U.S. Environmental Protection Agency
Office of Water Enforcement and Compliance
Washington, D.C. 20460
TECHNICAL EVALUATION OP THE
VERTICAL LOOP REACTOR PROCESS TECHNOLOGY
SEPTEMBER 1992
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: NOTICE
This document has been reviewed by the U.S. Environmental
Protection Agency and approved tor publication. Mention of trade
names or commercial products does not constitute endorsement or
recommendation for use. :
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ACKNOWLEDGEMENTS
This report was prepared for the U.S. Environmental
Protection Agency by J.M. Smith and Associates, Consulting
Engineers under subcontract to HydroQual, Inc. HydroQual Inc
personnel assisted in preparation and review of the report
Mr. Charles Vanderlyn of the Office of Water, Office of
Wastewater Enforcement and Compliance, Municipal Technology
Branch, was the Project Officer on this contract. Ms. Wendy Bell
was the Work Assignment Manager for the study.
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CONTENTS
Section Page
LIST OF FIGURES iii
LIST OF TABLES iv
EXECUTIVE SUMMARY . ES-1
FACT SHEET FS-1
1 INTRODUCTION 2
BACKGROUND AND OBJECTIVES 2
TECHNOLOGY DESCRIPTION 2
FINDINGS AND CONCLUSIONS 8
REFERENCES 10
2 TECHNOLOGY DEVELOPMENT 11
HISTORY 11
TECHNOLOGY STATUS 11
REFERENCES 14
3 TECHNOLOGY EVALUATION 16
PROCESS THEORY 16
Oxygen Transfer 16
Coarse Bubble Diffusers-- 16
Aeration Discs-- 18
Denitrificatiqn Oxygen Credits-- 22
Mixing and Circulation 24
Biological Concepts 25
Denitrif ication-- 25
Phosphorus Removal-- 26
Stormwater Bypass 28
Design Criteria 28
Hydraulic Design-- 30
Disc Aerator Placement-- 31
Diffuser Configuration-- 31
Process Design 32
Reactor Configurations 32
Vertical Loop Reactors in Series-- 32
Vertical Loop Reactors in Parallel-- 32
Weather Protection Equipment 33
COMMON MODIFICATION OF VERTICAL LOOP REACTOR DESIGNS 33
Intrachannel Clarifier 33
O&M COMPLEXITY AND REQUIREMENTS 33
Routine Maintenance 33
Major Maintenance 34
Operation 35
PERFORMANCE GUARANTEE 36
REFERENCES 37
4 PERFORMANCE . . . 39
PERFORMANCE SUMMARY 39
Performance During Periods of Excess Flows 39
APPLICATIONS AND LIMITATIONS 40
Applications 40
Limitations 40
REFERENCES 48
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COMPARISON WITH EQUIVALENT TECHNOLOGY 49
