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Nitrification and denitrification, the key biological processes for thermophilic nitrogen removal, have separately been established in bioreactors at 50 °C. A well-characterized set of kinetic parameters is essential to integrate these processes while safeguarding the autotrophs performing nitrification. Knowledge on thermophilic nitrifying kinetics is restricted to isolated or highly enriched batch cultures, which do not represent bioreactor conditions. This study characterized the stoichiometry and kinetics of two thermophilic (50 °C) nitrifying communities. The most abundant ammonia oxidizing archaea (AOA) were related to the Nitrososphaera genus, clustering relatively far from known species Nitrososphaera gargensis (95.5% 16S rRNA gene sequence identity). The most abundant nitrite oxidizing bacteria (NOB) were related to Nitrospira calida (97% 16S rRNA gene sequence identity). The nitrification biomass yield was 0.20-0.24 g VSS g -1 N, resulting mainly from a high AOA yield (0.16-0.20 g VSS g -1 N), which was reflected in a high AOA abundance in the community (57-76%) compared to NOB (5-11%). Batch-wise determination of decay rates (AOA: 0.23-0.29 d -1 ; NOB: 0.32-0.43 d -1 ) rendered an overestimation compared to in situ estimations of overall decay rate (0.026-0.078 d -1 ). Possibly, the inactivation rate rather than the actual decay rate was determined in batch experiments. Maximum growth rates of AOA and NOB were 0.12-0.15 d -1 and 0.13-0.33 d -1 respectively. NOB were susceptible to nitrite, opening up opportunities for shortcut nitrogen removal. However, NOB had a similar growth rate and oxygen affinity (0.15-0.55 mg O 2 L -1 ) as AOA and were resilient towards free ammonia (IC 50  > 16 mg NH 3 -N L -1 ). This might complicate NOB outselection using common practices to establish shortcut nitrogen removal (SRT control; aeration control; free ammonia shocks). Overall, the obtained insights can assist in integrating thermophilic conversions and facilitate single-sludge nitrification/denitrification., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In specific municipal and industrial cases, thermophilic wastewater treatment (>45 °C) might bring cost advantages over commonly applied mesophilic processes (10-35 °C). To develop such a novel process, one needs sound parameters on kinetics, sludge yield and sludge settleability of three heterotrophic conversions: aerobic carbon removal, denitritation and denitrification. These features were evaluated in acetate-fed sequencing batch reactors (30, 40, 50 and 60 °C). Higher temperatures were accompanied by lower sludge production and maximum specific removal rates, resulting mainly from lower maximum growth rates. Thermophilic denitritation was demonstrated for the first time, with lower sludge production (18-26%), higher nitrogen removal rates (24-92%) and lower carbon requirement (40%) compared to denitrification. Acceptable settling of thermophilic aerobic (60 °C) and anoxic biomass (50 and 60 °C) was obtained. Overall, this parameter set may catalyze the establishment of thermophilic nitrogen removal, once nitritation and nitratation are characterized. Furthermore, waters with low COD/N ratio might benefit from thermophilic nitritation/denitritation., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The development of thermophilic nitrogen removal strategies will facilitate sustainable biological treatment of warm nitrogenous wastewaters. Thermophilic denitrification was extensively compared to mesophilic denitrification for the first time in this study. Two sequential batch reactors (SBR) at 34 °C and 55 °C were inoculated with mesophilic activated sludge (26 °C), fed with synthetic influent in a first phase. Subsequently, the carbon source was switched from acetate to molasses, whereas in a third phase, the nitrate source was fertilizer industry wastewater. The denitrifying sludge maintained its activity at 55 °C, resulting in an immediate process start-up, obtaining nitrogen removal rates higher than 500 mg N g(-1) VSS d(-1) in less than one week. Although the mesophilic SBR showed twice as high specific nitrogen removal rates, the maximum thermophilic denitrifying activity in this study was nearly 10 times higher than the activities reported thus far. The thermophilic SBR moreover had a 73% lower sludge volume index, a 45% lower sludge production and a higher resilience towards a change in carbon source compared with the mesophilic SBR. The higher resilience was potentially related to a higher microbial diversity and evenness of the thermophilic community at the end of the synthetic feeding period. The thermophilic microbial community showed a higher similarity over the different feeding periods implying a more stable community. Overall, this study showed the capability of mesophilic denitrifiers to maintain their activity after a large temperature increase. Existing mesophilic process systems with cooling for the treatment of warm wastewaters could thus efficiently be converted to thermophilic systems with low sludge production and good settling properties., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Although efforts have been made the past few years, knowledge on genomic and phenotypic diversity and occurrence of the denitrification ability in Gram-positive bacteria are still fragmentary. Many environmental monitoring approaches have used nir, nor, and nos genes as marker genes for detection of denitrification or denitrifying bacteria. However, primers used in these methods often fail to detect the genes in specific bacterial taxa, such as Gram-positive denitrifiers. In this study, novel primer sets specifically targeting nirK, qnorB, and nosZ genes of the Firmicute genus Geobacillus were developed by genomic mining and tested in parallel with commonly used primers on a set of phylogenetically closely related denitrifying geobacilli. Novel nirK and qnorB sequences were recovered from all strains tested, whereas nosZ was detected in part of the strain set, which was in agreement with observed phenotypes. Interspecies and modest intraspecies variations in amplified fragment length polymorphism (AFLP) patterns were observed, verifying presence of genomic variation within the strain set. Our study shows that closely related Gram-positive denitrifiers may differ in denitrification phenotype and genotype. But foremost, novel primers targeting very divergent nirK, qnorB, and nosZ gene sequences of Gram-positive denitrifiers, are now available for cultivation-independent environmental surveys., (© 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.)

