f/EPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-092 July 1981
Project Summary
Chlorine Dioxide for
Wastewater Disinfection:
A Feasibility Evaluation
Paul V. Roberts, E. Marco Aieta, James D. Berg, and Bruce M Chow
Chlorine dioxide was compared
with chlorine for disinfecting waste-
water in laboratory experiments.
Chlorine dioxide disinfection was also
demonstrated at a full-scale waste-
water treatment plant. The criteria
compared included coliform kill, in-
activation of poliovirus and other
indicators, and formation of halogen-
ated organic byproducts.
Laboratory experiments were con-
ducted using mass doses of disinfec-
tant and contact time as independent
variables. The fractional survival of
coliform bacteria was correlated with
the project of disinfectant residual *
contact time.
In general, chlorine dioxide accom-
plished a given fractional kill of total
coliforms with a smaller product (re-
sidual x time) than did chlorine. For a
given contact time, the residual re-
quired to achieve a given fractional kill
of coliforms was 2 to 70 times smaller
for chlorine dioxide than for chlorine.
Considering both required residual
and disinfectant demand, the required
doses of the disinfectants were esti-
mated to satisfy three assumed coli-
form disinfection levels with two
types of effluents: conventional acti-
vated sludge and filtered, nitrified
activated sludge. The required mass
doses of the disinfectants were ap-
proximately equal for treating con-
ventional activated sludge effluent.
The required dose of chlorine was
approximately 2 to 10 times greater
than that of chlorine dioxide for treat-
ing filtered, nitrified effluent, depend-
ing on the coliform standard. The
results of studies conducted at a full-
scale plant generally agreed within a
factor of two with the predictions
from laboratory studies, when com-
pared on the basis of the product
(residual x time) required to accom-
plish a given fractional kill.
For the cases likely to be most
typical in practice, chlorine dioxide is
approximately two to five times as
expensive as chlorine for disinfection.
On the other hand, chlorine dioxide
forms much lower quantities of halo-
genated by products and is more ef-
fective in inactivating viruses than is
chlorine.
This Project Summary was devel-
oped by EPA's Municipal Environmen-
tal Research Laboratory. Cincinnati,
OH. to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at the back).
Introduction
The purpose of this report was to
evaluate CI02 as an alternative to con-
ventional chlormation for the disinfection
of wastewater.
The specific objectives were1
1. To assemble and evaluate the
available information concerning
the chemistry of CIO2 generation
and its behavior in aqueous solu-
-------
tion, the technology and costs of
manufacture, its effectiveness as
a disinfectant, and the possible
side effects of its use.
2. To establish the dose-effectiveness
relationship for CIO2 as a disin-
fectant of wastewater after sec-
ondary treatment and after various
stages of advanced treatment,
using the survival of coliform
bacteria as a criterion.
3. To compare the effectiveness of
CI02 with that of CI2, using a
variety of indicators.
4 To demonstrate continuous gen-
eration of and disinfection with
ClOa to fulfill coliform requirements
under conditions representative of
wastewater treatment.
5. To prepare a preliminary designfor
treatment plants of 0.04, 0.22,
0.44, 2.2, and 4 4 mVs capacity
and to estimate the costs of con-
struction and operation.
6. To obtain preliminary evidence as
to whether the formation of chlori-
nated organic byproducts during
wastewater disinfection conforms
to the results from studies of water
disinfection.
Procedures and Results
In the laboratory, CI02 was generated
by reacting NaCI02 solution with H2S04
to produce gaseous CI02, which was
purified by passing through a NaCI02
tower before being absorbed into water.
The concentration of CI02 in the prepared
solution was approximately 2 g/L. In
field experiments, CIO2 was generated
by continuously mixing NaCI02 solution
with either H2SO4, HCI, or CI2 gas in a
commercially available reactor system.
Chlorine species in the reaction product
were determined by a series of methods
that entailed measurement of ultraviolet
absorbance at 360 mm to determine
CIO2; amperometric titration at pH 7 to
determine CI02 and CI2; mdometric
titration at pH 2 to determine CI02, CI2,
and CI02~; lodometric titration in con-
centrated acid to determine CI02, CI2,
CI02~, and CI03"; and chloride mea-
surement by use of the Mercuric Nitrate
Method. The sensitivity and precision of
the determination are summarized in
Table 1.