OXIDATION DITCH TECHNOLOGY REVIEW 49
PERFORMANCE 49
OPERATION AND MAINTENANCE 57
Labor Requirements 58
Utility Requirements 58
LAND AREA ; 60
REFERENCES , ...'.. 61
NATIONAL IMPACT ASSESSMENT . : 63
ii
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FIGURES
Page
FS-1 FLOW DIAGRAM FS-4
FS-2 CONSTRUCTION COSTS AND ELECTRICAL ENERGY . . FS-5
1 BASIC REACTOR CONFIGURATION . 2
2 AIR BUBBLE FLOW PATTERN 4
3 FLOW PATTERN AND CONFIGURATION FOR VERTICAL LOOP
REACTORS IN SERIES 5
4 FLOW PATTERN AND CONFIGURATION FOR VERTICAL LOOP REACTORS IN
PARALLEL 6
5 VERTICAL LOOP REACTOR FLOW DIAGRAM 7
6 STORM FLOW BYPASS CONFIGURATION FOR VERTICAL LOOP
REACTORS IN SERIES 29
7 OXIDATION DITCH FLOW DIAGRAM 50
8 CARROUSEL OXIDATION DITCH BUDGET COSTS 53
9 VLR REACTOR BUDGET COSTS 56
111
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.TABLES
Number Page
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
LIST OF EXISTING VERTICAL LOOP REACTORS
DESIGN CRITERIA FOR EXISTING VLR SYSTEMS
VLR PROCESS AERATION EFFICIENCIES
VLR PROCESS AERATION EFFICIENCIES
AERATION DISC OPERATIONAL CHARACTERISTICS FOR
21 INCH DISC SUBMERGENCE .
BROOKFIELD DENITRIFI CATION
1
VERTICAL LOOP REACTOR DESIGN CRITERIA
USE OF CLAIMED VLR ADVANTAGES :
HOHENWALD EFFLUENT MONITORING DATA
BROOKFIELD EFFLUENT MONITORING DATA
FRIES EFFLUENT MONITORING DATA
BROOKVILLE EFFLUENT MONITORING DATA
HILLSBORO EFFLUENT MONITORING DATA
PERFORMANCE DATA FOR BROOKFIEIiD VLR DURING A
PERIOD OF EXCESS FLOWS . .
OXIDATION DITCH EFFLUENT MONITORING DATA .....
APPROXIMATE BUDGET COSTS FOR CARROUSEL OXIDATION DITCHES
BUDGET COSTS FOR VERTICAL LOOP REACTORS .....
LAND AREA REQUIREMENTS
11
13
19
20
21
26
30
36
41
43
44
46
47
48
51
55
57
60
IV
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EXECUTIVE SUMMARY
BACKGROUND AND OBJECTIVES
The EPA encourages the utilization of more efficient wastewater treatment
techniques by supporting the evaluation of new technologies. The EPA technology
transfer programs are designed to allow the development and application of new
and significant technologies before there is a chance for extensive field
evaluation. The EPA will also discourage certain technologies or specific
applications of certain technologies if the available information indicates
crucial limitations.
The primary objective in the evaluation of specific technologies is to
verify performance claims by process or equipment developers or manufacturers.
Technology evaluations may identify specific weaknesses or limitations in terms
of performance, cost, operation or maintenance. In addition, the results of the
evaluation may specify a range of conditions under which the technologies are not
as effective as the developers claim.
Conversely, other technologies may show good promise. In these cases, the
EPA is interested in introducing the new technologies to the public. The EPA
also wishes to provide the wastewater treatment community with all the available
information regarding new technologies which exhibit advantages over conventional
methods. Whether the evaluation finds the developer's or manufacturer's claims
accurate or misleading, the EPA recognizes the need to examine and document
significant new technologies.
TECHNOLOGY DESCRIPTION
A vertical loop reactor (VLR) is an aerobic suspended growth activated
sludge biological treatment process similar to an oxidation ditch. The
wastewater in an oxidation ditch circulates in a horizontal loop; the water in
a VLR circulates in a vertical loop around a horizontal divider baffle. A VLR
consists of a concrete or steel basin with a horizontal baffle extending the
entire width of the reactor and most of its length.
Currently, there is only one VLR manufacturer, Envirex Inc. Envirex claims
that the oxygen requirements for a VLR system are lower than the requirements for
an equivalent conventional oxidation ditch system. These claims are primarily
based on the location of the diffusers in the VLR and on the nitrate derived
oxygen returned to the biomass by denitrification.
ES-1
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FINDINGS AND CONCLUSIONS
The following summarizes the major findings and conclusions of this
evaluation of VLRs. The information contained herein is based on analysis of
available information from site visits, a detailed design of a full scale VLR
system by the report authors, information from consultants, VLR and oxidation
ditch manufacturers.
1. The VLR is a modification of; the conventional activated sludge process.
The unique features of the process are circulating mixed liquor around
a horizontal baffle with a dual aeration system of course bubble
diffused air beneath the horizontal baffle and disc aerators at the
surface of the aeration tank. The process operates as a plug flow
reactor with capability for varying dissolved oxygen profiles to
achieve biological phosphorus and nitrogen removal. The VLR process
also features a stormwater by-pass design for treatment of high peak to
average flows.
