Mixing and liquid-to-gas mass transfer under digester operating conditions

Trad, Zaineb; Vial, Christophe; Fontaine, Jean-Pierre; Larroche, Christian

doi:10.1016/j.ces.2017.01.056

Cited by 34 publications

(18 citation statements)

References 36 publications

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“…It has been observed that most of the studies on the evaluation of the effect of mixing regimes on biogas production are limited to lab-scale digesters [27,[48][49][50][51] and only a few represent the results regarding full-scale biogas plants [35,52,53]. The major challenge in mixer setup design is to scale up from a laboratory or pilot scale to a full-scale unit.…”

Section: Correlation Between Lab-scale and Large-scale Mixing In Anaerobic Digestersmentioning

confidence: 99%

“…From the intensive literature review, it was observed that the approach to studying mixing efficiency depends on the scale of the biogas digester. For instance, in the lab-scale experiments, the general focus is on the determination of the amount of biogas production rate [19,64], methane content [65,66], the behavior of microorganisms [36,67,68] and dead zones [27,51] by varying the rotational speed of the impeller. Each factor has its own significance and importance.…”

Section: Parameters For Evaluation Of Mixing In Anaerobic Digestermentioning

confidence: 99%

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Critical Analysis of Methods Adopted for Evaluation of Mixing Efficiency in an Anaerobic Digester

Singh

Čonka

et al. 2021

Sustainability

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The effect of slurry mixing in an anaerobic digester on biogas production was intensively studied in the last few years. This subject is still debatable due to fact that this process involves three phases, solid-gas-liquid, along with the involvement of microbes during biochemical reactions, which are highly vulnerable to changes in hydrodynamic shear stresses and mixing conditions. Moreover, the complexity in the direction of optimization of mixing magnifies due to the implication of both fluid mechanics and biochemical engineering to study the effect of mixing in anaerobic digestion (AD). The effect of mixing on AD is explored using recent literature and theoretical analysis, concentrating on the multi-phase and multi-scale aspects of AD. The tools and methods available to experimentally quantify the function of mixing on both the global and local scales are summarized in this study. The major challenge for mixing in an anaerobic digester is to minimize dead zones and maintain uniform distribution of viscosity and shear at low mixing intensities without disrupting the microbial flocs and syntrophic relationships between the bacteria during the AD process. This study is a critical analysis of various techniques and approaches adopted by researchers to evaluate the effectiveness of mixing regimes and mixing equipment. Most studies describe biogas production performance and hydrodynamic characteristics of the digesters separately, but the evaluation of mixing requires interdisciplinary experts, which include mechanical engineers, microbiologists and hydrodynamic experts. Through this review, the readers will be guided through intensive literature regarding agitation, the best possible way to scrutinize the agitation problems and the approach to answering the question “why is the optimization of mixing in an anaerobic digester still a debatable subject?”.

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Section: Correlation Between Lab-scale and Large-scale Mixing In Anaerobic Digestersmentioning

confidence: 99%

Section: Parameters For Evaluation Of Mixing In Anaerobic Digestermentioning

confidence: 99%

Critical Analysis of Methods Adopted for Evaluation of Mixing Efficiency in an Anaerobic Digester

Singh

Čonka

et al. 2021

Sustainability

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“…Flow pattern of slurry strongly depends on the off bottom and inter impeller clearance, the size and type of lower impeller. Z. Trad et al [14] studied the flow pattern of slurry by combining different types of impellers. An elephant ear turbine ( Fig.…”

Section: Types Of Mixersmentioning

confidence: 99%

Hydrodynamic factors in an anaerobic digester

Singh¹,

Szamosi²,

Siménfalvi³

2018

The Publications of the MultiScience - XXXII. MicroCAD International Scientific Conference

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“…For instance, the multi-impeller generates lower shear rates and promotes uniform power dissipation in the bioreactor. Trad et al [15] have found that the flow patterns of the slurry were highly affected by varying the inter impeller and off bottom clearances. Different combinations of MI, four-blade RT, six-blade RT, and elephant ear turbines were also analyzed.…”

Section: Introductionmentioning

confidence: 99%

Enhancing Efficiency of Anaerobic Digestion by Optimization of Mixing Regimes Using Helical Ribbon Impeller

et al. 2021

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The appropriate mixing system and approach to effective management can provide favorable conditions for the highly sensitive microbial community, which can ensure process stability and efficiency in an anaerobic digester. In this study, the effect of mixing intensity on biogas production in a lab-scale anaerobic digester has been investigated experimentally and via modeling. Considering high mixing efficiency and unique feature of producing axial flow, helical ribbon (HR) impeller is used for mixing the slurry in this experiment under various conditions. Three parallel digesters were analyzed under identical operating conditions for comparative study and high accuracy. Effects of different mixing speeds (10, 30, and 67 rpm for 5 min h−1) on biogas production rate were determined in 5-L lab-scale digesters. The results demonstrated 15–18% higher biogas production at higher mixing speed (67 rpm) as compared to 10 rpm and 30 rpm and the results proved statistically significant (p < 0.05). Biogas production at 10, 30, and 67 rpm were 45.6, 48.6, and 52.5 L, respectively. Higher VFA concentrations (7.67 g L−1) were recorded at lower mixing intensity but there was no significant difference in pH and ammonia at different speeds whereas the better mixing efficiency at higher speeds was also the main reason for increase in biogas production. Furthermore, model simulation calculations revealed the reduction of dead zones and better homogeneous mixing at higher mixing speeds. Reduction of dead zones from 18% at 10 rpm to 2% at 67 rpm was observed, which can be the major factor in significant difference in biogas production rates at various mixing intensities. Optimization of digester and impeller geometry should be a prime focus to scale-up digesters and to optimize mixing in full-scale digesters.

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Mixing and liquid-to-gas mass transfer under digester operating conditions

Cited by 34 publications

References 36 publications

Critical Analysis of Methods Adopted for Evaluation of Mixing Efficiency in an Anaerobic Digester

Critical Analysis of Methods Adopted for Evaluation of Mixing Efficiency in an Anaerobic Digester

Hydrodynamic factors in an anaerobic digester

Enhancing Efficiency of Anaerobic Digestion by Optimization of Mixing Regimes Using Helical Ribbon Impeller

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