Publication: Stormwater quality improvement by a porous pavement
Loading...
Date
2020-05-01
Authors
Makhtar, Salwa Mohd Zaini
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Increasing quantity and decreasing quality of stormwater runoff is natural but
problematic consequences of urbanization. In addressing the issue, the porous
pavement usage with modular installation system has been the new alternative being
experimented instead of the traditional impervious asphalt and concrete pavers. It
allows for reduction in surface runoff quantity while lowering the concentration of
hazardous stormwater pollutants, including the heavy metals, in the infiltrate. The
effectiveness of porous pavement in eliminating dangerous pollutants depends upon
the media materials used which are expected to capture most of the heavy metals. This
research examined the potentials of an invented surface fill arrangement to be used in
conjunction with the hexagonal modular system where the media tested consists of
granular activated carbon (GAC), sand and zeolite. The three paver materials were of
uniform gradations, respectively with hydraulic conductivity values of 0.052 cm/s,
0.064 cm/s and 0.068 cm/s, which can be considered as medium ranged. The batch
study was carried out to determine the adsorption capacity of each medium in reducing
the heavy metal impacts of lead (Pb), copper (Cu), cadmium (Cd) and zinc (Zn) in the
influent. The adsorption isotherms of GAC, sand and zeolite towards Pb, Cu, Cd and
Zn was found to follow the Langmuir model, the Langmuir adsorption capacities were
noticed respecting the order of Pb > Cu > Cd > Zn, while the adsorption kinetics on all
of the paver materials obeyed the Pseudo-Second Order model. Next, the Mixture
Simplex Lattice Design was used in the column study to determine the optimized usage
of the media in removing the heavy metals. The resulting optimum bed heights of 5
cm, 5 cm and 0 cm respectively for the GAC, sand and zeolite, corroborated with the
outcome of employing the optimization function, thus validating the reliability of the
given arrangement. The column study also gave percentage removals of 99 %, 88 %,
98 % 84 % for the Pb, Cu, Cd and Zn respectively. The concern for loss of efficiency
due to clogging was addressed by tests carried out on a hexagonal modular unit with 5
cm thick GAC positioned at the top, followed by 5 cm thick sand at the bottom.
Generally, the clogging agent was found trapped only on the mesh because of the sizes
of some of the material being larger than the size of mesh opening, while the voids of
the media material were found to be not of a major effect in this respect. With the GAC
and sand layers combined, the hydraulic conductivity was determined to be 0.097 cm/s
and this k value can be considered low for the purpose. Modelling using CFD ANSYS
FLUENT software and visualizing the changes in the hexagonal module filled with
GAC and sand of 5 cm thickness each resulted in a flow velocity of 3.5 x 10-5 m/s
while a physical experiment on the fixed filter bed media consisting of the two
materials gave an unsaturated velocity of 3.08 x 10-5 m/s. The 12 % difference between
the experimental and simulated velocities was considered acceptable. The results
showed that GAC and sand can be used as the media for the modular paver system that
treats stormwater for heavy metals contamination while serving as a practical porous
pavement alternative.