Application of the Stover–Kincannon kinetic model to nitrogen removal by Chlorella vulgaris in a continuously operated immobilized photobioreactor system

BACKGROUND: The aim of this study was to evaluate the ammonium nitrogen removal performance of algae culture Chlorella vulgaris in a novel immobilized photobioreactor system under different operating conditions and to determine the biokinetic coefficients using the Stover–Kincannon model. RESULTS: The photobioreactor was continuously operated at different initial ammonium nitrogen concentrations (NH₄‐N₀ = 10–48 mg L⁻¹), hydraulic retention times (HRT = 1.7–5.5 days) and nitrogen/phosphorus ratios (N/P = 4/1–13/1). Effluent NH₄‐N concentrations varied between 2.1 ± 0.5 mg L⁻¹ and 26 ± 1.2 mg L⁻¹ with increasing initial NH₄‐N concentrations from 10 ± 0.6 mg L⁻¹ to 48 ± 1.8 mg L⁻¹ at θ_H = 2.7 days. The maximum removal efficiency was obtained as 79 ± 4.5% at 10 mg L⁻¹ NH₄‐N concentration. Operating the system for longer HRT improved the effluent quality, and the percentage removal increased from 35 ± 2.4% to 93 ± 0.2% for 20 mg L⁻¹ initial NH₄‐N concentration. The N/P ratio had a substantial effect on removal and the optimum ratio was determined as N/P = 8/1. Saturation value constant, and maximum substrate utilization rate constant of the Stover–Kincannon model for ammonium nitrogen removal by C. vulgaris were determined as K_B = 10.3 mg L⁻¹ d⁻¹, U_max = 13.0 mg L⁻¹ day⁻¹, respectively. CONCLUSION: Results indicated that the algae‐immobilized photobioreactor system had an effective nitrogen removal capacity when the operating conditions were optimized. The optimal conditions for the immobilized photobioreactor system used in this study can be summarized as HRT = 5.5 days, N/P = 8 and NH₄‐N₀ = 20 mg L⁻¹ initial nitrogen concentration to obtain removal efficiency greater than 90%. Copyright © 2008 Society of Chemical Industry     

Influence of temperature and pH on the kinetics of the Sharon nitritation process

The SHARON (Single reactor High activity Ammonia Removal Over Nitrite) process is an innovative process that improves the sustainability of wastewater treatment, especially when combined with an Anammox process. It aims at ammonium oxidation to nitrite only, while preventing further nitrate formation. In order to optimize this process by means of modelling and simulation, parameters of the biological processes have to be assessed. Batch tests with SHARON sludge clearly showed that ammonia rather than ammonium is the actual substrate and nitrous acid rather than nitrite is the actual inhibitor of the ammonium oxidation in the SHARON process. From these batch tests the ammonia affinity constant, the nitrous acid inhibition constant and the oxygen affinity constant were determined to be 0.75 mgNH₃‐N L^?1, 2.04 mgHNO₂‐N L^?1 and 0.94 mgO₂ L^?1. The influence of pH and temperature on the oxygen uptake rate of SHARON biomass was determined, indicating the existence of a pH interval between 6.5 and 8 and a temperature interval from 35 to 45 °C where the biomass activity is maximal. The kinetic parameters of the SHARON process were determined based on batch experiments. These parameters can now be implemented in a simulation model for further optimization of the SHARON process. Copyright © 2007 Society of Chemical Industry     

Sustained nitrite accumulation in a membrane‐assisted bioreactor (MBR) for the treatment of ammonium‐rich wastewater

