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Anaerobic degradation of volatile fatty acids in continuous biogas reactors at very short hydraulic retention times.

Weimer, Anna Lea Auguste LU (2019) KMBM01 20182
Applied Microbiology
Biotechnology
Abstract
There is an increasing demand for safe, affordable and above allsustainable energy, due to the exhaustion of fossil fuels and increasing greenhousegas emissions. In this context, anaerobic digestion is of growing interest, as it enablesthe production of the versatile renewable energy source biogas from various types oforganic wastes. Though, in order to establish more efficient process policies, a deepunderstanding of the microbiology underlying this process is necessary.This master thesis project focused on the rate limiting steps of anaerobic digestion,acetogenesis and methanogenesis. Therefore, three lab-scale, continuous stirred tankreactors R1 (control) R2, R3 were fed with a synthetic medium, which contained thevolatile fatty acids,... (More)
There is an increasing demand for safe, affordable and above allsustainable energy, due to the exhaustion of fossil fuels and increasing greenhousegas emissions. In this context, anaerobic digestion is of growing interest, as it enablesthe production of the versatile renewable energy source biogas from various types oforganic wastes. Though, in order to establish more efficient process policies, a deepunderstanding of the microbiology underlying this process is necessary.This master thesis project focused on the rate limiting steps of anaerobic digestion,acetogenesis and methanogenesis. Therefore, three lab-scale, continuous stirred tankreactors R1 (control) R2, R3 were fed with a synthetic medium, which contained thevolatile fatty acids, acetic acid (45 % COD), butyric acid (45 % COD) and propionicacid (10 % COD) as the sole carbon source. The effect of reduced hydraulic retentiontimes (HRT) and increased organic loading rates (OLR) of volatile fatty acids (VFA)on the dynamics and composition of the microbiological community was studied byhigh-throughput MiSeqR©Illumina conserved marker gene amplicon sequencing ofthe 16S rRNA gene and themcrAgene. Thereby, the aim was to investigate thelink between operational parameters, microbial community present and the processperformance.The HRT of the reactors could be reduced to 1.9 days of HRT (R2) and2.7 days of HRT (R3) at which process breakdown occurred. Increased processefficiency and stable process performances were observed up to a HRT of 3.9 days(OLR of 7 g VFA L-1d-1). A surprisingly stable biomass concentration and microbialcommunity were observed over time, whereat only R2 showed an increased relativeabundance of the archaeal genusMethanothrixat reduced HRTs and increased OLRs.Unintended biofilm formation was found in all three reactors and is assumed to beinterrelated with this unexpected findings. (Less)
Popular Abstract
Environmental concerns are raised by depletion of fossil fuels, increased greenhouse gas emissions and increased production of organic wastes. As a result, renewable energies are of growing importance and popularity, since they can help to mitigate environmental impacts. In this context, anaerobic digestion (AD), the degradation of organic material by microorganisms under anaerobic conditions, is of growing interest, as it enables the production of the versatile renewable energy source biogas. Hereby, in particular, the storability of biogas and the opportunity to utilize several organic wastes and residues from agriculture and industry can be highlighted, making AD a very attractive renewable energy pathway. Beyond that, the second... (More)
Environmental concerns are raised by depletion of fossil fuels, increased greenhouse gas emissions and increased production of organic wastes. As a result, renewable energies are of growing importance and popularity, since they can help to mitigate environmental impacts. In this context, anaerobic digestion (AD), the degradation of organic material by microorganisms under anaerobic conditions, is of growing interest, as it enables the production of the versatile renewable energy source biogas. Hereby, in particular, the storability of biogas and the opportunity to utilize several organic wastes and residues from agriculture and industry can be highlighted, making AD a very attractive renewable energy pathway. Beyond that, the second product of AD, digestate can be utilized as a cheap and nutrient rich fertilizer. However, in defiance of the increasing full-scale application of the AD process, the process is not sufficiently effective yet, since the link between microbial consortium and process efficiency is not fully understood yet. To control the process in a more efficient manner and to ensure high yields, more knowledge is required about the underlying microbiology. Thereby, the economics of the process could be increased by the application of lower hydraulic retention times (HRT) (the time the feed spends in the reactor) and higher organic loading rates (OLR), i.e. more substrate could be treated in a shorter period of time and the digester volumes could be downsized, reducing both the investment and operational costs.
