Reaeration of Oxygen in Shallow,Macrophyte Rich Streams: I – Determination of the Reaeration Rate Coefficient

The rate coefficient K₂ for the exchange of oxygen between flowing water and the atmosphere (reaeration) has been studied in six Danish streams covering a relatively wide range of hydraulic conditions, pollutional loading, and macrophyte abundance. 103 K₂-measurements were performed in 1978–85. 82 measurements were obtained applying 5 different indirect methods all balancing the sources and sinks of stream dissolved oxygen under conditions of normal operation of the system (3 methods) and under artificial depletion of the oxygen concentration of the stream water by addition of sodium sulphite (2 methods). 21 K₂-values were determined directly applying a gaseous tracer (krypton-85) for reaeration. Guidelines for selecting a proper method to determine K₂ knowing macrophyte biomass and loading characteristics of the particular stream are provided.     

Studies on the kinetics and mechanism of BOD exertion in dilute systems

The mechanisms and kinetic course of BOD exertion were compared in both open and closed systems. Two open reactors, a simulated stream device, and an open stirred reactor were employed, and the closed systems consisted of standard BOD bottles and 2.4-liter vessels. In the closed systems, both quiescent and stirred conditions of incubation were examined. Biological solids concentration, bacteria and protozoa concentration, substrate analysis, and chemical oxygen demand as well as biochemical oxygen utilization were employed to assess the performance of these systems. Oxygen uptake rate constants were observed to increase with increasing concentration o carbon source, thus militating against irect use of the usual dilution technique for predicting rate of deoxygenation in receiving streams. The relationship between specific O₂ uptake rate and substrate concentration approximated a hyperbolic function similar to the Mono relationship for specific growth rate and substrate concentration. A technique using an open stirred reactor than the standard BOD bottle dilution technique is recommended.     

Response of river metabolism to restoration of flow in the Kissimmee River, Florida, U.S.A.

1. The single station diel oxygen curve method was used to determine the response of system metabolism to backfilling of a flood control canal and restoration of flow through the historic river channel of the Kissimmee River, a sub‐tropical, low gradient, blackwater river in central Florida, U.S.A. Gross primary productivity (GPP), community respiration (CR), the ratio of GPP/CR (P/R) and net daily metabolism (NDM) were estimated before and after canal backfilling and restoration of continuous flow through the river channel. 2. Restoration of flow through the river channel significantly increased reaeration rates and mean dissolved oxygen (DO) concentrations from <2 mg L⁻¹ before restoration of flow to 4.70 mg L⁻¹ after flow was restored. 3. Annual GPP and CR rates were 0.43 g O₂ m⁻² day⁻¹ and 1.61 g O₂ m⁻² day⁻¹ respectively, before restoration of flow. After restoration of flow, annual GPP and CR rates increased to 3.95 O₂ m⁻² day⁻¹ and 9.44 g O₂ m⁻² day⁻¹ respectively. 4. The ratio of P/R (mean of monthly values) increased from 0.29 during the prerestoration period to 0.51 after flow was restored, indicating an increase in autotrophic processes in the restored river channel. NDM values became more negative after flow was restored. 5. After flow was restored, metabolism parameters were generally similar to those reported for other blackwater river systems in the southeast U.S.A. Postrestoration DO concentrations met target values derived from free flowing, minimally impacted reference streams.     

Production of rosmarinic acid by<Emphasis Type="Italic">Lavandula vera</Emphasis> MM cell suspension in bioreactor: effect of dissolved oxygen concentration and agitation

The relationship between dissolved oxygen (DO) concentration, agitation rate and growth of Lavandula vera MM and rosmarinic acid biosynthesis was investigated in 3 l laboratory bioreactor. Lavandula vera MM cell suspension accumulated the highest amounts of biomass (34.8 g/l) and rosmarinic acid (1870.6 mg/l) on day 12 of cultivation at 50% dissolved oxygen and agitation speed 100 rpm and at 30% dissolved oxygen and agitation speed 300 rpm, respectively.     

