&EPA
United States
Environmental Protection
Agency
EPA/540/M.R-01/501
June 2001
US EPA Office of Research and Development
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Demonstration Bulletin
Biological Denitrification Process
EcoMat, Inc.
Technology Description: EcoMat, Inc. of Hayward, California
(EcoMat) has developed a 2-stage ex situ anoxic biofilter
biodenitrification process. The process is a fixed film
bioremediation, using biocarriers and specific bacteria to treat
nitrate-contaminated water. Unique to EcoMat's process is a
patented mixed bed reactor that retains the biocarrier within the
system, thus minimizing solids carryover. Fixed film treatment
allows rapid and compact treatment of nitrate with minimal
byproducts. Methanol is added as a source of carbon for cell
growth and for metabolic processes that remove free oxygen.
The resulting oxygen-deficient environment encourages the
bacteria to consume nitrate. Methanol is also important to as-
sure that conversion of nitrate proceeds to the production of
nitrogen gas rather than to the more toxic nitrite intermediate.
The mechanism for anoxic biodegradation of nitrate consists of
two sequential denitrification reactions. Oxygen must be con-
sumed to a dissolved oxygen concentration of <1 mg/L. In the
first denitrification step, the bacteria are forced to substitute the
nitrate as the electron acceptor and the nitrate is reduced to
nitrite. In the second step, the nitrite is further reduced to nitro-
gen gas. Nitrite production is an intermediate step and there is
no a priori reason to assume that the second reaction is at least
as fast and/or favored as the first reaction in the presence of a
specific bacterial population. Consequently, any evaluation
scheme must establish that there is no buildup of nitrite, particu-
larly since the nitrite-nitrogen maximum contaminant level (MCL)
is only 1 mg/L, one tenth that of nitrate. High concentrations of
nitrate and high nitrate/methanol ratios may also affect the con-
centration of residual nitrite in a particular process configura-
tion.
A simplified process diagram of the EcoMat treatment system
used during the demonstration is shown in Figure 1 .The system
is composed of two major components: a biodenitrification sys-
tem and a polishing or post-treatment system. The
biodenitrification system is intended to convert nitrates in the
groundwater to nitrogen, thus reducing nitrate concentrations.
The post-treatment system destroys or removes intermediate
compounds generated during the biological breakdown of ni-
trate and removes bacteria and suspended solids that are not
attached to the biocarrier. The post-treatment system can also
incorporate treatment for other contaminants, such as VOCs,
that may be present in the influent.
Biodenitrification is conducted in two reactors, identified as R1
and R2 on Figure 1. The majority of the oxygen removal step is
conducted in R1 where aerobic bacteria reduce dissolved oxy-
gen levels of the influent. Methanol is metered to the tank to en-
courage the bacteria to begin consuming nitrate. The resulting
oxygen-deficient water is pumped from the bottom of R1 to the
bottom of R2, which is densely packed with biocarrier media (1
cm) which have the appearance of small foam cubes. A patented
mixing apparatus within R2 directs the incoming water into a
circular motion, thus assuring intimate contact with the biocarrier.
Within R2, the majority of denitrification occurs by anaerobic bac-
teria that are continually fed methano! and populate on the large
mass of biocarrier media. After a sufficient retention time, de-
pending on concentration and goal, denitrified water drains by
gravity to an overflow tank, which allows for a continuous and
smooth transfer to the post-treatment system and removal of en-
trained bacteria and media.
Depending on the presence of other contaminants, the post-treat-
ment system consists of a series of varying sized filters down-
stream of one or more contaminant-specific treatment units. For
instance, ozonation may be used to oxidize any residual nitrite to
nitrate and to deactivate/destroy all residual biological materials
leaving the biodenitrification unit. If VOCs are present, an air strip-
per and/or carbon adsorption unit can be used. If state regula-
tions require chlorination of drinking water, then chlorine can be
added as a post-treatment, or directly to the overflow tank imme-
diately following denitrification.
