Environmental Engineering Reference
In-Depth Information
Figure 9.6. Water balance at
crowborough pasture (average a mual
loads)
In terms of SEM concentrations, reflecting the qualitative aspect of the media disposed
on the farm, results are presented in Table 9.1. Pollution loads to the farm are calculated
based on the average annual SEM flow rates and the corresponding average
concentrations during the period of study.
The effluent and application limiting values (maximum permissible values) with
respect to South Africa, France, EU and USA are based on literature data (WRC 1997,
Degremont 1991), and the Zimbabwe limiting values are based on WWEDR (2000).
Comparing SEM concentrations with recommended criteria, values near or exceeding
the recommended criteria have been found with respect to Cd, Cr and Ni only. During
this study, nitrogen concentrations have been determined as nitrates only and the
comparison with the criteria shows the concentrations are lower than the recommended
values. However, if the TKN concentrations were to be considered, the total nitrogen load
would be much higher. A direct comparison of the results of this study with those
performed earlier (Chapter 8, Table 8.2) with respect to SEM metal concentrations, is
difficult because of the different units, but it shows the same trend of increased Ni
concentrations.
Table 9.1. Concentrations of various parameters in
SEM and application rates to Crowborough farm
during 2002-2003.
Pb
Fe
Cd
Cr
Zn
Cu
Ni
TP
NO
3
SEM concentrations (mg/l)
0.83
7.80
0.11 5.94
0.54 0.15 1.99 6.48 31.93
Effluent limit ZW
5.00
-
0.01 0.10
-
0.20
0.20
-
-
Effluent limit ZW
20.00
-
0.05 20.00
-
5.00
2.00
-
50.00
Effluent limit SA
2.00
20.00
0.05 1.0
5.0
5.00
2.00
-
30.00
Effluent limit France
5.00
5.00
0.01 0.10
2.00
0.20
0.20
-
-
