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The use of impulse response tracer experiments in horizontal subsurface flow constructed wetland development

A research proposal submitted to the Faculty of Engineering and the
Built Environment, University of the Witwatersrand, in fulfillment of
the requirements for the degree of Master of Science in Engineering.
Johannesburg, 2016 / In the past three decades there has been an increased interest in constructed wetlands
(CW) and their effectiveness in treating water. The hydraulic efficiency of a CW can
be determined by using chemical reactor theory to develop residence time distribution
(RTD) parameters such as effective volume (Veff), normalized variance (σ2) and mean
residence time (τm). Five experiments were conducted to study the effects on these
RTD parameters in a CW by using a glass pilot-scale laboratory rig and varying the
inlet-outlet positions. The rig made use of a glass tank 250x250x500mm filled with
clear superabsorbent polymer balls as a packing. The clear tank and balls made it
possible for the flow to be observed when a FWT red impulse tracer dye was inserted
into the system. The flow was photographed at specific time intervals for visual
analysis and comparison. . The visual results showed the formation of a hull-shaped
velocity profile in all the experiments. The RTD was obtained by collecting tracer
samples at specific outlet positions during the course of each experiment. The five
inlet-outlet configurations RTD parameters results showed; a straight flow path from a
single inlet to outlet yielded the lease desirable hydraulic performance with dead
volumes contributing to up to 67% of the CW. An increase in the number of outlets
and changing the direction of flow diagonally showed up to a 96% improvement to the
effective volume of the system could be achieved when compared with single inline
inlet-outlet flow. The best result was achieved by combining the visual and RTD data
to make changes to the rigs geometry in order to eliminate dead zones and yielded up
to a 148% improvement in the effective volume of the system when compared with
single inline inlet-outlet flow. A well designed CW with respect to inlet-outlet position
can result in reduced land requirements and construction costs by minimizing the dead
volume and improving hydraulic efficiency. / MT2016
Date January 2016
CreatorsPieters, Werner
Source SetsSouth African National ETD Portal
Detected LanguageEnglish
FormatOnline resource (58 leaves), application/pdf, application/pdf

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