Effect of streptomycin sulphate on the nitrification system in activated sludge: insight into nitrification characteristic, antibiotic resistance gene and microbial community.

Wastewater with residual streptomycin sulphate usually contains high content of ammonia-nitrogen. However, the biological removal process of ammonia-nitrogen under streptomycin sulphate circumstance was unclear. In this study, short-term and long-term effects of streptomycin sulphate on biological nitrification systems, including AOB, NOB, SAOR, SNOR and SNPR, were evaluated comprehensively. The results indicated IC50 for AOB and NOB were 7.5 and 6.6 mg/L. SAOR and SNPR could be decreased to 3.43 ± 0.52 mg N/(g MLSS·h) and 0.24 ± 0.03 mg N/(g MLSS·h) while the addition of streptomycin sulphate was 10 mg/L. When streptomycin sulphate addition was stopped, nitrification ability recovered slightly, SAOR and SNPR increased to 9.37 ± 0.36 mg N/(g MLSS·h) and 1.66 ± 0.49 mg N/(g MLSS·h), respectively. The protein of EPS increased gradually during the acclimatization process, and the maximal protein value was 68.24 mg/g MLSS on the 100th day, however, no significant change of polysaccharose was observed during the acclimatization process. High abundance of ARGs and intI1 was detected in effluent and sludge of the biological treatment system. The maximal relative abundance of aadA1 in the sludge appeared on the 140th day, and increased by 0.99 orders of magnitude. Biological diversity decreased significantly during the acclimatization process, relative abundance of nitrosomonas was changed from 9.07% to 38.68% on the 61st day, while relative abundance of nitrobacter was changed from 1.30% to 0.64%. It should be noted that relative abundances of nitrosomonas and nitrobacter were reduced to 16.17% and 0.25% on the 140th day. This study would be helpful for nitrogen removal in wastewater with antibiotic.

Evaluating acute toxicity in enriched nitrifying cultures: Lessons learned.

Toxicological batch assays are essential to assess a compound's acute effect on microorganisms. This methodology is frequently employed to evaluate the effect of contaminants in sensitive microbial communities from wastewater treatment plants (WWTPs), such as autotrophic nitrifying populations. However, despite nitrifying batch assays being commonly mentioned in the literature, their experimental design criteria are rarely reported or overlooked. Here, we found that slight deviations in culture preparations and conditions impacted bacterial community performance and could skew assay results. From pre-experimental trials and experience, we determined how mishandling and treatment of cultures could affect nitrification activity. While media and biomass preparations are needed to establish baseline conditions (e.g., biomass washing), we found extensive centrifugation selectively destabilised nitrification activities. Further, it is paramount that the air supply is adjusted to minimise nitrite build-up in the culture and maintain suitable aeration levels without sparging ammonia. DMSO and acetone up to 0.03% (v/v) were suitable organic solvents with minimal impact on nitrification activity. In the nitrification assays with allylthiourea (ATU), dilute cultures exhibited more significant inhibition than concentrated cultures. So there were biomass-related effects; however, these differences minimally impacted the EC50 values. Using different nutrient-media compositions had a minimal effect; however, switching mineral media for the toxicity test from the original cultivation media is not recommended because it reduced the original biomass nitrification capacity. Our results demonstrated that these factors substantially impact the performance of the nitrifying inoculum used in acute bioassays, and consequently, affect the response of AOB-NOB populations during the toxicant exposure. These are not highlighted in operation standards, and unfortunately, they can have significant consequential impacts on the determinations of toxicological endpoints. Moreover, the practical procedures tested here could support other authors in developing testing methodologies, adding quality checks in the experimental framework with minimal waste of time and resources.

Immobilization of nitrifying bacteria on composite based on polymers and eggshells for nitrate production.