2. There are currently seven operating VLRs in the U.S. ranging in size
from 0.22 to 4.5 mgd. Three additional plants ranging in size from 3.0
to 5.0 mgd are in the design phase.
3. Performance data from operating VLRs show that this process is capable
of achieving effluent carbonaceous biochemical oxygen demand (CBOD)
levels of less than 10 mg/1; effluent total suspended solids (TSS)
levels of less than 10 mg/i; and effluent ammonia-nitrogen levels of
less than 1.0 mg/1. The process is further capable of achieving total
nitrogen and phosphorus removals of 60 to 80 percent.
4. The VLR process is applicable for flows ranging from 0.05 to over 10
mgd.
5. The claimed advantages of this process by the manufacturer include the
following:
a. Higher dissolved oxygen transfer than conventional equivalent
technology.
b. Improved response to peak flows due to a stormwater by-pass
feature.
ES-2
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c. A credit for oxygen release due to denitrification with the credit
based on 80 percent denitrification.
d. Increased mixed liquor settleability and process stability.
6. The design criteria for the existing VLRs are conservative. HRTs range
from 11.9 to 24 hours. Volumetric loading ranged from 13.6 to 23.1 Ibs
of CBOD per 1000 cubic feet. This loading is similar to that used for
extended aeration systems and is about 1/3 to 1/2 of that normally used
for conventional activated sludge designs.
7. The VLR technology has been designated as Innovative Technology by the
EPA for three plants due to a 20 percent claimed energy savings.
8. Based on this assessment, the 20 percent energy savings over competing
technology could not be verified.
9. The VLR was compared to oxidation ditches as "Equivalent Technology."
The results of this comparison indicated:
a. The VLR technology produces comparable to slightly improved
effluent levels of BOD.TSS and NH3-N than oxidation ditch plants.
b. Total removal of phosphorus and total nitrogen are equivalent to
oxidation ditches designed for the same level of treatment.
c. The energy requirements for aeration were found to be similar to
10 percent less than for oxidation ditches.
d. The land area required for VLRs were found to be approximately 40
percent less than for oxidation ditches based on equivalent
aeration tank loadings.
e. The VLR aeration basin cost was found to be approximately 30
percent less than for oxidation ditches for situations where rock
excavation is not required for the deeper VLR basin.
f. A definitive comparison of total VLR plant costs to total oxidation
plant costs could not be made. Data submitted from both
manufacturer's indicated a comparable cost for plants in the 0 -
2 mgd range. The reported VLR cost at plants ranging from 2 to 10
ES-3
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mgd were significantly less than oxidation ditch plant costs. This
would be expected because of the modular design and common wall
construction of the VLR compared to oxidation ditches.
g. The total operation and maintenance costs of the two technologies
were found to be similar.
ES-5
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VERTICAL LOOP REACTOR FACT SHEET
Description - A vertical loop reactor (VLR) is a patented activated sludge
biological treatment process similar to an oxidation di^tch. The wastewater in
an oxidation ditch circulates in a horizontal loop; the water in a VLR circulates
in a vertical loop around a horizontal baffle. A typical VLR consists of an 18
foot deep concrete or steel basin with a horizontal baffle extending the entire
width of the reactor and most of its length. Because a VLR is typically deeper
than an oxidation ditch, the VLR requires less land area.
Aeration in a VLR is provided by coarse bubble diffusers, which are located below
the horizontal baffle and by disc aeration mixers. The disc mixers also
circulate the wastewater around the baffle. Because the dif fusers are positioned
below the baffle, the air bubble residence time in a VLR is as much as six times
longer than the bubble residence time in a conventional aeration system. The
manufacturer claims this increases process aeration efficiency. Denitrification
in an anoxic zone also reduces oxygen requirements.
The VLR process is usually preceded by preliminary treatment such as screening,
communition or grit removal. Secondary settling of the VLR effluent is typically
provided by a separate clarifier.
