Bioregeneration of Activated Carbon in Biological Treatment - Activated Carbon for Water and Wastewater Treatment - page 204

consortium was isolated from the rhizosphere of Phragmitis communis in order to
colonize GAC and degrade the hardly biodegradable 4-chlorophenol (4-CP) that
was loaded on activated carbon [72]. A consortium of Pseudomonas strains was also
successfully employed for removing bioresistant surface-active substances from
activated carbon [25]. In another study, consortia of bacteria including Flavo-
bacterium sp. were able to degrade azo dyes by breaking azo bonds [76]. Accli-
mation of a mixed activated sludge to xenobiotics was also a very effective method
for the bioregeneration of activated carbons that were loaded with compounds
such as 2-CP and 2-NP [59, 65].
7.5.13
Substrate and Biomass Associated Products of Biodegradation
The quality of the BAC surface deteriorates during bioregeneration. This is
attributed to the adsorption of lyzed cells, slowly biodegradable substances, and
metabolites. Therefore, bioregeneration of activated carbon can hardly be a way of
avoiding the deterioriation of adsorbent quality, but bioregeneration can still
prolong the usage time of the adsorbent [54]. In any case, bioregeneration alone
will not be sufficient for the complete recovery of adsorption capacity [55].
In biological systems assisted by activated carbon, often a slime matrix including
decay products covers microorganisms and activated carbon. Figure 7.6 shows the
Scanning Electron Microscopy SEM images of activated carbon samples taken from
activated sludge reactors [16]. The slime is recognized as a bright white gelatinous
structure on the carbon surface.
Correspondingly, at high biomass concentrations (MLSS >2500mg L 1 )ina
PACT process, the carbon particles become trapped within the floc matrix, and the
carbon pores are closed [77]. The difficulty of desorption of microbial products and
the filling of pores with decay products of microbial cells are also mentioned in
other studies [5, 18, 55, 78].
In an offline bioregeneration study, in a GAC column the breakthrough perfor-
mance deteriorated gradually after each successive bioregeneration step, even in the
Figure 7.6 Scanning Electron Micrographs of slime matrix covering microorganisms and
carbon surface forming a bright white gelatinous structure [16].