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-

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     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

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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

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    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

RETURN POSTAGE GUARANTEED
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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,

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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

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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.

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                                      NT  ._, - -f
                                      - •% ^







Figure  3.    Filter trench after harvest of plants.

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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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