Dissolved Oxygen Concentration Level Research Articles

Modelling Nitrogen Removal in the Kibendera Wastewater Stabilization Ponds in Ruiru, Kenya

Application of waste stabilization ponds (WSP) in wastewater treatment in the tropical regions is primarily due to their affordability and relatively high treatment performance. Monitoring of 2-year nitrogen removal behavior in Kibendera WSP in Ruiru, Kenya, was undertaken between January 2021 and December 2022. The experimental work determined the concentrations and removal efficiencies of Ammonia, Nitrate, Nitrite, Organic Nitrogen and Total Nitrogen. Standard Methods for the examination of water and wastewater determined Nitrogen and Dissolved Oxygen (DO) concentrations. Based on the experimental data obtained, mass balance reaction rate models characterized the nitrogen transformation and removal behavior in the WSP. Whereas model calibration was achieved using observed data from January to December 2021, model validation was achieved using observed data from January to December 2022. Ammonia volatilization, sedimentation, mineralization, nitrification, denitrification and microbial ammonia uptake were the possible transformation and removal pathways. Whereas ammonia volatilization contributed the least to the overall nitrogen removal (0.01-0.02 mg/L.d), denitrification contributed the most (2.12-14.67 mg/L.d). Low DO levels and high ammonia concentrations were responsible for low nitrification rates and high microbial ammonia uptake respectively. Comparison between experimental and modelled effluent concentrations yielded correlation coefficients (<i>r</i>) of 0.77 and 0.69 for ammonia and organic nitrogen respectively during the calibration period. The corresponding model validation <i>r</i> values were 0.74 and 0.93 respectively. The good agreement between the model output and observed effluent concentrations implies that nitrogen removal prediction and optimization is possible. External aeration to spike DO concentration levels is necessary to enhance the long-term nitrification rates.

Effect of long-term hypoxia on the reproductive systems of female and male yellow catfish (Pelteobagrus fulvidraco).

This study investigated the effects of different levels of hypoxia on the reproductive system of yellow catfish. Yellow catfish (Pelteobagrus fulvidraco) were exposed to three dissolved oxygen concentration levels: normoxia (6.5 ± 0.2 mg/L), moderate hypoxia (MH, 3.8 ± 0.3 mg/L) and severe hypoxia (SH, 1.9 ± 0.2 mg/L) for 30 days. The gonadosomatic index of males, not females, significantly decreased in the SH group. In the SH group, for the females, the ratio of vitellogenic follicles significantly decreased, whereas the number of atretic follicles significantly increased. In male fish, a significantly reduced number of spermatozoa was observed in both the MH and SH groups. Elevated apoptosis levels in the testes and ovaries were observed only in the SH group. Serum 17β-estradiol and vitellogenin levels in females and testosterone levels in males significantly decreased in the SH group. The concentration of 11-ketotestosterone in males significantly decreased in both the MH and SH groups. In female fish, dysregulated expression of the hypothalamic-pituitary-gonadal (HPG) axis, steroidogenesis genes, and hepatic genes related to vitellogenesis were observed only in the SH group. However, in male fish, moderate hypoxia altered the expression of HPG genes, including gnrh1, lhcgr, and amh. Moreover, the MH group significantly altered the expression of steroidogenesis genes like star, 17β-hsd, and cyp17a1. The results of this study suggest that severe hypoxia can cause reproductive defects in female and male yellow catfish. Moreover, the reproductive system of male yellow catfish is more sensitive to moderate hypoxia than that of female catfish. Our findings contribute to our understanding of the response of the teleost reproductive system to long-term hypoxia.

