Addition Of HCl Research Articles

Extracellular acidification induces ROS- and mPTP-mediated death in HEK293 cells

The extracellular pH (pHe) is a key determinant of the cellular (micro)environment and needs to be maintained within strict boundaries to allow normal cell function. Here we used HEK293 cells to study the effects of pHe acidification (24h), induced by mitochondrial inhibitors (rotenone, antimycin A) and/or extracellular HCl addition. Lowering pHe from 7.2 to 5.8 reduced cell viability by 70% and was paralleled by a decrease in cytosolic pH (pHc), hyperpolarization of the mitochondrial membrane potential (Δψ), increased levels of hydroethidine-oxidizing ROS and stimulation of protein carbonylation. Co-treatment with the antioxidant α-tocopherol, the mitochondrial permeability transition pore (mPTP) desensitizer cyclosporin A and Necrostatin-1, a combined inhibitor of Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) and Indoleamine 2,3-dioxygenase (IDO), prevented acidification-induced cell death. In contrast, the caspase inhibitor zVAD.fmk and the ferroptosis inhibitor Ferrostatin-1 were ineffective. We conclude that extracellular acidification induces necroptotic cell death in HEK293 cells and that the latter involves intracellular acidification, mitochondrial functional impairment, increased ROS levels, mPTP opening and protein carbonylation. These findings suggest that acidosis of the extracellular environment (as observed in mitochondrial disorders, ischemia, acute inflammation and cancer) can induce cell death via a ROS- and mPTP opening-mediated pathogenic mechanism.

Zircon/fluid trace element partition coefficients measured by recrystallization of Mud Tank zircon at 1.5 GPa and 800–1000 °C

Hydrothermal zircon grains have trace element characteristics such as low Th/U, high U, and high rare earth element (REE) concentrations that distinguish them from magmatic, metamorphic, and altered zircon grains, but it is unclear whether these characteristics result from distinctive fluid compositions or zircon/fluid fractionation effects. New experiments aimed at measuring zircon/fluid trace element partition coefficients Dz/f involved recrystallizing natural Mud Tank zircon with low trace element concentrations in the presence of H2O, 1 m NaOH, or 1 m HCl doped with ∼1000 ppm of rare earth elements (REE), Y, U and Th and ∼500 ppm of Li, B, P, Nb, Ba, Hf, and Ta. Experiments were run for 168 h at 1.5 GPa, 800–1000 °C, and fO2 = NNO in a piston cylinder apparatus using the double capsule method. LA-ICP-MS analysis shows that run product zircon crystals have much higher trace element concentrations than in Mud Tank zircon starting material. Dz/f values were estimated from run product zircon analyses and bulk composition using mass balance.Most elements behave incompatibly, with median Dz/f being highest for Hf = 8 and lowest for B = 0.02. Addition of NaOH or HCl had little influence on Dz/f values. Dz/f for LREE are anomalously high, likely due to contamination of run product zircon with quenched solutes enriched in incompatible elements, so DLREE were estimated using lattice strain theory. Brice curves for +3 ions yield zircon/fluid DLu/DLa of ∼800–5000. A Brice curve fit to +4 ions yielded DCe4+ values. Estimated concentrations of Ce3+ and Ce4+ show that the average Ce4+/Ce3+ in zircon of 27 is much higher than in fluid of 0.02. Th and U show little fractionation, with median DTh/DU = 0.7, indicating that the low Th/U in natural hydrothermal zircon is inherited from the fluid. Natural fluid compositions estimated from measured Dz/f and published compositions of hydrothermal zircon grains from aplite and eclogite reflect the mineralogy of the host rock, e.g., fluid in equilibrium with eclogite garnet is depleted in heavy REE relative to middle REE, and has low Th/U.

Complexing agent-assisted highly dense CuInSe2 thin films prepared by one-step electrochemical deposition

Highly dense CuInSe2 (CISe) thin films were electrochemically deposited on Mo-coated soda-lime glass substrates in aqueous solution. Three compounds, CuCl2, InCl3, and SeO2, were used as precursors with glycine or oxalic acid as complexing agents. The deposition process was carefully selected through preliminary study of the individual electrochemical properties of the three precursors. To achieve ideal stoichiometry and uniform deposition of CISe thin films, the reaction temperature and acidity of precursor solution were investigated. As the reaction temperature increased, Cu deficiency was observed in the CISe thin film. The density and surface morphology of CISe films prepared by one-step electrodeposition were affected strongly by the acidity of deposition solution. The addition of HCl to solution improved the density and surface roughness of as-deposited CISe films. Denser and larger grain size CISe polycrystalline films were prepared in oxalic acid solution. Two-step heat treatments for the prepared CISe samples were applied to fabrication of CISe photovoltaic devices without an additional Se source.

