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Bioengineering
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Anaerobic Digestion Advances in Biomass and Waste Treatment
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Anaerobic Digestion Advances in Biomass and Waste Treatment

A special issue of Bioengineering (ISSN 2306-5354). This special issue belongs to the section "Biochemical Engineering".

Deadline for manuscript submissions: 31 December 2025 | Viewed by 7631

Special Issue Editors

Dr. Tina Kegl

E-Mail Website
Guest Editor
Faculty of Chemistry and Chemical Engineering, University of Maribor, 2000 Maribor, Slovenia
Interests: anaerobic digestion; microbial fuel cell; forward osmosis; mathematical modeling and optimization; numerical simulation; waste management; sustainable aviation fuels; nanotechnology; biodegradable plastics
Prof. Dr. Breda Kegl

E-Mail Website
Guest Editor
Faculty of Mechanical Engineering, University of Maribor, 2000 Maribor, Slovenia
Interests: waste to energy; anaerobic digestion; pyrolysis; alternative fuels; internal combustion engines; mathematical modeling and optimization; numerical simulation

Special Issue Information

Dear Colleagues,

Because the world's energy resources are limited and the waste representing an environmental problem contains energy-rich compounds and nutrients, increasing attention is being paid to research into technologies for converting various waste to energy. Considering technological, economic, environmental and social aspects, anaerobic digestion (AD) is a promising technology to reduce a large amount of various types of waste and produce renewable energy and other valuable products. In this context, there is a need for improvements in the AD process in (i) biogas plants in order to produce high-quality biogas, liquid and solid digestate, as well as (ii) microbial fuel cells in order to increase the amount of produced electricity.

This Special Issue of Biochemical Engineering will focus on original research and comprehensive reviews, dealing with the experiments, numerical simulation and optimization of the AD process in biogas plants and microbial fuel cells by considering technological, economic, environmental and social aspects.

The topics of interest for this Special Issue include, but are not limited to, the following:

  • Various biomass and waste pre-treatment methods: mechanical, chemical, biological, etc.;
  • Improvements in the AD process in biogas plants: experimental and numerical investigations, modeling of the AD process (mechanistically inspired models, empirical models, phenomenological models) and optimization of the AD process (deterministic and stochastic methods);
  • Improvements in microbial fuel cell systems: manufacturing of various MFC systems (3D printing), experimental and numerical investigations of various MFC systems (one chamber, two chambers, various types of electrodes and membranes), modeling of processes (AD process, etc.) in microbial fuel cells (mechanistically inspired models, empirical models, phenomenological models), optimization of microbial fuel cell systems (deterministic and stochastic methods);
  • AD products (biogas, liquid digestate, solid digestate) treatments and utilization (nutrient recovery from digestate, heavy metal removal from digestate);
  • Optimization of biogas plants and microbial fuel cells with respect to technical, economic, environmental and social aspects.

Dr. Tina Kegl
Prof. Dr. Breda Kegl
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Bioengineering is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • waste management
  • biomass and waste pre-treatments
  • anaerobic digestion
  • modeling and optimization
  • biogas plants
  • biogas production
  • digestate treatment
  • microbial fuel cells
  • electricity production

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Published Papers (5 papers)

