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Anaerobic Digestion Advances in Biomass and Waste Treatment

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

Deadline for manuscript submissions: 30 June 2026 | Viewed by 13084

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Special Issue Editors

Dr. Tina Kegl

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Guest Editor

Materials Research Laboratory, University of Nova Gorica, Vipavska 11c, 5270 Ajdovščina, 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

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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

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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 (9 papers)

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Research

Jump to: Review

18 pages, 2193 KB

Open AccessArticle

Impact of Ball-Milling and Thermal Hydrolysis on Physicochemical Properties and Anaerobic Digestion Kinetics of Mixed Slaughterhouse and Agricultural Wastes

by Sang Heon Lee, Oh Hyun Gweon, Hye Sun Lee, Byoung Seung Jeon, Youngwook Go, Chang Sook Jin, Youngseob Yu, Byoung-In Sang and Jin Hyung Lee

Bioengineering 2026, 13(3), 326; https://doi.org/10.3390/bioengineering13030326 - 11 Mar 2026

Viewed by 456

Abstract

Slaughterhouse by-products are promising feedstocks for anaerobic digestion due to their high lipid and protein content. However, their complex structures often limit hydrolysis, and excessive pretreatment can induce inhibitory conditions. This study evaluates the effects of ball-milling (BM), ball-milling with water (BM + water), and combined thermal hydrolysis and ball-milling (THP + BM) on the digestion performance of a mixed substrate of slaughterhouse and agricultural wastes. The results demonstrate that all BM-based pretreatments significantly improved digestion kinetics, reducing the lag phase by 26–66% and shortening the T₅₀ values by approximately 40% compared to the untreated substrate. While no statistically significant differences were observed in the ultimate methane yield, the onset of methanogenesis was markedly accelerated in the BM and BM + water treatments. In contrast, despite achieving superior solubilization, the THP + BM treatment failed to provide proportional kinetic enhancements. This was attributed to a severe initial metabolic imbalance—characterized by a pH drop below the inhibitory threshold (6.33)—which induced physiological stress and delayed the functional recovery of methanogens. These findings indicate that while ball-milling effectively facilitates digestion initiation by enhancing physical accessibility, the intensity of combined thermal-mechanical processes must be strategically optimized. For high-strength organic biomass, managing pretreatment severity is crucial to prevent initial acid stress and maximize process efficiency. Full article

(This article belongs to the Special Issue Anaerobic Digestion Advances in Biomass and Waste Treatment)

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18 pages, 6660 KB

Open AccessArticle

Biomethane Conversion of Hemicellulose: Biomethane Production, Kinetic Analysis, Substance Conversion, and Microbial Community Dynamics

by Xiteng Chen, Hairong Yuan and Xiujin Li

Bioengineering 2026, 13(3), 295; https://doi.org/10.3390/bioengineering13030295 - 2 Mar 2026

Viewed by 521

Abstract

As a key constituent of lignocellulosic biomass, the role of hemicellulose in anaerobic digestion (AD) remains inadequately characterized, particularly regarding its methane potential and degradation process patterns. This study systematically characterized the AD performance of hemicellulose using xylan as a representative substrate. The results showed that xylan achieved a high methane potential of 350–390 mL/g VS and 89.57% biodegradability, exhibiting a shorter lag phase (λ) and higher reaction rate (k) than other biomass fractions. Substantial acetic acid and ethanol accumulated within the first 24 h, while late-stage dissolved organic matter (DOM) shifted toward complex lignin/CRAM-like. The results of microbial dynamics indicated that the collaborative interaction among Anaerobium, Lactobacillus, and Clostridium accelerated xylan transformation. While methanogenesis was predominantly driven by the acetoclastic route (specifically Methanosarcina), hydrogenotrophic Methanobacterium thrived during temporary pH fluctuations. This work serves as a valuable guide for developing high-performance strategies in industrial lignocellulosic biogas plants. Full article

(This article belongs to the Special Issue Anaerobic Digestion Advances in Biomass and Waste Treatment)

