Grantee Research Project Results

2000 Progress Report: Hydrodynamics of Initial Mixing Zones of Wastewater Discharges

EPA Grant Number: R826216
Title: Hydrodynamics of Initial Mixing Zones of Wastewater Discharges
Investigators: Roberts, Philip J.W.
Institution: Georgia Institute of Technology
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1997 through September 30, 2000
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
Project Amount: $277,643
RFA: Exploratory Research - Physics (1997) RFA Text | Recipients Lists
Research Category: Water , Air , Safer Chemicals , Land and Waste Management

Objective:

The objectives of this study are to obtain experimental data on the physics of turbulent mixing processes in buoyancy-modified flows typical of industrial and municipal wastewater discharges. The data consist primarily of laser-induced fluorescence (LIF) images that are converted to tracer concentration fields. The data will be used to refine the mathematical models of dilution and mixing zones used by EPA, and to test the hypothesis that the end of the initial hydrodynamic mixing zone is caused by turbulence collapse under the influence of gravity forces.

Progress Summary:

The system consists of laser beam scanners, a high-speed video camera, a computer for image acquisition, and a separate computer for system timing and control. The scanning system consists of two orthogonal galvanometer mirrors that are driven by an analog waveform supplied by a National Instruments data acquisition card in the control computer. This card controls the overall timing of the system by sending a synchronized digital signal to control the camera image exposure and image acquisition. The camera is a Dalsa CD-6, capable of up to 260 frames per second, each frame having a resolution of about 512 by 512 pixels. The original imaging computer had two Xeon processors and two Gigabytes of memory to which the images were written directly through a PCI-bus frame grabber made by BitFlow. During the past year, we designed and installed the optics to collimate the laser beam and have been integrating the system components. We have completed thorough testing and calibration of the system; the results of preliminary experiments on round buoyant jets were reported in Roberts and Tian (2000a). Because the entire two gigabytes (GB) of computer memory is not available for image storage, we were not able to record experiments of sufficient duration to obtain stable statistical averages of turbulent quantities. We could only acquire about 6,000 images, corresponding to about 23 seconds of data. To solve this problem, we took advantage of advances in computer technology that have occurred since the project began, and designed and specified a new computer system based on faster processing chips, PCI bus data rate, and SCSI hard drives. This system is now fully operational, and allows us to stream the images to hard discs (four in parallel) in real time. The system is controlled by Video Savant real-time-to-disc software. This is a significant advance, as we are no longer limited by the short duration of the memory-based system. This system was described in Roberts and Tian (2000b), and we are now preparing a longer journal article to describe it. We have developed the software (written in C++) to read and process the image files. This includes the capability to calibrate the pixel response as a function of beam sweep rate and amplitude, exposure time, dye concentration, etc., and to correct the images for laser attenuation to convert them to quantitative spatial tracer concentration fields, to extract time series information at any point, and to generate three-dimensional views and animations. We have thoroughly tested the experimental system and verified it by comparisons with several well-studied flows: a round turbulent jet in a stationary environment, and vertical round buoyant jets in stratified and unstratified crossflows. The system reproduces these previous results closely.

Future Activities:

The focus of the remaining project is to perform the experiments with the actual flows that are the main topic of this project. These include flow conditions typical of wastewater discharges into rivers, lakes, and coastal waters, including single and multiple jets and plumes into stationary and flowing, homogeneous and density-stratified flows.

Journal Articles:

No journal articles submitted with this report: View all 2 publications for this project

Supplemental Keywords:

water, toxics, discharge, mixing zone, mathematical models, dilution., Scientific Discipline, Water, Environmental Chemistry, Wastewater, Hydrology, Physics, municipal wastewater treatment, three dimensional model, estuaries, industrial wastewater, dilution, wastewater discharges, mathematical model, initial mixing zones, high speed imaging, discharge, National Pollutant Discharge Elimination System (NPDES), laser induced fluorescence, hydrodynamics

Relevant Websites:

http://www.water.ce.gatech.edu/Research/Mixing/movie.gif

Progress and Final Reports:

Original Abstract

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.