Stillage, which is generated during bioethanol production, constitutes a promising substrate for biogas production within the scope of an integrated biorefinery concept. In this study, a microbial community was grown on thin stillage as mono-substrate in a continuous stirred tank reactor (CSTR) at a constant temperature of 55 °C, at an organic loading rate of 1.5 goTS/L*d and a retention time of 25 days. Using an amplicon-based dataset of 17,400 high-quality sequences of 16S rRNA gene fragments (V2-V3 regions), predominance of Bacteria assigned to the families Thermotogaceae and Elusimicrobiaceae was detected. Dominant members of methane-producing Euryarchaeota within the CSTR belonged to obligate acetoclastic Methanosaetaceae and hydrogenotrophic Methanobacteriaceae. In order to investigate population dynamics during reactor acidification, the organic loading rate was increased abruptly, which resulted in an elevated concentration of volatile fatty acids. Acidification led to a decrease in relative abundance of Bacteria accompanied with stable numbers of Archaea. Nevertheless, the abundance of Methanosaetaceae increased while that of Methanobacteriales decreased successively. These findings demonstrate that a profound intervention to the biogas process may result in persistent community changes and reveals uncommon bacterial families as process-relevant microorganisms.
The application of in situ hybridization with group specific oligonucleotide probes detected by epifluorescence microscopy and confocal laser scanning microscopy was tested to identify spatial gradients in the distribution of bacteria in biofilms of plug flow reactors and in the bottom sediment layer of a drinking water reservoir. The two tubular biofilm reactors were fed with the effluent from a full scale biological wastewater treatment plant to which were added the chlorophenols whole degradation was being investigated. One was operated as a continuous-flow reactor and the other as a sequencing batch reactor.
The vertical gradients in the microbial colonization of the sediment were analyzed by means of glass slides exposed to the sediment.
In the biofilms of both reactors the beta-Proteobacteria dominated. The Cytophaga-Flavobacterium group and the Gram-positive bacteria were also abundant. Only small amounts of gamma-bacteria could be detected. This is contrary to findings using traditional cultivation methods. Unlike the biofilms in the reactor, the bacterial Aufwuchs on the glass slides in the sediment presented a surprising diversity of morphological types and size classes of bacteria.
Stillage derived from bioethanol production process is a side stream conventionally used as feed additive after a cost‐intensive dehydration step. From economical and ecological points of view, it also represents an appealing substrate for biogas production. In this work, we examined the biomethanization of thin stillage in a stirred bioreactor under thermophilic conditions (55°C). Different organic loading rates and hydraulic residence times (HRTs) were tested over a long period of operation. Using thin stillage as a mono‐substrate, the maximum loading rate reached was 2.1 goTS/L/day (oTS, organic total solid). However, with the addition of a commercially available iron hydroxide additive, a maximum organic loading rate of 5.9 goTS/L/day was achieved. GC‐MS and denaturing gradient gel electrophoresis were used to study the metabolites and the microbial population dynamics within the biogas reactor under different process conditions. For all organic loading rates studied, volatile fatty acids were shown to give a clear indication of reactor instability. Products of aromatic amino acid degradation, especially phenyl acetic acid (PAA), were detected earlier in reactors even at very low organic loading rates. PAA concentration above 0.25 g/L indicated an unstable reactor performance and values above 0.5 g/L were found to be inhibitory to the biogas production in batch cultures.
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