Nitrification is a key step in biological nitrogen transformation which depends on the performance of specialized microorganisms. Generally, nitrifying bacteria present a low growth rate and performance which can be improved when immobilized as a biofilm. The development of new materials suitable for the immobilization of nitrifying microorganisms is very important in nitrification and wastewater treatment. In this study, the effect of eggshell powder on biofilm formation by Nitrosomonas europaea an ammonium-oxidizing bacteria and Nitrobacter vulgaris a nitrite-oxidizing bacteria, on new polymeric supports were analyzed. Polylactic acid, polyvinyl chloride and polystyrene were tested to produce polymer-eggshells powder composites and used as biofilm supports for nitrifying bacteria. The support material was characterized to identify the most suitable polymer-eggshells powder combination for the cell adhesion and biofilm formation. The nitrification results showed a highest nitrate production of 42 mg NO3--N/L with polylactic acid-eggshell composite, with the best surface properties for cellular adhesion. Finally, scanning electron microscopy micrographs confirmed the best biofilm formed on polylactic acid-eggshell.

Vitamin B12-dependent biosynthesis ties amplified 2-methylhopanoid production during oceanic anoxic events to nitrification.

Bacterial hopanoid lipids are ubiquitous in the geologic record and serve as biomarkers for reconstructing Earth's climatic and biogeochemical evolution. Specifically, the abundance of 2-methylhopanoids deposited during Mesozoic ocean anoxic events (OAEs) and other intervals has been interpreted to reflect proliferation of nitrogen-fixing marine cyanobacteria. However, there currently is no conclusive evidence for 2-methylhopanoid production by extant marine cyanobacteria. As an alternative explanation, here we report 2-methylhopanoid production by bacteria of the genus Nitrobacter, cosmopolitan nitrite oxidizers that inhabit nutrient-rich freshwater, brackish, and marine environments. The model organism Nitrobacter vulgaris produced only trace amounts of 2-methylhopanoids when grown in minimal medium or with added methionine, the presumed biosynthetic methyl donor. Supplementation of cultures with cobalamin (vitamin B12) increased nitrite oxidation rates and stimulated a 33-fold increase of 2-methylhopanoid abundance, indicating that the biosynthetic reaction mechanism is cobalamin dependent. Because Nitrobacter spp. cannot synthesize cobalamin, we postulate that they acquire it from organisms inhabiting a shared ecological niche-for example, ammonia-oxidizing archaea. We propose that during nutrient-rich conditions, cobalamin-based mutualism intensifies upper water column nitrification, thus promoting 2-methylhopanoid deposition. In contrast, anoxia underlying oligotrophic surface ocean conditions in restricted basins would prompt shoaling of anaerobic ammonium oxidation, leading to low observed 2-methylhopanoid abundances. The first scenario is consistent with hypotheses of enhanced nutrient loading during OAEs, while the second is consistent with the sedimentary record of Pliocene-Pleistocene Mediterranean sapropel events. We thus hypothesize that nitrogen cycling in the Pliocene-Pleistocene Mediterranean resembled modern, highly stratified basins, whereas no modern analog exists for OAEs.

The Chemistry, Biology, and Modulation of Ammonium Nitrification in Soil.

Approximately two percent of the world's energy is consumed in the production of ammonia from hydrogen and nitrogen gas. Ammonia is used as a fertilizer ingredient for agriculture and distributed in the environment on an enormous scale to promote crop growth in intensive farming. Only 30-50 % of the nitrogen applied is assimilated by crop plants; the remaining 50-70 % goes into biological processes such as nitrification by microbial metabolism in the soil. This leads to an imbalance in the global nitrogen cycle and higher nitrous oxide emissions (a potent and significant greenhouse gas) as well as contamination of ground and surface waters by nitrate from the nitrogen-fertilized farmland. This Review gives a critical overview of the current knowledge of soil microbes involved in the chemistry of ammonia nitrification, the structures and mechanisms of the enzymes involved, and phytochemicals capable of inhibiting ammonia nitrification.

Urine nitrification with a synthetic microbial community.

