Initial Dissolved Oxygen Concentration Research Articles

Ecological Significance of Dynamism of Physiologic Variance on Properties of Palm Oil Mill Effluents

Properties a given waste is essential for rationale comprehension of plausible way(s) for its remediation. In the present study, POME from oil milling centre at Anambra state showed high heterotrophic activity of microorganisms. Total viable counts of the organisms isolated from the waste water were 5.4 x 103 CFU/ml and 4.4 x 103 CFU/ml at day 0 and day 7 of the incubation respectively. These observations showed a significant variation from the control experiment at these recorded days of incubations which shows total viable cell counts (TVC) of 4.6 x 103 and 2.9 x 104 CFU/ml respectively. Total coliform counts (TCC) of the organisms isolated from the dairy waste water were 1.3 x 103 and 1.8 x 103 CFU/ml for the day 0 and day 7 incubation periods respectively while the TCC from the control experiment were: 8.0 x 102 and 3.2 x 102 CFU/ml for day 0 and day 7 incubation periods respectively. POME sample from Awka, Anambra state was subjected to various physicochemical profiling and was further optimized at different conditions to exert various variability. Biochemical oxygen demand (BOD5) is one of the important physical parameter widely used in assessment of quality of aqueous surroundings. Physicochemical properties of waste water from the milling centre showed the following: pH (5.0), temperature (41oC), conductivity (610); water dissolved minerals such as Cl-, K+, PO3, Mg2+, Ca2+ were all determined. Initial dissolved oxygen concentration (mg/l) of the waste water was determined using a probe connected to a meter with initial value of 39.4 mg/l. Biochemical oxygen demand (BOD5) was determined after five incubation days at room temperature in separate bottles optimized at varying pH of 4.0-9.0 in a range of 1.0 units. BOD5 decreases with increased pH values in all the tested samples incubated for 5 days. pH 5.0 gave a significant reduction of the oxygen exertion (1400 mg/ml) while pH 4.0, 6.0, 7.0 showed an oxygen exertion (BOD5) of 1978, 2778, and 2965 mg/ml respectively. Samples incubated at 8.0 and 9.0 showed oxygen exertion of 2945 and 2899 mg/ml respectively. Other contents of the dairy waste water such as total organic carbon (TOC), total organic matter contents (TOM) were all determined respectively. Samples was also collected from mapped area 0.5 km away from the waste water reservoir and used as the reference standard. Proceeding results from the present research study showed the compromised statues of our aquatic environment and also in a wider look gave a great insight of effective modalities in water treatment; as increasing population of myriads of processing industries in our country today pose great challenge to the competence of our aquatic body.

Hump and mass-transfer characteristics of dissolved oxygen induced by gaseous cavitation in a space micropump

Fuel transportation in on-orbit refueling and circulation systems used in space involves dynamic transitions in the gas–liquid behaviors. Based on our verified innovative computational model of dynamic dissolution and evolution, the interesting “hump characteristics” of the dissolved oxygen concentration (DOC) were discussed, and the space-spatial evolution of gas–liquid mass transfer were compared. The hump phenomenon is related to the evolution of gas in the suction chamber. The processes undergone by the released gas, including the local evolution, evolution expansion, and global evolution, which were observed for the first time in rotating machinery owing to the pressure fluctuations caused by the impeller. Limited by the mass-transfer rate, the pressure increase in the impeller was significantly greater than the increase in the DOC, and thus there was no gas evolution inside the impeller. With an increase in the initial DOC, the near-zero mass-transfer rate band split into two and moved downstream of the blade, indicating a dynamic balance between the dissolution and evolution. Moreover, the flow separation and vortices near the clearance widened the band and decreased the dissolution rate. The current research provides an in-depth understanding of the dynamic changes in the gas–liquid behavior of on-orbit refueling systems.

