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 limits which were  imposed in  July of 1988.(8)   Since  the  conversion to  VLR
 technology  (several  other  process  additions  and  modifications  were   made
 simultaneously).   The Brookville plant was designed for an average  daily  flow
 rate of 0.645 mgd and has treated an average flow of 0.7156 mgd over the last 30
 months.  The effluent BOD,  TSS and ammonia nitrogen concentrations have averaged
 4.4 mg/1,  7.5  and 0.55 mg/1,  respectively.<9)  This is compared  to an effluent
 limit of 10.0 mg/1  BOD,  12 mg/1 TSS and 1.5 mg/1  ammonia-nitrogen.

     Hillsboro.  Ohio:   Two  existing tanks were retrofit  and  one new  tank  was
 added during the  construction of the VLR system in Hillsboro,  Ohio.   The first
 basin in the series is 20'W x 127.7'L x 13.5'SWD; the second and third basins are
 15'W x 127.7'L x  13.5'SWD.  The first basin is  operated under  anoxic  conditions
 and was designed for biological phosphorus removal.   Despite  this, alum  is
 currently  added  to the final  clarifier  for  chemical phosphorus removal.(10)
 Aeration in  this  system is provided by  two 10  HP  disc  aerators,  two  15 HP  disc
 aerators and coarse bubble  diffusers.   The Hillsboro plant is designed for  an
 average  flow rate of  0.85 mgd and has operated at  an average flow rate of 0.894
 mgd for  the  May 1989  to January 1991 time period.   The  plant has achieved  an
 average  effluent  CBOD,  TSS and  ammonia-nitrogen concentration of 4.3,  11.3 and
 3.49 mg/1 respectively.  This is compared to an effluent limit of 10.0 mg/1 BOD,
 12  mg/1  TSS  and 1.5 mg/1 of ammonia-nitrogen.

     Ellilav. Georgia:   The  VLR   system  in  Ellijay,  Georgia  is  the  first
 installation to include an intrachannel  clarifier.  This 1.0 mgd system includes
 two 29'W x 125'L x 20.9' SWD reactors with two  15  HP aerators  per reactor.  The
 design criteria given in Table 2 are for one 0.5 mgd reactor but engineers later
 decided  to use two  identical 0.5 mgd reactors.  The system began operation  in
 January 1991 and operated for approximately two  months with limited flows.  Full-
 scale  operation  has  not yet been achieved and  no  valid operating data  is
 available because the VLR basins were  leaking badly due to poor construction.(2>

REFERENCES
 1.   Miscellaneous information provided by Envirex  regarding  design  criteria,
budget costs, etc.
 2.   Telephone  conversations and correspondence with George  Smith of Envirex
 during March, April, May and June of 1991.
 3.  Telephone conversation and correspondence with Ed Brown of Shaw, Weiss and
Denaples on May 24, 1991.
4.  Telephone conversation and correspondence with Tracy Mills of Floyd Browne
Associates, Inc.  on May 24, 1991.
                                      14

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5.  Telephone conversation and correspondence with Dewberry & Davis during June
of 1991.   .

6.  Performance data for the Hohenwald WWTP provided by the Tennessee Department
of Conservation.

7.  Operational Report:   Fries.  Virginia Process Aeration Efficiency Vertical
Loop Reactor.  November 14, 1990.

8.  Brandt, R.A. , E.J. Brown,  and G.B. Shaw.  Innovative Retrofit without Federal
Funds:  Brookville.  Ohio Wastewater Treatment Facilities.   Presented at the 63rd
Annual Meeting of the Ohio Wastewater  Pollution Control  Association,  June 16,
1989.

9.   Performance data  for the Brookfield WWTP,  the Hillsboro  WWTP and the
Brookville WWTP provided by the Ohio EPA.

10. Site visit to the Hillsboro, OH wastewater treatment plant on April 26, 1991.
The treatment plant operator,  Gary Davis, was interviewed during this site visit.
                                      15

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                                   SECTION 3
                             TECHNOLOGY EVALUATION

PROCESS THEORY

Oxygen Transfer

     Aeration in a VLR is typically provided by orbal aeration mixers  and a
coarse bubble diffuser system.   Submersible mixers may, however, be substituted
for the discs aerators.  To date,  the submersible mixers have been used only in
the test facility because they provide circulation but no aeration.(1)

     In designing a VLR  system,  as with any wastewater  treatment  system,  the
designer must consider both  average and peak loadings of both BOD and ammonia
when sizing the oxygen supply.   For a VLR system,  it is common practice to size
the aeration discs to provide sufficient oxygen to remove average BOD loadings
and to nitrify average ammonia loadings.  The coarse bubble diffusers are then
sized to provide the additional aeration capacity required for simultaneous peak
loadings of BOD and ammonia.

     This is  a logical approach because the amount of aeration provided by the
discs is not  easily adjustable.  Adjusting the quantity of oxygen provided by the
discs  generally requires altering the water depth  in the reactors,  thereby
changing  the  immersion  of the   discs  and  their aeration   capacity.    The
manufacturer offers five disc speeds varying from 43 to 55 rpm but does not offer
variable speed  drives  or two speed motors.   By  contrast,  the  amount of oxygen
provided by  the diffusers is adjusted simply by adjusting the output of the
blowers (if variable  speed blowers or multiple blowers are used) or by operating
the blowers intermittently.

     In designing aeration systems, the VLR manufacturer typically recommends a
mechanical alpha (for the disc aerators) of 0.95 and  a  diffused  air alpha of
0.85.<2)  These  values represent the high end of the range of values typically
used  in the  industry.   They  should  be  used  cautiously for  normal domestic
wastewater.  The value of beta used in all available designs is 0.98.  This is
not unreasonable but will vary with the composition of the wastewater.

     Coarse Bubble  Diffusers--

     In some VLR designs, the coarse bubble diffusers located near the bottom of
the reactor are the primary source of oxygen at maximum flow rates.  • For example,

                                       16

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the Willard VLR system is designed for 262.6 pounds of oxygen per hour supplied
by the discs and 294.2 pounds of oxygen per hour supplied by diffused air.  By
contrast, the Brookfield VLR system is designed for 112.8 pounds of oxygen per
hour supplied by the orbal discs  and only 23.2 pounds, of  oxygen supplied by
diffused air.<2>3)  The Brookfield  system was actually operated with no diffused
air for approximately seven months.   Since that period,  diffused air has been
used at Brookfield because operating without it  caused solids deposition in two
of the three reactors.(4)

    The VLR manufacturer states that positioning the diffusers below the baffle
produces an air bubble residence time  which is as much as six times longer than
the residence time for a  conventional aeration system.   The  air bubble flow
pattern is illustrated in Figure 5.<5)  The long residence time allows for more
oxygen transfer, producing an oxygen  transfer  efficiency  (OTE)  which the VLR
manufacturer claims is 1.5 to 2.5  times greater  than the OTE for a conventional
coarse bubble diffuser system.(6)  This would be  25 to 35 percent less than that
achievable  with state-of-art fine bubble diffusers.    The   oxygen  transfer
efficiencies used in various VLR designs is shown in Table 2.  Note that the OTE
varies with the diffuser submergence in a  VLR just as it does in a conventional
system.

    Results of Walworth County Testing:  Clean water oxygen transfer tests were
performed at the Walworth County wastewater treatment plant,  as mentioned in
Section 2.  Some of the tests were conducted by  an independent testing firm and
some were conducted by representatives of the VLR manufacturer.  All of the tests
performed by the testing firm were completed before the addition  of the air
release  plate.    This makes  it  difficult to  evaluate the  results,  as the
manufacturer claims  that the addition of  the air release  plate increased the
aeration efficiency.  The  manufacturer reports  that  the OTE for the diffusers
below the baffle was determined to be 16 percent and that the aeration efficiency
of the diffusers was found to be  over 4 Ibs 02 per horsepower-hour.(1)

    The  firm which conducted  the Walworth County tests was contacted to confirm
the results reported by the VLR manufacturer.  A representative of the testing
firm quoted the  following  test results:<7)

         Air Flow  Rate. SCFM        OTE.%       AE.lb 0,/HP-h
               57                   16.2             4.3
              100                   13.6             3.6
              150                   13.2             3.5
              240                   12.8             3.4

                                      17

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 The above clean water aeration efficiencies (AE) and oxygen transfer efficiencies
 (OTE)  are'for  the diffusers only.  The testing firm stated that the clean water-
 aeration efficiency for the  entirejaeration system (diffusers and orbal  disc
 aerators) was  approximately 3 Ib O2/tHP-h.(7)
                                    [
                                    i
     Aeration Discs—

     At low loadings, the coarse bubble diffusers may be operated intermittently
 to  conserve energy.  Under these circumstances, the orbal aeration discs, which
 also  circulate the  wastewater in a vertical  loop,  are the primary source of
 oxygen.  As was mentioned in the previous section, some VLR systems are  designed
 so  that the majority of the aeration | is . always. provided by the orbal discs.  The
 Brookfield plant is  the  most  extreme  example of this.   The  Brookfield  plant is
 designed so  that approximately  17  percent of  the  oxygen  can supplied by the
 diffusers. <2-3)                      I

     Results of Fries. Virginia  Testing;   Tests were  performed at the  Fries,
 Virginia VLR to determine process aeration efficiency. The wastewater flow rate,
 influent and effluent BOD,  temperature and dissolved oxygen (DO)  concentration
 were measured  five  times a month for ten months.  The  aeration discs were the
 primary source of oxygen during these tests because the loadings to the reactor
 were  low during the testing  period; and the  coarse  bubble  diffusers were not
 operated constantly.(8)

     The Fries  test report states that the diffusers were used 25 percent  of the
 time during the majority of the monitoring  period (October 1989 to May 1990) and
were used 50 percent of  the time during September of 1989 and June of 1990.(8)
 Since the diffusers were used only intermittently during this period, the Fries
 results primarily reflect the process aeration efficiency of the orbal  aeration
 discs.

     From the  monitoring results,  the VLR  manufacturer determined  that the
process aeration efficiency  (PAE) ranged from 1.43  to 4.03  Ibs.  02/HP-h  during
a ten-month period.<8) The values reported by the manufacturer are summarized
in Table 3.  The field correction factor (FCF)  shown in this  table was used to
convert the actual  oxygen requirements (AOR)  to standard oxygen requirements
 (SOR).  The FCF includes adjustments for temperature,  elevation, alpha, beta,
temperature and dissolved oxygen concentration.
                                      18

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                                     TABLE 3
                            VLR PROCESS AERATION EFFICIENCIES
                 (Calculated from Fries Operating Data by the VLR Manufacturer)


Month
Sept
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
June
1.



2.
3.
4.
5.
6.
BOD
in
mg/1
112
113
137
169
137
104
115
147
130
124
BOD BOD
Flow out rem
mgd mg/1 Ib/day
0.095
0.082
0.073
0.069
0.065
0.112
0.083
0.085
0.095
0.064
6 89
6 77
9 83
9 97
6 74
7 97
3 80
5 105
5 103
6 66
T«C
21
17
11
11
11
11
12
13
17
19
DO
mg/1
5.7
6.1
7.1
7.9
8.3
7.0
6.9
6.4
5.7
5.3
AOR
li/day
178
154
166
194
148
194
160
210
206
132


0
0
0
0
0
0
0
0
0
0

FCF
.248
.276
.302
.218
.176
.312
.297
.327
.317
.323
SOR
li/hr
29.9
23.2
22.9
37.1
35.0
25.9
22.4
25.9
27.1
17.0
Power
eHP
11.9
9.2
9.2
9.2
9.2
9.2
9.2
9.2
9.2
11.9
PAE
Ib/
eHP-h
2.51
2.52
2.49
4.03
3.80
2.82
2.43
2.82
2.97
1.43
Definition of terms:
AOR -
SOR -
FCF -
Assumes
Assumes
Assumes
Actual Oxygen
Requirement
Standard Oxygen Requirements


(adjusted to






standard conditions)
Field Correction Factor - AOR/SOR
that ammonia
that complete
is present at a
BOD:NH, ratio
of 10:1
.25.




nitrification occurs.
oxygen requirements of 1.5 Ib O,/lb
BOD; 4
.6 Ib Q,
per
Ib NH,.



AOR is calculated from the BOD loading, rather than the BOD removed.
BOD removed, Ibs/day,
es reported in
Column
5 is actually
BOD
loading
•


     The process  used  by  the  manufacturer  to  calculate  the  actual  oxygen
requirements  during  this  period must  be  evaluated.    The  manufacturer's
calculations  assumed  that 1.5 pounds of  oxygen were consumed per pound of BOD
loading.   It is  typical to assume  that 1.2  to  1.3 pounds  of  oxygen  will be
required for  every  pound of BOD removed.

