Effect of oxygen on denitrification in continuous chemostat culture withComamonas sp SGLY2

Continuous cultures ofComamonas sp SGLY2 were grown anaerobically prior to establishing steady states at different oxygen flow rates. At a low oxygen transfer rate, no dissolved oxygen accumulated in the medium and all nitrate was reduced to dinitrogen. Concurrently with the increase of dissolved oxygen concentration in the liquid phase, the rate of denitrification decreased. However, at a dissolved oxygen concentration near saturation (33 mg L^–1), a part of the electron flow always diverted to nitrate with production of dinitrogen: the aerobic denitrification rate was equivalent to 35% of that calculated under anaerobic conditions. These experiments reflected the co-utilization of oxygen and N-oxides and the production of dinitrogen, up to saturated conditions, which implied synthesis and activity of the four denitrifying enzymes under various aeration conditions.     

Diazotrophic growth of Rhodopseudomonas acidophila and Rhodopseudomonas capsulata under microaerobic conditions in the dark

Diazotrophy of Rhodopseudomonas acidophila and Rhodopseudomonas capsulata was not obligatorily linked to photosynthesis. In the dark R. acidophila grew with dinitrogen as sole nitrogen source at a dissolved oxygen tension of 15 Torr (= 2.0 kPa); the doubling time was 8 h. Acetylene reduction by whole cells was more sensitive to oxygen in the light than in the dark. 16.5 mg N₂ were fixed per g lactic acid consumed. R. capsulata synthesized nitrogenase and fixed dinitrogen in the dark at a dissolved oxygen tension of less than one Torr (= 0.13 kPa). The doubling time of this bacterium was 16 h and 10.5 mg N₂ were fixed per g lactic acid consumed.Abbreviation kPa kilopascal     

Anaerobic Methane Oxidation: Occurrence and Ecology

Anoxic sediments and digested sewage sludge anaerobically oxidized methane to carbon dioxide while producing methane. This strictly anaerobic process showed a temperature optimum between 25 and 37°C, indicating an active microbial participation in this reaction. Methane oxidation in these anaerobic habitats was inhibited by oxygen. The rate of the oxidation followed the rate of methane production. The observed anoxic methane oxidation in Lake Mendota and digested sewage sludge was more sensitive to 2-bromoethanesulfonic acid than the simultaneous methane formation. Sulfate diminished methane formation as well as methane oxidation. However, in the presence of iron and sulfate the ratio of methane oxidized to methane formed increased markedly. Manganese dioxide and higher partial pressures of methane also stimulated the oxidation. The rate of methane oxidation in untreated samples was approximately 2% of the CH₄ production rate in Lake Mendota sediments and 8% of that in digested sludge. This percentage could be increased up to 90% in sludge in the presence of 10 mM ferrous sulfate and at a partial pressure of methane of 20 atm (2,027 kPa).     

Nitrogen removal from wastewater with a low COD/N ratio at a low oxygen concentration

The goal of the study was to determine the effectiveness of nitrification and denitrification and the kinetics of ammonia removal from a mixture of wastewater and anaerobic sludge digester supernatant in an SBR at limited oxygen concentration. In addition, the COD removal efficiency and sludge production were assessed.In the SBR cycle alternating aerobic and anaerobic phases occurred; in the aeration phase the dissolved oxygen (DO) concentration was below 0.7 mg O₂/L. The low DO concentration did not inhibit ammonia oxidation-nitrification and the efficiency was ca. 96-98%. However, a relatively high COD concentration in the effluent was detected. The values of K_m and V_max, calculated from the Michaelis-Menten equation, were 43 mg N-NH₄/L and 15.64 mg N-NH₄/L h, respectively. Activated sludge production was almost stable (0.62-0.66 g MLVSS/g COD). A high net biomass production resulted from a low specific biomass decay rate of 0.0015 d⁻¹.     