Enhanced nitrogen removal from rural domestic sewage via partial nitrification-anammox in integrated vertical subsurface flow constructed wetland

This study aimed to improve the removal of nitrogen treating rural domestic sewage by developing a novel strategy for achieving partial nitrification-anammox (PNA) in an integrated vertical subsurface flow constructed wetland (VSFCW). The influent ammonia was oxidized to nitrite in the partial nitrification VSFCW (VSFCWPN), and 5 mg/L of hydroxylamine was added under the appropriate dissolved oxygen concentration level (1.2 ± 0.2 mg/L) to stabilize the average nitrite accumulation rate at 88.24% and maintain the effluent NO2--N/NH4+-N ratio at 1.26 ± 0.15. The effluent from VSFCWPN was introduced to the following chamber (VSFCWAN), where ammonia and nitrite were removed by the autotrophic anammox process. This implementation achieved high removal efficiencies for chemical oxygen demand, total nitrogen, and PO43--P, reaching 86.26%, 90.22%, and 78.94%, respectively, with influent concentrations of 120.75 mg/L, 60.02 mg/L, and 5.05 mg/L. Substrate samples were collected from 10 cm height (PN1, AN1) and 25 cm height (PN2, AN2). Microbial community analysis showed that Nitrosomonas dominated the community composition in VSFCWPN, with an increase from 1.61% in the inoculated sludgePN to 16.31% (PN1) and 12.09% (PN2). Meanwhile, Ca. Brocadia accounted for 44.81% (AN1) and 36.50% (AN2) in VSFCWAN. These results confirm the feasibility of the proposed strategy for establishing PNA and efficiently treating rural domestic sewage in an integrated VSFCW.

Study of dissolve oxygen, salinity and temperature around western Offshore: A case study around ONGC’S offshore Filed (HRA & NLM platform), Arabian Sea, India

Marine ecosystems cover approximately 71% of the Earth's surface and contain approximately 97% of the planet's water. Dissolve oxygen, which is a vital parameter in Ocean’s primary production, is having a sensitive integrating property reflecting physical and biogeochemical changes in the marine environment. The dissolve oxygen in the sea water is affected by parameters such as high organic load, high temperature and high salinity level. The higher the oil pollution load, less will be the dissolved oxygen concentration level. The solubility of oxygen decrease as temperature increases. Dissolved oxygen decreases exponentially as salt levels increase. Thus temperature and salinity have a great impact upon biological productivity and are important to understand the dynamics of water column. Nearly all living organisms need oxygen in order to carry out their biological processes. By analyzing the variation of dissolve oxygen, temperature and salinity, environmental status of that particular study area can be assessed. As a preventive measure to protect water bodies, Oil and Natural Gas Corporation Limited, India is regularly conducting Offshore Environment Monitoring around western continental shelf of Arabian Sea, where ONGC’s Platforms and Installations are located. An attempt has been made for assessment of marine environment around ONGC’s offshore Filed (HRA & NLM platform), Arabian Sea by the study of dissolve oxygen, salinity and Temperature etc. The paper includes the output of monitoring activities of ONGC considering three parameters i.e. temperature, salinity and dissolved oxygen for assessing the environmental health of the study area. The study of the three parameters ONGC’s offshore Filed (HRA & NLM platform) has been done considering the monitoring data for the year 2020-21 and their variation has been studied with the values of Reference location (situated at 10 km from the installation). It has been observed from the study that there is no significant changes in the mean values of three parameters compared to the reference mean values. This clearly establishes that the oil production activities at HRA & NLM platform is not affecting the dissolve oxygen level around the installation.

Effects of sub-atmospheric pressure and dissolved oxygen concentration on lesions generated in ex vivo tissues by high intensity focused ultrasound

BackgroundAcoustic cavitation plays an important role in the medical treatment using high-intensity focused ultrasound (HIFU), but unnecessarily strong cavitation also could deform the morphology and enlarge the size of lesions. It is known that the increase of ambient hydrostatic pressure (Pstat) can control the acoustic cavitation. But the question of how the decrease of Pstat and dissolved oxygen concentration (DOC) influence the strength of cavitation has not been thoroughly answered. In this study, we aimed to investigate the relationship among the Pstat, DOC and the strength of cavitation.MethodsEx vivo bovine liver tissues were immersed in degassed water with different DOC of 1.0 mg/L, 1.5 mg/L and 2.0 mg/L. Ultrasound (US) of 1 MHz and the spatial and temporal average intensity (Isata) of 6500 W/cm2 was used to expose two groups of in vitro bovine livers for 2 s; one group was under atmospheric pressure (Pstat = 1 bar) and the other was under sub-atmospheric pressure (Pstat = 0.1 bar). Acoustic cavitation was detected by a passive cavitation detector (PCD) during the exposure process. Echo signals at the focal zone of HIFU were monitored by B-mode ultrasound imaging before and after exposure. The difference between two pressure groups was tested using paired sample t-test. The difference among different DOC groups was evaluated by one-way analysis of variance (ANOVA).ResultsThe results demonstrated a significant difference of broadband acoustic emissions from the cavitation bubbles, echo signals on B-mode image, morphology of lesions under various conditions of ambient pressure and DOC. The lesion volume in tissue was increased with the increase of ambient pressure and DOC.ConclusionCavitation could be suppressed through sub-atmospheric pressure and low DOC level in liver tissue, which could provide a method of controlling cavitation in HIFU treatment to avoid unpredictable lesions.

