Bioreactor Scalability: Laboratory-Scale Bioreactor Design Influences Performance, Ecology, and Community Physiology in Expanded Granular Sludge Bed Bioreactors

Abstract

Studies investigating the feasibility of new, or improved, biotechnologies, such as wastewater treatment digesters, inevitably start with laboratory-scale trials. However, it is rarely determined whether laboratory-scale results reflect full-scale performance or microbial ecology. The Expanded Granular Sludge Bed (EGSB) bioreactor, which is a high-rate anaerobic digester configuration, was used as a model to address that knowledge gap in this study. Two laboratory-scale idealizations of the EGSB—a one-dimensional and a three- dimensional scale-down of a full-scale design—were built and operated in triplicate under near-identical conditions to a full-scale EGSB. The laboratory-scale bioreactors were seeded using biomass obtained from the full-scale bioreactor, and, spent water from the distillation of whisky from maize was applied as substrate at both scales. Over 70 days, bioreactor performance, microbial ecology, and microbial community physiology were monitored at various depths in the sludge-beds using 16S rRNA gene sequencing (V4 region), specific methanogenic activity (SMA) assays, and a range of physical and chemical monitoring methods. SMA assays indicated dominance of the hydrogenotrophic pathway at full-scale whilst a more balanced activity profile developed during the laboratory-scale trials. At each scale, Methanobacterium was the dominant methanogenic genus present. Bioreactor performance overall was better at laboratory-scale than full-scale. We observed that bioreactor design at laboratory-scale significantly influenced spatial distribution of microbial community physiology and taxonomy in the bioreactor sludge-bed, with 1-D bioreactor types promoting stratification of each. In the 1-D laboratory bioreactors, increased abundance of Firmicutes was associated with both granule position in the sludge bed and increased activity against acetate and ethanol as substrates. We further observed that stratification in the sludge-bed in 1-D laboratory-scale bioreactors was associated with increased richness in the underlying microbial community at species (OTU) level and improved overall performance.

Performance and Microbial Community Dynamics in Anaerobic Digestion of Waste Activated Sludge: Impact of Immigration

“…At the phylum level, Proteobacteria, Bacteroidetes, and Firmicutes were the major members (Figure 3). The dominant abundance of Proteobacteria in the bioreactors is similar to previous studies on sewage sludge and sludge AD [11,13,40], Firmicutes or Bacteroidetes have been reported to be the most abundant phyla in studies on AD of food waste [21,41], distillery wastewater [9], and mixed farm wastes [42].…”

“…Nine samples (two WAS, one AS, and six temporal bioreactor samples) were processed for high-throughput sequencing after pooling relevant DNA samples at equal volumes. After pooling, PCR was performed to amplify the V4 region of the 16S rRNA gene using modified F515 and F806 primers [9]. The reaction mixture composition [20] and the cycling conditions [21] were described previously.…”

“…This high content of cellular biomass in a sludge digester obscures the distinction between cells that are included in the WAS, but that function only as substrate, and cells that thrive in the digester and that produce enzymes during AD. Culture-independent molecular techniques such as high-throughput sequencing have revealed the microbial communities in different anaerobic digesters [8][9][10]. Substrate type [11,12] and digester operation conditions [13,14] are regarded as important factors that determine the microbial population patterns in AD.…”

Bacterial community analysis in upflow multilayer anaerobic reactor treating high‐solids organic wastes

“…These results suggest that the bacterial community structure might have shifted along the axis of the reactor flow (i.e., the vertical axis). A previous study showed that the bottom part (nearest to the substrate inlet) showed more diverged microbial community structure to the inoculum than the upper part in an expanded granular sludge bed, implying the reactor flow may have a significant impact on microbial community development …”

“…Although Xing et al . claimed that the spatial stratification of anaerobic microbes has contributed to the diversity of the anaerobic consortia inside the reactor and consequently to the performance of the anaerobic process, it is still highly underexplored whether this tendency is replicated in other types of high‐rate AD reactors . The level of stratification would be dependent on various factors such as the reactor configuration.…”