Although several Gram-positive denitrifiers have been characterized in the past, there is still uncertainty about the occurrence of the denitrification trait among these bacteria. In an isolation campaign on luvisol soil, Bacillus spp. were among the most abundant retrieved cultured denitrifiers next to members of Rhizobiaceae family and genus Cupriavidus. Subsequent screening of 180 representatives of the genus Bacillus (encompassing more than half of the current validly described species diversity in Bacillus) was performed and demonstrated the potential for dissimilatory reduction of nitrogen compounds in 45 of the 87 investigated species, with 19 species containing denitrifying members. The influence of several electron donors and acceptors was tested. The use of more than one electron acceptor, e.g. both nitrate and nitrite, was crucial to detect the denitrification potential of reference strains. Complex electron donors, most suitable for aerobic growth, were ideal for denitrification testing, while retrieval of denitrifiers from the environment was facilitated by the use of defined electron donors, due to less interference of other anaerobic growers. The outcome of the isolation campaign and screening of reference strain set suggest that bacilli may be potential contributors to denitrification in terrestrial and possibly other ecosystems., (Copyright © 2011 Elsevier GmbH. All rights reserved.)

Denitrifying organisms are essential in removing fixed nitrogen pollutants from ecosystems (e.g. sewage sludge). They can be detrimental (e.g. for agricultural soil) and can also produce the greenhouse gas N2O (nitrous oxide). Therefore a more comprehensive understanding of this process has become increasingly important regarding its global environmental impact. Even though bacterial genome sequencing projects may reveal new data, to date the denitrification abilities and features in Gram-positive bacteria are still poorly studied and understood. The present review evaluates current knowledge on the denitrification trait in Gram-positive bacteria and addresses the likely existence of unknown denitrification genes. In addition, current molecular tools to study denitrification gene diversity in pure cultures and environmental samples seem to be highly biased, and additional novel approaches for the detection of denitrifying (Gram-positive) bacteria appear to be crucial in re-assessing the real diversity of denitrifiers.