Metabolic balance of streams draining urban and agricultural watersheds in central Japan

Empirical data that describe the metabolic balance of stream ecosystems in human-dominated watersheds are scarce. We measured ecosystem metabolism in 23 open-canopied lowland streams draining urban and agricultural areas in the Fuji River Basin, central Japan. Gross primary production (GPP) and community respiration (CR) were estimated using the diurnal dissolved oxygen (DO) change technique, with the reaeration coefficient (K ₂) determined from seven empirical depth-velocity equations. Because the predicted values of K ₂ showed variation among the depth-velocity equations, the estimates of stream metabolism also varied according to the equations. However, CR was almost always greater than GPP, resulting in negative net ecosystem production (NEP) and GPP/CR ratios below unity for most of the study reaches. Highly heterotrophic streams were found in intensively farmed watersheds, suggesting that organic matter loading from agricultural lands is likely to be a source of allochthonous carbon fueling excess respiration in the study streams. In contrast, streams draining more urbanized areas were less heterotrophic. The present results suggest that lowland streams in agriculturally developed watersheds are associated strongly with terrestrial ecosystems as a source of organic carbon. The resultant strong respiration might become the dominant process in ecosystem metabolism, as reported for headwater streams, large downstream rivers, and estuaries.     

Ventilatory and behavioural responses of the marbled sole Pseudopleuronectes yokohamae to progressive hypoxia

This study identified ventilatory and behavioural responses in the marbled sole Pseudopleuronectes yokohamae under experimentally induced progressive decreases in dissolved oxygen (DO) levels. Ventilation frequency showed an increase with decreasing DO levels from normoxia to 2·75 mg O₂ l^?1, followed by a decrease in ventilation frequency at decreased DO levels from 2·00 to 0·75 mg O₂ l^?1. At DO levels below 2·00 mg l^?1, behaviours at the bottom were suppressed, whereas avoidance behaviours increased. A decrease in avoidance behaviours was observed from 1·00 to 0·75 mg O₂ l^?1. Upside‐down reversal and incapacitation at DO levels of 1·00–0·75 mg O₂ l^?1 suggested that sublethal effects on P. yokohamae were induced. The responses observed before the sublethal DO level could be interpreted as an effort to maintain oxygen uptake, reduce routine activities and facilitate avoidance. The observed DO level thresholds that induce behavioural responses, in addition to sublethal effects, indicate hypoxia‐tolerance that is important for understanding the effects of hypoxia on coastal ecosystems.     

A Stochastic Model for BOD and DO with Random Initial Conditions and Distance Dependent Velocity

A random differential equation arises in stream pollution models when the initial conditions are stochastic and the stream velocity is distance dependent. The mean squared solution gives the biochemical oxygen demand (BOD) and the dissolved oxygen (DO) at any distance downstream from the pollution source. The probability density function and some of the moments of the BOD and DO are obtained, thus completely characterizing the BOD and DO process. An example illustrates the results and compares them with previous ones.     

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.     

Effects of dilution on dissolved oxygen depletion and microbial populations in the biochemical oxygen demand determination

The biochemical oxygen demand (BOD) value is still a key parameter that can determine the level of organics, particularly the content of biodegradable organics in water. In this work, the effects of sample dilution, which should be done inevitably to get appropriate dissolved oxygen (DO) depletion, on the measurement of 5-day BOD (BOD₅), was investigated with and without seeding using natural and synthetic water. The dilution effects were also evaluated for water samples taken in different seasons such as summer and winter because water temperature can cause a change in the types of microbial species, thus leading to different oxygen depletion profiles during BOD testing. The predation phenomenon between microbial cells was found to be dependent on the inorganic nutrients and carbon sources, showing a change in cell populations according to cell size after 5-day incubation. The dilution of water samples for BOD determination was linked to changes in the environment for microbial growth such as nutrition. The predation phenomenon between microbial cells was more important with less dilution. BOD₅ increased with the specific amount of inorganic nutrient per microbial mass when the natural water was diluted. When seeding was done for synthetic water samples, the seed volume also affected BOD due to the rate of organic uptake by microbes. BOD₅ increased with the specific bacterial population per organic source supplied at the beginning of BOD measurement. For more accurate BOD measurements, specific guidelines on dilution should be established.     

