The innovative application of random packing material to enhance the hydraulic disinfection efficiency of small scale water systems
Date
2021
Authors
Baker, Jessica L., author
Venayagamoorthy, Subhas Karan, advisor
De Long, Susan K., advisor
Niemann, Jeffrey D., committee member
Leisz, Stephen J., committee member
Journal Title
Journal ISSN
Volume Title
Abstract
In a world where the quality of our water supplies is declining and our infrastructure is deteriorating, let alone the lack of available water in arid regions, the treatment of drinking water is becoming ever more challenging – especially for small scale systems that lack technical and financial support. The innovative application of random packing material (RPM) has been proposed as a possible tool to aid small water treatment systems (SWTSs) improve their disinfection contact systems in order to meet the Safe Drinking Water Act (SDWA) standards and provide the communities they serve with safe drinking water. While it has been demonstrated at the laboratory–scale that RPM can significantly improve the hydraulic disinfection efficiency of a contact basin in terms of baffling factor (BF) there was a lack of fundamental understanding of why RPM is so effective. Conceptually, the RPM slows and spreads the jet flow from a sharp inlet. Yet the mechanics of a jet flow through a highly porous material such as RPM is not well understood. Insight into the dynamics of such a flow is important in order to be able to use RPM in a manner that maximizes the benefits and minimizes the (unintended) drawbacks. The main aim of this dissertation is to use laboratory-scale experiments to study the mechanics of a turbulent jet flow from a long pipe through RPM and the impact on the hydraulic disinfection efficiency and final water quality for a disinfection contactor. There are three main objectives in this work: (1) To gain fundamental insights regarding turbulent jet flow through a highly porous media (such as RPM); (2) To address practical concerns for the application of the use of RPM in disinfection contactors; and (3) To provide guidance in terms of best practice for the innovative use of RPM to enhance hydraulic disinfection efficiency in SWTSs. The first part of this dissertation focuses on the resulting flow fields of a turbulent jet flow (5-20 gpm) through a wall of RPM of various thicknesses (L). An experiment was conducted in a flume using a Particle Image Velocimetry (PIV) system to map the flow fields downstream of the jet up to x⁄dj ≈ 30 (where dj is the diameter of the jet, i.e. inlet pipe). Once the PIV data were verified using a Laser-Doppler Anemometry (LDA) system and validated for a jet into an ambient (provided as a baseline), the velocity fields of the jet flow downstream of the walls of RPM were analyzed. A second order relationship was observed between the thickness of RPM and the spread of the flow. It was also observed that the jet velocities decay exponentially through RPM. With respect to flow rate, the spreading rate increased slightly, but there was a slight decrease in the decay of the jet as the flow rate increased. While the maximum velocities were reduced by over 90% after L ≈ 5dj, it was only after L ≈ 15dj that the flow downstream of the RPM was nearly uniform. Furthermore, the coefficients of drag showed a non-monotonic relationship with respect to the particle Reynolds number (Redp) that followed the well-established trend of a uniform flow around an infinitely long cylinder. This relationship provides valuable insight into the different regimes of the highly complex flow within and/or downstream of a highly porous material. Next, the potential improvement in the hydraulic disinfection efficiency and the possible energy loss as a result of the presence of random packing material in a laboratory-scale chlorine contactor were investigated. Tracer tests were conducted on a 55-gal drum tank filled with RPM in varying amounts in different configurations to measure the efficiency of each setup in terms of baffling factor. The bulk pressure drop was measured to determine the energy loss for each configuration. The results of this study show that securing RPM near the inlet, in any amount, improves the BF by 300% to more than 900%. The amount of RPM begins to have an impact at or above an inlet jet Reynolds number of 27,700. Also, changes in head loss due to the presence of RPM (in any amount, configuration, and/or flow rate) were generally considered to be negligible. Finally, a concern surrounding the potential for excessive biofilm growth is addressed through a long-term study. The inflow, outflow, and RPM were monitored for heterotrophic bacteria (via heterotrophic plate counts) and Pseudomonas aeruginosa as indicators of bacteriological water quality and the presence of biofilm. The results of this study show that there was no substantial biofilm growth in a lab-scale chlorine contactor and no substantial increase in bacterial counts for the bulk outflow over a 10-week period. Thus, the potential for excessive biofilm growth should not be considered a barrier concerning the use of RPM to improve the hydraulic disinfection efficiency of chlorine contactors in small drinking water treatment systems. Overall, this dissertation work aims to contribute a foundational understanding of turbulent jet flow through a highly porous material such as RPM as well as address some practical concerns for the innovative application of RPM to improve the hydraulic disinfection efficiency. From the results of the studies conducted, best practice guidelines have been developed to maximize the potential benefit of using RPM in disinfection contactors. Ultimately, the hope of this work is to promote the use of RPM to help SWTSs that are struggling to meet SDWA standards and to provide the communities they serve with safe drinking water.
Description
Rights Access
Subject
disinfection
random packing material
baffling factor
turbulent jet
energy loss