Computational model for predicting the dynamic dissolution and evolution behaviors of gases in liquids

Dynamic gas–liquid mass transfer behaviors are widely encountered in the chemical, environmental, and engineering fields. Referring to the Singhal full cavitation model, Henry's law, and Zhou's experiments, we innovatively developed a computational model for dissolved and released mass-transfer to revolutionize the independent unidirectional gas-to-liquid or liquid-to-gas theory. From a new perspective, coupled dissolution and evolution mechanisms were defined similar to how condensation and evaporation were redefined, where dissolution and release mass-transfer prediction methods that can be applied to three-dimensional calculations were integrated for the first time. The dissolved gas saturation concentration was the criterion for determining the direction of mass transfer. According to the theoretical derivation, the driving forces behind the dissolution and evolution are the remaining undissolved gas and real-time solution concentration, respectively. We confirmed the validity of the proposed dynamic model using an unsteady simulation after a grid independence study and an experimental verification of dissolved oxygen concentration in plug-discharge flow. The difference in dissolved oxygen concentration between simulations of this computational model and experiments could be low as 2.0%. A higher dissolved oxygen concentration was distributed in the flow separation and throat gas–liquid blocking zones, indicating that a surge in the flow velocity led to an increased mass transfer rate. In addition, a parametric study was conducted to consider the impact of the oxygen volume fraction and initial dissolved oxygen concentration on the real-time concentration.

Microbial Quality and Assessment of Dynamism of Physiologic Factors on Selected Physicochemical Properties of Waste Water

Physicochemical factors are important parameter widely used in assessing the quality/competence of surrounding ecosystem. Aquatic surrounding hold a vital point of every living system in the biosphere as compromised findings in the physicochemical properties of the aquatic system proves a point of danger to live progression. Cheap and effective way of waste treatment can be achieved easily when possible interactions and changes of responsible quality marking factors of a particular body is well understood.  Waste water sample were collected from Rumuekini, Rivers state, Nigeria. Reference Sample was sited 0.5 km away from the waste water reservoir. Microbial analysis of the waste water sample in the presence of the control experiment after seven (7) days of incubation showed total viable count (TVC) of 5.4 x 103 and 4.6 x 103 CFU/ml respectively for day 0; 4.4 x 103 and 2.9 x 104 respectively for day 7. Total coliform counts of the waste water in the presence of the control experiment showed total coliform count (TCC) of: 1.3 x 102 and 8.0 x 102 CFU/ml respectively for day 0; 1.8 x 103 and 3.2 x 102 CFU/ml respectively for day 7. Physicochemical properties of waste water from a dairy industry surge tank located at Rumuekini, Portharcourt showed the following: pH (5.0), temperature (41oC), conductivity (610); water dissolved minerals such as Cl-, K+, PO3, Mg2+, Ca2+ were all determined. Initial dissolved oxygen concentration (mg/l) of the waste water was determined using a probe connected to a meter with initial value of 39.4 mg/l. Biochemical oxygen demand (BOD5) was determined after five incubation days at room temperature in separate bottles optimized at varying pH levels of 4.0-9.0 in a range of 1.0 units. BOD5 decreased with increased pH values the tested samples incubated for 5 days. pH 5.0 gave a significant reduction of the oxygen exertion (1400 mg/ml) while pH 4.0, 6.0, 7.0 showed an oxygen exertion (BOD5) of 1978, 2778, and 2965 mg/ml respectively. Samples incubated at 8.0 and 9.0 showed oxygen exertion of 2945 and 2899 mg/ml respectively. Other contents of the dairy waste water such as total organic carbon (TOC), total organic matter (TOM) contents were all determined respectively. Proceedings from this study showed the compromised statues of our aquatic environment and also in a wider look gave a great insight of effective modalities in water treatment; as increasing population of myriads industries in our country today pose great challenge to the competence of our aquatic body.