In AD four steps can be distinguished, which can be differentiated by their respective reaction paths and metabolism products of the involved microorganisms. This project focused on the last two steps acetogenesis and methanogenesis, known as a bottleneck of the process.
To simulate the two last steps of AD, three lab scale continuously stirred tank reactors (CSTR) were fed with VFAs as the sole carbon source. The effect of reduced HRTs and increased OLR of VFAs on the reactor performance was studied. In addition, the effect dynamics and composition of the microbial community was examined by Illumina MiSeq conserved marker gene amplicon sequencing. Contrary to the frequently recommended HRTs of 10 - 25 days to prevent wash out of the slow growing microorganisms, a stable operation and biomass concentration along with an increased process efficiency could be shown for a HRT as low as 3.9 days. Moreover, in defiance to the expected dynamic in the microbial community towards lower HRTs and increased OLRs, little dynamic of the microbial community was observed over time. Whereat, the share of recognized or assumed syntropic VFA oxidizing bacteria in total bacterial community was lower as supposed. Interestingly, a growing share of the archaeal genus Methanothrix in relative abundance in the archaeal community was only observed for one of the reactors, though Methanothrix is reported to dominate Methanosarcina at higher acetate concentrations. The unintended formation of biofilm in the reactors, which causes biomass retention and could serve as a possible inoculum source, was assumed to contribute to this unexpected findings.
In conclusion, it was shown, that more knowledge is required about the actual doubling times of methanogens and syntrophic VFA oxidizing bacteria in environmental and engineered systems under various conditions. Furthermore, many organisms still belong to a candidate phylum or are yet unknown and need to be isolated and characterized to understand their role in the AD process. In addition, the unintended biofilm formation was assumed to improve the process performance, therefore it could be worthwhile to develop more methods for the intended formation of biofilm in operating reactors. (Less)
Please use this url to cite or link to this publication:
author
Weimer, Anna Lea Auguste LU
supervisor
organization
course
KMBM01 20182
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Anaerobic digestion, hydraulic retention time, organic loading rate, biogas, applied microbiology, teknisk mikrobiologi
language
English
id
8992750
date added to LUP
2019-09-12 14:11:04
date last changed
2019-09-12 14:11:04
@misc{8992750,
  abstract     = {{There is an increasing demand for safe, affordable and above allsustainable energy, due to the exhaustion of fossil fuels and increasing greenhousegas emissions. In this context, anaerobic digestion is of growing interest, as it enablesthe production of the versatile renewable energy source biogas from various types oforganic wastes. Though, in order to establish more efficient process policies, a deepunderstanding of the microbiology underlying this process is necessary.This master thesis project focused on the rate limiting steps of anaerobic digestion,acetogenesis and methanogenesis. Therefore, three lab-scale, continuous stirred tankreactors R1 (control) R2, R3 were fed with a synthetic medium, which contained thevolatile fatty acids, acetic acid (45 % COD), butyric acid (45 % COD) and propionicacid (10 % COD) as the sole carbon source. The effect of reduced hydraulic retentiontimes (HRT) and increased organic loading rates (OLR) of volatile fatty acids (VFA)on the dynamics and composition of the microbiological community was studied byhigh-throughput MiSeqR©Illumina conserved marker gene amplicon sequencing ofthe 16S rRNA gene and themcrAgene. Thereby, the aim was to investigate thelink between operational parameters, microbial community present and the processperformance.The HRT of the reactors could be reduced to 1.9 days of HRT (R2) and2.7 days of HRT (R3) at which process breakdown occurred. Increased processefficiency and stable process performances were observed up to a HRT of 3.9 days(OLR of 7 g VFA L-1d-1). A surprisingly stable biomass concentration and microbialcommunity were observed over time, whereat only R2 showed an increased relativeabundance of the archaeal genusMethanothrixat reduced HRTs and increased OLRs.Unintended biofilm formation was found in all three reactors and is assumed to beinterrelated with this unexpected findings.}},
  author       = {{Weimer, Anna Lea Auguste}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Anaerobic degradation of volatile fatty acids in continuous biogas reactors at very short hydraulic retention times.}},
  year         = {{2019}},
}