Résumé
|
The
impermeable area and the
peak discharge volume have been consistently increasing due to widening
of city
development and renewal. Thus, distortion of water cycle has been
serious problem
compared to the past. When it comes to NPS pollution, lack of
information on the
load and characteristics of pollutants led to the insufficient
reduction measures.
The purpose of this study is to investigate the effectiveness of
filters to control
micro particles from non-point sources, especially from road runoff and
Combined
Sewer Overflows (CSOs). The study first examined the particle size and
characteristics
of NPS pollutants, and then analyzed the head loss, treatment
efficiency and changes
in particle size distribution before and after the treatment using
device type facilities.
The four most commonly used filters - Expanded Polypropylene (EPP),
Expanded polystyrene
(EPS), and Perlite as floatability filtering materials, and Zeolite as
non-floatability
- were compared. The upward-type filtering equipment was manufactured
for the lab
experiment, and CFD modeling was conducted to identify optimized design
parameters.
The results showed that the ratio of micro particles (<100
µm), to which the
filtering process can be applied, was highest in samples from the road
runoff, followed
by one from the bridge, and from the parking lot. The results using
road runoff
displayed that EPP was most efficient with ratio of 89% to treat SS and
COD. The
removal rate of EPP for Zn and Cu was also high over 80%, which is 7 ~
40% higher
than those of other filters tested. The continuous filtering period
calculated was
again longest for EPP to reach 163 days. The calculated filtering
period for CSOs
was apparently shorter than that for road runoff, due to the hydraulic
loading and
SS quantity. The filters compared were not efficient to removeTN and TP
in CSOs.
The results from the numerical analysis for the particles over 100
µm, to which
the gravity sedimentation can be applied, showed that sedimentation
efficiency can
be improved by controlling the inflow velocity through the utilization
of the bent
pipe or baffle wall. The operation and management can be also easier by
placing
appropriate facilities such as manhole at the sedimentation point This
study suggested
the best filtration material to treat NPS pollutants tested by road
runoff and CSOs
samples. The experimental results shown in this study and following
discussions
may act as base information for proper design and operating parameters
of the filtering
facilities to control NPS pollutants.
|