The use of microtechnology’s in the construction of water aeration installations

Water aeration systems are highly efficient if the dispersion of air in the water is carried out in a controlled and uniform manner. The use of fine bubble generators ensures this and in addition, creates a small loss of pressure when air passes through them. The paper demonstrates that producing as few air bubbles as possible leads to a more efficient aeration process. Two water aeration installations are compared:- The first has a perforated plate with 152 orifices Ø 0.1 mm;- The second has four perforated plates, each with 113 orifices Ø 0.05 mm;Both installations are successively supplied with the same flow rate of compressed air, at the same temperature and at the same initial dissolved oxygen concentration in the water.

Frequency and power dependence of ultrasonic degassing

We investigated the time variation of ultrasonic degassing for air-saturated water and degassed water with a sample volume of 100 mL at frequencies of 22, 43, 129, 209, 305, 400, 514, 1018, and 1960 kHz and ultrasonic power of 15 W. Ultrasonic degassing was evaluated by dissolved oxygen concentration. Ultrasonic degassing was also investigated at a frequency of 1018 kHz and ultrasonic powers of 5, 10, 15, and 20 W. The dissolved oxygen concentration varied with the ultrasonic irradiation time and became constant after prolonged ultrasonic irradiation. The constant dissolved oxygen concentration value depended on the frequency and ultrasonic power but not the initial dissolved oxygen concentration. The degassing rate at 101.3 kPa was higher in the frequency range of 200 kHz to 1 MHz. The frequency dependence of the degassing rate was almost the same as that of the sonochemical efficiency obtained by the potassium iodide (KI) method. Ultrasonic degassing in the frequency range of 22–1960 kHz was also investigated under reduced pressure of 5 kPa. Degassing was accelerated when ultrasonic irradiation was applied under reduced pressure. However, under a reduced pressure of 5 kPa, the lower the frequencies, the higher is the degassing rate. The sonochemical reaction rate was examined by the KI method for varying dissolved air concentrations before ultrasonic irradiation. Cavitation did not occur when the initial dissolved oxygen concentration was less than 2 mg·L−1. Therefore, the lower limit of ultrasonic degassing under 101.3 kPa equals 2 mg·L−1 dissolved oxygen concentration. A model equation for the time variation of dissolved oxygen concentration due to ultrasonic irradiation was developed, and the degassing mechanism was discussed.

The Numerical Simulation of the rivalry between aerobic and anaerobic bacteria species in a chemostat model

We investigate a chemostat model that contains interaction between two bacteria species, the aerobic species, and a facultative anaerobic species. The competition is restricted on the dissolved oxygen where the aerobic species consumes the oxygen for growth, on the other hand, the facultative anaerobic species do not need the dissolved oxygen for growth. We found that the aerobic growth rate is more extensive compared to that of its competition, the anaerobic species. During our study of the chemostat system, we found three equilibria solutions. The first one is found at the initial dissolved oxygen concentration with the condition of both species washed out. The second equilibrium point is seen when both the dissolved oxygen and the aerobic species present, and finally, the third equilibrium point is found when the dissolved oxygen and the facultative anaerobic species present. We used MATLAB software to simulate these aforementioned three equilibria.

Dissolved oxygen transfer along falling water jets with developing surface disturbance

The dissolved oxygen (DO) concentration is an important index of water quality. It has a significant impact on the biodegradation process in water and the survival of aquatic organisms. Low DO concentrations often exist and may result in a deterioration in water quality and an increase in wastewater treatment expenses. An analysis of the oxygen transfer efficiency as correlated with the flow characteristics of a falling jet could help to solve these problems. Experiments related to oxygen transfer along a falling water jet were conducted, and the effects of the flowrate (Q), falling height (H) and initial DO concentration (cu) were considered. The results demonstrated that a falling jet in air could be an effective way of improving the DO concentration. The results also indicated that the oxygen transfer efficiency is linearly dependent on cu and has a negative exponential relation with H. To deeply analyze the oxygen transfer process, the jet disturbance process was divided into 3 parts for the first time based on flow features: a smooth zone, turbulent zone and breakup zone. The results showed that the jet outlet velocity had a limited influence on the smooth zone height but assisted in jet breakup. Thereafter, a correlation modeling DO reaeration along the falling jet considering jet disturbance characteristics was obtained. This correlation was also applied to predict the aeration efficiency in experimental cases from the literature and showed good agreement with the reported results.