During long-term extra-terrestrial missions, food is limited and waste is generated. By recycling valuable nutrients from this waste via regenerative life support systems, food can be produced in space. Astronauts' urine can, for instance, be nitrified by micro-organisms into a liquid nitrate fertilizer for plant growth in space. Due to stringent conditions in space, microbial communities need to be be defined (gnotobiotic); therefore, synthetic rather than mixed microbial communities are preferred. For urine nitrification, synthetic communities face challenges, such as from salinity, ureolysis, and organics. In this study, a synthetic microbial community containing an AOB (Nitrosomonas europaea), NOB (Nitrobacter winogradskyi), and three ureolytic heterotrophs (Pseudomonas fluorescens, Acidovorax delafieldii, and Delftia acidovorans) was compiled and evaluated for these challenges. In reactor 1, salt adaptation of the ammonium-fed AOB and NOB co-culture was possible up to 45mScm-1, which resembled undiluted nitrified urine, while maintaining a 44±10mgNH4+-NL-1d-1 removal rate. In reactor 2, the nitrifiers and ureolytic heterotrophs were fed with urine and achieved a 15±6mg NO3--NL-1d-1 production rate for 1% and 10% synthetic and fresh real urine, respectively. Batch activity tests with this community using fresh real urine even reached 29±3mgNL-1d-1. Organics removal in the reactor (69±15%) should be optimized to generate a nitrate fertilizer for future space applications.

[Effect of Temperature on the Activity Kinetics of Nitrobacter].

A sequencing batch reactor (SBR) was operated in this study to investigate the effect of temperature on the kinetics of Nitrobacter activity among nitrite oxidizing bacteria. At the beginning of the experiment, the NO2--N concentration in the influent was changed to enrich Nitrobacter. Then, the sludge with enriched Nitrobacter was employed to determine the variation of the specific nitrite oxidation rate (SNiOR) during the nitrite oxidation process in batch tests. Metagenomics species annotation and abundance analysis showed that Nitrobacter accounted for 40.3% of the total bacterial population. The variation of SNiOR in the nitrite oxidation process was investigated under different NO2--N concentrations. The effect of temperature on the kinetics of Nitrobacter was investigated using the Monod model. Furthermore, the kinetics model of the effect of temperature on Nitrobacter activity was fitted for statistical analysis. The results showed that SNiOR reached its maximum at 30℃, which was 1.31 g·(g·d)-1. Statistical analysis showed that the Monod equation could describe the effect of substrate concentration on Nitrobacter activity under different temperature conditions. Calculating the temperature coefficient (θ) in different temperature intervals based on the Phelps equation, showed that when the system temperature is lower than 25℃ or higher than 30℃, the reaction rate is more sensitive to temperature changes.

Cobalt-dependent inhibition of nitrite oxidation in Nitrobacter winogradskyi.

Nitrobacter winogradskyi is an abundant, intensively studied autotrophic nitrite-oxidizing bacterium, which is frequently used as a model strain in the two-step nitrification of ammonia (NH3) to nitrate (NO3-) via nitrite (NO2-), either in activated sludge, agricultural field studies or more recently in artificial microbial consortia for organic hydroponics. We observed a hitherto unknown cobalt ion-dependent inhibition of cell growth and NO2- oxidation activity of N. winogradskyi in a mineral medium, which strongly depended on accompanying Ca2+ and Mg2+ concentrations. This inhibition was bacteriostatic, but susceptible to natural chelators. l-Histidine effectively restored cell growth and NO2- oxidation activity of N. winogradskyi in mineral media containing Co2+ with >90% recovery. Our results suggest that Co2+ competed with alkaline earth metals during uptake and that its toxicity was significantly reduced by complexation.

Impact of free nitrous acid shock and dissolved oxygen limitation on nitritation maintenance and nitrous oxide emission in a membrane bioreactor.