Determination of Standard Oxygen Transfer Rate in Venturi Aeration System

The oxygen transfer is the process of atmospheric oxygen diffusion from a gas stage to a liquid stage in the form of dissolved oxygen (DO). The previous research works have successfully proven that the DO concentration level effortlessly rises by adopting a venturi as an aeration method in aquatic bodies. Present experimental study was conducted on laboratory scale aeration tank with two different sizes of venturi (40 and 80 mm throat length). The objective of the current study was to determine the oxygen transfer coefficient at different discharge rates through venturi aeration system. The system was operated with three different discharges of 0.50, 0.58 and 0.67 liter/second (l/s) to circulate 200 liter volume of water, was aimed for circulation in a closed loop system. During the operations, water moves through the inlet section into the contract section of the venturi, which increases the rate of water flow and reduces the pressure as per the Bernoulli’s theorem. In order to study the oxygen transfer coefficient at varying discharge, the system worked by a single hole and accordingly applied to the larger number of holes for both the throat lengths of venturi. It was observed that the oxygen transfer coefficient proportionally linked to the DO diffusion with increasing rate of discharge. The oxygen transfer coefficient found to be increased by 31% and 55% at 40 and 80 mm throat length respectively, with increasing the discharge. The rate of DO diffusion found higher causes more surface area of contact between air and water through maximum air entrainment. Moreover aeration efficiency also increases with the rate of increasing discharge for the maximum size of throat length. The maximum SOTR values was obtained 0.0035, 0.0041, and 0.0050 kgO2/h at varying discharge of 0.50, 0.58 and 0.67 l/s respectively for 40 mm throat length. For the 80 mm throat length, the SOTR values varies from 0.0042, 0.0062 and 0.0091 kgO2/h at increasing discharge of 0.50, 0.58 and 0.67 l/s respectively with increasing number of holes.

Overproduction of rhamnolipid by fed-batch cultivation of Pseudomonas aeruginosa in a lab-scale fermenter under tight DO control.

Rhamnolipids are one of the most well-known classes of biosurfactants having wide applications in various industries due to low toxicity, high biodegradability, and environmentally friendly. Dissolved oxygen (DO) concentration has the crucial effect on rhamnolipids production, particularly through fed-batch cultivation. In this study, the effect of different levels of DO concentrations on rhamnolipid production by Pseudomonas aeruginosa in both batch and fed-batch fermentation was investigated in a lab-scale fermenter under precise DO control. A maximal rhamnolipid production of 22.5g/l was obtained at a DO concentration of 40% in batch fermentation. In order to achieve the high rhamnolipid production, a fed-batch operation under tight DO control of 40% was conducted. As a result, the overall rhamnolipid production and productivity reached to 240g/l and 0.9 (g/lh), corresponding to a 10.7 and 4.8-fold improvement compared to the batch experiments. The high level of rhamnolipid production via the fed-batch cultivation can be attributed to both DO concentration and the feeding strategy. This achievement is promising for the production of rhamnolipid in industrial scale.

