Relative abundance of Deltaproteobacteria sequences in the 16S rRNA gene and 16S rRNA libraries RM, RC (A), RM1 and RM2 (B). Relative abundance of archaeal sequences in the 16S rRNA gene and 16S rRNA libraries for RM, RC (A), RM1 and RM2 (B).
INTRODUCTION
Anaerobic digestion (AD) of Ulva
- Potential of Ulva as AD feedstock
- Challenges of Ulva AD
3. al., 2016). Unwanted blooms of Ulva species can lead to serious coastal pollution and public hygiene problems. AD of Ulva biomass has been carried out in a number of studies, with most studies focused on testing methane potential.
Hydrogen sulfide production
- Significance of sulfide control in AD
- Conventional sulfide removal technology
Oxidation of sulfide with oxidants such as hydrogen peroxide, chlorine, and metal salts is also another example of a chemical sulfide removal method (Murugananthan et al., 2004). Due to the high affinity of SOB for H2S, much higher sulfide removal efficiency than chemical methods can be expected (Kobayashi et al., 1983).
Potential effect of conductive material on sulfidogenesis
- Direct interspecies electron transfer (DIET)
- Potential effect of DIET in sulfur-rich AD
For example, the syntrophic propionate oxidation via DIET is a more thermodynamically favorable reaction than the propionate oxidation via IET (Table 1-4) (Jing et al., 2017). Furthermore, a recent paper reported a significantly higher extracellular electron transfer rate (per cell) from DIET than from IET via hydrogen ( Storck et al., 2016 ).
Objectives of the dissertation
Introduction
STUDY 1] Investigating the potential of Ulva biomass in monodigestion with different reactor configurations. SBRs compared to conventional CSTRs, it is debatable whether sequence array operation would have a beneficial effect on AD of Ulva biomass.
Materials & methods
- Substrate preparation and inoculum
- Bioreactor operation
- Batch operation
- Repeated batch operation
- Continuous stirred tank reactor versus sequencing batch reactor operation
- Analytical methods
- Physicochemical analyses
- DNA extraction
- Denaturing gradient gel electrophoresis (DGGE)
- Real-time polymerase chain reaction (PCR)
- High-resolution melting (HRM) analysis
- Statistical analyses of microbial community data
PCR amplification and HRM analysis of aprA and dsrA were performed on the QuantStudio 12K Flex system as previously described (Kim & Lee, 2014). A matrix was constructed for aprA and dsrA based on the HRM peak profiles as described (Kim & Lee, 2014), with minor modifications.
Results & discussion
- Batch operation
- Repeated batch operation
- Continuous stirred tank reactor versus sequencing batch reactor operation
These findings indicate that the overall reaction rate increased with cycles, consistent with the general understanding that reaction rate generally increases over the early cycles (i.e. acclimation period) in SBR processes (Wilderer et al., 2001). However, methane yield per COD fed to the SBR (CODfed) decreased dramatically from the first to the third cycle (0.15 L/g COD fed to C1 and 0.08 L/g COD fed to C3) and remained low until the last cycle (0.07 L/) g COD fed into C5), while the methane content in biogas remained fairly constant, in the range of throughout the five consecutive batch cycles. In addition, methane productivity is directly correlated with the amount of other trace elements (e.g. Fe, Cu, Ni and Zn), but not with that of cobalt (Zandvoort et al., 2006; Zhang et al., 2003).
USB7, which showed high similarity to Solitalea canadensis, showed significantly higher band intensity in the later cycles, when methanogenesis activity significantly deteriorated compared to the initial level. This metabolic transition is thought to be due to the emergence and prevalence of SRBs, leading to increased consumption of the organic substrates for sulfate reduction, rather than methane production, in the later cycles (see following discussion). The initial COD removal (CODr) was much faster in Rs than in Rc during start-up, presumably due to the different operating modes (i.e. higher biomass retention in Rs) (Fig. 2-5).
Both genes showed significantly higher concentrations in the SM than in the CM and SE samples, suggesting that SRBs were present in much greater abundance in Rs than in Rc due to the improved biomass retention by sequencing batch operation .
Summary
Introduction
Another possibility could be regional and seasonal variations in the characteristics of the Ulva biomass used for experiments (Brown et al., 1999). It is worth noting that the H2S content was significantly lower v/v) in the co-digestion phases (data not shown). This suggests that the mixing ratio between Ulva and whey (i.e., substrate composition) seriously affected the evolution of the bacterial community structure in the experimental reactors.
These further support that the characteristics of the initial substrate had a decisive effect on the development of a microbial community structure in the experimental reactors and thus the performance of the reactors. The formation of SO in the presence of magnetite was further supported by fluorescence-probing image (Fig. 4-4). Relative abundance of bacterial sequences in the 16S rRNA gene and 16S rRNA libraries for RM, RC (A), RM1 and RM2 (B).
Such increases in hydrogenotrophic methanogens (i.e., Methanobacteriales and Methanombiotices) in the presence of magnetite have been recently reported (Baek et al., 2016; Li et al., 2015). Furthermore, the electrical syntrophy, which linked the oxidation of sulfide to S0 to the reduction of CO2 to CH4, was found to be feasible in the presence of magnetite. Clarification of electron transfer and metagenomic analysis of the microbial community in the methane production process with the addition of ferrous ferric oxide.
Materials & methods
- Substrate and inoculum
- Reactor operation
- Microbial analysis
- Statistical analysis
- Physicochemical analyses
Results & discussion
- Reactor performance
- Effects of co-digestion
- Microbial community analyses
- Changes in bacterial community structure
Summary
The anaerobic co-digestion of Ulva and cheese whey was investigated at different substrate mixing ratios in two CSTRs, where the proportion of Ulva was increased or decreased. Nutritional and/or acclimatization strategies during start-up can significantly influence the development of the microbial community and thus the process characteristics. Methanosaeta-related populations were the main methanogens responsible for methane production, regardless of the different substrate mixing ratios in both reactors.
