Environmental Engineering Reference
In-Depth Information
concentrations, compared to wastewater, the last two types could be recommended for
application.
Figure 2.4. Schematic presentation of a
dual-purpose basin.
Figure 2.5. A scheme representing
facultative pond reactions.
Facultative ponds have the purpose to remove solids by sedimentation, and organic
material by biological degradation. The major processes, taking place in a facultative
pond are shown in Figure 2.5.
Two distinct zones might be differentiated in a facultative pond - anaerobic zone,
close to the bottom, and aerobic zone in the rest of the pond volume. The aerobic zone is
of variable depth, depending on the volume of accumulated sediments, organic load,
wind direction and algae concentrations. The zone at mid-depth, where both anaerobic
and aerobic conditions might occur, is known as “facultative zone”, and microorganisms
in this zone are facultative - they can adjust and survive in both, aerobic and anaerobic
conditions. It should be noted that the different zones are not well defined and change
constantly in terms of depth variation. In addition, considerable interaction exists
between the different zones in terms of products and materials released. The
