Biofilm development on the membrane surface is one of the main reasons for membrane fouling in membrane bioreactors (MBRs) and it is a big problem for their stable operation. Precise information on ...the microbial community composition of the biofilm is needed for a better understanding of biofilm development. However, there have been limited investigations of the relationship between the biofilm formation process and the microbial community of activated sludge and biofilm in MBRs treating real sewage. In this study, relationships between the microbial community structure of biofilm and activated sludge at each biofilm formation stage were investigated and biofilm growth was elucidated by nondestructive observations. Two anoxic/oxic MBRs were operated and membrane fouling was induced. Permeability rapidly decreased in both reactors and live cell microcolonies were formed on dead cell conditioning film on the membrane surface. Principal component analysis based on 16S rRNA gene sequences showed that the biofilm microbial community changed significantly from middle stage to mature biofilm when compared with that of activated sludge. The abundance of specific bacteria, such as unclassified
Neisseriaceae
, increased in middle-stage biofilm and the diversity indexes of middle-stage biofilm were lower than those of mature biofilm and activated sludge. These results suggested that the presence of specific bacteria with colonization ability played a crucial role in biofilm formation. Strategies are needed to target membrane fouling mitigation during early- and middle-stage biofilm formation to reduce MBR membrane fouling.
Key points
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Microbial community of mature biofilm was approached to that of activated sludge.
• In the middle-stage biofilm, live cells colonized on a dead-cell-conditioning-film.
• Microbial diversity was lower in live cell colonizing stage than in activated sludge.
The aim of this study was to evaluate the contribution of dissolved organic carbon (DOC) and microbial community dynamics to membrane fouling development in membrane bioreactor (MBR). We operated ...laboratory-scale anoxic/oxic-MBRs under prolonged starvation conditions in different seasons and the dynamics and diversity of the microbial communities were investigated. Although fouled-MBRs showed DOC accumulation in the activated sludge (AS), the fouling-mitigated MBR suggested that dissolved oxygen was consumed and DOC of the sludge supernatant was degraded. 16S rRNA genes analysis of AS in the MBRs revealed that Chitinophagaceae and Candidatus Promineofilum specifically increased in the fouling-mitigated MBR, suggesting that they played important roles in membrane fouling mitigation; high microbial diversity in the reactor also contributed to fouling mitigation. In the fouled reactor, enrichment of Xanthomonadaceae might be related to fouling causing substances formation leading to membrane fouling development; lower microbial diversity also contributed to fouling development in the fouled MBR.
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•Microbial dynamics of fouled and mitigated MBR were investigated under starvation.•ΔDOC between activated sludge (AS) and effluent could be used as fouling parameter.•High diversity of AS community was important for fouling mitigation.•Xanthomonadaceae implicated in fouling development via EPS production.•Chitinophagaceae implicated in fouling mitigation via SMPs utilization.
The main objective of this study was to investigate the cause of gel fouling in membrane bioreactors (MBRs) treating real sewage in terms of soluble microbial products (SMPs) and microbial aspects. ...Two anoxic/oxic-MBRs were operated as the control reactor (S1) and the sludge loading rate increased reactor (S2). The reactors were operated under low-temperature around 11 °C conditions. Membrane permeability substantially decreased in S2, and gel layer biofilm was formed on membrane surface. In contrast, the permeability of S1 gradually decreased and cake layer formed. When gel fouling occurred, the protein and polysaccharide of SMP in S2 were 47 and 23 mg L−1, which were significantly lower than those recorded in S1 accounted for 118 and 68 mg L−1, respectively. Furthermore, the total organic carbon concentration of SMPs was 24 mg L−1, which was lower than the influent in S2, accounted for 62 mg L−1. Finally, Campylobacteraceae which exists in sewage and uncultured OD1, dominated the gel layer biofilm in S2, unlike the cake layer biofilm in S1. These results indicated that the gel layer biofilm might be composed of influent substances, demonstrating the importance of influent decomposition in MBR for gel fouling mitigation.
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•Low temperature and sludge loading rate change induced gel fouling.•The lowest SMP concentration exhibited at the highest sludge loading rate.•Sludge filterability was not associated with gel fouling occurrence.•Sewage derived bacteria was dominant in gel layer on membrane surface.
Membrane fouling in membrane bioreactors (MBR) remains a major issue and knowledge of microbes associated with biofilm formation might facilitate the control of this phenomenon, Thus, an anoxic/oxic ...membrane bioreactor (A/O-MBR) was operated under an extremely low organic loading rate (0.002 kg-COD·m
·day
) to induce membrane fouling and the major biofilm-forming bacteria were identified. After operation under extremely low organic loading condition, the reactor showed accumulation of total nitrogen and phosphorus along with biofilm development on the membrane surface. Thus, membrane fouling induced by microbial cell lysis was considered to have occurred. Although no major changes were observed in the microbial community structure of the activated sludge in the MBR before and after membrane fouling, uncultured bacteria were specifically increased in the biofilm. Therefore, bacteria belonging to candidate phyla including TM6, OD1 and Gammaproteobacteria could be important biofilm-forming bacteria.