A membrane‐assisted bioreactor (MBR) for sustained nitrite accumulation is presented, treating a synthetic wastewater with total ammonium nitrogen (TAN) concentrations of 1 kg N m^?3 at a hydraulic retention time down to 1 day. Complete biomass retention was obtained by microfiltration with submerged hollow fibre membranes. A membrane flux up to 189.5 dm³ day^?1 m^?2 could be maintained at a suction pressure below 100 kPa. Nitrification was effectively blocked at the nitrite stage (nitritation), and nitrate concentration was less than 29 g N m^?3. The rate of aeration was reduced to obtain a mixture of ammonium and nitrite, and after adjusting this rate the TAN/NO₂‐N ratio in the reactor effluent was kept around unity, making it suitable for further treatment by anaerobic oxidation of ammonium with nitrite. After increasing again the rate of aeration, complete nitrification to nitrate recovered after 11 days. It is suggested that nitrite accumulation resulted from a combination of factors. First, the dissolved oxygen (DO) concentration in the reactor was always limited with concentrations below 0.1 g DO m^?3, thereby limiting nitrification and preventing significant nitrate formation. The latter is attributed to the fact that ammonium‐oxidising bacteria cope better with low DO concentrations than nitrite oxidisers. Second, the MBR was operated at a high ammonia concentration of 7–54 g N m^?3, resulting in ammonia inhibition of the nitrite‐oxidising microorganisms. Third, a temperature of 35 °C was reported to yield a higher maximum growth rate for ammonium‐oxidising bacteria than for nitrite‐oxidising bacteria. Nitrite oxidisers were always present in the MBR but were out‐competed under the indicated process conditions, which is reflected in low concentrations of nitrate. Oxygen limitation was shown to be the most important factor to sustain nitrite accumulation. Nevertheless, nitritation was possible at ambient temperature (22–24 °C), lower ammonia concentration (<7 g N m^?3) and when using raw nitrogenous wastewater containing some biodegradable carbon. Overall, application of the MBR for nitritation was shown to be a reliable technology. © 2003 Society of Chemical Industry     

Denitrifying kinetics involving the distributed ratio of reductases

A suspended-growth batch reactor was used to denitrify synthetic wastewater containing various proportions of nitrate and nitrite. A competitive phenomenon between nitrate- and nitrite-reductase was studied utilizing various proportions of nitrate and nitrite in an anaerobic environment with a temperature of 30°C and methanol as carbon source. By using a non-linear regression technique, biokinetic constants of the maximum specific reduction rates of nitrate and nitrite (k₁, k₂) and the Monod half-saturation coefficients of nitrate and nitrite (K_s1, K_s2) for the proposed two-step denitrifying kinetics were 1·29 day^?1, 0·89 day^?1 and 14·3 mg NO-N dm^?3, 10.9 mg NO-N dm^?3, respectively. The result obtained from a series of chemostat studies indicated the Monod-type kinetic model was more accurate when the distributed ratio of nitrate- and nitrite-reductase in the proposed two-step denitrifying kinetics was taken into account.     

Respirometric estimation of the oxygen affinity constants for biological ammonium and nitrite oxidation

The nitrification process (ie biological ammonium oxidation to nitrate) is a two‐step process with nitrite as an intermediate product. As it is an aerobic process, its kinetics is highly dependent on the dissolved oxygen (DO) concentration in the medium. However, the influence of this limitation on the nitritation (first step) is shown to be less important than in the nitratation (second step). This dependence on DO concentration is generally described using a Monod‐type kinetics with K_O as the oxygen affinity constant. In this work, a procedure for the calculation of both affinity constants is presented. This procedure is based on monitoring the DO drop in the reactor when external aeration is stopped and the biomass is consuming without substrate (ammonium or nitrite) limitations. This methodology includes the contemplation of the oxygen transfer from the atmosphere, the response time of the DO probe and the inhibition of the nitratation step with sodium azide when estimating K_OA (nitritation oxygen affinity constant). The results obtained are K_OA = 0.74 ± 0.02 mg O₂ dm^?3 and K_ON = 1.75 ± 0.01 mg O₂ dm^?3. Moreover the influence of the aforementioned considerations on the estimated K_O values is also discussed. Copyright © 2005 Society of Chemical Industry     

Modelling a sequencing batch reactor to treat the supernatant from anaerobic digestion of the organic fraction of municipal solid waste

