Reaeration Process Research Articles

A coefficient identification problem for a system of advection-diffusion-reaction equations in water quality modeling

Abstract The inverse problem of reconstructing two space-varying coefficients in a system of one-dimensional (1-d) time-dependent advection-diffusion-reaction (ADR) equations is considered. The ADR system can be used as a water quality model which describes the evolution of the biochemical oxygen demand (BOD) and dissolved oxygen (DO) in a river or stream. The coefficients to be reconstructed represents the effect of the deoxygenation and superficial reaeration processes on the DO and BOD concentration in water. Hölder stability estimates for the coefficients of interest are established using the Carleman estimate technique.

Water Quality Influences Self-Purification in the Cihawuk and Majalaya Segments Upstream of the Citarum River, West Java, Indonesia

Self-purification plays an important role in water regulating ecosystem services aimed at protecting river water quality from pollutant inputs. The Citarum River is the longest river in West Java, Indonesia where the water quality has declined due to pollutant inputs from domestic and non-domestic activities. This study aims to investigate the status of self-purification ecosystem services and the influence of water quality in the upstream of the Citarum River, in the Cihawuk and Majalaya segments, which are rural and urban areas. The self-purification status was determined by the deoxygenation rate using Thomas’s slope method, and by the reaeration rate according to O’Connor and Dobbins’ method. The polynomial component regression (PCR) was performed to determine the significance of the influence of physicochemical factors on self-purification. The deoxygenation rates (k1) in the rural and urban areas upstream of the Citarum River were 0.044 per day and 0.058 per day, respectively, while the reaeration rates (k2) in the rural and urban areas were 0.196 per day and 0.156 per day, respectively. These deoxygenation and reaeration rates indicate that the self-purification status upstream of the Citarum River has been disturbed. This result also indicates that chemical factors have a significant influence on the deoxygenation process, while the reaeration process is most significantly influenced by physical factors. The deterioration of self-purification in the Citarum River poses a risk to the long-term availability of water resources. Therefore, this research encourages the reduction in the input of organic pollutants and develops a strategic plan for river management.

Experimental Verification of Namami Gange Project on Various Parameters of Gangas Water in Varanasi

The Pollution of India’s National River Ganges has become dangerous for people near it. After observing the data, it was found that Ganges in high profile cities like Kanpur, Varanasi and Allahabad was highly polluted. In this study water quality parameters were analysed in these highly polluted areas before and after the launching of Namami Gange project. In this research it is shown that if sewage treatment capacity is increased then how pollution in the river decreasing. Self-purification of Ganges is taken into account using de-oxygenation and re-aeration process. After analysing self-purification concept certain results are concluded about the pollution of river. It is advisable that sewage treatment network should be increased on a large scale in highly polluted stretches. The goal of this research is to determine the change in quality parameters of Ganges water due to Namami Gange project.

Quantitative study for the effect of water velocity on water quality change

Atmospheric reaeration process plays a key role in degradation of organic matter and self-purification processes affecting dissolved oxygen (DO) concentrations in rivers and streams. Moreover, water quality (WQ) processes can be highly dependent on flow velocity conditions. Where, highly reaeration rates are positively correlated with high flow velocity. Therefore, the present work reports deep insights on the role of flow velocity with reaeration process in the concentration of DO and biochemical oxygen demand (BOD5). This study was applied along the largest agricultural drainage water reuse project, El-Salam Canal in Egypt. The hydrodynamic (HD) characteristics and WQ parameters (DO and BOD5) along the canal were simulated using a one-dimensional HD and WQ model (MIKE 11). The simulated results indicated that the canal was deteriorated towards El-Salam Canal after mixing with El-Serw and Bahr Hadous drains. Statistical regression fitted line and Pearson correlation analysis, were performed on the simulation results of the reaeration rates with flow velocity and WQ values, indicating a significant correlation. Accordingly, water velocity should be taken into account as a key factor for describing the WQ change.

