Abstract
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EcoMat, Inc. of Hayward, California (EcoMat) has developed an ex
situ anoxic biofilter biodenitrification (BDN) process. The process
uses specific biocarriers and bacteria to treat nitrate-contaminated
water and employs a patented reactor that retains biocarrier within
the system, thus minimizing solids carryover. Methanol is added
to the system as a carbon source for cell growth and for inducing
metabolic processes that remove free oxygen and encourages the
bacteria to consume nitrate. Methanol is also important to assure
that the nitrate conversion results in the production of nitrogen
gas rather than the intermediate (and more toxic) nitrite.EcoMat's
BDN and post-treatment systems were evaluated under the SITE Program
at a former public water supply well in Bendena, Kansas. Nitrate
concentrations in the well groundwater have historically been
measured from approximately 20 to 130 ppm, well above the regulatory
limit of 10 mg/l. Low concentrations of VOCs, particularly carbon
tetrachloride (CCl4), are a secondary problem. The overall goal
of EcoMat (the developer) was to demonstrate the ability of their
process to reduce the levels of nitrate in the groundwater and
restore the well as a drinking water source. The SITE demonstration
occurred between May and December of 1999 and was conducted in
cooperation with the Kansas Department of Health and Environment
(KDHE). The study consisted of four separate sampling events over
7 1/2 months. During these events EcoMat operated their system
to flow between three and eight gallons per minute. During that
same time period nitrate-Nitrogen (nitrate-N) concentrations in
the well water varied from greater than 70 mg/l to approximately
30 mg/l. Since the post-treatment system implemented by EcoMat
varied for each of the four events, data from the four events
were analyzed separately. Formal statistical analyses were used
to address specific test objectives using a significance level
of 0.10. Events 1 and 2 were found to be successful in meeting
performance goals for significantly reducing levels of nitrate-N
and nitrite-N after BDN and after post treatment. Events 3 and
4 were not shown to be successful in significantly reducing levels
of nitrate-N and nitrite-N after BDN and after post treatment.
Dissolved oxygen (DO) measurements indicated that the deoxygenating
step of EcoMat's BDN process was not optimized throughout the
demonstration. The desired DO levels of < 1 mg/l following
the deoxygenating step in the process were measured only during
the first two events.
The effectiveness of the post-treatment systems was variable for
different parameters. None of the post treatment system combinations
used during the demonstration was effective in removing residual
methanol to the demonstration objective of < 1 mg/l. However,
the increased level of filtration incorporated following the first
two events appear to have had a substantial beneficial impact
on solids carryover.
Randy Parker