     The manufacturer further  assumed that  nitrification occurred and  that the
influent   ammonia  concentration  was   12.5  percent   of  the  influent   BOD
concentration.    If the  sludge age  was actually  40  to  50 days  during  the
monitoring period,  as   the   manufacturer   claims,   then  it  is  likely  that
nitrification did  occur.     It  is,  however,   impossible   to  prove   whether
nitrification occurred or how  much oxygen was  consumed  during the process since
no data is available  on  influent or effluent ammonia concentrations.
                                       19

-------
      Because of  the uncertain naturje  of the Actual Oxygen Requirements (AOR)
 values calculated by the manufacturer, the AOR was recalculated by assuming that
 1.2 pounds of oxygen were consumed per pound of BOD.   All assumptions made by the
 manufacturer regarding nitrification were retained.  These calculations yielded
 the process aeration efficiencies (PAE) shown in Table 4.   A quick comparison
 between Table 3 and Table 4 shows that the PAE's shown in Table 3 range from 1.43
 to 4.03 pounds of oxygen per horsepowjer-hour,  while the  corrected PAE's in Table
 4 range from 1.23 to 3.45 pounds  of  oxygen per horsepower-hour.

                                      TABLE 4
                             VLR PROCESS AERATION EFFICIENCIES
                            (Not Calculated by the Manufacturer)

BOD
in
IQff
Month T
Sept
Oct
Hov
Dec
Jan
Fab
Mar
Apr
May
June
1.



2.
3.
4.
5.
112
113
137
169
137
104
115
147
130
124
BOD
out
Flow mg_
rngd 1
0.095 6
0.082 6
0.073 9
0.069 9
0.065 6
0.112 7
0.083 3
0.085 5
0.095 5
0.064 6
BOD NH,
rem in
-a- ¥
84 14.0
73 14.1
78 17.1
92 21.1
71 17.1
91 13.0
78 14.4
101 18.4
99 16.3
63 15.5
NH,
out
¥;
o ;
0 !
o
0 1
0
0 ;
0
0
0
0
NH,
rem
£
11.1
9.7
10.4
12.2
9.3
12.1
10.0
13.0
12.9
8.3
DO
£ ¥
21 5.7
17 6.1
11 7.1
11 7.9
11 8.3
11 7.0
12 6.9
13 6.4
17 5.7
19 5.3
AOR
*
152
132
141
166
128
165
139
181
178
114
FCF

0.248
0.276
0.302
0.218
0.176
0.312
0.297
0.327
0.317
0.323
SOR
*
25.5
20.0
19.5
31.8
30.3
22.0
19.5
23.0
23.4
14.7
Power
eBP
11.9
9.2
9.2
9.2
9.2
9.2
9.2
9.2
9.2
11.9
PAE
Ib/
eHP-h
2.14
2.17
2.12
3.46
3.29
2.39
2.12
2.50
2.54
1.23
Definition of terms:
AOS «
SOR -
FCF -
Assumes
Assumes
Assumes
Actual Oxygen Requirement '
Standard Oxygen
Requirements
(adjusted to
standard conditions)
Field Correction Factor - AOR/SOR 1
that ammonia is
present at a
BOD:NH,
ratio of 10:1.25.
that complete nitrification occurs.
oxygen requirements of 1.2 Ib
Oj/lb BOD; 4
AOR is calculated from the BOD loading, rath
Results
er thi
of Brookfield. OH Testing:
.6 Ib 0, per Ib NH,.
in the BOD 1
Similar
ending
tests

were


conducted

at the
Brookfield, OH wastewater treatment plant.  From the results of these tests, the
manufacturer's representatives calculated an average process aeration efficiency
of  3.38  Ibs.  02/HP-h.cl)    It  is  difficult  to  evaluate  the  manufacturer's
calculations  for   the   Brookfield  plant's  efficiency  because  insufficient
supporting data was provided.  It should be noted, however, that the Brookfield
PAE calculations assumed an oxygen requirement of  1.4  pounds  per pound of BOD
removed.  It should also be noted that!these calculations are based on the period
of operation when Brookfield was  not! using any  diffused air.'1-*'  Brookfield
operators have since decided that diffused air should be used at their facility
to avoid solids deposition in the reactors and to maintain an adequate effluent

                                      120

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dissolved  oxygen concentration. (*'9)   It is  therefore misleading  to. use power
measurements  based on operation without the  use  of diffused air.

     The manufacturer's analysis  of the Brookfield data-.and results states that
the process aeration efficiency for a VLR with intermittent diffuser operation
is high  due to the rapid circulation of  the  wastewater.(1>8)  The disc aeration
mixers produce a wastewater circulation rate of  1.0 to 1.5  feet per second.
Depending  on  the dimensions of  the basin,  the top  and  bottom zones of the VLR
will interchange every one to three minutes.   The manufacturer believes that this
provides a constant surface renewal of oxygen, resulting in a high PAE.

     When designing the disc aeration systems for typical VLRs, the manufacturer
recommends a  process aeration efficiency of approximately 2.7  Ibs.  02/bHP-hr  at
field conditions,  or 3.4 Ib 02/bHP-hr in clean water.a)   The VLR manufacturer
states that  the PAE  used  in current designs is  the same as that used for the
aerators in their conventional oxidation ditch system, despite the fact that they
would  expect  the  PAE  in  a VLR to be  closer  to  3.4 Ib. 02/HP-h at field
conditions.   If the PAE is higher, as expected, the coarse bubble diffusers will
be used  less  than projected by the designs.

     The quantity of  oxygen provided by the aeration discs is a  function of the
immersion  depth and  the  shaft speed.   The  PAE  is also affected by the shaft
speed.  Aeration rates and efficiencies  for various immersions and  shaft speeds
are shown  in  Table 5.  These values were provided by the VLR manufacturer.(1)
                                      TABLE 5
                         AERATION DISC OPERATIONAL CHARACTERISTICS
                              FOR 21 INCH DISC SUBMERGENCE
Shaft
Speed
xjpiu
43
46
49
52
55
Hotes :
Base
Aeration
Lb. 0,/hr.
1.66
1.87
2.08
2.29
2.50

Forward
AE
Lb. Oj/bHP
3.46
3.30
3.20
3.10
3.01

Apex
Aeration
Lb. 0,/hr.
1.25
1.40
1.55
1.70
1.85

Forward
AE
Lb. 0,/bHP
3.47
3.38
3.30
3.25
3.19

            1.    The above values were provided by the VLR manufacturer.
            2.    bHP « brake horsepower
            3.    AE  - aeration efficiency (clean water)
            4.    The above values are for a disc immersion of 21".
                                       21

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                                     I TABLE 5
                          AERATION DISC OPERATIONAL CHARACTERISTICS
                              FOR 21 INCH DISC SUBMERGENCE
                                     (Continued
                 Notes:
                 5.   The following correction factors are recommended by the
                     manufacturer to adjust for other immersion levels.
DISC
SUBMERGENCE
(inches)
20
19
18
17
16
15
ADJUSTMENT OF
Lb. 0,/hr
0.95 '
0.91
0.87
0.83
0.79 :
0.75
DISC
SUBMERGENCE
( inches )
14
13
12
11
10
9
ADJUSTMENT
Lb. 0,/hr
0.71
0.67
0.63
0.59
0.55
0.51
     Denitrification  Oxygen Credits---

     In systems  designed  for denitrification,  the VLR manufacturer claims  an
oxygen credit for oxygen released during denitr if ication.   This oxygen credit is
subtracted from the oxygen requirements and the difference is used  to  size  the
oxygen supply.  Biological denitrification is considered a fully proven process
and  it is  not  within  the scope of ! this work to demonstrate that biological
denitrification can occur.  The biological concepts involved in denitrification
are discussed briefly in this section.   Additional details can be found  in  the
literature.<".11,12)

     The denitrification credit is based on  2.86  pounds of oxygen supplied  per
pound of nitrates as nitrogen denitriif ied, which is the same value used by  others
in the industry.   The  standard oxygen  requirement of 4.6 pounds per  pound of
ammonia as nitrogen nitrified  is also used.  A  typical denitrification  credit
calculation is  as  follows:
     Assume complete nitrification and  80  percent  denitrification.
     oxygen credit which can be taken is then developed as  follows:
                         The
              (80Z) *  (2.86  Ibs.  02/l!b.  N03-N)
                   (4.6 Ibs.  02/lb. NH3-N)
- 50Z
    That is, 50 percent of the oxygen  required for nitrification will be
    returned to the biomass by denitrification.
                                       22

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      It should be pointed out that the oxygen credit for denitrification in the
 VLR system is no  different  than  the  credit  that  could be granted for any other
 suspended growth biological system including oxidation ditches that are designed
 and operated to achieve either partial or complete single-stage nitrification or
 denitrif ication:   The VLR manufacturer has  chosen  to take credit for  this  in
 recommending sizing of  aeration  equipment.

     There  is sufficient evidence  available  to prove that denitrification did
 occur in the Brookfield VLR.   In March of  1991,  Brookfield began  monitoring
 influent TKN monthly and effluent nitrates and nitrites  three times  each week.
 In addition,   Brookfield continues to monitor effluent TKN.   The  data provided
 by Brookfield is summarized in Table 6.(9)
                                      TABLE 6
                               BROOKFIELD DENITRIFICATION
Date
March it
March 18
March 19
March 20
March 25
March 26
March 27
April 1
April 2
April 3
April 9
April 10
April 15
April 16
April 17
April 22
April 23
April 24
May
Average
August 1988 to
Effluent Influent
NO, and HO, TKN
mg/1 mg/1
6.08
7.68
6.78
6.78
6.20
6.24
6.44
7.90
7.90
8.13
5.06
4.80
5.86 22.6
5.54
5.15
4.64
4.97
4.97
24 '
6.18 17.56
January 1991 (average)
Effluent
TKN
Bg/1
1.89











1.37





1.16
1.47
1 55
    The percentage of nitrates  and nitrites  denitrified can be  calculated from
the data in Table 6 by the following procedure:
                                      23

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      1.   Assume that  the Influent concentration  of nitrates  and nitrites as
          nitrogen is negligible. (13)

      2.   Calculate   the   concentration   of  nitrates/nitrites   formed   by
          decomposition and  nitrification of the influent  organic and ammonia
          nitrogen according to the fpllowing equation:

              N03r     -    TKNin - TKNout (neglects  assimilated nitrogen)

          where                      ;
                                     i
              N03f     —    concentration, of nitrates and nitrites  (as nitrogen)
                            formed,  mg/1

              TKNin    -    influent TKN concentration, mg/1

                                     i
              TKNout    ~    effluent TKN concentration, mg/1

     3.   Calculate the percent denitirification by  the  following equation:

              % denitrification - (N03f - N03out)/N03f

     If the  average values  for each  parameter are used neglecting  nitrogen
assimilated by biomass (5 percent of incoming BOD) ,  the results indicate that 62
percent denitrification is occurring.!  If the measurements taken on April 15 are
used,  the results  indicate that 72 percent  denitrification is  occurring.   The
Brookf ield VLR was designed for 80 perjcent denitrification. (2-3)  Designers should
be aware  that closer control of operating parameters are required to assure the
                                     I
80 percent denitrification  oxygen  credit and  should  size aeration  equipment
accordingly.

       and Circulation
     In a standard  VLR,  the mixing  and circulation is  provided by   aeration
mixers.  Submersible mixers are available as an alternative;  the choice between
the two is based on  economics.  To date, submersible mixers were only used at the
VLR test facility.  They do not provide any aeration; therefore the power is used
more efficiently by the discs, which both mix and aerate.  Information from the
Brookfield  VLR indicates that  the diffused  air  equipment contributes  mixing
energy as well.(4>8)                   |
                                      24

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     Circulation around the horizontal baffle is normally designed for an average
rate of 1.0 to 1.5  feet per second.<6)  Two of the VLR systems described in Table
2 are designed  for a velocity  of 1.2  feet per second;  four of the systems are
designed for 1.0 feet per second.

     The design engineer for the Brookville VLR performed velocity tests but did
not document the results.  The only information available from these tests was
that  there was a  wide variation in the  velocity vertically  throughout the
tank.(1*)  Because  the  discs  are positioned near  the  surface, the water velocity
is believed to be highest near the surface of the water and near the bottom of
the VLR.