Experimental study of dissolved oxygen transport by regular waves through a perforated breakwater

The perforated breakwater is an environmentally friendly coastal structure, and dissolved oxygen concentration levels are an important index to denote water quality. In this paper, oxygen transport experiments with regular waves through a vertical perforated breakwater were conducted. The oxygen scavenger method was used to reduce the dissolved oxygen concentration of inner water body with the chemicals Na2SO3 and CoCl2. The dissolved oxygen concentration and wave parameters of 36 experimental scenarios were measured with different perforated arrangements and wave conditions. It was found that the oxygen transfer coefficient through wave surface, K1 a 1, is much lower than the oxygen transport coefficient through the perforated breakwater, K2 a 2. If the effect of K1 a 1 is not considered, the dissolved oxygen concentration computation for inner water body will not be greatly affected. Considering the effect of a permeable area ratio a, relative location parameter of perforations δ and wave period T, the aforementioned data of 30 experimental scenarios, the dimensional analysis and the least squares method were used to derive an equation of K2 a 2 (K2 a 2=0.0042a 0.5 δ 0.2 T -1). It was validated with 6 other experimental scenarios data, which indicates an approximate agreement. Therefore, this equation can be used to compute the DO concentration caused by the water transport through perforated breakwater.

Evaluation of surface water quality of the Buriganga River

The Buriganga River receives partially treated sewage effluent, sewage polluted surface runoff and untreated industrial effluent from Dhaka city. This study examines the present status of surface water quality of Buriganga River at different locations in Dhaka City. The values of dissolved oxygen (DO), pH, colour, total coliforms, turbidity and ammonia were always very high over the year 2011. The maximum level of DO concentration was 3.4 mg/l, which is below the acceptable limit for surface water. Results also showed that high turbidity and low colour values were found in the rainy season while low turbidity and high colour values were found in the dry season. Moreover, the values of all parameters were always high at Buri 2 (Hazaribagh) because of the proximity of industrial sites. It is important to improve the water quality of the Buriganga River by protecting it from pollution.

On-line estimation of cell growth from agitation speed in DO-stat culture of a filamentous microorganism,Agaricus blazei

A simple, but effective on-line method for estimating the mycelial cell mass concentration from agitation speed data, a most readily-available process variable, has been developed for DO-stat cultures ofAgaricus blazei. The dynamic change of dissolved oxygen concentration (DOC) in the initial transient period and the change in yield were considered in the development of the estimation algorithm or estimator. Parameters in the estimation algorithm were calculated from the agitation speed data at 20% of DOC. The proposed estimator could accurately predict the cell mass concentration regardless of DOC levels in the tested range of 10–40%, showing a good extrapolation capability.

Dissolved oxygen––a target indicator in determining use of the Gulf of Kachchh waters

Spatial and temporal variations of Dissolved Oxygen (DO) and Biochemical Oxygen Demand (BOD) in the Gulf of Kachchh (GoK), India are assessed based on data collected since 1976. DO concentrations in the interior GoK vary within a narrow range (6.05–6.86 mg l −1), whereas near-shore waters show wider variations (3.5–7.8 mg l −1). The DO concentration levels in the Gulf waters are close to saturation, varying from 75.4% to 108.6%, which is much higher than the 60% saturation level set for the SW-1 waters. BOD–DO simulation shows that when effluents containing a BOD concentration of 50.0 mg l −1 are introduced at three select locations, DO reduces from 5.1 mg l −1 to 3.1, 5.0 and 3.8 mg l −1, respectively, indicating a strong sensitivity to effluent load. Based on the DO analysis, BOD assimilation capacity of coastal waters around the Marine National Park (MNP) and Marine Sanctuary (MS) in the Gulf is determined. DO available for utilization for various categories of water use is illustrated, keeping in mind the ecology of MNP and MS areas. The significance of DO as a target indicator to zone the Gulf for different water use, is highlighted in this study.