Determination of Main Components of Glass-Forming Cu–Zr Alloys

A rapid procedure is developed for determination of copper and zirconium in their binary alloys Cu100–xZr x in the content ranges corresponding to the region of bulk amorphization (x = 30–70) using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The spectrometer operating conditions are optimized, and the analytical spectral lines (Cu II 224.700 nm and Zr II 354.262 nm) are selected, as well as calibration method and sampling procedure: dissolution in the mixture of HNO3 and HF with addition of HCl, providing for the minimum standard deviation of the analytical signal. A procedure of oxygen determination by inert gas fusion technique and a procedure for determination of copper by spectrophotometry and zirconium by gravimetric analysis in a single sample together with quality control of ICP-AES are developed for the considered alloys. The results of analysis of Cu100–xZr x alloys according to the developed procedures agree well between themselves and accounting for adjustment of oxygen content agree within the error limits (not more than 0.5 wt %) with the added content of copper and zirconium upon synthesis.

Closing the Loop on Transition-Metal-Mediated Nitrogen Fixation: Chemoselective Production of HN(SiMe3)2 from N2, Me3SiCl, and X-OH (X = R, R3Si, or Silica Gel).

Treatment of the Mo(IV) terminal imido complex, (η5-C5Me5)[N(Et)C(Ph)N(Et)]Mo(NSiMe3) (3), with a 1:2 mixture of iPrOH and Me3SiCl resulted in the rapid formation of the Mo(IV) dichloride, (η5-C5Me5)[N(Et)C(Ph)N(Et)]MoCl2 (1), and the generation of 1 equiv each of HN(SiMe3)2 and iPrOSiMe3. Similarly, a 1:2 mixture of Me3SiOH and Me3SiCl provided 1, HN(SiMe3)2, and O(SiMe3)2. Finally, silica gel, when coupled with excess equivalents of Me3SiCl, was also effectively used as the X-OH reagent for the generation of 1 and HN(SiMe3)2. A proposed mechanism for the 3 → 1 transformation involves formal addition of HCl across the Mo═N imido bond through initial hydrogen-bonding between X-OH and the N-atom of 3 to form the adduct IIIb, followed by chloride delivery from Me3SiCl to the metal center via a six-membered transition state (IV) that leads to the intermediate, (η5-C5Me5)[N(Et)C(Ph)N(Et)]Mo(Cl)(NHSiMe3) (V), and XOSiMe3 as a co-product. Metathetical exchange of the new Mo-N amido bond of V by a second equivalent of Me3SiCl then generates 1 and HN(SiMe3). These results serve to complete a highly efficient chemical cycle for nitrogen fixation that is mediated by a set of well-characterized transition-metal complexes.

Effect of three pretreatment techniques on the chemical composition and on the methane yields of Opuntia ficus-indica (prickly pear) biomass.

Opuntia ficus-indica (OFI) is an emerging biomass that has the potential to be used as substrate in anaerobic digestion. The goal of this work was to investigate the effect of three pretreatment techniques (thermal, alkaline, acidic) on the chemical composition and the methane yield of OFI biomass. A composite experimental design with three factors and two to three levels was implemented, and regression modelling was employed using a total of 10 biochemical methane potential (BMP) tests. The measured methane yields ranged from 289 to 604 NmL/gVSadded; according to the results, only the acidic pretreatment (HCl) was found to significantly increase methane generation. However, as the experimental values were quite high with regards to the theoretical methane yield of the substrate, this effect still needs to be confirmed via further research. The alkaline pretreatment (NaOH) did not noticeably affect methane yields (an average reduction of 8% was recorded), despite the fact that it did significantly reduce the lignin content. Thermal pretreatment had no effect on the methane yields or the chemical composition. Scanning electron microscopy images revealed changes in the chemical structure after the addition of NaOH and HCl. Modelling of the cumulated methane production by the Gompertz modified equation was successful and aided in understanding kinetic advantages linked to some of the pretreatments. For example, the alkaline treatment (at the 20% dosage) at room temperature resulted to a μmax (maximum specific methane production rate [NmLCH4/(gVSadded·d)]) equal to 36.3 against 18.6 for the control.