The yields of CI02 using several gen-
eration schemes are summarized in
Table 2. The yield of CI02 from a con-
tinuous generator at full-scale (2 kg
CIO2/hour) was higher than the yield
observed in a batch process in the
Table 1. Sensitivity and Precision of Analyses for the Reaction Yield Study
Species
Chlorine Dioxide
Chlorine
Chlorite
Clorate
Detection
Limit,
Mol/L
3 x 10~&
5.6 x 70~5
3 x W4
1.8 x W~4
Coefficient of
Variation, %*
0.1
0.6
1.7
0.4
precision
At Mean
Concentration, Mol/L
0.02
0.015
0.013
0.01
^(Standard deviation divided by mean) * 100 for 5 replicate measurements in
distilled water.
Table 2.
Yield of Chloride Dioxide
Type of Generation
H2SO* + NaCI02,
batch (laboratory)
H2S04 + NaCIO2,
continuous (field)
HCI + NaCI02,
continuous (field)
Clz + NaCIOz.
continuous (field)
Ratio of
Reactants
1 .7 Mol HzSO*
Mol CIOI
2 Mol HzSO*
Mol CIO~2
1.4 Mol HCI
Mol CIOI
0.52 Mol C/2
Mol CIO~2
Initial
Chlorite
Cone., M
0.083
1.56
1.35
1.92
Final
pH
1.8
2.1
2.2
5.3
Yield, %*
48
51
78.4 ± 4.4
95 + 3.5
n**
1
1
4
2
*Yield as (Mol CIO2 produced/Mot CIO2 feed) •< 100; mean ± standard deviation.
**n - Number of trials.
laboratory; this is attributed to the
higher concentration of NaCI02 used in
the full-scale, continuous system. The
yield from continuous generation was
increased when HCI was substituted for
H2SC>4 in the acid-chlorite process. The
yield from the chlorine-chlonte process
in the continuous generator was 95%,
even though a small excess of CI2 (4%
above the stoichiometric requirement)
was used.
Disinfection experiments were carried
out using secondary wastewater samples
from three plants (Figure 1). The levels
of treatment were: conventional acti-
vated sludge; nitrified activated sludge;
and filtered, nitrified activated sludge.
Laboratory disinfection experiments
were conducted in a 4-L batch reactor
with disinfectant dose levels of 2, 5, and
10 mg/L and contact time levels of 5,
15, and 30 mm as the independent
variables in a full factorial design. The
density of total cohforms was determined
by the membrane filter method; dis-
infectant residual concentrations were
determined by amperometric titration.
The results were correlated as survival
ratio, N(t)/N(0), versus the product of
residual x contact time (R x t). Typical
results from a set of experiments using
ClOs to disinfect conventional activated
sludge effluent are shown in Figure 2.
Full-scale disinfection experiments
were carried out at a treatment plant to
confirm the reliability of the laboratory
data to predict plant performance.
Laboratory and field data agreed well for
both CI02 and CI2.
CIO2 was found to be a more effective
disinfectant than CI2 when treating
conventional (nonnitrified) activated
sludge effluent (Figure 3). This difference
was shown to be statistically significant
by analysis of variance. When comparing
CIOz to CI2 at a given survival ratio, a
lesser value of R x t product suffices to
achieve a given degree of coliform
mactivation when CI02 is used (Figure
3). A similar comparison made for
nitrified effluent indicated no appreci-
able difference between the two disin-
fectants to inactivate coliforms. When
these comparisons were made for nitri-
fied filtered effluents, however, CI02
was more effective than CI2 based on
the same criteria.
The costs of disinfection with CIO2 are
compared with those of CI2 for six cases
corresponding to two levels of pretreat-
merit and three total coliform standards
-------
Palo Alto WWTP
Raw
WasTe
Primary
Treatment
Conventional
Secondary
Sample Point
Dublin — San Ramon WWTP
Raw
Waste
Extended Aeration
Secondary Treatment
with Nitrification
Filtration
T
Disinfection
Sample
Point
San Jose — Santa Clara WWTP
Raw
Waste
Primary
Treatment
»
Conventional
Secondary
Treatment
^
T1
>am
Poi
Nitrification
Process
S
ole i
it
t Filtration |)f| Disinfect/on
T
ample Sample
°oint Point
Figure 1. Wastewater treatment plant flow schemes and sampling points for
disinfection experiments.
