The combination of ciprofloxacin and dialkyldimethyl ammonium compound synergistically proliferated intracellular resistance genes in nitrifying system.

Antibiotics and quaternary ammonium compounds (QACs) usually co-exist in wastewater treatment plants. Hence, three sequencing batch reactors were established and named as R1, R2 and R3, to investigate the effects of individual and combined exposure of different concentrations of ciprofloxacin (CIP) (0.2, 1.0 and 2.0 mg/L) and dialkyldimethyl ammonium compound (DADMAC) (0.4, 2.0 and 4.0 mg/L) on the performance, microbial community structures and resistance genes (RGs) in nitrifying system during 150 days. Results showed that CIP had a slight effect on ammonia oxidation activity, while 2.0 and 4.0 mg/L DADAMAC could obviously inhibit it, and the combination of CIP and DADMAC had a synergistic inhibitory effect. Besides, both CIP and DADMAC caused partial nitrification, and the order of nitrite accumulation rate was ranked as R3 > R2 > R1. The combination of CIP and DADMAC had an antagonistic effect on the increase of sludge particle size and α-Helix/(ß-Sheet + Random coil) was lowest in R3 (0.40). The combination of CIP and DADMAC synergistically stimulated most intracellular RGs in sludge, and the relative abundances of target RGs (e.g., qacEdelta1-01, qacH-01 and qnrS) at the end of operation in R3 were increased by 4.61-18.19 folds compared with those in CK, which were 1.34-5.57 folds higher than the R1 and R2. Moreover, the combination of CIP and DADMAC also promoted the transfer of RGs from sludge to water and enriched more potential hosts of RGs, further promoting the spread of RGs in nitrifying system. Thus, the combined pollution of CIP and DADMAC in wastewaters should attract more attentions.

Effects of antibiotics on microbial nitrogen cycling and N2O emissions: A review.

Sulfonamides, quinolones, tetracyclines, and macrolides are the most prevalent classes of antibiotics used in both medical treatment and agriculture. The misuse of antibiotics leads to their extensive dissemination in the environment. These antibiotics can modify the structure and functionality of microbial communities, consequently impacting microbial-mediated nitrogen cycling processes including nitrification, denitrification, and anammox. They can change the relative abundance of nirK/norB contributing to the emission of nitrous oxide, a potent greenhouse gas. This review provides a comprehensive examination of the presence of these four antibiotic classes across different environmental matrices and synthesizes current knowledge of their effects on the nitrogen cycle, including the underlying mechanisms. Such an overview is crucial for understanding the ecological impacts of antibiotics and for guiding future research directions. The presence of antibiotics in the environment varies widely, with significant differences in concentration and type across various settings. We conducted a comprehensive review of over 70 research articles that compare various aspects including processes, antibiotics, concentration ranges, microbial sources, experimental methods, and mechanisms of influence. Antibiotics can either inhibit, have no effect, or even stimulate nitrification, denitrification, and anammox, depending on the experimental conditions. The influence of antibiotics on the nitrogen cycle is characterized by dose-dependent responses, primarily inhibiting nitrification, denitrification, and anammox. This is achieved through alterations in microbial community composition and diversity, carbon source utilization, enzyme activities, electron transfer chain function, and the abundance of specific functional enzymes and antibiotic resistance genes. These alterations can lead to diminished removal of reactive nitrogen and heightened nitrous oxide emissions, potentially exacerbating the greenhouse effect and related environmental issues. Future research should consider diverse reaction mechanisms and expand the scope to investigate the combined effects of multiple antibiotics, as well as their interactions with heavy metals and other chemicals or organisms.

Exploring potential impact(s) of cerium in mining wastewater on the performance of partial-nitrification process and nitrogen conversion microflora.

