A Process to Produce Penicillin G Acylase by Surface-Adhesion Fermentation Using <Emphasis Type="Italic">Mucor griseocyanus</Emphasis> to Obtain 6-Aminopenicillanic Acid by Penicillin G Hydrolysis

The production of extracellular and mycelia-associated penicillin G acylase (maPGA) with Mucor griseocyanus H/55.1.1 by surface-adhesion fermentation using Opuntia imbricata, a cactus, as a natural immobilization support was studied. Enzyme activity to form 6-aminopencillanic acid (6-APA) from penicillin G was assayed spectrophotometrically. The penicillin G hydrolysis to 6-APA was evaluated at six different times using PGA samples recovered from the skim milk medium at five different incubation times. Additionally, the effect of varying the penicillin G substrate concentration level on the PGA enzyme activity was also studied. The maximum reaction rate, V _max, and the Michaelis constant, K _M, were determined using the Michaelis–Menten model. The maximum levels for maPGA and extracellular activity were found to be 2,126.50 international unit per liter (IU/l; equal to 997.83 IU/g of support) at 48 h and 755.33 IU/l at 60 h, respectively. Kinetics of biomass production for total biomass showed a maximum growth at 60 h of 3.36 and 2.55 g/l (equal to 0.012 g of biomass per gram of support) for the immobilized M. griseocyanus biomass. The maPGA was employed for the hydrolysis of penicillin G to obtain 6-APA in a batch reactor. The highest quantity of 6-APA obtained was 226.16 mg/l after 40-min reaction. The effect of substrate concentration on maPGA activity was evaluated at different concentrations of penicillin G (0–10 mM). K _M and V _max were determined to be 3.0 × 10⁻³ M and 4.4 × 10⁻³ mM/min, respectively.     

Axenic Cultures of Nitrosomonas europaea and Nitrobacter winogradskyi in Autotrophic Conditions: a New Protocol for Kinetic Studies

As a part of a natural biological N-cycle, nitrification is one of the steps included in the conception of artificial ecosystems designed for extraterrestrial life support systems (LSS) such as Micro-Ecological Life Support System Alternative (MELiSSA) project, which is the LSS project of the European Space Agency. Nitrification in aerobic environments is carried out by two groups of bacteria in a two-step process. The ammonia-oxidizing bacteria (Nitrosomonas europaea) realize the oxidation of ammonia to nitrite, and the nitrite-oxidizing bacteria (Nitrobacter winogradskyi), the oxidation of nitrite to nitrate. In both cases, the bacteria achieve these oxidations to obtain an energy and reductant source for their growth and maintenance. Furthermore, both groups also use CO₂ predominantly as their carbon source. They are typically found together in ecosystems, and consequently, nitrite accumulation is rare. Due to the necessity of modeling accurately conversion yields and transformation rates to achieve a complete modeling of MELiSSA, the present study focuses on the experimental determination of nitrogen to biomass conversion yields. Kinetic and mass balance studies for axenic cultures of Nitrosomonas europaea and Nitrobacter winogradskyi in autotrophic conditions are performed. The follow-up of these cultures is done using flow cytometry for assessing biomass concentrations and ionic chromatography for ammonium, nitrite, and nitrate concentrations. A linear correlation is observed between cell count and optical density (OD) measurement (within a 10?% accuracy) validating OD measurements for an on-line estimation of biomass quantity even at very low biomass concentrations. The conversion between cell count and biomass concentration has been determined: 7.1?×?10¹² cells g dry matter (DM)^?1 for Nitrobacter and 6.3?×?10¹² cells g DM^?1 for Nitrosomonas. Nitrogen substrates and products are assessed redundantly showing excellent agreement for mass balance purposes and conversion yields determination. Although the dominant phenomena are the oxidation of NH ₄ ⁺ into nitrite (0.95?mol?mol N^?1 for Nitrosomonas europaea within an accuracy of 3?%) and nitrite into nitrate (0.975?mol?mol N^?1 for Nitrobacter winogradskyi within an accuracy of 2?%), the Nitrosomonas europaea conversion yield is estimated to be 0.42?g DM mol?N^?1, and Nitrobacter winogradskyi conversion yield is estimated to be 0.27?g DM mol?N^?1. The growth rates of both strains appear to be dominated by the oxygen transfer into the experimental setups.     

