Effect of agitation time on nutrient distribution in full-scale CSTR biogas digesters

Kress, Philipp; Nägele, Hans‐Joachim; Oechsner, Hans; Ruile, Stephan

doi:10.1016/j.biortech.2017.09.054

Cited by 62 publications

(15 citation statements)

References 17 publications

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“…The geometry of the digester tank and the mechanical mixer is only considered in the lab-scale experiments which makes it easier to determine the hydrodynamic characteristics of digesters. Whereas for the full-scale biogas plant, the mixing is evaluated in terms of power consumed per unit volume and per unit fresh feedstock added to the digester [14,75,76]. It is noted that the geometrical aspect is missing while studying the effect of mixing at large-scale biogas plants.…”

Section: Parameters For Evaluation Of Mixing In Anaerobic Digestermentioning

confidence: 99%

“…In addition, electrical power usage for agitation is often dependent on TS content, HRT and feed period [4,76]. In fact, owing to the variance in the geometrical parameters of the impellers and the rheological characteristics of the various substrates, the precise association of the basic electrical intake with the active tank volume and the moisture content is not known.…”

Section: Energy Consumptionmentioning

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: Parameters For Evaluation Of Mixing In Anaerobic Digestermentioning

confidence: 99%

Section: Energy Consumptionmentioning

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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“…The agitation intensity is reported to enhance the bioenergy yield by providing a sufficient environment for the nutrient transfer to the microorganisms, heat transfer, and release of the produced biogas from the digestate mixture [20]. However, the energy consumption for the agitation intensity is reported to be up to 50% of the overall energy input of the wastewater treatment process [21].…”

Section: Introductionmentioning

confidence: 99%

Effect of Localized Temperature Difference on Hydrogen Fermentation

Lee

Mostafa

et al. 2021

Energies

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In a lab-scale bioreactor system, (20 L of effective volume in our study) controlling a constant temperature inside bioreactor with a total volume 25 L is a simple process, whereas it is a complicated process in the actual full-scale system. There might exist a localized temperature difference inside the reactor, affecting bioenergy yield. In the present work, the temperature at the middle layer of bioreactor was controlled at 35 °C, while the temperature at top and bottom of bioreactor was controlled at 35 ± 0.1, ±1.5, ±3.0, and ±5.0 °C. The H2 yield of 1.50 mol H2/mol hexoseadded was achieved at ±0.1 and ±1.5 °C, while it dropped to 1.27 and 0.98 mol H2/mol hexoseadded at ±3.0 and ±5.0 °C, respectively, with an increased lactate production. Then, the reactor with automatic agitation speed control was operated. The agitation speed was 10 rpm (for 22 h) under small temperature difference (<±1.5 °C), while it increased to 100 rpm (for 2 h) when the temperature difference between top and bottom of reactor became larger than ±1.5 °C. Such an operation strategy helped to save 28% of energy requirement for agitation while producing a similar amount of H2. This work contributes to facilitating the upscaling of the dark fermentation process, where appropriate agitation speed can be controlled based on the temperature difference inside the reactor.

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“…Testing the different design concepts in anaerobic digesters, which are filled with biomass, is not only cost‐ and time‐intensive but also challenging, due to the insufficient optical access and chemistry of the atmosphere , . Therefore, many research laboratories are equipped with scaled‐down digester prototypes and safe and easy‐to‐handle artificial substrates to simplify the understanding of the physical systems .…”

Section: Introductionmentioning

confidence: 99%

Numeric Simulation‐Based Analysis of the Mixing Process in Anaerobic Digesters of Biogas Plants

2020

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Stirring systems with two rotational three-bladed propellers were analyzed using computational fluid dynamics. The propellers are located at three heights and seven angles in a tank with 9 m radius. The fluid was characterized by non-Newtonian rheology and simulated by applying the k-e turbulence model and the standard k-w model. Reynolds numbers were estimated. High fluid speeds were obtained with the propellers located at a height of 2 m and oriented at 90°with respect to the tank radius. In the top regions of the tank, the fluid velocity was generally less intense and less affected by the angle setting. The configurations identified as good mixing systems showed power consumptions broadly distributed around 30 kW.

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Effect of agitation time on nutrient distribution in full-scale CSTR biogas digesters

Cited by 62 publications

References 17 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

Effect of Localized Temperature Difference on Hydrogen Fermentation

Numeric Simulation‐Based Analysis of the Mixing Process in Anaerobic Digesters of Biogas Plants

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