Changes in the remaining concentrations of soluble COD (A), total VFA (B), acetic acid (C) and propionic acid (D) in the reactors, the community structure in each reactor changes --- 47 Figure Changes in the total methanogenic population (A) and absolute ( B) and relative (C) abundance of each methanogen group --- 59 Figure Changes in residual concentrations of total volatile fatty acids (A), acetic acid (B) and propionic acid (C) in reactors.
Changes in concentrations of volatile suspended solids and solid suspended solids in the reactors (VSS, volatile suspended solids; FSS, solid suspended solids). Cluster dendrograms generated from the OTU distribution in the archaeal 16S rRNA gene (A) and 16S rRNA (B) libraries and the bacterial 16S rRNA gene (C) and 16S rRNA (D) libraries --- 78. Relative abundance to representative interspecies electron transfer associated bacteria in the 16S rRNA gene and 16S rRNA libraries for each reactor --- 79.
Residual concentration profiles of total volatile fatty acids (A), acetic acid (B) and propionic acid (C). Cluster dendrograms and non-metric multidimensional scales (NMS) based on the distribution of operational taxonomic units (OTUs) of archaea (A) and bacteria (B) in 16S rRNA gene libraries.
INTRODUCTION
Indirect interspecies electron transfer (IIET) via hydrogen and formate as electron carriers is known as an important route for electron exchange between syntrophic microorganisms. Although most studies focus on IHT in syntrophic methanogenesis, IFT can sometimes function as an important electron transfer pathway. Furthermore, a recent study revealed that DIET showed even higher external electron transfer rates than hydrogen-based IET and e/cell pair(s) for DIET and IHT, respectively [25].
Extracellular electron transfer is thought to occur via three different mechanisms: (1) a soluble redox shuttle, (2) direct contact between an electron acceptor and a redox-active protein on the surface of the outer membrane, or (3) conducting filamentous structures [26]. Biological NUTRITION includes the second and third mechanisms in the form of cell-to-cell electron transfer via biological components such as c-type cytochromes and conducting pili. Cytochrome c-type is essential for the electron transfer mechanism of microbial species by oxidation and reduction.
Conducting pili are protein filaments produced by microorganisms for long-range electron transfer under appropriate conditions [ 33 ]. Through pili, longer-range electron transfer can occur without a direct contact mechanism to insoluble minerals, solid electrodes, other microorganisms, and even electrically conductive biofilms [ 34 ].
LITERATURE REVIEW
DGGE and further phylogenetic analyzes were performed to characterize the archaeal and bacterial community structures in the tested reactors. The archaeal and bacterial DGGE gel images were each converted into an intensity matrix based on the relative contribution of individual bands to the total band intensity (i.e. the sum of the intensities of all bands) in each. 4-2 shows the changes in the residual concentrations of sCOD and VFAs in RC and RM.
Changes in the residual concentrations of soluble COD (A), total VFA (B), acetic acid (C) and propionic acid (D) in the reactor community structure change in each reactor. Notably, on the NMS graph, the largest jump between two consecutive points (ie, the most significant change) was observed between days 181 and 216 in RC and between days 62 and 149 in RM. Changes in methanogen community composition in experimental reactors were analyzed based on the abundance of the 16S rRNA gene of methanogen target groups.
Changes in the total methanogen population (A) and the absolute (B) and relative (C) abundance of each methanogen group analyzed based on the quantification results of the 16S rRNA gene. A sudden increase in residual sCOD concentration was observed at RC after four working volume changes (Fig. 5-3). Recycling magnetite also requires the active biomass involved in the aggregate structures to be recovered and recycled to the reactor.
Samples were taken before the completion of magnetite addition to the RC (day 192) and at the end of the experiment (day 317) to assess the impact of magnetite on the microbial communities in the reactors. These aspects indicate that magnetite is likely to have a significant effect on the development of methanogenic community structure in experimental reactors. The bacterial community structure was much more diverse than the archaeal community structure in the analyzed biomass samples (Fig. 5-9B).
They were also responsible for the majority in the 16S rRNA libraries of the reactor samples (>82.0%). Archaeal and bacterial cluster dendrograms constructed based on the OTU distribution in the 16S rRNA gene and 16S rRNA libraries are shown in Fig. As evident in the phylum distribution (Figs. 5-9), the DNA- and RNA-based analyzes produced different clustering patterns for both archaeal and bacterial communities.
Cluster dendrograms generated based on the OTU distribution in the archaeal 16S rRNA gene (A) and 16S rRNA (B) libraries and the bacterial 16S rRNA gene (C) and 16S rRNA (D) libraries. Given that Methanosaetaceae was the most metabolically active methanogenic group when magnetite was available (Figs. 5–9), reactor microbial communities could develop an electrical syntrophy in the presence of magnetite. Taxonomic distribution of archaeal (A) and bacterial (B) sequences in the 16S rRNA gene libraries in the digester biomass samples.
One interesting point to note is that changes in the relative abundance of Parabacteroides were associated with the presence of magnetite particles, regardless of voltage application (Fig. 6-9D).
CONCLUSION
Effects of mixing on methane production during thermophilic anaerobic digestion of manure: laboratory-scale and pilot-scale studies. Control of interspecies electron flow during anaerobic digestion: significance of formate transfer versus hydrogen transfer during syntrophic methanogenesis in flocs. A new model for electron flow during anaerobic digestion: direct interspecies electron transfer to Methanosaeta for the reduction of carbon dioxide to methane.
Electroconductive pili of Geobacter species are a recently evolved feature for extracellular electron transfer. Quantitative and qualitative transitions of methanogen community structure during batch anaerobic digestion of cheese processing wastewater. Biostimulation of anaerobic digestion with (semiconductor) iron oxides: their potential for enhanced biomethanation.
Long-term study on the effect of magnetite addition in continuous anaerobic digestion of dairy sewage - Improvement of process efficiency and stability. Application of new magnetic foam glass particles in anaerobic digestion of sugar beet silage. Potential enhancement of direct interspecies electron transfer for syntrophic metabolism of propionate and butyrate by biochar in upflow anaerobic blanket reactors.
Enhanced methane production in an anaerobic digestion and microbial electrolysis cell-coupled system with co-cultivation of Geobacter and Methanosarcina. Potential for direct interspecies electron transfer in an electro-anaerobic system to increase methane production from sludge digestion. Enhancing biomethane yield and production rate with graphene: The potential of direct interspecies electron transfer in anaerobic digestion.
Bioelectrochemical reduction of CO2 to CH4 via direct and indirect extracellular electron transfer by a hydrogenophilic methanogenic culture. Effects of applied voltage on direct interspecies electron transfer through conducting materials for methane production. Metatranscriptomic evidence for direct interspecific electron transfer between Geobacter and Methanothrix species in methanogenic rice paddy soils.