Evaluation of dissolved oxygen sinks in water-stirring setups used in reaeration experiments

AbstractDissolved oxygen (DO) is an essential parameter of water quality, and the surface reaeration process (K2) is the main source of DO in aquatic ecosystems. On a laboratory scale, reaeration measurements are performed using water-stirring setups (WSSs), but possible physical DO sinks are not considered in the WSSs. This paper aimed to assess the presence of physical DO sinks in WSSs. The experiments were carried out in four WSSs: circular hydraulic channel (CHC); straight hydraulic channel (SHC); turbine-stirred tank (TST); and oscillating grid tank (OGT). The physical DO sink was estimated by inserting a first-order term (K3, day−1) in the classic equation of DO balance. All WSSs presented physical DO sinks during the reaeration experiments: SHC (mean K3 = 4.58 day−1) > TST (mean K3 = 1.30 day−1) > CHC (mean K3 = 1.12 day−1) > OGT (mean K3 = 0.13 day−1). Physical DO sinks were originated from low-pressure zones located in WSSs, which was confirmed by the negative correlation (r = −0.78) between K3 and the static pressure in the suction pipeline of the SHC. This study presented additional information about identifying, and quantifying, physical DO sinks in WSSs, which are essential to produce a correct estimation of the K2.

IDENTIFIKASI EFEKTIVITAS REAERASI MENGGUNAKAN MICROBUBBLE GENERATOR (MBG) PADA AIR EMBUNG

The retention basin at the Faculty of Engineering Gadjah Mada University was built as a flooding control into the Code river and improving the water quality. The water entering the basin, especially in the dry season, is characterized as greywater due to the dense settlements around the university. The purpose of this study was to determine the effectiveness of reaeration process using a Microbubble Generator (MBG) to increase DO, with the aim of this leading to an improved water quality. The MBG aerator with submersible pumps was installed at a depth of 40 cm from the water surface and placed in the middle of the pond. The aerator was permanently turned on. In situ monitoring of DO was carried out using a seri Lutron WA-2017SD DO meter. The increasing DO correlated with the changes of the surrounding weather which impact on water and air temperature. At the time of DO data collection, the water temperature ranged from 24.5oC - 27oC and the change in DO measured at the inlet and outlet of the reservoir was in the range 0.3 - 1.1 mg/l, with the DO directly surrounding the aerator reaching up to 2.4 mg/l from the inlet. With the DO increased, the concentration of pollutant organic loads can be reduced and the nitritation and nitratation processes has taken place properly so that it has reduced the pollutant load before the water enters the Code river.

ANFIS-ARIMA modelling for scheming re-aeration of hydrologically altered rivers

The discharge of a significant amount of wastewater from the urban agglomerations in the rivers is the primary cause for the degradation of the river’s assimilative capacity. The re-aeration process represents an interaction among the air–water interface to absorb oxygen from the atmosphere and indicates the capacity of the water to hold the oxygen that can be used in the degradation of pollutants without affecting the river’s health. Therefore, accurate estimation of re-aeration capacity is the prime requirement to maintain the riverine ecosystem. In this paper, an adaptive neuro-fuzzy inference system (ANFIS) is used to simulate the non-linear behaviour of various water quality parameters by estimating the re-aeration coefficient of Yamuna River, Delhi. The hydraulic and water quality parameters are used to identify the most optimal combination of input parameters for simulation through the Takagi-Sugeno (TS) ANFIS model. The results of ANFIS are ensembled with the time series autoregressive integrated moving average (ARIMA) model to minimize bagging, non-stationarity and biasing. The performance of the ANFIS models was measured using the coefficient of determination (R2), root mean square error (RMSE), and the coefficient of correlation (R). The ARIMA models are evaluated based on standard error, p-value, and t-test. Out of the five different ANFIS models, ANFIS-5 provides the optimal values of R during training and testing of the model as 0.966 and 0.989, respectively, and integrated with the ARIMA model to obtain the re-aeration coefficient for each sampling location. The results indicate that the ensembled ANFIS-ARIMA model reduces the variance significantly with the minimum error of 0.0075 and produces an exceptional improvement in predicting the re-aeration coefficient.

