Aeration Depth Research Articles

Experimental investigation and modeling on the supersaturated total dissolved gas (TDG) dissipation in aeration.

Supersaturated total dissolved gas (TDG) generation in rivers poses great harm to aquatic organisms. In this paper, 30 groups of supersaturated TDG dissipation experiments with aeration were carried out. These results showed that aeration actively promoted the dissipation of supersaturated TDG. The aeration rate decreased by 34.94% from 1.0 m3/h to 5.0 m3/h, the reduced proportion of aeration aperture was 35.51% from 215 mm to 260 mm, whereas the aeration depth increased by 16.93% from 0.4 m to 1.2 m for the TDG dissipation time required, resulting in corresponding the variation of TDG dissipation coefficients were 86.26%, 23.74% and -5.39%, respectively. In general, the effect on TDG dissipation is that the aeration rate is the largest, followed by the aeration aperture, and the aeration depth is the smallest. A quantitative relationship was established between TDG dissipation coefficient and aeration conditions, and followed a power function, while the aeration depth inhibited its dissipation. Moreover, what matters was that a numerical model was presented for predicting the TDG dissipation in Eulerian-Eulerian. When the parameter was β = 10.52, the error between the original experimental data and the simulated of a multiphase TDG dissipation model was 0.2%. The study provides essential scientific data for mitigating the harms of supersaturated TDG.

Experimental Aeration Investigations on Supersaturated Total Dissolved Gas Dissipation

Supersaturation of total dissolved gas (TDG) is mainly produced by high dam discharge, excess oxygen production by plant photosynthesis, and a sharp increase in water temperature, which may directly lead to fish and aquatic organisms suffering from “gas bubble disease” (GBD) or death. Aeration was one of the methods used to solve the dissipation of supersaturated TDG. In this paper, aeration had an obvious promotion effect on the dissipation of supersaturated TDG. For the calculation and analysis of supersaturated TDG dissipation coefficient, the aeration rate was proportional to TDG dissipation coefficient and had a promoting effect on it, while the aeration depth and aeration aperture were inversely proportional to TDG dissipation coefficient and played an inhibitory effect on it. The supersaturated TDG dissipation coefficient was affected by a factor of KTDG,Q> KTDG,D> KTDG,H. A quantitative relationship between the supersaturated TDG dissipation coefficient and aeration rate, aeration depth, and aeration aperture was obtained, respectively, as well as important expressions with comprehensive effect factors; their margins of error average within 10%. This research method has an important guiding significance for improving the living environment of fish and other aquatic organisms, alleviating the adverse effects of supersaturated TDG.

Research on the release relationship between dissolved oxygen (DO) and total dissolved gas (TDG) in standing water

Abstract Supersaturation of dissolved oxygen (DO) and total dissolved gas (TDG) is generated by high dam discharge, excess oxygen production in photosynthesis and increasing temperature in water, which may directly lead to fish suffering from ‘gas bubble disease’ or death. In this paper, under a series of experimental aeration conditions in standing water, it was concluded that aeration had a positively promoting effect on releases of supersaturated DO and TDG, while aeration aperture and aeration depth had inhibitory effects on them. For single factor analysis, aeration had the greatest effect on the release of DO and TDG, the second effect on DO was that of aeration depth and the smallest effect was that of aeration aperture, but the second effect on TDG was that of aeration aperture and the smallest effect was that of aeration depth. Most importantly, the release coefficient of DO was greater than that of TDG, and a quantitative relationship between the release coefficient of DO and TDG and aeration conditions, respectively, was established. An exponential function relationship of the release coefficients of DO and TDG was also established. The results of the research have important guiding significance and theoretical value for reducing the harm caused by supersaturated DO and TDG.

