Dataset Information

Aerobic granules: microbial landscape and architecture, stages, and practical implications.

ABSTRACT: For the successful application of aerobic granules in wastewater treatment, granules containing an appropriate microbial assembly able to remove contaminants should be retained and propagated within the reactor. To manipulate and/or optimize this process, a good understanding of the formation and dynamic architecture of the granules is desirable. Models of granules often assume a spherical shape with an outer layer and an inner core, but limited information is available regarding the extent of deviations from such assumptions. We report on new imaging approaches to gain detailed insights into the structural characteristics of aerobic granules. Our approach stained all components of the granule to obtain a high quality contrast in the images; hence limitations due to thresholding in the image analysis were overcome. A three-dimensional reconstruction of the granular structure was obtained that revealed the mesoscopic impression of the cavernlike interior of the structure, showing channels and dead-end paths in detail. In "old" granules, large cavities allowed for the irrigation and growth of dense microbial colonies along the path of the channels. Hence, in some areas, paradoxically higher biomass content was observed in the inner part of the granule compared to the outer part. Microbial clusters "rooting" from the interior of the mature granule structure indicate that granules mainly grow via biomass outgrowth and not by aggregation of small particles. We identify and discuss phenomena contributing to the life cycle of aerobic granules. With our approach, volumetric tetrahedral grids are generated that may be used to validate complex models of granule formation.

SUBMITTER: Gonzalez-Gil G

PROVIDER: S-EPMC4018849 | biostudies-other | 2014 Jun

REPOSITORIES: biostudies-other

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Aerobic granules: microbial landscape and architecture, stages, and practical implications.

Gonzalez-Gil Graciela G Holliger Christof C

Applied and environmental microbiology 20140321 11

For the successful application of aerobic granules in wastewater treatment, granules containing an appropriate microbial assembly able to remove contaminants should be retained and propagated within the reactor. To manipulate and/or optimize this process, a good understanding of the formation and dynamic architecture of the granules is desirable. Models of granules often assume a spherical shape with an outer layer and an inner core, but limited information is available regarding the extent of d ...[more]

PMID: 24657859

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Project description:Simultaneous nitrification-denitrification (SND) is, in theory, a key advantage of aerobic granular sludge systems over conventional activated sludge systems. But practical experience and literature suggests that SND and thus total nitrogen removal are limited during treatment of municipal wastewater using AGS systems. This study thus aims at quantifying the extent and understanding the mechanisms of SND during treatment of municipal wastewater with aerobic granular sludge (AGS) systems. Experiments (long-term and batch-tests) as well as mathematical modelling were performed. Our experimental results demonstrate that SND is significantly limited during treatment of low-strength municipal wastewater with AGS systems (14-39%), while almost full SND is observed when treating synthetic influent containing only diffusible substrate (90%). Our simulations demonstrate that the main mechanisms behind limited SND are (1) the dynamics of anoxic zone formation inside the granule, (2) the diffusibility and availability of electron-donors in those zones and (3) the aeration mode. The development of anoxic zones is driven by the utilisation of oxygen in the upper layers of the granule leading to transport limitations of oxygen inside the granule; this effect is closely linked to granule size and wastewater composition. Development of anoxic zones during the aerobic phase is limited for small granules at constant aeration at bulk dissolved oxygen (DO) concentration of 2 mgO2 L-1, and anoxic zones only develop during a brief period of the aerated phase for large granules. Modelling results further indicate that a large fraction of electron-donors are actually utilised in aerobic rather than anoxic redox zones - in the bulk or at the granule surface. Thus, full SND cannot be achieved with AGS treating low strength municipal wastewater if a constant DO is maintained during the aeration phase. Optimised aeration strategies are therefore required. 2-step and alternating aeration are tested successfully using mathematical modelling and increase TN removal to 40-79%, without compromising nitrification, and by shifting electron-donor utilisation towards anoxic redox conditions.

Project description:Trichophyton interdigitale had been regarded as anthropophilic, mainly causing non-inflammatory tinea unguium and tinea pedis. T. mentagrophytes, thought to be zoophilic, were regarded as responsible for more inflammatory dermatophytosis. Indian terbinafine-resistant strains, identified with ribosomal internal transcribed spacer as 'genotype VIII', have recently been termed Trichophyton indotineae based on clinical and mycological features. Some of these have shown selective azole resistance as well. Phenotypic studies have shown some similarities and some differences between Trichophyton indotineae, T. mentagrophytes, and T. interdigitale, which are optimally distinguished with HMG locus analyses as three main genotypic groups containing the type strains of T. indotineae (CBS 146623), T. interdigitale (CBS 428.63), and T. mentagrophytes (IHEM 4268) and having approximate differences in geographic distribution. Trichophyton interdigitale was prevalently isolated from superficial infections on exposed body sites such as the scalp and face, while also feet and nails. Trichophyton mentagrophytes has a similar predilection but are also often found on the trunk and genitals. Trichophyton indotineae is mostly restricted to the trunk and groin. T. indotineae lesions are generally highly inflammatory, strongly associated with tinea cruris, corporis, and faciei and less commonly with fingernail onychomycosis and tinea pedis. They cause papulosquamous, pustular, pseudo-imbricata (tinea faciei), lichenoid, and pityriasis rosea (tinea corporis of the neck) types of lesions and spread rapidly to multiple sites and cause painful lesions with itching or burning. Lipolytic abilities of T. mentagrophytes and T. interdigitale are very similar and are higher than those of T. indotineae, which is associated with a higher prevalence of T. mentagrophytes on the human scalp, which is relatively rich in lipids. Keratin degradation is significantly larger in T. interdigitale due to location (tinea pedis and tinea unguium). Identification of T. indotineae through culture alone may not be sufficient for effective treatment decision-making; genetic analysis for resistance profiles is needed for optimum treatment selection. In India, steroid-induced suppression of local cellular immunity as well as an altered cutaneous microbiome provided a window of opportunity for the unique, multidrug-resistant species Trichophyton indotineae.

Dataset Information

Aerobic granules: microbial landscape and architecture, stages, and practical implications.

Publications

Aerobic granules: microbial landscape and architecture, stages, and practical implications.

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