This study investigated the initiation and maintenance of nitritation in a membrane bioreactor (MBR) with long solids retention time (SRT) of 43.8 days. Nitritation was initiated within 65 days in the MBR via dissolved oxygen (DO) limitation (<0.5 mg/L). However, nitrite oxidizing bacteria (NOB) (Nitrospira and Nitrobacter) acclimated to the low DO environment and proliferated from day 81, leading to nitrate accumulation. Thereafter, the combined strategy of DO limitation and in-situ generated free nitrous acid (FNA) shock successfully restored and maintained stable nitritation for >70 days. Quantitative polymerase chain reaction (qPCR) results showed that cell abundances of Nitrospira and Nitrobacter decreased by between 50.0 to 68.9% and 60.6 to 96.4%, respectively following the FNA shocks. The maximum ammonium loading rate achieved was 1.81 kg N/(m3 day) with ammonium removal ratio and nitrite accumulation ratio of over 0.97 and 0.96, respectively. Average emission rate of N2O from the MBR was 2.1 ±â€¯0.72% of ammonium removed. FNA shock on day 195 reduced the N2O emission by 13.6%. The strategy developed in this study verified that spiked FNA shock together with DO limitation can be used for maintaining nitritation in MBRs with long SRTs. This method can potentially allow for maintaining nitritation at relatively low capital and operating expenditure when treating high concentration ammonium wastewater.

Analysis of Bacterial Communities in Partial Nitritation and Conventional Nitrification Systems for Nitrogen Removal.

This work studied the microbial community in partial nitritation and complete nitrification processes, which were applied to treat the low Carbon Nitrogen ratio wastewater. The phospholipid fatty acid and quantitative PCR analysis showed that the sludge circulating ratio of 75% resulted in a good microbial growth and a higher abundance of ammonia oxidizing bacteria relative to the nitrite oxidizing bacteria. The Betaproteobacteria were observed to compose the most abundant sludge bacterial groups in the two processes, based on phylogenetic analysis. The phylogenetic analysis of both 16S rRNA and amoA gene indicated that the Nitrosomonas sp. were the dominant ammonia oxidizing bacteria in the partial nitritation process. The relative abundance of nitrite oxidizing bacteria, such as Nitrobacter sp. and Nitrospira sp., were significantly lower in the partial nitritation system over the complete nitrification system. The abundance of Planctomycetes was higher in the partial nitritation process, indicating the anammox reaction occurred in the partial nitritation system. These results suggested the nitrite accumulation rate of circulating ratios 75% was the highest, with an average of 92%,and a possibility to treat the low Carbon Nitrogen ratio wastewater using the partial nitritation/anammox process.

Optimization of the medium for the growth of Nitrobacter winogradskyi by statistical method.

Although Nitrobacter winogradskyi is an important chemoorganotrophic organism for the study of nitrite-oxidizing bacteria physiology as well as nitrification, until now, the mixotrophic medium for this organism growth has not been optimized, comprehensively. In this study, we aimed to improve the growth medium of N. winogradskyi using the one-factor-at-a-time (NaNO2 , glycerol, pH) method. In addition, a further experimental design was carried out based on central composite design with response surface methodology. Different combinations of the three cultural parameters were fitted by multiple regression analysis to calculate the predicted response. Our results suggest that optimal culture condition for the growth of N. winogradskyi was a modified DSMZ 756a medium containing NaNO2 (5·74 g l-1 ) and glycerol (37·88 mmol l-1 ), pH 7·83, a temperature of 28°C and agitation at 120 rev min-1 . The results from a validation experiment (bacterial growth: OD600 1·0293) were close to the value predicted by the quadratic model (OD600 1·0994). In addition, we uncovered the potential mechanism at the cellular and ultrastructural levels. The results indicated that glycerol in the media enhanced the rate of cell division and cell growth by increasing the accumulation of polyphosphates and phosphorus, and high concentrations of NaNO2 provided sufficient energy for growth and contributed to the generation of carboxysomes in cells for CO2 fixation. SIGNIFICANCE AND IMPACT OF THE STUDY: Due to the extremely slow growth rate and the low growth yield of ammonia-oxidizing bacteria and NOB (nitrite-oxidizing bacteria), nitrification is still the rate-limiting step of nitrogen cycle in the current research. Nitrobacter winogradskyi, an important NOB, participates in the second step of nitrification in water and soil. This study reported an optimized culture condition for N. winogradskyi, which increased the growth yield by 5·06 times than that in the basal medium and uncovered the potential mechanism. We expect our study will contribute to the research on water and soil nitrogen cycle. In addition, the optimized culture conditions have the potential to be suitable for the chemoorganotrophic growth of other nitrifiers.

