In the context of biofuel production from marine microalgae, anaerobic digestion has the potential to make the process more sustainable and to increase energy efficiency. However, the use of ...salt-containing microalgae organic residues entails the presence of salts which inhibits methanogenesis. The search for suitable anaerobic microbial consortium adapted to saline conditions can boost the anaerobic conversion into methane. The anaerobic digestion performance of three different anaerobic microbial consortia was assessed in batch tests at different salinities between 15 and 150 g L(-1) and for three successive substrate additions. After an acclimation period, the methane (CH4) yield of the halophilic methanogens at 35 g L(-1) of salinity was close to the reference value without salt addition. Above 75 g L(-1) of salinity, methanogenesis was considerably slowed down. The results underline that methane production from halophilic sediment can be envisaged and promoted for practical application at a seawater concentration.
The aim of this study was to show the link between the initial characteristics of waste activated sludge (WAS) samples and their thermophilic anaerobic biodegradabilities, as determined by ...biochemical methane potential (BMP) tests, in order to develop relevant prediction indicators. Macroscopic parameters, biochemical composition and a fractionation of total solids by the Van Soest method were carried out on WAS samples which were taken from the inlet and outlet of full-scale sludge anaerobic digesters. Biodegradability was expressed as a function of WAS characteristics by the partial least square (PLS) regression technique. Among several PLS models, the most appropriated model was based on biochemical characterisation (carbohydrates, lipids and proteins) and two macroscopic parameters (soluble organic carbon and the ratio of chemical oxygen demand to total organic carbon). The biodegradability indicators developed in this study permitted the prediction of the methane production from WAS samples.
Biochemical characterization of organic matter is becoming of key importance in wastewater treatment. The main objectives are to predict organic matter properties, such as granulation or ...flocculation, and hence treatment performance. Although standardized methods do exist for some organic molecules, such as volatile fatty acids or lipids, there are no standard methods to measure proteins and carbohydrates content, both biochemical families being the main components of sewage sludge. Consequently, the aim of the present work is to investigate the efficiency of several colorimetric methods to determine proteins and carbohydrates content as well as their compatibility with the sludge matrices. The different methods have been evaluated based on statistical criteria such as sensitivity, linearity, accuracy, rightness, and specificity using standard molecules such as Bovine Serum Albumin (BSA), glucose, cellulose and a certified reference product. The Lowry and the Dubois methods have been shown to be the best compromise for the considered criteria after having been tested on sewage sludge samples obtained from different locations in a wastewater treatment plant. In average, the measured volatile fatty acids, lipids, proteins and carbohydrates contents represented 80 ± 7% (% volatile solids) of the organic matter. Proteins and carbohydrates represented in average 69 ± 3%.
This study underlined that the choice of a relevant methodology is of great importance for organic matter measurement.
► Statistical comparison for protein method assessment: Lowry best compromise. ► Statistical comparison for carbohydrates method assessment: Dubois better recovery. ► Method choice depends on matrix studied. ► Methods performance: 80% of organic matter recovered.
•A new disintegration/hydrolysis structure is introduced to the ADM1.•Two hydrolysable composite fractions of particulate organic matter were implemented.•A anaerobic batch test was used to calibrate ...model parameters.•Estimated parameters were representative of a continuous full-scale digester.
A new model structure for the hydrolysis step is introduced in the IWA anaerobic digestion model no 1 (ADM1) in order to better represent the bioaccessibility of particulate organic matter. Two particulate organic matter fractions for waste activated sludge (WAS) samples were defined: a readily hydrolysable fraction (Xcr) and a slowly hydrolysable fraction (Xcs). These fractions were hydrolyzed according to a surface-limiting reaction. Batch anaerobic digestion test of untreated WAS was used to develop the model and calibrate the kinetic parameters and biomass concentrations. The validation was carried out with a similar substrate than the calibration but a thermal pretreatment was applied at two different conditions (110°C and 220°C). The behavior of thermophilic anaerobic digestion of WAS samples was effectively represented by the proposed model. No changes among kinetic parameter sets were done and the model is able to represent produced methane volume following the intrinsic changes of the WAS composition through the different thermal pretreatment conditions. Moreover, estimated parameters in 20days of batch anaerobic digestion test were representative of continuous anaerobic digestion in a full-scale digester.
Anaerobic digestion disintegration and hydrolysis have been traditionally modeled according to first-order kinetics assuming that their rates do not depend on disintegration/hydrolytic biomass ...concentrations. However, the typical sigmoid-shape increase in time of the disintegration/hydrolysis rates cannot be described with first-order models. For complex substrates, first-order kinetics should thus be modified to account for slowly degradable material. In this study, a slightly modified IWA ADM1 model is presented to simulate thermophilic anaerobic digestion of thermally pretreated waste activated sludge. Contois model is first included for disintegration and hydrolysis steps instead of first-order kinetics and Hill function is then used to model ammonia inhibition of aceticlastic methanogens instead of a non-competitive function. One batch experimental data set of anaerobic degradation of a raw waste activated sludge is used to calibrate the proposed model and three additional data sets from similar sludge thermally pretreated at three different temperatures are used to validate the parameters values.