(Table 3). Estimates for a 0.44 mVs
plant are shown in Table 3; the report
presents cost estimates for a range of
capacities from 0.04 to 4.4 mVs. The
high cost of NaCIOz is responsible for
the generally high cost of disinfection
with CI02.
CI02 offered advantages that compen-
sate for its cost being higher than that of
chlorine. CI02 was found to be more
effective for inactivating inoculated
Poliovirus I and natural populations of
coliphage than was C\2 in both non-
nitrified and nitrified filtered waste-
water effluents. ClOa treatment formed
no measurable amounts of trihalometh-
ane byproducts, whereas Cla treatment
formed 0.5 to 5 /jMo\/L of tnhalometh-
anes, chiefly chloroform, in experiments
using wastewater effluents. Moreover,
CIO2 formed negligible amounts of the
broader class of halogenated organics
measured collectively as total organic
halogen (TOX)—less than 10% as much
TOX as did chlorine. These advantages
of CI02 should be considered, along
with the cost-effectiveness comparison
based oncoliform kill, to reach decisions
on using CI02 as a disinfectant in
wastewater treatment.
The full report was submitted in ful-
fillment of Grant No. R-805426 by
Stanford University under the sponsor-
ship of the U.S. Environmental Protec-
tion Agency.
10'
c
o
N(t)N(0)= [(R x TV1.56Y2 90
"/- = 0.86
* f
I I I Mill
il i i 11 mil i i 111 ml i i 11 mil
Figure 2.
70"1 70° 70 1 702
Residual - Time in mg -mm/L
Data correlation for disinfection of conventional activated sludge
effluent with chlorine dioxide (laboratory experiments).
C-frr2
5/0"
I/O-5
Cl 2 as
Disinfectant
Cl 2 as
Disinfectant
10
701
/O
Residual - Time in mg -m/n/L
Figure 3. Comparison of coliform
mactivation by chlorine
dioxide and chlorine in
conventional fnonmtrified)
activated sludge effluent.
> US GOVERNMENT PRINTING OFFICE 1981 757-012/7253
-------
Table 3. Summary of Dose Requirements and Costs
Type of
Effluent
Activated Sludge
Filtered, Nitrified
Activated Sludge
Case
A
B
C
D
E
F
Total
Coliform
Standard,
N/100 ml
2.2
200.
WOO.
2.2
200.
WOO.
Required
Disinfectant
Dose, mg/L
C/2 CI02
7.89 7.92
2.45 2.90
1.70 2.17
11.15 5.52
2.61 0.60
2.60 0.14
Total Costs, *
C/m
C/2
0.82
0.58
0.55
0.95
0.63
0.58
3
C/02
8.72
3.43
2.24
6.21
1.11
0.61
* January 1980 costs. 0.44 m3/s plant.
Paul V. Roberts, E. Marco A/eta, James D. Berg, and Bruce M. Chow are with the
Civil Engineering Department, Stanford University, Stanford, CA 94305
Mark C. Meckes is the EPA Project Officer (see below).
The complete report, entitled "Chlorine Dioxide for Wastewater Disinfection: A
Feasibility Evaluation," fOrder No. PB 81-213 357; Cost. $14.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at.
Municipal Environmental Research Laboratory
U S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
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-------
V-/EPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory •*
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-091 July 1981
Project Summary
Wastewater Treatment by
Rooted Aquatic Plants in
Sand and Gravel Trenches
Pamela R. Pope
A patented* process developed by
the Max Planck Institute (MPI) of West
Germany to treat industrial wastes
was evaluated as an energy-efficient
method to treat municipal waste-
water. The major goal was to achieve
effluents meeting the U.S. Federal
Effluent Standards using this novel
biological treatment process that re-
quires a minimal amount of
mechanical equipment and manpower
for normal operation.
The Moulton Niguel Water District
(MNWD) of Laguna, California, con-
structed and operated an earthen
trench system using rooted aquatic
plants for the treatment of waste-
water. Two trenches in series were
planted with the reed Phragmites and
the bulrush Scirpus, respectively.
A 2-month study using convention-
al secondary effluent as the trench
influent showed the system was not
effective for removing nitrogen and
phosphorus components.
An 11 -month study demonstrated
that raw screened wastewater applied
to the trench system at a rate not
exceeding 95 mVd (25,000 gpd)
could be treated to secondary effluent
quality. Spatial requirements were
about the same as for a septic tank
system.