Preparation of Biocomposite Microfibers Ready for Processing into Biologically Active Textile Fabrics for Bioremediation.

Biocomposites, i.e., materials consisting of metabolically active microorganisms embedded in a synthetic extracellular matrix, may find applications as highly specific catalysts in bioproduction and bioremediation. 3D constructs based on fibrous biocomposites, so-called "artificial biofilms," are of particular interest in this context. The inability to produce biocomposite fibers of sufficient mechanical strength for processing into bioactive fabrics has so far hindered progress in the area. Herein a method is proposed for the direct wet spinning of microfibers suitable for weaving and knitting. Metabolically active bacteria (either Shewanella oneidensis or Nitrobacter winogradskyi (N. winogradskyi)) are embedded in these fibers, using poly(vinyl alcohol) as matrix. The produced microfibers have a partially crystalline structure and are stable in water without further treatment, such as coating. In a first application, their potential for nitrite removal (N. winogradskyi) is demonstrated, a typical challenge in potable water treatment.

Effects of the ammonium loading rate on nitrite-oxidizing activity during nitrification at a high dose of inorganic carbon.

In this study, the effects of the ammonium loading rate (ALR) and inorganic carbon loading rate (ILR) on the nitrification performance and composition of a nitrifying bacterial community were investigated in a moving bed biofilm reactor, using poly(vinyl alcohol) (PVA) sponge cubes as a supporting carrier. Between the two ALRs of 0.36 and 2.16 kg-N m-1 d-1, stable partial nitritation was achieved at the higher ALR. Inorganic carbon was dosed at high levels: 33.1, 22.0, 16.4, 11.0, and 5.4 times the theoretical amount. Nonetheless, nitrification efficiency was not affected by the ILR at the two ALRs. Quantitative PCR analysis of ammonia- and nitrite-oxidizing bacteria revealed that ALR is an important determinant of partial nitritation by accumulating ammonia-oxidizing bacteria in the nitrification system. In comparison, two nitrite-oxidizing bacterial genera (Nitrobacter and Nitrospira) showed almost the same relative abundance at various ALRs and ILRs. Terminal restriction fragment length polymorphism targeting the gene of ammonia monooxygenase subunit A revealed that Nitrosomonas europaea dominated under all conditions.

Nitrite-oxidizing activity responds to nitrite accumulation in soil.

The factors influencing how soil nitrite (NO2-)- and ammonia (NH3)-oxidizing activities remain coupled are unknown. A short-term study (<48 h) was conducted to examine the dynamics of NO2--oxidizing activity and the accumulation of NO2- in three Oregon soils stimulated by the addition of 1 mM NH4+ in soil slurry. Nitrite initially accumulated in all three soils; its subsequent decline or slowing of the accumulation of the NO2- pool by 24 h was accompanied by an increase in the size of the nitrate (NO3-) pool, indicating a change in NO2- oxidation kinetics. Bacterial protein synthesis inhibitors prevented the NO2- pool decline, resulting in a larger accumulation in all three soils. Although no significant increases in NO2--oxidizing bacteria nxrA (Nitrobacter) and nxrB (Nitrospira) gene abundances were detected over the time course, maximum NO2- consumption rates increased 2-fold in the treatment without antibiotics compared to no change with antibiotics. No changes were observed in the apparent half saturation constant (Km) values for NO2- consumption. This study demonstrates phenotypic flexibility among soil NO2- oxidizers, which can undergo protein synthesis-dependent increases in NO2- consumption rates to match NH3 oxidation rates and recouple nitrification.

