Nitrification Kinetics Research Articles

Correction: Zajac et al. Changes in Nitrification Kinetics and Diversity of Canonical Nitrifiers and Comammox Bacteria in a Moving Bed Sequencing Batch Biofilm Reactor—A Long-Term Study. Water 2024, 16, 534

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Benefits and limits of biological nitrification inhibitors for plant nitrogen uptake and the environment

Plant growth and high yields are secured by intensive use of nitrogen (N) fertilizer, which, however, pollutes the environment, especially when N is in the form of nitrate. Ammonium is oxidized to nitrate by nitrifiers, but roots can release biological nitrification inhibitors (BNIs). Under what conditions does root-exudation of BNIs facilitate nitrogen N uptake and reduce pollution by N loss to the environment? We modeled the spatial–temporal dynamics of nitrifiers, ammonium, nitrate, and BNIs around a root and simulated root N uptake and net rhizosphere N loss over the plant’s life cycle. We determined the sensitivity of N uptake and loss to variations in the parameter values, testing a broad range of soil–plant-microbial conditions, including concentrations, diffusion, sorption, nitrification, population growth, and uptake kinetics. An increase in BNI exudation reduces net N loss and, under most conditions, increases plant N uptake. BNIs decrease uptake in the case of (1) low ammonium concentrations, (2) high ammonium adsorption to the soil, (3) rapid nitrate- or slow ammonium uptake by the plant, and (4) a slowly growing or (5) fast-declining nitrifier population. Bactericidal inhibitors facilitate uptake more than bacteriostatic ones. Some nitrification, however, is necessary to maximize uptake by both ammonium and nitrate transporter systems. An increase in BNI exudation should be co-selected with improved ammonium uptake. BNIs can reduce N uptake, which may explain why not all species exude BNIs but have a generally positive effect on the environment by increasing rhizosphere N retention.

Start-Up Performance and Process Kinetics of a Two-Stage Partial Nitrification–Anaerobic Ammonium Oxidation Reactor

The study of two-stage partial nitrification–anaerobic ammonium oxidation (PN/A) reactors, which are advantageous in engineering applications, still lacks research on process kinetics. Therefore, in this study, the start-up performance and process kinetics of a two-stage PN/A reactor were evaluated by controlling the reaction conditions, for which the two reactors were inoculated with sludge, incubated separately, and then operated in tandem. Increasing the ammonia load of the reactor during the 60 d stabilization period resulted in a nitrogen accumulation rate of 96.93% and a [NO2− − N]Eff/[NH4+ − N]Eff ratio of 1.33, which is close to the theoretical value of 1.32. Successful initiation of the A reactor was achieved after 55 d of operation by inoculating with anammox-activated sludge and granular activated carbon, and the PN and A reactors then successfully operated in combination for 20 d, with an average NH4+ − N efficiency of 99.04% and the NH4+ − N load of the A reactor showing an “S-shaped” curve. An analysis of the microbial growth kinetic models indicated that the removal of NH4+ − N could be successfully described by the logistic, modified logistic, modified Gompertz, and modified Boltzmann models. A strong association between the model and the dependent variable was observed. The process kinetic analysis showed that the removal of NH4+ − N from reactor A could be simulated under steady-state conditions, using the Grau second-order model. The parameters obtained from the model analysis are expected to help predict the denitrification performance of the reactor, facilitate operational management and control, and thus provide a promising research basis for the introduction of automated control systems.

Kinetics of ammonium removal from domestic wastewater by partial nitrification and anammox process

The research was conducted for 210 days on a partial nitrification/Anammox system (PN/A) using fixed bed biomass carrier to remove nitrogen in domestic wastewater. Total nitrogen and ammonium removal efficiency reached 69.8 % and 91.4 %, respectivety. In this study, we investigated three kinetic models (the first-order, Grau second-order and Stover Kincannon model) to determine which model is most suitable to describe the kinetics of the partial nitrification and anammox process. The results have shown that the Stover-Kincannon model is the most suitable and applicable for prediction the substrate concentration in the wastewater and the optimal volume of the reactor. The values of saturation constant (KB) and the max ultilizaion rate (Umax) were calculated for partial nitrification process as 15.489 and 8.038 (mg L−1 d−1). respectively. The research has also determined the values of KB and Umax for anammox process as 1.738 and 1.241 (mg L−1 d−1), respectively.