The role of heat treatment in light oxidation of fluid milk

Light-oxidized flavor (LOF) resulting from photooxidation of riboflavin following light exposure is one of the most common off-flavors in fluid milk. The sensory perception of LOF has been studied extensively in high temperature, short time pasteurized (HTST) milk, but few studies have evaluated ultrapasteurized (UP) milk. The objective of this study was to evaluate the role of heat treatment in the development of LOF in UP fluid skim milk. Skim milk was processed by HTST or by direct steam injection (DSI-UP) and subsequently exposed to 2,000-lx light-emitting diode light for various times. Sensory properties were monitored by descriptive analysis and threshold tests, and volatile compounds were evaluated by solid phase microextraction with gas chromatography-mass spectrometry. Dissolved oxygen and riboflavin were determined at each time point using an oxygen meter and ultra-performance liquid chromatography with a fluorescence detector, respectively. The entire experiment was performed in triplicate. Typical cardboard and mushroom flavors (LOF) were detected by trained panelists in HTST milk after 3.5 h of light exposure. In contrast, LOF was not detected by trained panelists in UP milk until 36 h of light exposure. Similarly, the best estimate threshold for LOF from untrained consumers (n = 101) was higher for DSI-UP milk (61.0 h) than for HTST milk (15.2 h). Milks with LOF were characterized by higher relative abundance of the lipid oxidation compounds hexanal and heptanal. Dissolved oxygen (DO) and riboflavin concentrations decreased with increased light exposure time, and the decrease was slower in UP milk compared with HTST milk. Initial DO concentration was investigated as a possible influence in LOF development because DSI-UP milks had lower initial DO concentrations than HTST milks. However, follow-up evaluations of deaerated HTST milks suggested that DO was not a significant factor in LOF development. These results demonstrate that UP milk is less sensitive to LOF than HTST milk, possibly due to sensory masking effects or antioxidant effects of volatile sulfur compounds. An enhanced understanding of light and storage effects on milks will assist with best practices when transporting and displaying fluid milk products for sale.

Modified activated carbon catalytic reduction of dissolved oxygen in reclaimed water

ABSTRACT Dissolved oxygen (DO) is the main corrosive substance in the transport process of urban reclaimed water by pipelines, and it can be removed by catalytic reduction. Activated carbon (AC) has been conventionally used as a carrier for catalysts. This paper focuses on the effect of modification conditions of AC on the catalytic performance for DO removal by hydrazine. The catalytic performance of modified AC (MAC) samples by single and combinatory methods has been investigated. The results showed that the combinatory method was better than the single method, and the MAC by combinatory method of high-pressure hydrothermal method followed by metal salt solution impregnation method could remarkably promote the catalytic activity for DO removal. The prepared catalyst GS270-5-Ni-60-3 had the optimal catalytic activity at the conditions of reaction temperature of 30°C, pH 10 and the initial DO concentration of 5.31 mg/L, and the DO removal rate could reach 98.74%. Meanwhile, the samples of AC and MAC were characterized using BET, SEM and FTIR technologies. The experimental results showed that the high-pressure hydrothermal method could significantly improve the pore structure of AC, and the clogging of AC was not obvious by impregnation modification. Furthermore, the surface group of MAC also has a certain influence on the DO removal in reclaimed water.

