Environmental Engineering Reference
In-Depth Information
from the dissolved form to the media matrix. This will contribute to the control
of receiving waters (surface and groundwater) pollution due to highway runoff.
Therefore, the immobilization of dissolved metal complexes and particulate-bound
metal elements through reactive filtration mechanisms can induce the development
of an innovative “in situ” retention technique, characterized by high heavy metal
retention efficiency and simple operational procedures.
In developing an effective treatment practice, feasibility must be evaluated based
on characteristics of the runoff loading and the physicochemical mechanisms that
can be utilized given the site
[5]
. The development of an “in situ” retention technique,
applying current construction materials with low variability proprieties, could help
to develop a prototype technical solution for the reduction of heavy metal pollution
from highway runoff.
Experimental studies with different filter bed types have been developed at a
laboratorial scale: iron-oxide-coated sand, natural zeolites and granular activated
carbon
[3]
.
The use of minerals in the constitution of reactive filter bed may enhance the
feasibility of this technical effluent at a real scale installation. However, the behavior
of the immobilized heavy metals by desorption must be known, since by this way
the retained heavy metals can return to the dissolved form. Therefore, the heavy
metals desorption behavior is relevant.
Laboratory experiments are necessary in order to evaluate infiltration data
and sorption-desorption phenomena in a reactive-filtration pilot-scale installation.
A research program was developed to study those data and related processes and
phenomena. Previous work has reported the heavy metals partitioning, the hydraulic
behavior, physicochemical control parameters and the efficiency of dissolved heavy
metal removal involved in the dual-media reactive filter, with a sand and kaolinite
filter bed, over a 1 year experimental study
[6]
.
This paper reports Zn, Cu and Pb mass retention in the filter media layers and
the immobilized heavy metals behavior by desorption procedures.
Experimental Details
The experimental installation consists of two reservoirs and three equal diameter
cylindrical columns of transparent polyethylene. The layout of the installation is
depicted in Fig.
1
.
The inner diameter of the columns is 172 mm. The bottom structure was
constructed in order to allow a sliding movement at the end of the experiment.
Downstream head control was established by means of a weir in order to easy
measure the head loss through the filter media.
In each column, different adsorptive filtration beds with 70 cm height where
installed: a single sand medium in column C1; a dual media of 10% of kaolinite and
90% of sand in column C2; a dual media of 20% kaolinite and 80% sand in column