Changes in Nitrification Kinetics and Diversity of Canonical Nitrifiers and Comammox Bacteria in a Moving Bed Sequencing Batch Biofilm Reactor—A Long-Term Study

A lab-scale pure moving bed sequencing batch biofilm reactor (MBSBBR) was employed to investigate changes in nitrification kinetics and microbial diversity. The MBSBBR operated under different aeration strategies (defined by the ratio of the duration of the subphases with (t1) and without (t2) aeration (R = t2/t1)) − continuous (R = 0) and intermittent (with constant time of non-aerated subphases (t2 = 10 min) and variable duration of subphases with aeration (t1 = 40 min–R = 1/4, t1 = 30 min–R = 1/3, t1 = 20 min–R = 1/2) and dissolved oxygen (DO) concentrations (6 mg/L; 3.5 mg/L). Moreover, the reactor’s organic (OLR) and nitrogen (NLR) loading rates were changed in the following ranges: OLR—537–402 gCOD/m3·d, NLR—64–48 gN/m3·d. The obtained results showed that, irrespective of changes introduced in particular series, a highly effective nitrification process (93.36 ± 2.13%) was achieved. The activity of bacteria capable of oxidizing ammonia nitrogen changed differently from that of bacteria capable of oxidizing nitrites (NOB). An increase in R was the primary factor changing the activity of ammonia-oxidizing microorganisms. NOB activity was affected only by the reduction of OLR and NLR. NOB were the predominant bacterial group, consistent with the kinetics studies. A DO decrease caused an increase in the abundance of AOB, NOB, and Comammox bacteria. Comammox bacteria were the most abundant at R = 1/2 and DO = 3.5 mg/L.

Nitrification kinetics, N2O emission, and energy use in intermittently aerated hybrid reactor under different organic loading rates

This study investigated the impact of intermittent aeration strategies and reduction in the reactor’s organic and nitrogen loading rates on the course of particular stages of the nitrification process, as well as energy consumption and N2O emissions in a hybrid reactor with nitrification/denitrification. Each of the analysed series revealed the greatest ammonia oxidation activity in activated sludge flocs. The highest activity of nitrite nitrogen oxidation was demonstrated in the case of biofilm. A reduction in the reactor’s organic and nitrogen loading rate value had a greater effect on changes in the activity of ammonia-oxidizing bacteria than nitrite-oxidizing bacteria. In a system where the operation of air pumps was controlled through switching them and off according to the adopted ratio between non-aerated and aerated sub-phase times and the assumed oxygen concentration, a reduction in the duration of aerated sub-phases caused no decrease in energy use for aeration. Lower N2O emission was recorded when the reactor operated with a longer duration of aerated sub-phases.

Effect of biocarrier material on nitrification performance during start-up in freshwater RAS

Biofilters are key components in recirculating aquaculture systems (RAS). For ensuring cost-efficient function of biofilters, characteristics of biocarriers such as shape, material, surface area, density, longevity, and price needs to be evaluated. In this study, we compared otherwise identical biocarriers made of polyethylene (PE) against ones made of polypropylene (PP) and PP biocarriers with three different levels of pigment (carbon black) addition (without added pigment, semi-pigmented, fully-pigmented). The four types of biocarriers were tested in 12 parallel moving bed bioreactors under identical conditions receiving water from a semi-commercial freshwater RAS with rainbow trout. Measurements of total ammonium nitrogen (TAN) and nitrite-nitrogen (NO2--N) removal rates and nitrification kinetics were carried out by spiking events with NH4Cl or NaNO2 two, four, and six weeks after start-up. The results showed all biofilters removed TAN only after two weeks of operation, and that biofilters with PP biocarriers had a shorter maturation time, reaching their maximum TAN removal rate at week 4, while PE biofilters reached equal maximum at week 6. Biofilters with PE had generally lower NO2--N removal rates and first-order reaction constants than PP biofilters. Pigmentation level had a minor effect on TAN and NO2--N removal rates and kinetics, as fully pigmented biocarriers initially were found to have lower removal rates and first order constants for TAN and NO2--N than semi-pigmented or biocarriers without added pigment. Overall, the results suggest that PE is inferior biocarrier material than PP, due to the longer start-up period and nitrite accumulation, which might be related to the differences in the surface characteristics between these two materials. Furthermore, the results indicate that pigment addition does not provide any extra benefit for nitrification.