A rotational sponge (RS) reactor was proposed as an alternative sewage treatment process. Prior to the application of an RS reactor for sewage treatment, this study evaluated reactor performance with ...regard to organic removal, nitrification, and nitrogen removal and sought to optimize the rotational speed and hydraulic retention time (HRT) of the system. RS reactor obtained highest COD removal, nitrification, and nitrogen removal efficiencies of 91%, 97%, and 65%, respectively. For the optimization, response surface methodology (RSM) was employed and optimum conditions of rotational speed and HRT were 18 rounds per hour and 4.8 h, respectively. COD removal, nitrification, and nitrogen removal efficiencies at the optimum conditions were 85%, 85%, and 65%, respectively. Corresponding removal rates at optimum conditions were 1.6 kg-COD m−3d−1, 0.3 kg-NH4+-N m−3d−1, and 0.12 kg-N m−3d−1. Microbial community analysis revealed an abundance of nitrifying and denitrifying bacteria in the reactor, which contributed to nitrification and nitrogen removal.
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•Performance of a rotational sponge reactor was studied using synthetic wastewater.•The reactor managed to remove organic and nitrogen simultaneously.•Rotational speed and HRT were optimized using response surface methodology.•Optimum conditions of rotational speed and HRT were 18 rph and 4.8 h.•The rotational sponge reactor has a potential for sewage treatment.
Carbon and nitrogen stable isotope ratios (δ13C and δ15N) were determined in activated sludge, which was exposed to endogenous conditions for 36 days and contained a wide diversity of organisms ...across several trophic levels. The aim of this study was to elucidate the fluctuation of δ13C and δ15N through trophic transfer in the microbial consortia. The sludge was evaluated in view of sludge mass, bacterial community, higher trophic organisms, sludge δ13C and δ15N, and δ15N and δ18O of nitrate. The results show that the activated sludge became more enriched with 15N as degradation proceeded. Eventually, the mixed liquor volatile suspended solid concentrations in the activated sludge decreased from 1610 to 710 mg/L and the δ15N of the sludge increased from 8.3‰ to 10.8‰. In contrast, the δ13C values of the sludge were stable. Microscope observations confirmed that consumers such as Rotifera, Tardigrada and Annelida (Aelosoma sp.) were present in the activated sludge for the entire operational period. The abundance of those organisms drastically changed during the operational periods, and the diversity in bacterial community also changed, resulting in community succession. Changes in biotic community, reduction in sludge mass, and increase in δ15N of the sludge occurred during the sludge degradation processes. This implies that the sludge degradation was partly caused by the trophic conversion of the sludge-derived nitrogen in the food web. The δ15N of the sludge can be used as an indicator of the sludge degradation through trophic transfer in wastewater treatment reactors. These findings provide new insights into understanding trophic transfer during microbial community succession and the effects of the feeding process on sludge degradation.
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•Stable isotope ratios (δ13C, δ15N, δ18O) were measured in activated sludge (AS).•δ15N was applied to determine the predation processes of the food web in AS.•δ15N increased and δ13C was nearly constant under degradation of AS.•Biotic community including bacteria, protozoa, and metazoa varied under degradation.
Microbial biofilm development on the membrane surface of bioreactors results in membrane flux decline (biofouling). Biofouling is one of the most severe problems limiting the use of these ...bioreactors. For detailed understanding of the biofouling, microbial community and dissolved organic matter analyses have been performed in recent decades. Although most previous studies have focused on mature biofilms at the end point of biofouling, understanding of the early stages is crucial to mitigate biofilm formation. Thus, recent studies have focused on the impact of early-stage biofilm development and indicated a clear difference in microbial communities between early-stage and mature biofilms. In addition, certain bacteria play a significant role in early-stage biofilms. The present mini-review systematically summarizes the foulants present during early-stage fouling, provides novel perspectives on fouling mechanisms, and discusses the neglected effect of planktonic bacteria.
Many measurement methods have been proposed for use in automated production. Existing methods for measuring three-dimensional surface height data operate by projecting fringe patterns onto a target ...object and capturing images of them. However, these methods do not work well for cutlery, such as table forks and spoons, because specular reflection causes exposure change on the cutlery surface. To overcome this difficulty, this paper presents a measurement method for cutlery with specular reflection. The proposed method is based on a well-known measurement technique, the gray coding method, which is robust to exposure change because the captured fringe patterns are handled by discretizing their values. Furthermore, the gray coding method is improved by introducing hue-channel information into the captured fringe patterns. The hue-channel information is more robust to exposure change than brightness, which is used in existing methods. Experimental results for real cutlery show that the proposed hue-based gray coding method enables more robust measurement than existing methods.
Bacillus species is an important microbial species in the activated sludge process. Some researchers reported that the predominance of Bacillus spp. improves treatment performance and good sludge ...settleability. The viable count of Bacillus spp. is usually measured by the plate culture method. Recently developed massive sequence technology has been applied to activated sludge samples; this technique provides more detailed information on its microbial community. However, the relationship between the number of Bacillus spp. and microbial compositions is not yet well understood. In order to elucidate this relationship, microbial community analyses based on 16S rRNA gene sequence and cell count of Bacillus spp. were conducted. Activated sludge samples, including those from conventional activated sludge, sequencing batch, and oxidation ditch processes, were collected and subjected to analysis. The results of microbial community analysis revealed that Proteobacteria and Bacteroides were the predominant bacterial phyla and overall community compositions resembled each other at the phylum level. The detection ratio for Bacillus spp. was 0–0.33%, and the number of Bacillus spp. ranged from 105 to more than 108 colonies/g-MLSS. The results showed that the number of Bacillus spp. and detection ratio showed a similar trend, and thus, these analyses could be complementary to each other.
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![[Paper] Development of Syst...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2186-7364/small "[Paper] Development of System to Classify Speckle Images for Visual Inspection of Cutlery")
