&ER&
                                 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 (%-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"4mVs(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 the  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 (10 ft) 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 a
 total gravity flow system, with the elimi-
 nation trenches so placed as to f acilirate
 this, but because of site conditions at
 this  location, the elimination trenches
 had  to be constructed 90 m (100 yd)
 north of the filter trenches. The two
 elimination trenches are 50 m (150 ft)
 long, 4 m (12 ft) wide, and 0.75 m (2.5ft)
 deep. They are divided in the center by a
 weir designed to allow composite samp-
 ling in this  area and to aid in aeration.
 The  filter trench  effluent enters two
 150-mm (6-in.) plastic pipes 4 m (12ft)
 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 (%
 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 (%-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

-------
 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
NHA-N
NOt-N
N03-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 layover
                          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 BODS  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  mVd
 (25,000 gpd) or less; for 6 months, 133
 mVd  (35,000  gpd). Secondary  treat-
 ment  requirements  for BOD5  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 BODs requirement was not
 achieved for 5 of the  6 months. The
 effluent violated both the concentration
 and  percent   removal   requiremerits
 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 NH<-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 rhVd, 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  mVd 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 BODs, 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 m3/d 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 mVm-d
(0.5 gpd/ft2).  Assuming  a per capita
wastewater discharge of  378 L (100
gal), the area required is 2 mVcapita (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 considerations for the
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.

-------
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  NH4-N  Org-N  NOt-N  N03-N    TP
Influent
Wastewater

Filter Trench
Effluent

Elimination
Trench Effluent

Overall Removal,
Percent
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
0.4     0.9
0.1    0.4
  88    91     79    33     31      —      —


             Flow of 35,000 gpd (133 mVd)


 171    181    405    25      17     0.0     0.3


  68    48   157    21      13     O.6     1.2


  35     19    93    19      11     0.3     0.6


  80    89    77    24      35     —      —
13


12


12


 8





13


13


13


 0
  Pamela R. Pope is with the Mouhon 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 81-213 241; Cost: $6.50, subject
    to change) will be available only from:
          National Technical Information Service
          5285 Port Royal Road
          Springfield, VA 22161
          Telephone: 703-487-4650
  The EPA Project Officer can be contacted at:
          Municipal Environmental Research Laboratory
          U.S. Environmental Protection Agency
          Cincinnati, OH 45268
                                                                                        -757-012/7203

-------