Performance and microbial community in the biocathode of microbial fuel cells under different dissolved oxygen concentrations

The use of microbial fuel cells (MFC) in the field of electricity generation and wastewater treatment is attracting considerable research attention. Nitrate removal relies on nitrification and denitrification in the cathode. Dissolved oxygen (DO) is an important factor influencing MFC. In this work, the performance of a two-chambered MFC that uses nitrogen wastewater as a substrate was investigated under three different initial catholyte DO microenvironments anoxic (1.5mg/L), normal-value (3.4mg/L), and oxygen-rich (4.4mg/L) conditions. Results indicated that MFC performance depended on the initial DO concentration of the cathode. Power density was the highest under anoxic condition. Furthermore, high-throughput sequencing was used to explore the cathode biofilm and microbial-communities suspension in each stage. Results showed that the predominant genus of cathode electrodes changed from Pirellula to Thermomonas and finally to Azospira. Heterotrophic denitrifying bacterial activity was inhibited under anoxic condition, and the proportion of nitrobacteria increased. Overall, this study showed that MFC can be used for simultaneous power generation and decomposed‑nitrogen treatment by controlling the catholyte DO and improving the reduction efficiency of the cathode.

Stress corrosion cracking of laser alloyed 304L stainless steel with Ru in hot chloride solution

The exceptional ductility and good uniform corrosion resistance of austenitic stainless steels especially the commonly used 304L stainless steel is lost with its severe embrittling in aqueous conditions in the presence of chlorides at elevated temperatures. With the addition of ruthenium (Ru) the corrosion resistance of 304L stainless steel is enhanced, as well as the resistance to stress corrosion cracking. However, the cost of Ru is high and this limits the possibilities. Therefore, to lower the cost of Ru, a layer of approximately 950 ± 90 μm was laser cladded on the surface of 304L stainless steel. The purpose of this investigation is to evaluate the effectiveness of Ru additions to surface layer through laser cladding to mitigate cracking. Ru was applied to the surface of 304L stainless steel with a Nd:YAG laser as a metal powder with Ru concentrations of 1, 2, 5 and 10 wt%. With these methods, the cost of Ru is kept low while it can still cause inhibition of cracking. Three-point bend stressed samples were exposed to distilled water with 100 ppm sodium chloride at 200 °C with an initial dissolved oxygen concentration of 8 ppm at 25 °C. As expected the as-received 304L stainless steel was susceptible to stress corrosion cracking. With the addition of Ru to 304L stainless steel, the resistance to cracking improved markedly, the minimum and maximum crack propagation rate attained was 0.013 and 0.023 μm/s respectively. The crack propagation rate decreased as the Ru content was increased, and cracking was inhibited at 5 and 10 wt% Ru.

Operational parameters affecting MB/Red-light photosensitized degradation of pharmaceuticals

Abstract The methylene blue photosensitization under red light irradiation (MB/Red-light) is a promising and powerful tool for removal of pharmaceuticals from wastewater. To further develop this new technology, the present work aimed at studying the effect of operational parameters on the performance of MB/Red-light pharmaceuticals removal processes. Three pharmaceuticals, i.e. diclofenac (DFN), propranolol (PRP), and sulfamethoxazole (SFZ), were used as model compounds, and degradation rate constants and total compound removal were examined. The three operational parameters studied were initial MB concentration (0–5.0 mg/L), initial pharmaceutical concentration (0.1–2.0 mg/L), aeration rate (0–5.0 L/min), and for DFN also the pH. The results show that degradation of pharmaceuticals was promoted with increasing initial MB concentration at values of [MB] below 0.5 mg/L, and leveled off to constant values at [MB] values higher than 2.0 mg/L. Initial pharmaceutical concentration and aeration rate were found to have no significant impact. Moreover, rapid degradation of pharmaceuticals can take place even at low initial dissolved oxygen concentrations (2.0 mg/L, i.e. situations without aeration). In order to better understand the effect of pH on the MB/Red-light pharmaceutical degradation processes, DFN was chosen for more detailed investigation, with identification of the degradation products formed under neutral and alkaline conditions identified by LC–MS/MS. The pH was found to play an important role on the transformation pathways and formation of degradation products.