In this study, a lab‐scale sequencing batch reactor (SBR) has been tested to remove chemical oxygen demand (COD) and NH₄⁺‐N from the supernatant of anaerobic digestion of the organic fraction of municipal solid waste. This supernatant was characterized by a high ammonium concentration (1.1 g NH₄⁺‐N L^?1) and an important content of slowly biodegradable and/or recalcitrant COD (4.8 g total COD L^?1). Optimum SBR operating sequence was reached when working with 3 cycles per day, 30 °C, SRT 12 days and HRT 3 days. During the time sequence, two aerobic/anoxic steps were performed to avoid alkalinity restrictions. Oxygen supply and working pH range were controlled to promote the nitrification over nitrite. Under steady state conditions, COD and nitrogen removal efficiencies of more than 65% and 98%, respectively, were achieved. A closed intermittent‐flow respirometer was used to characterize and model the SBR performance. The activated sludge model ASM1 was modified to describe the biological nitrogen removal over nitrite, including the inhibition of nitrification by unionized ammonia and nitrous acid concentrations, the pH dependency of both autotrophic and heterotrophic biomass, pH calculation and the oxygen supply and stripping of CO₂ and NH₃. Once calibrated by respirometry, the proposed model showed very good agreement between experimental and simulated data. Copyright © 2007 Society of Chemical Industry     

Start‐up and enrichment of a granular anammox SBR to treat high nitrogen load wastewaters

BACKGROUND: Landfill leachate is characterized by low biodegradable organic matter that presents difficulties for the complete biological nitrogen removal usually performed by conventional biological nitrification/denitrification processes. To achieve this, the anaerobic ammonium oxidation (anammox) process is a promising biological treatment. This paper presents an anammox start‐up and enrichment methodology for treating high nitrogen load wastewaters using sequencing batch reactor (SBR) technology. RESULTS: The methodology is based on the gradual increase of the nitrite‐to‐ammonium molar ratio in the influent (from 0.76 to 1.32 mole NO₂^?‐N mole^?1NH₄⁺‐N) and on the exponential increase of the nitrogen loading rate (NLR, from 0.01 to 1.60 kg N m^?3 d^?1). 60 days after start‐up, anammox organisms were identified by polymerase chain reaction (PCR) technique as Candidatus Brocadia anammoxidans. After one year of operation, NLR had reached a value of 1.60 kg N m^?3 d^?1 with a nitrogen (ammonium plus nitrite) removal efficiency of 99.7%. The anammox biomass activity was verified by nitrogen mass balances with 1.32 ± 0.05 mole of nitrite removed per mole of ammonium removed and 0.23 ± 0.05 mole of nitrate produced per mole of ammonium removed. Also, enrichment of anammox bacteria was quantified by fluorescence in situ hybridization (FISH) analysis as 85.0 ± 1.8%. CONCLUSIONS: This paper provides a methodology for the enrichment of the anammox biomass in a SBR to treat high nitrogen loaded wastewaters. Copyright © 2007 Society of Chemical Industry     

Biological treatment of high salinity produced water by microbial consortia in a batch stirred tank reactor: Modelling and kinetics study

This study was performed to evaluate the potential of acclimated halophilic microorganisms, commercial microorganisms, and microorganisms from polluted soil to degrade crude oil in high salinity oily wastewater (synthetic produced water) at different salt concentrations ranging from zero to 250,000?mg?L^?1 of total dissolved solids (TDS). The highest degradation of crude oil (>60%) was found for acclimated halophilic microorganisms at TDS of 35,000?mg?L^?1. An increase in the TDS concentrations above 145,000?mg?L^?1 leads to a significant decrease in the growth of microorganisms. The results showed that efficiency of the commercial microorganisms was less than the acclimated halophilic microorganisms. The oil biodegradation followed substrate inhibition kinetics and the specific growth rate were fitted to the Haldane model. The biokinetic constants for the saline oily water at TDS of 35,000?mg?L^?1, i.e., Y, K_s, µ_max, and 1/K_i, were 0.21?mg?MLSS/mg crude oil, 0.27?mg?L^?1, 0.019?h^?1, and 0.002?mg?L^?1, respectively.     

Improvement of the settling properties of Anammox sludge in an SBR

Biological systems for the treatment of wastewater have to provide optimum sludge retention to achieve high removal efficiencies. In the case of slow‐growing micro‐organisms, such as anaerobic ammonia‐oxidizing (Anammox) bacteria, episodes of flotation involving biomass wash‐out are especially critical. In this study a strategy based on the introduction of a mix period in the operational cycle of the Anammox Sequencing Batch Reactor (SBR) was tested for its effects on biomass retention and nitrite removal. Using this new cycle distribution the biomass retention inside the reactor improved as the solids concentration in the effluent of the SBR decreased from 20–45 to 5–10 mg VSS dm^?3 and the biomass concentration inside the reactor increased from 1.30 to 2.53 g VSS dm^?3 in a period of 25 days. A decrease of the sludge volume index (SVI) from 108 to 60 cm³ g VSS^?1 was also observed. Complete depletion of nitrite was achieved in the reactor only with the new cycle distribution treating nitrogen loading rates (g N‐NO₂^? + g N‐NH₄⁺ dm^?3 d^?1) up to 0.60 g N dm^?3 d^?1. Copyright © 2004 Society of Chemical Industry     