The role of aeration and agitation in the production of glucose oxidase in submerged culture. II

The main purpose of the work reported here was to establish the effectiveness of aeration and agitation, and to determine the best conditions of aeration for the growth and production of glucose oxidase of Aspergillus niger, on a semi-industrial scale. Concentration of dissolved O₂, O₂ consumption and CO₂ production were measured. It was found that the rate of growth and the activity of glucose oxidase per gram mycelium increased with the increase of speed of agitation. The concentration of dissolved oxygen of the fermentation broth, as well as the rate of respiration (O₂ consumption and CO₂ production) increased in direct proportion to the increase of speed of agitation, while assimilation of sugars was accelerated. The values of the respiratory ratio showed a fluctuation according to the presence or absence of sugar in the medium.     

Influence of agitation and aeration on growth and antibiotic production by <Emphasis Type="Italic">Xenorhabdus nematophila</Emphasis>

The effect of agitation and aeration on the growth and antibiotic production by Xenorhabdus nematophila YL001 grown in batch cultures were investigated. Efficiency of aeration and agitation was evaluated through the oxygen mass transfer coefficient (K _L a). With increase in K _L a, the biomass and antibiotic activity increased. Activity units of antibiotic and dry cell weight were increased to 232 U ml⁻¹ and 19.58 g l⁻¹, respectively, productivity in cell and antibiotic was up more than 30% when K _L a increased from 115.9 h⁻¹ to 185.7 h⁻¹. During the exponential growth phase, DO concentration was zero, the oxygen supply was not sufficient. So, based on process analysis, a three-stage oxygen supply control strategy was used to improved the DO concentration above 30% by controlling the agitation speed and aeration rate. The dry cell weight and activity units of antibiotic were further increased to 24.22 g l⁻¹ and 249 U ml⁻¹, and were improved by 24.0% and 7.0%, compared with fermentation at a constant agitation speed and a constant aeration rate (300 rev min⁻¹, 2.5 l min⁻¹).     

Working design for a 5-liter controlled continuous culture apparatus

A continuous culture apparatus of 5-liter capacity is described which is capable of control of dissolved oxygen. Combined turbidostat and constant feed operation permit control of cell population density and one or more nutrients. A system for the measurement of oxygen uptake and CO₂ output is described. Sufficient detail is supplied to enable construction and operation of the apparatus.     

Nitrous oxide in brackish Lake Nakaumi, Japan II: the role of nitrification and denitrification in N2O accumulation

In order to understand the role of nitrification and denitrification in the accumulation of nitrous oxide (N₂O) in the hypolimnetic water of brackish Lake Nakaumi, the effects of dissolved oxygen (DO) concentration on these activities were investigated by incubation experiments. N₂O was produced during the oxidation of NH₄ ⁺ to NO₂ ⁻ in nitrification and during the reduction of NO₃ ⁻ to N₂ in denitrification. N₂O-producing activity by nitrification (N₂O_N) increased markedly with decreasing concentrations of DO. Low DO (10%–30% saturation) induced high N₂O_N. In contrast to nitrification, N₂O-producing activity by denitrification (N₂O_D) decreased with decreasing concentrations of DO. Little N₂O was accumulated during denitrification under low-level conditions of DO (10%–30%), because of further reduction of N₂O to N₂. It can therefore be assumed that N₂O produced as the by-product of nitrification is concurrently reduced to N₂ by denitrification under low-DO conditions. This would result in no substantial accumulation of N₂O during active nitrification in the hypolimnetic water of Lake Nakaumi. Received: July 6, 2001 / Accepted: December 10, 2001     

Ecosystem Metabolism in Piedmont Streams: Reach Geomorphology Modulates the Influence of Riparian Vegetation