Modeling of Nitrification Kinetics in a Respirometric Biosensor under Suboptimal Conditions

Sensitive detection with cell biosensors requires optimization of their working conditions and standardization of the response in variable physicochemical conditions. The introduction of an analyte to a sensor, which contributes to this variability, may account for the modeling of microbial metabolism. We constructed a multiparameter model of a water toxicity sensor of Automatic Biodetector for Water Toxicity (ABTOW), developed by our group and based on nitrifying bacteria. The model describes the kinetics of nitrification as a function of four orthogonal parameters: temperature, pH, oxygen and ammonium concentration. Furthermore, we characterized the signal-to-noise ratio (SNR) of the ABTOW readout as a function of these parameters. Thus, a region of parameter space corresponding to optimal ABTOW operation is identified and its sensitivity quantified. We applied the model to describe the ABTOW performance in non-equilibrium conditions produced by rapid changes in pH and temperature. In sum, the model based on four physicochemical parameters describes changes in the biosensor’s activity, the biological element of which are nitrifying bacteria characterized by simple chemolithoautotrophic metabolism. The description of reaction kinetics through multiparameter modeling in combination with stability analysis can find application in process control in biotechnology, biodetection and environmental research.

Effect of peracetic acid solution on a nitrifying culture: Kinetics, inhibition, cellular and transcriptional responses

Peracetic acid (PAA) has been widely used as a disinfectant in many industries. However, information related to the potential inhibitory effect of PAA solutions (PAA and H2O2) on biological wastewater treatment processes is very limited. The work reported here assessed the effect of PAA and H2O2 solutions on nitrification kinetics and inhibition, cellular level responses and gene expression of a suspended-growth nitrifying culture. The initial ammonia removal and nitrate production rates significantly decreased at 1/0.14 to 3/0.42 mg/L PAA/H2O2. H2O2 up to 3 mg/L did not impact nitrification, cell viability or related respiratory activities; thus, the impact of the PAA solution is attributed to PAA alone or in some combination with H2O2. Nitrification inhibition by PAA was predominantly related to enzyme inhibition, rather than to loss of cell viability and/or cell lysis. PAA and H2O2 negatively affected Nitrosomonas but resulted in Nitrosospira enrichment. Most nitrogen metabolism-related genes (e.g., hydroxylamine oxidoreductase and nitrite oxidoreductase genes) as well as oxidase genes (e.g., cytochrome c oxidase, catalase-peroxidase, and peroxidase genes) were upregulated in PAA- and H2O2-amended cultures. Major ATPase genes were downregulated while ATP synthase genes upregulated under the effect of PAA and/or H2O2. Upregulation of ATP-dependent protease genes indicates protein damage predominantly caused by PAA rather than H2O2. The transcriptional level of genes related to cell division and DNA repair did not show a particular pattern; thus, cell division functionality and DNA integrity were not significantly affected by PAA or H2O2. The results of this study have significant implications in the design and operation of effective biological nitrogen removal systems for the treatment of PAA-bearing wastewater.