Solving hindered groundwater dynamics in restored tidal marshes by creek excavation and soil amendments: A model study

Groundwater fluxes in tidal marshes largely control key ecosystem functions and services, such as vegetation growth, soil carbon sequestration, and nutrient cycling. In tidal marshes restored on formerly embanked agricultural land, groundwater fluxes are often limited as compared to nearby natural marshes, as a result of historical agricultural soil compaction. To improve the functioning of restored tidal marshes, knowledge is needed on how much certain design options can optimize soil-groundwater interactions in future restoration projects. Based on measured data on soil properties and tidally induced groundwater dynamics, we calibrated and evaluated a 2D vertical model of a creek-marsh cross-section, accounting for both saturated and unsaturated groundwater flow and solute transport in a variably saturated groundwater flow model. We found that model simulations of common restoration practices such as soil amendments (increasing the depth of porous soil on top of the compact layer) and creek excavation (increasing the creek density) increase the soil aeration depth and time, the drainage depth and the solute flux, and decrease the residence time of solutes in the porewater. Our simulations indicate that increasing the depth to the compact layer from 20 cm to 40 cm, or increasing the creek density from 1 creek to 2 creeks along a 50 m marsh transect (while maintaining the total creek cross-sectional area), in both cases more than doubles the volume of water processed by the marsh soil. We discuss that this may stimulate nutrient cycling. As such, our study demonstrates that groundwater modelling can support the design of marsh restoration measures aiming to optimize groundwater fluxes and related ecosystem services.

An insight into the current oil spills and on-site bioremediation approaches to contaminated sites in Nigeria.

Land oil spills in Nigeria have a long history of contaminating the soil, groundwater, vegetation, and streams with spill extension being the primary of numerous ordeals. These have left the host communities of oil fields and pipelines in crucial need of soil rehabilitation. Thus, this review provides insights into the current state of land oil spills and the effectiveness of on-site remediation approaches across communities. A total of 44 incidents of land oil spills of ≥ 500 bbl, amounting to 53,631 bbl between 2011 and 2019, was recorded by the Shell Petroleum Development Company, which primarily attributed to 83% of the total sabotage. Over 73% of the 53,631 bbl spills were unrecovered from the spill areas, which had deleterious impacts on farmlands, fishponds, rivers, and residential areas. Remediation by enhanced natural attenuation (RENA) is a feasible technique for restoring petroleum hydrocarbon-contaminated sites, but it might be ineffective when limited to tiling, windrows, and fertilizer applications due to the presence of non-biodegradable residues and contaminants beyond the aeration depth. However, bioremediation techniques ranging from non-supplemented in-situ and fertilizer supplemented in-situ to mixed in-situ and ex-situ bio-cells supplemented RENA are feasible approaches for spill sites. However, challenging limitations with regard to RENA application failures in the region include delayed responses to spill emergency, large amounts of un-recovered spilled oil, and un-implemented legislative guidelines for spill cleanup. Nevertheless, the temperature, moisture, nutrient, oxygen, and pH of the soil are essential parameters to be considered when implementing a landfarming remediation approach.

Dynamics of nitrogen transformation and bacterial community with different aeration depths in malodorous river.

In this research, the dynamics of nitrogen transformation and bacterial community in malodorous river were investigated with different aeration depths. Computational flow dynamics (CFD) and Reynolds number (Re) were specially used to characterize the hydrodynamics condition under different aeration depths. The results indicated that aeration depth had vital impact on nitrogen transformation and bacterial community structure. It was found that a range of aeration depth (0.20-0.45m above sediment-water interface) facilitated the removal of NH4+-N and TN with Re ranging between 6211 and 8930. Proteobacteria took over Firmicutes to become the predominant phylum (36-78%) under aeration, and the main subdivisions of γ-, β- and δ-Proteobacteria also varied greatly with different aeration depths. Interestingly, there was a marked shift of the inferentially identified dominant functional role within Proteobacteria from organic-matter degradation to nitrogen metabolism and then to sulfur metabolism as well as the coupling of nitrogen and sulfur with the increase of disturbance. The redundancy analysis (RDA) further confirmed the importance of aeration disturbance in shaping bacterial community. These findings help to gain improved understanding of endogenous N-behavior and aquatic microbial ecology, and underline the need for integrating the hydrodynamics factors with microbial community.