Common Modifications - An intrachannel clarifier may be used for secondary
settling in place of a separate clarifier. Vertical loop reactors may be
operated in parallel or series. When a series of VLRs are used, the. dissolved
oxygen profile can be controlled to provide nitrification, denitrification and
biological phosphorus removal at hydraulic detention times of 10 to 15 hours.
Technology Status - There are currently (June 1991) six municipal wastewater
treatment facilities in the United States with the VLRs. There are also at least
four VLR systems in the United States currently in the design and construction
stages.
Typical Equipment/Number of Manufacturers - The VLR is a patented process of the
Envirex Corporation (one manufacturer). Disc aeration mixer/1; coarse bubble
diffusers/>10,
Applications - VLR technology is applicable in any situation where conventional
or extended aeration activated sludge treatment is appropriate. The technology
is applicable for nitrification and denitrification. Biological phosphorus
removal may be incorporated in the system design. Power costs may be lower for
FS-1
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a VLR system than for other aerated biological treatment systems, due to improved
oxygen transfer efficiency. |
i , ,
Limitations - Limited operating information is available and 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 removal.
Performance - The average effluent BOD and TSS concentrations for five operating
VLR facilities are 4.2 and 7.1 mg/1, respectively. The average effluent ammonia
concentration is 0.8 mg/1 (based on data from four plants). Only one of the VLRs
studied was designed for biological phosphorus removal; the average effluent.
phosphorus concentration for this pljant was 1.45 mg/1 and alum was added in the
final clarifiers. A second VLR facility was not designed for biological
phosphorus removal but was required to monitor phosphorus. This plant had an
average effluent phosphorus concentration of 2.19 without any chemical addition.
Chemicals Required - None.
i
Residuals Generated - Secondary sludge is generated at quantities similar to the
activated sludge process depending on the system operation conditions (SRT and
organic load). >
Design Criteria - BOD loading: 'l3.6 to 22.0 BOD/1,000 ft3/day
SRT: |'17.0 to 36.5 days
Detention Time: ill.9 to 24.0 hours
I
Unit Process Reliability - The following table indicates the percent of time the
monthly average effluent concentration of the given pollutants was less than the
concentration given in the first column. This table was developed from the data
discussed In the performance section of this sheet, although some start-up data
were eliminated. No significant difference in results were observed between
winter and summer data.
i
Percentage of
Monthly Average Concentration
Concentration
(ns/L)
0.2
0.5
1.0
2.0
5.0
10.0
20.0
Plants
BOD
0
0
0 1
20 I
71
97
100 i
5 '•
HH3-N
30
65
83
88
95
96
100
5
TSS
0
1
1
5
43
75
96
5
P
2
10
24
65
93
100
100
1
FS-2
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Environmental Impact - Solid waste, odor and air pollution impacts are similar
to those encountered with standard activated sludge processes.
Toxic Management - The same potential for sludge contamination, upsets and pass-
through of toxic pollutants exists for VLR systems as standard activated sludge
process.
Energy Notes
Energy requirements are based on the following assumptions:
Water Quality Influent Effluent
BOD5 200 20
TKN 35 1
Design Basis
Oxygen transfer efficiency - 2.5 Ib 02/Hp hour
Nitrification occurs
Operating Parameters -
Oxygen Requirement 1.5 Ib 02/lb BOD5 removed
4.57 Ib 02/lb TKN oxidized
Type of Energy - Electrical
Costs
Construction Costs - Very limited data available. Only a few plants, some
of which are retrofits, have been built.Construction costs (March 1991 dollars)
supplied by manufacturer are shown. Costs are for VLR only.
Operation Costs - Similar to oxidation ditch type treatment plant.
Reference
Technical Evaluation of the Verticle Loop Reactor Process Technology, J.M. Smith
& Associates, USEPA, November 1991.