Modeling and simulation of oxygen-limited partial nitritation in a membrane-assisted bioreactor (MBR)

Combination of a partial nitritation process and an anaerobic ammonium oxidation process for the treatment of sludge reject water has some general cost-efficient advantages compared to nitrification-denitrification. The integrated process features two-stage autotrophic conversion of ammonium via nitrite to dinitrogen gas with lower demand for oxygen and no external carbon requirement. A nitrifying membrane-assisted bioreactor (MBR) for the treatment of sludge reject water was operated under continuous aeration at low dissolved oxygen (DO) concentrations with the purpose of generating nitrite accumulation. Microfiltration was applied to allow a high sludge retention time (SRT), resulting in a stable partial nitritation process. During start-up of the MBR, oxygen-limited conditions were induced by increasing the ammonium loading rate and decreasing the oxygen transfer. At a loading rate of 0.9 kg N m(-3) d(-1) and an oxygen concentration below 0.1 mg DO L(-1), conversion to nitrite was close to 50% of the incoming ammonium, thereby yielding an optimal effluent within the stoichiometric requirements for subsequent anaerobic ammonium oxidation. A mathematical model for ammonium oxidation to nitrite and nitrite oxidation to nitrate was developed to describe the oxygen-limited partial nitritation process within the MBR. The model was calibrated with in situ determinations of kinetic parameters for microbial growth, reflecting the intrinsic characteristics of the ammonium oxidizing growth system at limited oxygen availability and high sludge age. The oxygen transfer coefficient (K(L)a) and the ammonium-loading rate were shown to be the appropriate operational variables to describe the experimental data accurately. The validated model was used for further steady state simulation under different operational conditions of hydraulic retention time (HRT), K(L)a, temperature and SRT, with the intention to support optimized process design. Simulation results indicated that stable nitrite production from sludge reject water was feasible with this process even at a relatively low temperature of 20 degrees C with HRT down to 0.25 days.     

Factor influencing photoproduction of ammonia from dinitrogen byNostoc muscorum

Effective photoproduction of ammonia from dinitrogen has been achieved in a system consisting of a cell suspension of cyanobacteriumNostoc treated with a low concentration ofl-methionine sulfoximine (MSX). As a result of inactivation of cellular glutamate-ammonia ligase by MSX, growth was prevented, the rate of nitrogenase activity increased and about 90% of ammonia resulting from dinitrogen fixation was exported and accumulated in the ambient medium. The rate of NH₄ ⁺ production was found to be regulated by different factors such as light-dark cycle, cell density, depth of culture and air bubbling. Ammonia production was stimulated by (i) a culture density corresponding to 1.5 μg chlorophyll a per mL, (ii) a depth of 10 mm, and (iii) continuous illumination for 24 h. The nitrogenase activity was found to be enhanced in the experimental sets where ammonia production was maximal.     

Use of the glucose oxidase system to measure oxygen transfer rates

This investigation used the glucose oxidase system to simulate oxygen transfer rate in fermentation broths. It was demonstrated that the fungal preparation contained sufficient lactonase activity so that D -glucono-δ-lactone did not accumulate and that the rate of production of gluconic acid was proportional to the oxygen uptake rate. Enzyme concentrations of 1.5–2 g/1 were found adequate to determine oxygen absorption rates in shake flasks while maintaining the dissolved oxygen concentration of low levels. The apparent Michaelis constant for oxygen, K_m(O₂), was found to be 27% saturation with air; this value along with experimentally determined uptake rates could be used to calculate dissolved oxygen concentration in lieu of using a dissolved oxygen probe. Enzyme concentrations of 5 g/l were sufficient to give linear acid production and low dissolved oxygen concentrations in a bench-scale fermenter with no foaming or enzyme deactivation. The method is considered more valid and easier to employ than previously utilized techniques such as sulfite oxidation. Extension of the system to evaluating aeration effectiveness and scaleup of fermentation equipment is discussed.     

Vertical migration of aggregated aerobic and anaerobic ammonium oxidizers enhances oxygen uptake in a stagnant water layer

Ammonium can be removed as dinitrogen gas by cooperating aerobic and anaerobic ammonium-oxidizing bacteria (AerAOB and AnAOB). The goal of this study was to verify putative mutual benefits for aggregated AerAOB and AnAOB in a stagnant freshwater environment. In an ammonium fed water column, the biological oxygen consumption rate was, on average, 76 kg O₂ ha⁻¹ day⁻¹. As the oxygen transfer rate of an abiotic control column was only 17 kg O₂ ha⁻¹ day⁻¹, biomass activity enhanced the oxygen transfer. Increasing the AnAOB gas production increased the oxygen consumption rate with more than 50% as a result of enhanced vertical movement of the biomass. The coupled decrease in dissolved oxygen concentration increased the diffusional oxygen transfer from the atmosphere in the water. Physically preventing the biomass from rising to the upper water layer instantaneously decreased oxygen and ammonium consumption and even led to the occurrence of some sulfate reduction. Floating of the biomass was further confirmed to be beneficial, as this allowed for the development of a higher AerAOB and AnAOB activity, compared to settled biomass. Overall, the results support mutual benefits for aggregated AerAOB and AnAOB, derived from the biomass uplifting effect of AnAOB gas production.     