The Use of a GroEL-BLI Biosensor to Rapidly Assess Preaggregate Populations for Antibody Solutions Exhibiting Different Stability Profiles

An automated method using biotinylated GroEL-streptavidin biosensors with biolayer interferometry (GroEL-BLI) was evaluated to detect the formation of transiently formed, preaggregate species in various pharmaceutically relevant monoclonal antibody (mAb) samples. The relative aggregation propensity of various IgG1 and IgG4 mAbs was rank ordered using the GroEL-BLI biosensor method, and the least stable IgG4 mAb was subjected to different stresses including elevated temperatures, acidic pH, and addition of guanidine HCl. The GroEL-BLI biosensor detects mAb preaggregate formation mostly before, or sometimes concomitantly with, observing soluble aggregates and subvisible particles using size-exclusion chromatography and microflow imaging, respectively. A relatively unstable bispecific antibody (Bis-3) was shown to bind the GroEL biosensor even at low temperatures (25°C). During thermal stress (50°C, 1 h), increased Bis-3 binding to GroEL-biosensors was observed prior to aggregation by size-exclusion chromatography or microflow imaging. Transmission electron microscopy analysis of Bis-3 preaggregate GroEL complexes revealed, in some cases, potential hydrophobic interaction sites between the Fc domain of the Bis-3 and GroEL protein. The automated BLI method not only enables detection of transiently formed preaggregate species that initiate protein aggregation pathways but also permits rapid mAb formulation stability assessments at low volumes and low protein concentrations.

Compound-specific amino acid δ15 N values in archaeological shell: Assessing diagenetic integrity and potential for isotopic baseline reconstruction.

Reconstructing stable isotope (SI) ratios at the base of paleo-food webs is often challenging. For coastal systems, the SI ratios of organic matter in archeological shell represents a possible solution, providing a direct record of primary consumer SI ratios in the littoral zone. However, shell is often porous, with organic compounds susceptible to diagenetic alteration or contamination. If molecular isotopic information is well preserved, compound-specific amino acid isotope analysis (CSI-AA) has the potential to provide direct proxies for baseline SI ratios, bypassing many contamination issues, and to allow assessment of the diagenetic state. We collected shell from both archeological middens and nearby littoral zones in coastal Alaska, and used a simple organic extraction approach based on decalcification with sequential weak HCl additions to liberate organic material. We measured CSI-AA patterns, molar AA distributions, and the CSI-AA degradation parameter (ΣV), in the context of bulk SI ratios in fossil shell, modern shell, and soft tissue from five common taxa (urchin, limpet, mussel, periwinkle, chiton). CSI-AA patterns in both soft tissue and shell were consistent with primary consumers, and were indistinguishable in most modern and fossil shell pairs, showing that amino acid δ15 N values can be well preserved in archeological shell. AA molar distributions were also similar, although most fossil shell was enriched in Asx and Gly. Comparison between CSI-AA results from modern specimens confirmed that the source AA group (tracking isotopic baselines) are transferred without substantial modification into the shell record. In contrast, the Trophic AA group had elevated δ15 N values in shell versus soft tissue for all taxa examined, suggesting that a correction factor will be required for any CSI-AA proxies using these AAs. Overall, this new data indicates that the CSI-AA analysis of fossil shell represents a promising new approach to determining isotopic baselines in coastal paleo-ecosystems.

The Effect of Phosphatation and Granulation Zeolite in the Adsorption of Cr(VI)