Cerium Ce(III) is one of the major pollutants contained in wastewater generated during Ce(III) mining. However, the effect(s) of Ce(III) on the functional genera responsible for removing nitrogen biologically from wastewater has not been studied and reported. In this study, the effects of Ce(III) on aspects of partial-nitritation-(PN) process including ammonia oxidation rate (AOR), process kinetics, and microbial activities were investigated. It was found that the effect of dosing Ce(III) in the PN system correlated strongly with the AOR. Compared to the control, batch assays dosed with 5 mg/L Ce(III) showed elevated PN efficiency of about 121%, an indication that maximum biological response was feasible upon Ce(III) dose. It was also found that, PN performance was not adversely affected, given that Ce(III) dose was ≤20 mg/L. Process kinetics investigated also suggested that the maximum Ce(III) dose without any visible inhibition to the activities of ammonium oxidizing bacteria was 1.37 mg/L, but demonstrated otherwise when Ce(III) dose exceeded 5.63 mg/L. Compared to the control, microbes conducted efficient Ce(III) removal (averaged 98.66%) via biosorption using extracellular polymeric substances (EPS). Notably, significant deposits of Ce(III) was found within the EPS produced as revealed by SEM, EDX, CLSM and FTIR. 2-dimensional correlation infrared-(2DCOS-IR) revealed ester group (uronic acid) as a major organic functional group that promoted Ce(III) removal. Excitation-emission matrix-(EEM) spectrum and 2DCOS-IR suggested the dominance of Fulvic acid, hypothesized to have promoted the performance of the PN process under Ce(III) dosage.

Adding NBPT to urea increases N use efficiency of maize and decreases the abundance of N-cycling soil microbes under reduced fertilizer-N rate on the North China Plain.

Urease inhibitor (UI) and nitrification inhibitor (NI) can reduce N losses from agricultural soils but effects of inhibitors on N cycle are unclear. A field experiment was conducted with maize to test effects of UI (N-(n-Butyl) thiophosphoric, NBPT) and NI (3,4-dimethylepyrazolephosphate, DMPP) on N uptake and N-cycling soil microbes. Five treatments were imposed: no N fertilizer input (CK), conventional fertilization (CF) and 80% of urea input with NBPT (80%U+UI), with DMPP (80%U+NI) and with half NBPT and half DMPP (80%U+1/2(UI+NI)). There were no significant differences in biomass between 80%U+UI, 80%U+NI and CF but harvest index was increased under 80%U+UI and 80%U+NI. Compared to CF, N use efficiency of grain under 80%U+UI was increased by 7.1%, whereas grain yield and N uptake under 80%U+1/2(UI+NI) were decreased by 8.2% and 9.4%, respectively. The peak soil [Formula: see text] content was at about 15 days after fertilization (DAF) under CF but 30 DAF under the inhibitor treatments. In soils of 80%U+UI, the activities of urease and nitrate reductase were decreased between 15-45 DAF and between 5-30 DAF. The abundance of N-cycling soil microbes was affected: 80%U+UI and 80%U+NI reduced the copies of the amoA AOA and nir genes at about 15 days and reduced the copies of the amoA AOB gene at about 30 days. Correlation analysis indicated that there were significant positive relationships between amoA AOB gene and [Formula: see text], as well as between nirK gene and [Formula: see text]. Overall, urea applied with NBPT has greater potential for improving maize N use efficiency and inhibiting nitrification under reduced fertilizer-N applications.

Short-term effects of Mn2O3 nanoparticles on physiological activities and gene expression of nitrifying bacteria under low and high dissolved oxygen conditions.

The short-term effects of Mn2O3 nanoparticles (NPs) were examined for nitrifying bacterial enrichments exposed under low and high dissolved oxygen (DO) conditions using substrate (ammonia) specific oxygen uptake rates (sOUR), reverse transcriptase - quantitative polymerase chain reaction (RT-qPCR) assays, and by analysis of 16S rRNA sequences. Samples from nitrifying bioreactor were exposed in batch vessels to Mn2O3 NPs (1, 5 and 10 mg/L) for either 1 or 3 h under no additional aeration or 0.25 L/min aeration. There was increase in nitrification inhibition as determined by sOUR with increasing dosages of Mn2O3 NPs for both low and high DO. At 10 mg/L Mn2O3 NPs, the inhibition was about 7-10% for 1 and 3 h exposure in both cases. There was notable reduction in the transcript levels of amoA, hao and nirK for 10 mg/L of Mn2O3 NPs under 3 h, high DO exposure, which corresponded well with sOUR. The 16S rRNA sequencing showed that there was an inhibitory effect on ammonia oxidizers activity upon exposure to 10 mg/L of Mn2O3 NPs. Collectively, the findings in this study advanced understanding of the different effects of Mn2O3 NPs on nitrifying bacteria.