We measured the impact of riparian zone vegetation on ecosystem metabolism in paired forested and meadow reaches on 13 streams in southeastern Pennsylvania and Maryland, USA. Metabolism estimates were based on open-system measurements of dissolved oxygen changes, with reaeration determined from propane evasion. Daily gross primary productivity (GPP) in meadow and forested reaches averaged 2.85 and 0.86 g O₂ m⁻² d⁻¹, respectively, at water temperatures of 12°C or greater when the forest canopy was developed and 1.74 and 1.09 g O₂ m⁻² d⁻¹, respectively, at temperatures below 12°C when the canopy was bare. Community respiration (CR₂₄) also was greater in meadow reaches than in forested reaches, averaging 5.58 and 3.57 g O₂ m⁻² d⁻¹, respectively, in the warm season and 4.87 and 2.88 g O₂ m⁻² d⁻¹, respectively, during the cold season. Thus, both meadow and forested reaches were heterotrophic. Forested reaches were always wider and nearly always shallower than companion meadow reaches. When ecosystem function was assessed per unit of stream length, the difference in average GPP between meadow and forested reaches was reduced from three-fold to 1.9-fold in the warm season, and mean GPP was greater in the forested reaches during the cold season. Mean CR₂₄ per meter stream length was greater in forested reaches during both seasons. Even though riparian shading reduced primary productivity per unit area of streambed, the greater stream width of the forested reaches counteracted that reduction in part. Thus, when rates of ecosystem function were expressed per length of stream, differences between reaches were always smaller than when expressed per area, and activity per unit stream length was sometimes greater in forested reaches than in meadow reaches.     

A flow injection analysis system with encapsulated high-density <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> cells for rapid determination of biochemical oxygen demand

The biochemical oxygen demand (BOD) determination was studied using a novel flow injection analysis (FIA) system with encapsulated Saccharomyces cerevisiae cells and an oxygen electrode and was compared with conventional 5-day BOD tests. S. cerevisiae cells were packed in a calcium alginate capsule at a dry cell weight of 250 g/l of capsule core. The level of dissolved oxygen (DO) was reduced due to the enhanced respiratory activity of the microbial cells when the injected nutrient passed through the bioreactor. The decrease in DO (ΔDO) was intensified with the amount of microbial cells packed in the bioreactor. However, the specific ΔDO decreased as the amount of cells loaded in the bioreactor increased. The ΔDO value was dependent on the pH and temperature of the mobile phase and reached its maximum value at 35°C and pH 7–8. Also, ΔDO became larger at longer response times as the flow rate of the mobile phase decreased. The measurement of ΔDO was repeated more than six times consecutively using a 20-ppm standard glucose and glutamic acid solution, which confirmed the reproducibility with a standard deviation of 0.95%. A strong linear correlation between ΔDO and BOD was also observed. The 5-day BOD values of actual water and wastewater samples were in accordance with the BOD values obtained by this FIA method using encapsulated S. cerevisiae cells. Unlike the cell-immobilized bead system, there was no contamination of the bioreactor resulting from any leak of yeast cells from the sensor capsules during BOD measurements.     

Effects of dissolved oxygen levels and the role of extra- and intracellular amino acid concentrations upon the metabolism of mammalian cell lines during batch and continuous cultures

The effects of dissolved oxygen and the concentration of essential amino acids upon the metabolism of two mammalian cell lines (rCHO producing human active (t-PA) and a mouse-mouse hybridoma) were investigated in batch, chemostat, and perfusion cultures. Intracellular amino acid concentrations were measured for both cell lines during repeated batch cultures and the K_S-values for the essential amino acids were calculated using Monod equations via computer simulation. The K_S-values were in the range of 10 mmol L⁻¹ and the pool of most intracellular amino acids remained constant at about 10–100 fold higher in concentration than in the medium. No significant differences were observed between the hybridoma and CHO cell. The specific nutrient uptake rates corresponded with the cell specific growth rate and the effects of reduced dissolved oxygen concentrations only became evident when the DO dropped below 5% of air saturation (critical concentration below 1%). Nevertheless, a correlation between nutrient concentration and specific oxygen uptake was detected. This revised version was published online in June 2006 with corrections to the Cover Date.     

The role of dissolved oxygen and function of agitation in hyaluronic acid fermentation

The role of dissolved oxygen (DO) and function of agitation in hyaluronic acid fermentation by Streptococcus zooepidemicus ATCC 39920 were explored. With controlled DO levels, it was found that the present strain grew as well under both aerobic and anaerobic conditions. Dissolved oxygen plays a role as a stimulant in the HA synthesis; the intrinsic factor affecting the efficiency of HA synthesis is DO level; and there existed a critical DO level of 5% air saturation for the HA synthesis. On the other hand, agitation functions to mix the broth, to enhance oxygen absorption, but not to release HA capsule. In addition, vigorous agitation would lengthen the operation time. It therefore suggests that the relevant criteria for scaling up the fermentor are to maintain DO level above the critical value, and to provide a mild agitation for homogeneity in the fermentor.     

