This finding is what caused
us at TRA to pursue more
research on biofiltration.
Why is manganese a problem?
When manganese gets into
your distribution system, it can
cause colored water episodes.
Transitioning to biofiltration will
require changing the location
of the chlorine addition, which
subsequently could cause manganese to break off of filters and
into the treated water, causing
a nuisance to our customers. We wanted to study whether
we could retain that accumulated manganese on the filters,
and have continued and enhanced removal of manganese.
Why not replace all of the filter media?
Replacing the filter media would not solve the problem,
because manganese was still going to be coming from the
raw water supply. Plus, the cost estimate for that was $2–3
million. We thought it was a better investment to do the
research on long-term and sustained manganese removal.
Can you tell me more about the City of Arlington’s
The City of Arlington began to experience filter clogging after
running the biofilters for a number of years. Upon taking them
apart, it was determined that a biological mass clogged the
caps in the filters. This led to a Tailored Collaboration project
with the Water Research Foundation, to look at how to optimize the operation of those biological filters. This research
found that the bacteria were stressed under certain conditions,
and that was contributing to an extra polymeric substance
(EPS). This caused filter clogging, which then resulted in
head loss and more frequent and longer backwash times.
As the Water Research Foundation celebrates its 50th anniversary, we are showcasing several subscriber utilities that
have achieved great things, in part because of their use of
and participation in WRF research projects. Recently, the
Water Research Foundation spoke with Julie Hunt, Assistant
Northern Region Manager of Trinity River Authority, in
Arlington, TX, to discuss the utility’s experience with the WRF
Tailored Collaboration project, “Optimizing Filter Conditions
for Improved Manganese Control During Conversion to
Biofiltration” (project #4448, forthcoming). The Trinity River
Authority ( TRA) is a regional provider of drinking water as well
as wastewater treatment services in the Dallas/Ft. Worth area.
Ms. Hunt also previously served on WRF’s Board of Trustees and
was Director of the City of Arlington Water Utilities Department,
where they partnered with WRF on a number of projects.
Water Research Foundation: What is biofiltration, and
why is Trinity River Authority implementing this
Julie Hunt: Biofiltration is a treatment processes that can
remove dissolved organic and inorganic compounds from
water. Biofiltration is typically used when you utilize ozone
for primary disinfection. Biofiltration does not have a heavy
energy footprint compared to other treatment technologies. It
can save water utilities money because it is not expensive to
operate biological filters, compared to some other treatments.
During our last plant expansion, we installed ozone to deal
with taste and odor issues, and planned to begin using ozone
for primary disinfection. When you do that, you need to have
biological filtration as a complimentary treatment process so
that the assimilable organic carbons created as a by-product
from the ozone can be consumed by the biofiltration.
Another reason to use biofiltration is manganese. Lake
Arlington, where we get our source water, has periodic high
levels of manganese. Our staff has struggled to keep man-
ganese from breaking through into the distribution system.
A neighboring city, Arlington, participated in a Tailored
Collaboration project with WRF in 2009, which found that
biological filtration could enhance manganese removal.
Q&A with Julie Hunt
Assistant Northern Region Manager of Trinity River Authority
Trinity River Authority and Biofiltration