Microbial-induced CaCO3 precipitation has been widely applied in bacterial-based self-healing concrete. However, the limited biogenetic CaCO3 production by bacteria after they were introduced into the incompatible concrete matrix is a major challenge of this technology. In the present study, the potential of combining two metabolic pathways, urea hydrolysis and nitrate reduction, simultaneously in one bacteria strain for improving the bacterial CaCO3 yield has been investigated. One bacterial strain, Ralstonia eutropha H16, which has the highest Ca2+ tolerance and is capable of performing both urea hydrolysis and nitrate reduction in combined media was selected among three bacterial candidates based on the enzymatic examinations. Results showed that H16 does not need oxygen for urea hydrolysis and urease activity was determined primarily by cell concentration. However, the additional urea in the combined medium slowed down the nitrate reduction rate to 7 days until full NO3− decomposition. Moreover, the nitrate reduction of H16 was significantly restricted by an increased Ca2+ ion concentration in the media. Nevertheless, the overall CaCO3 precipitation yield can be improved by 20 to 30% after optimization through the combination of two metabolic pathways. The highest total CaCO3 precipitation yield achieved in an orthogonal experiment was 14 g/L. It can be concluded that Ralstonia eutropha H16 is a suitable bacterium for simultaneous activation of urea hydrolysis and nitrate reduction for improving the CaCO3 precipitation and it can be studied later, on activation of multiple metabolic pathways in bacteria-based self-healing concrete. [ABSTRACT FROM AUTHOR]

The microbial consumption of nitrous oxide ( N2O) has gained great interest since it was revealed that this process could mitigate the greenhouse effect of N2O. The consumption of N2O results from its reduction to dinitrogen gas ( N2) as part of the denitrification process. However, there is ongoing debate regarding an alternative pathway, namely reduction of N2O to NH4+, or assimilatory N2O consumption. To date, this pathway is poorly investigated and lacks unambiguous evidence. Enrichment of denitrifying activated sludge using a mineral nitrogen-free medium rendered a mixed culture capable of anoxic and oxic N2O consumption. Dilution plating, isolation and deoxyribonucleic acid fingerprinting identified a collection of P seudomonas stutzeri strains as dominant N2O consumers in both anaerobic and aerobic enrichments. A detailed isotope tracing experiment with a P seudomonas stutzeri isolate showed that consumption of N2O via assimilatory reduction to NH4+ was absent. Conversely, respiratory N2O reduction was directly coupled to N2 fixation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nitratation in an OLAND RBC could be controlled through the immersion level. [•] 85–89% of the O2 input was directly absorbed during the air exposure of the discs. [•] Process control strategies solely based on DO level did not seem to be effective. [ABSTRACT FROM AUTHOR]

Energy-positive sewage treatment can be achieved by implementation of oxygen-limited autotrophic nitrification/denitrification (OLAND) in the main water line, as the latter does not require organic carbon and therefore allows maximum energy recovery through anaerobic digestion of organics. To test the feasibility of mainstream OLAND, the effect of a gradual temperature decrease from 29 to 15 °C and a chemical oxygen demand (COD)/N increase from 0 to 2 was tested in an OLAND rotating biological contactor operating at 55–60 mg NH 4+–N L −1 and a hydraulic retention time of 1 h. Moreover, the effect of the operational conditions and feeding strategies on the reactor cycle balances, including NO and N 2O emissions were studied in detail. This study showed for the first time that total nitrogen removal rates of 0.5 g N L −1 day −1 can be maintained when decreasing the temperature from 29 to 15 °C and when low nitrogen concentration and moderate COD levels are treated. Nitrite accumulation together with elevated NO and N 2O emissions (5 % of N load) were needed to favor anammox compared with nitratation at low free ammonia (<0.25 mg N L −1), low free nitrous acid (<0.9 μg N L −1), and higher DO levels (3–4 mg O 2 L −1). Although the total nitrogen removal rates showed potential, the accumulation of nitrite and nitrate resulted in lower nitrogen removal efficiencies (around 40 %), which should be improved in the future. Moreover, a balance should be found in the future between the increased NO and N 2O emissions and a decreased energy consumption to justify OLAND mainstream treatment. [ABSTRACT FROM AUTHOR]

