| 1. |
- Liebana, Raquel, 1986, et al.
(author)
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Combined Deterministic and Stochastic Processes Control Microbial Succession in Replicate Granular Biofilm Reactors
- 2019
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In: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 53:9, s. 4912-4921
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Journal article (peer-reviewed)abstract
- Granular sludge is an efficient and compact biofilm process for wastewater treatment. However, the ecological factors involved in microbial community assembly during the granular biofilm formation are poorly understood, and little is known about the reproducibility of the process. Here, three replicate bioreactors were used to investigate microbial succession during the formation of granular biofilms. We identified three successional phases. During the initial phase, the successional turnover was high and alpha-diversity decreased as a result of the selection of taxa adapted to grow on acetate and form aggregates. Despite these dynamic changes, the microbial communities in the replicate reactors were similar. The second successional phase occurred when the settling time was rapidly decreased to selectively retain granules in the reactors. The influence of stochasticity on succession increased and new niches were created as granules emerged, resulting in temporarily increased alpha-diversity. The third successional phase occurred when the settling time was kept stable and granules dominated the biomass. Turnover was low, and selection resulted in the same abundant taxa in the reactors, but drift, which mostly affected low-abundant community members, caused the community in one reactor to diverge from the other two. Even so, performance was stable and similar between reactors.
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| 2. |
- Liebana, Raquel, 1986, et al.
(author)
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Stability of nitrifying granules exposed to water flux through a coarse pore mesh.
- 2015
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Conference paper (other academic/artistic)abstract
- The study of the strength and stability of aerobic granules is essential for the application of aerobic granular sludge membrane bioreactors (AGMBR). In this study, a coarse pore nylon mesh membrane was used to study the differences in compressibility and breakage of 78 aerobic granules submitted to different water fluxes. Confocal laser scanning microscopy was employed to investigate the distribution of extracellular polymeric substances of cryosectioned granules. The tested granules were able to withstand fluxes much higher than those typically applied in MBRs, with pressures ranging from 0.2 to 4.5 kN m-2 before breakage. Cells, β-polysaccharides and proteins were present in higher abundance in the outer layers, while calcium ions were abundant in the outer- as well as the inner layers of the granule. The results shows that the use of coarse pore meshes operated at very high flux is a feasible technique for biomass separation in AGMBR.
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| 3. |
- Szabo, Enikö Barbara, 1985, et al.
(author)
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Comparison of the bacterial community composition in the granular and the suspended phase of sequencing batch reactors
- 2017
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In: Amb Express. - : Springer Science and Business Media LLC. - 2191-0855. ; 7
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Journal article (peer-reviewed)abstract
- Granulation of activated sludge is an increasingly important area within the field of wastewater treatment. Granulation is usually achieved by high hydraulic selection pressure, which results in the wash-out of slow settling particles. The effect of the harsh wash-out conditions on the granular sludge ecosystem is not yet fully understood, but different bacterial groups may be affected to varying degrees. In this study, we used high-throughput amplicon sequencing to follow the community composition in granular sludge reactors for 12 weeks, both in the granular phase and the suspended phase (effluent). The microbiome of the washed out biomass was similar but not identical to the microbiome of the granular biomass. Certain taxa (e.g. Flavobacterium spp. and Bdellovibrio spp.) had significantly (p < 0.05) higher relative abundance in the granules compared to the effluent. Fluorescence in situ hybridization images indicated that these taxa were mainly located in the interior of granules and therefore protected from erosion. Other taxa (e.g. Meganema sp. and Zooglea sp.) had significantly lower relative abundance in the granules compared to the effluent, and appeared to be mainly located on the surface of granules and therefore subject to erosion. Despite being washed out, these taxa were among the most abundant members of the granular sludge communities and were likely growing fast in the reactors. The ratio between relative abundance in the granular biomass and in the effluent did not predict temporal variation of the taxa in the reactors, but it did appear to predict the spatial location of the taxa in the granules.
