Chemistry Reference
In-Depth Information
3.2.2.5
Attachment and Growth of Microorganisms on the Surface of Activated Carbon
One of the most important features of activated carbon is that it also provides a vast
surface for attachment of microorganisms. The activated carbon surface contains
functional groups which enhance attachment of microorganisms. It also provides
shelter for microorganisms from fluid shear forces [20]. The enrichment of sub-
strates, nutrients, oxygen, and so on favors growth of microorganisms.
If sufficient time is allowed for immobilization of bacteria, a biofilm is formed
on the carbon surface as shown in Figure 3.6. Biofilm formation is particularly
pronounced in BAC reactors. To some extent also in suspended-growth systems
the PAC surface can be occupied by microorganisms.
3.2.2.6
Biological Regeneration (Bioregeneration) of Activated Carbon
In early studies, removal of inhibitory compounds and bioregeneration of activated
carbon were proposed as the two most important phenomena leading to the
synergism observed in integrated systems [21].
As shown in Figure 3.6, activated carbon may serve as a depot for pollutant
molecules. However, it is also probable that adsorbed molecules desorb out of
carbon upon the reversal of concentration gradient between carbon surface and
bulk medium. Upon desorption, the molecules may be removed by biological
action, a process known as bioregeneration. Also, microbial enzymes secreted
from microorganisms into carbon pores, can bring about the extracellular biode-
gradation of adsorbed organics and bioregeneration of activated carbon. Thus,
bioregeneration of activated carbon is based on the three fundamental processes,
adsorption, desorption, and biological removal. Conditions leading to bior-
egeneration of activated carbon are discussed in detail in Chapter 7.
3.2.3
Behavior and Removal of Substrates in Dependence of their Properties
The behavior of a substance in an integrated systemdepends on its biodegradability,
adsorbability, volatility, and inhibitory properties. A substrate present in a carbon-
biomass environment is often characterized by one or more properties (Table 3.3).
For example, phenol is an adsorbable, biodegradable, and semi-volatile substance. It
can be biodegraded at relatively low concentrations whereas it exerts self-inhibition
at high concentrations. Phenol may also exert an inhibitory effect on others.
3.3
Integration of Granular Activated Carbon (GAC) into Biological Wastewater
Treatment
3.3.1
Positioning of GAC Reactors in Wastewater Treatment
Figure 3.7 illustrates the options for the positioning of GAC adsorption in was-
tewater treatment. The GAC adsorption can be used as a stand-alone unit process
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