     The contract  specifications  for the Brookfield VLR required a velocity of
1.0 to 1.5 feet per second in the reactors. Performance tests were conducted to
determine the velocity but  the results  were found to be unreliable due to the
turbulence in the basin.   The velocity test was  then replaced by a mixed liquor
suspended solids profile test.  The initial MLSS profile showed solids deposition
in the smaller  two of the three  basins.   The  disc speed was increased and the
diffused air system began (or resumed)  operation.  After these changes were made,
the mixing equipment passed the MLSS profile test.(4) It is suggested that both
average velocity and mixing criteria be included in VLR specifications.

     The  operator  of  the  Hohenwald WWTP  noted that the  configuration  of the
diffusers in the VLRs has a significant effect on the circulation.   A further
discussion on diffuser configuration can be found in this section.  The operator
changed the diffuser configuration and checked  the surface velocity by timing the
movement of a piece of styrofoam. He  found that  the new diffuser configuration
increased the velocity by one foot per  second over the previous configuration.(15)

Biological Concepts

     Denitrification--

     Biological nitrification  and  BOD  removal  require  oxygen.   Biological
denitrification is sometimes incorrectly referred to as a anaerobic process.  In
actuality, denitrification is accomplished by facultative bacteria which utilize
nitrates (N03)  and nitrites  (N02) in place of oxygen under  anoxic  conditions.(11)
This process consumes carbonaceous materials without removing free oxygen from
the system, thus reducing the  total oxygen requirement  of the total system.
                                      25

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      Denitrification is a two-stage [process.   In the first stage, nitrates and
 carbonaceous materials are consumed, -producing nitrites and water.  In the second
 step, nitrites and carbonaceous materials are consumed, producing nitrogen gas
 (N2), carbon dioxide (C02) , water  and hydroxide  ions  (OH~).  The hydroxide ions
 contribute  to  the alkalinity  of  the wastewater,  replacing a portion  of the
 alkalinity which was removed during 'nitrif ication(11>.

      The manufacturer states that  the stratified oxygen profile frequently used.
 in  VLRs   configured  in  series  allows  BOD  removal,   nitrification  and.
 denitrification to occur in the same ;basin.(2)  When a VLR system is designed for
 BOD  removal,   nitrification  and   denitrification,  a  dissolved  oxygen  (DO)
 concentration close  to zero  is maintained, in the first basin.   A  higher  DO
 concentration will be maintained in |the remaining basins--the DO concentration.
 in the last basin should be above 2.0 mg/1. Some VLR designs have reported D.O.
 levels of 2 to 9 mg/1,  which  is much higher than the process needs.

     Mixed liquor from the last basin'is transferred to the final clarifier. The
 return activated sludge from the final clarifier is recycled to the first basin
 or wasted.   This sludge has a high DO concentration,  although the mixed liquor
 in the first basin has  a low DO.  The manufacturer claims that this combination
 provides sufficient oxygen for nitrification and BOD removal  to occur in certain
 zones in the first basin, while other zones in the same basin are anoxic and are
 denitrifying.C2)                     '.

     Phosphorus Removal—            '

     Biological phosphorus  removal has  been  documented in  various  types  of
 activated  sludge treatment plants where the wastewater  is  subjected to  both
 anaerobic  and aerobic conditions.   When an anaerobic  stage is  placed at the
 beginning of the activated sludge system, it will exert a particularly positive
 effect on  the  development of phosphorus-storing microorganisms.   The  high BOD
 concentration of the wastewater entering the anaerobic stage causes fermentation,
 which produces acetate and other fermentation products.   The  phosphorus-storing
 microorganisms are able to assimilate the fermentation products in this anaerobic
 environment.   Because many competing microorganisms cannot function in  this
 manner, this type of operation gives the phosphorus-storing microorganisms a
 distinct advantage. (16-17)

     During the aerobic phase, the phosphorus-storing microorganisms will  take
up  more phosphorus  than  they actually require  to function  and  store the
phosphorus as polyphosphates.  This "luxury uptake" of phosphorus is maximized

                                      26

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at dissolved oxygen concentrations of 2.0 mg/1 or higher.  If the microorganisms
are  subjected to  an  environment  with  a  low DO  concentration,  the  excess
phosphorus will be released.  It is therefore essential  to biological phosphorus
removal that  the sludge be wasted under  aerobic conditions to ensure that the
phosphorus is not released from the sludge back  into the wastewater.  For similar
reasons,  an aerobic environment should be maintained in the  final clarifiers and
for the return activated sludge.

     The  above process theory  is  utilized in VLRs  designed for  biological
phosphorus  removal.   At Hillsboro, for  example, the  design  dissolved oxygen
concentrations are 0.5 mg/1,  0.5 mg/1 and 2  mg/1 in the first, second and third
basins, respectively.(1)  The Willard VLR  system is also designed for biological
phosphorus removal.  Design DO concentrations are 0 mg/1, 0 mg/1, 1 mg/1 and 2
mg/1 in the first, second, third and fourth reactors, respectively.<2>3)

     The  VLRs  at   the  Hillsboro WWTP  are  not achieving  adequate  biological
phosphorus removal.  Supplementary alum is added in the final clarifier but data
received from the  Ohio EPA indicates that the effluent phosphorus concentration
still exceeds the  effluent limit of 1.0  mg/1 over  half of the time.(18)  It is
unclear whether the apparent problems with biological phosphorus  removal at
Hillsboro are due  to the VLR design or the lack of operator training.(19)

     The  operators at the Hillsboro did  not receive  significant  training from
either the  design  engineer or the VLR manufacturer.   Representatives  of both
companies stated that training was not provided because it was not specified by
the contract.*2-20'  As a result,  at the  time of the site visit the Hillsboro VLR
was apparently being operated with DO concentrations appropriate for phosphorus
removal but the operational theory had never been explained to the  operators.(19)

     The  Brookfield  WWTP  is  required  to  monitor  effluent  concentrations of
phosphorus despite the fact  that the plant's NPDES  permit does not specify an
effluent phosphorus concentration.   The phosphorus  concentration is measured
monthly and  performance data is provided in Chapter 4.   The average effluent
phosphorus  concentration  for the reporting period was 2.2  mg/l.U8)  Typical
untreated weak domestic wastewater contains 4  mg/1  of phosphorus,(13)  but the
Brookfield wastewater is extremely weak (the average influent BOD concentration
during the reporting period was 85 mg/1).   Since the influent concentration is
not monitored, it  is not  possible  to  determine whether significant biological
phosphorus  removal is occurring.   No significant operating  data is currently
available from the Willard VLR system.
                                      27

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Storovater  Bypass                   '

     The manufacturer claims that VLR systems which are configured in series and
include a stormwater bypass are capable of handling storm flows up to five times
the average design  flow without significant solids washout  (Storm-flow as used
herein is defined as high Infiltratipn/Inflow in separate sanitary sewers).  If
the treatment facility is experiencing excess flows or expects high flows in the
near  future,  the  storm  flow  bypass  can  be used  to ensure  treatment  while
minimizing  solids washout.

     A typical storm flow configuration is shown  in Figure 6.  During  high flows,
the influent is channeled into  the third reactor, bypassing the first two tanks.
The effluent from the VLR flows to the final  clarifier and the  return activated
sludge from the clarifier is pumped into the first reactor  in  the series.  The
effluent quality is lower than average  but the MLSS concentration in the first
and second reactors is preserved and' solids washout is prevented.  This ensures
that the system effluent will return! to normal almost  immediately when the flow
rates  decrease and the  bypass is i discontinued.    Section 4  describes  the
performance 'of the Brookfield VLR in the stormwater bypass mode during a period.
of excess flows.                    !

     Conventional  activated sludge systems may  experience excess solids  carry-
over from the secondary clarifiers due to high clarifier  overflow rates and the
fact that all of the MLSS is subject! to hydraulic wash-through  to the secondary
clarifier.  This can be mitigated somewhat by higher  return solids  pumping but
does not offer  the  advantage of MLSS basin isolation.  The  stormwater by-pass
feature described herein is not unique to the VLR, but may also be incorporated
into conventional plug flow aeration basins.

Design Criteria
     Design  criteria for  a  typical  domestic  waste  with  an influent  BOD
concentration of 220 mg/1 are  shown in Table 7.  In addition, designs  for plants
currently  in operation  or under 'construction can be  found  in Table 2.   A
representative  of the VLR manufacturer stated that  their recommended design
criteria becomes increasingly conservative as  the flow rates decrease. A larger
safety factor is recommended for the design of small systems to account for  the
increased probability and severity  of shock loadings. <2.3,i«.2i>
                                      28

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Storm Row Bypass Configuration for
  Vertical Loop Reactors in Series

-------

-------
                                        TABLE 7
                            VERTICAL LOOP REACTOR DESIGN CRITERIA1
Design size, mgd:
BOD loading, lbs/1,000 ft3
MLSS, mg/1
HRT, hours
SRT , days
Lb. solids produced/lb. BOD
Sludge age, days
Aerobic digestion, days
Lb. Qj required/lb. BOD2
Lb. Oj required/lb. ammonia
Denitrification credit, Z
Alpha mechanical
Alpha diffused
Beta
DO in tank #1, mg/1
DO in tank #2, mg/1
DO in tank #3, mg/1
Channel velocity, ft/sec
Power use per disc, bHP
Lb. 02 per disc
Diffuser clean water OTE, Z
Diffuser submergence, ft.
Blower efficiency
1.0 2.0 5.0 or more
19 27 - 34
4,000 A, 500 5,000
17 12 . 10
28 23 20
0.82 0.82 0.82
11.2
20
1.15
4.6
BO
0.95
0.85
0.98
0.0
1.0
2.0
1.0
0.32
1.1
18
19
0.7
 Clarifier loading, gpd/ft2                                                     353
 1    These design criteria are based on a •temperature of 20V. an influent BOD concentration of 220
      mg/1, 25 mg/1  of ammonia to be nitrified,  an  effluent BOD concentration of 5 to 10 mg/1,  an
      effluent suspended solids concentration of 5 to 10 mg/1 and an effluent ammonia concentration of
      0.0 to 0.5 mg/1.
 2    Note that this value is significantly lower than that used by the VLR manufacturer to determine
      aeration efficiency as shown on Table 3.

     Hydraulic  Design--


     If  the  stormwater bypass  feature is to be  included  in  a VLR design,  the
influent or effluent  structure must  include  the necessary  bypass gates,  valves
or weirs to allow for bypass operation.   Depending  on the  bypass configuration
used,  the VLR influent may be  channeled  to a reactor which is at the end of  the
reactor series during normal operation.   The other option is  to channel the  VLR
                                            30

-------

-------
effluent  such  that it flows out of the first or second reactor, bypassing all
subsequent.reactors.

     The bypass design must also include gates between the reactors such that one
or more of the reactors in a series can be isolated. Wastewater should not flow
to or from the  isolated reactors, although the return activated sludge must be
pumped to one  of the  isolated reactors.  Ideally,  all bypass equipment will be
electronically  actuated so that the stormwater bypass  can be easily and quickly
activated or/deactivated.

     In certain cases, it will be advantageous to include an effluent weir  in the
reactor design.  An effluent weir gate will make it possible to  adjust  the water
level in  the  VLRs, thereby adjusting the aeration disc  immersion.   This will
generally be  the  only  practical way to adjust  the disc  immersion,  which is
necessary if it is  desired to adjust the amount of aeration provided by the disc
aerators.   The first  two VLRs  installed did  not have level  control but the
following three (Brookville, Fries and Hillsboro)  all have  some degree  of level
control.

     Disc  Aerator Placement--

     When  multiple  VLRs are designed with common walls,  it is prudent to stagger
the location of the disc aerators.  That is, the drive for a disc aerator  in the
first basin should not be directly across from the drive for an aerator  in the
second basin.   Experience has shown that this type of configuration makes it more
difficult to access the drives for maintenance purposes.(19)  A specific situation
where the drives for three basins are in the same  line is mentioned further on
in this section.

