Part One: The Effect of Immigration on Microbial Community Dynamics in Full-Scale Anaerobic Digester Systems A six-year investigation into twent...
Published on by Hossein Ataei Far, Deputy Manager of the Research, Technology Development, and Industry Relations Center at NWWEC
🌍Abstract:
Anaerobic digestion ♻️ is widely used for treating organic waste in wastewater treatment plants, with significant potential for optimizing operations through a deeper understanding of the underlying microbiology 🧬. This study investigates microbial communities in 32 full-scale anaerobic digesters in Denmark over six years, utilizing 16S rRNA gene amplicon sequencing 🔬. Our findings reveal that several abundant populations within these systems are likely inactive 💤 and introduced via influent sludge. This suggests that failing to account for immigration can lead to inaccurate assessments 🚫 of the microbial communities actively growing within the digesters. Additionally, the study highlights the limitations of existing taxonomies 🧩, as several abundant OTUs could not be classified at the genus level, prompting updates to the MiDAS taxonomy 🗂️. The results demonstrate that individual digester communities are remarkably similar, with 300 OTUs comprising 80% of the total reads across all plants 🌱, and 15% identified as non-growing, possibly inactive immigrants 🚶. These insights pave the way for targeted characterization 🎯 of crucial organisms in anaerobic digestion, enhancing our understanding of the process.
🌍Introduction:
Biogas production ⚡ through the anaerobic digestion of organic waste is gaining popularity as a renewable energy source 🌞, driven by the need for clean energy and the potential for wastewater treatment plants to become net energy producers. Methane production, facilitated by tightly coupled microbial activities, is the primary outcome of this process. Despite its robustness, anaerobic digestion can face operational challenges such as foaming 🌊 and efficiency drops 📉. Understanding the microbiology underlying these processes is key to optimizing them 🧠.
Identifying active and abundant microorganisms 🔍 and linking them to their functional roles is crucial for understanding anaerobic digester ecology 🌱. Previous 16S rRNA gene amplicon studies have identified a set of microorganisms consistently present in similar digesters over time ⏳. However, a significant portion of the microbial community observed in anaerobic digesters may originate from dead or inactive cells ❌ introduced with the influent biomass. This can distort the correlation between microbial community dynamics and process performance, leading to false conclusions 🚫.
🌍Study Scope:
This study represents the most comprehensive survey of full-scale anaerobic digester systems to date, encompassing 32 Danish reactors at 20 wastewater treatment plants over six years 🗓️. The reactors included both mesophilic (~37°C) 🌡️ and thermophilic (~55°C) processes, with varying operational parameters such as ammonium levels, acetate concentrations, and sludge retention times.
🌍Results:
1. Archaea Community Structure:
📝 The archaeal community 🧬 was dominated by the phylum Euryarchaeota, with mesophilic reactors primarily featuring the acetoclastic genus Methanosaeta 🔬, while thermophilic reactors were dominated by the hydrogenotrophic genus Methanothermobacter 💥.
📝 Diversity was lower in thermophilic reactors compared to mesophilic ones.
2. Bacteria Community Structure:
📝 The bacterial community showed distinct clustering 🧩 between thermophilic and mesophilic reactors, with additional differentiation observed in reactors with thermal hydrolysis pre-treatment 🛠️.
📝 Dominant phyla included Firmicutes, Proteobacteria, Actinobacteria, Bacteroidetes, and Chloroflexi 🌿, with notable differences in microbial composition based on reactor conditions.
3. Immigration Effects on Community Composition:
📝 Analysis of primary and surplus sludge revealed distinct microbial communities 🦠 in the feedstock compared to the digesters, indicating that several genera do not grow in mesophilic digesters but are introduced with the feed 🛢️.
🌍Conclusion:
This study identifies the abundant and growing organisms 🌍 in full-scale anaerobic digesters and provides an updated taxonomy 📚 for more accurate classification. By acknowledging the role of immigration 🚶♀️ and the limitations of current taxonomic databases, it lays the groundwork for improving our understanding 🧠 and optimization of anaerobic digestion processes.
Reference:
[1] Rasmus H. Kirkegaard et al., (2017), "The impact of immigration on microbial community composition in full-scale anaerobic digesters."
Figure 1. Principal component analysis of the microbial communities in ADs, highlighting samples by process type (mesophilic, thermophilic, mesophilic with thermal hydrolysis pretreatment (THP)). (A) The separation of archaeal communities colored by process type, (B) The separation of bacterial communities colored by process type, (C) The bacterial communities of mesophilic plants colored and labeled by plant location, (D) The bacterial communities of thermophilic plants colored and labeled by plant location.