Interactions of cell morphology and transport processes in the lovastatin fermentation

The cholesterol lowering drug, Lovastatin (Mevacor), acts as an inhibitor of HMGCoA reductase, and is produced from an Aspergillus terreus fermentation.Pilot scale studies were carried out in 800 liter fermenters to determine the effects of cell morphology on the oxygen transport properties of this fermentation. Specifically, parallel fermentations giving (i) filamentous mycelial cells, and (ii) discrete mycelial pellets, were quantitatively characterized in terms of broth viscosity, availability of dissolved oxygen, oxygen uptake rates and the oxygen transfer coefficient under identical operating conditions.The growth phase of the fermentation, was operated using a cascade control strategy which automatically changed the agitation speed with the goal of maintaining dissolved oxygen at 50% saturation. Subsequently stepwise changes were made in agitation speed and aeration rate to evaluate the response of the mass transfer parameters (DO, OUR, and k _L a). The results of these experiments indicate considerable potential advantages to the pellet morphology from the standpoint of oxygen transport processes.List of Symbols DO % sat. Dissolved oxygen concentration - k _L a h^–1 Gas-liquid mass transfer coefficient - OUR mmol/dm³h Oxygen uptake rate - P/V KW/m³ Agitator power per unit volume - V _s m/s Superficial air velocity - _app cP Apparent viscosity     

Comparison of several methods to calculate reaeration in streams,and their effects on estimation of metabolism

Metabolism is an integrative measurement of stream and river ecosystem functioning, and thus, could be used to assess impairment. Stream metabolism is measured by different methods which often yield contrasting results. Furthermore, open-channel measurements of metabolism, which offer the best potential for continuous monitoring of stream functioning, rely on calculations of gas exchange with the atmosphere, for which a plethora of methods exists. Therefore, to incorporate metabolism in stream monitoring programs, it is necessary to determine which methods yield comparable results under a given set of environmental conditions. We studied 21 streams in the Basque Country (northern Spain), ranging widely in physical characteristics and water quality. We calculated reaeration during summer baseflows using three different approaches: the night-time drop in oxygen, the lag between noon and peak oxygen concentration, and ten empirical equations relating depth and velocity with reaeration coefficients obtained from the literature. Differences among methods were very large, especially at the shallower sites. The results obtained with most empirical equations were highly correlated, but showed little agreement with the night-time and peak lag methods. We then analyzed the response of reaeration rate to river stage: reaeration calculated by the night-time method during 1 year of continuous monitoring was regressed against discharge at each site, and the resulting model was compared to the results of empirical equations, using software HecRas 2.2 to model hydraulic conditions at different river stages. The shape of reaeration-discharge plots differed greatly and in a site-dependent manner, and there was little agreement between methods. Finally, we investigated the effects of reaeration rate on estimates of metabolism. The choice of method greatly affected the estimates of both primary production and respiration. The empirical equations, except E₇ and E_10, yielded the most unrealistic estimations of stream metabolism. Overall, the night-time method, especially when regressed against discharge, seems to be the most robust and reliable among those tested, with the energy dissipation method (E₁₀) appearing to be a viable alternative when the night-time method does not work.     

Inhibitory effect of oxygen accumulation on the growth of Spirulina platensis

Summary The growth of Spirulina platensis was studied in a light-limited culture under various dissolved oxygen (DO) concentrations. At high DO concentration, e.g. at 1.25 mM DO, the growth rate was decreased up to 36 % compared with that of 0.063 mM DO. The retarded growth rate at high DO concentrations seemed to be coupled with the degeneration of photosynthetic activity in terms of O₂ evolution. Under higher DO concentrations, superoxide dismutase and ascorbate peroxidase activities tended to increase, while the contents of photosynthetic pigment, such phycocyanin, carotenoid and chlorophyll-a decreased distinctly.