Design of GAC Contactors” (project #4235)
will evaluate the appropriateness of other
GAC scale-up approaches to develop a
methodology that can be successfully
adopted by drinking water utilities to scale
up bench-scale results to simulate field-scale GAC adsorbers. The goal is to save
time, effort, and cost over the use of pilot-scale adsorbers. This project is expected to
be completed in 2013.
For utilities currently using GAC filter caps,
project #4101, “Evaluation of Granular
Activated Carbon Filter Caps for Control
of Disinfection By-Product Precursors
and Trace Organic Contaminants,” will
demonstrate the feasibility of retrofitting
filter caps for DBP control. This project
will also provide guidance for improving
efficiency and long-term performance
of GAC. This project is expected to be
completed in 2011.
Another new project #4294, “Effectiveness
of Sub-Micrometer Sized Powdered
Activated Carbon for the Combined
Removal of Disinfection By-Product
Precursors and Trace Organic Pollutants,”
will investigate the effects of the particle
size of PAC on DBP precursor and
micropollutant removal. This project
will identify physical and chemical sub-micrometer PAC characteristics that
produce effective DBP precursor and
micropollutant removal. This project is
expected to be completed in 2012.
GAC Biological Filters
for Precursor Removal
In the studies discussed above, GAC was
operated as an adsorber. The Foundation
has also sponsored research on removal
of THM and HAA precursors using GAC
in a biological mode. As early as 1994, the
Foundation published the report, Ozone
and Biological Treatment for DBP
Control and Biological Stability (1994,
order #90649/project #504). It concluded
that the combination of ozonation and
biological filtration reduced the formation
of chlorinated by-products to a greater
extent than conventional treatment without
ozone. The combination, on the other hand,
did not appear to remove chlorinated by-products as effectively as physical-chemical
treatment such as sedimentation.
One concern utilities may have is bacterial
regrowth in distribution systems after
biological filtration. The authors of Ozone
and Biological Treatment for DBP
Control and Biological Stability did not
observe regrowth problems in distribution
systems even though ozone increased
the bioavailability of NOM, as long as the
water was filtered after ozonation or high
disinfectant residual was maintained in
distribution systems.
Recently the Foundation and its utility
subscribers have co-funded two GAC
biological filtration projects for removal of
DBP precursors and other contaminants.
“GAC Biofilters in Retrofit Applications:
An Approach for Cost Effective Regulatory
Compliance” (project #4155) aims to
demonstrate the efficacy of GAC biological
filters retrofitted in a conventional
treatment plant. The research phase of
this project is complete and the report is
under review. “Enhancing Biofiltration to
Achieve Sustained Removal of Multiple
Inorganic and Organic Contaminants,
Including EDCs, MIB, and Geosmin”
(project #4215) focuses on evaluating
methods for restoring and enhancing the
performance of existing ozone–biological
filtration systems. This project is expected
to be completed in 2010.