Temperature affects the oxidation kinetics of co-cultured Nitrobacter winogradskyi and Nitrobacter hamburgensis in nitrite-oxidizing bioreactor

Nitrobacter is an important chemolithoautotrophic nitrite-oxidizing bacteria and has exhibited potential for the oxidation of nitrite to nitrate in natural and engineered ecosystems. Microbial kinetics of Nitrobacter have been widely reported and are used to model the nitrite oxidation process and optimize the design parameters of the biological processes for wastewater treatment. However, limited information is available about the nitrite oxidation kinetics of the two coexisting Nitrobacter stains, namely the Nitrobacter winogradskyi and the Nitrobacter hamburgensis. The current work mainly focuses on the influence of temperature on the kinetic characteristics of the coexistence of N. winogradskyi and hamburgensis, which were enriched in a lab-scale sequencing batch reactor (SBR) through 419 operating cycles. The results for the kinetic properties of nitrite oxidation of the enrichments within the temperature range of 15–35 °C showed that the maximum specific rate (rmax), half-saturation coefficients (KS), growth-rate constants (μmax), and temperature coefficient (θ) lied within the ranges of 22.91–93.58 mM/g/d, 0.13–2.47 mM, 0.026–0.105 1/d, and 1.038–1.137, respectively. The maximum activity and nitrite affinities of tested microorganisms were sensitive to temperature. Furthermore, the relationships between temperature and normalized kinetic parameters (rmax, μmax, and θ) were developed as: 0.069T − 0.076 (15–30 °C), 0.0057T − 0.062 (15–30 °C), and 5.7T40.9+T+T210.5 (15–35 °C), respectively. Moreover, the capabilities of N. winogradskyi and N. hamburgensis to oxidize nitrite were lost at the temperature of 35 °C and were non-recoverable at temperature of 25 °C. Overall, the findings of the present work can provide available data for future study about the mathematic models of nitrification kinetics and ecological niche differentiation of Nitrobacter species.

The Role of Microbial Biofilm in Removing Ammonia in Floating Treatment Wetlands

Abstract Laboratory experiments were conducted under controlled conditions to quantify the potential of microbial transformation associated with floating matrix of floating treatment wetland (FTW) in ammonia removal and nitrification kinetics. The effect of different design parameters on ammonia removal from synthetic medium was investigated to optimize system performance. Effects of surface area of mat material, range of ammonia concentrations, and aeration on ammonia removal kinetics were studied using microcosm systems. A simple dynamics model of mineral nitrogen transformation was used as a framework for interpreting the experimental results. The results revealed that ammonia removal was enhanced in FTWs, and the magnitude of removal was controlled by the design factors examined. Removal by nitrification was directly proportional to mat surface area. The higher ammonia removal efficiency was caused by a larger surface area, which could support the growth of more microbes. Removal rate constants for treatments were 0.011, 0.015, 0.026, 0.035, and 0.033 day–1 for T1, T2, T3, T4, and T5, respectively. There was also a clear inhibitory effect of NH3 on second-stage nitrification manifested as low production of NO3–. Quantitative index of optimized knit/calibrated knit indicated high inhibition effects of NH3 at high concentration of total ammonia (60 mg N L–1). There was no major effect of oxygen saturation on NHx removal using aerated and nonaerated conditions. Better mechanistic understanding of the fundamental processes operating in FTWs should provide the basis for improving FTW design and efficacy.

Comparisons of nitrite accumulation, microbial behavior and nitrification kinetic in continuous stirred tank (ST) and plug flow (PF) moving bed biofilm reactors

Two types of continuous stirred tank moving bed biofilm reactors (ST-MBBR) and plug flow MBBR (PF-MBBR) were compared for nitrification. PF-MBBR showed strong shock resistance to temperature, and ammonium oxidation ratio (AOR) was 9.63% higher than that in the ST-MBBR, although the average biomass and biofilm thickness of ST-MBBR were 7.32–18.59%, 9.44–14.06% higher than those in the PF-MBBR. Meanwhile, a lower nitrite accumulation ratio (NAR) was observed (54.88%) in the PF-MBBR than the ST-MBBR (78.92%) due to different operation modes, and the divergence was demonstrated by the microbial quantitative analysis. Nitrification kinetics revealed that the temperature coefficient (θ) in the ST-MBBR (1.068) was much higher than that in the PF-MBBR (1.006–1.015), proving the contrasting nitrification performances caused by temperature shock. According to the Monod equation, the half-saturation coefficient (KN) in the ST-MBBR was 0.19 mg/L while it varied around 0.12–0.24 mg/L in the PF-MBBR, revealing various NH4+ affinity owing to different biofilm thickness and microbial composition. Finally, MBBR optimization related to operation mode, temperature, and free ammonium (FA) inhibition for nitrite accumulation was discussed.

