Environmental Engineering Reference
In-Depth Information
Evaluation of Zn, Cu and Pb Sorption-Desorption
Phenomena in Kaolinite-Sand Media Filtration
Pilot Scale Installation
Paulo J. Ramísio and José M.P. Vieira
Introduction
A large number of heavy metals and organic micro pollutants in highway runoff
appear as a result from automobile traffic. Cu, Pb, Zn and Cd - sometimes Ni and
Cr - are considered the most important heavy metals associated with both mobile
and stationary sources
[1]
. These metals are either dissolved in the stormwater or
bound to particulates
[2, 3]
. Unlike organics and xenobiotic compounds, metal elements
are not degraded in the environment. As a consequence metal elements exert both
a short-term toxicity impact, characterized by concentration or activity, and a long-term
toxicity impact, characterized by mass accumulation
[4]
.
Previous studies of highway runoff have shown that Zn, Cd, Ni and Cu are
predominately dissolved; Pb and Cr are equally distributed between dissolved and
particulate-bound phases, while Fe and Al are predominately bound to particles
[4]
.
Strategies for highways runoff contaminants control, such as infiltration methods,
detention methods, vegetated filter strips and wetlands have been proposed.
Using infiltration ponds particles can be retained in pond bottom layers, but
dissolved heavy metals might contaminate aquifers. Even with detention ponds,
where particles could settle, small particles and dissolved heavy metals can contribute
to groundwater contamination.
A decision with regard to the effectiveness of filtration or sedimentation is
balanced by particle size gradation and density characteristics as well as loading
characteristics and specific site constraints.
Since filtration media are mainly designed for mechanical retention removal,
they only contribute to the removal of heavy metals in the particulate form. The use
of a reactive bed for the filter media will enhance the dissolved heavy metals
retention processes due to sorption and precipitation, transferring pollutants
P.J. Ramísio and J.M.P. Vieira
University of Minho, Portugal
