Elevated Dissolved Oxygen Levels Research Articles

Application of Fine Bubbles in Biofloc Aquaculture: Towards Environmental Sustainability

Biofloc Technology (BFT) is specifically designed to tackle critical challenges in aquaculture, including the reduction of excessive water usage, minimizing effluent discharge, optimizing nutrient utilization from feed, and strengthening overall biosecurity on farms. This innovative approach utilizes clusters of bacteria, algae, or protozoa within a matrix rich in particulate organic matter to enhance water quality, improve waste management, and control diseases. Given the system loading rates, there is a heightened need for elevated dissolved oxygen levels and optimal flow rates. Acknowledging the limitations of traditional aeration systems, this review hypothesizes employing fine bubbles as a panacea. The article, therefore, condenses information on fine bubble impacts in biofloc with a special focus on faster biofloc establishment, favorable microbial diversity, improved respiratory health, accelerated growth rates, optimized metabolism, improved feed conversion ratios, reducing costs, and enhanced overall aquatic health. The suitability of fine bubbles in diverse aquaculture environments is also explored with highlights on areas for further research to optimize and scale up fine bubble-fueled biofloc as an environmentally friendly aquaculture.

Effects of LED exposure on the sensory properties of soybean oil.

Soybean oil is an important commodity in the US and abroad. As lipids are vulnerable to oxidation, damage to soybean oil has been previously reported to arise from prolonged light exposure. Here, we assessed the extent of damage to samples of soybean oil from light, tested with sensory evaluation, assaying the effects of both LED and fluorescent lighting (both at 2000 lux) exposure to oil in PET bottles, using a variety of sensory approaches. Threshold testing (n=66) suggested that differences in the sensory properties of soybean oil could be detected by a human panelist after only 32h of LED exposure. Sensory flash profiling (n=21) again confirmed that light-exposed samples were perceived differently to shielded samples, with LED-exposed samples clustering together, but separately from those instead exposed to fluorescent light. These differences did not necessarily result in a drop in liking of the samples, assessed with consumer testing (n=94), despite a trend for lower liking in exposed versus shielded samples. With similar levels of light exposure, elevated dissolved oxygen levels could be mitigated with O2 scavenging. Our results suggest that soybean oil may be reaching the consumer at a differing quality than intended, which may be mitigated with superior packaging technologies. PRACTICAL APPLICATION: Soybean oil is used widely in the US and global food systems; however, it can be damaged via light oxidation. Here, we show that human panelists can readily detect the sensory signals from light damage in oil exposed for only short periods of time, via either fluorescent or LED light sources. The results suggest that superior soybean oil could be delivered to the market if improvements in packaging technologies were considered.

Efficient nitrogen removal from onsite wastewater by a novel continuous flow biofilter

Soil-based passive biofiltration system is an economically feasible technology for nitrogen removal from onsite wastewater. However, the conventional design requires a large system footprint with limited treatment capacity. In this study, a novel continuous flow biofilter (CFB) with adjustable recirculation and continuous flow pattern was developed for onsite wastewater treatment with a small footprint. Efficient total nitrogen removal (80.1–97.5%) was observed at various hydraulic loadings (0.03–0.12 m3 m−2 d−1), nitrogen loadings (1.1–8.6 g N m−2 d−1) and recycle ratios (2–3) when treating septic tank effluent (STE), with low effluent TN (0.7–13.6 mg N L−1). Nitrous oxide was observed in the denitrification effluent indicating incomplete denitrification at elevated dissolved oxygen levels (3.3–5.8 mg L−1). Nitrogen removal rate (2.9–7.0 g N m−2 d−1) and ammonium removal rate (2.4–7.2 g N m−2 d−1) were positively correlated with nitrogen loadings increase (1.1–8.6 g N m−2 d−1) but were not significantly impacted by the hydraulic loading rate change (0.08–0.12 m3 m−2 d−1). The total biomass abundance and nitrifying microorganisms decreased significantly as the nitrification columns depth increased, while homogeneous microbial distribution was observed in the denitrification columns. The abundance of ammonium oxidizing archaea (AOA) increased significantly at increased hydraulic and nitrogen loading rate, while the ammonium oxidizing bacteria (AOB) abundance remained steady. The abundance of functional genes involved in denitrification process (nirS, nirK and nosZ) responded differently when hydraulic and nitrogen loading rate changes. Collectively, this study suggested the CFB could efficiently remove nitrogen from onsite wastewater with fluctuating influent compositions and various hydraulic loadings.