Alkalinity and dissolved oxygen as controlling parameters for ammonia removal through partial nitritation and ANAMMOX in a single-stage bioreactor

The oxidation of ammonia to dinitrogen through partial nitritation and anaerobic ammonium oxidation (ANAMMOX) in a single-stage bioreactor is based on suppressing the nitratation process. The single-stage process operated on a laboratory-scale fixed film bioreactor achieved ammonia removal of 0.7 kg NH₄-N/(m³ day) at 4 h hydraulic retention time (HRT) by controlling the nitratation process through a ‘three-way control mechanism’ comprising control of electron donor (nitrite), electron acceptor (oxygen) and carbon source (bicarbonate). The control of alkalinity and dissolved oxygen (DO) concentrations in feed to maintain an alkalinity to ammonia ratio of less than 8 and DO loading of less than 0.06 mg O/(mg N day), respectively, was necessary for inhibiting nitratation and enhancing partial nitritation and ANAMMOX. Therefore, feed alkalinity along with DO concentrations are critical controlling parameters in a single-stage biological process for nitrogen removal.     

Optimal operational factors for nitrite accumulation in batch reactors

The environmental factors that affected the accumulation of nitrite in nitrifying reactors were investigated using a mixed culture. A batch reactor with 50 mg-N/l of ammonia was used. The pH, temperature and dissolved oxygen concentration were varied. The concentration of unionized free ammonia also changed with the oxidation of ammonia and the variation of pH and temperature. The accumulation of nitrite was affected sensitively by pH and temperature. A higher nitrite concentration was observed at pH 8-9 or temperature around 30 °C. The dissolved oxygen also affected, giving the highest nitrite accumulation at around 1.5 mg/l. These were the favoredconditions for nitrite production. The free ammonia concentration influenced thenitrite accumulation also, by inhibiting nitrite oxidation. The inhibition becameapparent at a concentration of approximately 4 mg/l or above, but insignificant atbelow 1 mg/l. Thus, simultaneously high free ammonia concentration and maximumspecific ammonia-oxidation rate (above 15 × 10^-3 mg-N/mg-VSSh)were needed for a significant nitrite accumulation. When the two conditions were met, thenthe highest accumulation was observed when the ratio of the maximum specific oxidationrate of ammonia to the maximum specific oxidation rate of nitrite (k_a/k_n) was highest.Under the optimal operating conditions of pH 8, 30 °C and 1.5 mg/l of dissolvedoxygen, as much as 77% of the removed ammonia accumulated in nitrite.     

Effect of dissolved oxygen concentration on sludge settleability

This laboratory study presents a detailed evaluation of the effects of dissolved oxygen concentration and accumulation of storage polymers on sludge settleability in activated sludge systems with an aerobic selector. The oxygen and substrate availability regime were simulated in laboratory sequencing batch reactor systems. The experiments showed that low dissolved oxygen concentration (1.1 mg O₂ l^–1) had a strong negative effect on sludge settleability, leading to the proliferation of filamentous bacteria (Thiothrix spp., Type 021N and Type 1851). This negative effect was stronger at high chemical oxygen demand loading rate. This indicates that a compartmentalised (plug flow) aerobic contact tank, designed at short hydraulic residence time to guarantee a strong substrate gradient, with low dissolved oxygen concentration, might be worse for sludge settleability than an "overdesigned" completely mixed contact tank. Contrary to the general hypothesis, the maximum specific acetate uptake rate, poly--hydroxybutyrate production rate, and resistance to short starvation periods are similar in both poor- and well-settling sludge. The results of this study support our previous hypothesis on the importance of substrate gradients for the development of filamentous structures in biological flocs, from soluble organic substrate gradients to dissolved oxygen gradients in sludge flocs.     