Electrocatalytic oxidation of nitrite at a terpyridine manganese(II) complex modified carbon past electrode

A carbon past electrode modified with [Mn(H₂O)(N₃)(NO₃)(pyterpy)], ( \textpyterpy = 4￠- ( 4 - \textpyridyl ) - 2,2￠:\text6￠,\text2￠￠- \textterpyridine ) \left( {{\text{pyterpy}} = 4\prime - \left( {4 - {\text{pyridyl}}} \right) - 2,2\prime:{\text{6}}\prime,{\text{2}}\prime\prime - {\text{terpyridine}}} \right) complex have been applied to the electrocatalytic oxidation of nitrite which reduced the overpotential by about 120 mV with obviously increasing the current response. Relative standard deviations for nitrite determination was less than 2.0%, and nitrite can be determined in the ranges of 5.00 × 10⁻⁶ to 1.55 × 10⁻² mol L⁻¹, with a detection limit of 8 × 10⁻⁷ mol L⁻¹. The treatment of the voltammetric data showed that it is a pure diffusion-controlled reaction, which involves one electron in the rate-determining step. The rate constant k′, transfer coefficient α for the catalytic reaction, and diffusion coefficient of nitrite in the solution, D, were found to be 1.4 × 10⁻², 0.56× 10⁻⁶, and 7.99 × 10⁻⁶ cm² s⁻¹, respectively. The mechanism for the interaction of nitrite with the Mn(II) complex modified carbon past electrode is proposed. This work provides a simple and easy approach to detection of nitrite ion. The modified electrode indicated reproducible behavior, anti-fouling properties, and stability during electrochemical experiments, making it particularly suitable for the analytical purposes.     

Direct electrochemistry and electrocatalysis of nitrite based on nano-alumina-modified electrode

Simple and sensitive electrochemical method for the determination of nitrite, based on a nano-alumina-modified glassy carbon electrode (GCE), is described. Nitrite yields a well-defined oxidation peak whose potential is 0.74 V at the nano-alumina-coated GCE in 0.1 mol L⁻¹ phosphate buffer (pH 5.0). Compared with bare GCE, the nano-alumina-modified GCE has evident catalytic effect towards the oxidation of nitrite, and its peak current can be significantly enhanced. Some of the experimental parameters were optimized for the determination of nitrite. The oxidation peak current was proportional to nitrite concentration in the range of 5.0 × 10⁻⁸–1.1 × 10⁻³ mol L⁻¹, and a detection limit of 1.0 × 10⁻⁸ mol L⁻¹ was obtained. This method has been successfully used to the determination of nitrite in sausage sample. Furthermore, results obtained by the method have been compared with spectrophotometric method.     

Protection by methylated urates of oxyhemoglobin oxidation induced by sodium nitrite

When 60 μM sheep oxyhemoglobin was treated with 1.2 mM sodium nitrite, the oxyhemoglobin was completely converted to methemoglobin in 7 min. The addition of increasing concentrations of uric acid (1–10 μM) resulted in a decrease in the rate of methemoglobin formation; at 10 μM, uric acid completely protected the oxyhemoglobin. At a concentration of 5 μM, uric acid and all of the mono- and dimethylurates, with the exception of 3,9-dimethyluric acid, protected oxyhemoglobin from oxidation to methemoglobin by 1.2 mM sodium nitrite; 1,3,9-trimethyl-, 3,7,9-trimethyl-, and 1,3,7,9-tetramethyluric acid did not protect oxyhemoglobin. It was concluded that the hydrogens at nitrogens 3 and 9 of uric acid are necessary for it to prevent the oxidation of oxyhemoglobin by sodium nitrite.     

Novel structures of Zn(II) biometal cation with the biologically active substituted acetic acid and nitrogen donor ligands: Synthesis,spectral, phosphate diester catalytic hydrolysis and anti‐microbial studies

The complexes [Zn(methoxyacetate)₂1,10‐phenanthroline] 1 and [Zn₂(phenylacetate)₄(quinoline)₂] 2 , were prepared and characterized by IR‐spectroscopy, UV–Visible spectroscopy, ¹H and ¹³C NMR spectroscopy, single crystal X‐ray diffraction. BNPP hydrolysis of the complexes and their parent nitrogen ligands were scanned, the results indicated that the hydrolysis rates of BNPP were 4.5 × 10⁴ and 6.2 × 10⁵ for ( 1 ) and ( 2 ), respectively. In addition, anti‐bacterial activities were scanned to investigate the effect of complexation on their activity against Gram‐positive (S. epidermidis , S. aureus , E. faecalis , M. luteus and B. Subtilis ) and Gram‐negative (K. pneumonia , E. coli , P. Mirabilis and P. Aeruginosa ) bacteria using agar well‐diffusion method. Complex 1 showed high activity against G⁻and G ⁺ bacteria except against E. faecalis and P. Aeruginosa . Complex 2 did not show any activity against G⁻ or G ⁺ bacteria.     