This Project Summary was develop-
ed by EPA's Municipal Environmental
Research Laboratory, Cincinnati, OH,
to announce key findings of the
research project which is fully docu-
*U S Patent 3,770,623, November 6, 1973
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
The MPI process utilizes higher
aquatic plants, such as reeds and bul-
rushes, for the treatment of waste-
water The system consists of two
earthen trenches, lined with impervious
membranes, operated in series. The
first, designated as the filter trench,
removes coarse suspended solids from
the wastewater. The second, desig-
nated as the elimination trench,
removes dissolved materials from the
effluent of the first trench.
The MNWD services a residential
area, and the wastewater is domestic in
nature. The MPI system, as it was
installed at the MNWD 3A facility, con-
sists of two filter trenches and two
elimination trenches. Two species of
plants were used—a reed Phragmites
communis in the filter trench and a
bulrush Scirpus lacustris in the elimina-
tion trench. A view of the elimination
trench system during construction is
shown in Figure 1
Filter Trenches
The two filter trenches are each 25 m
(75 ft) long, 4 m (12 ft) wide, and 1.3 m (4
ft) deep. They are filled with three layers
of gravel—150 mm (6 in.) of 50-mm (2-
in.) gravel on the bottom; 225 mm (9 in.)
of 19-mm (34-in.) gravel in the middle,
-------
Figure 1. Construction of elimination trench.
and 75 mm (3 in.) of pea gravel on top. A
75-mm (3-in.) layer of silica sand covers
the top. The raw wastewater enters the
MNWD 3A facility at the north side of
the plant and is passed through a roto-
strainer to remove large particles.
The screened influent flows down an
influent channel and is pumped to the
MPI system at a rate of approximately
8.8 to 9.5 X 10~4m3/s(14-15gpm). The
influent then flows south through a
control valve into the east end of the
filter trenches. Every 24 hr the flow is
alternated between the two trenches.
Each filter trench contains a central
150-mm (6-in.) plastic pipe with an
open slit running its entire length;
alternating long and short 100-mm (4-
in.) plastic pipes extend from it for even
dispersion of the influent. The waste-
water flows down the central pipe
through the extending pipes and onto
cement splash pads located directly
below. The wastewater percolates
through the trench in a vertical filtering
action leaving a sludge layer on top. The
sand filters out tne suspended solids
while the plant system draws moisture
and nutrients. Slow drying of the
deposited solids occurs, and extensive
growth of the plant rootlets and runners
aid in degrading the sludge layer on top
of the sand. Each trench has a perfor-
ated 100-mm (4-in.) plastic pipe extend-
ing the entire length of the trench from
the surface to the bottom in a "U"-
shaped configuration. Flow from the
underdrain goes into this pipe and
through pipe extensions and a butterfly
valve into a sump. This pipe not only
transports the flow but allows aeration
to the bottom since it has openings to
the surface. The sump is a 1.3-m (4-ft)
concrete pipe 3.3 m(10ft) in height and
is buried 2.6 m (8 ft). A small 0.25-kW
(0.33-hp) pump, activated by a float,
periodically pumps the flow to the
elimination trenches.
Elimination Trenches ^
Normally, this process would be «
total gravity flow system, with the elimi
nation trenches so placed as to facilitate
this, but because of site conditions a
this location, the elimination trenches
had to be constructed 90 m (100 yd
north of the filter trenches. The twc
elimination trenches are 50 m (150ft
long, 4 m (12 ft) wide, and 0.75 m (2.5ft
deep. They are divided in the center by e
weir designed to allow composite samp-
ling in this area and to aid in aeration
The filter trench effluent enters twc
150-mm (6-in.) plastic pipes 4 m (12 ft;
long set perpendicular to the trenches at
the south side. The side facing the
trenches is open, and the liquid is
allowed to flow out into an area 1.3 m (4
ft) by 4.0 m (12 ft) in a waterfall-like
action. This area is filled with 15 mm (5/s
in.) gravel held in place by 50- X 100-
mm (2- X 4-in.) wood baffles. A later
observation (by BWP of New York Inc.)
showed that eliminating the baffles
reduced the operational problems. The
liquid percolates down in a horizontal
manner at a level approximately up to
50 mm (2 in.) below the surface of the
trenches. The trenches are filled with
15-mm (5/a-in.) gravel with 75 mm (3 in.)
of pea gravel on top. The flow passes'
through the weir and runs into two
standpipes that lead into a sump. The
level of the liquid flow is governed by
raising or lowering the standpipes. A
valve in the bottom of the weir allows
periodic draining of the liquid in the
lower portions of the trenches. The total
retention times for the entire system are
estimated to be 6 hr and 8.5 hr at flows
of 133 mVd and 95 mVd, respectively.