Applying EFDC Explorer model in the Gallinas River, Mexico to estimate its assimilation capacity for water quality protection

Sanitary and industrial wastewater discharged into rivers, is a general problem that occurs in most of the world and Mexico is not the exception, the main goal of this research is to determine based on simulations of pollutants concentrations, the assimilation capacity of the Gallinas River against discharges of agricultural and industrial wastewater from the cultivation and processing of sugar cane under two different hypothetical simulation scenarios, based on reproducing two well know scenarios. In sugarcane cultivation, large quantities of fertilizers are used whose main active components are based on nitrogen or phosphorus compounds, therefore, the wastewater resulting from sugarcane processing contains a high organic content from 20 to 40% of inorganic compounds, such as nitrogenous substances, organic acids, and phosphorous sulfates. For this reason, the physical–chemical variables of interest analyzed in this work are the PO_4 (phosphate), NO_3 (nitrate), and DO (dissolved oxygen). With the simulation results according to each scenery, it can be determined, that despite the continuous discharge of polluting elements, the Gallinas River has a good assimilation capacity thanks to reaeration processes that permit efficient recovery of the dissolved oxygen in the water column. Gallinas River is located in the region known as the Huasteca Potosina, this investigation is relevant for the region due to the River is of vital importance being the main tributary that allows socioeconomic development activities in this zone. To carry out the simulations, was used the Explorer Modeling System 8.4 (EFCD) model and was performed two samplings campaign along 15 km in the water body to calibrate the numerical model to represent the dry and wet seasons during May and September respectively named as calibration scenarios.

An integrated model to predict and prevent hypoxia in floodplain-river systems

Hypoxia can occur following rewetting of floodplains and cause severe impacts on aquatic biota and biogeochemical processes. The likelihood of such events is influenced by a number of factors including temperature, the mass of plant litter on the floodplain (which is influenced by the duration between inundation events), the volume of water available for dilution of oxygen-demanding dissolved organic matter, and the exchange of water to dilute and disperse that material. Using constructed infrastructure to generate managed inundations on floodplains increases the likelihood of hypoxic “blackwater” events relative to unregulated floods, as larger areas of floodplain are inundated at lower flow rates. A model (the “DODOC plugin”) was developed for the Source hydrological modelling software to inform risk mitigation strategies for these managed inundation events. This development enables the interaction between complex hydrology and floodplain inundation on the resulting release of dissolved organic carbon (DOC), and subsequent consumption of dissolved oxygen (DO), to be represented. Key functionality of the plugin includes the ability to represent (i) spatial variability in organic litter build up and degradation, (ii) DOC leaching from litter when inundated, (iii) DO consumption arising from microbial decomposition of the DOC, and (iv) reaeration processes from autotrophic productivity and turbulence as water passes over water level regulating structures. The model is configurable on both river channels (links) and floodplains (storages) to represent changes in DO from both natural and managed inundation events at the scale of an individual floodplain up to multiple floodplains and river reaches. The plugin was parameterised to successfully simulate DOC (R2 = 0.84–0.93) and DO (R2 = 0.74–0.92) along an approx. 100 km study reach of the River Murray in South Australia, once the different behaviour of the labile and refractory components of the DOC was represented in the model. A number of hypothetical operational scenarios were tested using the model to demonstrate parameter sensitivity and to inform planning of managed inundations. The development of the DODOC plugin demonstrates that complex water quality processes can be integrated into the Source (or other) hydrological software, to represent cumulative implications of floodplain inundation events and to minimise the risk of hypoxia.