Stable partial nitritation of mature landfill leachate in a continuous flow bioreactor: Long-term performance,microbial community evolution,and mechanisms

A continuous flow bioreactor was operated for 300 days to investigate partial nitritation (PN) of mature landfill leachate, establishing the long-term performance of the system in terms of the microbial community composition, evolution, and interactions. The stable operation phase (31–300 d) began after a 30 days of start-up period, reaching an average nitrite accumulation ratio (NAR) of 94.43% and a ratio of nitrite nitrogen to ammonia nitrogen (NO₂⁻-N/NH₄⁺-N) of 1.16. Some fulvic-like and humic-like compounds and proteins were effectively degraded in anaerobic and anoxic tanks, which was consistent with the corresponding abundance of methanogens and syntrophic bacteria in the anaerobic tank, and organic matter degrading bacteria in the anoxic tank. The ammonia-oxidizing bacteria (AOB) Nitrosomonas was found to be the key functional bacteria, exhibiting an increase in abundance from 0.27% to 6.38%, due to its collaborative interactions with organic matter degrading bacteria. In-situ inhibition of nitrite-oxidizing bacteria (NOB) was achieved using a combination of free ammonia (FA) and free nitrous acid (FNA), low dissolved oxygen (DO) with fewer bioavailable organics conditions were employed to maintain stable PN and a specific ratio of NO₂⁻-N/NH₄⁺-N, without an adverse impact on AOB. The synergistic relationships between AOB and both denitrifying bacteria and organic matter degrading bacteria, were found to contribute to the enhanced PN performance and microbial community structure stability. These findings provide a theoretical guidance for the effective application of PN-Anammox for mature landfill leachate treatment.     

Voltammetric sensor for nitrite determination based on its electrocatalytic reduction at the surface of p-duroquinone modified carbon paste electrode

A p-duroquinone (tetramethyl-p-benzoquinone) modified carbon paste electrode (DMCPE) was employed to study the electrocatalytic reduction of nitrite in aqueous solutions using cyclic voltammetry (CV), double potential-step chronoamperometry, and differential pulse voltammetry (DPV). It has found that under an optimum condition (pH 1.00), the reduction of nitrite at the surface of DMCPE occurs at a potential of about 660 mV less negative than that of an unmodified carbon paste electrode (CPE). The catalytic rate constant, k′_h, based on Andrieux and Saveant theoretical model was calculated as for scan rate 10 mV s^-1. Also, the apparent diffusion coefficient, D _app, was found as 2.5 × 10^–10 and 3.61 × 10^–5 cm² s^-1 for p-duroquinone in carbon paste matrix and nitrite in aqueous buffered solution, respectively. The values for αn_α were estimated to be −0.65 and −0.19 for the reduction of nitrite at the surface of DMCPE and CPE, respectively. The electrocatalytic reduction peak currents showed a linear dependence on the nitrite concentration, and a linear analytical curve was obtained in the ranges of 5.0 × 10^–5 M to 8.0 × 10^–3 M and 6.0 × 10^–6 M to 8.0 × 10^–4 M of nitrite concentration with CV and DPV methods, respectively. The detection limits (2σ) were determined as 2.5 × 10^–5 M and 4.3 × 10^–6 M by CV and DPV methods. This method was also applied as a simple, selective and precise method for determination of nitrite in real samples (the weak liquor from the wood and paper factory of Mazandaran province in Iran) by using a standard addition method.     

Assay of femtogram level nitrite in human urine using luminol–myoglobin chemiluminescence

In this paper, a sensitive flow injection chemiluminescence system luminol–myoglobin was described for determining femtogram nitrite. Nitrite bound myoglobin producing the ferric heme nitrite complexes, which catalyzed the electron transfer of luminol to myoglobin leading to fast chemiluminescence. The chemiluminescence intensity in the presence of nitrite was remarkably enhanced compared with that in the absence of it. Under the optimum reaction conditions the chemiluminescence increment produced was proportional to the concentration of nitrite in the range of 0.05 pg ml^− 1–1.0 ng ml^− 1 (R² = 0.9991), with a detection limit (3σ) of 20.0 fg ml^− 1. At the flow rate of 2.0 ml min^− 1, the whole process including sampling and washing could be completed in 0.5 min offering the sampling efficiency of 120 h^− 1 accordingly, and the relative standard deviation (RSD) was less than 2.60% (n = 5). It was satisfactory for the application to determine nitrite in human urine samples, and the possible mechanism was proposed.     