Factors contributing to bacteria inactivation in the Galdieria sulphuraria-based wastewater treatment system

Our previous pilot scale studies showed concurrent removals of biochemical oxygen demand and nutrients, and inactivation of pathogens in urban wastewaters by an extremophilic alga, Galdieria sulphuraria. The current work evaluated the following as potential factors contributing to the observed pathogen inactivation, using E. coli as a surrogate: bacterial toxicity of algal metabolites, culture pH and temperature, sunlight, dissolved oxygen and adsorption to algal biomass. Microtox toxicity results implied that algal metabolites were free of bacterial toxicants as the toxicity in the reactor decreased from 38.8% to zero in 4 days. Low cultivation pH of 4 was identified as the primary factor influencing E. coli reductions. At neutral pH, under sunlight, E. coli were reduced to undetectable levels in 24 h. But, in the presence of live algal biomass and sunlight, E. coli were reduced to undetectable levels within 12 h. We attribute this accelerated reduction of E. coli to the synergistic effect of sunlight and elevated dissolved oxygen levels generated by biomass in the reactor. Temperatures below 45 °C and adsorption of bacteria to algal biomass did not appear to cause inactivation of E. coli. Simulation of pilot-scale conditions confirmed that the synergistic effects of pH, sunlight, algal biomass, and dissolved oxygen contributed to the superior fecal coliform inactivation observed in the algal wastewater treatment system.

Microbial community functional structure in response to micro-aerobic conditions in sulfate-reducing sulfur-producing bioreactor

Limited oxygen supply to anaerobic wastewater treatment systems had been demonstrated as an effective strategy to improve elemental sulfur (S0) recovery, coupling sulfate reduction and sulfide oxidation. However, little is known about the impact of dissolved oxygen (DO) on the microbial functional structures in these systems. We used a high throughput tool (GeoChip) to evaluate the microbial community structures in a biological desulfurization reactor under micro-aerobic conditions (DO: 0.02–0.33 mg/L). The results indicated that the microbial community functional compositions and structures were dramatically altered with elevated DO levels. The abundances of dsrA/B genes involved in sulfate reduction processes significantly decreased (p < 0.05, LSD test) at relatively high DO concentration (DO: 0.33 mg/L). The abundances of sox and fccA/B genes involved in sulfur/sulfide oxidation processes significantly increased (p < 0.05, LSD test) in low DO concentration conditions (DO: 0.09 mg/L) and then gradually decreased with continuously elevated DO levels. Their abundances coincided with the change of sulfate removal efficiencies and elemental sulfur (S0) conversion efficiencies in the bioreactor. In addition, the abundance of carbon degradation genes increased with the raising of DO levels, showing that the heterotrophic microorganisms (e.g., fermentative microorganisms) were thriving under micro-aerobic condition. This study provides new insights into the impacts of micro-aerobic conditions on the microbial functional structure of sulfatereducing sulfur-producing bioreactors, and revealed the potential linkage between functional microbial communities and reactor performance.

Closing in on upper limits for root zone aqueous ozone application in mineral wool hydroponic tomato culture