     Diffuser  Configuration--

     The Hohenwald  WWTP operator noted that the configuration of the diffusers
in a VLR has a significant effect on the circulation.  When the Hohenwald VLR was
originally constructed,  the diffusers were perpendicular  to  the  flow in the
reactor.  The operator suspected that this was impeding the circulation, so he
rearranged the  diffused air system in one basin  such  that the diffusers were
parallel to the flow.  He found that this diffuser configuration increased the
velocity by one foot per second over the original configuration.  He has since
reconfigured a second basin and plans to change the third basin when he has the
opportunity.(15)   A  representative  of the VLR  manufacturer  stated  that VLR
systems are currently designed with the diffusers parallel to the flow.(2)

                                      31

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process Design                      '                                .
                                    i
     The VLR manufacturer will provide assistance to individuals who are involved
in designing a new or renovated wastewater treatment system which includes a VLR.
In addition, the manufacturer will provide a process warranty for their designs.
The performance  guarantee provided for the Willard WWTP  is discussed in this
section.                            i
                                    i
     In the design of a VLR system,  the oxygen requirements recommended by the
manufacturer may be of particular concern.  In past designs,  some engineers have
decided to  follow the oxygen requirements recommended by the manufacturer and
have subtracted the denitrification credit from the amount of oxygen required for
BOD removal and nitrification.  Other engineers have chosen  a more conservative
approach when determining total oxygefr requirements.  This is a choice which must
be made by  the individual designer. |

Reactor Configurations
     VLRs  may be  configured  in  parallel  or  in  series.    Flow  patterns  and
configurations for VLRs in parallel and in series  are  shown  in  Figures 2 and 3,
respectively.

     Vertical Loop Reactors  in Series--
                                    I          " «,„   .
     Five  of the  seven operating  VLR isystems are configured  in  series.  VLRs in
series can  be operated with  stratified dissolved oxygen  (DO)  profiles, which
provides several advantages.  Stratified DO profiles are particularly useful in
systems designed for denitrification and/or phosphorus removal. Details on the
application of stratified DO profiles to denitrification and phosphorus removal
are found in this section.

     Vertical Loop Reactors  in Parallel—

     The VLR system in Fries,  Virginia  includes two reactors which are designed
for parallel operation,  although  only one is currently  in use. Parallel reactors
have several advantages over individual reactors.  These include reduced material
costs (they share  a common  wall) and increased process flexibility.  Parallel
reactors  are convenient  for treatment facilities which  currently have  low
loadings but project significant increases in the future.
                                    I
                                    I
     For a typical plant, however, it will generally be advantageous to operate
multiple VLRs in series rather than in parallel.  The Hohenwald VLR system can
                                      32

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be operated in series or in parallel.  The Hohenwald VLRs are currently operated
in  series  because   this  produces  a  better  effluent  than  does  parallel
operation.(15)

Weather Protection Equipment

     Optional equipment  is available  to  protect  the  VLR  components in cold
weather.  Hoods may be installed to cover the aeration discs and prevent snow and
rain freezing on the  discs.  Ice guards may be installed upstream of each aerator
to keep large pieces  of ice away from the discs.  Splash guards are  available for
the ends of the aerator  shafts.  These may be used to avoid splashing wastewater
onto the bearings.(1)

COMMON MODIFICATION  OF VERTICAL LOOP REACTOR DESIGNS

Intrachannel Clarifier

     The VLR  system  in Ellijay,  Georgia  includes  an  intrachannel clarifier,
thereby  eliminating  the  need  for a  separate clarifier.    The   intrachannel
clarifier also eliminates the return activated sludge (RAS)  pumping required in
a standard configuration.(1)  It is not possible to  evaluate  the performance of
the intrachannel clarifier when installed  in the VLR process at this time, as no
significant operating data is available.

O&M COMPLEXITY AND REQUIREMENTS

Routine Maintenance

     The operators  of all municipal wastewater  treatment  plants which have
employed VLRs for over six months were interviewed during the preparation of this
report.   Site visits were made  to Brookville, Hillsboro and Brookfield;  the
operators of the Fries and Hohenwald wastewater treatment plants were interviewed
on the  telephone.   All operators stated that the VLR did  not  require much
maintenance.  The operators' estimates of the VLR maintenance time ranged from
two hours per week to two  hours per  day and did not seem to be related to the
design flow rate.  The maintenance tasks listed by the operators included adding
oil,  changing the oil, lubricating bearings and cleaning. (8.15.19,22,23)

     Operators who had previously worked with other types of biological  treatment
systems were asked to compare the maintenance requirements of those systems to
a VLR.  The Hillsboro operator stated that  the maintenance requirements for a VLR

                                      33

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were about the same as for a two-stage activated sludge system.(19>  The Hohenwald
operator said that the VLR maintenance did not require much more time than the
trickling filter he had worked with previously.(15)  A third operator stated that
the Brookville VLR requires only about half as much maintenance as the activated
sludge system it replaced.(22)       !

     Definitive comparisons between the maintenance requirements of VLRs versus.
competing technologies cannot be made based on the limited data available.  It
would seem reasonable however to expect a slightly higher maintenance cost for
VLRs than  for oxidation ditches became  of the dual  aeration  system,  limited
access to diffusers, and the mechanical components associated with the adjustable
effluent weir.
                                    i
Major Maintenance
                                    I
                                    I
     During the  preparation  of  this  report,  a  site visit was  made  to the
Brookville WWTP.  The  Brookville VLR has  been in operation for over two and a
half years.  During this period,  it has not been necessary to repair or replace
any portion of the VLR.C22)          >

     The  second site visit was to the| Hillsboro VLR, which has been in operation
for approximately two years.  At the time of the visit, the plant employees were
preparing to replace a bearing in  a|disc  aerator drive shaft.   To the best of
their knowledge, this was the first repair on the VLR since  start-up (the plant
has three basins and six disc aerators).  The bearing was under warranty, so a
new bearing was supplied by the manufacturer at no cost to  the plant.(19)
                                    i
     The  Hillsboro operator was disappointed,  however, that the manufacturer was
not willing to make the repair.  Replacing a bearing in the Hillsboro VLR system
is particularly difficult because  the disc aerator  drives  in  the three  tanks
interfere with each other.  This makes it necessary to  raise the  drive shaft much
higher than  would be  required  in  a different  system.   For this  reason, the
operator plans  to have false  work  installed  in the basin to support a jack to
lift the drive shaft.   The  design issues associated with this  problem were
discussed previously in this  section.

     The  Hillsboro  operator also mentioned a problem which occurred at start-up.
The turning vanes on the Hillsboro VLR collapsed when the water began circulating
through the basins.  They were repaired and strengthened and have not presented
any further problems.(19>
                                      34

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     The third site visit was made at the Brookfield WWTP, where a VLR system has
been in operation since November of 1987.   The only major VLR maintenance which
has been required was  the  replacement of a  bearing on one of the four  disc
aerator  drives.   The operator believes that  the  problem was caused by faulty
installation, since the bearing failed out almost immediately after start-up and
no other bearings have  required replacement.'8*

     Both of the  operators  who  participated  in  telephone  interviews   have
experienced  problems  with their disc  aerator drives.   The Hohenwald operator
stated  that  he has  replaced six aerator  drives in less than  four years of
operation.   The  Hohenwald WWTP has  four disc  aerators,  indicating an average
drive life of about two and a half years.   When  this  problem  was  discussed  with
the manufacturer, a  representative  stated  that the  Hohenwald plant has had to
replace  a number  of drives  because  the  wrong type  of lubricant  was being
used.<2>15)

     The operator  of the  Fries treatment plant stated that  the  only major
maintenance required on the Fries VLR involved the gearbox which drives the  disc
aerators.  It has been necessary to replace bearings in each of  the two aerators
in this VLR system.<23>  These VLRs have been  in  operation for over three years,
but only one aerator is used at a time. Based on this  information, each of the
aerator drives at the Fries WWTP has  required  one or more new bearings  after  less
than one and a half years of operating time.

Operation

    When operators were  questioned  about  the time  required to operate a VLR
system, their responses varied from one to three hours per day.   Operating tasks
included  monitoring  dissolved oxygen concentrations,  pH,  sampling,  sample
analysis and reporting.(9fl5>19i22>23)  The variation in operating times seemed to
be primarily dependent  on the amount  of sample analysis  done in-house.  Design
flow rates did not have a significant effect on operating time.

    The Hillsboro operator stated  that the operational complexity and  time
requirements of  a VLR were similar  to those  for  a  two-stage activated sludge
system.  The  only operational difference he  mentioned was  that he found it easier
to handle upsets  in  a two-stage activated sludge system than  in a VLR.(19)  A
second  operator  stated  that it  is  more  difficult  to  operate  a VLR  than a
trickling filter  because the VLR requires more testing.  He  also mentioned,
however, that the VLR seems to handle upsets  better than  a trickling  filter.(15)
The Brookville operator commented that it was possible to operate the  VLR system

                                      35

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under  a  wide  range  of  MLSS  concentrations  and still  meet  the  effluent
requirements . {22>
                                     [
     Table 8 summarizes the use of unique design features of the VLR by five of
the  seven plants  evaluated.   Interviews with  operators  of the  VLR systems
indicated  that in general,  the operators  were unfamiliar  with,  the overall
capability  and flexibility of  the  VLR  system  to  achieve varying  levels  of
nutrient  control.   Adequate site  specific, process  oriented  training  was
notprovided by either the manufacturer or the design engineer  for  any  of the VLR
systems evaluated.
                                     TABLE 8
                             USE OF CLk^KED VLR ADVANTAGES  .
                                     i   Stormwater      Effluent      Biological
           Facility        Denitrification      Bypass _ Heir _ P Removal
Hohenwald, TO
Brookfiold, OH
Fries, VA
Brookville, OH
Hillsboro. OH
Unknown
Y«E
Ho :
Unknown |
Unknown 1
Yes
Yes
No
No
No
No
No
Yes
Yes
No
Mo
Mo
Ho
Ho
Ho
PERFORMANCE GUARANTEE
     The manufacturer will provide a performance guarantee for VLR installations.
The parameters specified include the effluent concentrations of CBOD5, suspended
solids, NH3-N and phosphorus.<24)     i
                                     \
     In addition to  the above process  guarantee, the manufacturer provides a
mixing  guarantee  that states that  the  mixing equipment  must  maintain a "MLSS
concentration within 10 percent of  the high  and low readings in each tank."  If
the disc aerators do not meet the mixing guarantee, the manufacturer "shall, at
no  cost to  the owner,  provide and install  velocity deflector  baffles,  and
demonstrate the desired velocities  and mixing."(2A)

     The performance guarantee is based on the following condition!?:

     1.   The VLR  must be installed and built in "strict compliance"  with the.
         manufacturer's  specifications.

     2.   The VLR system must be installed and built in "strict compliance" with
         the specifications of the  design engineer.

     3.   The owner shall provide operational conditions  and influent wastewater
         which meet  certain criteria.

                                       36

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     The  performance  guarantee  describes  the  circumstances  of  a  60  day
 "Performance Test" in detail.  Before the Performance Test will be conducted,  the
 entire treatment plant must be  operational  and the VLR must operate within  a
 specified set of operating conditions for a minimum of thirty consecutive days.
 However,  the Performance Test must also be conducted within a certain time frame.
 If the owner does not  begin  testing within this time period,  the ''system shall
 be deemed accepted. "(2A) The "Performance Test" specified by the manufacturer is
 highly qualified and  contains terms  and  conditions  that  severely limits  the
 manufacturer's liability  in  the  event of a legitimate process  failure.

     The performance guarantee does  not  appear to directly address the issue of
 oxygen supply.  That is, the guarantee provided to Willard, OH does not guarantee
 that the  system will be able to  achieve  the  design  DO concentrations.   Rather,
 the oxygen content in the  reactors is one of the operational conditions which  the
 owner  must supply for the performance  guarantee  to be valid.   However,  the
 performance specifications do  state that if "the results of the test  indicate  a
 deficiency in the system to  meet  the  performance or  design guarantees"  the
 manufacturer  will  "take  additional  data, perform design and engineering work,
 make adjustments to the system, check and revise the owner's operating procedures
 and then  request a new performance  test."

 REFERENCES

 1.  Miscellaneous  information provided  by Envirex  regarding design criteria,
 budget  costs,  etc.
 2.  Telephone conversations and correspondence with George  Smith of  Envirex
 during  March, April, May  and June of 1991.
 3.  Telephone  conversation and correspondence with Tracy Mills of Floyd Browne
Associates, Inc. on May 24, 1991.
4.  Floyd Browne Associates,  Inc. Performance Certification Report.  Submitted
 to Trumbull County on April 29,  1989.
 5.  Brandt, R.A. , E.J. Brown,  and G.B. Shaw.  Innovative Retrofit without  Federal
Funds:   Brookville. Ohio Wastewater Treatment Facilities. Presented at the 63rd
Annual  Meeting of the  Ohio Wastewater Pollution Control Association, June 16,
1989.
6.  Huibrestse, G.L., G.W. Smith, D.J. Thiel, and J.W. Wittmann.  Introduction
to the Vertical Loop Reactor Process.   June 12, 1986.
7.  Telephone conversations with  Greg Hubert of Radian on April 30, 1991  and May
2, 1991.
8.  Operational  Report:   Fries.  Virginia Process Aeration  Efficiency Vertical
Loop Reactor.  November 14, 1990.
                                      37

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9.  Site visit to the Brookfield, OH jwastewater treatment plant on May 15, 1991.
The treatment plant operator, Daniel Earhart, was interviewed during this site
visit.