Primings of soil organic matter and denitrification mediate the effects of moisture on nitrous oxide production

Nitrogen-fertilized agricultural soils are major emitters of the potent greenhouse gas nitrous oxide (N2O). Although soil moisture is known to drive N2O production, the influence of moisture on the priming effects of labile N additions, which alter the N2O production from native soil organic matter (SOM), remains understudied. We investigated how moisture impacts N2O primings, nitrification kinetics, and allocation of N2O sources between nitrification and denitrification. We evaluated urea additions at five water-filled pore spaces (WFPS): 31, 41, 53, 65, and 78%. Based on δ15N–N2O site preference (SP), the denitrification source (encompassing bacterial- and nitrifier-denitrification) amply dominated across all moistures. At moistures >60% WFPS, SP exhibited a narrow range of 1.2–1.6‰, whereas at 31% WFPS, SP rose to 9.4‰ (P < 0.001). These SPs translated into denitrification sourcing consistently four-fifth of the N2O production in the wettest soils. With drier soils, denitrification gradually decreased, but it still produced three-fifth of the N2O even at the driest soil (31% WFPS). Based on time courses of ammonium and nitrate concentrations, first-order kinetics (k1) modelling showed much slower nitrification rates at 31% WFPS (0.1 day−1) than the peak nitrification witnessed consistently at both 65 and 78% WFPSs (1.0 day−1). By using isotopically-labelled urea, we further allocated N2O production into SOM-N and urea-N sources. In soils receiving urea, SOM-N contribution to N2O production changed from being 77% in the driest soils to 46% in the wettest soil. Along this aeration-to-moisture gradient, net N2O priming steadily switched from being negative (−20%) in the driest soils to become positive (+14%) at the wettest soil, and this shifting trajectory intercepted the neutral 0% priming at 60% WFPS. Results indicate that pulse N2O emissions commonly reported in recently N-fertilized fields are triggered by soil moisture surpassing this threshold, which collectively accelerates positive primings of SOM and denitrification.

Nitrification characteristics of long-term idle aerobic activated sludge during domestication.

Nitrite accumulation usually occurred when domesticating the idle aerobic activated sludge. A sequencing batch reactor (SBR) was used to investigate whether the short-cut nitrification sludge could be cultivated using the idle sludge as inoculated sludge. The results showed that the nitrification process consisted of three stages. In the first stage, the activity of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were very low with almost no nitrification performance. In the second stage, the activity of AOB started to recover with the effluent NH4+-N gradually decreased to 0.29mgL-1, while NOB was alternately inhibited by free ammonia (FA), free nitrous acid (FNA), and nitrite. The effluent NOx--N was mainly NO2--N with an average nitrite accumulation ratio of 74.00%. In the third stage, the nitrification altered from short-cut nitrification to complete nitrification, and the nitrification kinetics of AOB and NOB were both well-fitted to the Monod equation (R2 > 0.92). The variations of effluent pH and ORP between cycles could indicate the recovery stage of the nitrifying ability. Through monitoring the curves of effluent pH and ORP, when the domestication process is between the pH peak and ORP plateau, the short-cut nitrification sludge could be cultivated. This study revealed the mechanism of nitrite accumulation during the domestication of long-term idle aerobic activated sludge, and established a control strategy to accelerate the domestication.