Dynamic aeration for improved oxygen mass transfer in the wastewater treatment process

Wastewater treatment is responsible for about 1% of the total electric energy consumption in developed countries. The dynamic aeration method, which applies oscillations to the gas flow, shows a high potential for increase of oxygen mass transfer and energy efficiency of the biological wastewater treatment process. We investigated the mass transfer of pulsed aeration modes in comparison to constant flow aeration in a test geometry in a numerical study. The effects of flow rate, pulsation frequency, bubble size and injection depth on mass transfer were studied. Gas was pulsated with a square wave pattern in on/off mode for the application in aeration basins of wastewater treatment plants. A geometry with up to 4 m aeration depth was investigated. The air supply was pulsed with frequencies in the range of 0.1–4 Hz. An increase of oxygen mass transfer rate by up to 24% is determined compared to continuous aeration. Moreover, comparable mass transfer rates are achieved for lower gas mass flow rates during pulsation. Thus, air demand in compression and energy consumption can be reduced when dynamic aeration is applied. The oxygen transfer efficiencies derived from the simulations are in good agreement with the experimental results from Alkhalidi et al. (2016).

Laboratory Investigation on Hydrodynamic Performance of an Innovative Aeration Device with a Wave-Driven Heaving Buoy

Coastal seawater quality is of significance for the environment, ecology and fisheries. In recent years, the hypoxia or anoxia problems of bottom seawater aggravated due mainly to the seawater stratification and eutrophication. This paper addresses an innovative aeration device with a wave-driven heaving buoy to enhance the dissolved oxygen concentration for bottom water. A series of physical experiments was conducted to investigate its hydrodynamic performance and air flow rate. The response amplitude of heaving components and the average value of air flow rate were examined with the related parameters, including incident wave height, incident wave steepness and aeration depth. It was found that with increasing incident wave height, the average heaving displacement and the average air flow rate increase respectively. With the increase of incident wave steepness, the relative value of average heaving displacement increases obviously for high wave period scenarios, it increases slightly for small wave period scenarios in comparison and the relative value of air flow rate increases evidently. With the increase of aeration depth, the average heaving displacement and the average air flow rate decrease respectively. With the increase of relative aeration depth, the relative value of average heaving displacement and the relative value of air flow rate decrease respectively. In addition, the dimensional analysis and the least squares methods were used to obtain the prediction formulas for the average heaving displacement and the average air flow rate, and they agreed well with the related experimental data.

Oxygen Transfer Numerical Investigation Using Intermittent Aeration Technology Under Regular Waves

Based on a combination of Reynolds-Averaged Navier-Stokes equations, standard k-e equations, and VOF technique, a 2-D dissolved oxygen transport mathematical model was conducted to investigate oxygen-supply characteristics for regular waves with a given still water depth d and various hydrodynamic parameters (incident wave height H and wave period T equivalent to incident wave length L) and intermittent aeration parameters (air flow rate per unit width q, aeration period Ta, aeration depth da and air source area Aa). A series of experiments were conducted to validate the mathematical model, and they agreed well with each other. In addition, a series of dimensionless parameters were conducted to assess their relationships with oxygen transfer coefficient respectively. It was found that oxygen transfer coefficient increased slightly with the increase of $$ q/{g}^2{T}_a^3 $$ . With the increasing $$ {d}_a^2/{A}_a $$ , oxygen transfer coefficient increased obviously for the small $$ {d}_a^2/{A}_a $$ scenarios; however, it increased slightly for the high $$ {d}_a^2/{A}_a $$ scenarios. With increasing HL/d2, a linear increase tendency of oxygen transfer coefficient appeared approximately. Furthermore, a simple prediction formula for oxygen transport coefficient was conducted using the numerical data, the dimensional analysis, and the least squares method, and it was validated well with the related experimental data.

Historical peat loss explains limited short-term response of drained blanket bogs to rewetting

This study assessed the short-term impacts of ditch blocking on water table depth and vegetation community structure in a historically drained blanket bog. A chronosequence approach was used to compare vegetation near ditches blocked 5 years, 4 years and 1 year prior to the study with vegetation near unblocked ditches. Plots adjacent to and 3 m away from 70 ditches within an area of blanket bog were assessed for floristic composition, aeration depth using steel bars, and topography using LiDAR data. No changes in aeration depth or vegetation parameters were detected as a function of ditch-blocking, time since blocking, or distance from the ditch, with the exception of non-Sphagnum bryophytes which had lower cover in quadrats adjacent to ditches that had been blocked for 5 years. Analysis of LiDAR data and the observed proximity of the water table to the peat surface led us to conclude that the subdued ecosystem responses to ditch-blocking were the result of historical peat subsidence within a 4–5 m zone either side of each ditch, which had effectively lowered the peat surface to the new, ditch-influenced water table. We estimate that this process led to the loss of around 500,000 m3 peat within the 38 km2 study area following drainage, due to a combination of oxidation and compaction. Assuming that 50% of the volume loss was due to oxidation, this amounts to a carbon loss of 11,000 Mg C over this area, i.e. 3 Mg C ha−1. The apparent ‘self-rewetting’ of blanket bogs in the decades following drainage has implications for their restoration as it suggests that there may not be large quantities of dry peat left to rewet, and that there is a risk of inundation (potentially leading to high methane emissions) along subsided ditch lines. Many peatland processes are likely to be maintained in drained blanket bog, including support of typical peatland vegetation, but infilling of lost peat and recovery of original C stocks are likely to take longer than is generally anticipated.