10. Johnson, W.K.  and  Schroepfer,  G.J.   Nitrogen Removal  by Nitrification and
Denitrificatlon.  Journal WPCF, August 1964.

11.  Process Design Manual for Nitrogen Control.  U.S. Environmental Protection
Agency.  October, 1975.

12.   Schroeder,  E.D.   and  Busch,  A.y.   The  Role of Nitrate Nitrogen  in Bio-
Oxidation.  Journal WPCF, November 1968.

13. Metcalf & Eddy, Inc.  Wastewater Engineering:  Treatment. Disposal. Reuse.
McGraw-Hill, 1979.                  .

14.  Telephone conversation and correspondence with Ed Brown of Shaw, Weiss, and
Denaples on May 24, 1991.

15.   Telephone interview  of Paul Webb on  April 18, 1991.   Mr.  Webb is the
Hohenwald, TN wastewater treatment plant operator.

16. Design Manual for Phosphorus Removal.  EPA/625/1-87/001, U.S. Environmental
Protection  Agency,  Center  for Environmental  Research  Information and Water
Engineering Research Laboratory, Cincinnati, OH, September, 1987.

17. Goronszy,  M.C.  Simplified Biological  Phosphorus Removal  in  a Fed-Batch
Reactor Without Anoxic Mixing Sequences.

18.   Performance  data for  the Brookfield  WWTP, the Hillsboro WWTP  and the
Brookville WWTP provided by  the Ohio EPA.

19.   Site  visit to the Hillsboro, OH wastewater treatment plant  on April 26,
1991.  The treatment plant operator, Gary Davis, was interviewed during this site
visit.

20.  Telephone conversations with Wpolpert engineers during May of 1991.

21.   Telephone  conversation and correspondence with Dewberry and Davis during
June 1991.

22.   Site  visit  to the Brookville, 0H wastewater treatment plant on April 19,
1991.  During this visit, Ron Brandt and Jon Weist were interviewed.  Mr. Brandt;
is the Brookville WWTP operator; Mrj Weist is his assistant,

23.  Telephone interview of Eugene GJraham on April 18, 1991.  Mr. Graham is the
Fries, VA wastewater treatment plant operator.

24.  Willard, OH wastewater  treatment plant performance specifications.
                                      38

-------
                                  SECTION 4
                                  PERFORMANCE

PERFORMANCE SUMMARY
     Performance  data for  the  five VLRs which have  over six months  of valid
operating data is summarized in Tables 9 through 13.  This data was -obtained from
the state and local agencies in Ohio, Tennessee and Virginia. (1'2-3)

     As shown in Table 9, the Hohenwald plant is operating below the design flow
rate of  1.1  mgd but is  meeting effluent requirements easily.   Hohenwald has
exceeded its 30-day ammonia permit limit only once (excluding the first three
months of operation)  and has  never  exceeded  its  30-day  BOD5  permit limit
(excluding the first two months of operation)."'   Similarly,  the Fries VLR is
operating below the design flow rate of 0.22  mgd  and has never,  excluding the
first month of operation, exceeded the effluent 30-day BOD5  limit.<2)

     As shown in Table  10,  the Brookfield system is operating above the design
flow rate of 1.3 mgd and is consistently achieving effluent concentrations well
below the  required levels.(1)   Brookville  is  also operating well.   The plant
effluent has only  exceeded the 30-day TSS limit twice  and  the  30-day ammonia
limit once in thirty months of operation.  The 30-day BOD5 limit has never been
exceeded.(1)

     The  Hillsboro  VLR, Table 13, which has an  average flow rate slightly higher
than the design capacity of 0.85 mgd, has experienced numerous violations of 30-
day effluent limits for ammonia, TSS and phosphorus.  The 30-day BOD limit has
also been exceeded twice.U)  The effluent BOD  appears to be related to the flow
rate. The two months with excessive effluent BOD's were also the  two months with
the highest influent flow rates.

Performance During Periods of Excess Flows

     Performance data was collected  at  the  Brookfield VLR,  during a period of
excess flows.   This plant was  constructed with the  stormwater  bypass  feature
discussed in Section 3.   The design flow rate is 1.3 mgd; a flow  of 4.8 million
gallons  was recorded for a 24-hour period during  this  event.   The VLR bypass
configuration described in Section 3. was used with excellent results.  The data
collected  during  this   period of  excess  flows  was  obtained  from  the  VLR
manufacturer   and   is   presented  in  Table  14.<4)    The   Brookfield  VLR
performanceduring  this  period of excess flows may be compared  to the  overall
performance data for the Brookfield facility, which  is shown in Table 10.

                                      39

-------
APPLICATIONS AND LIMITATIONS

Applications

     As shown in Tables 9  through 13, VLRs are capable of producing a very high
quality effluent (CBOD5 less than 10 mg/1; TSS less than 10 mg/1; NH3-N less than
1.0 mg/1) .  The VLR technology may be appropriate for wastewater treatment plants
which have stringent ammonia or BOD limits.   The process is also applicable for
moderate degrees (60 to 80 percent) of total nitrogen and phosphorus removal.

     VLRs are applicable  over  a wide range of flow  rates  and  influent  BOD
loadings.  The multiple basin series arrangement with the stormwater bypass is
applicable for facilities with high peak to  average flow ratios.

     A VLR facility should be considered when land area  is an important concern.
A VLR requires significantly less area than an oxidation ditch  or a conventional
activated sludge treatment plant.  Land area requirements are discussed further
in Section 5.

     VLRs should also  be  considered I when it is possible  to  retrofit existing
basins to meet increased flow or more stringent effluent requirements.  Two of
the VLR systems  currently  in operation were constructed as retrofits of existing
aeration basins.  The  effluent from jthe aeration basins which were used at the
Brookville WWTP prior to 1988  did not meet the requirements of the NPDES permit
issued to Brookville effective  July 1,  1988.  The  summer ammonia limit of 1.5
mg/1  was of  particular concern.   The  retrofit,  which  did  not  require  the
construction of any additional aeration basins, has  allowed Brookville to comply
with this ammonia limit.<5)

     The Hillsboro VLR  system  includes two retrofit  reactors and one new basin.
The  Hillsboro operator stated  that I the  previous activated sludge  system was
designed for approximately 0.5 mgd, while the current VLR system is designed for
0.85 mgd.(6>

Limitations

     Because  there is  a limited amount of  operating  information available on
VLRs, the operators may feel  that they cannot get  assistance with operational
problems.  There appears to  be a lack of  understanding on  the  part of both
designers and operators concerning |the  applicability and flexibility of the
process for nutrient control.       '
                                    i
                                      40

-------
                TABLE 9.
   HOHENWALD EFFLUENT MONITORING DATA
(Monthly Averages from Operating Reports)
Month/Year
Jul 1987
Aug 1987
Sep 1987
Oct 1987
Nov 1987
Dec 1987
Jan 1988
Feb 1988
Mar 1988
Apr 1988
May 1988
Jun 1988
Jul 1988
Aug 1988
Sep 1988
Oct 1988
Nov 1988
Dec 1968
Jan 1989
Feb 1989
Mar 1989
Apr 1989
May 1989
Jun 1989
Jul 1989
Aug 1989
Sep 1989
Oct 1989
Nov 1989
Dec 1989
Flow
mgd
0.489
0.594
0.339
0.347
0.313
0.624
0.7E1
0.875
0.674
0.610
0.346
0.218
0.270
0.286
0.326
0.232
0.4SO
0.603
0.860
0.872
0.628
0.532
0.536
0.520
0.811
0.351
0.483
0.514
0.561
0.225
Temp
•C






10.0
10.6
13.3
16.5
19.0
21.8
23.0
23.8
22.8
20.7
17.9
14.8
13.6
12.9
14.0
16.4
19.0
21.0
22.3
23.4
22.7
20.9
17.9
13.5
BOD5
mg/1
37.0
52.0
5.0
4.0
5.0
6.0
5.0
4.0
4.2
4.0
4.0
4.0
4.0
4.0
3.0
4.0
4.0
5.0
5.0
5.0
3.0
3.0
3.0
1.8
2.0
2.5
2.0
1.8
2.0
2.5
TSS
mg/1
37.0
9.0
5.0
4.0
8.0
11.0
10.0
8.0
8.0
7.0
7.0
6.0
7.0
5.0
4.0
3.0
4.0
7.0
5.0
4.0
3.0
2.0
4.0
4.5
3.0
3.0
3.0
1.9
2.1
3.0
NHj-N
mg/1
11.10
14.00
3.00
0.50
0.54
0.26
0.40
0.12
0.13
0.15
0.37
0.33
0.36
0.25
0.50
0.18
0.22
0.30
0.11
0.12
0.11
0.18
0.40
0.20
0.40
0.20
0.20
0.10
0.10
0.17
MLSS
mg/1
,,





3263
3508
3916
5155
5766
6637
5948
3526
3794
3256
2417
2135
2549
3556
3606
3168
4B14
3688
5266
4290
4390
4224
3893
3589
VLR
DO
mg/1






4.9
5.9
2.5
2.9
2.3
2.3
2.9
3.7
3.7
4.1
4.6
5.1
5.5
4.4
3.0
3.1
1.5
1.6
3.0
1.2
3.6
4.9
5.0
5.8
                 41

-------
                 TABLE  9
   HOHENWALD EFFLUENT MONITORING DATA
(Monthly Averages front  Operating Reports)
               (Continued)
Month/Year
Jan 1990
Feb 1990
Mar 1990
Apr 1990
May 1990
Jun 1990
Jul 1990
AUE 1990
Sep 1990
Oct 1990
Hov 1990
Dec 1990
Jan 1991
Feb 1991
Mar 1991
Apr 1991
Suomary: Minimum
F^yjmugn
Average
Limit
Motes :
1. Ice Hohenwald VLR began
Flow
mgd
0.704
0.639
0.596
0.389
0.655
0.368
0.387
0.238
0.236
0.186
0.300
0.752
0.529
0.7*7
0.613
0.789
0.186
0.875
0.508
HA

operation
Temp
•C
12.9
|
14.3
14.9
16.2
18.3
20.5
22.0
23.0
23.0
21.0
18.0
15.0
13.0
12.9
14.0
17.0
10.0
23.8
17.7
IIA
i
in; July
BOD,
mg/1
2.3
2.4
2.3
2.0
2.4
3.0
3.0
3.0
2.0
2.0
3.0
3.0
4.0
4.0
4.0
2.3
1.8
52.0
5.1
25.0

1987.
TSS
mg/1
3.0
3.0
3.7
4.0
3.0
4.0
4.0
4.0
3.0
2.0
5.0
4.0
4.0
5.0
4.9
3.3
1.9
37.0
5.4
45.0


NH,-N
mg/1
0.20
0.14
0.15
0.13
0.20
0.40
0.30
0.20
0.20
0.20
0.40
0.13
0.80
0.90
1.30
0.50
0.10
14.00
0.89
1.00


MLSS
mg/1
3023
3260
3467
4150
4418
6405
4409
3835
3636
3322
3314
2300
2787
3076
2844
3997
2135
6637
3865
HA


VLR
DO
mg/1
5.7
5.6
4.1
3.4
2.4
1.8
2.8
2.0
1.4
1.7
3.5
5.9
4.2
4.3
3.6
1.5
1.2
5.9
3.5
HA


2. Blank cells indicate data which was not available.
                   42

-------
                                        TABLE 10.
                           BROOKFIELD EFFLUENT MONITORING DATA
                         (Monthly Averages from Operating Reports)
Month/Year
Aug 1988
Sep 1988
Oct 1988
Nov 1988
Dec 1988
Jan 1989
Feb 1989
Mar 1989
Apr 1989
May 1989
Jun 1989
Jul 1989
Aug 1989
Sep 1989
Oct 1989
Nov 1989
Dec 1989
Jan 1990
Feb 1990
Mar 1990
Apr 1990
May 1990
Jun 1990
Jul 1990
Aug 1990
Sep 1990
Oct 1990
Mov 1990
Dec 1990
Jan 1991
Sunmary : Minimum
Maximum
Average
Limit
Flow
mgd
1.128
1.176
1.144
1.794
1.433
1.732
1.736
1.748
1.891
1.976
2.825
1.546
1.091
1.508
1.219
1.374
1.212
1.745
2.726
1.425
1.841
1.406
1.376
1.961
1.268
1.698
1.918
1.464