FS-3
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VERTICAL LOOP REACTOR
AERATION
DISK
SCREENED AND
DEGRITTED
WASTEWATER
AIR RELEASE
PLATE
EFFLUENT
RETURN SLUDGE
EXCESS
SLUDGE
Rgure FS-1
Row Diagram
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m—*
CO 03 ^
z-o
O
ra 10
IX C
10
1
0.1
= i i mini
=
~ 0
i i i nun
i i i mm i i HUH
~
0 _
0
o E
-
i i i nun i i ' "in
0.1 1 10
DESIGN FLOW (mgd)
100
a
UJ
rr
LU
cc
cc>
tu
UJ-
u
UJ
UJ
10'
10'
10 c
0.1
TTTT
FLOW (mgd)
1.0 10.0
i i i mm—i i
io4l—i 11 nun—i i limn i i n|
10s 1C4 10°
OXYGEN REQUIRED (Ibs/day)
Figure FS-2
Construction Costs and Electrical Energy
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SECTION 1
INTRODUCTION
BACKGROUND AND OBJECTIVES
The EPA encourages the utilization of more efficient wastewater treatment
techniques by supporting the evaluation of new technologies. The EPA technology
transfer programs are designed to allow the development and application of new
and significant technologies before there is a chance for extensive field
evaluation. The EPA will also discourage certain technologies or specific
applications of certain technologies if the available information indicates
crucial limitations.
The primary objective in the evaluation of specific technologies is to
verify performance claims by process or equipment developers or manufacturers.
Technology evaluations may identify specific weaknesses or limitations in terms
of performance, cost, operation or maintenance. In addition, the results of the
evaluation may specify a range of conditions under which the technologies are not
as effective as the developers claim.
Conversely, other technologies may show good promise. In these cases, the
EPA is interested in introducing the new technologies to the public. The EPA
also wishes to provide the wastewater treatment community with all the available
information regarding new technologies which exhibit advantages over conventional
methods. Whether the evaluation finds the developer's or manufacturer's claims
accurate or misleading, the EPA recognizes the need to examine and document
significant new technologies.
TECHNOLOGY DESCRIPTION
A vertical loop reactor (VLR) is an aerobic suspended growth activated
sludge biological treatment process similar to an oxidation ditch. The
wastewater in an oxidation ditch circulates in a horizontal loop; the water in
a VLR circulates in a vertical loop around a horizontal divider baffle, as shown
in Figure 1. Figure 1 also illustrates the basic reactor configuration for a
VLR-(1) A VLR consists of a concrete or steel basin with a horizontal baffle
extending the entire width of the reactor and most of its length.
Existing VLR basins have side-wall depths which range from approximately ten
to twenty-two feet.(2) The length and width of the VLR are determined by the
required capacity but, as a rule, the length is at least twice the width. The
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DISC AERATION MIXER
AIR RELEASE SECTION
-HORIZONTAL DIVIDER BATTLE
•COARSE BUBBLE DIFFUSERS
Figure 1
Basic Reactor Configuration
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baffle is generally five to eleven feet below the surface of the water. Existing
tanks or basins may be retrofitted to serve as VLRs.
Standard VLRs utilize disc aeration mixers to provide continuous circulation
of the wastewater at a velocity of 1.0 to 1.5 feet per second.(3) Submersible
mixers are also available and may be used in place of the disc aeration mixers.
When the aeration disc mixers are used, they are the primary source of aeration
at low loadings because the amount of aeration provided by the discs is not
easily adjustable.
Coarse bubble diffusers near the bottom of the reactor provide additional
aeration and may be the primary source of oxygen at maximum flow rates or
loadings. The amount of oxygen supplied by the diffusers is easily adjustable,
so it is usually decreased when the flow rates or loadings are low. The basic
reactor configuration shown in Figure 1 illustrates the locations of all major
aeration system components.
An air release plate is fastened to the horizontal baffle, as shown in
Figure 2. The holes in this plate serve to break up the air bubbles from the
diffusers and, according to the manufacturer's claims, improve the oxygen
transfer efficiency. VLR systems frequently consist of more than one VLR. In
these cases, the reactors may be configured in series or in parallel. Series and
parallel configurations are discussed in Section 3 and are illustrated on Figures
3 and 4, respectively.