Under-ice CO2 and O2 variability in a freshwater lake

Autonomous, in situ sensors for the partial pressure of CO₂(pCO₂) and dissolved oxygen (DO) were deployedin a freshwater lake during the winters of 1997 and 1998 to evaluate magnitudeand sources of variability during ice-covered periods. Gas variability ondiel or shorter time scales was small or undetectable during most of thedeployment periods, only becoming significant prior to ice-out whenrunoff and light penetration increased, promoting convective currents andbiological production. A surprising 7.6 d period oscillation,apparently driven by a baroclinic seiche, dominated the short-termvariability during the first year. The gas trends associated with the seicheoscillations and periodic profile measurements revealed that ice formation ledto gas gradients directly under the ice. Long-term variability wascharacterized by increasing CO₂ and decreasing DO as a consequenceofbiological oxidation of organic matter. The results suggest that both spatialand temporal variability can be significant over intervals which would not beresolved by traditional sampling-based studies.     

The induction and repression of benzene and catechol oxidizing capacity of Pseudomonas putida ML2 studied in perturbed chemostat culture

The oxidation of catechol, an intermediate in benzene catabolism, was studied using transient variations in dissolved oxygen tension (DOT) when a succinate limited steady state culture of Pseudomonas putida ML2 was perturbed with a pulse of another substrate. A model was developed and tested for the effect of fluctuations in oxidizing enzyme activity on DOT. It was found that the rate of induction of catechol oxidizing enzymes was independent of dilution rate up to a relative growth rate /_max of 0.75. Only at higher dilution rates was catabolite repression observed.Abbreviations DOT dissolved oxygen tension - K _L a gas transfer coefficient - specific growth rate - _max maximum specific growth rate - K_s substrate saturation constant     

Venturi aeration and thermophilic aerobic sewage sludge digestion in small-scale reactors

Summary The aeration performance of two venturi aeration reactors (operating volumes 381 and 251) was studied for an air-water system. It was found that the mass transfer coefficient (k _la) could be described in terms of the superficial gas velocity (V _s) alone by the simple expressionk _La=aV _infb ^supS with constantsa=0.313,b=0.579 for the 38-1 reactor anda=0.214,b=0.534 for the 25-1 reactor. A similar relationship was obeyed when the 38-1 reactor was aerated with a diffuser tile (a=17.0,b=1.52). A linear relationship betweenk _La and gas hold-up was observed for the 38-1 reactor with both venturi and diffuser aeration. The 25-1 reactor was used successfully for the thermophilic aerobic digestion of sewage sludge. A mean sludge temperature rise of 30°C was observed. Chemical oxygen demand, pH, and total solids content of the digested sludge differed significantly from the feed sludge and were similar to values obtained for full-scale thermophilic aerobic digestion. No significant differences between inorganic solids content, dissolved oxygen concentration, or redox potential were observed between feed and digested sludge.     

A rationale for the appropriate amount of inoculum in ready biodegradability tests

Several screening methods at the so-called ready biodegradability level are suitable to test poorly soluble substances. Typical for these tests is that mineralization is evaluated from monitoring oxygen uptake or carbon dioxide production. Unfortunately, they suffer from a rather low precision in the calculated percentage of mineralization caused by subtracting a too high inoculum control measurement from the response in the test system. Criteria for blank oxygen consumption, due to the metabolic activity of the inoculum, are proposed from which maximum amounts of activated sludge or secondary effluent per litre test medium can be derived to be used as an appropriate inoculum. Both for current and future standardized tests the precision of the method can be kept within acceptable margins. Inoculum material was sampled from 40 communal biological waste water treatment plants. From endogenous respiration rates it was derived that the concentration of secondary effluent in the Closed Bottle Test can be increased up to 50 mL/L but that in respirometry tests inoculated with activated sludge the appropriate concentration is 10 mg/L dry matter or below, depending of the design of the test system.List of abbreviations BOD biological oxygen demand - CBT Closed Bottle Test - C _as inoculum concentration in mg dry solids of activated sludge per litre test medium - C _ef inoculum concentration in ml secondary effluent per litre test medium - C _ss dry weight content of activated sludge (g/L) - CFU colony forming units - DO_7d dissolved oxygen concentration (mg/L) after 7 days - ISO International Organization for Standardization - NEN Dutch Organization for Standardization - O _c oxygen capacity in mg oxygen per litre vessel volume - OECD Organisation for Economic Co-operation and Development - Ox _as oxygen consumption after one week in mg oxygen per mg dry weight activated sludge - Ox _ef oxygen consumption after one week in mg oxygen per mL secondary effluent - Ox _ef [n] oxygen consumption after one week in mg oxygen per n mL secondary effluent - Ox _flask oxygen uptake in mg per litre flask volume - RBT Ready Biodegradability Test - SLR sludge loading rate in kg O₂/kg dry weight·d - ThOD theoretical oxygen demand - TPCBT Two Phase Closed Bottle Test - V _a volumes of air and water per litre vessel - V _w volume, respectively - _a concentration of oxygen in air at 20° C and 101.5 kPa - _s saturation oxygen concentration in te aqueous phase     

