Environmental Engineering Reference
In-Depth Information
Figure 3.2. Manyame basin schematic
map with water and wastewater
treatment plants.
data regarding the corresponding water qualities. The availability of data regarding the
quality of different types of water fluxes in the basin - natural water, storm water,
effluents and potable water, should support the decision - making process, and should be
the basis of optimal and cost-effective measures in order to provide for the development
of the city and surrounding areas, in a safe and well-protected environment.
Earlier studies (Moyo 1997) show that the Lake Chivero is at an advanced stage of
eutrophication. Typical signs of enhanced eutrophication, such as algae and other water
aquatic vegetation blooms, are visible. Enhanced eutrophication results in periodical
depletion of the dissolved oxygen of the lake's water and a general change of the
environmental habitat. Several occurrences of massive fish deaths have been experienced
during the last 30 years.
An additional effect of the lake's eutrophication is related to the increased operational
and maintenance cost of the treatment of water for potable purposes, especially in dry
years, when the water level in the lake subsides. The increase in the suspended solids
concentration of the water, resulting from increased algae concentrations, necessitates a
higher dosage rate of chemicals to be added, increases the WASHING frequency of the
rapid sand filters, leading to increased electricity costs. During the treatment process the
volumes of sludge and backwash water are increased considerably, thus leading to an
increase in the cost of their conveyance and treatment. Also, a specific earthy taste is
