United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/046 May 1986
Project  Summary
Trickling   Filter/Solids   Contact
Process:   Full-Scale   Studies

Raymond N. Matasci, Arthur H. Benedict, and Denny S. Parker
  This report outlines the characteristics
that distinguish the trickling filter/solids
contact  (TF/SC) process for municipal
wastewater treatment from other similar
processes.  The  SC feature provides  a
short aerobic contact period between the
TF effluent and  the recycled underflow
solids from the secondary clarifier to pro-
mote solids capture and produce a final ef-
fluent with a low  suspended  solids
concentration.
  The report also summarizes the results
of field studies at TF/SC facilities in Ocon-
to Falls, Wisconsin; Tolleson,  Arizona;
Medford, Oregon; and Chilton, Wisconsin.
These studies and a review of historical
operating records at these plants and at
Corvallis, Oregon (where the process was
first successfully demonstrated in 1979),
provide additional insight into the perfor-
mance of the TF/SC process under differ-
ent design and loading conditions.
  This Project Summary was developed
by  EPA's Water  Engineering Research
Laboratory,  Cincinnati, OH, to announce
key findings of the research project that
is fully documented in a separate  report
of the same title (see Project Report order-
ing information at back).

Introduction
  In certain circumstances, the trickling
filter/solids  contact process (TF/SC) for
municipal wastewater treatment may qual-
ify for funding as innovative technology;
but more information is required about the
design and performance of this  process.
The objectives of this study were therefore
as follows:
  1. To develop a definition of the TF/SC
    process that distinguishes it from
    other similar processes
  2. To document the design and per-
    formance information available from
    existing TF/SC facilities, and
  3. To  conduct special field  investiga-
     tions to provide additional insight into
     the TF/SC process. The project was
     not  intended  to produce a. design
     manual, since field investigations and
     operating data were limited.

Process Characteristics
  TF/SC is a biological and physical pro-
cess that includes (1) a TF, (2) an aerobic
solids contact period,  (3) a flocculation
period, and (4) secondary clarification.
Two operating  features are also important:
Solids must be maintained in an aerobic
flocculant state, and solids are recycled
from the secondary clarifier to combine
with TF effluent as a mixed liquor.
  The primary  function of the first element
in the TF/SC process, the TF, is to reduce
the soluble BOD in the wastewater. The
aerobic solids contact period is then used
to provide contact between finely divided
solids in the  TF  effluent  and recycled
biological solids and to provide additional
soluble BOD removal if  necessary. The
contact  opportunity provides  for initial
flocculation of dispersed solids into floe.
The length of  the aerobic solids contact
period is governed by the requirements for
particulate and soluble BOD removal. The
third element in the TF/SC process is the
flocculation period. Flocculation is initiated
in the contact tank and continues in the
clarifier, perferably in a mildly stirred en-
vironment of a center well.  The floccula-
tion  step promotes clear  effluent and
growth of large, settleable floe  that  is
removed during secondary  clarification.
  The following primary characteristics
distinguish TF/SC from other processes:
  1. The  main function  of the contact
    tank and clarifier flocculation fea-
    tures is to increase flocculation and
    solids capture and reduce particulate
    BOD.

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  2. The majority of soluble BOD removal
     occurs in the TF.
  3. Return sludge solids are mixed with
     TF effluent rather than with primary
     effluent,  as  with  some  other
     processes.
  4. The aerated solids contact tank is
     not  designed  to  nitrify,  although
     nitrification may occur in the TF.
  5. The aerated solids contact time is 1
     hr or less, based  on total flow in-
     cluding recycle.
  6. The solids retention time (SRT) of
     the aerated solids contact tank is
     less than approximately 2 days.

Performance of Existing Facilities
  Design and  performance data were re-
viewed for six facilities located in Chilton,
Wisconsin; Corvallis, Oregon;  Medford,
Oregon;  Norco, California; Oconto Falls,
Wisconsin; and Tolleson, Arizona. Most of
the information used in the process evalu-
ation comes from the four facilities de-
scribed in Table 1.
  The Corvallis plant was the first TF/SC
plant in operation. The Oconto Falls facility
was originally a rock TF plant that was not
meeting its discharge limits; modifications
to the facility included addition of a solids
contact chamber  and a new flocculator
clarifier for secondary clarification. Tol-
leson was originally a two-stage rock TF
plant treating  industrial  and residential
flows. The first-stage rock filter was re-
placed with  a  20-ft-deep plastic media
filter with intermediate clarification, and
the remaining rock filter was followed by
aerated SC and a flocculator clarifier. The
Medford plant was originally an activated
sludge (AS) plant  that was converted to
a coupled TF/AS plant. This plant presently
operates in the TF/SC mode since its flows
and  loads are significantly below design
levels.
  Monthly performance data for the four
facilities listed in Table 1 are presented in
Table 2.  Clearly, these  plants produce  a
high-quality effluent in all cases.