The VLR process is usually preceded by some type of preliminary treatment
such as screening, comminution or grit removal. Secondary settling of the VLR
effluent is typically provided by a separate clarifier, although intrachannel
clarifiers are available. A typical flow scheme is shown on Figure 5.
Major Process Claims
Currently, the only VLR manufacturer (Envirex Inc.) claims that the oxygen
requirements for a VLR system are lower than the requirements for an equivalent
conventional system. These claims are primarily based on the location of the
diffusers in the VLR and on the nitrate derived oxygen returned to the biomass
by denitrification. Oxygen requirements are discussed in detail in Section 3.
The VLR manufacturer states that because the diffusers are positioned below
the baffle, the air bubble residence time is as much as six times longer in a VLR
than in a conventional aeration system, producing an improved process aeration
efficiency."5
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HORIZONTAL DIVIDER BAFFLE
EFFLUENT
COARSE BUBBLE D1FFUSERS
;DISC AERATION MIXERS ^FLOW PATTERN
INFLUENT
AIR RELEASE PLATE-
Rgure 2
Air Bubble Flow Pattern
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EFFLUENT
5-#^
AERATOR
RETURN ACTIVATED
SLUDGE
(FROM CLAROTER)
INFLUENT
Figured
Flow Pattern and Configuration for
Vertical Loop Reactors in Series
-------
.IXSC
- AERATOR
AERATOR
INFLUENT
Figure 4
Row Pattern and Configuration for
Vertical Loop Reactors in Parallel
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SCREENED AND
DEGRITTED RAW
WASTEWATER
VERTICAL
LOOP
REACTOR
EFFLUENT
RETURN SLUDGE
EXCESS SLUDGE
Rgure 5
Vertical Loop Reactor Row Diagram
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The VLR manufacturer also claims an oxygen credit for the oxygen released
when nitrates and nitrites are reduced to nitrogen gas during denitrification.
In a system designed for complete denitrification, this credit would be
equivalent to 63 percent of the oxygen required for nitrification. The
calculation of the oxygen credit is typically based on no more than 80 percent
denitrification. This topic is discussed further in Section 3.
VLRs are frequently designed to provide nitrification and BOD reduction;
some are designed for biological denitrification and phosphorus removal, as well.
The manufacturer states that VLRs can be designed to allow nitrification,
denitrification and BOD removal to occur simultaneously.**' The biological
concepts of particular importance in VLRs and similar systems are discussed in
Section 3.
The final major claim made by the manufacturer involves the VLRs ability to
treat excessive flows without solids washout. VLR systems can be designed with
a stormwater bypass feature, which is described further in Section 3.
FINDINGS AND CONCLUSIONS
The following summarizes the major findings and conclusions of this
evaluation of VLRs. The information contained herein is based on analysis of
available information from site visits, a detailed design of a full scale VLR
system by the report authors, information from consultants, VLR and oxidation
ditch manufacturers.
1. The VLR is a modification of the conventional activated sludge process.
The unique features of the process are circulating mixed liquor around
a horizontal baffle with a dual aeration system of course bubble
diffused air beneath the horizontal baffle and disc aerators at the
surface of the aeration tank. The process operates as a plug flow
reactor with capability for varying dissolved oxygen profiles to
achieve biological phosphorus and nitrogen removal. The VLR process
also features a stormwater by-pass design for treatment of high peak to
average flows.
2. There are currently seven operating VLRs in the U.S. ranging in size
from 0.22 to 4.5 mgd. Three additional plants ranging in size from 3.0
to 5.0 mgd are in the design phase.
3. Performance data from operating VLRs show that this process is capable
of achieving effluent carbonaceous biochemical oxygen demand (CBOD)
8
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levels of less than 10 mg/1; effluent total suspended solids (TSS)
levels of less than 10 mg/1, and effluent ammonia-nitrogen levels of
less than 1.0 mg/1. The process is further capable of achieving total
nitrogen and phosphorus removals of 60 to 80 percent.