Summary
Formic acid, acting as both carbon and energy source, is a safe alternative to a carbon dioxide, hydrogen and dioxygen mix for studying the conversion of carbon through the ...Calvin–Benson–Bassham (CBB) cycle into value‐added chemical compounds by non‐photosynthetic microorganisms. In this work, organoautotrophic growth of Ralstonia eutropha on formic acid was studied using an approach combining stoichiometric modeling and controlled cultures in bioreactors. A strain deleted of its polyhydroxyalkanoate production pathway was used in order to carry out a physiological characterization. The maximal growth yield was determined at 0.16 Cmole Cmole−1 in a formate‐limited continuous culture. The measured yield corresponded to 76% to 85% of the theoretical yield (later confirmed in pH‐controlled fed‐batch cultures). The stoichiometric study highlighted the imbalance between carbon and energy provided by formic acid and explained the low growth yields measured. Fed‐batch cultures were also used to determine the maximum specific growth rate (μmax = 0.18 h−1) and to study the impact of increasing formic acid concentrations on growth yields. High formic acid sensitivity was found in R eutropha since a linear decrease in the biomass yield with increasing residual formic acid concentrations was observed between 0 and 1.5 g l−1.
In this work, organoautotrophic growth of Ralstonia eutropha on formic acid was studied using an approach combining stoichiometric modeling and controlled cultures in bioreactors. The maximal growth yield was determined at 0.16 Cmole.Cmole‐1 and corresponded to 76 to 85% of the theoretical yield.
Summary
Formic acid, acting as both carbon and energy source, is a safe alternative to a carbon dioxide, hydrogen and dioxygen mix for studying the conversion of carbon through the
C
alvin–
B
enson–
...B
assham (
CBB
) cycle into value‐added chemical compounds by non‐photosynthetic microorganisms. In this work, organoautotrophic growth of
R
alstonia eutropha
on formic acid was studied using an approach combining stoichiometric modeling and controlled cultures in bioreactors. A strain deleted of its polyhydroxyalkanoate production pathway was used in order to carry out a physiological characterization. The maximal growth yield was determined at 0.16
C
mole
C
mole
−1
in a formate‐limited continuous culture. The measured yield corresponded to 76% to 85% of the theoretical yield (later confirmed in
pH
‐controlled fed‐batch cultures). The stoichiometric study highlighted the imbalance between carbon and energy provided by formic acid and explained the low growth yields measured. Fed‐batch cultures were also used to determine the maximum specific growth rate (μ
max
= 0.18 h
−1
) and to study the impact of increasing formic acid concentrations on growth yields. High formic acid sensitivity was found in
R
eutropha
since a linear decrease in the biomass yield with increasing residual formic acid concentrations was observed between 0 and 1.5 g l
−1
.
Formic acid, acting as both carbon and energy source, is a safe alternative to a carbon dioxide, hydrogen and dioxygen mix for studying the conversion of carbon through the Calvin–Benson–Bassham ...(CBB) cycle into value‐added chemical compounds by non‐photosynthetic microorganisms. In this work, organoautotrophic growth of Ralstonia eutropha on formic acid was studied using an approach combining stoichiometric modeling and controlled cultures in bioreactors. A strain deleted of its polyhydroxyalkanoate production pathway was used in order to carry out a physiological characterization. The maximal growth yield was determined at 0.16 Cmole Cmole−1 in a formate‐limited continuous culture. The measured yield corresponded to 76% to 85% of the theoretical yield (later confirmed in pH‐controlled fed‐batch cultures). The stoichiometric study highlighted the imbalance between carbon and energy provided by formic acid and explained the low growth yields measured. Fed‐batch cultures were also used to determine the maximum specific growth rate (μmax = 0.18 h−1) and to study the impact of increasing formic acid concentrations on growth yields. High formic acid sensitivity was found in R eutropha since a linear decrease in the biomass yield with increasing residual formic acid concentrations was observed between 0 and 1.5 g l−1.
Summary
Formic acid, acting as both carbon and energy source, is a safe alternative to a carbon dioxide, hydrogen and dioxygen mix for studying the conversion of carbon through the
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alvin–
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enson–
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assham (
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) cycle into value‐added chemical compounds by non‐photosynthetic microorganisms. In this work, organoautotrophic growth of
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R
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alstonia eutropha
on formic acid was studied using an approach combining stoichiometric modeling and controlled cultures in bioreactors. A strain deleted of its polyhydroxyalkanoate production pathway was used in order to carry out a physiological characterization. The maximal growth yield was determined at 0.16
<styled-content style='fixed-case'>C</styled-content>
mole
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mole
−1
in a formate‐limited continuous culture. The measured yield corresponded to 76% to 85% of the theoretical yield (later confirmed in
<styled-content style='fixed-case'>pH</styled-content>
‐controlled fed‐batch cultures). The stoichiometric study highlighted the imbalance between carbon and energy provided by formic acid and explained the low growth yields measured. Fed‐batch cultures were also used to determine the maximum specific growth rate (μ
max
= 0.18 h
−1
) and to study the impact of increasing formic acid concentrations on growth yields. High formic acid sensitivity was found in
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R
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eutropha
since a linear decrease in the biomass yield with increasing residual formic acid concentrations was observed between 0 and 1.5 g l
−1
.
