Environmental Engineering Reference
In-Depth Information
and industrial wastewater is treated together, or in cases of purely industrial wastewater, a
more cautious approach should be applied in terms of its beneficial reuse. Such
applications would require a special investigation of the effluent quality and a
corresponding choice of beneficial reuse, which would not lead to environmental or
public health hazards.
A wise approach to water resources exploitation and a water demand orientated
practice is an international trend followed in developed and in developing countries, but it
is of highest priority and importance in countries where water resources are limited.
Thus, considering wastewater reuse as an alternative source of water in general, and the
specific case of ponds effluents reuse, are of significant importance for the water
resources management practice in the region, especially considering the fact that the
beneficial reuse of such effluents is not widely applied. This Chapter aims to help in this
direction by:
• Presenting the most common design and operational aspects of WSPS, which would
ensure a safe effluent quality, appropriate for further beneficial use;
• Revising guidelines and criteria for safe irrigation practice in cases of different types of
agricultural applications, as well as regulatory aspects of such practice;
• Discussing the impacts on soils and ground water by presenting a specific case study of
long-termirrigation of pastures with ponds effluent in Chitungwiza, Harare.
2 WASTE STABILIZATION PONDS - DESIGN AND OPERATION
2.1
Waste stabilization pond systems
Conventional sewage treatment systems, discussed in Chapter 8, are designed to speed up
the process of natural aeration and bio-oxidation of organic material by forced aeration.
They require a constant and usually high input of energy together with regular
maintenance in order to achieve the required reduction of organic pollution, suspended
material, nutrients and pathogens. In contrast, WSPS provides a cheap and easy to
maintain alternative, which has considerable advantages especially when a high level of
removal of organic material and nutrients is not required, as it is the case of beneficial
reuse of the effluent. Another specific advantage of WSPS is their significant buffer
capacity with respect to shock hydraulic, organic and metal loads. This means that the
quality of the effluent would not be affected adversely due to such loads, but they will be
absorbed in the system, due to the long retention time. The disadvantages of the
application of WSPS could be summarized as follows:
• Large area requirement, correspondingly the land to place the treatment plant should be
available and the cost should not be prohibitive;
• Release of malodors to the vicinity and possible breeding site for insects and
mosquitoes;
• Possible pollution of ground water, in cases where the water table is high;
• Last but not least - high evaporation rates leading to a considerable loss of the volume
of water available for reuse.