4. The VLR process is applicable for flows ranging from 0.05 to over 10
mgd.
5. The claimed advantages of this process by the manufacturer include the
following:
a. Higher dissolved oxygen transfer than conventional equivalent
technology.
b. Improved response to peak flows due to a stormwater by-pass
feature.
c. A credit for oxygen release due to denitrification with the credit
based on 80 percent denitrification.
d. Increased mixed liquor settleability and process stability.
6. The design criteria for the existing VLRs are conservative. HRTs range
from 11.9 to 24 hours. Volumetric loading ranged from 13.6 to 23.1 Ibs
of CBOD per 1,000 cubic feet. This loading is similar to that used for
extended aeration systems and is about 1/3 to 1/2 of that normally used
for conventional activated sludge designs.
7. The VLR technology has been designated as Innovative Technology by the
EPA for three plants due to a 20 percent claimed energy savings.
8. Based on this assessment, the 20 percent energy savings over competing
technology could not be verified.
9. The VLR was compared to oxidation ditches as "Equivalent Technology."
The results of this comparison indicated:
a. The VLR technology produces comparable to slightly improved
effluent levels of BOD,TSS and NH3-N than oxidation ditch plants.
-------
Total removal of phosphorus and total nitrogen are equivalent to
oxidation ditches desijgned for the same level of treatment.
The energy requirements for aeration were; found to be similar to
10 percent less than for oxidation ditches.
The land area required for VLRs were found to be approximately 40
percent less than fojr oxidation ditches based on equivalent
aeration tank loadings.
The VLR aeration basin cost was found to be approximately 30
percent less than for oxidation ditches., for situations where rock
excavation is not required for the deeper VLR basin.
A definitive comparison of total VLR plant costs to total
oxidation plant costs could not be made. Data submitted from both
manufacturer's indicated a comparable cost for plants in the 0 to
2 mgd range. The reported VLR cost at plants ranging from 2 to 10
mgd were significantly less than oxidation ditch plant costs .
This would be expected because of the modular design and common
wall construction of the VLR compared to oxidation ditches .
g. The total operation and maintenance costs of the two technologies
were found to be similar.
REFERENCES
1. 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. '
2. Miscellaneous information provided by Envirex regarding design criteria,
budget costs, etc. i
3. Huibrestse, G.L., G.W. Smith, DjJ. Thiel, and J.W. Wittmann.
to the Vertical Loop Reactor Process. June 12, 1986.
Introduction
A. Telephone conversations and cojrrespondence with George Smith of Envirex
during March, April, May and June of 1991.
10
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SECTION 2
TECHNOLOGY DEVELOPMENT
HISTORY
The VLR was developed by Mr. George Smith, who is currently employed by the
VLR manufacturer. Portions of the VLR technology were derived from the Orbal
process, an oxidation ditch also marketed by the VLR manufacturer.
Large-scale pilot testing of the VLR technology began in December, 1983 at
a wastewater treatment plant in Walworth County, Wisconsin. An existing plug-
flow basin was retrofitted as a VLR and clean-water oxygen transfer tests were
conducted by an independent tester and by the VLR manufacturer. The manufacturer
states that the clean water aeration efficiency (AE) of the coarse bubble
diffusers below the baffle was found to be over 4 Ibs. 02/HP-hr.(1)
TECHNOLOGY STATUS
There are currently seven operating municipal wastewater treatment plants
which employ the VLR technology. There is also a pretreatment facility which
utilizes a VLR to treat a high-strength industrial wastewater. Industrial
treatment will not be discussed further in this report. Locations, start-up
dates, and capacities for existing VLR facilities are shown in Table l.(2>3> The
VLR system in Ellijay, Georgia mentioned in Table 1 is not actually in operation
for reasons discussed below. Table 1 also includes a partial list of VLR systems
which are currently in the design and construction phases.