Evaluation of the stability of shortcut nitrification-denitrification process based on online specific oxygen uptake rate monitoring

Shortcut nitrification-denitrification (SCND) is widely concerned because of its low energy consumption and high nitrogen removal efficiency. However, the current difficulty lies in the stable maintenance of SCND performance, which leads to the challenge of large-scale application of this new denitrification technology. In this study, the nitrogen removal pathway from complete nitrification-denitrification (CND) to SCND was rapidly realized under high free ammonia (FA), high pH and low dissolved oxygen (DO) conditions. The variations of specific oxygen uptake rate (SOUR) of activated sludge in both processes were investigated by an online SOUR monitoring device. Different curves of SOUR from CND to SCND process were observed, and the ammonia peak obtained based on SOUR monitoring could be used to control aeration time accurately in SCND process. Accordingly, the SOUR ratio of ammonia oxidizing bacteria (AOB) to nitrite oxidizing bacteria (NOB) (SOUR_AOB/SOUR_NOB) was increased from 1.40 to 2.93. 16S rRNA Miseq high throughput sequencing revealed the dynamics of AOB and NOB, and the ratio of relative abundance (AOB/NOB) was increased from 1.03 to 3.12. Besides, SOUR_AOB/SOUR_NOB displayed significant correlations to ammonia removal rate (P<0.05), ammonia oxidation rate / nitrite oxidation rate (P < 0.05), nitrite accumulation rate (P < 0.05) and the relative abundance of AOB/NOB (P < 0.05). Thus, a strategy for evaluation the SCND process stability based on online SOUR monitoring is proposed, which provides a theoretical basis for optimizing the SCND performance.     

Maximization of β-Galactosidase Production: A Simultaneous Investigation of Agitation and Aeration Effects

In this work, the agitation and aeration effects in the maximization of the β-galactosidase production from Kluyveromyces marxianus CCT 7082 were investigated simultaneously, in relation to the volumetric enzyme activity and the productivity, as well as the analysis of the lactose consumption and production of glucose, and galactose of this process. Agitation and aeration effects were studied in a 2 L batch stirred reactor. A central composite design (2² trials plus three central points) was carried out. Agitation speed varied from 200 to 500 rpm and aeration rate from 0.5 to 1.5 vvm. It has been shown in this study that the volumetric enzyme production was strongly influenced by mixing conditions, while aeration was shown to be less significant. Linear models for activity and productivity due to agitation and aeration were obtained. The favorable condition was 500 rpm and 1.5 vvm, which lead to the best production of 17 U mL⁻¹ for enzymatic activity, 1.2 U mL⁻¹ h⁻¹ for productivity in 14 h of process, a cellular concentration of 11 mg mL⁻¹, and a 167.2 h⁻¹ volumetric oxygen transfer coefficient.     

Determination of nitrite with the electrocatalytic property to the oxidation of nitrite on thionine modified aligned carbon nanotubes

A thionine modified aligned carbon nanotubes (ACNTs) electrode was fabricated and was used to electrochemically determine nitrite. The thionine modified ACNTs electrode exhibited enhanced electrocatalytic behavior to the oxidation of nitrite. The electrochemical mechanism of the thionine/ACNTs electrode towards the oxidation of nitrite was discussed. The thionine modified ACNTs electrode exhibited fast response towards nitrite with a detection limit of 1.12 × 10⁻⁶ mol  L⁻¹ and a linear range of 3 × 10⁻⁶ – 5 × 10⁻⁴ mol  L⁻¹. The proposed method was successfully applied in the detection of nitrite in real samples.     

The oxidation and reduction behavior of nitrite at carbon nanotube powder microelectrodes

Carbon nanotube electrodes were fabricated using powder microelectrode method, and the carbon nanotube powder microelectrodes (CNTPMEs) were characterized by the electro-oxidation and electro-reduction of nitrite. It was found that the kinetics of oxidation and reduction were greatly improved at CNTs compared with that at conventional graphite, indicating that CNTs could catalyze the electrochemical process of nitrite. The kinetic parameters of these process at CNTs were calculated, i.e. k was 0.593 cm s⁻¹, and (1-α)n_α was 0.501±0.018 for the nitrite oxidation. This CNTPME was also used as a nitrite carbon nanotube sensor, and the results showed that the detection limit was 8 μM.     