Test of MPI System as a
Tertiary Treatment Process
Secondary effluent from the MNWD
extended aeration plant was introduced
to the MPI system on July 1, 1978, at a
loading rate of 56 mVd (15,000 gpd);
the flow was increased to 95 mVd
(25,000 gpd) in August.
The analytical results for samples
obtained during the time extended
aeration effluent was applied to the
system are shown in Table 1.
Overall removal of BOD5, VSS, and
TSS was about 50 percent each month.
COD reduction was about 40 percent.
Ammonium nitrogen removal of 67 per-
cent during August was superior to the
40 percent removal in July. Considera-
tion of the NH4-N, N03-N, and N02-N
values between the 2 months indicates I
-------
Table 1. Tertiary Treatment Results for MPI System, Average Values
Item, mg/L
MNWD Secondary Filter Trench
Effluent Effluent
Elimination Overall
Trench Effluent Removal, %
Flow of 25,000 gpd (95 mVd)
BODS
TSS
VSS
COD
NHt-N
A/02-/V
NOz-N
TP
15
15
10
58
12
0.8
2.1
11.5
9
8
6
50
8
2
5.5
10
7
7
4
35
6
1.1
7.2
10
53
53
60
39
50
—
—
13
nitrification and subsequent denitrifica-
tion were more active in the system
during the warmer month of August.
TKN samples were not collected during
this period. The MPI system operated as
a tertiary process did not efficiently
remove TP. The extended aeration efflu-
ent applied to the system was of good
quality. The filter trench achieved the
greater part of the overall pollutant
removals; the elimination trench
showed only marginal incremental
removal.
Test of MPI System as a
Secondary Treatment Process
Screened raw wastewater was used
as the influent tothe MPI system in mid-
September at a rate of 56 mVd (15,000
gpd). The flow was increased to 95 mVd
(25,000 gpd) in October and 133 mVd
(35,000 gpd) in January, remaining at
this rate through July. The growth of the
bulrush Scirpus in the elimination
trench is shown in Figure 2.
A thin sludge layer built up and com-
pletely covered the filter trenches by the
end of October. At this time, the
Phragmites had not spread throughout
the trenches. Algae also started to grow
on the sludge layer and may have con-
tributed to later clogging problems. By
mid-December, algae covered a large
portion of the sludge layer, which was
not drying or breaking up as the flow
was directed into the alternate trench.
The problem occurred equally in both
filter trenches. Operation was sus-
pended at this time to consider this
problem and to harvest the Phragmites
from the filter trenches. The Phragmites
had turned brown because of unusually
cold weather and had begun to lay over
because of their mature height and
weight. When the sludge layer was
skimmed off a little at a time, about 25
mm (1 in.) of sludge was found deposi-
ted on the filter media; this sludge layer
was wet and becoming septic. Below
this was a layer of compacted organic
matter and fibers that were black in
appearance and felt greasy; this inter-
mingled with the sand, formed an
almost impermeable layer. If a hole was
poked through this layer, the liquid held
in the sludge layer immediately drained
through the remaining sand. The only
solution at this time was to allow the
filter trenches to dry after the harvest-
ing and then to rake out the semidry top
sludge layer carefully. Figure 3 shows
the plants after harvesting.
Subsequent tests conducted in Long
Island, New York, by BWP of New York,
Inc., showed that using four parallel
filter trenches to allow increased drying
time and that draining the filter
trenches three times a week minimized
this sludge problem.
The major objective of this project
was to evaluate the MPI system as a
low-cost wastewater treatment alterna-
tive that would satisfy federal discharge
requirements. These requirements are
attained if final effluent BOD5 and SS
concentrations do not exceed 30 mg/L
for 30 days average values, or 85 per-
cent overall removal, whichever is more
stringent. The fate of nitrogen and
phosphorus was also monitored. Table
2 summarizes all the data collected.