Do soil property variations affect dicyandiamide efficiency in inhibiting nitrification and minimizing carbon dioxide emissions?

Nitrification inhibitors (NIs) are used to retard the nitrification process and reduce nitrogen (N) losses. However, the effects of soil properties on NI efficacy are less clear. Moreover, the direct and indirect effects of soil property variations on NI efficiency in minimizing carbon dioxide (CO2) emissions have not been previously studied. An incubation experiment was conducted for 40 days with two treatments, N (200 mg N-urea kg-1) and N + dicyandiamide (DCD) (20 mg DCD kg-1), and a control group (without the N) to investigate the response of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to DCD application and the consequences for CO2, nitrous oxide (N2O) and ammonia (NH3) emissions from six soils from the Loess Plateau with different properties. The nitrification process completed within 6-18 days for the N treatment and within 30->40 days for the N + DCD treatment. AOB increased significantly with N fertilizer application, while this effect was inhibited in soils when DCD was applied. AOA was not sensitive to N fertilizer and DCD application. The nitrification rate was positively correlated with the clay (p < 0.05) and SOM contents (p < 0.01); DCD was more effective in loam soil with low SOM and high soil pH. Soil pH significantly was decreased with N fertilizer application, while it increased when DCD was applied. Moreover, DCD application decreased CO2 emissions from soils by 22%-172%; CO2 emissions were negatively correlated with the clay and SOM contents. DCD application decreased N2O emissions in each soil by 1.0- to 94-fold compared with those after N fertilizer application. In contrast, DCD application increased NH3 release from soils by 59-278%. NH3 volatilization was negatively correlated with clay (p < 0.05) and SOM (p < 0.01) contents and positively correlated with soil pH (p < 0.01). Therefore, soil texture, SOM and soil pH have significant effects on the DCD performance, nitrification process and gaseous emissions.

Trichloroethylene inhibits nitrogen transformation and microbial community structure in Mollisol.

Trichloroethylene (TCE) is the most ubiquitous halogenated organic pollutant in the environment, it is one of the 129 priority control pollutants. In order to clarify the influence of TCE on microorganisms and nitrogen transformation in Mollisol is the core purpose of this study. Results showed that 10 mg kg-1 TCE is the concentration limit of ammonification in Mollisol. When the concentration of TCE reached 10 mg kg-1 and the effect lasted for over 7 days, the process of ammonia oxidation to nitric acid in Mollisol will be affected. TCE affected the process of nitrate (NO3-) transformation into nitrite (NO2-) by affecting the activity of nitrate reductase, thereby affected the denitrification process in soil. When the concentration of TCE is more than 10 mg kg-1 it reduced the ability of soil microorganisms to obtain nitrogen, thereby affecting soil nitrogen transformation. RDA (Redundancy analysis) showed that the activity of nitrate reductase and the number of nitrifying bacteria and denitrifying bacteria in soil was negatively correlated with the incubation of TCE. In addition, soil nitrate reductase, nitrite reductase, peroxidase activity, ammonifying bacteria, nitrifying bacteria and denitrifying bacteria were negatively correlated with TCE concentration. Beyond that PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) of functional gene structure depend on KEGG (Kyoto Encyclopedia of Genes and Genomes) showed that 20 mg kg-1 TCE significantly inhibited the metabolism of energy and other substances in Mollisol. Based on the above, it is found that TCE significantly affected nitrification and denitrification in Mollisol, thus the nitrogen transformation in Mollisol was affected by TCE contamination.

Tetracyclines lead to ammonium accumulation during nitrification process.

The effect of tetracyclines used for swine food-production (tetracycline and oxytetracycline) on enriched nitrifying bacteria cultures over time was investigated in this study. Short-term exposure assays were performed in different concentrations of each antibiotic, using ammonia oxidizing bacteria (AOB) culture and nitrifying bacteria. The results pointed out a higher inhibitory effect of tetracycline on both bacterial communities. The AOB was more sensitive to antibiotic exposure when compared to the nitrifying culture. Although high antibiotic concentrations were applied, the half maximal inhibitory concentration (IC50) was achieved only for the AOB culture exposed to tetracycline at a concentration of 273 mg L-1. Nonetheless, the long-term exposure assay demonstrated a reduction of the tetracycline inhibition effect against AOB. The exposure to 100 mg L-1 of tetracycline (TC) did not show relevant influence over ammonium conversion efficiency; however, at 128 mg L-1 of TC, the efficiency decreased from 94% to 72%. Further investigation revealed that TC reduced the final effluent quality due to the development of a resistance mechanism by AOB culture against this antibiotic. This mechanism involves increasing the excretion of extracellular polymeric substances (EPS) and soluble microbial products (SMP), which probably increases BOD, and reduces ammonia consumption by the bacterial culture.

