The influence of ammonium-nitrogen on the specific activity of pelletized methanogenic sludge

455

246

The influence of environmental parameters on the diversity of methanogenic communities in 15 full-scale biogas plants operating under different conditions with either manure or sludge as feedstock was studied. Fluorescence in situ hybridization was used to identify dominant methanogenic members of the Archaea in the reactor samples; enriched and pure cultures were used to support the in situ identification. Dominance could be identified by a positive response by more than 90% of the total members of the Archaea to a specific groupor order-level probe. There was a clear dichotomy between the manure digesters and the sludge digesters. The manure digesters contained high levels of ammonia and of volatile fatty acids (VFA) and were dominated by members of the Methanosarcinaceae, while the sludge digesters contained low levels of ammonia and of VFA and were dominated by members of the Methanosaetaceae. The methanogenic diversity was greater in reactors operating under mesophilic temperatures. The impact of the original inoculum used for the reactor start-up was also investigated by assessment of the present population in the reactor. The inoculum population appeared to have no influence on the eventual population.Anaerobic digestion is a simple and effective biological process for the treatment of different organic wastes and the production of energy in the form of biogas (1). A number of full-scale anaerobic digesters for biogas production have been developed and installed in Denmark during the last 20 years (27). They have been designed mainly for the codigestion of manure with a smaller fraction of other waste as a supplemental substrate. Specific environmental and operating factors influence anaerobic conversion processes in these codigestion plants, and similar factors also have an influence on wastewater primary and activated sludge (WW sludge) digesters. Some of the more important factors are temperature (4), ammonia level (7), and loading rate, which affects overall process stability, generally as measured by the concentrations of volatile fatty acids (VFA) in the digester (2).Anaerobic digestion is a multistep microbial process mediated by functionally different microbial groups-saccharide and amino acid fermenters, VFA oxidizers, and methanogens (17, 21). The two functional groups of methanogens (hydrogenotrophic and aceticlastic) have been well described in terms of physiology and phylogeny (11). Hydrogenotrophic methanogenesis and aceticlastic methanogenesis are also the key processes within anaerobic digestion, as when these processes are inhibited, digestion is effectively blocked at acidogenesis. Optimization of methanogenesis is difficult, because of both low growth rates and the susceptibility of the organisms to toxins (6).Organisms described as mediating hydrogenotrophic and aceticlastic methanogenesis are found within five phylogenetic orders (12). One of the hydrogenotrophic orders, Methanopyrales, has only hyperthermophilic member species and will not be considered further. The main orders and t...

Section: Discussionsupporting

confidence: 81%

Influence of Environmental Conditions on Methanogenic Compositions in Anaerobic Biogas Reactors

Karakashev

Batstone

Angelidaki

2005

455

246

“…This has been observed as a dominant pathway in highammonia anaerobic bioreactors (14,15). Stress due to high am-monia concentrations inhibits the aceticlastic methanogenic pathway more so than the hydrogenotrophic methanogenic pathway (16), thereby selecting for syntrophic acetate oxidation as a significant pathway for forming methane from acetate (17). Although this selection has been characterized empirically, and individual syntrophic strains have been enriched, it remains elusive whether or not enriched strains represent keystone populations in reactor microbiomes or if syntrophic acetate oxidation is a function of a heterogeneous and dynamic community.…”

mentioning

confidence: 99%

Microbial Community Dynamics and Stability during an Ammonia-Induced Shift to Syntrophic Acetate Oxidation

Werner

García

Perkins

et al. 2014

133

g Anaerobic digesters rely on the diversity and distribution of parallel metabolic pathways mediated by complex syntrophic microbial communities to maintain robust and optimal performance. Using mesophilic swine waste digesters, we experimented with increased ammonia loading to induce a shift from aceticlastic methanogenesis to an alternative acetate-consuming pathway of syntrophic acetate oxidation. In comparison with control digesters, we observed shifts in bacterial 16S rRNA gene content and in functional gene repertoires over the course of the digesters' 3-year operating period. During the first year, under identical startup conditions, all bioreactors mirrored each other closely in terms of bacterial phylotype content, phylogenetic structure, and evenness. When we perturbed the digesters by increasing the ammonia concentration or temperature, the distribution of bacterial phylotypes became more uneven, followed by a return to more even communities once syntrophic acetate oxidation had allowed the experimental bioreactors to regain stable operation. The emergence of syntrophic acetate oxidation coincided with a partial shift from aceticlastic to hydrogenotrophic methanogens. Our 16S rRNA gene analysis also revealed that acetatefed enrichment experiments resulted in communities that did not represent the bioreactor community. Analysis of shotgun sequencing of community DNA suggests that syntrophic acetate oxidation was carried out by a heterogeneous community rather than by a specific keystone population with representatives of enriched cultures with this metabolic capacity.

“…However, the high content of ammonia is a concern due to its association with unstable process performance and increased risk of process failure (10). The potential inhibitory effects on the biogas-producing consortia and in particular the acetate-utilizing methanogens are considered to be the main causes of decline in process performance (21,35).…”

mentioning

confidence: 99%

Bioaugmentation of Syntrophic Acetate-Oxidizing Culture in Biogas Reactors Exposed to Increasing Levels of Ammonia

Westerholm

Levén

Schnürer

2012

185

119

bThe importance of syntrophic acetate oxidation for process stability in methanogenic systems operating at high ammonia concentrations has previously been emphasized. In this study we investigated bioaugmentation of syntrophic acetate-oxidizing (SAO) cultures as a possible method for decreasing the adaptation period of biogas reactors operating at gradually increased ammonia concentrations (1.5 to 11 g NH 4 ؉ -N/liter). Whole stillage and cattle manure were codigested semicontinuously for about 460 days in four mesophilic anaerobic laboratory-scale reactors, and a fixed volume of SAO culture was added daily to two of the reactors. Reactor performance was evaluated in terms of biogas productivity, methane content, pH, alkalinity, and volatile fatty acid (VFA) content. The decomposition pathway of acetate was analyzed by isotopic tracer experiments, and population dynamics were monitored by quantitative PCR analyses. A shift in dominance from aceticlastic methanogenesis to SAO occurred simultaneously in all reactors, indicating no influence by bioaugmentation on the prevailing pathway. Higher abundances of Clostridium ultunense and Tepidanaerobacter acetatoxydans were associated with bioaugmentation, but no influence on Syntrophaceticus schinkii or the methanogenic population was distinguished. Overloading or accumulation of VFA did not cause notable dynamic effects on the population. Instead, the ammonia concentration had a substantial impact on the abundance level of the microorganisms surveyed. The addition of SAO culture did not affect process performance or stability against ammonia inhibition, and all four reactors deteriorated at high ammonia concentrations. Consequently, these findings further demonstrate the strong influence of ammonia on the methane-producing consortia and on the representative methanization pathway in mesophilic biogas reactors.