Cost-Effective Regulatory Compliance
With GAC Biofilters
Hsiao-wen Chen, Water Research Foundation research manager
Biofiltration is a treatment process that can
remove turbidity, dissolved organic matter,
taste-and-odor-causing compounds, iron,
and manganese. In addition, it can improve
the biological stability of finished water and
minimize microbial regrowth in distribution
systems. It was the process of choice for
Cost-Effective Regulatory Compliance With
GAC Biofilters (2010, order/project #4155)
as the treatment alternative for compliance
with the Stage 2 Disinfectants and
Disinfection By-products (DBP) Rule.
In addition to pilot-scale biofilters,
demonstration-scale biofilters were
tested specifically for developing design
criteria for a full-scale rehabilitation and
retrofit of convention filters to granular
activated carbon (GAC) biofilters without
pre-ozone. Lessons learned from this
project are as follows:
• Particle removal
– All the biofilters tested maintained
turbidity at <0.1 NTU for the majority of
the study with levels consistently well
below 0.3 NTU.
– Chlorination of filter influent and
backwash did not positively or negatively
impact particle removal.
– The anthracite and GAC biofilters
achieved similar particle removal.
– Media depth and empty bed contact time
(EBCT) had little effect on particle removal.
• Natural organic matter (NOM) removal
– Adsorption and biodegradation were the
two mechanisms that removed NOM in
the GAC biofilters.
– During the adsorption phase, chlorination
of the filter influent and backwash did not
appear to affect NOM removal. During
the steady-state biodegradation phase,
the biofilters with unchlorinated influent
and chlorinated backwash removed more
NOM than those with chlorinated influent
and chlorinated backwash. Nevertheless,
biodegradation of NOM still occurred
in the biofilters when the influent was