Environmental Engineering Reference
In-Depth Information
Table 2
Site mean concentrations (SMC) and removal eficiency in the stormwater
pond for selected contaminants during the analyzed storm events, fall 2004
SMC
SMC
Removal
Parameters
In
Out
(%)
Suspended matter
TSS (mg/L)
47
18
62
VSS (mg/L)
19.1
9.3
52
Nutrients
NO2-N (mg/L)
0.02
0.03
−65
NO3-N (mg/L)
0.90
2.39
−164
NH3-N (mg/L)
0.18
0.16
12
Tot-N (mg/L)
2.05
3.39
−66
PO4-P (mg/L)
0.06
0.07
−15
Tot-P (mg/L)
0.14
0,10
29
Indicator organisms
E. coli
(CFU/100 mL)
7,240
7,100
2.0
Tot coliforms (CFU/100 mL)
60,000
54,300
9.4
SRC (CFU/100 mL)
295
251
15
SC (CFU/100 mL)
229
574
−151
F-RNA (CFU/100 mL)
204
499
−145
IE (CFU/100 mL)
749
691
7.8
Heavy metals
Cd (µg/L)
0.30
0.23
24
Cu (µg/L)
41.4
24.3
41
Pb (µg/L)
9.16
4.67
49
Zn (µg/L)
143
91.3
36
PAH
16 USEPA PAH
a
(µg/L)
0.94
0.31
67
a
Method from the US-EPA
[12]
.
TSS and VSS respectively), as well as heavy metals (~25-50%). On the other hand,
the reduction was weak for the nutrients and the indicator microorganisms.
An increase of the contaminant concentrations in the outflow was observed for
nitrite and nitrate, as well as for nitrogen as a total. For the indicator organisms,
a removal was observed for the bacteria while an increase was observed for the
bacteriophages.
Present results are in sharp contrast to a study performed in another Swedish
stormwater pond, Flemingsberg, where a removal of faecal coliforms and entero-
cocci were observed in the range of 97-99.9%. In the same study somatic coliphages
were removed to around 70%. The high removal of microbial organisms in that
pond was explained with the reduction of suspended solids being the main factor
for the bacterial reduction
[7]
.
Factors affecting the removal efficiency in the pond include physical sedimenta-
tion, die-off, accumulation and resuspension of the microorganisms. Indicator
bacteria as well as bacteriophages may settle in the pond during low flow condi-
tions and re-enter into the water phase later on as a result of high stormwater