Nitrite accumulation characteristics of high strength ammonia wastewater in an autotrophic nitrifying biofilm reactor

Selective nitrification was carried out to accumulate nitrite from high strength ammonia wastewater in an autotrophic nitrifying biofilm reactor. Nitrification efficiencies and nitrite accumulation characteristics were investigated at various operating conditions such as ammonium load, oxygen supply and free ammonia concentration. The biofilm reactor showed very stable nitrification efficiencies of more than 90% at up to 2 kg NH₄‐N m^?3 d^?1 and the nitrite content was maintained at around 95%. Inhibition by free ammonia on nitrite oxidizers seems to be the major factor for nitrite accumulation. Batch kinetic analyses of ammonium and nitrite oxidation showed that nitrite oxidation activity was selectively inhibited in the presence of free ammonia. However, the activity recovered quickly as the free ammonia concentration decreased below the threshold inhibition concentration. Examination of specific ammonia and nitrite oxidation activities and the most probable number indicated that the number of nitrite‐oxidizing microorganisms in the nitrite‐accumulating system was less than that in the normal nitrification system due to long‐term free ammonia inhibition of the nitrite oxidizers. The reduced population of nitrite oxidizers in the biofilm system was also responsible for the accumulation of nitrite in the biofilm reactor. © 2003 Society of Chemical Industry     

Effects of electrolytes on the reduction of 2,4‐dinitrotoluene by zero‐valent iron

BACKGROUND: Dinitrotoluenes (DNTs) are environmentally persistent, making the remediation of contaminated streams and groundwater difficult. Zero‐valent iron (Fe⁰) can be used as an electron source for the reduction of recalcitrant DNTs in waste‐water and thus enhance their biodegradability. However, little is known about the qualitative effects of major anions and cations present in waste‐water on the reduction of DNTs by Fe⁰. RESULTS: The presence of Na₂SO₄ and NaCl at levels between 0.25 and 2 mmol L^?1 was observed to enhance the reactivity of Fe⁰ towards 2,4‐DNT. The positive effect of K₂SO₄ is stronger than that of Na₂SO₄ at the same level (1 mmol L^?1). Varying (NH₄)₂SO₄ from 0.1 to 1.0 mmol L^?1 improved the efficiency of 2,4‐DNT degradation by Fe⁰. The effects of varying NaNO₃ and NaNO₂ from 0 mmol L^?1 to 4.7 mmol L^?1 and 0 mmol L^?1 to 5.8 mmol L^?1, respectively, were also investigated. Both NaNO₃ and NaNO₂ at low concentration improved the efficiency of 2,4‐DNT degradation by Fe⁰, however, at high concentration, inhibiting effects appeared. CONCLUSION: SO₄^2?, Cl^?, Na⁺, K⁺ and NH₄⁺ notably enhanced 2,4‐DNT reduction by Fe⁰ at the tested concentrations. The positive effect of K⁺, Cl^? was relatively stronger than that of Na⁺ and sulfate (SO₄^2?). However, the effect of NH₄⁺ was relatively weaker at concentrations greater than 1.0 mmol L^?1. The presence of low concentrations of NO₃^? and NO₂^? promoted 2,4‐DNT reduction by Fe⁰ and inhibited the reaction. The results suggest that 2,4‐DNT reduction by Fe⁰ can be controlled by the ions composition of the waste‐water. Copyright © 2010 Society of Chemical Industry     

The effects of nitrate and nitrate‐supplemented leachate addition on methanogenesis from Municipal Solid Waste

