Environmental Engineering Reference
In-Depth Information
5
E. coli
Intestinal enterococci
Sulfite-reducing clostridia
Somatic coliphages
F-specific RNA coliphages
4
3
2
Inlet
Outlet
Fig. 2
Event mean concentrations (log-values) of three different indicator bacteria and two types
of coliphages. Median concentrations for the three storm events are given with min and max in
error bars
The stormwater pond reduced heavy metals as well as organic contaminants, and
may therefore act as a barrier to prevent the receiving water from chemical con-
taminants associated with stormwater discharges.
The microbial concentrations, measured at the inlet and outlet of the Järnbrott
stormwater pond are shown in Fig.
2
. Results for the indicator bacteria show that
E. coli
, intestinal enterococci and sulphite-reducing clostridia were detected at dif-
ferent levels, with
E. coli
levels more than 1 log-unit higher than the others.
Comparing concentrations from inlet and outlet samples, the results indicate that
the pond did not significantly reduce faecal bacteria. Results for the bacteriophages,
measured at two events in the pond, instead exhibited an increase in concentrations
from the inlet to the outlet, including a source term in the pond. Comparing inlet
and outlet concentrations for the separate events indicated variations between the
events, especially for the F-specific coliphages. For one event these were slightly
reduced while in the other event a high increase in concentration was observed
comparing inlet to outlet of the pond.
Removal Efficiencies
The site mean concentrations of the various contaminants, together with the
removal efficiency (%), are calculated for the three storm events (Table
2
). The
Järnbrott stormwater pond effectively reduced suspended solids (62% and 52% for