Microplastics affect sedimentary microbial communities and nitrogen cycling.

Microplastics are ubiquitous in estuarine, coastal, and deep sea sediments. The impacts of microplastics on sedimentary microbial ecosystems and biogeochemical carbon and nitrogen cycles, however, have not been well reported. To evaluate if microplastics influence the composition and function of sedimentary microbial communities, we conducted a microcosm experiment using salt marsh sediment amended with polyethylene (PE), polyvinyl chloride (PVC), polyurethane foam (PUF) or polylactic acid (PLA) microplastics. We report that the presence of microplastics alters sediment microbial community composition and nitrogen cycling processes. Compared to control sediments without microplastic, PUF- and PLA-amended sediments promote nitrification and denitrification, while PVC amendment inhibits both processes. These results indicate that nitrogen cycling processes in sediments can be significantly affected by different microplastics, which may serve as organic carbon substrates for microbial communities. Considering this evidence and increasing microplastic pollution, the impact of plastics on global ecosystems and biogeochemical cycling merits critical investigation.

Evaluation of partial nitrification efficiency as a response to cadmium concentration and microplastic polyvinylchloride abundance during landfill leachate treatment.

The partial nitrification efficiency response to the presence of cadmium (Cd2+) and microplastics was investigated. Microplastics polyvinylchloride (PVC) abundance was 0-10,000 particles/L, and Cd2+ concentration was 0-10 mg/L. Cd-only inhibited the NH4+-N oxidation rate 1.21, 1.23, and 1.18 times with concentrations at 1, 5, and 10 mg/L, respectively. PVC-only inhibited NH4+-N oxidation rate 1.01, 1.21 and 1.05 times with PVC abundance at 1000, 5000 and 10,000 particles/L, respectively. The ammonia oxidation rate was improved with the co-existence of PVC and Cd2+ at the conditions PVC1000 and PVC5000, which could be attributed to the PVC. PVC at 1000 particles/L could act as carrier and mitigate the negative effect of Cd2+ to the partial nitrification process. Moreover, the partial nitrification process was largely inhibited with PVC abundance at 10,000 particles/L. First-order kinetic models could simulate the NH4+-N, NO2-N, and NO3--N changes in the partial nitrification process.

Effects of silver nanoparticles on coupled nitrification-denitrification in suspended sediments.

The effects of varying concentrations of Ag NPs on coupled nitrification and denitrification (CND) in two suspended sediments (SPSs) sizes were investigated using isotopic tracer method. In general, 0.5 and 5 mg/L Ag NPs had less effect on CND, while 2 and 10 mg/L Ag NPs exhibited the improvement and inhibition effect, respectively. The CND improvement by 2 mg/L NPs was mainly due to the enhanced nitrifying and denitrifying enzyme activity. However, 10 mg/L Ag NPs inhibited NH4+ oxidation by directly reducing the AMO activity and AOB abundance. The inhibition on NAR and NIR activity and their encoding narG and nirK gene abundance further inhibited NO3- and NO2- reduction, leading to a dramatic decrease in the 15N-N2 production. The above inhibition effects were attributed to the nano-effects of Ag NPs, which led to the excessive ROS amount and the decreased T-AOC level in microbial systems. But the connection between nitrification and denitrification was not broken after Ag NPs exposure. Moreover, the results indicated that N-cycling in clay and silt-type SPS systems could be more sensitive than sand-type SPS systems to NP exposure. The findings provide a basis for evaluating the environmental risks of Ag NPs in water-sediment systems.

Diazole and triazole inhibition of nitrification process in return activated sludge.