The recirculation of nitrified leachate through landfill sites, followed by in situ denitrification, represents a novel and more sustainable approach for the removal of ammonia from leachate, prior to discharge. The effects of nitrate and leachate supplementation on methanogenesis in Municipal Solid Waste (MSW) were studied in batch cultures. The addition of a range of nitrate concentrations to MSW samples had an inhibitory effect on methanogenesis. The effects were dose‐dependent, such that recovery of methane production was recorded within 5 and 23 days with added 100 and 750 mg NO₃ dm^?3, respectively. Even after 24 days, no recovery was observed in cultures challenged with 1000 mg NO₃ dm^?3. The enumeration of denitrifying bacteria in a range of fresh, actively methanogenic and aged, well‐decomposed MSW confirmed the potential of MSW for rapid denitrification. Methanogenesis was not inhibited by the addition of leachate (20–100% strength) that contained high concentrations of VFAs. However, when the same leachate was supplemented with nitrate (250 mg NO₃ dm^?3), methanogenesis was inhibited by the addition of leachate concentrations ≥20%, which was attributed to inhibition of denitrification by VFAs. Propionate accumulated, confirming the importance of methanogenesis as an electron sink. With the removal of nitrate and the recovery of methanogenesis, net propionate concentrations decreased. Copyright © 2004 Society of Chemical Industry     

Nitrification in a packed bed bioreactor integrated into a marine recirculating maturation system under different substrate concentrations and flow rates

BACKGROUND: A packed bed bioreactor (PBBR) activated with an indigenous nitrifying bacterial consortia was developed and commercialized for rapid establishment of nitrification in brackish water and marine hatchery systems in the tropics. The present study evaluated nitrification in PBBR integrated into a Penaeus monodon recirculating maturation system under different substrate concentrations and flow rates. RESULTS: Instant nitrification was observed after integration of PBBR into the maturation system. TAN and NO₂‐N concentrations were always maintained below 0.5 mg L^?1 during operation. The TAN and NO₂‐N removal was significant (P < 0.001) in all the six reactor compartments of the PBBR having the substrates at initial concentrations of 2, 5 and 10 mg L^?1. The average volumetric TAN removal rates increased with flow rates from 43.51 (250 L h^?1) to 130.44 (2500 L h^?1) gTAN m^?3 day^?1 (P < 0.05). FISH analysis of the biofilms after 70 days of operation gave positive results with probes NSO 190 ((β ammonia oxidizers), NsV 443 (Nitrosospira spp.) NEU (halophilic Nitrosomonas), Ntspa 712 (Phylum Nitrospira) indicating stability of the consortia. CONCLUSION: The PBBR integrated into the P. monodon maturation system exhibited significant nitrification upon operation for 70 days as well as at different substrate concentrations and flow rates. This system can easily be integrated into marine and brackish water aquaculture systems, to establish instantaneous nitrification. Copyright © 2011 Society of Chemical Industry     

Aerobic biodegradation and inhibition kinetics of poly‐aromatic hydrocarbons (PAHs) in a petrochemical industry wastewater in the presence of biosurfactants

BACKROUND: In Izmir, Turkey, wastewaters from the petrochemical industry are treated using conventional activated sludge systems. A significant proportion of poly‐aromatic hydrocarbons (PAHs) with high‐molecular weights remains in this treatment system and inhibits the biological activity. Biosurfactants increase PAHs degradation by enhancing the solubility of the petroleum components. The aerobic inhibition kinetics of PAHs has not previously been investigated in the presence of biosurfactants for a real petrochemical industry wastewater. RESULTS: Among the kinetic models used (Monod‐type, zero, first‐order and second‐order) it was found that the Monod kinetic was effective for describing the biodegradation of PAHs in petrochemcal industry wastewater in the presence of three biosurfactants, namely Rhamnolipid (RD), Surfactine (SR) and Emulsan (EM) in an aerobic activated sludge reactor (AASR). The maximum PAH removal rate (R_max) and specific growth rate of PAH degrading bacteria (µ_max) increased, while the half saturation concentration of PAH (K_s) decreased at 15 mg L^?1 RD concentration compared with the control without biosurfactant at a sludge retention time (SRT) of 25 days. CONCLUSION: PAH oxidation is typified by competitive inhibition at RD concentrations > 15 mg L^?1 resulting in increases in K_s values with PAH accumulation. Low inhibition constant (K_ID) values reflect difficulties in the metabolizability of PAHs. Metabolite production decreased at RD = 25 mg L^?1 in the PAHs indeno (1,2,3‐cd) pyrene (IcdP), flourene (FLN), phenanthrene (PHE) and benzo(a)pyrene (BaP). Copyright © 2011 Society of Chemical Industry     