BIODENITRIFICATION POST
TREATMENT
Methanol
Figure 1. Simplified Flow Diagram
Recycled/Recyclable
Printed with vegetable-based ink on
§aper that contains a minimum of
0% post-consumer fiber content
processed chlorine free.
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United States
Environmental Protection Agency
National Risk Management Research Laboratory
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
PRESORTED STANDARD
POSTAGE & FEES PAID
EPA
PERMIT NO. G-35
EPA/540/MR-01/501
Waste Applicability: Anoxic biodenitrification using one or more
biocarriers should be applicable to industrial wastewaters and
leachate from commercial, industrial and hazardous waste sites
containing various nitrate concentrations, as well as for treat-
ment of groundwater (the medium treated during the demon-
stration). The presence of other contaminants could play a sig-
nificant role in the effectiveness and viability of the overall treat-
ment system. For example, if volatile chlorinated hydrocarbons
are present along with nitrate, a post-nitrate treatment system
(e.g. carbon filters) may be necessary to remove those com-
pounds to acceptable levels.
Demonstration Results: A SITE demonstration of the EcoMat
biodenitrification system was conducted at the location of a
former public water supply well in Bendena, Kansas. This study,
which occurred from May until December of 1999, was con-
ducted in cooperation with the Kansas Department of Health
and Environment (KDHE). The KDHE provided a small building
and necessary utilities for the EcoMat systems. In addition, the
slate is analyzing water samples independently.
The demonstration focused on treating contaminated water from
the Bendena Rural Water District No. 2 Public Water Supply
(PWS) Well No. 1. This former railroad well, constructed in the
early 1900s, was at one time the sole source of water for the
town of Bendena. The primary contaminant in the water is nitrate
from uncertain sources ranging from 20 to 130 mg/L. Low con-
centrations of VOCs, particularly carbon tetrachloride (CCI4), in
the groundwater is a secondary problem ranging from 2 to 31
ug/L.
EcoMat's main goal of the study was to demonstrate that its
biodenitrification system could reduce incoming nitrate-N in
excess of 20 mg/L to a combined nitrate plus nitrite concentra-
tion below 10 mg/L. A second goal of the study was to demon-
strate that the post-treatment system used would produce treated
water that would meet applicable drinking water standards with
respect to nitrate-N and nitrite-N; and that the final effluent would
not contain turbidity of greater than 1 NTU, detectable levels of
methanol (1 mg/L), increased levels of biological material or
suspended solids, and will have a pH in the acceptable 6.5 to
8.5 range.
To evaluate both the biodenitrification system and the post-treat-
ment system adequately, water samples were collected from
four specific points along the entire process. These were: 1) an
influent sample point between PWS #1 and R1; 2) a partial
treatment sample point between R1 and R2; 3) an intermediate
effluent sample point between the biodenitrification system and
post-treatment system; and 4) a final effluent sample point down-
stream of the post-treatment system. To assure a statistically
adequate number of samples, an average of 30 influent and 30
effluent samples were collected for each of four separate sam-
pling episodes. Over an approximate seven and one-half month
period, EcoMat operated its system at a flow between three and
eight gallons per minute.
Results from the EcoMat biodenitrification process were en-
couraging when the entire system was operating at optimal per-
- formance: In those instances-where the final combined nitrate-
nitrite effluent concentration was above the regulatory limit, op-
erational problems (mostly mechanical) were suspected as the
primary cause.
For Further Information:
EPA Project Manager: Randy Parker
U.S. EPA, National Risk Management Research Laboratory
26 W. Martin Luther King Dr.
Cincinnati, OH 45268
(513) 569-7271
E-mail: parker.randy@epamail.epa.gov
Technology Developer Contact:
Peter Hall, EcoMat, inc.
26206 Industrial Blvd.
Hayward, CA 94545
(510) 783-5885
E-mail: ecomat@wenet.net
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