Azoles are emerging contaminants that are resistant to biodegradation during wastewater treatment. Their presence has been widely reported in wastewater effluents and receiving waters. In this work, the potential inhibition of nitrification process by six different azole compounds in wastewater treatment plants was investigated in batch bioassays. The azoles studied included three diazoles: pyrazole (Pz); 1-methylpyrazole (MePz); 3,5-dimethylpyrazole (DMePz); and three triazoles: 1,2,4-triazole (Tz); benzotriazole (BTz); and 5-methyl benzotriazole (MeBTz). The concentration of azoles causing 50% inhibition (IC50) increased (azoles became less inhibitory) in the following order (mg L-1): BTz (1.99) < MeBTz (2.18) < Pz (2.69) < Tz (3.53) < DMePz (17.3) < MePz (49.6). No clear structure-inhibitory relationships were found using Log P and pKa as structural properties. The toxicity of any given azole may be related to the role of substituent groups on disabling/enabling binding to the active sites of metallo-enzymes in nitrifying microorganisms. This is exemplified by the low toxicity of MePz, which has a cyclic N blocked by a methyl group. The observed inhibition caused to nitrifying bacteria is more severe than their cytotoxicity to other target organisms (e.g., methanogens and heterotrophic bacteria), suggesting a specific inhibition to the copper-containing enzyme, ammonium monooxygenase, in ammonia oxidizing nitrifying microorganisms.

Effects of warming and elevated O3 concentrations on N2O emission and soil nitrification and denitrification rates in a wheat-soybean rotation cropland.

The effects of warming and elevated ozone (O3) concentrations on nitrous oxide (N2O) emission from cropland has received increasing attention; however, the small number of studies on this topic impedes understanding. A field experiment was performed to explore the role of warming and elevated O3 concentrations on N2O emission from wheat-soybean rotation cropland from 2012 to 2013 using open-top chambers (OTCs). Experimental treatments included ambient temperature (control), elevated temperature (+2 °C), elevated O3 (100 ppb), and combined elevated temperature (+2 °C) and O3 (100 ppb). Results demonstrate that warming significantly increased the accumulative amount of N2O (AAN) emitted from the soil-winter wheat system due to enhanced nitrification rates in the wheat farmland and nitrate reductase activity in wheat leaves. However, elevated O3 concentrations significantly decreased AAN emission from the soil-soybean system owing to reduced nitrification rates in the soybean farmland. The combined treatment of warming and elevated O3 inhibited the emission of N2O from the soybean farmland. Additionally, both the warming and combined treatments significantly increased soil nitrification rates in winter wheat and soybean croplands and decreased denitrification rates in the winter wheat cropping system. Our results suggest that global warming and elevated O3 concentrations will strongly affect N2O emission from wheat-soybean rotation croplands.

Denitrification responses to increasing cadmium exposure in Baltic Sea sediments.

Benthic ecosystems have come under intense pressure, due to eutrophication-driven oxygen decline and industrial metal contamination. One of the most toxic metals is Cadmium (Cd), which is lethal to many aquatic organisms already at low concentrations. Denitrification by facultative anaerobic microorganisms is an essential process to transform, but also to remove, excess nitrate in eutrophied systems. Cd has been shown to decrease denitrification and sequester free sulfide, which is available when oxygen is scarce and generally inhibits complete denitrification (i.e. N2O to N2). In polluted sediments, an interaction between oxygen and Cd may influence denitrification and this relationship has not been studied. For example, in the Baltic Sea some sediments are double exposed to both Cd and hypoxia. In this study, we examined how the double exposure of Cd and fluctuations in oxygen affects denitrification in Baltic Sea sediment. Results show that oxygen largely regulated N2O and N2 production after 21 days of exposure to Cd (ranging from 0 to 500 µg/L, 5 different treatments, measured by the isotope pairing technique (IPT)). In the high Cd treatment (500 µg/L) the variation in N2 production increased compared to the other treatments. Increases in N2 production are suggested to be an effect of 1) enhanced nitrification that increases NO3- availability thus stimulating denitrification, and 2) Cd successfully sequestrating sulfide (yielding CdS), which allows for full denitrification to N2. The in situ field sediment contained initially high Cd concentrations in the pore water (∼10 µg/L) and microbial communities might already have been adapted to metal stress, making the effect of low Cd levels negligible. Here we show that high levels of cadmium pollution might increase N2 production and influence nitrogen cycling in marine sediments.

