ID: MS-096 (2010, September 28)

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See detailThermophilic digestion of cellulose at high organic loading rates
Golkowska, Katarzyna UL; Greger, Manfred UL

in Engineering in Life Sciences (2010), 10(6), 600-606

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See detailAnaerobe Vergärung von Mais und Cellulose - Vergleich des Abbauverhaltens
Golkowska, Katarzyna UL; Greger, Manfred UL

in Chemie Ingenieur Technik (2010), 82(9), 1514-1514

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See detailModelling thermophilic anaerobic digestion of maize silage
Beierlein, Nomathamsanqa Nonjabulo UL; Golkowska, Katarzyna UL; Greger, Manfred UL

in Proceedings Venice 2010, Third International Symposium on energy from Biomass and Waste, 8-11.11.2010, Venice (2010)

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See detailUntersuchungen zur Oberflächenqualität von Selbstverdichtendem Beton
Weisheit; Waldmann, Danièle UL; Greger, Manfred UL

Scientific Conference (2010)

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