Supersaturated Total Dissolved Gas Research Articles

A Numerical Model to Simulate the Mass Transfer Process of Supersaturated Total Dissolved Gas in Aerated Conditions

AbstractHydropower provides continuous and clean energy for human consumption but also brings a series of environmental concerns to local watersheds. Gas bubble disease or mass mortality in fish can be attributed to total dissolved gas (TDG) supersaturation, which occurs when water is released from dams. It is possible to create temporary refuges for fish suffering from supersaturated total dissolved gas (STDG) by strategically arranging aeration facilities along rivers or reservoirs and using the bubbles generated by aeration to increase the dissipation of STDG. The critical limitation to the widespread application of this approach in engineering is the insufficient understanding of the mass transfer mechanisms of STDG under aerated conditions and the transport characteristics of STDG in water flows. In this work, the mass transfer (MT) mechanisms of STDG under aerated conditions were systematically studied via experiments, image processing, and numerical simulation. An innovative three‐dimensional numerical model was established to forecast the MT process of STDG under aerated conditions. The determination of STDG MT in the model incorporated a sophisticated approach that accounted for the dynamic changes in bubble sizes resulting from diverse mechanisms of bubble coalescence and breakup. To validate and calibrate the model, precise aeration experiments were executed at various aeration intensities to gather data on the bubble size distribution, total gas holdup, and STDG dissipation rates. Furthermore, a numerical model was used to quantitatively investigate the impact of the aerator installation depth on STDG dissipation performance. The results revealed that the relationship between the dissipation coefficients of STDG and the aerator installation depth followed a power function. This research can enhance the understanding of the MT characteristics of STDG under aeration conditions while also providing a useful tool for studying the design and optimization of facilities related to STDG engineering treatment via aeration measures.

Study on the effect of aeration system on the mass transfer performance of supersaturated total dissolved gas

ABSTRACT The release of supersaturated total dissolved gas (STDG) from dams has been linked to the development of gas bubble disease, which can ultimately result in the death of fish. In order to minimize the impact of STDG on aquatic ecology, the effect of aeration on mass transfer at the air–liquid interface is taken into account. This paper selects four commonly used aerators to carry out indoor aeration tower experiments under different aeration conditions (aeration aperture, aeration water depth, and aeration volume), exploring aerators that can efficiently promote STDG release. The results indicated that the diaphragm aerator was found to have the greatest effect on STDG release, followed by corundum and spin mix aerator. In contrast, a pinhole aerator was found to have the least beneficial impact on STDG release. The increase in the release coefficient for the diaphragm aerator in comparison to the pinhole aerator is 32%. A prediction model for the aeration system was developed based on the mass transfer mechanism at the gas–liquid interface. The parameters in the model were determined using experimental data, which effectively improved the model's prediction accuracy. The findings of this study may serve as a reference point for the selection of the most suitable aerator in the actual engineering of STDG mitigation by aeration technology.

Research on the adsorption rule of porous media on supersaturated total dissolved gas

AbstractDischarge of high dams may result in supersaturated total dissolved gas (TDG) in water, which could cause fish that live downstream river to suffer from gas bubble disease. If supersaturated TDG water was taken as a water source for breeding and proliferation stations, farmed fish was confined and may face more severe problems than fish living in the river. Therefore, it is critical to develop strategies to reduce the negative effects of supersaturated TDG. In this research, the adsorption effect of porous media on supersaturated TDG was explored, including biofilter adsorption experiments and previously existing activated carbon adsorption experiments. The experimental results showed that adding porous media to the water effectively accelerated the dissipation of supersaturated TDG, and the adsorption effect was associated with the specific surface area, mass density, and initial TDG saturation. To quantitively evaluate the adsorption effects of the porous media, the porous adsorption coefficient was proposed to express the adsorption rate of porous media on supersaturated TDG. The porous adsorption coefficient was related to the initial TDG saturation and the specific surface area of the porous media. The porous adsorption coefficient increased with increasing the specific surface area and decreasing initial TDG saturation. Based on this, an equation related to the specific surface area, initial TDG saturation, and the porous adsorption coefficient was developed. This equation may be used to evaluate the adsorption effect of porous media on supersaturated TDG. This study could serve as a crucial resource in reducing the adverse impacts of supersaturated TDG.

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 study on the dissipation performance of supersaturated total dissolved gas in microbubble treatment.

The production of total dissolved gas (TDG) supersaturation resulting from dam discharges has been identified as a causative factor for gas bubble disease (GBD) or mass mortality in fish. In this study, the mitigation solution for fish refuge in supersaturated TDG water was explored by using microbubbles generated by aeration to enhance supersaturated TDG dissipation. The effects of various aeration factors (aeration intensity, water depth, and aerator size) on the dissipation processes of supersaturated TDG were quantitatively investigated through a series of tests conducted in a static aeration column. The results indicated that the dissipation rates of supersaturated TDG increased as a power function with the factors of aeration intensity and aerator size and decreased as a power function with increasing water depth. A universal prediction model for the dissipation rate of supersaturated TDG in the aeration system was developed based on the dimensional analysis of the comprehensive elements, and the parameters in the model were determined using experimental data. The outcomes of this study can furnish an important theoretical foundation and scientific guidance for the utilization of aeration as a measure to alleviate the adverse impacts of supersaturated TDG on fish.