Influence of chlorothalonil and carbendazim fungicides on the transformation processes of urea nitrogen and related microbial populations in soil.

To improve crop yielding, a large amount of fungicides is continuously applied during the agricultural management, while the effects of fungicides residues on microbial processing of N in soil need further study. In the present study, two broad spectrum fungicides, chlorothalonil and carbendazim, were applied at the rates of 5, 10, and 50 mg of active ingredient (A.I.) per kg of dry soil combined with urea with 200 mg of N per kg of dry soil under laboratory conditions. The results showed that chlorothalonil obviously retarded the hydrolysis of urea, whereas carbendazim accelerated it in 4 days after the treatments (P < 0.05). Chlorothalonil reduced denitrification, nitrification, and N2O production (P < 0.05), but not for carbendazim. Further analysis on N-associated microbial communities showed chlorothalonil reduced nitrosomonas populations at the rates of 10 and 50 mg of A.I. per kg and autotrophic nitrifying bacterial populations at three application rates (P < 0.05), but Carbendazim decreased nitrosomonas populations only at the rate of 50 mg of A.I. per kg and also autotrophic nitrifying bacterial populations at three rates and heterotrophic nitrifying bacterial populations at the rates of 10 and 50 mg of A.I. per kg. The reasons for this difference were ascribed to arrest urea hydrolysis and impediment of denitrification and nitrification processes by chlorothalonil. In conclusion, to improve crop yielding, chlorothalonil might be more beneficial to conserve soil N by improving soil N fertility, compared with carbendazim.

Tetracycline-induced effects on the nitrogen transformations in sediments: Roles of adsorption behavior and bacterial activity.

Nitrification and denitrification are the most important nitrogen transformation processes in the environment. Recently, due to widespread use, antibiotics have been reported to lead to environmental risks. Tetracycline (TC) is one of the most extensively used antibiotics in many areas. However, its reported effects on nitrogen transformations were conflicting in previous studies. In this study, the effects of TC on nitrogen transformations in sediment were investigated by analyzing TC transport and bacterial activity. It was found that the adsorption of TC onto the sediment was favorable and spontaneous, with adsorption capacity 54.3 mg/kg. The adsorption kinetics of TC onto the sediment and the isotherm fitted the Elvoich and Freundlich models, respectively, indicating that the adsorption was a chemisorption process, including electrostatic interactions and chemical bonding between TC and the sediment. TC showed no effect on nitrification in the sediment, but significantly inhibited the reduction of nitrate and nitrite during denitrification, consistent with observations made for the model denitrifier Paracoccus denitrificans under TC stress. Mechanistic study indicated that TC at 130 µg/g-cell inhibited 50.7% of P. denitrificans growth and 61.6% of cell viability. Meanwhile, the catalytic activities of the key denitrifying enzymes, nitrate reductase (NAR) and nitrite reductase (NIR), decreased to 29.1% and 68.0% of the control levels when the TC concentration was 130 µg/g-cell, suggesting that NAR was more sensitive to the TC than NIR, which contributed to a delay in nitrite accumulation.

Long-term impact of sulfate on an autotrophic nitrogen removal system integrated partial nitrification, anammox and endogenous denitrification (PAED).

A nitrogen removal system integrating partial nitrification, anaerobic ammonium oxidation (Anammox) and endogenous denitrification (PAED) was established in a sequencing batch reactor (SBR) for treating low nitrogen sewage (approximately 40 mg L-1 ammonia-nitrogen). The impact of sulfate on PAED sludge was investigated in five identical SBRs, fed with different levels of sulfate (0, 50, 100, 200 and 400 mg L-1). Ammonia oxidation was improved by the addition of Results showed that the sulfate addition in low concentration of sulfate (≤50 mg L-1), but was profoundly suppressed by higher levels of sulfate. Sulfate feeding enhanced both total nitrogen removal by Anammox and endogenous denitrification, with the abundance of Candidatus Kuenenia increasing to 4.39% in 400 mg L-1 sulfate from 0.83% in the control reactor, and Denitratisoma increasing to 6.35% from 2.77%. The results proved the feasibility of the PAED system in treating low nitrogen sewage with sulfate, which also enhanced the nitrogen-sulfate interaction.

