Generalities
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from the sludge. Sludge is recycled to the aeration tank to maintain a sufficient concentration
of purifying bacteria (Rejsek, 2002).
According to the National sanitation office, biological wastewater treatment using activated
sludge is the most widely used treatment in Algeria.
The advantages and disadvantages of activated sludge are summarized in the following table
Below.
Table 7: Advantages and disadvantages of activated sludge (Grosclaude, 1999).
 Fixed culture
Fixed culture biological treatment is based on contact between wastewater and purifying
biomass fixed on a mineral or synthetic support. We can distinguish :
• Bacterial beds
This process consists of attaching a bacterial culture to a substrate such as crushed stone,
pozzolan (volcanic sand) or plastic. The bacterial film developed on the substrate surfaces
forms a biofilm that degrades organic matter (Abouzlam, 2006).
Process
Advantages
Disadvantages
Activated sludge
- Suitable for all community sizes (except
very small ones).
- Good elimination of all pollution
parameters (SS, COD, BOD5, by nitrification
and denitrification).
- Suitable for protecting sensitive
receiving environments.
- Slightly stabilized sludge.
- Easy to implement simultaneous
simultaneous dephosphatization.
-Substantial investment costs.
- High energy consumption.
-Need for qualified personnel and regular
monitoring.
- Sensitivity to hydraulic overloads.
- Sludge settleability not always easy to control.
- High sludge production must be concentrated.