The purpose of this research to study effect of contact time on adsorption of Cr(VI) ion using Granules Alumino Silico Phosphate (GASP) and the effect of Cr (VI) concentration on adsorption capacity at GASP. The GASF synthesis process is carried out in several main stages: 1) activation of zeolite with addition of HCl, 2) zeolite phosphatation with addition of NH 4 H 2 PO 4 ratio Si/P = 1/6 at 235ᴼC for 5 hours, 3) how make GASP with addition of zeolite phosphate (Alumino Silicone Phosphate) and chitosan gel with a syringe pump speed of 50 mL/min. GASP is characterized using XRF, FT-IR and SAA. The contact time effect is tested using 0.1 g of GASF in K 2 CrO 4 100 mg/L with a contact time variation of 0.5; 1.0; 1.5; 2.0 and 2.5 hours. The concentration effect on adsorption capacity is tested out using 0.1 g of GASP in K 2 CrO 4 with concentration variation 25, 50, 75, 100 and 150 mg / L for 2 hours (optimum contact time). The adsorption capacity can be determined using the Langmuir equation. XRF characterization results showed a decrease in SiO 2 levels of 18.10% and Al 2 O 3 by 2.2% after phosphatation process. FTIR characterization results indicate the presence of O-H, N-H and C-H chitosan on absorption bands 1-3. The success of the phosphatation process was evidenced by the shift of wave numbers to the lower regions in the bands 7, 9 and 12 the absorption of tetrahedral silica and alumina shifted to bands 8, 10 and 13 tetrahedral phosphate uptake in accordance with Hooke's law. The result of the research showed that the optimum contact time occurred in the adsorption process for 2 hours. The concentration variation was directly proportional to the increase of the adsorbed Cr (VI) ion mass. The presence of phosphatation and chitosan addition process can increase the value of adsorption capacity by 48,077 mg / g.

The effect of HCl and steam on cyclic CO2 capture performance in calcium looping systems

Calcium looping is CO2 capture technology that is considered to be technically feasible at an industrial scale using a variety of fuels such as natural gas, coals, biomass, refuse derived fuels, and biofuels. Unfortunately, many of these fuels contain significant quantities of chlorine which principally converts to gaseous HCl during combustion or gasification. To date, very few studies have examined the effect of HCl on sorbent CO2 capture performance using calcium-based sorbents under realistic carbonation and calcination conditions. In this work, experiments were conducted using thermogravimetric analysis and fixed bed reactor testing to determine the effect of HCl addition during carbonation and calcination over repeated cycles using a Canadian limestone. The presence of HCl was found to increase sorbent reactivity towards CO2 capture when steam was injected during calcination. The resulting decomposition of CaCl2 to CaO during calcination caused changes in the particle morphology, which in turn decreased the CO2 diffusional resistance during carbonation. Fixed bed test results provided confirmation of full sorbent dechlorination under typical oxy-fuel calcination conditions. It was shown that both particle surface area and pore volume were higher during tests where HCl was present during carbonation and that greater than 99% HCl capture could be achieved without adversely affecting sorbent CO2 capture performance when steam was present during both carbonation and calcination.

Effect of hydrochloric acid on grain size analysis of the Quaternary red clay rich in tiny ferromanganese nodules, Jiangxi province, southern China

There are many tiny ferromanganese nodules that cannot be found and eliminated easily in Quaternary red clay in southern China. The existence of these tiny ferromanganese nodules may influence grain size analysis results. Therefore, this paper focuses on the effects of the ferromanganese nodules on the grain size analysis and the effects of hydrochloric acid (HCl) on removing these nodules. The experimental results showed that the nodules clearly influenced the results of grain size analysis. The tiny ferromanganese nodules increased the coarse fraction and show a low peak in the coarse fraction of >100 μm on the frequency curves. The addition of HCl in the pretreatment process of grain size analysis can eliminate the effects of these tiny nodules effectively. Additionally, the HCl reacts with clay minerals and causes a reduction of the <4 μm fraction.

DETERMINATION OF CARBONATE CONTENT OF SOILS AND CLAYS BY USING CO_2 DETECTOR TUBE : IMPROVEMENT OF THE METHOD AND SOME APPLICATIONS

We improved the method for determination of carbonate in soils and clays (Wada (1997) Soil Sci. Plant Nutr., 43, 45-50). A sample was placed in a flexible gas-tight plastic bag attached with stopcock and heat-sealed. The carbonate in the sample was decomposed by addition of HCl and the generated CO 2 was diluted by injecting a known amount of air followed by determination of the CO 2 concentration of the gas in the bag. The carbonate content of the sample was calculated by summing the amount of gaseous and dissolved CO 2 , the latter of which was estimated with the aid of Henry's law. A series of test using standard carbonate minerals showed a 20 min of digestion was sufficient for complete dissolution. The improved method was applied to some clays and soil samples. Some Japanese soils from greenhouses contained about 0.08 to 0.35 mol kg -1 of carbonate, while their soil pH values were significantly lower than those expected from carbonate equilibrium.