The oxygen-limited autotrophic nitrification/denitrification (OLAND) process comprises one-stage partial nitritation and anammox, catalyzed by aerobic and anoxic ammonium-oxidizing bacteria (AerAOB and AnAOB), respectively. The goal of this study was to investigate whether quorum sensing influences anoxic ammonium oxidation in an OLAND biofilm, with AnAOB colonizing 13% of the biofilm, as determined with fluorescent in situ hybridization (FISH). At high biomass concentrations, the specific anoxic ammonium oxidation rate of the OLAND biofilm significantly increased with a factor of 1.5 ± 0.2 compared to low biomass concentrations. Supernatant obtained from the biofilm showed no ammonium-oxidizing activity on itself, but its addition to low OLAND biomass concentrations resulted in a significant activity increase of the biomass. In the biofilm supernatant, the presence of long-chain acylhomoserine lactones (AHLs) was shown using the reporter strain Chromobacterium violaceum CV026, and one specific AHL, N-dodecanoyl homoserine lactone (C-HSL), was identified via LC-MS/MS. Furthermore, C-HSL was detected in an AnAOB-enriched community, but not in an AerAOB-enriched community. Addition of C-HSL to low OLAND biomass concentrations resulted in a significantly higher ammonium oxidation rate ( p < 0.05). To our knowledge, this is the first report demonstrating that AHLs enhance the anoxic ammonium oxidation process. Future work should confirm which species are responsible for the in situ production of C-HSL in AnAOB-based applications. [ABSTRACT FROM AUTHOR]

The free radical nitric oxide (NO) is an important signaling molecule in the gastrointestinal tract. Besides eukaryotic cells, gut microorganisms are also capable of producing NO. However, the exact mechanism of NO production by the gut microorganisms is unknown. Microbial NO production was examined under in vitro conditions simulating the gastrointestinal ecosystem using L-arginine or nitrate as substrates. L-arginine did not influence the microbial NO production. However, NO concentrations in the order of 90 ng NO-N per L feed medium were produced by the fecal microbiota from nitrate. 15N tracer experiments showed that nitrate was mainly reduced to ammonium by the dissimilatory nitrate reduction to ammonium (DNRA) pathway. To our knowledge, this is the first study showing that gastrointestinal microbiota can generate substantial amounts of NO by DNRA and not by the generally accepted denitrification or L-arginine pathway. Further work is needed to elucidate the exact role between NO produced by the gastrointestinal microbiota and host cells. [ABSTRACT FROM AUTHOR]

Gene sequence analysis of cnorB and qnorB, both encoding nitric oxide reductases, was performed on pure cultures of denitrifiers, for which previously nir genes were analysed. Only 30% of the 227 denitrifying strains rendered a norB amplicon. The cnorB gene was dominant in Alphaproteobacteria, and dominantly coexisted with the nirK gene, coding for the copper-containing nitrite reductase. Both norB genes were equally present in Betaproteobacteria but no linked distributional pattern of nir and norB genes could be observed. The overall cnorB phylogeny was not congruent with the widely accepted organism phylogeny based on 16S rRNA gene sequence analysis, with strains from different bacterial classes having identical cnorB sequences. Denitrifiers and non-denitrifiers could be distinguished through qnorB gene phylogeny, without further grouping at a higher taxonomic resolution. Comparison of nir and norB phylogeny revealed that genetic linkage of both genes is not widespread among denitrifiers. Thus, independent evolution of the genes for both nitrogen oxide reductases does also occur. [ABSTRACT FROM AUTHOR]

