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A critical review of experimental and CFD techniques to characterize the mixing performance of anaerobic digesters for biogas production

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Abstract

Biogas from anaerobic digestion (AD), as an important alternative to fossil fuels, has contributed to energy recovery and environmental sustainability. Incomplete or inefficient mixing within anaerobic reactors can result in poor biogas production or energy wastage. Thus, identifying mixing performance is meaningful for the digester design, operation and maximum biogas production. Over the years, various experimental and computational fluid dynamics (CFD) techniques have been developed to characterize the mixing performance of digesters. This review described the critical impact of mixing on biogas production in AD. Then, experimental techniques available on local and global scales were reviewed and compared in terms of their advantages, disadvantages, characterization capabilities and scope of application. Moreover, the implementation, reliability, indicators and application of CFD techniques in AD were thoroughly discussed. Based on the above discussion, mixing significantly affects AD methane production, and intermittent mixing is preferred for maximum biogas production. Local experimental techniques have been considered to be the simplest and cheapest for arbitrarily sized digesters; global experimental techniques relying on computer systems have received increasing attention for their applications in AD flow fields. More research efforts are needed to discover new experimental techniques that overcome the limitations of digestate opacity and industrial reactor geometries, in addition, compartmental models based on CFD to couple hydrodynamics with biokinetics are interesting and allow for greater implementation of CFD applications.

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Abbreviations

AD:

Anaerobic digestion

ADM1:

Anaerobic digestion model no. 1

CFD:

Computational fluid dynamics

CARPT:

Computer automated radioactive particle tracking

CT:

Computer tomography

DES:

Detached-Eddy simulations

ERT:

Electrical resistance tomography

ECT:

Electrical capacitance tomography

HRT:

Hydraulic retention time

LDA:

Laser Doppler anemometer

LES:

Large Eddy simulation

MRF:

Multiple reference frame

UI:

Uniformity Index

OLR:

Organic loading rate

PIV:

Particle image velocimetry

PLIF:

Planar laser-induced fluorescence

PEPT:

Positron emission particle tracking

RPT:

Radioactive particle tracking

RTD:

Residence time distribution

RANS:

Reynolds-averaged Navier Stokes

RSM:

Reynolds stress models

RNG:

Re-normalization group

Re:

Reynolds numbers

SST:

Shear stress transfer

VOF:

Volume of fluid

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Acknowledgements

This research was funded under the auspices of the National Key Research and Development Program of China (No. 2018YFC1900902) and the State Key Laboratory of Urban Water Resources and Environment (2022DX07).

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Authors and Affiliations

Authors

Contributions

Lili Li: Conceptualization, Methodology, Writing–original draft, Writing – review & editing. Kun Wang: Conceptualization. Qingliang Zhao: Conceptualization, Supervision, Writing–review & editing, Funding acquisition. Qingwei Gao: Methodology, Writing–review & editing. Huimin Zhou: Writing–original draft. Junqiu Jiang: Funding acquisition. Wangyang Mei: Writing–original draft.

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Correspondence to Qingliang Zhao.

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The authors declare no conflict of interest.

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Li, L., Wang, K., Zhao, Q. et al. A critical review of experimental and CFD techniques to characterize the mixing performance of anaerobic digesters for biogas production. Rev Environ Sci Biotechnol 21, 665–689 (2022). https://doi.org/10.1007/s11157-022-09626-z

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  • DOI: https://doi.org/10.1007/s11157-022-09626-z

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