Bioregeneration of Activated Carbon in Biological Treatment - Activated Carbon for Water and Wastewater Treatment - page 224

could be maximized, ensuring that biodegradation began as soon as possible after
startup. Putz and co-workers suggested that modeling becomes much simpler by
considering only equilibrium situations in BAC columns compared to kinetic
models [56]. Equilibrium conditions reflect the steady-state situation, whereas
kinetic models also consider non-steady conditions, which makes modeling more
complex. The BASM model helped to determine in which cases it was possible to
benefit from employing simultaneous biodegradation and adsorption rather than
solely adsorption by applying several hundreds of hypothetical scenarios.
Speitel and co-workers also developed a kinetic model called the Multiple-
Component Biofilm Diffusion Biodegradation and Adsorption model (MDBA),
which described both adsorption and biodegradation in multicomponent GAC
columns [97]. The MDBA model combined the single component adsorption and
biodegradation model developed by the same group [64] with the Ideal Adsorbed
Solution Theory (IAST). Details of the IAST are presented in Chapter 2. The
MDBA model adjusted the IAST equation by using a correction factor to account
for differences between predicted and measured equilibrium concentrations,
assumed homogeneous surface diffusion inside activated carbon considering that
pore diffusion was insignificant, and assumed that biodegradation of multi-
components occurred simultaneously in order to simplify the model. In another
study, a good correlation was found between the MDBA model fits and the mea-
sured effluent concentrations and between the simulated and measured loadings
on activated carbon [56]. The authors used the model to predict the cumulative
bioregeneration over time [56]. In that study, bioregeneration was measured to
take place more rapidly than in the simulated model, but the same value was
reached at the end.
The Freundlich adsorption concept as used by Vinitnantharat and co-workers
[11] for quantification of bioregeneration was employed by the same group in
another study [63] to develop a predictive isotherm model. The model aimed to
evaluate the extent of bioregeneration, as described in Section 7.6.2. In this study,
the modeling of bioregeneration was conducted with phenol and 2,4-dichlor-
ophenol in both single- and bisolute systems and also in the presence and absence
of biodegradation by-products. The loadings on activated carbon in batch and BAC-
Sequencing Batch Reactors (BAC-SBR) were estimated using Freundlich isotherm
constants. The results were compared with experimental loadings that were
obtained by the direct measurement method, in which the solute was extracted
with methylene chloride, as described in Section 7.6.4. When metabolic by-pro-
ducts were excluded from isotherms, the loadings on carbon were overestimated.
However, when metabolic by-products were included in isotherms, the model
predicted bioregeneration with reasonable consistency, in the case of both single
and bisolute systems and in batch and BAC-SBR reactors. The study indicated that
metabolic intermediates and by-products should be taken into account in the
modeling of bioregeneration [63]. This necessity arises because by-products
forming as a result of incomplete biodegradation may decrease the adsorption
capacity of activated carbon for target compounds.