Kinetically Controlled Coassembly of Multichromophoric Peptide Hydrogelators and the Impacts on Energy Transport.

We report a peptide-based multichromophoric hydrogelator system, wherein π-electron units with different inherent spectral energies are spatially controlled within peptidic 1-D nanostructures to create localized energy gradients in aqueous environments. This is accomplished by mixing different π-conjugated peptides prior to initiating self-assembly through solution acidification. We can vary the kinetics of the assembly and the degree of self-sorting through the choice of the assembly trigger, which changes the kinetics of acidification. The hydrolysis of glucono-δ-lactone (GdL) provides a slow pH drop that allows for stepwise triggering of peptide components into essentially self-sorted nanostructures based on subtle pKa differences, whereas HCl addition leads to a rapid formation of mixed components within a nanostructure. Using 1H NMR spectroscopy and fiber X-ray diffraction, we determine the conditions and peptide mixtures that favor self-sorting or intimate comixing. Photophysical investigations in the solution phase provide insight into the correlation of energy-transport processes occurring within the assemblies to the structural organization of the π-systems.

Supramolecular Hydrogel Formation in a Series of Self-Assembling Lipopeptides with Varying Lipid Chain Length.

The self-assembly in aqueous solution of three lipopeptides comprising a bioactive motif conjugated at the N terminus to dodecyl, tetradecyl or hexadecyl lipid chains has been examined. The bioactive motif is the peptide block YEALRVANEVTLN; a C-terminal fragment of the lumican proteoglycan. This study was motivated by our previous studies on the hexadecyl homologue C16-YEALRVANEVTLN, which showed aggregation into β-sheet structures above a critical aggregation concentration (cac), but most remarkably, we found that these aggregates were stable to dilution below the cac.1 Here we find that the C12- and C14-homologues also self-assemble above a cac into β-sheet nanotapes based on bilayer packing. The cac decreases with increasing lipopeptide hydrophobicity. Unexpectedly, the β-sheet secondary structure is present upon dilution and the aggregates are thermally stable. These results indicate that the dilution trapping of β-sheet secondary structure is not associated with lipid chain melting behavior. Instead, we associate it with pH-dependent favorable intermolecular electrostatic interactions. Investigation of the pH-dependence of aggregation led to the discovery of conditions for formation of lipopeptide hydrogels (initial sample preparation at pH 10 in NaOH solution, followed by reduction to pH ∼ 1 by addition of HCl). The lipopeptide hydrogels comprise networks of bilayer-based peptide nanotape bundles and to our knowledge this type of hydrogel is unprecedented. These hydrogels may have future applications based on processes such as encapsulation and release that involve fast switches between solution and hydrogel nanostructures.

Optically Multiresponsive Heteroleptic Platinum Dithiolene Complex with Proton-Switchable Properties.

Both linear- and nonlinear-optical properties of Bu4N[Pt(L1)(L2)] (1; L1 = [4',5':5,6][1,4]dithiino[2,3-b]quinoxaline-1',3'dithiolato; L2 = (R)-α-MBAdto dithiooxamidate, where (R)-α-MBA = (R)-(+)-α-methylbenzyl) upon HCl addition at room temperature change dramatically: the color turns from deep blue to green; the luminescence switches from deep red to green; the nonlinear-optical response (first hyperpolarizability) increases by a factor of 12. Thus, 1 behaves as a unique multiresponsive optical switch whose properties can be followed by the naked eye.

Isolable and Readily Handled Halophosphonium Pre-reagents for Hydro- and Deuteriohalogenation.

Although the addition of acid halides across olefins is well-studied, limitations remain with a number of substrate classes that possess leaving groups, polyunsaturation, and acid-sensitive moieties, particularly polyenes prone to cyclization. The process is also challenging when conducted on a small scale, and moreover, methods for the addition of their deuterated counterparts typically require special techniques, especially when control of stoichiometry is required. Herein is described a readily synthesized and handled reagent class which can accomplish the controlled and selective Markovnikov addition of both HCl and HBr across several alkene classes under mild reaction conditions tolerant of diverse functionality. The process is particularly valuable on a laboratory scale, and direct comparisons to other methods are provided. As a result of in-depth mechanistic studies seeking to understand how these novel tools work and the active species behind their efficacy, the means to easily add DCl and DBr using a controlled amount of D2O was discovered along with the critical role of hydrolysis in leading to active hydrohalogenation species.