Equilibrium and kinetic studies on the extraction of gadolinium(III) from nitrate medium by di‐2‐ethylhexylphosphoric acid in kerosene using a single drop technique

The liquid–liquid extraction of Gd(III) from aqueous nitrate medium was studied using di‐2‐ethylhexylphosphoric acid (HDEHP) in kerosene. On the basis of the slope analysis data, the composition of the extracted species was found to be [Gd A₃(HA)] with the extraction equilibrium constant (K_ex) = (1.48 ± 0.042) × 10^?12 mol dm^?3. The results of the effect of temperature on the value of the equilibrium extraction constant indicated the endothermic character of the extraction system. The kinetics of the forward extraction of Gd³⁺ from nitrate medium by HDEHP in kerosene was investigated using the single drop column technique. The rate of flux (mass transfer per unit area) was found to be proportional to [Gd(III)], [H₂A₂]_(o), [NO₃^?], and [H⁺]^?1 in the liquid drop organic phase. The forward extraction rate constant, k_f, was 2.24 × 10^?3 m s^?1 using the equation: Copyright © 2005 Society of Chemical Industry     

Development of a membrane‐assisted hybrid bioreactor for ammonia and COD removal in wastewaters

A new membrane‐assisted hybrid bioreactor was developed to remove ammonia and organic matter. This system was composed of a hybrid circulating bed reactor (CBR) coupled in series to an ultrafiltration membrane module for biomass separation. The growth of biomass both in suspension and biofilms was promoted in the hybrid reactor. The system was operated for 103 days, during which a constant ammonia loading rate (ALR) was fed to the system. The COD/N‐NH₄⁺ ratio was manipulated between 0 and 4, in order to study the effects of different organic matter concentrations on the nitrification capacity of the system. Experimental results have shown that it was feasible to operate with a membrane hybrid system attaining 99% chemical oxygen demand (COD) removal and ammonia conversion. The ALR was 0.92 kg N‐NH₄⁺ m^?3 d^?1 and the organic loading rate (OLR) achieved up to 3.6 kg COD m^?3 d^?1. Also, the concentration of ammonia in the effluent was low, 1 mg N‐NH₄⁺ dm^?3. Specific activity determinations have shown that there was a certain degree of segregation of nitrifiers and heterotrophs between the two biomass phases in the system. Growth of the slow‐growing nitrifiers took place preferentially in the biofilm and the fast‐growing heterotrophs grew in suspension. This fact allowed the nitrifying activity in the biofilm be maintained around 0.8 g N g^?1 protein d^?1, regardless of the addition of organic matter in the influent. The specific nitrifying activity of suspended biomass varied between 0.3 and 0.4 g N g^?1 VSS d^?1. Copyright © 2004 Society of Chemical Industry     

Aerated membrane‐attached biofilm reactor as an effective tool for partial nitrification in pretreatment of anaerobic ammonium oxidation (ANAMMOX) process

BACKGROUND: A laboratory‐scale membrane aeration bioreactor was employed to treat synthetic ammonium‐rich wastewater to yield an appropriate NH₄⁺/NO₂^? ratio for anaerobic ammonium oxidation (ANAMMOX). The main objectives of this study were to steadily obtain 50% partial nitrification in batch experiments, to evaluate the effects of aeration and to identify the dominant bacterial community of the biofilm for partial nitrification. RESULTS: Some of the ammonium in the synthetic wastewater was partially nitrified. A suitable NH₄⁺/NO₂^? ratio (1:1 to 1:1.3) for the ANAMMOX process was obtained after 24 h. The dissolved oxygen (DO) level in the treated water was very low (below 0.6 mg L^?1). Both the appropriate NH₄⁺/NO₂^? ratio and the low DO level make this bioreactor an ideal pretreatment system for ANAMMOX. In addition, a molecular biotechnology method was applied to prove that the ammonia‐oxidizing bacteria dominated the biofilm. CONCLUSION: This system achieved surprising cost savings in the aeration process compared with traditional aeration systems. The combination of this system with the subsequent ANAMMOX process has great potential as a favorable short‐cut in the treatment of ammonium‐rich wastewater. Copyright © 2007 Society of Chemical Industry     