Field Investigations
  A  total  of 29 weeks of field investiga-
tions were undertaken at four facilities to
augment  the information available from
historical operating records. Special study
objectives were as follows:
  1.  To assess the influence of cosettling
     waste secondary  solids with  raw
                   sewage solids on primary sedimen-
                   tation tank performance.
                2.  To assess soluble  BOD  removal
                   kinetics with TF depth.
                3.  To assess the effect of TF loading on
                   TF/SC performance.
                4.  To assess the  effect of media type on
                   aerated   solids  contact   tank
                   performance.
                5.  To assess the effect of aerated solids
                   contact tank operating parameters
                   on TF/SC performance.
                6.  To assess soluble BOD removal in the
                   aerated solids contact  tank.
                7.  To assess the effect of  aeration rate
                   on TF/SC performance.
                8.  To assess the effect of secondary
                   clarifier overflow rate on final effluent
                   quality.
                9.  To assess the  effect of coagulant ad-
                   dition for phosphorus  removal on
                   TF/SC performance.

              Conclusions
                The following conclusions  are based on
              the special study results and a review of
              historical operating records:
                1.  Cosettling —Primary treatment  sus-
              pended solids (SS) removal  averaged 53
Table 1.    Design Data for Operating TF/SC Facilities
    Element
           Tolleson
 Oconto Falls
                    Corvallis
                                                                          Medford*
Design flow, m3/s (mgd)
  ADWF
  PWWF

Design loading, 1,OOO kg/d (1,000 Ib/dayl
  BOD
  SS

Primary overflow  rate, m3/m2 d tgal/day/ft2)

Trickling filter
  Media type
  BOD loading, g/m3'd (lb/day/1,000 ft3)

Return sludge aeration time,1 min

Aerated solids contact time," min

Flocculator center well
  Percent of clarifier area
  Detention time,* min
Secondary clarifier
  Overflow rate,+ + rrP/rrf-d (gal/day/ft2)
  Side water depth, m (ft)
  Sludge removal system

Weir Location
       0.36  18.3)
       0.78 (17.7)
       10.9 (24.0)
       9.80 (21.61

       39.5  (970)
      Plastic/rock*
 881/146+ (55/9.1)
               13
               25

       17.9  (440)
        4.9   (16)
     Suction header

           Inboard
0.017 (0.38)
0.033 (0.75)


0.30  (0.67)
0.36  (0.79)

15.1   (37O)
561
       Rock
       (35)
         16
         38

12.2  (300)
 4.6    (15)
Suction  tube

     Inboard
                 0.43  (9.7)
                 1.23 (28.0)
                 4.94 (10.9)
                 5.22(11.5)

                 39.9  (98O)
       Rock
 384   (24)

          9

          2


         12
         25

 19.1  (4701
  5.5  (18)
Suction tube

    Inboard
                            0.79 (18)
                            2.63 (60)
                            15.9 (35)
                            12.7 (28)

                         41.8 <1,O25)
     Plastic
1,840 (115)
                                                    5
                                                    5

                                          29.3 (720)"
                                              4.6 (151
                                     Suction header- 1
                                       Suction tube -o
                                               Inboarc
 *'Originally designed as coupled TF/AS plant. Design data for TF/AS.
 + First stage/second stage.
 1Based on 33 percent return rate.
 ^Not used at this plant.
 "Based on total flow including recycle.
 * *Contact time at existing flow of 8.8 mgd plus 33 percent return is 39 min.
 + +Based on total clarifier area.
 tfBased on existing number of clarifiers.

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Table 2. Monthly Performance at Operating TF/SC Facilities
Tolleson *
Parameter
Influent flow
Average, m3/s
(mgdt
Influent characteristics
BOD, mg/L
SS, mg/L
Temperature, °C
Primary effluent
BOD, mg/L
SS, mg/L
TF effluent
BOD, mg/L
SS, mg/L
Return sludge SS, g/L
Mixed liquor SS, mg/L
Secondary effluent*"
BOD, mg/L
CBOD, mg/L
SS, mg/L
High

0.29
(6.71

350
300
_ t

373
400

42. 51
45. S1
_#
1.621

15.4
_t
20.2
Low

0.22
<5.0)

222
192
_ t

107
57

T0.41
5.31
_tt
55 1

3.5
_ t
4.0
Average

0.27
16.1)

277
224
_ t

173
121

22. 8"1
23. ff1
_tt
1,042

7.2
t
8.5
High

0.02
10.46)

179
152
19

T
t

_t
_t
_#
_ t

31.7
_ t
22.6
Oconto Falls"
Low

0.01
10.28)

119
100
8

_ t
_ t

_t
_ t
_#
_ t

14.2
_ t
6.7
Average

0.02
10.36)