Effects of the chemical characteristics and concentration of inorganic suspended solids on nitrification in freshwater.

The effect of inorganic suspended solids (ISS) on nitrification in freshwater samples has been described inconsistently and remains unclear. This study therefore investigated the effects of the chemical characteristics and concentration of ISS on the nitrification rate by focusing on Nitrosomonas europaea and Nitrobacter winogradskyi as the two most dominant nitrification species in freshwater. Batch-wise experiments were conducted using three chemically well-characterized ISS (i.e. the clay minerals montmorillonite, sericite, and kaolinite in the concentration range 0-1,000 mg L-1). The results show that the ammonium oxidation rate constant (kNH4) was significantly affected by the ISS type, whereas changes in the ISS concentration had an insignificant effect on kNH4, except for kaolinite. The highest kNH4 was observed in samples containing sericite (kNH4, 0.067 L mg-1 day-1), followed by samples containing montmorillonite (kNH4, 0.044 L mg-1 day-1). The ammonium oxidation rate was low in the control and kaolinite samples. Nitrite oxidation was enhanced in the presence of all types of ISS. The rate constants of ISS-mediated nitrite oxidation (kNO2, 0.13-0.21 L mg-1 day-1) were not significantly different among the three types of ISS, but kNO2 was significantly affected by ISS concentration. Overall, our study indicated various effects of the ISS type and concentration on nitrification and, in particular, a notable positive effect of sericite.

Nitrospira are more sensitive than Nitrobacter to land management in acid, fertilized soils of a rapeseed-rice rotation field trial.

Nitrite oxidation is recognized as an essential process of biogeochemical nitrogen cycling in agricultural ecosystems. How nitrite-oxidizing bacteria (NOB) respond to land managements (the effect from the long-term straw incorporation and environmental variability caused by the shift from the upland stage to the paddy stage) in a rapeseed-rice rotation field remains unclear. We found the nitrite oxidation (NO) in soils increased from the upland stage to the paddy stage. An inhibitory effect of the long-term straw incorporation on NO was detectable in the upland stage. The abundance of Nitrospira was always greater than Nitrobacter, and it was affected by the rice-growing and straw incorporation while Nitrobacter was not. NO correlated positively with the abundance of Nitrospira and with soluble sulfate (SO42-), soil moisture, pH and NH4+. The high-throughput sequencing analysis of the nitrite oxidoreductase nxrA and nxrB genes for Nitrobacter- and Nitrospira-like NOB was performed respectively. The dominating (relative abundance>1%) operational taxonomic units (OTUs) from Nitrobacter were closely related to Nitrobacter hamburgensis, whereas those from Nitrospira were affiliated with or related to lineage II, lineage V and several unknown groups. Heatmap analysis showed that a few dominant Nitrobacter OTUs were affected by the straw treatment or the rice-growing, and half of the dominant Nitrospira ones were explained by at least one of the variables. Multi-response permutation procedure (MRPP) and redundancy analyses showed that the Nitrospira-like NOB community changes were significantly shaped by the land managements and the soil chemical properties, including pH, moisture and NH4+, whereas that of the Nitrobacter-like NOB community was not. These results suggested that Nitrospira are more sensitive than Nitrobacter to land management in acid and fertilized soils of a rapeseed-rice rotation field trial.

Effect of the dilution rate on microbial competition: r-strategist can win over k-strategist at low substrate concentration.

