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Open research questions in Anaerobic Digestion and Biogas Production

25 unresolved questions extracted from the limitations and future-work sections of 516 Anaerobic Digestion and Biogas Production papers in our library. Each links back to the study that raised it.

What the literature leaves open

  • Metagenomes represent a useful source for identification of novel and potentially important lineages within, for example, full industrial AD reactor systems. Even though metagenomic analyses are limited to only reveal potential metabolic pathways without possibility to conclude on actual functions within a community as a whole, they form a basis for follow-up studies focusing in detail on novel identified lineages and their potential role and interdependencies within a system. This is evident from the exploratory nature of this study where still multiple new families and genera were identified that are worth of further investigation regarding their potential as syntrophic fatty acid oxidizers. MAGs with incomplete pathways and/or low-identity homologs, as were found for multiple novel groups, should not be excluded for future research. First, because those MAGs are incomplete and the missing genes can still be present in the part of the genome that was not recovered. Second, homologs with lower similarity likely represent genes that are more distantly related to the genes of the known syntrophic taxa. Last, it is possible that a gene performing a similar function is simply not yet identified. A high fraction of homologs   identified in a pathway could still infer a potential role in AD involving syntrophic VFA oxidation, especially for MAGs in which multiple SGA protein domains were identified.  Journals (/journals) In this study, we also increased the knowledge of potentially important lineages present in granular AD sludges. The microbial diversity present in anaerobic microbial granules  Books (/booksbrowse)  ®  deserves more focus in future studies as many groups identified here from granular sludges are not yet cultivated. Cultivation approaches can focus on physical separation between individual cells and their environments, e.g.

    Uncovering syntrophic potential from genome-resolved metagenomics of suspended and granular AD sludges · 2026 · DOI

  • Different feedstocks exhibit unique characteristics, such as varying organic matter content, nutrient profiles, and inhibitory compounds, which can affect the accuracy and applicability of kinetic models. Based on model assumptions, it is noteworthy that kinetic models rely on simplifying assumptions, such as uniform microbial populations and ideal mixing conditions, which may not accurately represent real-world anaerobic digestion systems. Accurate estimation of kinetic parameters requires high-quality experimental data, which can be challenging to obtain, particularly for complex feedstocks or co-digestion systems. During the review, findings may not directly translate to industrial-scale anaerobic digestion systems, where factors such as temperature fluctuations, pH variations, and equipment design can impact process performance. Furthermore, the study did not account for all potential inhibitory factors, such as toxic compounds, heavy metals or excessive ammonia production, which can impact microbial activity and process stability. Having established this, the choice of kinetic model can significantly affect prediction accuracy, and different models may be more suitable for specific feedstocks or process conditions. Finally, the quality and reliability of the experimental data used for model calibration and validation can significantly impact the accuracy of kinetic model predictions, which is also a limitation of the study. Addressing these limitations and challenges, kinetic modelling becomes an even more effective tool for optimizing anaerobic digestion systems and promoting the widespread adoption of biogas production technologies.

    Kinetic Modelling of Anaerobic Digestion of Biogas Production from Different Wastes: A Review · 2026 · DOI

  • However, further studies are needed, including low-temper- ature BMP assays, controlled anaerobic bioaugmentation experiments, the use of different culture media to better reproduce the Antarctic environment, sequencing of other soil samples, and functional metagenomics to address the limitations of this study.

    Biogas production using the microbial community present in the soil from Deception Island, maritime Antarctica · 2026 · DOI

  • Water binding dynamics and thermal activity during the 20-day anaerobic digestion process were mentioned in relation to dry matter changes, but actual temperature profiles, moisture retention curves, and their correlation with biogas production kinetics were not provided for the poultry-livestock waste system.

    Biogas Production Efficiency and Slurry Fertilizer Quality Using Poultry and Livestock Organic Waste Under Anaerobic Composting · 2026 · DOI

  • The mixed treatment of poultry manure and livestock dung is hypothesized to balance reactivity and structural fiber content for stable digestion, but the optimal mixing ratio and its effect on methane yield, digestion stability (volatile fatty acid accumulation), and final digestate nutrient composition were not experimentally defined.

    Biogas Production Efficiency and Slurry Fertilizer Quality Using Poultry and Livestock Organic Waste Under Anaerobic Composting · 2026 · DOI

  • The study confirmed absence of pathogenic bacteria in the final digestate but did not specify which pathogens were tested (e.g., Salmonella, E. coli, Clostridium perfringens, enteroviruses) or provide quantitative log-reduction values, limiting validation of the digestate's safety for use as poultry and fish feed ingredient as recommended.

    Biogas Production Efficiency and Slurry Fertilizer Quality Using Poultry and Livestock Organic Waste Under Anaerobic Composting · 2026 · DOI

  • The paper states that lipid-containing wastes (higher in livestock dung) generate more methane per gram than carbohydrates, but this was not experimentally validated in the current mixed-waste system; comparative biogas yield data for lipid-rich versus carbohydrate-rich substrate fractions under identical digestion conditions is absent.