2.180
1.091
2.825
1.639
HA
Temp
•C
22.3
20.2
16.9
13.0
9.8
8.7
7.6
8.8
10.2
12.8
16.4
19.2
20.4
19.7
16.5
12.9 ,
8.6
8.2
8.1
9.5
11.1
14.2
17.2
19.2
20.3
19.3
16.5
13.5

7.9
7.6
22.3
14.1
HA
TSS
mg/1
1.4
1.8
2.0
2.3
1.8
1.6
2.7
5.7
2.5
3.1
6.0
2.1
2.3
4.0
3.2
2.8
2.4
2.4
3.1
4.4
2.7
3.0
2.2
3.4
2.0
3.4
3.3
5.7

2.5
1.4
6.0
3.0
12.0
HHj-N
mg/1
0.15
0.07
0.21
0.13
0.16
0.14
0.15
0.30
0.30
0.12
0.50
0.17
0.18
0.75
0.16
0.15
0.14
0.14
0.21
0.18
0.23
0.18
0.16
0.20
0.16
0.23
0.35
0.12

0.26
0.07
0.75
0.21
(2)
TKN
mg/1
2.19
2.66
1.79
1.43
1.60
1.11
1.15
1.19
1.36
1.45
2.58
2.00
1.68
2.72
1.33
1.93
1.10
0.94
1.27
1.18
1.01
1.23
1.44
1.35
1.49
1.69
1.57
1.26

1.32
0.94
2.72
1.55
NA
t
mg/1
3.78
4.00
3.60
2.20
1.00
2.20
1.40
1.80
1.20
1.70
1.00
3.60
4.00
2.00
3.80
4.60
1.90
2.20
0.90
1.40
2.40
0.00
1.14
5.28
1.46
1.04
1.20
1.84

0.84
0.00
5.28
2.19
HA
BODj
mg/1
1.7
1.8
1.6
1.7
1.5
1.6
1.6
2.2
1.7
1.7
2.2
1.7
1.7
1.8
1.6
1.6
1.5
1.5
1.8
1.5
1.5
1.2
1.1
1.6
1.2
1.7
1.4
1.2

1.5
1.1
2.2
1.6
10.0
Notes:
      The Brookfield VLR started up in November 1987.
1.

2.


3,
      The 30-day  average  affluent  ammonia  limits  are  1.5 mg/1 in the Bummer and 3.0 mg/1
      in the winter.
      Blank cells indicate data which was not available.
                                           43

-------
             TABLE  11.
  FRIES EFFLUENT MONITORING DATA
(Monthly Averages from DMR Reports)
Month/Year
Fob 1988
Mar 1988
Apr 1988
Hay 1988
Jun 1988
Jul 1988
Aug 1988
Sep 1988
Oct 1988
Nov 1988
D.c 1988
Jan 1989
F«b 1989
Mar 1989
Apr 1989
May 1989
Jun 1989
Jul 1989
Aug 1989
Sep 1989
Oct 1989
Nov 1989
Dae 1989
Jan 1990
Fob 1990
Mar 1990
Apr 1990
May 1990
Jun 1990
Jul 1990
Aug 1990
Sep 1990
Oct 1990
Nov 1990
Dec 1990
Flow
ted
0.080
0.079
0.090
0.041
0.048
0.046
0.041
0.042
0.028
0.033
0.033
0.037
0.040
0.029
0.028
0.045
0.034
0,071
0.039
0,095
0.082
Ok073
0.069
0.065
0.112
0.083
0,085
0.095
0.064
0.032
0.032
0.037
0.090
0.074
0.072
BOD,
ng/1
73.0
14.7
10.1
6.3
4.2
9.9
9.2
18.4
9.7
S.9
6.6
5.3
8.8
5.4
4.5
6.5
6.8
5.8
5.3
6.1
3.8
9.3
9.9
6.8
6.9
3.3
5.4
5.3
5.5
6.4
6.6
5.9
6.5
5.6
6.9
TSS
ms/1
60.0
21.8
17.6
14.9
11.9
38.7
18.3
24.2
16.2
9.4
7.8
15.3
12.9
5.4
4.2
7.5
8.7
9.8
9.1
6.9
4.5
11.8
7.9
11.6
8.1
6.8
7.3
S.6
9.3
12.2
12.9
10.8
11.1
5.5
8.8
               44

-------
             TABLE 11.
  FRIES EFFLUENT MONITORING DATA
(Monthly Averages  from DMR Reports)
            (Continued)
Month/Date
Jan 1991
Feb 1991
Mar 1991
Apr 1991
Summary : Minimum
Maximum
Average
Limit
Flow
mgd
0.072
0.094
0.134
0.113
0.028
0.134
0.063
0.220
Notes :
1. The Fries VLR began operation
BOD/TSS measurement was taken in
is not included in this summary.
BOD,
mg/1
4.3
5.2
3.9
4.3
3.3
18.4
6.9
30.0
on February 22,
February, so the
TSS
mg/1
4.9
5.1
4.5
6.2
4.2
38.7
11.0
30.0
1988 and only one
data from that month
                45

-------
                TABLE 12.
   BROOKVILLE EFFLUENT MONITORING DATA
(Monthly Averages from Operating Reports)
Month/Yaax
Aug 1S88
Sap 1988
Get 1988
Nov 1S8B
Dec 1988
Jan 1989
Feb 1989
Mar 1989
Apr 1989
May 1989
Jim 1989
Jul 1989
Aus 1989
Sep 1989
Oct 1989
Nov 1989
Doc 1989
Jan 1990
Fab 1990
Mar 1990
Apr 1990
May 1990
Jim 1990
Jul 1990
Aus 1990
Sep 1990
Oct 1990
Hov 1990
Dec 1990
Jan 1991
Sucmary: Mini mm
Maximum
Average
Limit
Notes:
Flow
mgd
0.485
0.543
0.529
0.809
0.640
0.970
0.821
1.068
1.213
1.276
0.597
0.592
0.548
0.706
0.511
0.616
0.463
0.700
1.169
0.821
0.912
1.144
0.705
0.666
0.693
0.609
0.769
0.607
0.828
0.463
1.276
0.766
HA

1. The Brookville VLR started up in August
2. Blank calls
indicate data which was not
Temp
*c
25.8
22.0
18.6
^6.2
13.2
JL2.7
10.9
12.0
M.I
is. 4
J9.7
?3.7
22.2
ki.s
IB. 3
16.9
12.8
fcl.4
12.4
^.3.3
14.1
15.5
16.8
20.1
21.9
20.3
is. 7
14.6
112.1
10.9
25.8
16.8
RA

1988.
available .
TSS
mg/1
7.3
6.3
6.7
14.9
8.8
13.2
10.9
11.6
8.7
9.3
7.1
10.8
9.1
7.6
11.3
6.4
5.4
5.9
5.3
6.7
8.7
3.8
3.8
5.6
3.8
4.1
5.7
4-7
4.4
3.8
14.9
7.5
12.0



NHj-N
mg/1
0.67
0.07
0.43
0.60
0.49
0.09
0.13
0.56
0.64
0.50
0.13
1.11
0.69
1.73
0.86
0.24
1.33
0.36
0.28
0.42
0.34
0.50
0.88
0.60
0.52
O.S8
0.59
0.29
0.40
0.07
1.73
0.55
1.50



BOD,
mg/1
3.0
2.7
3.8
4.4
2.3
3.2
2.7
3.9
2.9
6.2
3.1
4.2
4.6
4.5
4.3
6.3
4.5
8.5
6.4
7.3
6.0
3.1
5.9
4.0
4.1
5.0
4.6
4.4
2.3
2.3
8.5
4.4
10.0



                   46

-------
                TABLE  13.
   HILLSBQ80 EFFLUENT MONITORING DATA
(Monthly Averages  from Operating Reports)
Month/Year
May 1989
Jun 1989
Jul 1989
Aug 1989
Sep 1989
Oct 1989
Nov 1989
Dec 1989
Jan 1990
Feb 1990
Mar 1990
Apr 1990
May 1990
Jun 1990
Jul 1990
Aug 1990
Sep 1990
Oct 1990
Nov 1990
Dec 1990
Jan 1991
Summary: Minimum
Maximum
Average
Limit
Notes:
1. The Hillsboro
2. The Hillsboro
supplementary
Flow
mgd
1.272
0.749
0.647
0.755
0.632
0.667
0.656
0.651
0.945
1.209
0.907
0.927
1.346
0.840
0.600
0.751
0.823
1.151
0.788

1.565
0.600
1.565
0.894
NA

Temp
•C
15.1
19.1
21.5
22.0
20.9
17.3
14.6
10.0
10.3
10.7
12.0
13.3
15.5
19.2
21.6
21.8
21.1
18.0
15.5

10.8
10.0
22.0
16.5
HA

TSS
mg/1
31.6
21.1
16.8
15.4
12.0
11.8
9.0
10.5
12.4
13.3
11.6
10.3
25.3
0.3
6.8
5.4
3.6
4.4
2.3

1.8
0.3
31.6
11.3
12.0

NH.-N
mg/1
4.65
11.56
13.36
12.99
4.08
0.08
0.28
0.10
0.30
0.05
0.48
0.85
2.28
1.40
3.51
5.18
4.58
3.31
0.55

0.31
0.05
13.36
3.49
1.50

P
mg/1
1.83
1.93
1.32
6.11
5.06
1.77
0.69
0.70
0.44
0.58
0.42
0.61
2.50
2.15
1.32
1.65
2.05
1.52
1.31

0.48
0.42
6.11
1.72
1.00

BOD,
mg/1
20.3
9.0
6.4
2.5
2.1
2.0
2.0
2.0
2.0
2.0
2.1
2.0
11.9
2.3
2.9
6.8
2.0
2.4
2.0

2.4
2.0
20.3
4.3
10.0

VLR started up in May 1989.
VLR was designed for
alum is added
phosphorus removal in the VLR
in the
(if any)
3. Blank cells indicate data which was not
biological
phosphorus removal but
final clarifier.
The extent of
is not known.
available.



                 47

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                                        TABLE 14
                             PERFORMANCE DATA FOR BROOKFIELD VLR
                               DURING A PERIOD OF EXCESS FLOWS
    Design flow rat*:
    Flow rat* during this period:

    Design hydraulic retention time:
    ERT during this period:

    Design clarifier overflow rate:
    Clarifier overflow rate during this period:

    HLSS concentrations before excess flows:
    HLSS concentrations during this period:
    Effluent concentrations during this period:
 1.3 mgd
 4.8 .mgd

14.3 hours
 <1 hour

 331 g/sf-d
1,223 g/sf-d

Tank 1 - 6,200 mg/1
Tank 2 - 6,200 mg/1
Tank 3 - 6,200 mg/1

Tank 1 - 7,400 mg/1
Tank 2 - 7,400 mg/1
Tank 3 - 1,600 mg/1

BOD    5   mg/1
SS     5   mg/1
HH,-H  1.1 mg/1
REFERENCES
1.    Performance data  for the Brookfield  WWTP,  the  Hillsboro WWTP  and the
Brookville WWTP provided by the Ohio EPA.
2.   Performance data for the Fries  WWTP provided by the  Virginia Water Control
Board.                                  i
3.  Performance data for the Hohenwald WWTP provided by the Tennessee Department:
of  Conservation.
4.   Miscellaneous  information provided by  Envirex  regarding design criteria,
budget costs,  etc.
5.  Brandt, R.A. , E.J. Brown,  and G.B[. Shaw.  Innovative Rp-trofit without Federal
Funds;   Brookville.  Ohio Wastewater Treatment  Facilities.  Presented at  the 63rd
Annual Meeting of the Ohio Wastewater Pollution Control  Association, June 16,
1989.                                  j
6.  Site visit to the Hillsboro, OH wastewater treatment plant on April 26,  1991,.
The treatment plant  operator, Gary Davis,  was interviewed during this site visit,,
                                          48

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                                   SECTION 5
                     COMPARISON WITH EQUIVALENT TECHNOLOGY

OXIDATION DITCH TECHNOLOGY REVIEW

     As stated  earlier,  the VLR technology  is  capable  of  meeting stringent
effluent limitations for CBOD, TSS and ammonia-N.  The process is further capable
of 60 to 80 percent total nitrogen and phosphorus removal.

     A comparison of this technology  could be made  with modified conventional
activated sludge systems as well as-with proprietary designs for nutrient removal
that are capable  of  the same  system performance.   It was decided, however, to
compare the VLR with a conventional  oxidation ditch became of the similarity of
process concept.   In the late  1970's, there were  approximately 650 oxidation
ditch  installations  in the United  States  and Canada.(1)   A typical oxidation
ditch flow diagram is shown in Figure 7.