Oxygen concentration and conversion distributions in a layer-by-layer UV-cured film used as a simplified model of a 3D UV inkjet printing system

Three-dimensional (3D) ultraviolet (UV) inkjet printers represent a versatile technology for creating complex functional structures. During their operation, 3D objects are formed by repeating cycles of drawing a UV-curable resin with inkjet nozzles and then solidifying it with UV irradiation. In this study, the activity performed by a 3D UV inkjet printer was simulated by spin casting a 33µm thick layer of UV-curable resin (containing diurethanedimethacrylate and 1-hydroxycyclohexyl phenyl ketone compounds mixed at a weight ratio of 99:1) onto a Si wafer followed by photopolymerization for 2s at a UV irradiation of 10mWcm−2. Afterwards, the second resin layer with a thickness of 33µm was spun-cast onto the first layer and photopolymerized under the same conditions. The conversion distribution of C=C bonds in the UV-curable resin was investigated via confocal laser Raman microscopy and numerical calculations, which took into account the kinetics of photopolymerization and oxygen inhibition reactions. The confocal laser Raman microscopy technique provided a unique distribution of the C=C bond conversion across the film depth. Thus, the conversion magnitude at a depth of 0µm was zero and increased to 0.2 at 6µm. Afterwards, the slope of the conversion distribution plot became moderate until the conversion reached the value of 0.43 at a film depth of 28µm. Between the film depths of 28 and 38µm, the conversion remained constant with a variation not exceeding 0.03. After that, the conversion value increased again, reaching the magnitude of 0.48 at a depth of 50µm and remained constant in the region between 50 and 56µm (with a variation not exceeding 0.04). At higher depths, the graph slope became moderate again, and the conversion value increased gradually to 0.51 at 66µm, after which the silicon wafer was reached. As a result, two different plateaus were observed on the conversion distribution plot: between 28 and 38µm and between 50 and 56µm (the corresponding conversion variation in these regions was below 0.05). The obtained experimental data were in good agreement with the results of numerical calculations, which attributed the existence of the two plateaus on the plot of the C=C bond conversion distribution to the formation of an oxygen-lean point. In addition, the effects of the UV intensity, irradiation time, lamination time, photoinitiator concentration, and concentration of dissolved oxygen on the oxygen concentration and conversion distributions across the depth direction have been examined. The obtained results revealed that the increases in the UV intensity, irradiation time, and photoinitiator concentration as well as the decrease in the initial dissolved oxygen concentration effectively increased the conversion of C=C bonds in the resin film and decreased the thickness of an unpolymerized layer.

Effect of Dissolved Iron and Oxygen on Stability of Hydrolyzed Polyacrylamide Polymers

Summary This paper describes an experimental study of the stability of a hydrolyzed polyacrylamide (HPAM) polymer and an HPAM-2-acrylamido-tertbutylsulfonic acid (ATBS) terpolymer in the presence of varying initial levels of dissolved oxygen (0 to 8,000 ppb), Fe2+ (0 to 220 ppm), and Fe3+ (0 to 172 ppm). A special method was developed to attain and confirm dissolved-oxygen levels. Stability studies were performed at 23 and 90°C. For Fe2+ concentrations between 0 and 30 ppm, viscosity losses were insignificant after 1 week when the initial dissolved oxygen concentration was 200 ppb or less. Above this level, significant viscosity losses were seen, especially if iron was present. If the temperature is high, a greater need arises to strive for very low dissolved-oxygen content. For samples stored for 1 week at 90°C with only 10-ppb initial dissolved oxygen, contact with steel caused HPAM-ATBS solution viscosity losses greater than 30%. In contrast at 23°C, contact with steel caused no significant degradation when the dissolved O2 concentration was 1,000 ppb or less. Several different methods are discussed to control oxidative degradation of polymers during field applications. We advocate physical means of excluding oxygen (e.g., stopping leaks, better design of fluid transfer, gas-blanketing, gas-stripping) rather than chemical means. Addition of Fe3+ to polymer solutions caused immediate crosslinking. Because crosslinked polymers were never observed during our studies with Fe2+, we conclude that free Fe3+ was not generated in sufficient quantities to form a visible gel.