Silver particle-decorated carbon paste electrode based on ionic liquid for improved determination of nitrite

A simple silver particle-modified carbon paste electrode is proposed for the determination of low concentration levels of nitrite ions. The electrode consists of a carbon powder decorated with silver sub-micrometre particles (AgPs) and a hydrophobic ionic liquid trihexyltetradecylphosphonium chloride as a binder. It has been shown that AgPs exhibit a strong electrocatalytic effect on the nitrite oxidation. For optimal electroanalytical performance the electrode was conditioned via silver oxidation/reduction cycle. The electrode revealed a linear square-wave voltammetric response in a wide examined concentration range of 0.05 to 1.0 mmol L^− 1, limit of detection (LOD) of 3 μmol L^− 1 and excellent repeatability with RSD of 0.3%.     

Influence of the water molecules (n?=?1–6) on the interaction between Li+, Na+, K+ cations and indole molecule as tryptophan amino acid residue

Influence of the addition of water molecules (n = 1–6) on the interaction energy between Li⁺, Na⁺, K⁺ cations and indole molecule as tryptophan amino acid residue is considered at MP2(FULL)/6-311++G(d,p)//B3LYP/6-311++G(d,p) levels of theory. The calculations suggest that the size of cation and the number of water molecules are two important factors that affect the interaction energy between the hydrated metal cation and indole molecule. The strength of cation–π interactions get substantially reduced when the metal ion is solvated or the size of metal cation increases. Quantum theory of atoms in molecules analysis of cation–π interaction indicates that there is a correlation between the electron density (ρ(r)) in the cage critical points generated upon complexation and the distance between metal cation and centroid of phenyl ring in indole molecule.     

Modelling spur chemistry for alkaline and acidic water at high temperatures

The effect of pH and associated ionic strength on the primary yields in the radiolysis of pressurised water has been assessed by diffusion-kinetic calculations for temperatures in the range 100–300°C. Account has been taken for ionic strength I up to 0.1 mol kg⁻¹, assuming that the counter ions of H⁺ in acid solutions and of OH⁻ in base solutions have unit charge. In acid solutions, the H⁺ ions react with e⁻ _aq. The decrease in G(e⁻ _aq) and the increase in G(H) with decreasing pH becomes substantial for [H⁺] ≥ 1 × 10⁻⁴ m, but the primary yields of oxidising species are almost constant. In alkaline solutions, the OH⁻ anions affect the spur chemistry of radiation-generated protons and hydroxyl radicals for [OH⁻] ≥ 1 × 10⁻⁴ m. The scavenging of H atoms and hydrogen peroxide becomes significant for [OH⁻] ≥ 1 × 10⁻² m. The total yields G(OH) + G(O⁻) and G(H₂O₂) + G(HO₂ ⁻) are independent of base concentration below 0.01 m. In more alkaline solutions, G(OH) + G(O⁻) increases, whereas G(H₂O₂) + G(HO₂ ⁻) decreases with increasing [OH⁻]. Calculations showed the substantial yield of the reaction O⁻ + e⁻ _aq in 0.1 m base solution. Spur chemistry in alkaline hydrogenated water is not affected by the presence of H₂ if less than 0.001 m of hydrogen is added.     

Carrier-facilitated liquid membrane extraction of penicillin G from aqueous streams

Kinetics and mechanism for the carrier-facilitated transport of penicillin G from aqueous solutions through a supported liquid membrane containing Amberlite LA-2 were investigated. The strip phase was either phosphate buffer or sodium carbonate solution. Experiments were performed as a function of the pH, the concentrations of penicillin G in the feed phase and of amine in the membrane phase. A transport model was proposed considering aqueous film diffusion, interfacial chemical reaction, and membrane diffusion. The calculated rates were found to agree with the measured ones (average standard error, 12%). Under the conditions investigated (feed pH 5.02–7.83, penicillin G concentration 10–500 mol/m³, amine concentration 50–1000 mol/m³), the present transport process was shown to be governed by combined interfacial chemical reaction and membrane diffusion.     