Electrochemical Reduction of 2,4,6-Trinitrotoluene

A laboratory-scale reactor was used to study the electrochemical reduction of 2,4,6-trinitrotoluene (TNT). A graphite cylinder impregnated with glassy carbon (zero porosity) was used as the cathode, and a platinum wire was used as the anode. Initially, experiments simulating batch conditions were conducted to evaluate the effect of electrolyte type, molar concentration of the electrolyte, and the applied current on the reduction kinetics of TNT. Results showed that the rate of TNT reduction increased with an increase in molar concentration of the electrolyte and the applied current. For the various currents studied, no significant changes in rate constants were observed for experiments conducted with sodium sulfate or lithium sulfate as electrolyte in the feed. Continuous flow experiments were conducted to evaluate the performance of the reactor. Three different currents (150, 200, and 250 mA) using 6 and 9 mM concentration of sodium sulfite as the electrolyte were used. Sodium sulfite was used as the electrolyte in the feed to maintain strict anoxic conditions, thereby preventing the formation of solid dimers. Under undetectable dissolved oxygen concentration levels in the system, the reactor operated continuously at a stable performance for the total experimental period conducted (105 days). On average, TNT reduction efficiency in the mid-80% levels was achieved for the three currents studied. The only intermediate observed in the aqueous phase was 2,4,6-trimainotoluene (TAT). A mole balance closure of 85–92% was achieved. A combined overall TNT reduction efficiency over 99% was achieved by using three reactors in series.

Sensitivity analysis of a biofilm model describing a one-stage completely autotrophic nitrogen removal (CANON) process.

A mathematical model for nitrification and anaerobic ammonium oxidation (ANAMMOX) processes in a single biofilm reactor (CANON) was developed. This model describes completely autotrophic conversion of ammonium to dinitrogen gas. Aerobic ammonium and nitrite oxidation were modeled together with ANAMMOX. The sensitivity of kinetic constants and biofilm and process parameters to the process performance was evaluated, and the total effluent concentrations were, in general, found to be insensitive to affinity constants. Increasing the amount of biomass by either increasing biofilm thickness and density or decreasing porosity had no significant influence on the total effluent concentrations, provided that a minimum total biomass was present in the reactor. The ANAMMOX process always occurred in the depth of the biofilm provided that the oxygen concentration was limiting. The optimal dissolved oxygen concentration level at which the maximum nitrogen removal occurred is related to a certain ammonium surface load on the biofilm. An ammonium surface load of 2 g N/m2. d, associated with a dissolved oxygen concentration level of 1.3 g O2/m3 in the bulk liquid and with a minimum biofilm depth of 1 mm seems a proper design condition for the one-stage ammonium removal process. Under this condition, the ammonium removal efficiency is 94% (82% for the total nitrogen removal efficiency) (30 degrees C). Better ammonium removal could be achieved with an increase in the dissolved oxygen concentration level, but this would strongly limit the ANAMMOX process and decrease total nitrogen removal. It can be concluded that a one-stage process is probably not optimal if a good nitrogen effluent is required. A two-stage process like the combined SHARON and ANAMMOX process would be advised for complete nitrogen removal.

Effects of oxygen on the nitrogen transformations in a slow‐flowing open channel†

This study investigated the effects of dissolved oxygen ( DO) concentration and flow conditions on the conversion rates and pathways of nitrogenous compounds in an pilot open channel. Ammonium sulfate and glucose were added externally as the substrates in the investigation. The experimental results showed that under conditions of constant flow velocity and DO concentration above 1 mg/1, the removal rates of total nitrogen (including nitrite, nitrate and ammonium nitrogens) varied linearly with the removal rates of ammonium nitrogen. Comparison of the removal rate for each individual nitrogenous component reveals the following order of removal rates: ammonium nitrogen>total nitrogen>nitrate nitrogen> nitrite nitrogen. Moreover, the nitrite concentration was found to increase in all tests and the nitrate concentration was increased only when the DO concentration was within the range of 3 to 5 mg/l. In contrast, when the DO concentration was less than 1 mg/l, all nitrogenous compounds were removed and the following order of removal rates of nitrogenous compounds was observed: total nitrogen>nitrate nitrogen>nitrite nitrogen>ammo‐nium nitrogen. The results indicated that the conversion pathways of nitrogenous compounds can be divided into four different types depending on the DO concentration level. The test results also revealed that an increase in the flow velocity significantly influenced the conversion rates of nitrogenous compounds. While a V‐shaped relation of the removal rates of total nitrogen vs the Reynolds numbers was observed for low DO below 1.5 mg/1, an inverted V‐shaped relation occurred at high DO above 5 mg/1.