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.

Re-establishing fish migration channel of large reservoirs in Jinsha River Basin of China by using an eco-friendly reservoir operation method

Re-establishing fish migration channel of large reservoirs in Jinsha River Basin of China by using an eco-friendly reservoir operation method

Experimental investigations on the growth of wall-attached bubble in total dissolved gas supersaturated water.

Due to dam discharge, waterfalls, sudden increases in water temperature and oxygen production by photosynthesis, the total dissolved gas (TDG) in water is often supersaturated, which may have serious effects on aquatic ecology. When the atmospheric pressure is lower than the TDG pressure in water, the supersaturated dissolved gas in water will slowly release into air. Wall-attached bubbles were formed during the TDG release process. The generation and departure of wall-attached bubbles influence the release process of TDG in water. To simulate the growth period of the wall-attached bubbles under different pressures, a decompression experimental device was designed to record the supersaturated TDG release process. Based on experimental data and mathematical calculations, the quantitative relationship between the bubble growth rate and environmental pressure was obtained. The supersaturated TDG dissipation rate increases monotonically with increasing relative vacuum degree. Applied the calculation method about the wall-attached bubble growth rate, a formula of the supersaturated TDG adsorption flux was proposed, and a prediction method of the TDG release coefficient was established. The simulation results show that with the increasing relative vacuum degree, the TDG release coefficient increases correspondingly, and the adsorption from wall surface area can be obviously promoted. This study provides an important theoretical basis for the accurate calculation of the TDG release process and provides a scientific basis for the accurate prediction of the spatial and temporal distribution of supersaturated TDG under different pressure and solid wall conditions.

Mortality risk evaluation methods for total dissolved gas supersaturation to fish based on a mitigation measure of utilizing activated carbon

Mortality risk evaluation methods for total dissolved gas supersaturation to fish based on a mitigation measure of utilizing activated carbon

Experiments about the removal of supersaturated total dissolved gas from water environment by activated carbon adsorption.

Water environment conditions directly support aquatic life. It is important to maintain a suitable water environment to improve the efficient use of water resources. Supersaturation of total dissolved gas (TDG) in the water will cause fish suffer from gas bubble disease and even mortalities. Measures should be taken to mitigate the adverse effect of supersaturated TDG. Considering the adsorption effect of porous medium, activated carbon (AC) was utilized in this experiment to explore the effect of AC on supersaturated TDG removal. The effects of AC properties, AC dosage, and initial TDG saturation were investigated. The results showed that adding AC in the water could effectively accelerate the supersaturated TDG removal rate, which was positively correlated with the AC specific surface area and dosage. Meanwhile, the average dissipation rate of TDG increased and then decreased with increasing initial TDG saturation. The adsorption characteristics of AC on supersaturated TDG were also explored. The maximum equilibrium adsorption capacity and removal rate were 0.262 mg/g and 48.5% respectively. It was concluded that the adsorption process of AC on supersaturated TDG conformed to the Langmuir equation and pseudo-first-order kinetic model. Recycling test indicated that the used AC could be reused after drying. It was hoped that this research could contribute to improving water environment and ensuring the healthy development of the aquatic livings.

Prediction model and application of machine learning for supersaturated total dissolved gas generation in high dam discharge

Prediction model and application of machine learning for supersaturated total dissolved gas generation in high dam discharge

Experimental study of the growth period of wall-attached bubbles

Abstract Due to dam discharge, waterfalls, sudden increases in water temperature and oxygen production by photosynthesis, the total dissolved gas (TDG) in water is often supersaturated, which may have serious effects on aquatic ecology. Wall-attached bubbles formed during the TDG release process and the generation and departure of wall-attached bubbles influenced the release of TDG from water. Therefore, an experiment was performed to simulate the growth of wall-attached bubbles at various water flow velocities, a quantitative relationship between the wall-attached bubble growth period and flow velocity was obtained. Another quantitative relationship, between the wall-attached bubble departure diameter and turbulent kinetic energy of flowing water, was also determined. The analysis results of the TDG release rate proved that the adsorption of TDG on solid walls was considerably affected by flow velocity. The analysis models the TDG release mechanism through complex experiments and provides a method to better identify sites for supersaturated TDG adsorption. This study serves as an important theoretical basis for revealing the mechanism by which solid surfaces promote the release process of supersaturated TDG in natural water.