The immobilization of Cytochrome c on MWNT–PAMAM–Chit nanocomposite incorporated with DNA biocomposite film modified glassy carbon electrode for the determination of nitrite

A novel and sensitive biosensor was developed for the determination of nitrite. Firstly, multi-walled carbon nanotubes–poly(amidoamine)–chitosan (MWNT–PAMAM–Chit) nanocomposite along with the incorporation of DNA was used to modify the glassy carbon electrode. Then the immobilization of Cyt c was accomplished using electrochemical deposition method by consecutive cyclic voltammetry (CV) scanning in a neutral Cyt c solution. CV behaviors of the modified electrodes showed that the MWNT–PAMAM–Chit nanocomposite is a good platform for the immobilization of DNA and Cyt c in order, at the same time, an excellent promoter for the electron transfer between Cyt c and the electrode. At high potential, the immobilized Cyt c could be further oxidized into highly reactive Cyt c π-cation by two-step electrochemical oxidation, which could oxidize NO₂ ⁻ into NO₃ ⁻ in the solution. Therefore, a nitrite biosensor based on the biocatalytic oxidation of the immobilized Cyt c was fabricated, which showed a fast response to nitrite (less than 5 s). The linear range of 0.2–80 μM and a detection limit of 0.03 μM was obtained. Finally, the application in food analysis using sausage as testing samples was also investigated.     

Study of antagonism between some intestinal bacteria with high-speed micellar electrokinetic chromatography

In this work, high-speed micellar electrokinetic chromatography with LIF detection was applied to study the antagonism between three intestinal bacteria, Escherichia coli (E. coli), Bacillus licheniformis (B. licheniformis) and Bacillus subtilis (B. subtilis). The fluorescent derivatization for the bacteria was performed by labeling the bacteria with FITC. In a high-speed capillary electrophoresis (HSCE) device, the three bacteria could be completely separated within 4 min under the separation mode MEKC. The BGE was 1 × TBE containing 30 mM SDS and 1.5 × 10^–5 g/mL polyethylene oxide. The limits of detection for E. coli, B. licheniformis and B. subtilis were 2.80 × 10⁶ CFU/mL, 1.60 × 10⁶ CFU/mL and 1.90 × 10⁶ CFU/mL respectively. Lastly, the method was applied to investigate the antagonism between the three bacteria. The bacteria were mixed and cultured for 7 days. The samples were separated and determined every day to study the interaction between bacteria. The results showed that B. licheniformis and B. subtilis could not inhibit each other, but they could effectively inhibit the reproduction of E. coli. The method developed in this work was quick, sensitive and convenient, and it had great potential in the application of antagonism study for bacteria.     

Effect of inorganic anions on the titanium dioxide-based photocatalytic oxidation of aqueous ammonia and nitrite

In this study, we investigated the effects of four inorganic anions (Cl⁻, SO₄²⁻, H₂PO₄⁻/HPO₄²⁻, and HCO₃⁻/CO₃²⁻) on titanium dioxide (TiO₂)-based photocatalytic oxidation of aqueous ammonia (NH₄⁺/NH₃) at pH ∼ 9 and ∼10 and nitrite (NO₂⁻) over the pH range of 4–11. The initial rates of NH₄⁺/NH₃ and NO₂⁻ photocatalytic oxidation are dependent on both the pH and the anion species. Our results indicate that, except for CO₃²⁻, which decreased the homogeneous oxidation rate of NH₄⁺/NH₃ by UV-illuminated hydrogen peroxide, OH scavenging by anions and/or direct oxidation of NH₄⁺/NH₃ and NO₂⁻ by anion radicals did not affect rates of TiO₂ photocatalytic oxidation. While HPO₄²⁻ enhanced NH₄⁺/NH₃ photocatalytic oxidation at pH ∼ 9 and ∼10, H₂PO₄⁻/HPO₄²⁻ inhibited NO₂⁻ oxidation at low to neutral pH values. The presence of Cl⁻, SO₄²⁻, and HCO₃⁻ had no effect on NH₄⁺/NH₃ and NO₂⁻ photocatalytic oxidation at pH ∼ 9 and ∼10, whereas CO₃²⁻ slowed NH₄⁺/NH₃ but not NO₂⁻ photocatalytic oxidation at pH ∼ 11. Photocatalytic oxidation of NH₄⁺/NH₃ to NO₂⁻ is the rate-limiting step in the complete oxidation of NH₄⁺/NH₃ to NO₃⁻ in the presence of common wastewater anions. Therefore, in photocatalytic oxidation treatment, we should choose conditions such as alkaline pH that will maximize the NH₄⁺/NH₃ oxidation rate.