A Study and Analysis on the Physical Shading Effect of Water Quality Control in Constructed Wetlands

This study mainly utilized model basins to conduct relevant water quality analyses and tests to understand the influence of the shading effect of wetland plants in the natural water purification system on algae control and eutrophication of water bodies. The model basin tests are based on the physical shading effect in order to evaluate and further understand the influence of algae control and water quality parameters. The physical shading tests were conducted at different rates (100, 70, 50, 30, and 0%) and the research results indicate that the initial dissolved oxygen concentration of each group is between 5 - 7 mg/L. On Day 5, the average dissolved oxygen concentration of the 100 (aerobic) , 100 (anaerobic), 70, 50, 30 and 0% groups is respectively 9.22 ± 1.24, 8.54 ± 1.23, 18.8 ± 3.74, 21.71 ± 0.41, 22 ± 0, and 22 ± 0 mg/L while that of the 70, 50, 30, and 0% groups significantly increases. The initial concentration of Chlorophyll a of the 100 (aerobic) , 100 (anaerobic), 70, 50, 30 and 0% groups is, respectively, 5.27 ± 0.93, 5.92 ± 0.00, 7.9 ± 5.59, 5.92 ± 0.00, 7.9 ± 5.59 and 13.82 ± 2.79 μg/L. On Day 5, the average concentration of Chlorophyll a is, respectively, 57.27 ± 11.17, 9.87 ± 2.79, 244.86 ± 50.34, 280.4 ± 32.92, 329.77 ± 15.55 and 250.78 ± 32.21 μg/L. In general, the physical shading effect can prevent photosynthesis by algae in water by absorbing light and converting light into chemical energy for self growth and proliferation that cause a rapid increase in the number of algae. The physical shading effect, however, cannot reduce nutrients; this leads to a high nutrient level in water bodies during the latter stages of the tests. After the introduction of the Carlson Tropic State Index (CTSI), the completely shaded water bodies at the initial stage of tests are mesotrophic water bodies that contain neutral nutrients. The partially shaded water bodies are eutrophic. In the latter stages of the tests, the former turned eutrophic while the latter turned mesotrophic. The main cause lies in the relatively higher weight CTSI placed on total phosphorous content.

Trichloroethylene Transformation by Natural Mineral Pyrite: The Deciding Role of Oxygen

The transformation of trichloroethylene (TCE) in natural mineral iron disulfide (pyrite) aqueous suspension under different oxygen conditions was investigated in laboratory batch experiments. TCE transformation was pursued by monitoring its disappearance and products released with time. The effect of oxygen was studied by varying the initial dissolved oxygen concentration (DO(i)) inside each reactor. Transformation rates depended strongly on DO(i) in the system. In anaerobic pyrite suspension, TCE did not transform as it did under aerobic conditions. The transformation rate increased with an increase in DO(i). The TCE transformation kinetics was fitted to a pseudo-first-order reaction with a rate constant k (h(-1)) varying from 0.004 to 0.013 for closed systems with DO(i) varying from 0.017 to 0.268 mmol/L under the experimental conditions. In the aerobic systems, TCE transformed to several organic acids including dichloroacetic acid, glyoxylic acid, oxalic acid, formic acid, and finally to CO2 and chloride ion. Dichloroacetic acid was the only chlorinated intermediate found. Both TCE and the pyrite surface were oxidized in the presence of O2. Oxygen consumption profiles showed O2 was the common oxidant in both TCE and pyrite oxidation reactions. Ferric ion cannot be used as an alternative oxidant to oxygen for TCE transformation.