146
118
13

_ t
t

_t
_t
-#
_ t

20.5
_ t
12.8
High

0.78
117.9)

188
191
22

114
82

39
72
17.2
4,982

9
7
13
Corvallis*
Low

0.25
15.6)

48
112
13

35
56

22
54
5.4
1,557

5
4
7
Average

0.46
(10.5)

108
154
17

70
66

30
59
11.3
3,127

6.8
5.1
9.4
High

0.43
(9.9)

173
159
22

90
38

81
$9
_»
1,868

23
11
9
Medford^
Low

0.36
(8.2)

142
119
16

76
29

51
39
_»
1,475

14
6
6
Average

0.39
(8.9)

157
138
19

81
34

66
71
_#
1,615

19
8
8
"April 1983 through March 1984.
+April 1984 through July 1984.
'Not routinely measured.
"intermediate clarifier effluent.
"Return sludge aeration not used.
* 'Monthly averages.
to 62 percent at three TF/SC plants that
cosettle and 74 percent at Medford, which
does not cosettle. The Meford results are
exceptional.  Primary  sludge concentra-
tions were 3.7 and 5.3 percent at the two
plants practicing cosettling where samples
could be obtained for analysis.
  2. TF Soluble BOD  Removal-The Velz
equation  successfully modeled soluble
carbonaceous BOD5  removal  with TF
depth at Tolleson.
  3. TF Loading—In the range of average
TF BOD6 loadings studied under this pro-
ject (5.8 to 29 Ib/day per 1000 ft3), BOD5
loading does not always exert a strong in-
fluence on final effluent SS. Final effluent
SS  were  always correlated with TF ef-
fluent  SS, which are  most sensitive to
primary effluent SS concentration. The
results show the need  for reliable primary
treatment and consideration of the effect
of primary effluent SS  on  final effluent
quality.
  4. Solids Retention Time (SRT)—Correl-
ations between SRT in the aerated solids
contact tank and final effluent  SS were
not statistically significant at Corvallis and
Tolleson.  A statistically  significant  but
weak  correlation was  observed at
Medford.
  5. Mixed  Liquor Suspended  Solids
(MLSS) —MLSS concentrations of 900 to
2300 mg/L at Medford and Tolleson did
not affect final effluent SS significantly
and only produced an average increase of
about 2 mg/L at Corvallis where the MLSS
concentration varied from 1500 to 7000
mg/L.  The insensitivity to mixed liquor
level means simplification of  operation,
since less attention can be given to sludge
inventory management.
  6. Sludge  Volume  Index  (SVI)-SVI
values varied from 60 to 130 mL/g at Med-
ford, and increasing values were correlated
with reduced final effluent SS. No correla-
tion was observed at Tolleson or Corvallis.
Corvallis  and  Tolleson have large floc-
culator center wells, whereas those at
Medford are much smaller.
  7. Solids  Flocculation —Field test re-
sults at Medford suggest the majority of
flocculation in the aerated solids contact
channel occurs within the first 12 min of
aerated solids contact time in a channel
that has a total hydraulic retention  time of
39 min. Additional SS  removal occurs in
the flocculator center well. The  results
agree  with  observations  at  Corvallis,
Oregon.
  8. Contact Tank Soluble BOD Removal
—Although the primary function  of  the
contact tank is to flocculate SS and par-
ticulate BOD, a significant fraction of the
filter effluent soluble BOD can be  remov-
ed. The Medford contact tank removed an
average  of 75 percent ,of the residual
soluble BOD from the filter in 39 min of
contact time.
  9. Secondary Clarifier Overflow Rate—
Secondary clarifiers that include inboard
launders, high sidewater depths, and floc-
culator center wells are insensitive to 1300
gpd/ft2 at Corvallis and up to 700 gpd/ft2
at Tolleson. These are the maximum over-
flow rates at these respective plants.
  10. Coagulant Addition—Ferric chloride
addition in the aerated solids contact tank
for phosphorus removal at Oconto Falls did
not adversely affect TF/SC operation.
  The full report was submitted in partial
fulfillment of Contract No. 68-03-1818 by
Brown and Caldwell Consulting Engineers
under the sponsorship  of  the  U.S.  En-
vironmental Protection Agency.

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      RaymondN. Matasci, Arthur H. Benedict, and Denny S. Parker are with Brown and
        Caldwell Consulting Engineers. Pleasant Hill, CA 94523.
      James F. Kreissl is the EPA Project Officer (see below).
      The complete report, entitled "Trickling Filter/Solids Contact Process: Full-Scale
        Studies," (Order No. PB 86-183 100/A S; Cost: $ 16.95, 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:
              Water Engineering Research Laboratory
              U.S. Environmental Protection Agency
              Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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EPA/600/S2-86/046
                      0169064    WERL
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                                                IL    60604

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