Environmental Engineering Reference
In-Depth Information
With respect to the impacts of long term irrigation with ponds effluent at the Imbwa
pasture, it could be mentioned that:
• The effluent quality was substandard, showing an inadequate functioning of the WSPS
and leading to high pollution loading. In addition, the irregular practice of irrigation
was observed with selected portions of the pasture irrigated more intensively,
compared to others, due to equipment breakdown.
• The major benefits of a 25-years period of irrigation with ponds effluent were the
enrichment of the soil with essential plant nutrients especially nitrogen, phosphorus
and potassium. It also raised the pH of naturally acid soils, thus reducing the need for
lime application and the risks of trace metal phyto-toxicity.
• The major drawback observed during this study was associated with the transport of
contaminants of wastewater-origin down the soil profile, resulting in elevated levels of
trace metals, nutrients and coli-form bacteria in the underlying groundwater. The
major pollutant constituents of concern were ammonia, ortho-P, Cr and Cd. With
respect to metals, FC and phosphorous, the contamination levels were lower,
compared to Crowborough farm, which was irrigated with an effluent and sludge
mixture.
• In order to prevent groundwater pollution in the future, the farm and treatment plant
management should consider the changed hydraulic loads due to the new treatment
plant of the town, together with rehabilitation of the WSPS, proper maintenance of the
irrigation system, adequate monitoring program and the enforcement of municipal by-
laws in terms of the prevention of discharges of high metals concentrations to the
sewer system.
Acknowledgements
- The authors would like to thank the management of the WREM
program, through the “Collaborative Program for Capacity Building in the Water Sector
in Zimbabwe and the Southern Africa Region”, jointly executed by the Civil Engineering
Department-UZ, IWSD and IHE-Delft, for the financial support offered during this study.
To the technical staff and the management of all laboratories involved - thanks for their
support and understanding.
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