Velocity gradient as a tool to characterise the link between mixing and biogas production in anaerobic waste digesters

Sindall, Rebecca; Bridgeman, John; Carliell-Marquet, Cynthia

doi:10.2166/wst.2013.206

Cited by 56 publications

(38 citation statements)

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“…The formation of pockets within the reactor can occur under laminar flow conditions. 15 Within these pockets, the formation of microbial granules can evolve, so that the intercellular metabolite exchange is accelerated. 16 This can even cause a positive effect on the gas production.…”

Section: ■ Discussionmentioning

confidence: 99%

Multiposition Sensor Technology and Lance-Based Sampling for Improved Monitoring of the Liquid Phase in Biogas Processes

et al. 2015

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The current installations of sensors in the liquid phase in digesters are usually not sufficient for the fast detection of disturbances. Thus, the application of strategies for process control is restricted. In this paper, multiparameter (micro-) sensors as novel process analytical tools are introduced, which are coupled with wireless data transmission and are designed for an easy integration into digesters. Furthermore, the combination with a lance-based sampling system, which enables sampling in the core of the liquid phase, is described. The monitoring and sampling devices allow for the measurement at various positions in the liquid phase for the purpose of the identification of gradients. Three case studies were performed: (i) at an open hydrolysis basin, (ii) a mid-sized biogas plant with a concrete roof, and (iii) a larger biogas plant equipped with a flexible roof. Online measurements of the redox potential and offline analysis of the dry matter, ammonia, and acetic acid concentrations indicate plant-specific gradients, which appear in the liquid phase. Thus, the concept is not only suitable to improve the monitoring in digestion processes but also to identify the most suitable locations for installing sensors and sampling ports for a fast detection of process disturbances.

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Section: ■ Discussionmentioning

confidence: 99%

Multiposition Sensor Technology and Lance-Based Sampling for Improved Monitoring of the Liquid Phase in Biogas Processes

et al. 2015

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“…In waste degradation for energy generation, there are advances indicating the relevance of mixing process. Although good mixing can favor the material homogenization and exchange process between microorganisms and their environment, excessive mixing may also disrupt biological activities such as trophic processes [12,13].…”

Section: Geometric Characteristics Of Containersmentioning

confidence: 99%

CFD Analysis of Turbulence Models to Achieve the Digester Mixing Process

Flores-Velázquez¹,

Arzeta-Ríos²,

Ojeda-Bustamante³

et al. 2018

Computational Fluid Dynamics - Basic Instruments and Applications in Science

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Mixing efficiency defines the features of physicochemical and biological reactions carried out in reactors or digesters. The reason for this influence is because it conditions the heat and mass transfer. That is why the mixing level and intensity become important aspects to study to know the effects they have on the processes. Furthermore, it should be noted that most of the mixing processes are carried out under turbulent conditions. Mixing enhancement evaluation is achieved in two ways, that is, experimentally and performing simulations. Simulations are based on numerical methods approximating solutions to results in line with reality. In this context, turbulence models applied in systems have great influence on the final numerical solution and, therefore, on the interpretation of improved mixing in reactors. It is also necessary to consider the influence of rheology in these simulations, since the working fluid does not always have a linear stress-strain relationship. In this way, an analysis of turbulence models and their applications in mixing characterization and the adequacy of these models to the reactor configuration and operating conditions is carried out. Mention is also made of the experiences around the study of turbulence in mixing tanks.

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“…Mixing in the digester can be conducted out by various methods, such as impeller mixing, slurry recirculation and gas sparging, depending on the digester design and substrate. In the case of mechanical mixing, the impellers are rotated while being submerged in the slurry [8,9]. Whereas in slurry recirculation, the slurry is drawn from the center of the digester by an external centrifugal pump and is diffused in the digester through nozzles [10].…”

Section: Introductionmentioning

confidence: 99%

Impact of mixing intensity and duration on biogas production in an anaerobic digester: a review

Singh

Szamosi

Siménfalvi

2020

Critical Reviews in Biotechnology

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This paper is a critical evaluation of the effect of mixing on biogas production rates in an anaerobic digester. Mixing plays a prominent role in determining the efficiency of the anaerobic digestion process. This review analyzes the miscellaneous effects of mixing (on the microbial community, methane content and volatile fatty acids) at various mixing intensities and during different stages of the digestion process. Intermittent mixing (mixing at intervals) seems preferable in terms of the quality and quantity of biogas produced, and results in lower power consumption and maintenance costs associated with large-scale biogas production. Preferable mixing time (the length at intervals) and the intensity depends on the geometry of the digester and impeller. The conclusion is drawn that the study of the slurry rheology is very crucial in the designing of the mixing equipment, the shape and size of the digester, and the pipe transport system which can assist in minimizing the initial investment and operational costs. Accordingly, this paper focuses on the parameters which determine the potency of mixing, such as viscosity, total solid content and digester design. Empirical data demonstrated by various researchers regarding rheological characteristics is compared and reviewed. Consequently, close attention should be paid toward the optimization of mixing in terms of its speed, mixing time and impeller geometry, especially during different stages of the digestion process (hydrolysis, acidogenesis, acetogenesis and methanogenesis). Finally, readers will be guided to the extensive publications regarding optimization, directions of future research, and troubleshooting of the mixing operation in an anaerobic digester. This investigation will help to improve mixing efficiency with biogas plants. HIGHLIGHTSEffect of shear rate on different stages of an anaerobic digestion process. Methane content varies with the variation in mixing speeds. Mixing effect is significant when the total solid content is higher. Intermittent mixing is favorable when compared to continuous mixing. The geometry of the digester and mixer is essential to evaluate digester mixing. ARTICLE HISTORY

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Velocity gradient as a tool to characterise the link between mixing and biogas production in anaerobic waste digesters

Cited by 56 publications

References 0 publications

Multiposition Sensor Technology and Lance-Based Sampling for Improved Monitoring of the Liquid Phase in Biogas Processes

Multiposition Sensor Technology and Lance-Based Sampling for Improved Monitoring of the Liquid Phase in Biogas Processes

CFD Analysis of Turbulence Models to Achieve the Digester Mixing Process

Impact of mixing intensity and duration on biogas production in an anaerobic digester: a review

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