    Biogas Production Efficiency and Slurry Fertilizer Quality Using Poultry and Livestock Organic Waste Under Anaerobic Composting · 2026 · DOI

  • The recommendation to test 'different bacteria as inoculum' for biogas production is mentioned without specifying which microbial consortia, methanogenic communities, or specific bacterial strains should be evaluated, nor does it define the selection criteria (e.g., tolerance to lipid content, performance with lignocellulosic fiber degradation) relevant to poultry and livestock waste digestion.

    Biogas Production Efficiency and Slurry Fertilizer Quality Using Poultry and Livestock Organic Waste Under Anaerobic Composting · 2026 · DOI

  • The paper documents nitrogen depletion during anaerobic composting through microbial mineralization and deamination, but lacks quantitative tracking of nitrogen fate distribution—specifically the relative proportions of ammonia volatilization, nitrate formation, and incorporation into microbial biomass during the 20-day digestion period for the poultry-livestock mixed waste system.

    Biogas Production Efficiency and Slurry Fertilizer Quality Using Poultry and Livestock Organic Waste Under Anaerobic Composting · 2026 · DOI

  • The study achieved a 20-day biogas production cycle using poultry manure and livestock dung mixtures, but the recommendations mention investigating 'higher levels of biogas process' without specifying what operational parameters (temperature range, pH buffering capacity, retention time variations, or reactor scale) should be tested to optimize methane yield beyond the current findings.

    Biogas Production Efficiency and Slurry Fertilizer Quality Using Poultry and Livestock Organic Waste Under Anaerobic Composting · 2026 · DOI

  • The data presented in Table 3 includes only 21 organic compounds; the generalizability of the derived correlations to a broader range of complex organic matter compositions requires testing with additional diverse substrates.

    Integration of Mathematical Framework and Thermochemical Equation for Counting Heat of Anaerobic Digestion, Heat of Bioredox, and Heat of Biohydrolysis · 2026 · DOI

  • The study is limited to organic molecules with regular oxidation numbers (ONH = +1, ONO = −2, ONX = −1, ONN = −3, ONS = −2, and ONP = +5); applicability to molecules with irregular or variable oxidation states is not addressed.

    Integration of Mathematical Framework and Thermochemical Equation for Counting Heat of Anaerobic Digestion, Heat of Bioredox, and Heat of Biohydrolysis · 2026 · DOI

  • The correlations between SC of BEq and ∆Ho biohydrolysis-AD show moderate R² values (0.617 for nH2O and 0.6612 for nCH4), indicating that these relationships explain only 61-66% of the variance, leaving substantial unexplained variation.

    Integration of Mathematical Framework and Thermochemical Equation for Counting Heat of Anaerobic Digestion, Heat of Bioredox, and Heat of Biohydrolysis · 2026 · DOI

  • To address these gaps in the literature, this review examines the factors mentioned above, focusing on the drawbacks of waste‐to‐energy conversion and proposing solutions targeted at governments, policymakers, investors, entrepreneurs, and researchers seeking to understand and mitigate the challenges in this sector.

    From refuse to resource: exploring technological and economic dimensions of waste‐to‐energy · 2025 · DOI

  • This result suggests that further study of metabolic patterns of PNSB presented with various carbon sources may prove useful in exploring the viabil­ity of single-stage conversion of waste sugars into biohydrogen fuel.

    <b>A Metabolic Study of Biohydrogen-Producing Photosynthetic Bacteria:</b>The Effects on Growth Rates of Rhodobacter capsulatus JP91 Hup- and Rhodopseudomonas palustris when Acetate is replaced by Glucose as the Primary Carbon Source · 2014 · DOI

  • Knowledge about mixing in biogas digesters is still insufficient, so the objective of this study was to fill the information gaps in the literature by determining the minimal retention time of substrates fed into anaerobic digesters and to describe substrate distribution and washing out rates from investigated digesters.

    Determination of mixing quality in biogas plant digesters using tracer tests and computational fluid dynamics · 2013 · DOI

  • Research limitations/implications: The basic structure of the laboratory device is welded from stainless steel (inox) and is limited by the following dimensions: 2500 mm length, 1000 mm height and 350 mm width.

    Analysis of different substrates for processing into biogas · 2009

  • Using molasses as feedstock, the research demonstrates effectiveness across reactors with varied hydraulic retention times at lab scale, indicating potential for further investigation into scalability and automation.

    Automated real-time feeding control for microbial electrolysis cell-anaerobic digestion systems using finite state machine · 2026 · DOI

  • The paper does not discuss how the mathematical framework scales to industrial anaerobic digestion systems with multiple substrates, mixed microbial communities, and varying operational conditions.

    Integration of Mathematical Framework and Thermochemical Equation for Counting Heat of Anaerobic Digestion, Heat of Bioredox, and Heat of Biohydrolysis · 2026 · DOI

  • Leachate augmentation with enzymes (prior to its recirculation) to enhance waste degradation and gas production in landfill bioreactors is a relatively new concept and very little is known about its applicability.

    Enhancing Gas Production in Landfill Bioreactors: Flow-Through Column Study on Leachate Augmentation with Enzyme · 2012 · DOI

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25 open questions have been extracted from the limitations and future-work passages of 516 Anaerobic Digestion and Biogas Production papers in our library. Each one below links back to the study that raised it, so you can read the original claim in context.

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