Both experimental reactors showed that co-digestion with whey proved beneficial for the biomethanation of Ulva, with methane yields being up to 1.6 times greater in the co-fermentation phases than in the mono-fermentation phases of Ulva. Taking into account the methane recovery along with the Ulva treatment capacity, it is suggested that the optimal fraction of Ulva in the substrate mixture is 50-75% for efficient co-digestion.
Introduction
Materials and methods
- Inoculum and substrate
- Experimental design
- Bioreactor operation
- Batch experiment
- Analytical methods
- Physicochemical analysis
- Magnetite quantification
- Extracellular S 0 analysis
- Cyclic voltammetry (CV)
- Electron transport system (ETS) activity
- Scanning electron microscopy (SEM)
- Preparation of nucleic acids
- High-throughput sequencing
In the first experiment, two identical continuous stirred tank reactors (CSTRs), RM and RC, with working volumes of 1.5 L were operated. In the second experiment, two identical CSTRs, RM1 and RM2, with working volumes of 2 L were operated in duplicate. Both reactors were operated under the same conditions with RM and RC in the first experiment, except for magnetite addition.
To examine the reproducibility of the reactor performance that was observed in the first experiment, both RM1 and RM2 were continuously varied with magnetite at selected doses of 0, 8, and 20 mM Fe. The H2S content in the biogas was monitored using both a 7890A gas chromatograph (Agilent) equipped with a photometric flame detector and an HP-1 column (Agilent), as well as the gas detector tubing systems consisting of the intake pump of gas samples (GV-100S, GASTEC) and detector tubes (4H, GASTEC). CV cells for RM and RC solutions were supplemented with magnetite (8 mM Fe) and FeCl2 (2 mM Fe), respectively, to create the same conditions as in the reactors (i.e., Stage M5 and C2).
The sequences obtained in this study have been deposited in the NCBI Sequence Read Archive (SRA) under bioproject accession number (PRJNA579001).
Results and discussions
- Reactor performance: methanogenesis and sulfidogenesis
- Fate of sulfur
- Microbial community dynamics
- Role of magnetite in sulfide oxidation
- Possible sulfide oxidation mechanism
All observations in the magnetite-added reactors (i.e., RM, RM1, and RM2) indicated that magnetite changed the fate of sulfur as S0, which likely contributed to the decrease in H2S production in the presence of magnetite. This suggests that sulfate reduction by SRBs is likely necessary for the oxidation of sulfide to S0 in the presence of magnetite and deserves further investigation. In addition, the residual concentration of magnetite in RM1 and RM2 (Table 4-5) ruled out the possibility of magnetite dissolution in the reactors.
Methanotrichaceae accounted for 79.3% and 95.0% of the total archaeal sequences in the DNA and RNA libraries, respectively, at the magnetite dose of 20 mM Fe. Meanwhile, in both RM1 and RM2, the relative abundance of family Methanotrichaceae greatly decreased while that of order Methanobacteriales and Methanomicrobiales increased at the DNA level in the presence of magnetite (Fig. 4-9B). The effect of the addition of Fe compounds is particularly evident in the archaeal cluster dendrograms, especially the one on the rRNA libraries.
Cluster dendrograms constructed from the distribution of OTUs in bacterial (A) and archaeal (B) 16S rRNA gene libraries and in bacterial (C) and archaeal (D) 16S rRNA libraries obtained in RM and RC by high-throughput sequencing. Cluster dendrograms constructed from the distribution of OTUs in bacterial (A) and archaeal (B) 16S rRNA gene libraries and in bacterial (C) and archaeal (D) 16S rRNA libraries obtained in RM1 and RM2 by high-throughput sequencing. Although numerically small, the relative abundance of Geobacter, the best-known exoelectrogenic genus, was markedly greater in the presence of magnetite at both the DNA and RNA levels (Figure 4-12).
Summary
Although further research is required to elucidate the underlying mechanism, the present study proposes a new electrotrophic sytrophy via DIET between ASOBs and electrotrophic methanogens, and this sytrophy couples the oxidation of sulfide to S0 with the reduction of CO2 to CH4. Our observations reveal a novel pathway of anaerobic sulfur metabolism and suggest the possibility to control H2S production in situ by promoting DIET in sulfur-rich methanogenic environments. Furthermore, an interesting feature of magnetite-assisted in situ sulfide control is the accumulation of extracellular S0.
Given that extracellular S0 is strongly associated with microbial cells, which are aggregated with magnetite particles (Fig. 4-15), it is suggested that recovery of sulfur from S0-rich sludge, for example, via magnetic separation and physical pre-treatment. it is likely possible.
CONCLUSION
Conducting magnetite nanoparticles accelerate the microbial reductive dechlorination of trichloroethene by promoting interspecies electron transfer processes. Bioelectrochemical enhancement of direct electron transfer between species in upstream anaerobic reactor with wastewater recirculation for acid distillery wastewater. Potential for direct interspecies electron transfer in synergistic enhancement of methanogenesis and sulfate removal in an upstream anaerobic sludge blanket reactor with magnetite.
Potential direct interspecies electron transfer of methanogenesis to syntrophic metabolism under sulfate-reducing conditions with stainless steel. Improved efficiency of anaerobic digestion through direct interspecies electron transfer at mesophilic and thermophilic temperature ranges. A new model of electron flow during anaerobic digestion: direct interspecies electron transfer to Methanosaeta for the reduction of carbon dioxide to methane.
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