Designing key parameters of bubble plumes to restore water quality by using conceptual models: a case study in a sub-deep reservoir

Abstract Bubble plumes are a popular hypolimnetic reaeration technique in deep-water reservoirs since they have the advantage of delivering direct reaeration to the hypolimnion. Improving the understanding of the integrated reaeration processes is beneficial to optimize the reaeration capacity of the aeration or oxygenation system. In this study, the discrete bubble model was first employed to design an oxygenation system for a sub-deep reservoir (the Aha Reservoir, southwest China, with water depths of 10–30 m). A new approach involving the discrete bubble model was used to determine the initial bubble size of the bubble plume applied. The intrusion models were demonstrated to be useful for designing the gas flow rate of the reaeration system. Using the intrusion models, we predicted the intrusion thickness and intrusion distance during operation for the first time. Subsequently, we verified the predictions and produced more realistic empirical formulas. At present, reports about recommendations on initial bubble size and gas flow rate are rare, and practical verification is absent. Taking the Aha Reservoir as an example, the initial bubble radius of 1 mm and the gas flow rate of 20 m3·h−1 were recommended for bubble plume oxygenation and were found to be successful in the field. Our understanding of the reaeration processes during the operation of the bubble plume system is far from comprehensive, but this study serves to highlight the potential of the discrete bubble model and the intrusion models for designing a bubble plume system in an individual lake.

Estimate of gas transfer velocity in the presence of emergent vegetation using argon as a tracer: Implications for whole-system denitrification measurements

Denitrification associated with emergent macrophytes is a pivotal process underlying the treatment performance of wetlands and slow-flow waterways. Laboratory scale experiments targeting N losses via denitrification in sediments colonized by emergent macrophytes require the use of mesocosms that are necessarily open to the atmosphere. Thus, the proper quantification of N2 effluxes relies on the accurate characterization of the air–water gas exchanges. In this study, we present a simple approach for direct measurements of the gas transfer velocity, in open-top mesocosms with Phragmites australis, by using argon as a tracer. Different conditions of water velocity (0, 1.5, 3, and 6 cm s−1) and temperature (8.5, 16, and 28 °C), were tested, along with, for the first time, the presence of emergent vegetation. The outcomes demonstrated that water velocity and temperature are not the only factors regulating aeration at the mesocosm scale. Indeed, the gas transfer velocity was systematically higher, in the range of 42–53%, in vegetated compared to unvegetated sediments. The increase of small-local turbulence patterns created within water parcels moving around plant stems translated into significant modifications of the reaeration process. The adopted approach may be used to improve the accuracy of denitrification measurements by N2 efflux-based methods in wetland and slow-flow waterway sediments colonized by emergent macrophytes. Moreover, the present outcomes may have multiple implications for whole-system metabolism estimations from which largely depend our understanding of biogeochemical dynamics in inland waters that have strong connections to worldwide issues, such as nitrate contamination and greenhouse gas emissions.

Numerical Simulation of Hydrodynamics and Reaeration over a Stepped Spillway by the SPH Method

Aerated flows are characterized by complex hydrodynamics and mass-transfer processes. As a Lagrangian method, smoothed particle hydrodynamics (SPH) has a significant advantage in tracking the air-water interface in turbulent flows. This paper presents the application of an SPH method to investigate hydrodynamics and reaeration over stepped spillways. In the SPH method, the entrainment of dissolved oxygen (DO) is studied using a multiphase mass transfer SPH method for reaeration. The numerical results are compared with the hydrodynamics data from Chanson and DO data from Cheng. The simulation results show that velocity distribution and the location of free-surface aeration inception agree with the experimental results. Compared with the experimental results, the distribution of DO concentration over the stepped spillway is consistent with the measurement results. The study shows that the two-phase DO mass transfer SPH model is reliable and reasonable for simulating the hydrodynamics characteristics and reaeration process.

