Empirical and theoretical approaches for engineering nitrification

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Inoculum pre-treatment affects the fermentative activity of hydrogen-producing communities in the presence of 5-hydroxymethylfurfural

To enhance the productivity of mixed microbial cultures for fermentative bio-hydrogen production, chemical-physical pre-treatments of the original seed are needed to suppress the activity of hydrogen (H2)-consuming microbes. This approach might influence negatively the composition and diversity of the hydrogen-producing community with consequences on the functional stability of the H2-producing systems in case of perturbations. In this study, we aimed at investigating the effect of different types of pre-treatment on the performance of hydrogen production systems in the presence of an inhibitor, such as 5-hydroxymethylfurfural (HMF). The efficiency and the microbial community structure of batch reactors amended with HMF and inoculated with non-pretreated and pretreated (acid, heat shock, and aeration) anaerobic sludge were evaluated and compared with control systems. The type of pre-treatments influenced the microbial community assembly and activity in inhibited systems, with significant effect on the performance. Cumulative H2 production tests showed that the pre-aerated systems (control and HMF inhibited) were the most efficient, while the difference of the lag phase of the pre-acidified control and HMF-added test was negligible. Analyses of the structure of the enriched microbial community in the systems through PCR-denaturing gradient gel electrophoresis (DGGE) followed by band sequencing revealed that the differences in performance were mostly related to shifts in the metabolic pathways rather than in the predominant species. In conclusion, the findings suggest that the use of specific inoculum pre-treatment could contribute to regulate the metabolic activity of the fermentative H2-producing bacteria in order to enhance the bio-energy production

Algae as promising feedstocks for fermentative biohydrogen production according to a biorefinery approach: A comprehensive review

Interest is growing in the production of biohydrogen from algae through dark fermentation, as alternative to fossil fuels. However, one of the limiting steps of biohydrogen production is the conversion of polymeric carbohydrates into monomeric sugars. Thus, physical, chemical and biological pretreatments are usually employed in order to facilitate carbohydrates de-polymerization and enhancing biohydrogen production from algae. Considering the overall process, biohydrogen production through dark fermentation leads generally to negative net energy balances of the difference between the energy produced as biohydrogen and the direct ones (heat and electricity) consumed to produce it. Thus, to make the overall process economically feasible, dark fermentation of algae must be integrated in a biorefinery approach, where the outlets are valorized into bioenergy or value added biomolecules.The present study reviews recent findings on pretreatments and biohydrogen production through dark fermentation of algae looking at the perspectives of integrating side streams of dark fermentation from algal biomass, according to a biorefinery approach

Non-conventional pretreatments mitigate the inhibitory effect of 5-hydroxymethylfurfural in dark fermentation process

Dark fermentation carried out by mixed microbial cultures is considered a promising process for the production H2 biofuel. However, this process is still not cost effective and unreliable. In mixed culture based systems, the H2 production is enhanced by pretreating the initial seed to suppress the H2 consumers activity. However, this approach has been reported to influence the structure and diversity of H2 producing bacteria (HPB), which may have negative effects on the resilience and resistance of the system when changes of environmental conditions, or presence of inhibitors, occurs. 2. Objectives This study evaluates the effect of pretreatments on the performance and structure of the enriched microbial community and its potential response to an inhibitor (5-hydroxymethylfurfural, HMF). All systems produced hydrogen with a yield ranging between 0.6-0.9 mol H2/mol glucose. HMF decreased the H2 production of 19.1±2.9 % in most of the systems. However, in the pre-aerated systems the hydrogen potential was 22% higher than the other systems without significant difference between C and HMF reactors. Extended lag phases were observed in the pre-acidified tests, though the discrepancy of the lag time in the C and HMF tests was smaller than the other bottles. The high performance of the pre-aerated and acidified HMF was due to increased metabolic activity of the main taxa observed in the systems (Paenibacillus and Clostridium spp.) rather than significant changes in the community composition. In conclusion, pre-aeration and acidification of the initial inoculum can mitigate the negative effect of the HMF. The stressful conditions applied to the original inoculum may have activated cell/community response mechanisms able to counteract the toxicity of the HMF

Invasibility of resident biofilms by allochthonous communities in bioreactors

Invasion of non-native species can drastically affect the community composition and diversity of engineered and natural ecosystems, biofilms included. In this study, a molecular community fingerprinting method was used to monitor the putative establishment and colonization of allochthonous consortia in resident multi-species biofilms. To do this, biofilms inoculated with tap water or activated sludge were grown for 10 days in bubble column reactors W1 and W2, and S, respectively, before being exposed to non-native microbial consortia. These consortia consisted of fresh activated sludge suspensions for the biofilms inoculated with tap water (reactors W1 and W2) and of transplanted mature tap water biofilm for the activated sludge biofilm (reactor S). The introduction of virgin, unoccupied coupons into W1 and W2 enabled us to additionally investigate the competition for new resources (space) among the resident biofilm and the allochthonous consortia. CE-SSCP revealed that after the invasion event changes were mostly observed in the abundance of the dominant species in the native biofilms rather than their composition. This suggests that the resident communities within a bioreactor immediately outcompete the allochthonous microbes and shape the microbial community assemblage on both new coupons and already colonized surfaces for the short term. However, with time, latent members of the allochthonous community might grow up affecting the diversity and composition of the original biofilms. (C) 2015 Elsevier Ltd. All rights reserved

