Experiments on density currents dynamics over conic roughness elements

Density currents are flows driven by density differences caused by suspended fine solid material, dissolved contents, temperature gradient or a combination of them. Reservoir sedimentation is often related to sediment transport by density currents. This sedimentation can block bottom outlets, reduce the capacity of reservoir and harms the dam power plants. The head is the leading edge of density currents. In this paper, the influences of artificially roughened beds on dynamics of the frontal region of density currents are investigated experimentally. Three rough beds using conic roughness elements and a smooth bed were tested. The observed trend is that as the surface roughness increases the head concentration and velocity decreases

The influence of roughness on the propagation of density currents

Density currents occur when fluid of one density propagates along a horizontal boundary into fluid of a different density. They are also called turbidity currents when the main driving mechanism is from suspended sediments. Reservoir sedimentation is often related to sediment transport by turbidity currents. The leading edge of a density current is deeper than the following current and is called head or front. In this paper, the effects of bed roughness on density currents propagation were studied. Experiments were carried out over a smooth bed as well as three artificially roughened beds by cylindrical roughness elements. Temporal and spatial evolutions of the current front were analyzed. In experiments performed over rough beds, the measured head velocities were smaller than that of smooth bed. The observed trend is that as the surface roughness increases the front velocity decreases

Two-dimensional simulation of nitrate transport in an agriculture-intensive region

A two-dimensional steady-state solute transport model is developed to simulate movement of non-point sources of pollution in anisotropic porous media. The migration of chemicals dissolved in groundwater is governed by advective-dispersive processes which are also affected by the velocity of the flowing groundwater. Therefore, groundwater flow equation is solved for hydraulic gradient and hydraulic conductivity to approximate the average linear velocity of the fluid. The advection-dispersion is used to approximate the spatial and temporal distribution of non-reactive dissolved chemical in a flowing groundwater. A computer code is developed in MATLAB to solve the groundwater flow and solute transports equations by finite difference methods. The developed program is verified with soil-tank experimental data. The solute transport model is used to simulate non-point source of nitrate pollution in an agriculture-intensive region. Finally, the model outputs are analyzed to understand the factors that influence the pollution transport in the study area

Experimental investigation on density currents propagating over smooth and rough beds

Density currents occur when fluid of one density propagates along a horizontal boundary into fluid of a different density. They are also called turbidity currents when the main driving mechanism is from suspended sediments. Reservoir sedimentation is often related to sediment transport by turbidity currents. The leading edge of a density current is deeper than the following current and is called head or front. In this paper, the effects of bed roughness on density currents propagation were studied. Experiments were carried out over a smooth bed as well as three artificially roughened beds by cylindrical roughness elements. Temporal and spatial evolutions of the current front were analyzed. In experiments performed over rough beds, the measured head velocities were smaller than that of smooth bed. The observed trend is that as the surface roughness increases the front velocity decreases

Density currents dynamics over rough beds

Density currents are flows driven by density differences caused by suspended fine solid material, dissolved contents, temperature gradient or a combination of them. Reservoir sedimentation is often related to sediment transport by density currents. This sedimentation can block bottom outlets, reduce the capacity of reservoir and harms the dam power plants. The head is the leading edge of density currents. In this paper, the influences of artificially roughened beds on dynamics of the frontal region of density currents are investigated experimentally. Three rough beds using conic roughness elements and a smooth bed were tested. The observed trend is that as the surface roughness increases the head concentration and velocity decreases

Design of a compact and effective greywater treatment system in Malaysia

Water shortage has been one of the major concerns faced by about 2.7 billion people around the world due to several factors, including water pollution, climatic change, etc. Several nations have been seeking practical alternatives to address this issue and one of the most pragmatic approaches is the development and implementation of greywater treatment systems. To date, a great assortment of greywater treatment systems have been developed. The current study presents a different water treatment system to treat residential, commercial and industrial greywater in Malaysia. Unlike most existing systems which involve separate steps of treatment, the proposed method integrates aeration, disinfection and membrane filtration in a compact reactor, which could potentially reduce the operational cost, space and equipment. Aeration is required to promote pollutant degradation by aerobic microorganisms, while disinfection (UV) is needed to eliminate pathogenic bacteria. Subsequently, membrane filtration is used to remove suspended and dissolved pollutants of which are relatively smaller in size. The results have proven that the proposed system is effective in improving the quality of greywater, in which, the parameters (BOD, turbidity, total suspended solids, TDS, pH, DO) are reported to be in good agreement with the standards. While this study is conducted in a laboratory environment, its excellent results suggest that the proposed system is potentially practical for commercial use in future. © 2019 Desalination Publications. All rights reserved

Temporal and spatial variation of grey water (sullage) properties from commercial and residential catchments

Water pollution has been one of the major concerns in Malaysia and its increasing severity impacts negatively on the sustainability of water resources. It limits the total water availability dramatically due to the exorbitant cost for treating polluted waters and in some cases, polluted waters are not treatable for consumption. Grey water (sullage) is one of the important sources of pollution, which is released from residential and commercial premises into the rivers without prior treatment. Before initiating measures into developing or implementing grey water reuse and treatment systems, it is more appropriate to conduct a detailed study on the discharged grey water quality and characteristics. The present research studies the chemical, biological and physical characteristics of grey water released from residential and commercial premises near the Melana River, which is located at Skudai, Johor, Malaysia. The variations in parameters, namely, BOD, COD, pH and turbidity, with respect to different days and times (temporal) as well as different sampling sites (spatial) are investigated. The results reveal that grey water quality and characteristics are almost similar to those taken from literature and suggest that the treatment of grey water is necessary for intended reuse purposes

Operational parameters effects on photocatalytic reactors of wastewater pollutant: a review

This study presents the operational parameters effects on photocatalytic degradation of liquid pollutants using titanium dioxide. Organic pollutants photodegradation is the most widely studied method, where photocatalysis is observed in many forms. Due to the cost efficiency of titanium dioxide as a photocatalyst, it has a greater role in this process as compared to other semiconductors. The operating parameters effects on photocatalytic degradation in wastewater pollutant using titanium dioxide based photocatalyst are presented in this paper. The findings are used to identify and explain the individual influence of different parameters, such as the photocatalyst composition, catalyst loading, initial pH, pollutant concentration, light intensity and temperature, on wastewater pollutants photocatalytic degradation. The successful application of laboratory scale techniques and the choice of treatment are generally dependent on the wastewater composition, however, much research is needed from the aspects of modelling and engineering design for a large scale operation. Besides that, a general overview of a prevailing trend in the use of titanium dioxide photocatalyst is presented with the emphasis placed on its achievements and problems