Improved Model for Predicting Total Dissolved Gas Generation With the Residence Time of the Water in the Stilling Phase

Quantitative predictions of total dissolved gas (TDG) super-saturation are essential for developing operation schemes for high dams. Most TDG generation prediction models have various shortcomings that affect the accuracy of TDG super-saturation estimation, such as oversimplification of influencing factors and uncertainty in parameter values. In this study, the TDG generation process was divided into three parts, gas-liquid mass transfer process in the stilling phase, dilution resulting from the water jet plunging into the stilling phase, and outflow of TDG–super-saturated water from the stilling phase, while considering the water body and bubbles in the stilling phase as a whole. The residence time of the water in the stilling phase (Tr) was introduced to estimate mass transfer time, along with dimensional analysis methods. The properties of TDG generation were evaluated experimentally under varying Tr values. Based on the theoretical analysis and experimental results, a basic water renewal model was proposed and was validated using experimental data. Furthermore, prediction results of this model were compared with those of a classical empirical model and mechanical model based on observed data from a field survey at Xiluodu Dam. The results show that the relative errors between the predicted and experimental measurements were all less than 5%, indicating that the developed prediction model has a good performance. Compared with the mechanism model, the developed model could reduce the standard error (SE), normalized mean error (NME), and error of maximum (REMAX) by 60, 96, and 15%, respectively. Meanwhile, the developed model could reduce the SE, NME, REMAX by 17.4, 36, and 23%, respectively, compared with the empirical model. Considering all the error indexes, it can be concluded that the prediction performance of the water renewal model is the best among the three models. The proposed model was also more generically versatile than the existing models. Prediction results of water regeneration model for TDG could aid the drafting of governing strategies to minimize the risk of super-saturated TDG.

Microanalysis of supersaturated gas release based on wall-attached bubbles

Microanalysis of supersaturated gas release based on wall-attached bubbles

Numerical study on the cumulative effect of supersaturated TDG through the spillway

Numerical study on the cumulative effect of supersaturated TDG through the spillway

Influence of Channel Regulating Structures on the Transportation and Dissipation of Supersaturated Total Dissolved Gas

Bubble dissolution during the flood discharge creates high total dissolved gas (TDG) concentration zones downstream of the dams. The dissipation of supersaturated TDG is a very slow process. Thus, the elevated TDG may remain through the water body for hundreds of kilometers downstream and lead to gas bubble disease (GBD) and even mortality in fish. To improve the navigation conditions of waterways, dikes (i.e., a solid structure) of varied sizes and shapes are commonly constructed. However, this would affect the dissipation and transportation of the supersaturated TDG. It would significantly change the turbulence intensity and hydropressure of the flow, which dominates the dissipation of TDG. Therefore, TDG distribution in the waterway differs from that in the natural river. In this study, a numerical simulation of the TDG at the Yangtze River’s upper reaches (one of the inland waterways in China) was conducted with the establishment of a two‐dimensional TDG dissipation model. The effect of the dikes’ size and shape was analyzed to assess the influence of the regulation structures on the dissipation and transportation of the supersaturated TDG. Meanwhile, simulation in the study area with the natural topography was also set as blank control. Based on that, impact evaluation of TDG supersaturation on fish under different simulation scenarios was made. This study can provide a scientific basis for reducing the adverse effect of supersaturated TDG in fish and the construction of ecological waterway therefore.

Improvement on numerical modeling of total dissolved gas dissipation after dam

Improvement on numerical modeling of total dissolved gas dissipation after dam

Experimental investigations on the dissipation process of supersaturated total dissolved gas: Focus on the adsorption effect of solid walls

Experimental investigations on the dissipation process of supersaturated total dissolved gas: Focus on the adsorption effect of solid walls

Ecological regulation of cascade hydropower stations to reduce the risk of supersaturated total dissolved gas to fish

Ecological regulation of cascade hydropower stations to reduce the risk of supersaturated total dissolved gas to fish

Effects of Total Dissolved Gas Supersaturation in Fish of Different Sizes and Species.

Two endemic fish in the upper Yangtze River, the Rock Carp (Procypris rabaudi) and Prenant’s Schizothoracin (Schizothorax prenanti), were used as research objects in this study to assess the effects of total dissolved gas (TDG) supersaturation on fish of varying sizes. Fish were exposed to TDG-supersaturated water at the levels of 145, 140, 135, 130, and 125%. The results showed that fish swam slowly, responded clumsily, and then exhibited spiral swimming performance after a period of exposure to TDG-supersaturated water. Fish exhibited exophthalmos, body swelling, gill bleeding, and caudal fin bleeding when they died in the TDG-supersaturated water. With the increase in TDG supersaturation, the tolerance capacity of fish to supersaturated TDG significantly reduced. At high supersaturation, the difference in survival time between species was not significant, while fish with smaller sizes showed greater tolerance capacity. At low supersaturation, the tolerance capacity of fish was mainly affected by species, and the influence of size was relatively small. With the decrease in TDG supersaturation, the catalase (CAT) activity first increased and then decreased. Rock Carp displayed significantly less activity than Prenant’s Schizothoracin on exposure to TDG-supersaturated water. At high supersaturation levels, the CAT activity of Prenant’s Schizothoracin of small size was greater than that of large Prenant’s Schizothoracin. In contrast, small Prenant’s Schizothoracin showed less CAT activity at low TDG levels than did large individuals.