Influence of the extraction process on dissolved oxygen in olive oil

AbstractThe influence of the olive oil processing steps [paste malaxation (PM), decanter centrifugation (DC), and vertical centrifugation (VC)] on the dissolved oxygen (DO) concentration in virgin olive oil (VOO) right after production was investigated at industrial plant scale for two successive years. The influence of this parameter on quality decay during shelf life, assessed by peroxide value (PV) analysis, was also monitored. The VC step showed the higher oxygenation effect (50% increase in comparison to the control), and a good linear regression (r2 = 0.83) was found between the initial DO concentration and the PV after 2 days. An 18‐months shelf life test, performed on VOO sampled before and after the VC, indicated the slowest decay kinetics in the oils with the lower initial DO concentration, i.e. the non‐centrifuged oils.

Kinetics and equilibrium of dissolved oxygen adsorption on activated carbon

The macroscopic adsorption behavior of dissolved oxygen on a coconut shell-derived granular activated carbon has been studied in batch mode at 301 and 313 K for initial dissolved oxygen concentrations of 10–30 mg/l and oxygen/carbon ratios of 2–180 mg/g. BET (Brunauer, Emmett, and Teller) surface area, micropore volume, and pore size distribution were determined from N 2 isotherm data for fresh and used samples of carbon. The surface groups were characterized using Boehm titrations, potentiometric titrations, and FTIR study. The material is characterized by its high specific surface area ( 1307 m 2 / g ) , microporocity (micropore volume 0.54 cm 3 / g ), its basic character ( 0.57 meq / g total basic groups) and its high iron content (15,480 ppm Fe). BET n-layer isotherm describes adsorption equilibrium suggesting cooperative adsorption and important adsorbate–adsorbate interactions. Kinetic data suggest a process dependent on surface coverage. At low coverage a Fickian, intraparticle diffusion rate model assuming a local equilibrium isotherm (oxygen dissociation reaction) adequately describes the process. The calculated diffusion coefficients ( D ) vary between ( 4.7 – 8.2 ) × 10 - 9 m 2 / min and ( 3.5 – 5.3 ) × 10 - 9 m 2 / min for initial oxygen concentration of 10 and 20 mg/l, respectively. Sensitivity analysis shows that the oxygen dissociation equilibrium constant determines the equilibrium concentration, whereas the diffusion coefficient controls the kinetic rate of the adsorption process having no effect at the final equilibrium concentration. A combined kinetic mass transfer model with concentration-dependent diffusion (parabolic form) has been developed and successfully applied on the dissolved oxygen adsorption system at high surface coverage. For equilibrium uptake of 0.08 mg / m 2 the estimated mean mass transfer coefficient and adsorption rate constant are 3.38 × 10 - 5 m / min and 1.0 × 10 - 2 l / ( m 2 min ) , respectively.

A 2-D transient multicomponent simulation model: Application to pipe wall corrosion

A transient multicomponent water quality (WQ) model of a distribution system is developed and then applied to the problem of predicting the concentration of corrosion-related chemicals released into a bare pipe system. The modeled reactions include dissolved oxygen (DO) which oxidizes iron (Fe) at the pipe wall to produce ferrous and hydroxide ions (Fe 2+and OH −). These chemicals can then interact to produce substances like iron hydroxide, which ultimately deposits on the pipe wall. In this study, 1-D and 2-D simulation models are considered and the movement of each chemical is represented by the advection–diffusion-reaction equation (ADRE), which is coupled to the continuity and momentum equations for flow. A five-region turbulence model is used to represent cross-sectional variations and a combination of finite difference and characteristic methods are used to integrate the governing equations. The effects of key parameters (e.g., pH, initial DO concentration, and pipe diameter) are briefly explored and clearly show an increase in dissolved iron with increasing initial DO and pH, and in smaller pipes. The study highlights the influence of velocity profile on the diffusion of oxidants from the bulk flow to the pipe wall and thus underlines the importance of both the turbulence structure and pipe diameter to reactions in general and to corrosion in particular.