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Research

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13 pages, 1611 KB  
Article
Adsorbents Made from Cotton Textile Waste—Application to the Removal of Tetracycline in Water
by Fadila Akkouche, Katia Madi, Farida Aissani-Benissad, Fekri Abdulraqeb Ahmed Ali, Amine Aymen Assadi, Amir Achraf Assadi, Ahmed Amine Azzaz and Idris Yahiaoui
Bioengineering 2025, 12(11), 1230; https://doi.org/10.3390/bioengineering12111230 - 10 Nov 2025
Viewed by 418
Abstract
The adsorptive removal of tetracycline (TC) in aqueous solution, a widely used antibiotic, was investigated using activated carbon derived from cotton textile waste. The valorization of textile waste provides a sustainable strategy that not only reduces the growing accumulation of discarded textiles but [...] Read more.
The adsorptive removal of tetracycline (TC) in aqueous solution, a widely used antibiotic, was investigated using activated carbon derived from cotton textile waste. The valorization of textile waste provides a sustainable strategy that not only reduces the growing accumulation of discarded textiles but also supports a circular economy by transforming waste into efficient adsorbent materials for the removal pharmaceutical contaminants. This dual environmental and economic benefit underscores the novelty and significance of using cotton-based activated carbons in wastewater treatment. In this study, cotton textile waste was utilized as a raw material for the preparation of adsorbents via pyrolysis under nitrogen at 600 °C followed by chemical modification with H2SO4 solutions (1, 2, and 3 M). The sulfuric-acid modified-carbons (SMCs) were characterized by BET surface area analysis, FTIR spectroscopy and SEM imaging. Batch adsorption experiments were carried out to evaluate the effects of key operational parameters including contact time, initial TC concentration and solution pH. The results showed that the material treated with 2 M H2SO4 displayed the highest adsorption performance, with a specific surface area of 700 m2/g and a pore volume of 0.352 m3/g. The pH has a great influence on TC adsorption; the adsorbed amount increases with the initial TC concentration from 5 to 100 mg/L and the maximum adsorption capacity (74.02 mg/g) is obtained at pH = 3.8. The adsorption behavior was best described by Freundlich isotherm and pseudo-second-order kinetic models. This study demonstrates that low-cost and abundantly available material, such as cotton textile waste, can be effectively repurposed effective adsorbents for the removal of pharmaceutical pollutants from aqueous media. Full article
(This article belongs to the Special Issue Anaerobic Digestion Advances in Biomass and Waste Treatment)
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30 pages, 4593 KB  
Article
Methane Concentration Prediction in Anaerobic Codigestion Using Multiple Linear Regression with Integrated Microbial and Operational Data
by Iván Ostos, Iván Ruiz, Diego Cruz and Luz Marina Flórez-Pardo
Bioengineering 2025, 12(11), 1133; https://doi.org/10.3390/bioengineering12111133 - 22 Oct 2025
Viewed by 842
Abstract
Anaerobic codigestion of organic residues is a proven strategy for enhancing methane recovery. However, the complexity of microbial interactions and variability in operational conditions make it difficult to estimate methane concentration in real time, particularly in rural contexts. This study developed a multiple [...] Read more.
Anaerobic codigestion of organic residues is a proven strategy for enhancing methane recovery. However, the complexity of microbial interactions and variability in operational conditions make it difficult to estimate methane concentration in real time, particularly in rural contexts. This study developed a multiple linear regression model to predict methane concentration using operational data and microbial community profiles derived from 16S rRNA gene sequencing. The system involved the codigestion of cassava by-product and pig manure in a two-phase anaerobic reactor. Predictor variables were selected through a hybrid approach combining statistical correlation with microbial functional relevance. The final model, trained on 70% of the dataset, demonstrated satisfactory generalization capability on the other 30 test set, achieving a coefficient of determination (R2) of 0.92 and a mean relative error (MRE) of 6.50%. Requiring only a limited set of inputs and minimal computational resources, the model offers a practical and accessible solution for estimating methane levels in decentralized systems. The integration of microbial community data represents a meaningful innovation, improving prediction by capturing biological variation not reflected in operational parameters alone. This approach can support local decision making and contribute to Sustainable Development Goal 7 by promoting reliable and affordable technologies for clean energy generation in rural and resource-constrained settings. Full article
(This article belongs to the Special Issue Anaerobic Digestion Advances in Biomass and Waste Treatment)
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12 pages, 1893 KB  
Article
Solid-State Anaerobic Digestion of Organic Solid Poultry Waste for Biomethane Production
by Faryal Fatima and Raghava R. Kommalapati
Bioengineering 2025, 12(7), 712; https://doi.org/10.3390/bioengineering12070712 - 29 Jun 2025
Cited by 1 | Viewed by 1324
Abstract
This study examines biodegradability (BD) and optimum conditions for the solid-state anaerobic digestion (SS-AD) of organic solid poultry waste (organs, intestines, offal, and unprocessed meat) to maximize biomethane production. Three main parameters, substrate-to-inoculum (S/I) ratio, pH, and temperature, were evaluated for the SS-AD [...] Read more.
This study examines biodegradability (BD) and optimum conditions for the solid-state anaerobic digestion (SS-AD) of organic solid poultry waste (organs, intestines, offal, and unprocessed meat) to maximize biomethane production. Three main parameters, substrate-to-inoculum (S/I) ratio, pH, and temperature, were evaluated for the SS-AD of organic solid poultry waste. pH was evaluated at non-adjusted pH, initially adjusted pH, and controlled pH conditions at a constant S/I ratio of 0.5 and temperature of 35 ± 1 °C. The S/I ratios were examined at (0.3, 0.5, 1, and 2) at a controlled pH of ≈7.9 and temperature of 35 ± 1 °C. The temperature was assessed at mesophilic (35 ± 1 °C) and thermophilic (55 ± 1 °C) conditions with a constant S/I ratio of 0.5 and controlled pH of ≈7.9. The results demonstrate that the highest biomethane production and BD were achieved with a controlled pH of ≈7.9 (689 ± 10 mg/L, 97.5 ± 1.4%). The initially adjusted pH (688 ± 14 mg/L, 97.3 ± 1.9%) and an S/I ratio of 0.3 (685 ± 8 mg/L, 96.8 ± 1.2%) had approximately equivalent outcomes. The thermophilic conditions yielded 78% lower biomethane yield than mesophilic conditions. The challenge of lower biomethane yield under thermophilic conditions will be resolved in future studies by determining the rate-limiting step. These observations highlight that SS-AD is a promising technology for biomethane production from solid organic poultry waste. Full article
(This article belongs to the Special Issue Anaerobic Digestion Advances in Biomass and Waste Treatment)
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22 pages, 4765 KB  
Article
Mathematical Model-Based Optimization of Trace Metal Dosage in Anaerobic Batch Bioreactors
by Tina Kegl, Balasubramanian Paramasivan and Bikash Chandra Maharaj
Bioengineering 2025, 12(2), 117; https://doi.org/10.3390/bioengineering12020117 - 26 Jan 2025
Cited by 4 | Viewed by 1881
Abstract
Anaerobic digestion (AD) is a promising and yet a complex waste-to-energy technology. To optimize such a process, precise modeling is essential. Developing complex, mechanistically inspired AD models can result in an overwhelming number of parameters that require calibration. This study presents a novel [...] Read more.
Anaerobic digestion (AD) is a promising and yet a complex waste-to-energy technology. To optimize such a process, precise modeling is essential. Developing complex, mechanistically inspired AD models can result in an overwhelming number of parameters that require calibration. This study presents a novel approach that considers the role of trace metals (Ca, K, Mg, Na, Co, Cr, Cu, Fe, Ni, Pb, and Zn) in the modeling, numerical simulation, and optimization of the AD process in a batch bioreactor. In this context, BioModel is enhanced by incorporating the influence of metal activities on chemical, biochemical, and physicochemical processes. Trace metal-related parameters are also included in the calibration of all model parameters. The model’s reliability is rigorously validated by comparing simulation results with experimental data. The study reveals that perturbations of 5% in model parameter values significantly increase the discrepancy between simulated and experimental results up to threefold. Additionally, the study highlights how precise optimization of metal additives can enhance both the quantity and quality of biogas production. The optimal concentrations of trace metals increased biogas and CH4 production by 5.4% and 13.5%, respectively, while H2, H2S, and NH3 decreased by 28.2%, 43.6%, and 42.5%, respectively. Full article
(This article belongs to the Special Issue Anaerobic Digestion Advances in Biomass and Waste Treatment)
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Review

