Environmental Engineering Reference
In-Depth Information
relatively low organic loading, the amount of biogas released in this type of ponds is not
substantial.
Maturation ponds have the primary function to provide adequate conditions for the
pathogen removal process. The mechanism of this process is not fully understood, but
empirical data shows that stabilization ponds have high pathogens' removal efficiency,
much higher compared to conventional treatment systems. This is associated with the
long retention time, with the bactericide effect of the ultraviolet rays in the sunlight and
with the higher values of pH due to algae activity. The design of M ponds is based on
empirical equations, which assume a first order kinetic reaction to describe the removal
of fecal coliforms, where the kinetic rate constant is determined based on empirical data
and the retention time and temperature would determine the removal effect. The
equations consider the retention time and removal effects at the previous treatment stages
in AP and F ponds.
During the design process, the configuration, size, treatment efficiency and the layout
of the ponds on the specific terrain, are determined. Another important consideration
during this phase is to provide proper hydraulic conditions in the pond, in order to
achieve a full use of the available volumes and avoid short-circuits of the flow in the
pond. The latter could happen due to the improper design of the inlet and outlet facilities,
due to high volumes of sludge accumulation, as well as irregular sludge deposition
patterns. Short-circuiting leads to a considerable reduction of the actual retention time,
compared to the originally anticipated one during the process of design, thus leading to
much lower treatment efficiency than the anticipated ones. It could be avoided by a
proper design of inlet and outlet facilities to each pond, together with adequate
geometrical proportions of the ponds layout. In some cases, the provision of baffles in F
and M ponds could improve the ponds hydraulics.
2.3
Operation and maintenance requirements
It has already been emphasized, that one of the major advantages of WSPS is the easiness
of operation. It does not require high skills personnel, there is no mechanical equipment,
or it is limited to screening and pumping facilities. An energy input would be required
only for pumping purposes, and if the topography allows, could be avoided by careful
design and the provision of gravity flow throughout the system. All these make them a
very attractive treatment alternative for developing countries and for population centers
or institutional/industrial centers in remote areas. Unfortunately, in many cases of
application of WSPS in the region, they have been completely neglected, resulting in a
very poor effluent quality. One example of such a case is described in Chapter 11. It
should be well understood by the managing authorities that the easiness of operation does
not mean lack of operation. A good operation and maintenance practice could achieve a
long life of the treatment facility, during which effluent with a good quality could be
provided. It should be remembered that if the ponds effluent would be used for irrigation,
a high level of operation and maintenance should be provided in order to maintain a high
and reliable quality of the effluents.
The most common WSPS operation requirements are:
• Regular desludging in order to provide for the minimum retention time of the
wastewater in the pond;