Deoxygenation rate, reaeration and potential for self-purification of small tropical urban stream

Mathematical models used to simulate the water quality and the processes of self-purification of water bodies are important tools to support effective water resource management. The objective of this study was to evaluate the impact of organic pollution on water quality and the assimilative capacity of organic matter in the Ribeirao Vermelho stream situated in the city of Lavras in Minas Gerais. The deoxygenation rate (K1) and reaeration (K2) were determined and tested in three segments of the Ribeirao Vermelho over two seasons (summer and winter). The purification process simulation was performed using the Streeter- Phelps model. The highest K1 and K2 values occurred during the winter period which was characterized by lower flows. Simulation of the dissolved oxygen profile and biological oxygen demand fitted the model well, indicating the prevalence of carbonaceous deoxygenation due to nitrification and also demonstrating the importance of natural reaeration as part of the purification process. Different response was observed during the winter, in which the high primary productivity values stood in the reaeration process stream. Biological oxygen demand values did not meet the limits recommended by the Resolution of the Ministry of the Environment 357/2005 throughout the river system and the entire study period. In conclusion, the Ribeirao Vermelho is unable to self-purify along its entire length, and water quality is influenced by effluent discharge which intensifies degradation.

Reaeration Model for a Still-Water Body

AbstractAn investigation on the influence of temperature (21.6–39.6°C) on the reaeration rate was performed. The recipient still water body was homogeneous and unstratified. The findings of the experimental study showed that the reaeration rate increases with temperature within the range of the temperature investigated. A mathematical model for estimating the reaeration rate is also presented. A new temperature correction factor for the conversion of the kinetic rate coefficient at different temperatures has been developed and was found to better reflect the reaction rates associated with the reaeration process.

Influence of Small Water Surface Perturbations on the Reaeration Process

AbstractThis paper aims to develop a general reaeration model for water bodies subject to small surface perturbation, such as ripples that may be induced by wind, waves, and surface current. A test rig was specially designed and fabricated to study the influence of waves on the reaeration process. The wave frequency varied from 0.125 Hz to 0.425 Hz for various wave heights, H, ranging from 0.15 cm to 1.5 cm. Based on the findings of the experimental study, the authors developed a modified film model and introduced a diffusive film-layer thickness δD as the characteristic length scale for the reaeration process. The thickness of the diffusive film layer may be determined readily in one of two ways: (1) as the ratio between the molecular diffusivity of dissolved oxygen and the measured oxygen transfer coefficient; and (2) estimated using its established functions with other concentration boundary layers proposed by various researchers. The modified film model was found to unify the present experimental data...

Effect of waves on reaeration

Mechanically generated surface waves and their influence on oxygen transfer were investigated. The experiments were conducted in a reaeration column (Reynolds number from 125–937). The water surface was set in oscillatory motion to simulate periodic surface level fluctuation. The wave frequency used ranged from 0.125 Hz to 0.425 Hz for various wave heights ranging from 0.15 cm to 1.5 cm. After bleeding the water column with nitrogen, dissolved oxygen concentration was measured over time below the water surface. A modified surface renewal model was proposed and found to describe the oxygen transfer phenomenon well. In addition, it was found that the mean film thickness δD, may be used as the characteristic length to describe the reaeration process under the influence of small perturbation and surface water waves. The proposed model was also extended to include the reaeration process under larger waves reported by other researchers. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4839–4845, 2013

Options for Managing Hypoxic Blackwater in River Systems: Case Studies and Framework