TABLE 1
LIST OF EXISTING VERTICAL LOOP REACTORS
(NOVEMBER 1991)
Plant Location
IN OPERATION:
Hohenwald, Tennessee
Brookfield, Ohio
Frias, Virginia
Brookville, Ohio
Billsboro, Ohio
Industrial
Ellijay, Georgia
Hillard, Ohio
IN DESIGN/CONSTRUCTION PHASE:
Hurricane, West Virginia
Winchester, Tennessee
Warren County, Ohio
Wells ton, Ohio
Design Flow, togd
1.1
1.3
0.22
0.645
0.85
0.06
1.0
4.5
3.0
5.0
3.64
Start-up Date
July 1987
November 1987
January 1988
August 1988
May 1989
February 1990
January 1991
April 1991
11
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Design criteria for all operating
which are 'under construction was
design engineers and is provided in
operating VLRs follows.
municipal VLRs as well as several VLRs
obtained from the manufacturer or from the
Table 2.<2-3>A'5) Brief descriptions of six
Hohenwald. Tennessee: The first VLR to begin operation is located in
Hohenwald, Tennessee. The design flow rate is 1.1 mgd and the system consists
of three reactors in series. The first basin is 20 'W x 141. 83 'L x 16' SWD; the
second and third basins are 10 'W x 141. 83 'L x 16 'SWD. The manufacturer states
that four 10 horsepower disc aerators provide the majority of the oxygen, since
the coarse bubble diffusers are not j usually needed.
I
The operating data for this £lant indicates an average flow rate of
approximately 0.5 mgd, or less than 'half of the design flow rate. Under these
circumstances , it is not surprising that the system usually has no problem
meeting its permit limits. (6> Average monthly operating data for the Hohenwald
WWTP since the startup of the VLR system can be found in Section 4.
Brookfield. Ohio: The second VLR was installed at the Brookfield (Trumbull
County), Ohio WWTP. The design flow was 1.3 mgd; average flow rates for 1988 and
1989 were 1.283 mgd and 1.654 mgd, respectively. The Brookfield system consists
of three reactors in series and is equipped with a stormwater bypass . The first
basin is 20'W x 128.79'L x 19.75'SWD|; the next two reactors are 10'W x 128.79'L
x 19 . 75 ' SWD . Aeration is provided Jby four 15 HP disc aerators as well as by
coarse bubble diffusers. The Brookfield plant has demonstrated excellent
performance for a 30 month period. Effluent BOD, TSS and TKN have averaged 1.6,
3.0 and 1.55 mg/1 respectively compared to a permit level of 10 mg/1 BOD, 12 mg/1
TSS and a summertime/wintertime ammonia-nitrogen limit of 1.5/3.0 mg/1.
i
Fries. Virginia: The VLR in Fr^.es, Virginia is the smallest in operation.
The design flow is low (0.22 mgd) and the plant is underloaded. Only one of the
two parallel 20 'W x 62 'L x 12' SWD basins is used. Each reactor has one 10 HP
disc aerator but the manufacturer reports that the aerator in the operating basin
is only operated at a power draw of 6.4 wire HP (12" immersion). The
manufacturer further reports that coarse bubble diffusers are typically operated
15 minutes per hour but are used 50 percent of the time during months with higher
loadings. {7> ;
Brookville .
tanks in series.
Ohio ; The VLR system in Brookville, Ohio consists of three
The VLR basins are retrofits of 30'W x 60.3'L x 10.7'SWD steel
aeration tanks. The aeration basins! were converted to VLRs to meet new effluent
12
-------
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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
-------
-------
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
-------
-------
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
-------
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
EmjUENT
(TO CtARlFlER)
£• A£AAT6ft
ca
*
CD
I
0
d.
c D
t A
i
i
CD
o
c!
&AT6R
E TOR
p P|g?
P og:
c JXSC
^ AERATOR
RETURN ACTIVATED
SJLKXX:
(FROM OARFCR)
INFUIENT
Rgure 6
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
-------
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
-------
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
-------
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
-------
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
-------
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
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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
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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
-------
-------
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
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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
60
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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.
61
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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.
62
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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.
63
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