The conditions present in both in vitro and in vivo ecosystems determine the microbial population harbouring it. One commonly accepted theory is that a species with a high substrate affinity and low growth rate (k-strategist) will win the competition against a second species with a lower substrate affinity and higher growth rate (r-strategist) if both species are subjected to low substrate concentrations. In this study two nitrite oxidizing bacteria (NOB), Nitrospira defluvii (k-strategist) and Nitrobacter vulgaris (r-strategist), were cultivated in a continuous reactor systems. The minimal hydraulic retention time (HRT) required for maintaining the slower growing Nitrospira was first determined. A reactor containing Nitrobacter was set to the same HRT and Nitrospira was injected to evaluate the effect of the dilution rate on the competition between both species. By following the microbial population dynamics with qPCR analysis, it was shown that not only the substrate affinity drives the competition between k- and r-strategists but also the dilution rate. Experimental data and numerical simulations both revealed that the washout of Nitrobacter was significantly delayed at dilution rates close to the µmax of Nitrospira. The competition could be even reverted towards Nitrobacter (r-strategist) despite of low nitrite concentrations and dilution rates lower than the µmax of Nitrospira.

Enhanced biodegradation of phenolic compounds in landfill leachate by enriched nitrifying membrane bioreactor sludge.

The role of autotrophic nitrification on the biodegradation of toxic organic micro-pollutants presented in landfill leachate was assessed. A two-stage MBR system consisting of an inclined tube incorporated anoxic reactor followed by aerobic submerged membrane reactor was operated under long sludge age condition in which nitrifying bacteria could be enriched. During the reactor operation, organic removal efficiencies were more than 90% whereas phenolic compounds including bisphenol A (BPA) and 4-methyl-2,6-di-tert-butylphenol (BHT) were removed by 65 and 70% mainly through biodegradation in the aerobic reactor even at high feed concentrations of 1000µg/L for both compounds. Batch experiments revealed that enriched nitrifying sludge with nitrifying activities could biodegraded 88 and 75% of BPA and BHT, largely improved from non-nitrifying sludge and enriched nitrifying sludge with the presence of inhibitor. The first-order kinetic rates of BHT and BPA removal were 0.0108 and 0.096h-1, also enhanced by 44% from the non-nitrifying sludge.

Growth modelling of Nitrosomonas europaea ATCC® 19718 and Nitrobacter winogradskyi ATCC® 25391: A new online indicator of the partial nitrification.

The aim of the present work was to study the growth of two nitrifying bacteria. For modelling the nitrifying subsystem of the MELiSSA loop, Nitrosomonas europaea ATCC® 19718 and Nitrobacter winogradskyi ATCC® 25931 were grown separately and in cocultures. The kinetic parameters of a stoichiometric mass balanced Pirt model were identified: µmax=0.054h(-1), decay rate b=0.003h(-1) and maintenance rate m=0.135gN-NH4(+)·gX(-1)·h(-1) for Nitrosomonas europaea; µmax=0.024h(-1), b=0.001h(-1) and m=0.467gN-NO2(-)·gX(-1)·h(-1) for Nitrobacter winogradskyi. A predictive structured model of nitrification in co-culture was developed. The online evolution of the addition of KOH is correlated to the nitritation; the dissolved oxygen concentration is correlated to both nitritation and nitratation. The model suitably represents these two variables so that transient partial nitrification is assessed. This is a clue for avoiding partial nitrification by predictive functional control.

Co-cultivation of microalgae and nitrifiers for higher biomass production and better carbon capture.

The aim of this work was to study co-cultivation of nitrifiers with microalgae as a non-intrusive technique for selective removal of oxygen generated by microalgae. Biomass concentration was, at least, 23% higher in mixed-cultures where nitrifiers kept the dissolved oxygen concentration below 9.0µLL(-1) than in control Chlorella vulgaris axenic-cultures where the concentration of dissolved oxygen was higher than 10.0µLL(-1). This approach to eliminating oxygen inhibition of microalgal growth could become the basis for the development of advanced microalgae reactors for removal of CO2 from the atmosphere, and concentrated CO2 streams. CO2 sequestration would become a chemically and geologically safer and environmentally more sound technology provided it uses microalgal, or other biomass, instead of CO2, for carbon storage.