Hypoxic blackwater events occur when large amounts of organic material are leached into a water body (e.g., during floodplain inundation) and rapid metabolism of this carbon depletes oxygen from the water column, often with catastrophic effects on the aquatic environment. River regulation may have increased the frequency and severity of hypoxic blackwater events in lowland river systems, necessitating management intervention to mitigate the impacts of these events on aquatic biota. We examine the effectiveness of a range of mitigation interventions that have been used during large-scale hypoxic blackwater events in the Murray-Darling Basin, Australia and that may be applicable in other environments at risk from hypoxic blackwater. Strategies for hypoxia mitigation include: delivery of dilution flows; enhancement of physical re-aeration rates by increasing surface turbulence; and diversion of blackwater into shallow off-channel storages. We show that the impact of dilution water delivery is determined by relative volumes and water quality and can be predicted using simple models. At the dilution water inflow point, localized oxygenated plumes may also act as refuges. Physical re-aeration strategies generally result in only a small increase in dissolved oxygen but may be beneficial for local refuge protection. Dilution and natural re-aeration processes in large, shallow lake systems can be sufficient to compensate for hypoxic inflows and water processed in off-channel lakes may be able to be returned to the river channel as dilution flows. We provide a set of predictive models (as electronic supplementary material) for estimation of the re-aeration potential of intervention activities and a framework to guide the adaptive management of future hypoxic blackwater events.

Developing flow in skimming flow regime on embankment stepped spillways

In hydraulic engineering, stepped spillways are effective structures in regard to both energy dissipation and re-aeration processes. It is well known that flow depths and flow velocities generally depend on the spillway geometry in terms of slope and step-induced macro-roughness height on the one hand and the discharge on the other hand. Moreover, these parameters affect the air entrainment process and hence, the amount and the size of entrained air bubbles which are directly linked to the specific air–water interface being of particular significance for oxygen transfer. In this study, physical model investigations on a stepped spillway scaled 1:10 of varying step height, chute angle and discharge are conducted with the objective to analyse the development of these air–water flow properties in the non-uniform flow region. Measurements of air–water mixture velocity and air concentration are carried out by the use of an intrusive double-tip conductivity probe. It is found that the step-induced macro-roughness has a differing effect on particular flow characteristics.

Effect of Submerged and Floating Plants on Dissolved Oxygen Dynamics and Nitrogen Removal in Constructed Wetlands

Dissolved oxygen (DO) concentration affects the treatment processes in constructed wetlands. This study examined the dissolved oxygen dynamics and total nitrogen removal in constructed wetlands with submerged and floating plants. Four constructed wetland units each with the surface area of 3 x 1 m² were constructed at University of Peradeniya. Two of those with the depths of 0.3 m (A) and 0.6 m (B) were planted separately with <em>Hydrilla verticillata</em> (submerged) and <em>Lemna minor</em> (floating), respectively. Other two (C and D) were constructed with two sections of 0.3 and 0.6 m depths and planted with <em>H. verticillata</em> and <em>L. minor</em>, respectively in each section. Secondary effluent from student hostel was fed with hydraulic retention time of 6 days. DO was measured at different depths of water, 0.0, 0.1, 0.2, 0.4 and 0.5 m from the water surface and along the longitudinal axis of the wetland at 6 hours interval. The total nitrogen was measured for water samples at inlet and outlets. The average dissolved oxygen concentrations of A and B were 17.7 and 0.4 mg L^-1 respectively. Oxic condition was maintained in the submerged plant units. Anoxic condition resulted throughout the day in floating plant system. DO varied significantly with depths in oxic condition. DO dynamics in these wetlands can be explained by photosynthesis, respiration, deaeration and reaeration processes. The highest total nitrogen removal was achieved in unit D where combined anoxic and oxic conditions were maintained together <em>H. verticillata</em> and <em>L. minor</em> could effectively be used to maintain required dissolved oxygen in constructed wetlands for nitrate removal. DOI: http://dx.doi.org/10.4038/tar.v21i4.3311 <em>TAR </em>2010; 21(3): 353-360

PENDEKATAN SISTEM 2D MODEL STREETER-PHELPS UNTUK MODEL POLUSI SUNGAI

Applications to positive 2D system can follow Steeter-Phelps model to river flow model. bymodifying the discrete values. mathematical model structure provided by the river flow at timestep t is proportional to the length of rivers and water velocity. The variables that influence isDissolved oxygen (DO) and Biological oxygen demand (BOD), both these variables arecalculated by balance considerations equetion with the screening process, the process ofreaeration, and the source of BOD established a mathematical model of positive 2D systems