Low Activation Energy Pathway for the Catalyzed Reduction of Nitrogen Oxides to N<Subscript>2</Subscript> by Ammonia

A low activation energy pathway for the catalytic reduction of nitrogen oxides to N₂, with reductants other than ammonia, consists of two sets of reaction steps. In the first set, part of the NO _x is reduced to NH₃; in the second set ammonium nitrite, NH₄NO₂ is formed from this NH₃ and NO + NO₂. The NH₄NO₂ thus formed decomposes at ~100 °C to N₂ + H₂O, even on an inert support, whereas ammonium nitrate, NH₄NO₃, which is also formed from NH₃ and NO₂ + O₂, (or HNO₃), decomposes only at 312 °C yielding mainly N₂O. Upon applying Redhead's equations for a first order desorption to the decomposition of ammonium nitrite, an activation energiy of 22.4 is calculated which is consistent with literature data. For the reaction path via ammonium nitrite a consumption ratio of 1/1 for NO and NO₂ is predicted and confirmed experimentally by injecting NO into a mixture of NH₃ + NO₂ flowing over a BaNa/Y catalyst. This leads to a yield increase of one N₂ molecule per added molecule of NO. Little N₂ is produced from NH₃ + NO in the absence of NO₂.     

Kinetics of syntrophic acetogenesis in a saline medium

BACKGROUND: The anaerobic degradation kinetics of volatile fatty acids (VFA) in a saline (24 g NaCl dm^?3) and mesophilic (37 °C) medium was studied under batch test conditions. The acetate production kinetics without inhibition by propionic, butyric and valeric acids was determined. The inhibition of acetate production during syntrophic acetogenesis by VFA and pH was studied. The acetogenesis without inhibition was modelled using a Monod equation. The pH inhibition was represented by a Michaelis pH function, while the inhibition by acetic acid (HAc) was represented by a non‐competitive model. RESULTS: The specific maximum degradation rate and saturation constant (k_{max, VFA}, K_{S, max}) values were (5.89, 15.95), (7.97, 25.99) and (7.75 g VFA g^?1 volatile suspended solids day^?1, 11.52 mg VFA dm^?3) for propionic, butyric and valeric acids respectively, with maximum velocity at pH 7. The inhibition constants (K_{I, HAc}) were 1295, 671 and 572 mg HAc dm^?3 for propionic, butyric and valeric acids respectively. CONCLUSION: VFA and pH can be inhibitory for acetogenesis under these conditions. Copyright © 2008 Society of Chemical Industry     

Evaluation of heterotrophic nitrite removal by a sulphide and acetate oxidizing mixed culture originated from an oil reservoir

BACKGROUND: Shortcut biological nitrogen removal (SBNR) has attracted much attention in recent years due to lower aeration and chemical oxygen demand (COD) requirements, shorter residence time and smaller biomass production. In this work an oil reservoir denitrifying culture, with the ability to function under autotrophic and heterotrophic conditions was used for heterotrophic denitritation. Using freely suspended cells, effects of nitrite concentration (10–50 mmol L^?1) and temperature (15–35 °C) on the kinetics of denitritation were investigated and a kinetic model was developed. Potential for enhancement of nitrite removal rate, and impacts of nitrite concentration and loading rate were investigated in a continuous biofilm reactor. RESULTS: Nitrite did not impose any inhibitory effect, even at the highest applied concentration of 50 mmol L^?1. Increase of temperature in the range 15–35 °C enhanced the reduction rate significantly. Fitting the experimental data into the model developed, values of biokinetic coefficients (µ_max?NO2, K_S?NO2, Y_X?NO2, Y_X?Ace?NO2 and Eµ‐_NO2) were determined. In the biofilm reactor increases in nitrite loading rate (through flow rate or feed nitrite concentration) led to a linear increase of nitrite removal rate, with the highest removal rate of 140.6 mmol L^?1 h^?1 achieved with a residence time of 0.19 h. CONCLUSION: The enrichment culture used in this study is not only a superior biocatalyst for simultaneous removal of sulphide, nitrate and BOD, it could also be used effectively in the denitritation step of an SBNR process. The kinetic model developed would certainly have beneficial applications in the design, operation and control of the SBNR process. Copyright © 2011 Society of Chemical Industry