Stereoselective functionalization of 1-alkoxy-2-(phenylethynyl)cyclopropanes via lithiation and subsequent reactions with electrophilic reagents

trans-1-Alkoxy-2-(phenylethynyl)cyclopropanes undergo lithiation at the hydrogen atom in the α-position to the triple bond on treatment with BuLi in THF at–(65—70) °C. The resulting organolithium derivatives react with acetaldehyde, acetone, dimethyl disulfide, and methyl chloroformate giving the corresponding alcohols, sulfides, and esters with the yields up to 69% with complete retention of cyclopropane ring stereoconfiguration. The obtained methyl 3-alkoxy-2,2-dimethyl-1-(phenylethynyl)cyclopropanecarboxylates and the corre-sponding acid readily undergo ring opening with addition of water molecule or HCl.

Microbial use of low molecular weight DOM in filtered and unfiltered freshwater: Role of ultra-small microorganisms and implications for water quality monitoring

Dissolved organic matter (DOM) plays a central role in regulating productivity and nutrient cycling in freshwaters. It is therefore vital that we can representatively sample and preserve DOM in freshwaters for subsequent analysis. Here we investigated the effect of filtration, temperature (5 and 25°C) and acidification (HCl) on the persistence of low molecular weight (MW) dissolved organic carbon (DOC), nitrogen (DON) and orthophosphate in oligotrophic and eutrophic freshwater environments. Our results showed the rapid loss of isotopically-labelled glucose and amino acids from both filtered (0.22 and 0.45μm) and unfiltered waters. We ascribe this substrate depletion in filtered samples to the activity of ultra-small (<0.45μm) microorganisms (bacteria and archaea) present in the water. As expected, the rate of C, N and P loss was much greater at higher temperatures and was repressed by the addition of HCl. Based on our results and an evaluation of the protocols used in recently published studies, we conclude that current techniques used to sample water for low MW DOM characterisation are frequently inadequate and lack proper validation. In contrast to the high degree of analytical precision and rigorous statistical analysis of most studies, we argue that insufficient consideration is still given to the presence of ultra-small microorganisms and potential changes that can occur in the low MW fraction of DOM prior to analysis.

Influence of Support Acidity and Ir Content on the Selective Ring Opening of Decalin over Ir/SiO2–Al2O3

The influence of the addition of HCl and Ir (1 wt %) to different SiO2–Al2O3 supports of varying silica content was studied in the reaction of selective ring opening of decalin. The addition of HCl to silica–alumina supports containing 70 and 80 wt % SiO2 was found to have little influence in the distribution of reaction products compared to the calcined supports. The incorporation of Ir to the silica–alumina catalysts has a beneficial effect, increasing the decalin conversion, being this effect more noticeable in the low acidity supports, i.e., those containing 30–40 wt % SiO2. The iridium-containing materials display the highest yield of cracking products, ring opening products, and ring contraction products. Increasing the reaction temperature promotes cracking and dehydrogenation but markedly decreases the selectivity to ring contraction products. At 350 °C a slight decrease in selectivity to ring opening products occurs, though the overall increase in conversion results in an increased yield of these...

Distinctive NO and N2O emission patterns in ammonia oxidizing bacteria: Effect of ammonia oxidation rate, DO and pH

This study aims at investigating the relationship between the nitric oxide (NO) and nitrous oxide (N2O) production rates with the ammonia oxidation rate (AORsp) in an enriched AOB culture. Different concentrations of ammonia were applied in a sequential batch reactor (SBR) performing partial nitritation in order to determine the effect of AORsp on N2O and NO production rates. Results showed that NO linearly correlates with the AORsp whereas N2O presents an exponential relationship. The effect of changes on the dissolved oxygen (DO) concentration on the overall NO and N2O emissions was assessed by increasing and decreasing the DO maintaining a constant pH at 7. When DO decreased the AORsp was maintained at the level achieved with the starting DO and led to lower NO and N2O emissions than when DO was increased. Finally, the effect of pH on N2O and NO was also tested by maintaining the DO at 1.5–2mg O2/L while pH was gradually decreased from 8 to 6.5. Results show that NO was chemically produced due to the addition of HCl when decreasing the pH whereas N2O was only produced biologically and was not affected by the addition of HCl.