MASTER'S THESIS - SuSanA

4 Presentation of technologies for rural areas
Aerated ponds are open aerated reactors and used for wastewater treatment after mechanical pretreatment.
Wastewater is mixed for aeration and suspension of the organisms to allow deeper ponds and
higher organic load. Therefore, they need less area than WSP, but constant electricity supply.
Advantages of aerated ponds are the good resistance against shock loading and high pathogen removal,
while disadvantages are the still large area demand, the electricity demand and the need of secondary
treatment or appropriate discharge of the effluent (Tilley et al. 2008).
Aquacultural ponds (see Figure 4.11) refer to „controlled cultivation of aquatic plants and animals“ (Tilley et
al. 2008). Fish eat algae that grow in the nutrient rich water and therefore cleaning of the wastewater takes
place. Floating plant (macrophyte) ponds (see Figure 4.12) have floating plants that can eliminate the
nutrients from the wastewater while roots provide settling surface for bacteria that degrades the organic
load of the wastewater. In both types of ponds, the sludge settles down to the ground and has to be
removed regularly. Both solutions can be built with local materials, but require a large area. The floating
plant pond also requires trained staff for operation (Tilley et al. 2008).
Figure 4.11: Aquaculture pond (Tilley et al. 2008) Figure 4.12: Floating plant pond (Tilley et al. 2008)
According to (Choukr-Allah 2011), ponds are used especially in Europe for smaller rural communities (up to
2.000 PE, but also bigger systems are existing) and in warmer climates (the Middle East, Africa, Asia, and
Latin America) even for larger population up to 1 million people.
(Nowak 2011,a) gives average values of the area demand for ponds with 10 – 15 m²/PE for biological
treatment.
4.3.4.2 Oxidation ditch
An oxidation ditch consists of a ring shaped channel, equipped with mechanical aeration devices, and is
used for treatment of pre-treated wastewater (see Figure 4.13, p. 38). Compared with the aerobic pond,
this system uses less area but requires more electricity and more complex O&M. Technology can be used for
up to 20,000 PE. BOD removal ranges between 85 and 95 % (Wehrle et al. 2007).
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