Contingent Effects of Liming on N2O-Emissions Driven by Autotrophic Nitrification

Liming acidic soils is often found to reduce their N2O emission due to lowered N2O/(N2O + N2) product ratio of denitrification. Some field experiments have shown the opposite effect, however, and the reason for this could be that liming stimulates nitrification-driven N2O production by enhancing nitrification rates, and by favoring ammonia oxidizing bacteria (AOB) over ammonia oxidizing archaea (AOA). AOB produce more N2O than AOA, and high nitrification rates induce transient/local hypoxia, thereby stimulating heterotrophic denitrification. To study these phenomena, we investigated nitrification and denitrification kinetics and the abundance of AOB and AOA in soils sampled from a field experiment 2–3 years after liming. The field trial compared traditional liming (carbonates) with powdered siliceous rocks. As expected, the N2O/(N2O + N2) product ratio of heterotrophic denitrification declined with increasing pH, and the potential nitrification rate and its N2O yield (YN2O: N2O-N/NO3–-N), as measured in fully oxic soil slurries, increased with pH, and both correlated strongly with the AOB/AOA gene abundance ratio. Soil microcosm experiments were monitored for nitrification, its O2-consumption and N2O emissions, as induced by ammonium fertilization. Here we observed a conspicuous dependency on water filled pore space (WFPS): at 60 and 70% WFPS, YN2O was 0.03-0.06% and 0.06–0.15%, respectively, increasing with increasing pH, as in the aerobic soil slurries. At 85% WFPS, however, YN2O was more than two orders of magnitude higher, and decreased with increasing pH. A plausible interpretation is that O2 consumption by fertilizer-induced nitrification cause hypoxia in wet soils, hence induce heterotrophic nitrification, whose YN2O decline with increasing pH. We conclude that while low emissions from nitrification in well-drained soils may be enhanced by liming, the spikes of high N2O emission induced by ammonium fertilization at high soil moisture may be reduced by liming, because the heterotrophic N2O reduction is enhanced by high pH.

Modeling of the effect of zeolite concentration on the biological nitrification process in the presence of sulfide and organic matter

The evaluation of the nitrification kinetics in the simultaneous presence of sulfide and organic matter using zeolite as improver was the main goal of this work. According to the sensitivity and collinearity analyses, five parameters were the most sensitive in the model, whose calibrated values were: μ max, AOB = 0.02642 ± 0.002 h−1; μ max, NOB = 0.3307 ± 0.416 h−1; K S,NOB = 1.65·10−6 ± 2.85·10−6 mgHNO2-N/L; k S2 = 0.8213 ± 0.076 and n = 0.6537 ± 0.030. A good fit between the experimental data and the model’s results including the effect of zeolite on the kinetic parameters was obtained, with Theil inequality coefficient values between 0.109 and 0.007 for all the variables studied, with all of these values lower than 0.3. Thus, the model proposed is robust and can simulate the nitrification process in the presence of sulfide and organic matter when zeolite was used as improver.

Niche Differentiation of Bacterial Versus Archaeal Soil Nitrifiers Induced by Ammonium Inhibition Along a Management Gradient.

Soil nitrification, mediated mainly by ammonia oxidizing archaea (AOA) and bacteria (AOB), converts ammonium (NH4+) to nitrite (NO2−) and thence nitrate (NO3−). To better understand ecological differences between AOA and AOB, we investigated the nitrification kinetics of AOA and AOB under eight replicated cropped and unmanaged ecosystems (including two fertilized natural systems) along a long-term management intensity gradient in the upper U.S. Midwest. For five of eight ecosystems, AOB but not AOA exhibited Haldane kinetics (inhibited by high NH4+ additions), especially in perennial and successional systems. In contrast, AOA predominantly exhibited Michaelis-Menten kinetics, suggesting greater resistance to high nitrogen inputs than AOB. These responses suggest the potential for NH4+-induced niche differentiation between AOA and AOB. Additionally, long-term fertilization significantly enhanced maximum nitrification rates (Vmax) in the early successional systems for both AOA and AOB, but not in the deciduous forest systems. This was likely due to pH suppression of nitrification in the acidic forest soils, corroborated by a positive correlation of Vmax with soil pH but not with amoA gene abundance. Results also demonstrated that soil nitrification potentials were relatively stable, as there were no seasonal differences. Overall, results suggest that (1) NH4+ inhibition of AOB but not AOA could be another factor contributing to niche differentiation between AOA and AOB in soil, and (2) nitrification by both AOA and AOB can be significantly promoted by long-term nitrogen inputs.

