Environmental Engineering Reference
In-Depth Information
Table 9.7
Classification of anaerobic systems for wastewater treatment.
Anaerobic system
Type of reactors
Anaerobic suspended growth
• Complete mix reactor
• Anaerobic contact process
• Anaerobic sequencing batch reactor
Anaerobic sludge blanket
• Up-flow sludge blanket reactor
• Anaerobic baffled reactor
• Anaerobic migrating blanket reactor
Attached growth
• Up-flow packed bed attached growth reactor
• Up-flow attached growth anaerobic expanded bed reactor
• Attached growth anaerobic fluidized bed reactor
• Down-flow attached growth
Other systems
• Covered anaerobic lagoons
• Membrane separation anaerobic treatment
Adapted from Tchobanoglous et al., 2004.
Attached growth processes.
●
Other systems.
●
Each system in this classification contains several types of reactors, which are listed in
Table 9.7. Only a few of the most important reactors will be described in this section, so read-
ers with interest in learning about the rest of the technologies can consult specialized literature
in wastewater treatment, such as Tchobanoglous et al. (2004).
Complete mix reactor
Complete mix reactors are basically a tank with some type of mixing system such as propel-
lers, gas injection, or pumps. They are suitable for waste streams with high content of solids
or when dissolved solids make the wastewater viscous (Tchobanoglous et al., 2004).
In complete mix reactors, wastewater is fed at the bottom of the tank and the liquid outlet
located at the top discharges treated water to a settling tank. After sedimentation, the liquid
from the surface is sent to a polishing step (if needed) and the sludge that precipitated to the
bottom is recycled into the complete mix reactor (Fig. 9.7A).
Up-flow anaerobic sludge blanket reactor
The up-flow reactor is the most common among the anaerobic sludge blanket (UASB) reactor.
Its operation is based on the fact that microorganisms form agglomerates (sludge blanket) that
rise to a certain point in the reactor. Wastewater is fed at the bottom of the tank and flows up
going through the sludge and as a result microorganisms degrade the organic matter and the
clarified treated liquid exits at the top of the tank (Fig. 9.7B). A minimal feeding velocity is
needed to have the sludge suspended. Gas bubbles produced during the digestion rise though the
sludge and promote mixing, thus eliminating the need for mechanical stirring. Gas is then col-
lected on top of the reactor by a conical collecting dome (Henze et al., 2008).
Up-flow (or down-flow) packed bed attached growth reactor
This type of reactors, also known as “anaerobic filter process,” uses some type of support
(e.g., rocks or plastic packing) to allow the microbial attachment. It is best suited for the
treatment of wastewater with solubilized organic matter instead of effluents with particles in
suspension (Fig. 9.7C) (Miyamoto, 1997).