Thermophilic nitrification has been proven in lab-scale bioreactors at 50 °C. The challenge is now to develop a solution for thermophilic nitrogen removal, integrating nitrification with denitrification and aerobic carbon removal. This pioneering study aimed at a single-sludge nitrification/denitrification process at 50 °C, through exposing nitrification in a step by step approach to anoxia and/or organics. Firstly, recurrent anoxia was tolerated by a nitrifying community during long-term membrane bioreactor (MBR) operation (85 days), with high ammonium oxidation efficiencies (>98%). Secondly, five organic carbon sources did not affect thermophilic ammonium and nitrite oxidation rates in three-day aerobic batch flask incubations. Moving to long-term tests with sequencing batch reactors (SBR) and MBR (>250 days), good nitrification performance was obtained at increasing COD/N influent ratios (0, 0.5, 1, 2 and 3). Thirdly, combining nitrification, recurrent anoxia and presence of organic carbon resulted in a nitrogen removal efficiency of 92–100%, with a COD/N removed of 4.8 ± 0.6 and a nitrogen removal rate of 50 ± 14 mg N g−1 VSS d−1. Overall, this is the first proof of principle thermophilic nitrifiers can cope with redox fluctuations (aerobic/anoxic) and the aerobic or anoxic presence of organic carbon, can functionally co-exist with heterotrophs and that single-sludge nitrification/denitrification can be achieved. Image 1 • The concept of single-sludge nitrification/denitrification was demonstrated at 50 °C • Thermophilic nitrifiers can cope with redox fluctuations (aerobic/anoxic) • Thermophilic nitrifiers can functionally co-exist with heterotrophs • 92–100% nitrogen removal was achieved at COD/N removed 4.8 ± 0.6 [ABSTRACT FROM AUTHOR]

Microbial self-healing of concrete has been widely investigated, yet the suggested microbial pathways are limited to ureolysis and the aerobic oxidation of carbon sources. Each of these pathways has certain environment and process related drawbacks which arise a need for an alternative pathway to proceed further. This study presents the NO 3 − reduction as an alternative microbial self-healing strategy. In the tests, we used previously described NO 3 − reducing bacteria, and two different porous protective carriers. The highest crack width healed by the bacteria was 370 ± 20 μm in 28 days and 480 ± 16 μm in 56 days. Water tightness regain up to 85% was achieved at the end of 56 days for 465 ± 21 μm crack width. Precipitates were identified as forms of CaCO 3 and were abundant in microbial specimens particularly on the inner crack surface. The findings evidence the potential of the NO 3 − reduction pathway for development of microbial self-healing concrete. [ABSTRACT FROM AUTHOR]

Abstract: Three identical sequential batch reactors (SBRs) were each inoculated with sludge from a full-scale wastewater treatment plant (WWTP) treating a waste stream of different origin, i.e. a hospital, a meat processing company, and a municipal WWTP. The SBRs were run in parallel for 84 consecutive days to investigate whether the reactors would become more phylogenetically similar or stay separated concerning their functionality and microbial communities. Overall, the nitrification functionality was high throughout the experiment, and the size and structure of the sludge flocs were very similar. The total bacterial and ammonia-oxidizing bacterial (AOB) communities were analyzed by PCR-DGGE. Cluster analysis demonstrated very distinct bacterial communities in the three SBRs, not showing any trend becoming more similar. The carrying capacity, dynamics and functional organization of the communities were assessed by DGGE analysis and based on these patterns the range-weighted richness, moving window analysis, and constructing Pareto–Lorenz evenness distribution curves were calculated. Between the SBRs, highly comparable internal structure and dynamics of the AOB communities were observed, although they had only one AOB DGGE band in common. These observations indicate that community characteristics such as the extent of biodiversity and dynamics are more important indicators of good microbial functionality than the presence of certain specific species. [Copyright &y& Elsevier]