Aqueous ozone is increasingly used to treat irrigation source water in greenhouse and nursery operations; however, the ozone is typically removed prior to crop application. Until recently, this was appropriate as there was a paucity of data to suggest any other course of action. Recent research examining the application of aqueous ozone, through drip irrigation, to a mineral wool grown hydroponic tomato crop suggests that ozone can remain in solution during distribution to the crop without negative effect. What is not known from this recent work is the upper limit or phytotoxic threshold for aqueous ozone application, beyond which crop damage would occur. The present study examined the effects of high aqueous ozone concentrations applied daily in this same production system. Suppression of some growth metrics was observed at 6.0mgL−1. The ancillary effect of enhanced oxygenation of the irrigation solution, as a result of the ozonation process, was also examined to disentangle the oxygen/aeration effects from the ozone effects. No significant productivity effects were observed at elevated dissolved oxygen levels relative to the fully aerated control, therefore any productivity influence was attributed to aqueous ozone. The degree to which aqueous ozone penetrated the mineral wool substrate was also examined to aid in the development of horticultural management protocols. Even at volumetric ratios well in excess of typical commercial irrigation events, aqueous ozone still did not penetrate the mineral wool medium beyond 4cm, with most of the ozone being lost in the upper 2cm. Only after excessive volumes of aqueous ozone solution had been applied was a residual observed past 4cm. Based on the results of this study and previous work, an upper limit of 3.0mgL−1 for this type of production system is recommended until further research is completed.

Stimulation of the biosynthesis of carotenes by oxidative stress in Blakeslea trispora induced by elevated dissolved oxygen levels in the culture medium

The adaptive response of the fungus Blakeslea trispora to the oxidative stress induced by elevated dissolved oxygen concentrations during carotene production was investigated by measuring the specific activities of catalase (CAT) and superoxide dismutase (SOD) and the micromorphology of the fungus using a computerized image analysis system. Changes in the ratio of the volume of air (Va) over the medium and the volume of medium (Vm) in the flask caused changes of the morphology of microorganism from clumps to pellets and increases in the specific activities of CAT and SOD. The oxidative stress in B. trispora resulted in a significant increase in carotene production, and a maximum proportion of β-carotene (60%), γ-carotene (50%), and lycopene (10%) (as percentages of total carotenes) was observed at a ratio Va/Vm of 15.7, 4.0 and 1.5, respectively. The highest concentration of carotenes (115.0mg/g dry biomass) was obtained in Va/Vm ratio of 9.0.

Aspergillus terreus Broth Rheology, Oxygen Transfer, and Lovastatin Production in a Gas-Agitated Slurry Reactor

A 20 L gas-agitated slurry bubble column bioreactor was used to investigate the effects of nonmechanical low-intensity agitation on development of broth rheology and fungal pellet morphology during production of lovastatin by the filamentous fungus Aspergillus terreus. Fermentations were carried out under elevated dissolved oxygen levels (400% of air saturation) at gassing rates that ranged from 0.5 to 1.5 vvm. Various initial concentrations of the growth limiting nitrogen source were used to attain different total biomass concentrations, to observe the effect of this variable on development of pellets and the rheology of the fermentation broth. The non-Newtonian rheology of the fermentation broth was influenced both by the biomass concentration and the size of the fungal pellets. The stable pellet diameter ranged from ∼2300 to ∼2900 μm. Too low turbulence (gassing rate of 0.5 vvm) and low dissolved oxygen levels adversely affected lovastatin production. The best biomass specific production of lovastatin ...

EFFECT OF HYPEROXIA ON THE GROWTH AND PHOTOSYNTHESIS OF POLAR SEA ICE MICROALGAE1

Sea ice algal communities are naturally exposed to very high concentrations of dissolved oxygen, which are likely to lead to increasing stress levels and declines in productivity. To test this hypothesis, cultures of Fragilariopsis cylindrus (Grun?) Hasle, Pseudo‐nitzschia sp., Fragilariopsis curta (Van Heurch), Porosira glacialis (Grunow), and Entomoneis kjellmannii (Cleve) from Antarctic sea ice and Nitzschia frigida from Arctic sea ice were exposed to elevated dissolved oxygen levels, and their growth, maximum quantum yield, relative maximum electron transport rate, and photosynthetic efficiency were measured. At oxygen concentrations equivalent to approximately four times air saturation (89% oxygen), the growth rate and maximum quantum yield were significantly reduced in all taxa. When the oxygen concentration was regularly allowed to drop, the effect on growth and quantum yield was reduced. At lower dissolved oxygen concentrations (52%), the declines in growth and quantum yield were reduced but were still mostly significantly different from the controls (21% oxygen). It is likely that the generation of excess active oxygen radicals in the presence of free oxygen is responsible for most of the decline in growth, maximum quantum yield, relative maximum electron transport rate, and photosynthetic efficiency in all species.