     An oxidation ditch is an activated sludge reactor in which the wastewater
circulates constantly  in a loop.   The  reactor is typically  shown  as  an oval
"racetrack"  but many  other closed loop  configurations  are  also  available.
Oxidation ditches  can be anywhere between four and sixteen  feet  deep.   Many
oxidation ditch designs incorporate sloping sidewalls, although the system being
considered uses straight sidewalls.<1>2>   The first oxidation  ditch of this type
in the U.S.  began operation in December  of 1976.  In August of 1990, there were
169  plants   in operation  which  used this  type  of  oxidation ditch,  while
approximately  69  additional projects were  in the  design phase  or  were under
construction.(2>

     Although a particular oxidation ditch was the source of the majority of the
data used in this  study,  early information from other oxidation ditch designs is
also used.  This particular oxidation ditch uses low speed, mechanical surface
aerators  to  provide  aeration  and  circulation  through  the  ditch.(2)   Other
oxidation ditches may use horizontal brush, cage, or disc-type aerators.C1>

PERFORMANCE

     Based  on random  interviews,  it was  determined  that the  majority  of the
operators and supervisors at wastewater treatment plants with oxidation ditches
are extremely pleased with the operation and reliability of their systems-(3/*>5)
Performance data for ten selected oxidation ditch systems  is presented in Table
                                      49

-------

-------
SCREENED AND
DEGRITTED RAW
WASTEWATER
OXIDATION
  DITCH
                        ERATOR
                                                           FINAL  \ EFFLUENT,
                                                        tCLARIFIER
                               RETURN SLUDGE
                                                              EXCESS
                                                              SLUDGE
                                      Rgure 7
                            Oxidation Ditch Row Diagram

-------

-------
15.(2>   This data  represent well operated  and conservatively designed,oxidation

ditches  and reflects  the best expected performance.
                                       TABLE 15
                           OXIDATION DITCH EFFLUENT MONITORING DATA
                                   (Monthly Averages)
Location
Baraboo, HI





Danville, KY





Corbin. KY





Keomerer, WY





Deland, FL






Month/Year
Sep 1983
Oct 1983
Nov 1983
Dec 1983
Jan 1984
Feb 1984
Jul 1981
Aug 1981
Sep 1981
Oct 1981
Nov 1981
Dec 1981
Oct 1982
Hov 1982
Dec 1982
Jan 1983
Feb 1983
Mar 1983
Sep 1983
Oct 1983
Nov 1983
Dec 1983
Jan 1984
Feb 1984
Jun 1981
Jul 1981
Aug 1981
Sep 1981
Oct 1981
Nov 1981
Dec 1981
Flow
mgd
1.44
1.35
1.40
1.30
1.30
1.50
2.36
2.14
1.98
2.32
2.00
3.06
1.06
1.75
2.75
2.05
2.66
2.06
0.78
0.64
0.64
0.67
0.71
0.77
1.45
1.50
1.50
1.50
1.60
1.60
1.65
Temp
Tocf
18.5
16.0
13.3
8.8
7.1
7.5
23.0
23.0
31.0
19.0
16.0
13.0







14.0
12.0
9.0
8.0
8.0







SS
ng/1
4
5
6
6
7
12
3
5
5
8
7
15
6
5
8
6
8
5
10
11
7
14
2
2
5
4
3
5
4
4
5
NHj-N
B8/1






1.6
0.4
0.3
0.6
1.0
0.7
2.1
1.4
1.3
1.8
1.3
1.2
0.1
0.3
0.1
0.1
<0.1
<0.1

10.0
10.0
3.0
2.0
0.3
10.0
BOD, NOj-N TN
mg/1 ' mg/1 mg/1
5
5
5
8
11
11
8
4
6
6
7
13
11
8
7
7
6
4
35
4
5
3
2

15
11 0.06
12 0.03
7 0.50
8 0.40
7 3.00
7 0.30
                                        51

-------
                TABLE 15
OXIDATION DITCH EFFLUENT MONITORING DATA
           (Monthly Averages)
               (Continued)
Location Month/Year
Evanston, WY Sep 1985
Oct 1985
Hov 1985
Dec 1985
Jan 1986
Fab 1986
Mar 1986
Ball* Glade, FL Jan 1986
Feb 1986
Max 1986
Apr 1986
May 1986
Jun 1986
Jul 1986
AUE 1986
Sep 1986
Oct 1986
Nov 1986
Dec 1986
Smyrna, TN Sep 1965
Oct 1985
Nov 1985
Dec 1985
Jan 1986
Feb 1986
Brad in ton, FL Jan 1987
Feb 1987
Mar 1987
Apr 1987
May 1987
Flow ! Tamp
mgd ToC
2.10 16.0
Z.OO 14.0
1.90 11.5
2.00 8.5
2.00 8.0
2.60 7.5
2.40 ' 8.5












1.7
1.7
1.7
1.6
1.6
1.8
3.7
3.7
4.7
4.8
3.9
SS
08/1
6
7
5
8
10
9
6
6.9
3.8
6.6
4.6
3.0
3.3
4.2
2.6
2.4
3.8
2.8
3.6
1.6
2.4
2.7
3.5
3.3
3.7
6
6
12
11
9
NH,-N .
mg/1
0
0
0
0
0
0
0
0.4
0.1
0.2
0.2
0.1
0.1
0.2
0.4
0.3
0.3
0.2
0.1
0.1
0.1
0.2
0.2
0.3
0.1





BOD,
08/1
7
5
4
5
7
8
6
6.3
8.6
10.0
12.2
11.3
7.3
3.5
2.6
2.7
3.3
3.2
2.7
1.9
2.2
2.3
3.0
4.0
2.4
8
8
10
10
10
NO,-N TN
mij/1 mg/1







13.1
10.5
11.6
9.3
4.5
6.0
9.0
12.7
11.0
9.4
3.8
5.6






4.8
6.7
9.5
5.2
6.4
                  52

-------
                                      TABLE 15
                          OXIDATION DITCH EFFLUENT MONITORING DATA
                                  (Monthly Averages)
                                     (Continued)
Location Month/Year
Bernards Twp, NJ Jan 1985
Feb 1985
Mar 1985
Apr 1985
May 1985
Jun 1985
Jul 1985
Aug 1985
Sap 1985
Hayden Lake, ID Oct 1988
Hov 1988
Dec 1988
Jan 1989
Feb 1989
Flow
mgd
0.86
1.05
0.92
0.75
1.00
0.85
0.78
0.78
0.98
0.17
0.18
0.19
0.22
0.26
Temp
ToC
8.5
8.8
10.5
14.0
17.0
18.9
21.7
21.5
20.6





SS
og/1
4.6
2.9
2.8
10.0
6.0
9.0
7.6
4.4
4.5
6
4
5
6
7
HHj-N "
mg/1
0.19
0.34
0.34
0.80
0.78
0.69
0.76
0.68
0.33





BOD, NOj-N TN
mg/1 ing/l mg/1
3.1
4.1
3.1
3.8
3.1
3.0
3.0
2.0
2.3
6
4
3
3

     The performances of five VLR systems are summarized  in Tables  9  through 13
 and discussed in Section 4.  A comparison of the performance data  from  the  two
 technologies indicates  comparable results for CBOD, TSS and NH3-N removal.  Less
 data were available on total nitrogen  or phosphorus removal for the oxidation
 ditches  since these plants were not designed for nutrient control.

 COSTS
     Budget  costs  for oxidation ditch  systems  are  provided  in Table  16.
Construction cost data from the first quarter of 1983 was used in the preparation
of this  table  and was provided by the manufacturer  of this oxidation ditch.(2)
The  1983 costs were  adjusted to current values  through the  ENR U.S. 20-city
average construction index (4006 for  March 1983; 4772.65 for February 1991).  The
1991 budget cost information  is also represented in graphical form in Figure 8.

     The  budget costs given in Table  16 are both construction costs and capital
costs.  Construction costs include dewatering, site work and buildings; capital
costs include dewatering,  site work, buildings,  engineering fees, construction
supervision  and contingencies.   The  construction costs were provided  by an
oxidation  ditch manufacturer,  as mentioned  in the previous paragraph.   The
reactor costs shown in this  table were taken as 30 percent of the total plant
capital cost.

                                      53

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-------
o g
*• s

IS

m
               Construction Cost
                                  4            6


                                     Design Flow. MOD
     8            10




-t-    Capital Cost
                                           Figure 8
                           Carrousel Oxidation Ditch Budget Costs

-------

-------
                                     TABLE 16
                   APEROXIMATE BUDGET COSTS TOR CARROUSEL OXIDATION. DITCHES
Design
Flow mgd
0.3
0.6
1.0
3.0
5.0
8.0
10.0
12.0

Construction
Cost, $
1,250,944
1,451,095
2,025,338
4,896,553
7,743,940
12,104,374
15,011,331
17,870,632
Total Plant
Capital Cost, S
1,626,227
1,886,424
2,632,940
6,365,519
10,067,122
15,735,687
19,514,730
23,231,821
Reactor
Capital Cost, $
487,868
565,927
798,882
1,909,655
3,020,136
4,720,706
5,854,419
6,969,546
     The 30 percent value was  obtained from a detailed breakdown  of oxidation
ditch plant costs developed in reference.(6)  Capital costs were estimated from
construction costs.  The total  cost for engineering and construction supervision
was assumed to be 15 percent of the construction costs.  Fifteen percent of the
construction cost was  also  added for  contingencies.

     A side-by-side comparison of total VLR plant costs versus,  total oxidation
ditch plant costs are difficult to make because of the variation in total plant
costs due  to site  specific factors for those plants where  data was available.
Budget construction cost and capital  cost data  for VLRs  are shown  in Table 17,
and  a  cost  curve  is  shown  in Figure  9.   These  costs  were  quoted  by  a
representative of the  VLR  manufacturer in March of 1991.<7)  Note  that the VLR
costs are  for the reactors  only.

     The comparison of  reactor  cost (concrete plus miscellaneous metal) shown in
Tables  16  and 17  provide  the best judgement  as to  an  overall  process  cost
comparison.  This comparison indicates a VLR reactor cost  is approximately 23
percent less than a comparable oxidation  ditch  plant at  1.0 mgd.  The VLR cost
became significantly less expensive at  the higher design  flows.

     A separate comparison  of  in-place  concrete cost for equal  volume  VLR and
oxidation aerators was made as  a part of this analysis.  A 20 foot aeration basin
was used for the VLR and a 10 foot depth was used for the oxidation ditch.  The
in place concrete cost  for a 120,000 cu.ft.  reactor (approximately 2.0 mgd design
flow) showed the VLR reactor to be 29.7 percent less costly than the oxidation
ditch.  In this analysis, excavation costs were assumed to be the same for both
designs. As mentioned earlier, the possibility of increased rock excavation cost
                                      55

-------

-------
 n «
 O c
 0.0
3
m
               Construction Coat
                                     Dcaign Flow. MOD
                                                          Coprlol Coat
                                          Rgure 9
                                 VLR Reactor Budget Costs

-------

-------
 for VLR designs  may increase  the cost  of VLR reactors at  locations where the
 plant hydraulic profile  dictates greater depths.
                                       TABLE 17
                            BUDGET COSTS FOR VERTICAL LOOP REACTORS
Flow
mgd
1.0
2.0
5.0
10.0
Construction
Cost, $
470,000
646,000
1,231,000
2,193,000
Capital
Cost, $
611,000
839,800
1,600,000
2,850,900
               Notes:
               1.   Construction costs based on information provided by Envirex, Inc.
               2.   Construction costs  include equipment, concrete divider,  blower,
                   concrete and installation.
               3.   Capital costs  calculated  from  construction  costs  using  the
                   following factors:  engineering and construction supervision - 15
                   percent of construction  cost;  contingencies - 15  percent  of
                   construction cost.
               4.   Capital costs  include equipment,  concrete  divider,   blower,
                   concrete, installation, engineering, construction supervision and
                   contingencies.