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22 pages, 1379 KB

Open AccessArticle

The Energy Potential, Environmental Impact, and Occupational Health and Safety Potential of Biogas Obtained from Filter Cake in Artisanal Panela Production

by Reni Danilo Vinocunga-Pillajo, Estela Guardado Yordi, Josselyn Pico Poma, Leidy Pico Poma, Diego Sarabia Guevara, Karel Diéguez-Santana and Amaury Pérez Martínez

Bioengineering 2026, 13(2), 182; https://doi.org/10.3390/bioengineering13020182 - 4 Feb 2026

Viewed by 750

Abstract

Filter cake (or cachaza), a residue generated in the artisanal production of panela, represents an under-explored source of renewable energy in the Ecuadorian Amazon. Valorizing filter cake could reduce the use of solid biomass and emissions associated with traditional combustion. Our objective was to determine the energy potential of the biogas obtained and its contribution to the sustainability of the panela (unrefined cane sugar) production system. A sequential procedure was applied that included the physicochemical characterization of filter cake, feed flow modeling, and stoichiometric simulation under mesophilic conditions. The anaerobic digestion of filter cake with the optimal Composition 6 generated up to 1736.40 m³·day⁻¹ of biogas with 40.7% methane and a calorific value of 14,350 kJ·m⁻³. This was enough to replace 1.24 t·day⁻¹ of wood or 2.38 t·day⁻¹ of bagasse in the production system. This represents an annual saving of 631.08 t of solid biomass, equivalent to conserving 3.63 ha·year⁻¹ of the Amazon rainforest. The Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) analysis showed impacts on climate change (17.40 kg CO₂ eq/m³) and acidification (0.00516 kg SO₂ eq/m³), attributable to unburned methane and residual H₂S. Meanwhile, the social assessment using the Occupational Health and Safety Potential (OHSP) indicator showed high risks in terms of handling filter cake and cleaning the digestate. Full article

(This article belongs to the Special Issue Anaerobic Digestion Advances in Biomass and Waste Treatment)

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22 pages, 1464 KB

Open AccessArticle

Optimal Recycling Ratio of Biodried Product at 12% Enhances Digestate Valorization: Synergistic Acceleration of Drying Kinetics, Nutrient Enrichment, and Energy Recovery

by Xiandong Hou, Hangxi Liao, Bingyan Wu, Nan An, Yuanyuan Zhang and Yangyang Li

Bioengineering 2026, 13(1), 109; https://doi.org/10.3390/bioengineering13010109 - 16 Jan 2026

Viewed by 672

Abstract

Rapid urbanization in China has driven annual food waste production to 130 million tons, posing severe environmental challenges for anaerobic digestate management. To resolve trade-offs among drying efficiency, resource recovery (fertilizer/fuel), and carbon neutrality by optimizing the biodried product (BDP) recycling ratio (0–15%), six BDP treatments were tested in 60 L bioreactors. Metrics included drying kinetics, product properties, and environmental–economic trade-offs. The results showed that 12% BDP achieved a peak temperature integral (514.13 °C·d), an optimal biodrying index (3.67), and shortened the cycle to 12 days. Furthermore, 12% BDP yielded total nutrients (N + P₂O₅ + K₂O) of 4.19%, meeting the NY 525-2021 standard in China, while ≤3% BDP maximized fuel suitability with LHV > 5000 kJ·kg⁻¹, compliant with CEN/TC 343 RDF standards. BDP recycling reduced global warming potential by 27.3% and eliminated leachate generation, mitigating groundwater contamination risks. The RDF pathway (12% BDP) achieved the highest NPV (USD 716,725), whereas organic fertilizer required farmland subsidies (28.57/ton) to offset its low market value. A 12% BDP recycling ratio optimally balances technical feasibility, environmental safety, and economic returns, offering a closed-loop solution for global food waste valorization. Full article

(This article belongs to the Special Issue Anaerobic Digestion Advances in Biomass and Waste Treatment)

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13 pages, 1611 KB

Open AccessArticle

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

Cited by 1 | Viewed by 832

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 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

Open AccessArticle

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

Cited by 1 | Viewed by 1307

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 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

Open AccessEditor’s ChoiceArticle

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 1907

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 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

Open AccessArticle

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 2258

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 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

Open AccessReview

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 2 | Viewed by 1997

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 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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