Environmental Engineering Reference
In-Depth Information
(0.51)
(0.36)
(0.55)
BOD
5
4.61
(7.35)
5.05
(10.65)
3.31
(5.3)
30[120]
Nitrates
1.93
(3.05)
5.8
(7.55)
3.75
(5.15)
3[10]
Total Nitrogen**
4.13
(7.1)
9.63
(12.75)
11.5
(37.6)
10[50]
(..)-Maximum measured values; [..]-Maximum permissible limit (high hazard)
*
The value is given as free and saline ammonia
**
Total Nitrogen = TKN+ Nitrates
4.4.3 Assessing surface water quality
The discussion regarding the river water quality status is based on the data presented in
Table 8.4. The critical parameters, exceeding the stipulated values in the acting
regulations, are TP and TKN. The average value of TP at the control point exceeds
significantly the safe value but is lower than the high hazard value. Contribution from the
farmland is significant at SW
3
, where the high hazard values have been exceeded. The
average TKN values are high at all three points, with a significant contribution from the
pasture, indicating that the high hazard prescribed concentrations for ammonia could be
significantly exceeded at SW
2
and SW
3
. The average and maximum Total Nitrogen
values at SW
2
and SW
3
exceed the safe limit, but are lower than the high hazard limit.
The average values of Ni, Cr
+6
and Pb at all points exceeded the safe limits, but only
Ni average concentrations exceeded the high hazard limits as well Cd average values
exceed up to four times the safe limit, but are lower than the high hazard value. The acute
toxicity threshold criterion for the protection of aquatic life of 0.002 mg Cd/l and 0.08 mg
Zn/l (Roy et al. 1998) has been exceeded more than ten times for both elements.
Earlier studies on the water quality of Marimba River (Mathuthu et al. 1997),
conveyed at the location of SW
1
, show concentrations of TKN ranging from 40 to50 mg/l
and ortho-phosphates ranging from 2 mg/l to 15 mg/l. Concentrations of Cd, Cr, Pb and
Ni varied from 0.002 mg/l to 0.07 mg/l, and Zn varied from 0.21 mg/l to 0.35 mg/l. The
comparison with the results of the present study indicates the same trend of high TKN
and P concentrations, while the concentration of heavy metals is considerably increased
regarding Pb, Ni and Zn.
5 CONCLUSIONS
The practice of sludge land application on pastures has a considerable treatment effect
with respect to the assimilation of organic pollution and nutrients. Also, it has the
advantage of providing a buffer capacity during periods of low irrigation water
requirements, thus the need of large storage requirements is avoided. However, the
present case study shows that due to the high hydraulic and pollution loads, the pasture
affects natural surface water quality adversely, and is a source of diffuse pollution to
surface water. TP and TKN contributions from the pasture were significant during the dry