Enhanced ethylene production by primary roots of Zea mays L. in response to sub-ambient partial pressures of oxygen

Ethylene production by primary roots of 72–h-old intact seedlings of Zea mays L. cv. LG11 was studied under ambient and sub-ambient oxygen partial pressures (pO₂) using a gas flow-through system linked to a photoacoustic laser detector. Despite precautions to minimize physical perturbation to seedlings while setting-up, ethylene production in air was faster during the first 6h than later, in association with a small temporary swelling of the roots. When roots were switched from air (20–8kPa O₂) to 3 or 5kPa O₂ after 6h, ethylene production increased within 2—3 h. When, the roots were returned to air 16 h later, ethylene production decreased within 2—3 h. The presence of 10kPa CO₂ did not interfere with the effect of 3kPa O₂. Transferring roots from air to 12–5kPa did not change ethylene production, while a reduction to 1 kPa O₂ induced a small increase. The extra ethylene formed in 3 and 5 kPa O₂ was associated with plagiotropism, swelling, root hair production, and after 72 h, increased amounts of intercellular space (aerenchyma) in the root cortex. Root extension was also slowed down, but the pattern of response to oxygen shortage did not always match that of ethylene production. On return to air, subsequent growth patterns became normal within a few hours. In the complete absence of oxygen, no ethylene production was detected, even when anaerobic roots were returned to air after 16 h.     

Relationship between respirometric activity and community of entrapped nitrifying bacteria: Implications for partial nitrification

Activated sludge obtained from two municipal wastewater treatment facilities (WWTF) was used as seed sludge for enriched nitrifiers, which were later entrapped in polyvinyl alcohol. Seed sludge from one WWTF was acclimated to high ammonia level (1813 mg NH₃-N l^?1) through the return of sludge digester supernatant back to primary clarifier while seed sludge from the other WWTF was un-acclimated. To elucidate on how to control partial nitrification by entrapped cells, which could be different from suspended cells, kinetics of entrapped enriched nitrifiers were studied using a respirometric assay. The community of nitrifiers within the entrapment matrix, which was observed by fluorescence in situ hybridization (FISH) technique, was related to the nitritation and nitratation kinetics based on oxygen uptake rate. Maximum oxygen uptake rate, and substrate and oxygen affinities of both ammonia oxidizing bacteria (AOB) for nitritation and nitrite oxidizing bacteria (NOB) for nitratation in entrapped cells were lower than those of corresponding suspended cells. Under dissolved oxygen (DO) limiting conditions, nitratation was more suppressed than nitritation for suspended cells, while for the entrapped cells, the results were the contrary. A free ammonia (FA) inhibition affected only the un-acclimated sludge. Either FA inhibition or DO limitation might not be a sole effective control parameter to achieve partial nitrification by entrapped cells. FISH results revealed that Nitrosomonas europaea was the dominant AOB while Nitrobacter species was the dominant NOB in all cases. Heterotrophs were also present in the entrapment at 22.8 ± 18.6% and 41.5 ± 4.3% of total bacteria for acclimated and un-acclimated originated sludge. The availability of substrate and oxygen governed the distributions of AOB, NOB and heterotrophs within the entrapment and nitritation kinetics of entrapped nitrifiers.     

The Use of the Wide-Bore Dropping-Mercury Electrode for the Determination of Rates of Oxygen Uptake and of Oxidation of Ammonia by Micro-Organisms

S ummary : Convenient and reliable polarographic methods, using a wide-bore dropping-mercury electrode, for determining the dissolved oxygen content and the rate of respiration of sewage and activated sludge are described and verified by independent procedures. Using thiourea to inhibit Nitrosomonas spp., a technique was developed by which the uptake of oxygen by heterotrophs could be distinguished from that used in ammonia oxidation. Conditions are discussed under which accurate estimates of the rate of uptake of oxygen due to the oxidation of ammonia could be made. Typical values are given for the rates of respiration and of nitrification of activated sludge and also for the rates of respiration of a phenol-destroying pseudomonad.