The system was evaluated for sec-
ondary treatment effectiveness for 11
months. For 5 of the months, the flow
through the system was 95 m3/d
(25,000 gpd) or less; for 6 months, 133
m3/d (35,000 gpd). Secondary treat-
ment requirements for BODs and SS
were achieved all 5 months at the lower
flow SS residuals and percent removals
met secondary requirements all 6
months at the higher flow rate; how-
ever, the BOD5 requirement was not
achieved for 5 of the 6 months. The
effluent violated both the concentration
and percent removal requirements
three times (January, April, and July);
the percent removal requirement only
was violated twice (May and June).
There was little difference in overall
COD removal for the two application
rates.
The NH4-N and Org-N concentration
values in the effluent during the periods
of 95 mVd application were represen-
tative of conventional secondary treat-
ment residuals Variations in percent
removals were because of fluctuations
in influent concentrations. The overall
removal of total nitrogen varied from 61
percent in September to 32 percent in
March.
During application of 133 mVd, the
Org-N residuals were about twice the
values of the lower flow rate results.
During February, a negative removal of
Org-N was noted. The overall removal of
total nitrogen was much lower than
during the 95 mVd application, 18
percent in January to 36 percent in
June.
Nitrite and nitrate nitrogen concen-
trations for all the sample periods show
that nitrification did not occur to any
significant extent at either of the two
flow rates.
The MPI system during both the 95
mVd and the 133 m3/d application
rates was not effective for total
phosphorus removal. During the higher
application rate, 2 months (January and
June) showed negative removals.
The major increment of BODg, SS,
VSS, and COD removal occurs at the
filter trench, and the elimination trench
serves as a polishing process (Table 2).
Both trenches in series are necessary
for satisfactory treatment.
The MPI system operated with raw
screened wastewater at an application
rate of 95 mVd did achieve secondary
effluent quality. Using the trench meas-
urements, the spatial requirements of
-------
Figure 2. Aquatic plant growth in elimination trench.
the MPI system equate to 0.02 mVrrvd
(0.5 gpd/ft2). Assuming a per capita
wastewater discharge of 378 L (100
gal), the area required is 2 m2/capita(21
ftVcapita). These two values are very
similar to spatial requirements of a
septic tank system located in a satisfac-
tory percolating soil.
Several operating problems, expected
with new technology development,
were experienced during this
demonstration study. Many of the same
operational problems were encount-
ered at the Long Island, New York.
Several operating problems, expected
with new technology development,
were experienced during this demon-
stration study. Many of the same opera-
tional problems were encountered at
the Long Island, New York, installation.
Remedial measures applied at Long
Island included:
2. Recommend harvesting plants not
more than once a year. Frequent
harvesting of the plants used in
the system promotes extra growth
of the root systems and this con-
tributes to clogging.
3. If plant growth becomes excessive
during the year, individual plants
are culled by pulling to thin the
growth.
This initial assessment of the effi-
ciency and spatial considerationsforthe
MPI system for secondary treatment
indicates it is worthy of further develop-
ment.
The full report was submitted in ful-
fillment of Grant No. R-805279 by the
Moulton Niguel Water District under the
sponsorship of the U.S. Environmental
Protection Agency.
1. Provision for increased area for
the filter trenches, thereby allow-
ing longer idle times for drying.
-------
NT ._, - -f
- •% ^
Figure 3. Filter trench after harvest of plants.
-------
Table 2. Secondary Treatment Results for MPI System, Average Values in mg/L
Sample
Location
BODs TSS COD NHt-N Org-N NOZ-N N03-N TP
Influent
Wastewater
Filter Trench
Effluent
Elimination
Trench Effluent
Overall Removal,
Percent
Flow of 25,000 gpd (95 mVd)
210 225 405 24 13 0.0 0.1
77 41 179 19
26 20 86 16
88 91 79 33 31
0.4 0.9
13
12
0.1 0.4 12
Flow of 35,000 gpd (133 mVd)
Influent
Wastewater
Filter Trench
Effluent
Elimination
Trench Effluent
Overall Removal,
Percent
171
68
35
80
181
48
19
89
405
157
93
77
25
21
19
24
17
13
11
35
0.0 0.3 13
0.6 1.2 13
0.3 0.6 13
0
Pamela R. Pope is with the Moulton Niguel Water District, Laguna Niguel. CA
92677.
Ronald F. Lewis is the EPA Project Officer (see below).
The complete report, entitled "Wastewater Treatment by Rooted Aquatic Plants
in Sand and Gravel Trenches," (Order No. PB 81-213241; Cost: $6.50, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
<, US OOVERNMENTPRINTINGOFFICE IWt -757-012/7203
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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