Lab-scale testing of operation parameters for algae based treatment of piggery wastewater

BACKGROUND: Microalgae–bacteria-based processes are among the most promising low-cost technologies to treat livestock wastewaters. The current literature reports the need for pretreatment or dilution of piggery wastewater for adequate microalgal growth. The aim of this study is to optimize the potential of microalgal–bacterial communities to treat undiluted and untreated piggery wastewater by investigating the influence of some operational parameters such as phosphorus and CO 2 availability and hydraulic retention time on the nitrogen removal efficiency and biomass productivity. RESULTS: The microalgal community (dominated by Chlorella spp.) developed quickly and remained quite stable. The rates of biomass production and NH 4 -N removal were 55 ± 30 mg TSS L −1  day −1 and 13 ± 3 mg NH 4 -N L −1  day −1 respectively. CO 2 adjustment had a positive effect on microalgal growth and NH 4 -N removal. CONCLUSION: Data confirm the ability of the microalgal–bacterial consortium to grow on undiluted and untreated piggery wastewater under semi-continuous conditions. Synergy between algae and bacteria seems positive since photosynthesis produces the oxygen needed for ammonia oxidation. © 2019 Society of Chemical Industry

Metataxonomy and functionality of wood-tar degrading microbial consortia

Wood-tar is a liquid material obtained by wood gasification process, and comprises several polycyclic aromatic hydrocarbons (PAH). Tar biodegradation is a very challenging task, due to its toxicity and to its complex chemistry. The ‘microbial resource management’ concerns the use of environmental microbial communities potentially able to provide us services. We applied this concept in tar biodegradation. Tar composed by several PAH (including phenanthrene, acenaphthylene and fluorene) was subjected to a biodegradation process in triplicate microcosms spiked with a microbial community collected from PAH-rich soils. In 20 days, 98.9% of tar was mineralized or adsorbed to floccules, while negative controls showed poor PAH reduction. The dynamics of fungal and bacterial communities was assessed through Automated Ribosomal Intergenic Spacer Analysis (ARISA), 454 pyrosequencing of the fungal ITS and of the bacterial 16S rRNA. Quantification of the degrading bacterial communities was performed via quantitative Real Time PCR of the 16S rRNA genes and of the cathecol 2,3-dioxygenase genes. Results showed the importance of fungal tar-degrading populations in the first period of incubation, followed by a complex bacterial dynamical growth ruled by co-feeding behaviors

Multi-scale modeling of activated sludge floc structure formation in wastewater bioreactors

reserved5A multi-scale computational model was created for the formation of activated sludge floc structure. The model couples mass balances for substrates and biomass at reactor scale with an individual-based approach for the floc morphology, shape and micro-colony development. Among the novel model processes included are the group attachment of micro-flocs to the core structure and the clustering of nitrifiers. Simulation results qualitatively describe the formation of globular colonies of ammonia and nitrite oxidizers in the extracellular polymeric substance produced by heterotrophic microorganisms, as also observed in fluorescence in situ hybridization images. These results are the first step towards a multi-scale model of the activated sludge wastewater treatment systems, which could also be extended to other engineered biological systems.mixedOfiteru, ID; Bellucci, M; Lavric, V; Picioreanu, C; Curtis, TPOfiteru, Id; Bellucci, M; Lavric, V; Picioreanu, C; Curtis, T

Correlation of seasonal nitrification failure and ammonia-oxidizing community dynamics in a wastewater treatment plant treating water from a saline thermal spa

In this work we evaluated the effect of a perturbation on nitrification performance in a wastewater treatment plant (WWTP) treating urban and saline thermal bath wastewater, which regularly occurred during summer months. We wanted to find out if this related to changes in the ammonia oxidizing communities. The bacterial and ammonia-oxidizing bacterial (AOB) community from three different basins of the WWTP were evaluated using PCR-DGGE and cloning and sequencing of 16S rRNA gene fragments, over a six month survey. Both eubacterial and AOB communities underwent continuous change over time, with a particularly prominent shift between the third and fourth month of monitoring for eubacteria and the fourth month and fifth month for AOB. At the same time, reduction of nitrification performance was observed in the WWTP. The AOB community in the activated sludge was dominated by clones with high 16S rRNA sequence identity to halophilic-halotolerant organisms from the Nitrosomonas oligotrohpa and Nitrosomonas marina clusters. A significant correlation (R = 0.97) was detected between the structure of the AOB community and environmental parameters, indicating that the AOB community structure changed in line with the environmental changes that took place over the sampling period. This study reports a clear association of microbial community dynamics (strongly correlated to salinity, temperature, and dissolved oxygen) to nitrification performance. Particularly, ammonia-oxidizing bacteria are severely affected by drastic changes in operational conditions, with direct consequences on WWTP performance