Ammonia Volatilization Loss and Corn Nitrogen Nutrition and Productivity with Efficiency Enhanced UAN and Urea under No-tillage.

New urease and nitrification inhibitors and polymer coatings were introduced in recent years, but their effects on N loss and plant N nutrition were scarcely examined in agronomic no-tillage production systems. A field experiment of urea treated with efficiency enhancers was conducted on no-tillage corn (Zea mays L.) in Tennessee, the USA during 2013-2015. A field experiment on urea and ammonium nitrate (UAN) treated with efficiency enhancers was carried out on no-tillage corn in Tennessee in 2014 and 2015. Urea treated with N-(n-butyl) thiophosphoric triamide (NBPT) at concentrations of 20% (NBPT1), 26.7% (NBPT2), or 30% (NBPT3) and polymer coated urea (PCU) were effective but maleic-itaconic copolymer treated urea was ineffective in reducing ammonia volatilization loss and improving N nutrition, grain yield, and N agronomic use efficiency of corn compared with untreated urea. Specifically, NBPT1, NBPT2, or NBPT3 treated urea and PCU reduced the total ammonia volatilization loss by 29.1-78.8%, 35.4-81.9%, 77.3-87.4%, and 59.1-83.3% during the 20 days after N applications, but increased grain yield by 15.6-31.4%, 12.9-34.8%, 18.7-19.9%, and 14.6-41.1%, respectively. The inhibitory effect of NBPT on ammonia volatilization did not improve with NBPT concentration increased from 20% to 30%. UAN treated with NBPT3 or a combination of urease and nitrification inhibitors resulted in 16.5-16.6% higher corn yield than untreated UAN only when they were surface applied. In conclusion, when urea-containing fertilizers are surface applied without any incorporation into the soil under no-tillage, their use efficiencies and performances on corn can be enhanced with an effective urease inhibitor in areas and years with noticeable urea N losses.

PAC dosing to an MBBR - Effects on adsorption of micropollutants, nitrification and microbial community.

Two nitrifying MBBR reactors were operated in parallel, one with PAC dosing and one without, to determine the effects of PAC dosing on nitrification and micropollutant adsorption in municipal wastewater. The removal of micropollutants was evaluated for several doses of PAC and batch experiments were performed to measure adsorption kinetics and nitrification rates. The influence of PAC on the nitrifying microbial community was examined by high-throughput amplicon sequencing. Long-term operation of the pilot reactors showed that nitrification could be maintained while supplying PAC at increasing doses, as confirmed by high nitrification rates and significant abundance of nitrifying bacteria. The adsorption of organic micropollutants could be controlled by the PAC dose, and increased dosing resulted in corresponding improvements in removal efficiency. Biomass, suspended or attached to carriers, did not interfere with the adsorption of organic micropollutants. Freundlich isotherms obtained from the batch experiments were used to predict removal of organic micropollutants in the pilot reactors, suggesting that batch adsorption experiments can be used to predict micropollutant removal on a full scale. Collectively, the results show that nitrification and adsorption of organic micropollutants can be performed simultaneously in an MBBR.

Acute and chronic toxicity of nickel to nitrifiers at different temperatures.

This study investigated the acute nickel toxicity on nitrification of low ammonia synthetic wastewater at 10, 23, and 35°C. The nickel inhibition half-velocity constants (KI,Ni) for ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) based on Ni/MLSS ratio at 10, 23, and 35°C were 5.4 and 5.6 mg Ni/g MLSS, 4.6 and 3.5 mg Ni/g MLSS, and 9.1 and 2.7 mg Ni/g MLSS, respectively. In addition, chronic toxicity of nickel to nitrification of low ammonia synthetic wastewater was investigated at 10°C in two sequencing batch reactors (SBRs). Long-term SBRs operation and short-term batch tests were comparable with respect to the extent of inhibition and corresponding Ni/MLSS ratio. The µmax, b, and Ko of AOB were 0.16 day-1, 0.098 day-1 and 2.08 mg O2/L after long-term acclimatization to nickel of 1 mg/L at 10°C, high dissolved oxygen (DO) (7 mg/L) and long solids retention time (SRT) of 63-70 days. Acute nickel toxicity of nitrifying bacteria was completely reversible.