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| 4. |
- Szabo, Enikö Barbara, 1985
(author)
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Composition and dynamics of the bacterial community in aerobic granular sludge reactors
- 2017
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Doctoral thesis (other academic/artistic)abstract
- The aerobic granular sludge (AGS) technology is probably the future standard for wastewater treatment, due to its low footprint and low energy consumption. Although achieving granulation is usually not a challenge anymore, our understanding of the community assembly during start-up, and of the microbial ecology of these reactors in general, is incomplete. Earlier studies have shown that high removal efficiency and stable process performance in bioreactors are dependent on the microbial community composition. High functional redundancy, which is a result of high evenness and phylogenetic variability, was found to be the key to a resilient bioreactor.The research presented in this thesis aimed to expand on the current knowledge about the composition and dynamics of the bacterial community in AGS reactors, using molecular biology techniques including qPCR, T-RFLP and Illumina MiSeq. The harsh wash-out conditions, typical for the start-up of AGS reactors, were found to drastically decrease the abundance of nitrifiers. A stepwise decrease of settling time enabled better retention of nitrifying organisms, but seemed to have no long term effects on the general composition of the community. The community assembly was affected mainly by deterministic factors – e.g. short settling time – during start-up, and the stochastic components became evident only when the strong selection pressure decreased. Reactors with different operational parameters were found to be dominated by different taxa, but high functional redundancy was observed within all key guilds in all reactors. Certain functional groups – denitrifiers, EPS and PHA producers – were over-represented in granular sludge compared to the flocculated seed sludge. The typical AGS reactor operation seems to favor these traits, but whether these are necessary for successful granulation and reactor operation depends on the intended function of the reactor.At present, microbial ecology studies – including our experiments – on AGS processes are predominantly of descriptive nature. However, it was suggested that in the future microbial ecology may provide a tool to predict or even design diversity and thus process stability. The increasing availability of next generation sequencing methods allows us to study the rare biosphere in AGS reactors and gain insights in how we can integrate ecology in biotechnology.
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| 5. |
- Szabo, Enikö Barbara, 1985, et al.
(author)
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Effects of Wash-Out Dynamics on Nitrifying Bacteria in Aerobic Granular Sludge During Start-Up at Gradually Decreased Settling Time
- 2016
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In: Water (Switzerland). - : MDPI AG. - 2073-4441 .- 2073-4441. ; 8:5, s. 172-
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Journal article (peer-reviewed)abstract
- The aerobic granular sludge process is a promising technology for the removal of nutrients and organic contaminants from wastewater. However, a large amount of the sludge is often washed out during the start-up of granular reactors, which results in reduced process performance and a protracted start-up phase. In this study, the possibility of a rapid start-up of the nitrification process through a stepwise decrease of the settling time was investigated, and the bacterial population dynamics in two lab-scale sequencing batch reactors were studied. The results demonstrated that the stepwise decrease of the settling time enabled fast granulation and rapid start-up of the process. Small cores of granules were already observed after 10 days of operation, and the biomass was dominated by granules after 28 days. The removal of organic matter and ammonium was >95% after one day and 14 days, respectively. The bacterial community composition changed rapidly during the first 21 days, resulting in strongly reduced richness and evenness. The diversity increased at a later stage, and the bacterial community continued changing, albeit at a slower pace. The rate of the stepwise decrease in settling time strongly affected the abundance of nitrifying organisms, but not the general composition of the bacterial community. The results of this study support the idea that a stepwise decrease of the settling time is a successful strategy for the rapid start-up of aerobic granular sludge reactors.
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| 6. |
- Szabo, Enikö Barbara, 1985, et al.
(author)
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Microbial Population Dynamics and Ecosystem Functions of Anoxic/Aerobic Granular Sludge in Sequencing Batch Reactors Operated at Different Organic Loading Rates
- 2017
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In: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 8
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Journal article (peer-reviewed)abstract
- The granular sludge process is an effective, low-footprint alternative to conventional activated sludge wastewater treatment. The architecture of the microbial granules allows the co-existence of different functional groups, e.g., nitrifying and denitrifying communities, which permits compact reactor design. However, little is known about the factors influencing community assembly in granular sludge, such as the effects of reactor operation strategies and influent wastewater composition. Here, we analyze the development of the microbiomes in parallel laboratory-scale anoxic/aerobic granular sludge reactors operated at low (0.9 kg m(-3) d(-1)), moderate (1.9 kg m(-3) d(-1)) and high (3.7 kg m(-3) d(-1)) organic loading rates (OLRs) and the same ammonium loading rate (0.2 kg NH4-N m-3 d(-1)) for 84 days. Complete removal of organic carbon and ammonium was achieved in all three reactors after start-up, while the nitrogen removal (denitrification) efficiency increased with the OLR: 0% at low, 38% at moderate, and 66% at high loading rate. The bacterial communities at different loading rates diverged rapidly after start-up and showed less than 50% similarity after 6 days, and below 40% similarity after 84 days. The three reactor microbiomes were dominated by different genera (mainly Meganema, Thauera, Paracoccus, and Zoogloea), but these genera have similar ecosystem functions of EPS production, denitrification and polyhydroxyalkanoate (PHA) storage. Many less abundant but persistent taxa were also detected within these functional groups. The bacterial communities were functionally redundant irrespective of the loading rate applied. At steady-state reactor operation, the identity of the core community members was rather stable, but their relative abundances changed considerably over time. Furthermore, nitrifying bacteria were low in relative abundance and diversity in all reactors, despite their large contribution to nitrogen turnover. The results suggest that the OLR has considerable impact on the composition of the granular sludge communities, but also that the granule communities can be dynamic even at steady-state reactor operation due to high functional redundancy of several key guilds. Knowledge about microbial diversity with specific functional guilds under different operating conditions can be important for engineers to predict the stability of reactor functions during the start-up and continued reactor operation.
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