Relationship between production of carrot somatic embryos and dissolved oxygen concentration in liquid culture

To evaluate the relationship between somatic embryogenesis and dissolved oxygen concentration, somatic embryo cultures of carrot (Daucus carota L.) were cultured under various dissolved oxygen concentration levels (bubble free aeration with 4%, 7%, 20%, 30%, and 40% oxygen in flasks). The system used allows dissolved oxygen concentration control without bubble aeration or mixing speed modification. The total number of somatic embryos was not affected by the dissolved oxygen (DO) concentration tested. Even if globular-stage embryos were induced at a low level of oxygen aeration, heart-stage embryo formation was still repressed. Oxygen enrichment (20%, 30% and 40% oxygen) enhanced torpedo and cotyledonary-stage embryo production. The oxygen-enriched aeration was effective in promoting the growth of the late developmental stages. Sugar consumption did not increase when the oxygen concentration was enriched above the ambient level. The number of heart-stage embryos increased as oxygen concentration increased up to the 7% level, while above the 20% level no change in production was observed. The production of cotyledonary-stage embryos was directly related to oxygen concentration. These results support that oxygen-enriched aeration provides oxygen to the low oxygen areas in somatic embryo. After the heat-stage embryos, which were grown at the 7% level were transferred to a flask with ambient, they developed an elongated root part and eventually grew to normal plantlets.

Analysis of nitrate in near‐surface aquifers in the midcontinental United States: An application of the Inverse Hyperbolic Sine Tobit Model

A nonnormal and heteroscedastic Tobit model is used to determine the primary factors that affect nitrate concentrations in near‐surface aquifers, using data from the U.S. Geological Survey collected in 1991. Both normality and homoscedasticity of errors are rejected, justifying the use of a nonnormal and heteroscedastic model. The following factors are found to have significant impacts on nitrate concentrations in groundwater: well screen interval, depth to top of aquifers, percentages of urban residential, forest land, and pasture within 3.2 km, dissolved oxygen concentration level, and presence of a chemical facility and feedlot. The effects of explanatory variables on nitrate concentration are explored further by calculating elasticities. Dissolved oxygen concentration level has more notable effects on nitrate concentrations in groundwater than other variables.

Mechanism of fermentation performance of Zymomonas mobilis under oxygen supply in batch culture

The mechanism of the fermentation performance of Zymomonas mobilis against oxygen supply in batch culture was investigated in detail. It was found that the decline in the metabolic activities under high oxygen supply to the broth was due to the inhibition by accumulated acetaldehyde. Acetaldehyde decreased both the maximum specific growth rate ( μ max) and the cell yield ( Y X/S). Accumulation of acetaldehyde started just after the inoculation and its accumulation rate increased with increases in the initial volumetric oxygen transfer coefficient ( k L a 0). The ratio of ethanol to acetaldehyde production was largely affected by the dissolved oxygen concentration level. By changing the oxygen supply to the broth from high to low during the culture, the cells could not recover from the inhibition but the ethanol productivity was recovered. Acetaldehyde also inhibited the specific oxygen consumption rate ( Q 02). However, the Q 02 increased back to its initial level when acetaldehyde was removed. The changes in Q 02 of washed cells were very similar and was neither affected by the k L a 0 value nor by the oxygen concentration. A mechanism of fermentation performance of the strain against oxygen supply was discussed on the basis of the results of various physiological studies.

Modelling and control of dissolved oxygen in an estuary

The two-dimensional spatial distribution of dissolved oxygen in Jamaica Bay, New York, is formulated as a multipoint boundary value problem. The problem, which includes the interactions involving the carbonaceous biochemical demand and the total unoxidized nitrogen, was solved by a multiple shooting technique. The resulting model is used to determine optimal economic nitrification treatment levels at each of the polluting sources discharging into the bay in order that a minimum dissolved oxygen concentration level of 5 mg 1 −1 is achieved throughout the bay.

Modelling and Control of Dissolved Oxygen in an Estuary

The two-dimensional spatial distribution of dissolved oxygen in Jamaica Bay, New York, is formulated as a multi-point boundary value problem. The problem, which includes the interactions involving the carbonaceous biochemical demand and the total unoxidized nitrogen, was solved by a multiple shooting technique.The resulting model is used to determine optimal economic nitrification treatment levels at each of the polluting sources discharging into the bay in order that a minimum dissolved oxygen concentration level of 5mg/1 is achieved throughout the bay.