Influence of aeration modes on leachate characteristic of landfills that adopt the aerobic–anaerobic landfill method

As far as the optimal design, operation, and field application of the Aerobic–Anaerobic Landfill Method (AALM) are concerned, it is very important to understand how aeration modes (different combinations of aeration depth and air injection rate) affect the biodegradation of organic carbon and the transformation of nitrogen in landfill solid waste. Pilot-scale lysimeter experiments were carried out under different aeration modes to obtain detailed information regarding the influence of aeration modes on leachate characteristics. Results from these lysimeter experiments revealed that aeration at the bottom layer was the most effective for decomposition of organic carbon when compared with aeration at the surface or middle layers. Moreover, the air injection rate led to different nitrogen transformation patterns, unlike the lesser influence it has on organic carbon decomposition. Effective simultaneous nitrification and denitrification were observed for the aeration mode with a higher air injection rate (=1.0L/min). On the other hand, the phenomenon of sequenced nitrification and denitrification could be observed when a low air injection rate (=0.5L/min.) was employed. Finally, it is concluded that, for AALM, air injection with a higher air injection rate at the deepest layer near the leachate collection pipe tends to accelerate the stabilization of landfill waste as defined in terms of the enhancement of denitrification as well as organic carbon decomposition.

Drying Kinetics of Extruded Pellets in Fixed Beds

To study the drying behavior of extruded feed pellets in a fixed bed, the drying kinetics were investigated in a laboratory-scale dryer. The effect of types of aeration, air temperature, and bed depth on drying curves and moisture nonuniformity was analyzed. The results showed that drying was mainly affected by the air flow direction, air temperature, and bed depth. The moisture nonuniformity was 2% for an alternating air flow direction drying, where as it was 7% for one-way drying at a bed depth of 15 cm at 33 min. Alternating direction drying improved moisture uniformity, but the drying rate was decreased at a bed depth of 20 cm. A constant drying stage was observed at a critical bed depth, where as an increasing drying rate stage was observed for a deeper bed. The pressure drop (ΔP/L) was studied by ventilation experiments considering the effect of air flow rate, moisture content, bed type, and bed depth. The result showed that pressure drop in a double bed was greater than that in a single bed with the same bed depth. The pressure drop increased with air flow rate and decreased with moisture content and bed depth.

Aeration efficiency influenced by venturi aerator arrangement, liquid flow rate and depth of diffusing pipes

The effect of aerator module configuration, liquid flow rate and diffuser submergence on oxygen transfer efficiency was examined in a surface aeration system with venturi injectors using the clean water test. Six venturi aerator modules were evaluated and the results indicated that better aeration efficiencies could be achieved by simply changing the way the venturi aerators were connected. Among all the configurations examined (modules a–f), two and three aerators connected in parallel (modules d, e and f) were able to bring more oxygen into water than the others. An increase in liquid flow rate led to an enhancement of the oxygen transfer coefficients, but the improvement was reduced if the liquid flow rate was too high. The oxygen transfer coefficient was found to have a relationship with the depth of diffusing pipes (surface aeration depth) for the surface aeration system and an optimal depth of around 40 cm was obtained from this study.