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23 pages, 1249 KB  
Review
Guiding Microbial Crossroads: Syngas-Driven Valorisation of Anaerobic-Digestion Intermediates into Bio-Hydrogen and Volatile Fatty Acids
by Alvaro dos Santos Neto and Mohammad J. Taherzadeh
Bioengineering 2025, 12(8), 816; https://doi.org/10.3390/bioengineering12080816 - 29 Jul 2025
Cited by 1 | Viewed by 1364
Abstract
Anaerobic digestion (AD) has long been valued for producing a biogas–digestate pair, yet its profitability is tightening. Next-generation AD biorefineries now position syngas both as a supplementary feedstock and as a springboard to capture high-value intermediates, hydrogen (H2) and volatile fatty [...] Read more.
Anaerobic digestion (AD) has long been valued for producing a biogas–digestate pair, yet its profitability is tightening. Next-generation AD biorefineries now position syngas both as a supplementary feedstock and as a springboard to capture high-value intermediates, hydrogen (H2) and volatile fatty acids (VFA). This review dissects how complex natural consortia “decide” between hydrogenogenesis and acetogenesis when CO, H2, and CO2 co-exist in the feedstocks, bridging molecular mechanisms with process-scale levers. The map of the bioenergetic contest between the biological water–gas shift reaction and Wood–Ljungdahl pathways is discussed, revealing how electron flow, thermodynamic thresholds, and enzyme inhibition dictate microbial “decision”. Kinetic evidence from pure and mixed cultures is integrated with practical operating factors (gas composition and pressure, pH–temperature spectrum, culture media composition, hydraulic retention time, and cell density), which can bias consortia toward the desired product. Full article
(This article belongs to the Special Issue Anaerobic Digestion Advances in Biomass and Waste Treatment)
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