     The  only facility which provided  a  detailed  construction  cost  for  a
 treatment plant  which incorporated the VLR  technology was the  Brookfield WWTP.
 The Brookfield WWTP was very nearly a new plant  including new preliminary  and
 secondary  treatment  facilities,  chlorination/dechlorination  facilities,   and
 secondary control  and maintenance buildings.  Two existing anaerobic digesters
 were retrofitted to form  an aerobic digester and a sludge  holding tank.   The
 total   construction  cost  was   approximately   $5,575,000  for  this  1.3   mgd
 facility. <8>

     Cost data were also  available for a VLR  facility that  was  installed as  a
 retrofit of existing basins.  Design engineers for the Brookville WWTP estimated
 that the  capital  cost for converting three existing aeration basins to VLRs would
 be  $1,475,000  (in  1987-1988).  A cost-effectiveness analysis that compared  the
 VLR retrofit to a completely mixed activated  sludge retrofit was developed by  the
 design engineers.  Both  capital  and  operating costs  were  considered.    The
 completely mixed activated sludge  system was determined  to  be 4 percent more
 expensive than the VLR system.(8)

 OPERATION AND MAINTENANCE
     Operating costs for both VLRs  and oxidation ditches  are primarily made up
 of labor  and utility costs. All plant personnel interviewed stated that they  did
not  use  chemicals  in  their  oxidation  ditches  or VLRs,  and  that costs   for
maintenance materials  were similar. <3'*i5>10'11>12il3il*>
                                        57

-------
Labor Requirements

     VLR operators reported operating labor  requirements  of 9 to 27 hours per
week for VLR  operation and  maintenance.   Typical tasks  for both  VLRs and
oxidation ditches included daily dissolved oxygen concentration measurements, oil
changes and minor cleaning and repair (i.e.  remove  large  solids such as pieces
of cloth, etc.  from aerators) .(3>*-5'10f11>12>13>1A)   The above estimate of operating
labor  did  not  include  blower maintenance or  major repair  or replacement of
blower, motors, disc aerators or pumps.
                                    I
     This information indicates that VLRs  may require more labor than oxidation
ditches.  When comparing the labor requirements, however,  it must  be noted that
the VLR operators included sample analysis time in their labor estimates,  while
the  oxidation ditch labor estimate  does not  appear  to include  this task.

Utility Requirements

     Process  aeration efficiency is the primary factor  influencing the utility
requirements for both oxidation ditches and VLRs.   During the evaluation of the
VLR,  designs provided  by  the VLR manufacturer  and  by an  oxidation   ditch
manufacturer were compared.  Based on standard  oxygen requirements (SOR's), the
VLR was designed for 3.4 pounds of  oxygen per brake horsepower-hour, while the
oxidation ditch was designed for  3j5  pounds of  oxygen per brake horsepower-
hour. (2-7>

     In both  the  VLR  and oxidation  ditch plants,   the  installed  aeration
horsepower is typically 20  to 30 percent greater than the peak oxygen demand.
the  aeration energy requirements  typically vary from  a low of 20 percent to a
high of 70 percent of total plant energy requirements depending on influent and
interprocess pumping,  type of digestion employed and other appurtenant equipment.
A survey of total plant  energy requirements has little if any value in comparing
the  aeration efficiency of VLRs  compared to oxidation  ditches.   Of the  seven
plants included in this survey,  it was not possible to separate aeration energy
from total plant requirements for VLRs.

     Our assessment of available data including  a survey of the energy usage from
21  oxidation  ditch  plants  along with  test  data  submitted  to  USEPA for
qualifyingVLRs  as  "Innovative Technology" suggest  that there is  less than 10
percent  difference in  the aeration  requirements  of  VLRs  versus,  oxidation
ditches.C6)
                                      58

-------
      Both technologies  employ similar surface or brush aerators.   The VLR adds
 course bubble diffused air beneath  the  horizontal  baffle to increase aeration
 efficiency.  both  technologies  can  utilize  the denitrification energy credit.
 The VLR manufacturer publicizes this feature to a much greater extent than the
 oxidation ditch manufacturer.

      A survey of the energy use of 21 oxidation ditch plants showed approximately
 20 percent reduction in total plant energy needs for plants designed for nitrogen
 removal versus  those  designed  for  nitrification.(6)    In this same  survey  of
 oxidation ditches,  the total plant energy usage varied from a low of 296,000 kwh
 per year per mgd to a high of 740,000 kwh per year per mgd.

      The installed HP for VLRs is somewhat  lower than the average value used for
 oxidation ditches.   Oxidation ditches are  commonly designed for 50 to 60 HP per
 million gallons  of flow,  this is compared to 35 to 45 HP per million recommended
 gallons used by the current VLR designs.

      Three of the existing VLRs (Hohenwald, Fries and  Hillsboro) received USEPA
 funding based  on  innovative  technology  designations.'15'    In  order  to  be
 designated innovative, a technology must meet the following criteria established
 by the  United States Environmental Protection Agency  (USEPA):  the  technology
 must be one which has not been fully proven and which can demonstrate  1)  life
 cycle cost savings of at  least 15 percent,  2)  energy savings of at least  20
 percent,   or  3)  significant  environmental  or  operational  benefits   over
 conventional technology.   The innovative technology designations given  to the
 Hillsboro,  Hohenwald  and Fries wastewater  treatment plants  were  based  on
 projected  energy savings of at  least 20 percent.(7>15)

     Brookfield applied to  the Ohio EPA and the USEPA Region V for an innovative
 technology designation.  The most recent submission by the design engineer was
based on operational data and stated that the Brookfield wastewater  treatment
plant demonstrated  energy  savings  of 22.7 percent over a wastewater  treatment
plant with  a  conventional activated  sludge  (CAS) system using  fine bubble
diffusers.(15)

     However, Region V assessment of the operating data indicated that the energy
savings of the VLR  over the CAS system were no more  than 8.2  percent.  Other
statements made by the EPA were more qualitative and could not be associated with
exact quantities of energy, so it is impossible to place an exact value on the
energy savings of the VLR over the CAS system  (if any).

     The  request submitted by  the Hillsboro design engineer concluded that the
energy requirements for the Hillsboro VLR system were approximately 25 percent

                                      59

-------
 less that the requirements for a comparable single stage aeration process, while
 the reeval'uation performed by the Ohio EPA indicated a projected energy savings
 of approximately 5 percent.(16)      ]

 LAND AREA
     Because the depth of a VLR may he as much as twice  the depth of an oxidation
 ditch designed for  a  similar  flow,  the  land  area  required for  a  VLR  is
 significantly  less  than  that  required for  an  oxidation  ditch   of  the  same
 capacity.  The land area requirements  for  nine VLR systems and seven oxidation
 ditch aeration basins are shown in Table 18.(2'7)
                                     •TABLE 18
                                 LAND AREA REQUIREMENTS.
                    (Vertical Loop Reactor Versus Carrousel Oxidation Ditch)
now
mgd
VERTICAL
0.220
0.6*5
0.850">
1.000
1.100
1.300
3.000
4.500°'
5.000
Avarage
OXIDATION
0.100
0,100"»
0.140
0.150
0.800
1.000
3.200
Average
Hote«:
1. Sy*t*
Area
sq. ft.
Depth
ft. «"
Dimensions
ft. (Number of Basins)
BOD
Removed
Ib/day
HHj-N
Removed
li/day
Loading
gpd/sf
Loading
Ubs
BOD/sf-d
LOOP REACTOR:
2,460
5.427
6.375
7. 250
5.673
5,150
15.912
14,964
13,400

DITCH:
1,529
2,215
2,879
3,085
15,773
8,822
17.742


us marked
12.0
10.7
13.5
20.9
16.0
19.8
21.2
20.0
20.0


6.25
5.5-
7.25
6.5
6.5
10.0
10.0
11.0


with an
62* x 20* x 12* deep (2)
60.3' x 30* x 10.7' deep (3)
127.5' x 20' (1) & 127.5' x 15' (2)
125' x 29' x 20.9' deep (2)
141.8' x 20' (1) & 141.8' x 10' (2)
128.8* x 29' (1) £ 128.8' x 10' (2)
102* x 26' x 21.2' daap (6)
129' x 29' x 20' deep (4)
112' x 20' x 20' deep (6)

68.17' x 25' x 6. deep
Complicated
77.33' diameter x 6.5' deep
77.17' diameter x 6.5* deep
213' x 84* x 10* deep
120.5' x 42.67' x 10' deep (2)
118' x 92' x 11* dejep (2)


396
807
1361
2252

1301

6192
8757

192
192
222
238
1635
1376
5071


0
100
162
105

146

357
1022

24
24
34
49
267
325
0


88.7
US. 9
i:93.3
137. 8
1133.9
252.4
11:18. 5
300.7
372.0
1(98.5
65.4
45.1
48.6
48.6
50.7
113.3
100.4
78.9

0.160
0.149
0.214
0.311

0.253

0.414
0.652
0.307
0.125
0.087
0.077
0.077
0.104
0.156
0.286
0.130

asterisk are designed for phosphorus removal.
2. Average depth for two or more basins.
     A comparison of the average loadings  in Ibs BOD removed per square foot of
reactor shown in Table 18 indicates that the land area required for an oxidation
ditch is  approximately 2.5 times  the area required for a VLR designed for the
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 same  flow rate.   The smaller land area  required for the VLR  may be offset,

 however,  by  the deeper  tank design  which  is  more  likely to  require rock

 excavation.


 REFERENCES


 1.  Innovative  and Alternative Technology Assessment Manual.  Office of Water
 Program  Operations, Washington D.C.  and  Office of  Research and Development,
 Cincinnati, OH,  U.S.  Environmental Protection Agency.  February, 1980.

 2.  Telephone conversations and correspondence with Eimco representatives during
 March of  1991.

 3.  Telephone conversation with Gary, IL  treatment plant operator (Gary uses a
 Carrousel oxidation ditch).

 A.  Telephone conversation with Bradenton,  FL treatment plant operator (Bradenton
 uses a Carrousel oxidation ditch).

 5.  Telephone conversation with East Chicago,  In treatment plant operator (East
 Chicago uses a Carrousel oxidation ditch).

 6.  A comparison of oxidation ditch plants to  competing processes for secondary
 and advanced treatment of Municipal Wastes; EPA 600/2-78-051, March 1978.

 7.  Telephone conversations and  correspondence with George  Smith  of Envirex
 during March, April, May and June of 1991.

 8.  Floyd Browne Associates,  Inc.  Performance Certification Report.  Submitted
 to Trumbull County  on April 29, 1989.

 9.  Brandt, R.A. , E.J. Brown,  and G.B. Shaw.  Innovative Retrofit without Federal
 Funds:  Brookville. Ohio Wastewater Treatment Facilities.   Presented at the 63rd
 Annual Meeting of  the Ohio Wastewater Pollution Control  Association,  June 16,
 1989.

 10. Site  visit  to  the Brookville, OH Wastewater  treatment plant  on April 19,
 1991.   During this  visit, Ron Brandt and Jon Weist were interviewed.  Mr. Brandt
 is the Brookville WWTP operator; Mr. Weist is his assistant.

 11. Site visit to the Hillsboro, OH Wastewater treatment plant on April 26, 1991.
The treatment plant operator, Gary Davis, was interviewed during this site visit.

 12. Site visit to the  Brookfield, OH Wastewater treatment plant on May 15, 1991.
The treatment plant operator, Daniel Earhart,  was interviewed during this site
visit.

 13.   Telephone   interview of  Paul Webb on April 18,  1991.   Mr.  Webb  is  the
Hohenwald, TN wastewater treatment plant operator.

 14.  Telephone interview of Eugene Graham  on April 18,  1991.  Mr. Graham is the
 Fries, VA wastewater treatment plant operator.

 15. Floyd Browne Associates, Inc.  Report submitted to prove that the Brookfield
VLR deserved innovative funding.  Submitted to Trumbull County on February 15,
 1989.
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16. Letter to the City of Hillsboro from the Ohio EPA.  This letter informed the
City that the Ohio EPA was  withdrawing its  innovative technology designation of
the Hillsboro VLR system.
                                    i
17. Report  and Recommendation prepared by the  USEPA Region V  in  response to
Brookfield's request for designation as an innovative technology.
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                                   SECTION  6
                          NATIONAL IMPACT ASSESSMENT

     The  development  of  the  VLR  adds another  competing  activated  sludge
biological process to the existing technologies.  Its advancement will add to the
existing alternatives  and will help  encourage  all treatment  technologies  to
remain competitive in terms  of capital costs,  operating costs  and  effluent
levels.

     Similarly,  the  costs of conventional  systems will  help  keep  the  VLR
competitive. Note, however, that the price stability of a single-vendor supplied
proprietary technology such  as the VLR  is more volatile than  the  price  of a
technology marketed by multiple vendors.

     Based on existing information, it is likely  that the VLR technology will be
well-accepted by wastewater treatment  professionals, particularly because it is
possible to retrofit existing basins to serve as VLRs.

     The  proven applications  of VLR systems are many  and include BOD  removal,
nitrification and denitrification.  Phosphorus removal may be a valid application
as well,  but no significant data is currently available.
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