Formation mechanism of nitrifying granules observed in an aerobic upflow fluidized bed (AUFB) reactor

Tsuneda, Satoshi; Ejiri, Y.; Nagano, Tatsuo; Hirata, Akira

doi:10.2166/wst.2004.0796

Cited by 27 publications

(20 citation statements)

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“…This has also been reported in other case studies on anaerobic and aerobic granules (2,13,29,37). Different layers were sometimes composed of distinct bacterial species with various functional tasks, such as nitrification, denitrification, or ammonia oxidation (1,4,38). In this study on aerobic granules, different structured zones could be identified as well.…”

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confidence: 84%

Microbial Composition and Structure of Aerobic Granular Sewage Biofilms

Weber

Ludwig

Schleifer

et al. 2007

Appl Environ Microbiol

168

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Aerobic activated sludge granules are dense, spherical biofilms which can strongly improve purification efficiency and sludge settling in wastewater treatment processes. In this study, the structure and development of different granule types were analyzed. Biofilm samples originated from lab-scale sequencing batch reactors which were operated with malthouse, brewery, and artificial wastewater. Scanning electron microscopy, light microscopy, and confocal laser scanning microscopy together with fluorescence in situ hybridization (FISH) allowed insights into the structure of these biofilms. Microscopic observation revealed that granules consist of bacteria, extracellular polymeric substances (EPS), protozoa and, in some cases, fungi. The biofilm development, starting from an activated sludge floc up to a mature granule, follows three phases. During phase 1, stalked ciliated protozoa of the subclass Peritrichia, e.g., Epistylis spp., settle on activated sludge flocs and build tree-like colonies. The stalks are subsequently colonized by bacteria. During phase 2, the ciliates become completely overgrown by bacteria and die. Thereby, the cellular remnants of ciliates act like a backbone for granule formation. During phase 3, smooth, compact granules are formed which serve as a new substratum for unstalked ciliate swarmers settling on granule surfaces. These mature granules comprise a dense core zone containing bacterial cells and EPS and a loosely structured fringe zone consisting of either ciliates and bacteria or fungi and bacteria. Since granules can grow to a size of up to several millimeters in diameter, we developed and applied a modified FISH protocol for the study of cryosectioned biofilms. This protocol allows the simultaneous detection of bacteria, ciliates, and fungi in and on granules.During the last 20 years, intensive research in the field of biological wastewater treatment and other applications has demonstrated that biofilms are often more efficient for water purification than suspended activated sludge. Today, the application of anaerobic and aerobic granular sludge in wastewater treatment is regarded as one of the most useful and promising biotechnologies. Granular sludge was described first for strictly anaerobic systems (26). In the late 1990s, the formation and application of aerobic granules was reported (30). Such granules are spherical compact aggregates of microorganisms, mainly bacteria, and extracellular polymeric substances (EPS). Granules can be described as "biofilm in suspension" and are considered to be a special case of biofilm formation, composed of self-immobilized cells (9,16,20). The application of granules for wastewater treatment shows many advantages. An outstanding feature is the excellent settleability (high settling velocity), which is a prerequisite to handle high liquid flows. Moreover, granular sludge provides high and stable rates of metabolism, resilience to shocks and toxins due to protection by a matrix of EPS (40), long biomass residence times, biomass immobilization i...

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Section: Downloaded Fromsupporting

confidence: 84%

Microbial Composition and Structure of Aerobic Granular Sewage Biofilms

Weber

Ludwig

Schleifer

et al. 2007

Appl Environ Microbiol

168

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“…Therefore, there is a need for a simple yet effective method of immobilizing nitrifying bacteria within a reactor. Nitrifying granule production is one method of immobilization used to preserve a large population of nitrifying bacteria within a reactor (12,(40)(41)(42)(43). Tsuneda et al (41) produced nitrifying granules in inorganic wastewater using an aerobic upflow fluidized bed (AUFB) reactor.…”

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Microbial Population Dynamics and Community Structure during the Formation of Nitrifying Granules to Treat Ammonia-Rich Inorganic Wastewater

et al. 2010

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Microbial population dynamics were investigated during the formation of nitrifying granules in an aerobic upflow fluidized bed (AUFB) reactor fed ammonia as a sole energy source. Analyses of clone libraries of 16S rRNA gene and the ammonia monooxygenase subunit A gene (amoA) revealed that although the clones obtained from the seed sludge were widely distributed among the ammonia-oxidizing bacteria (AOB) isolates, the community structure of AOB shifted towards the Nitrosomonas mobilis lineage as granulation proceeded. Quantitative fluorescence in situ hybridization showed that changes in the bacterial population occurred concomitantly with changes in nitrification performance and the size of granules. AOB associated with the N. mobilis lineage were predominant in the early stages as nitrifying granules formed (average diameter, 126 µm). In mature granules (average diameter, 270 µm), at least three types of AOB, N. mobilis, Nitrosomonas oligotropha, and Nitrosomonas europaea, formed different niches and coexisted. Nitrite-oxidizing bacteria (NOB) affiliated with Nitrospira spp. were detected in the start-up period, but were replaced by NOB affiliated with Nitrobacter spp. after granules formed.Key words: community structure, population dynamics, nitrifying bacteriaThe removal of biological nitrogen from various types of wastewater is becoming increasingly important owing to the implementation of strict regulations concerning nitrogen discharge. The process of nitrification involves the conversion of ammonia (NH3) or ammonium ions (NH4. Two types of nitrifying bacteria, namely, lithoautotrophic ammonia-oxidizing bacteria (AOB) and lithoautotrophic nitrite-oxidizing bacteria (NOB), play important roles in this process. AOB are classified into two phylogenetic lineages based on their 16S rRNA gene sequences; Nitrosomonas sp. and Nitrosospira sp. belonging to Betaproteobacteria, and Nitrosococcus oceani and Nitrosococcus halophilus belonging to Gammaproteobacteria (19). NOB are mainly classified into two phylogenetic lineages based on the cell morphology of isolated organisms and on 16S rRNA gene sequences. The most intensively studied NOB, Nitrobacter and Nitrospira, fall within the Alphaproeobacteria and separate phyla in Bacteria, respectively (2).It is generally accepted that nitrifying bacteria have a low growth rate and tend to be washed out from reactors. Thus, it is difficult to retain large numbers of them within a reactor. Therefore, there is a need for a simple yet effective method of immobilizing nitrifying bacteria within a reactor. Nitrifying granule production is one method of immobilization used to preserve a large population of nitrifying bacteria within a reactor (12,(40)(41)(42)(43). Tsuneda et al. (41) produced nitrifying granules in inorganic wastewater using an aerobic upflow fluidized bed (AUFB) reactor. These granules exhibited a good settling ability and a high rate of ammonia removal (1.5 kg-N m −3 d −1 ). Therefore, nitrifying granule production is a promising method for the effective remov...

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“…By means of energy dispersive X-ray spectroscopy, it has been found that Fe accumulated at the core of nitrifying granules. 7 On the other hand, it was reported that a shorter settling time accumulated more phosphorous and thus increased the ash solids fraction. However, the other poly-valence cations, i.e.…”

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confidence: 99%