La gestion des boues d’épuration constitue un réel enjeu économique et environnemental en raison de l’augmentation de leur quantité et des contraintes réglementaires. Toutefois, leur valorisation ...sous forme de biogaz, énergie renouvelable, répond aux critères de développement durable. Dans un contexte industriel, la mesure de la biodégradabilité anaérobie des boues à traiter est nécessaire afin de mettre en place un système de traitement adapté. Or, outre des essais expérimentaux de longues durées (potentiel méthane) et lourds d’un point de vue analytique, il n’existe actuellement aucun moyen de caractériser cette biodégradabilité. De plus, les modèles de digestion anaérobie, proposés pour représenter les performances, possèdent des lacunes concernant l’étape d’hydrolyse en raison d’une description limitée des mécanismes chimiques et biochimiques de cette étape. Ainsi les travaux de la thèse se sont intéressés à l’étude du lien entre la caractérisation chimique et biochimique de la matière organique et les performances de digestion anaérobie. Une étude statistique par PLS a permis d’élaborer un modèle du potentiel méthane des boues étudiées. La caractérisation biochimique (protéines, glucides et lipides) ainsi que deux paramètres macroscopiques (degré d’oxydation et carbone organique soluble) se sont révélés comme des indicateurs initiaux pertinents de la biodégradabilité. Le suivi de dégradation en réacteur batch d’une boue non traitée et prétraitée thermiquement a montré que la phase de méthanogénèse est étroitement reliée à l’étape d’hydrolyse. En effet, une phase de latence sur la production de méthane est observée, ainsi qu’une production importante d’acétate les premiers jours de la dégradation. De plus, les variations des concentrations en composés solubles ainsi que la cinétique de production de méthane ont mis en évidence l’existence de deux phases distinctes d’hydrolyse des composés particulaires. La bioaccessibilité de la matière particulaire au sein des boues d’épuration est donc un facteur important sur les performances de dégradation. Un modèle de digestion anaérobie, basé sur l’ADM1, a également été proposé afin de représenter l’impact de la composition initiale des boues d’épuration sur les dynamiques de dégradation anaérobie. Deux modifications ont été effectuées afin d’obtenir une meilleure représentation des phénomènes réactionnels, et notamment de l’accessibilité de la matière. Ainsi, une vitesse de réaction de Contois pour les étapes de désintégration et d’hydrolyse et deux variables d’entrée, une fraction facilement hydrolysable Xcr et une fraction lentement hydrolysable Xcs, ont été introduites. Le modèle modifié est capable de représenter les cinétiques de dégradation, obtenues en conditions batch et continue.
The sewage sludge management represents economical and environmental issues. However, the sludge valorisation into biogas, renewable energy, contributes to the sustainable development. In an industrial context, the measurement of anaerobic biodegradability is a challenge in order to elaborate an optimised treatment process. Nowadays, aside from experimental anaerobic degradation tests, demanding laboratory work and time-consuming, the biodegradability cannot be characterised. Moreover, the anaerobic digestion models, used to represent the performances, have some limitations for the description of hydrolysis step. Indeed, the first order kinetic equation used to represent the physicochemical and biochemical mechanism is too simple. The aim of thesis was thus to study the relationship between chemical and biochemical characterisation and anaerobic digestion performances. The potential methane of studied sludge samples could be predicted thanks to a partial least square (PLS) regression. The biochemical characterisation (proteins, carbohydrates and lipids) and two macroscopic parameters (oxidation state and soluble organic carbon) seem to be relevant parameters to assess the anaerobic biodegradability of WAS samples. The degradation of untreated and thermally pretreated WAS samples was monitored in batch reactors. The methanogenesis was shown to be driven by the hydrolysis. Indeed a latency period and a high acetate production were observed during the first days of experiment. Moreover, the soluble compound concentration variations and the methane production kinetics showed two distinct hydrolysis phases of particulate matter. The WAS degradation is therefore dependent on the bioaccessibility of particulate organic matter. A modified structure of Anaerobic Digestion Model n°1 (ADM1) was proposed in order to represent the impact of WAS initial composition on the anaerobic degradation dynamics. Two modifications were performed for enhancing the representation of hydrolysis step and the particulate matter accessibility. Thus the Contois model was used to describe disintegration and hydrolysis steps and two particulate organic matter fractions: a readily hydrolysable fraction Xcr and a slowly hydrolysable fraction Xcs, were introduced. The modified model was able to simulate the degradation performances in batch and continuous conditions.
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