Redox dynamics of a tidally-influenced wetland on the San Jacinto River

The stage height, dissolved oxygen, and redox potential of the surface water and sediments of an intertidal Texas wetland were evaluated using continuous monitoring techniques. Surface water oxygenation was most drastically affected by photosynthesis, which served to elevate daytime oxygen concentrations compared to those measured at night. Colder temperatures affected dissolved oxygen concentrations by increasing solubility and decreasing heterotrophic consumption. Waters of the San Jacinto River were generally more oxygenated than those in the wetland, and incoming tides typically elevated dissolved oxygen levels unless the tide was in direct conflict with the daily photosynthetic cycle. The redox potentials in the sediments could not be correlated with a daily cycle as was found in the surface waters. Redox potentials in the intertidal zone fluctuated between −150 mV and 300 mV throughout normal cycles of periodic inundation and exhibited decreasing potentials with depth. Sediments further from the waterline had denser vegetation and exhibited higher redox potentials under similar hydrodynamic loading. During extremely dry periods, redox potentials varied from 300 mV to 600 mV, and deeper sediments were often more oxygenated than sediments closer to the sediment-air interface, due to the higher rates of metabolism in the upper stratum. Rates of oxidation and reduction in the sediments were lognormal and evenly distributed about the steady state, with maximum rates of 300 mV min−1 during intermittent periods of inundation. The results show that biological carbon oxidation in sediments can entirely deplete oxygen from surface waters overlying the mud flats, that vegetation serves to oxygenate the rhizosphere, and although redox potential changes can be large in the dynamic intertidal zone, large changes are infrequent.

Morphological and enzymatic responses of a recombinant Aspergillus niger to oxidative stressors in chemostat cultures

Continuous chemostat cultures of a recombinant strain of Aspergillus niger (B1-D), engineered to produce the marker protein hen egg white lysozyme, were investigated with regard to their susceptibility to oxidative stress. The culture response to oxidative stress, produced either by addition of exogenous hydrogen peroxide (H 2O 2) or by high dissolved oxygen tension (DOT), was characterised in terms of the activities of two key defensive enzymes: catalase (CAT) and superoxide dismutase (SOD). Since the morphology is so critical in submerged fungal bioprocesses, the key morphological indices were analysed using a semi-automated image analysis system. Both oxidant stressors, H 2O 2 and elevated DOT, increased both enzyme activities, however, the extent was different: exogenous H 2O 2 led mainly to increased CAT activity, whereas gassing with O 2 enriched air, which resulted in a DOT of 165% of air saturation, increased both enzyme activities more than 2-fold compared with the control steady state culture. Addition of exogenous H 2O 2 resulted in shorter hyphae compared with control steady state cultures. These findings indicate that it is unsound to use exogenous H 2O 2 to simulate oxidative stress induced by elevated dissolved oxygen levels since the response to each might be quite different, both in terms of enzymatic (defensive) responses and in terms of culture morphology.

“Oxidative stress” response in submerged cultures of a recombinant Aspergillus niger (B1‐D)

A recombinant strain of Aspergillus niger (B1-D), engineered to produce the marker protein hen egg white lysozyme, was investigated with regard to its susceptibility to “oxidative stress” in submerged culture in bioreactor systems. The culture response to oxidative stress, produced either by addition of exogenous hydrogen peroxide or by high-dissolved oxygen tensions, was examined in terms of the activities of two key defensive enzymes: catalase (CAT) and superoxide dismutase (SOD). Batch cultures in the bioreactor were generally found to have maximum specific activities of CAT and SOD (Umg · protein−1) in the stationary/early-decline phase. Continuous addition of H2O2 (16 mmole L−1 h−1), starting in the early exponential phase, induced CAT but did not increase SOD significantly. Gassing an early exponential-phase culture with O2 enriched (25 vol%) air resulted in increased activities of both SOD and CAT relative to control processes gassed continuously with air, while gassing the culture with 25 vol% O2 enriched air throughout the experiment, although inducing a higher base level of enzyme activities, did not increase the maximum SOD activity obtained relative to control processes gassed continuously with air. The profile of the specific activity of SOD (U mg CDW−1) appeared to correlate with dissolved oxygen levels in processes where no H2O2 addition occurred. These findings indicate that it is unsound to use the term “oxidative stress” to encompass a stress response produced by addition of a chemical (H2O2) or by elevated dissolved oxygen levels because the response to each might be quite different. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 70: 662–669, 2000.

