Environmental Engineering Reference
In-Depth Information
season mainly, and were very high with respect to SW
3
only, while the contribution of
nitrates was significant during all seasons, and was more pronounced at SW
2
. significant
contribution from the pasture was found only with respect to Ni at both points and is
attributed to the very high application rates. Seasonal variations for the three points show
a significant increase during the beginning of the wet season for Ni, Pb and Cd, which
could be associated with diffuse pollution from runoff upstream the study area. The
average measured concentrations of the Marimba River water quality at the three points
exceed the safe regulation limits regarding all parameters, but the TP vales exceed the
high hazard regulated limit at SW
3
, indicating a serious level of pollution.
With respect to the general practice of sewage sludge application on land, it could be
recommended that:
1. Hydraulic, nutrients and metal loading rates should not exceed the recommended
criteria for long-term application and should be based on projections with respect to a
future increase in the number of the population served. They should be based on a
thorough investigation of the soil and ground water characteristics at the designated
site.
2. Engineering measures to protect surface runoff from the area or direct leak (in the case
of wet applications) should be provided, in order to protect surface water pollution.
3. The design and the operation of the wastewater treatment plant and the sludge disposal
site should be conveyed in a systematic way, considering that the quantity and quality
of the sludge produced, as the output of the treatment process, would be the input to
the disposal site and would determine its effective operation.
4. A continuous and regular monitoring program to control surface and ground water
quality and soil characteristics should be applied, in order to provide public health and
environmental protection.
Acknowledgements
- SIDA/SAREC Water Project (grant SR15/98) provided the funding
for this study. The author would like to thank the sponsors for the financial support
offered, the City of Harare authorities for providing information and access to the study
area, and the technical staff of the Department of Civil Engineering and the Department
of Chemistry, University of Zimbabwe, for their constant support during the sample
collection and analysis process.
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AQUASTAT 2003 FAO's Information System on Water and Agriculture at
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