Abstract: The autotrophic two-species biofilm from the packed bed reactor of a life-support system, containing Nitrosomonas europaea ATCC 19718 and Nitrobacter winogradskyi ATCC 25391, was analysed after 4.8 years of continuous operation performing complete nitrification. Real-time quantitative polymerase chain reaction (Q-PCR) was used to quantify N. europaea and N. winogradskyi along the vertical axis of the reactor, revealing a spatial segregation of N. europaea and N. winogradskyi. The main parameters influencing the spatial segregation of both nitrifiers along the bed were assessed through a multi-species one-dimensional biofilm model generated with AQUASIM software. The factor that contributed the most to this distribution profile was a small deviation from the flow pattern of a perfectly mixed tank towards plug-flow. The results indicate that the model can estimate the impact of specific biofilm parameters and predict the nitrification efficiency and population dynamics of a multispecies biofilm. [Copyright &y& Elsevier]

Microbial healing of concrete cracks is a relatively slow process, and meanwhile the steel rebar is exposed to corrosive substances. Nitrate reducing bacteria can inhibit corrosion and provide crack healing, by simultaneously producing NO 2 − and inducing CaCO 3 precipitation. In this study, the functionality of one non-axenic and two axenic NO 3 − reducing cultures for the development of corrosion resistant self-healing concrete was investigated. Both axenic cultures survived in mortar when incorporated in protective carriers and became active 3 days after the pH dropped below 10. The non-axenic culture named “activated compact denitrifying core” (ACDC) revealed comparable resuscitation performance without any additional protection. Moreover, ACDC induced passivation of the steel in corrosive electrolyte solution (0.05 M NaCl) by producing 57 mM NO 2 − in 1 week. The axenic cultures produced NO 2 − up to 26.8 mM, and passivation breakdown and pitting corrosion were observed. Overall, ACDC appears suitable for corrosion resistant microbial self-healing concrete. [ABSTRACT FROM AUTHOR]

Ammonia gas is conventionally treated in nitrifying biofilters; however, addition of organic carbon to perform post-denitrification is required to obtain total nitrogen removal. Oxygen-limited autotrophic nitrification/denitrification (OLAND), applied in full-scale for wastewater treatment, can offer a cost-effective alternative for gas treatment. In this study, the OLAND application thus was broadened toward ammonia loaded gaseous streams. A down flow, oxygen-saturated biofilter (height of 1.5 m; diameter of 0.11 m) was fed with an ammonia gas stream (248 ± 10 ppmv) at a loading rate of 0.86 ± 0.04 kg N m-3 biofilter d-1 and an empty bed residence time of 14 s. After 45 days of operation a stable nitrogen removal rate of 0.67 ± 0.06 kg N m-3 biofilter d-1, an ammonia removal efficiency of 99%, a removal of 75-80% of the total nitrogen, and negligible NO/N2O productions were obtained at water flow rates of 1.3 ± 0.4 m3 m-2 biofilter section d-1. Profile measurements revealed that 91% of the total nitrogen activity was taking place in the top 36% of the filter. This study demonstrated for the first time highly effective and sustainable autotrophic ammonia removal in a gas biofilter and therefore shows the appealing potential of the OLAND process to treat ammonia containing gaseous streams. [ABSTRACT FROM AUTHOR]

The presence of elevated concentrations of nitrates in drinking water has become a serious concern worldwide. The use of autotrophic denitrification in microbial fuel cells (MFCs) for waters with low ionic strengths (i.e., 1000 μS·cm-1) has not been considered previously. This study evaluated the feasibility of MFC technology for water denitification and also identified and quantified potential energy losses that result from their usage. The low conductivity (<1600 μS·cm-1) of water limited the nitrogen removal efficiency and power production of MFCs and led to the incomplete reduction of nitrate and the nitrous oxide (N2O) production (between 4 and 20% of nitrogen removed). Cathodic overpotential was identified as the main energy loss factors (83-90% of total losses). That high overpotential was influenced by denitrification intermediates (NO2- and N2O) and the potential used by microorganisms for growth, activation, and maintenance. [ABSTRACT FROM AUTHOR]