반응조의 물리적 인자와 알칼리도가 암모니아 탈기에 미치는 영향에 관한 연구

Abstract : The effect of the physical parameters in the reactor (aeration depth, bubble size, and surface area) and the alkalinity of the solution on the ammonia stripping by bubbling were evaluated. When an airflow of 30 L/min was bubbled below the solutionsurface in the range 6-53 cm, the ammonia removal rate were observed to be the same regardless of the bubbling depths. At pH 10.0 and a temperature of 30℃, the average rate constant and the standard deviation were 0.178 h -1 and 0.004. No appreciable changes in the ammonia removal rate were also observed with varying the bubble size and the air-contacting surface area. Alkalinity of the solution was found to affect the ammonia removal rate indirectly. This is expected because the pH of the solu-tion would vary with dissolution of gaseous CO 2 by air bubbling. The real wastewaters from landfill site and domestic wastewater treatment plant were tested. In the case of domestic wastewater (pH = 7.1, alkalinity = 75 mg/L), the ammonia removal rate was poor even with the control of pH to 9.3. The raw landfill leachate (pH = 8.0, alkalinity = 6,525 mg/L), however, showed the appre-ciable removal rate with increasing pH during aeration. When the initial pH of the leachate was adjusted 9.4, the removal rate was significantly increased without changing the pH during aeration.

An experimental study of nozzle diameters, aeration depths and angles on standard aeration efficiency (SAE) in a venturi aerator

A 1.1 kW submersible water pump with a venturi air injector was used in this study to examine the effects of three factors including nozzle diameter (14, 17 and 20 mm), aeration depth (20, 40 and 60 cm), and aeration angle (0, 22.5 and 45°) on standard aeration efficiency (SAE). For maximum air entrainment, HT / DT ratio and DT / DN ratio were equal to zero and 2, respectively. Among the first factor experiments, 14 mm nozzle diameter showed the highest SAE value (P<0.05). Although, 60 cm aeration depth and 45° aeration angle had more SAE value among other depths and angles, but there was not a significant difference (P>0.05) in each aeration depths and angles. Only, the determination coefficient for effect of nozzle diameters on SAE value showed a good result (R2= 0.958). The greatest oxygen transfer efficiency in this study has been achieved with using 14 mm nozzle size, 60 cm depth of aeration, and 45° angle of venturi tube in water aeration that was 1.166 kgO2/ kWh. Venturi aerators are very inexpensive in comparison with other aerators and have some other advantages that can be considered as one of the best devices for water aeration.

Improvement of oxygen transfer efficiency in aerated ponds using liquid-film-assisted approach

In aerated ponds, oxygen is generally supplied through either diffused or mechanical aeration means. Surface transfer and bubble transfer both contribute significantly to oxygen transfer in a diffused aeration system. In the present study, a liquid-film-forming apparatus (LFFA) is successfully developed on a laboratory scale to improve considerably the surface transfer via the unique liquid film transfer technique. The experimental results show that the volumetric mass transfer coefficient for LFFA alone is found to be as much as 5.3 times higher than that for water surface and that the total volumetric mass transfer coefficient for the liquid film aeration system increases by 37% in comparison with a conventional aeration system. Additionally, by tuning finely the structural parameters of the LFFA, it can also lead to high dissolved oxygen (DO) water with the DO percent saturation greater than 90%. More importantly, this result is accomplished by simply offering a single-pass aeration at a depth as shallow as 26 cm. As a result, the objective of economical energy consumption in aerated ponds can be realized by lowering the aeration depth without sacrificing the aeration efficiency. It is noteworthy that the data presented in this study are acquired either numerically or experimentally.

Enhancement of Oxygen Transfer Efficiency in Diffused Aeration Systems using Liquid-Film-Forming Apparatus

Surface transfer and bubble transfer both contribute significantly to oxygen transfer in a diffused aeration system. In the present study, liquid-film-forming apparatus is successfully developed on a laboratory scale to improve considerably the surface transfer via the unique liquid film transfer technique. The experimental results show that the volumetric mass transfer coefficient for liquid-film-forming apparatus alone is found to be as much as 5.3 times higher than that for water surface and that the total volumetric mass transfer coefficient for liquid film aeration system increases by 37 % in comparison with conventional aeration system. Additionally, by tuning finely the structural parameters of the liquid-film-forming apparatus, it can also lead to high dissolved oxygen water with the dissolved oxygen percent saturation greater than 90 %. More importantly, this result is accomplished by simply offering a single-pass aeration at the depth as shallow as 26 cm. As a result, the objective of economical energy consumption in diffused aeration systems can be realized by lowering the aeration depth without sacrificing the aeration efficiency.