Brittle star distribution patterns and population densities on the continental slope off central California (Echinodermata: Ophiuroidea)

The ophiuroid communities on the continental slope off central California were examined using box cores and trawls. Box cores were taken between 550 and 3085 m at sites southwest of the Farallon Islands, and otter and beam trawls were used below 2300 m at three sites between the Farallon Islands and Point Sur. Eighteen ophiuroid species from six families were identified. Eighty percent of the individuals collected with box cores belonged to two species, Ophiura leptoctenia and Ophiacantha normani, which were dominant between 1000 and 2000 m. The largest ophiuroid faunal break occurred at around 2000 m and was associated with elevated dissolved oxygen levels, decreasing sediment grain size, and increasing sediment organic content. A comparison of box-core and trawl data from below 2300 m showed that box cores undersampled the ophiuroid community on the continental slope, missing almost 50% of the species collected by trawls within the same area, whereas trawls underestimated ophiuroid densities, reporting on average 243 times fewer ophiuroids per m 2 than did box cores. There was a change in species relative abundance patterns between sampling locations. Ophiuroids exhibited patchy spatial distribution patterns on both a small scale of around 0.1 m 2 and a large scale on the order of 100–1000 s of square meters.

"Oxidative stress" response in submerged cultures of a recombinant Aspergillus niger (B1-D).

A recombinant strain of Aspergillus niger (B1-D), engineered to produce the marker protein hen egg white lysozyme, was investigated with regard to its susceptibility to "oxidative stress" in submerged culture in bioreactor systems. The culture response to oxidative stress, produced either by addition of exogenous hydrogen peroxide or by high-dissolved oxygen tensions, was examined in terms of the activities of two key defensive enzymes: catalase (CAT) and superoxide dismutase (SOD). Batch cultures in the bioreactor were generally found to have maximum specific activities of CAT and SOD (Umg x protein(-1)) in the stationary/early-decline phase. Continuous addition of H2O2 (16 mmole L(-1) h(-1)), starting in the early exponential phase, induced CAT but did not increase SOD significantly. Gassing an early exponential-phase culture with O2 enriched (25 vol%) air resulted in increased activities of both SOD and CAT relative to control processes gassed continuously with air, while gassing the culture with 25 vol% O2 enriched air throughout the experiment, although inducing a higher base level of enzyme activities, did not increase the maximum SOD activity obtained relative to control processes gassed continuously with air. The profile of the specific activity of SOD (U mg CDW(-1)) appeared to correlate with dissolved oxygen levels in processes where no H2O2 addition occurred. These findings indicate that it is unsound to use the term "oxidative stress" to encompass a stress response produced by addition of a chemical (H2O2) or by elevated dissolved oxygen levels because the response to each might be quite different.

Effect of Oxygen on the Adsorption of Pentachlorophenol by Peat from Water

Pentachlorophenol (PCP), a versatile biocide has been extensively used in industry and agriculture. PCP has been designated as a priority organic pollutant by the United States Environmental Protection Agency (USEPA) and its use in consumer products has been banned since 1984. Extensive use of PCP as a wood preservative has led to soil, surface water and groundwater pollution. Batch adsorption studies using peat at various dissolved oxygen (DO) levels in water showed that higher PCP removals can be attained at elevated DO levels. This effect can be quantified by a comparison of the adsorption capacities of peat from linearized Freundlich isotherms developed for different oxygen levels. An increase of approximately 300% in adsorption was observed for an increase in the DO level from 2 to 26 mg L-1. Thus, molecular oxygen was found to significantly impact the removals of PCP by peat. The increase in adsorptive capacity of peat was not very significant for an increase in DO level from 2 mg L-1 to 10 mg L-1.However a rapid increase in adsorptive capacity was observed for an increase in DO level from 10 to 26 mg L-1.