This study assessed the technical feasibility to treat digested black water from vacuum toilets (> 1000 mg NH4+-NL-1) in a lab-scale oxygen-limited autotrophic nitrification/denitrification (OLAND) rotating biological contactor. After an adaptation period of 2.5 months, a stable nitrogen removal rate of ca. 700 mg NL-1d-1 was reached over the subsequent 5 months. Suppression at the nitrite oxidizing bacteria at free ammonia levels above 3 mg NL-1 resulted in a nitrogen removal efficiency of 76%. The favorable ratios of both organic and inorganic carbon to nitrogen guaranteed endured anammox activity and sufficient buffering capacity, respectively. Quantitative FISH showed that aerobic and anoxic ammonium-oxidizing bacteria (AerAOB and AnAOB) made up 43 and 8% of the biofilm, respectively. Since a part of the AerAOB was probably present in anoxic biofilm zones, their specific ammonium conversion was very low, in contrast to the high specific AnAOB activity. DGGE analysis showed that the dominant AerAOB and AnAOB species were resistant to the transition from synthetic medium to digested black water. This study demonstrates high-rate nitrogen removal from digested black water by one-stage partial nitritation and anammox, which will allow a significant decrease in operational costs compared to conventional nitrification/denitrification. [ABSTRACT FROM AUTHOR]

An evolutionary algorithm was applied to study the complex interactions between medium parameters and their effects on the isolation of denitrifying bacteria, both in number and in diversity. Growth media with a pH of 7 and a nitrogen concentration of 3 mM, supplemented with 1 ml of vitamin solution but not with sodium chloride or riboflavin, were the most successful for the isolation of denitrifiers from activated sludge. The use of ethanol or succinate as a carbon source and a molar C/N ratio of 2.5, 20, or 25 were also favorable. After testing of 60 different medium parameter combinations and comparison with each other as well as with the standard medium Trypticase soy agar supplemented with nitrate, three growth media were highly suitable for the cultivation of denitrifying bacteria. All evaluated isolation conditions were used to study the cultivable denitrifier diversity of activated sludge from a municipal wastewater treatment plant. One hundred ninety-nine denitrifiers were isolated, the majority of which belonged to the Betaproteobacteria (50.4%) and the Alphaproteobacteria (36.8%). Representatives of Gammaproteobacteria (5.6%), Epsilonproteobacteria (2%), and Firmicutes (4%) and one isolate of the Bacteroidetes were also found. This study revealed a much more diverse denitrifying community than that previously described in cultivation-dependent research on activated sludge. [ABSTRACT FROM AUTHOR]

Techniques for bacteria based self-healing concrete are currently limited to indirect bacterial activity measurements and visual crack closing effects after self-healing has occurred. In the present study, direct and reliable bacteria survival measurements after encapsulation in protective carriers were carried out by utilizing microcalorimetry analysis. After further incorporation in mortar oxygen consumption was determined by use of an optical oxygen sensing system. The microscope analysis showed that a 90% sporulation of Bacillus sphaericus was achieved after 24 h incubation. Microcalorimeter measurements detected the heat generation from microbial activity on the third day of incubation which provides direct evidence that bacteria can be activated after encapsulation inside the hydrogel. The application of the O 2 sensing film on cracked mortar showed a high oxygen concentration reduction (66%) near the crack opening. This confirmed the activation of B. sphaericus and use of oxygen as an electron acceptor for their metabolism after incorporation inside mortar specimens. • Urea hydrolysis and nitrate reduction were combined for inducing CaCO3 precipitation. • Microcalorimetry provides direct evidence of bacteria activation inside the hydrogel. • O 2 concentration reduction near the crack mouth proves the activity of encapsulated bacteria in mortar. [ABSTRACT FROM AUTHOR]