Evaluation of nitrification kinetics for treating ammonium nitrogen enriched wastewater in moving bed hybrid bioreactor

Nitrification kinetics of wastewater characterized by high nitrogen and very low organic carbon was evaluated using a moving bed hybrid bioreactor (MBHBR) in batch mode by varying initial ammonium nitrogen (NH4+-N) concentration in the range of (500–1000) mg L−1 at a pH of 7.8 ± 0.15 and temperature around 28 ± 2°C. A maximum removal efficiency of 89 % in terms of ammonium nitrogen was achieved with initial NH4+-N concentration of 900 mg L−1 having a total biomass concentration around 2000 mg L−1 and at a batch period of 5 days. The experimental results were analyzed in the light of Monod’s kinetic theory and coefficients for nitrification were obtained as maximum substrate removal rate coefficient (μmax) = 0.52 day−1, yield coefficient (Y) = 0.63 mg VSS/mg NH4+-N, half saturation constant (Ks) =603.11 mg NH4+-NL−1 and endogenous decay constant (kd) = 0.008 day−1. The study confirms better nitrification efficiency in presence of attached biomass as compared to suspended growth condition. An interesting observation from the nitrate nitrogen profile establishes the possibility of denitrification, occurring simultaneously even in absence of organic carbon in the wastewater in aerobic MBHBR. This can be supported by the fact that the suspended flocs and/or attached biofilms in hybrid reactor was deep enough for creating necessary conditions for denitrification and the required organic carbon was partially obtained from endogenous degradation of the microorganisms.

Nitrifying biomass can retain its acclimation to 2,4,6-trichlorophenol

Many municipal wastewater treatment plants in China receive industrial wastewater that contains inhibitory organic chemicals, such as chlorinated phenols. For the common aerobic biological treatment, nitrification is a key step, but nitrifying bacteria are notably sensitive to inhibition by chlorinated phenols. In this work, normal activated sludge (containing nitrifying biomass) was acclimated to 2,4,6-trichlorophenol (TCP). The acclimated biomass had more than 2-fold faster nitrification kinetics than normal biomass when exposed to TCP, and it also achieved effective TCP removal in parallel. When suddenly exposed to TCP after as much as two months without TCP input, the acclimated nitrifying biomass retained effective nitrification and TCP biodegradation: The nitrification rate and TCP removal rate were 0.325 mM/h and 0.049 mM/h for the acclimated biomass, compared to only 0.165 mM/h and 0.001 mM/h for normal biomass. Resistance to TCP inhibition also was retained for 5 generations of sub-culturing without TCP exposure. High-throughput sequencing confirmed that the acclimated biomass contained nitrifying bacteria and heterotrophic bacteria capable of degrading TCP, although the key genera changed during sub-culturing.

'Nitrification kinetics and microbial community dynamics of attached biofilm in wastewater treatment'.

A comparative bench-scale and field site analysis of BioCord was conducted to investigate seasonal microbial community dynamics and its impact on nitrogen removal in wastewater. This was assessed using metabolite (NO3 -) stable isotope analysis, high-throughput sequencing of the 16S rRNA gene, and RT-qPCR of key genes in biological treatment representing nitrification, anammox, and denitrification. Bench-scale experiments showed an increase in nitrifiers with increasing ammonia loading resulting in an ammonia removal efficiency up to 98 ± 0.14%. Stable isotope analysis showed that 15ɛ and δ18ONO3 could be used in monitoring the efficiency of the enhanced biological nitrification. In the lagoon field trials, an increase in total nitrogen promoted three principle nitrifying genera (Nitrosomonas, Nitrospira, Candidatus Nitrotoga) and enhanced the expression of denitrification genes (nirK, norB, and nosZ). Further, anaerobic ammonia oxidizers were active within BioCord biofilm. Even at lower temperatures (2-6°C) the nitrifying bacteria remained active on the BioCord.