EPA/600/R-94/108
August 1994
CHARACTERIZATION OF CLEAN AND FOULED
PERFORATED MEMBRANE DIFFUSERS
by
Lloyd Ewing and Joseph Kitzinger
Ewing Engineering Co.
Milwaukee, Wisconsin 53209
Cooperative Agreement No. CR812167
Project Officer
Richard C. Brenner
Water and Hazardous Waste Treatment Research Division
Risk Reduction Engineering Laboratory
Cincinnati, OH 452 68
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 452 68

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4. TITLE AND SUBTITLE
Characterization of Clean and Fouled Perforated
Membrane Diffusers
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before comple
1. REPORT NO.
EPA/600/R-94/108
2.
3.
6. PERFORMING ORGANIZATION CODE
5. REPORT DATE
August 1994
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Lloyd Ewing and Joseph Kitzinger
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
Ewing Engineering Co.
Milwaukee, Wisconsin
53209
11. CONTRACT/GRANT NO.
CR-812167
12. SPONSORING AGENCY NAME AND ADDRESS
Risk Reduction Engineering Laboratory—Cincinnati, OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
13. TYPE OF REPORT AND PERIOD COVERED
Project Report
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer - Richard Brenner (513) 569-7657
16. ABSTRACT
Laboratory analyses were conducted on plasticized PVC perforated membrane
tube diffusers after varying periods in service at two different municipal wastewater
treatment facilities. One set of diffuers from Cedar Creek, NY, was in service for
26 months. The other set from the Green Bay Metropolitan Sewerage District facility
was in service for approximately 47 months. Tests on the membranes included dynamic
wet pressure (DWP), flow uniformity, weight, dimensions, tensile modulus of elasticity
hardness, and standard oxygen transfer efficiency (SOTE).
Results of this brief study indicate a significant increase in DWP and decrease
in flow uniformity and SOTE after service. Following membrance cleaning, there was a
nonrecoverable reduction in DWP below that of a new membrane; an increase in specific
gravity, durometer hardness, and circumferential modulus of elasticity; and a
decrease in weight, length, and strain at failure. These findings were in good
agreement with other field tests performed with these diffusers.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
activated sludge process, diffusers,
aeration, oxygenation
b. IDENTIF IE RS/OPEN ENDED TERMS
c. COSATl Field/Group
fine pore diffusers,
plastic membrane dif-
fusers, oxygen transfer
efficiency, dynamic wet
pressure, diffuser foul-
ing, diffuser cleaning
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
unclassified
21. NO. OF PAGES
16
20. SECURITY CLASS (This page)
unclassified
22. PRICE
EPA Form 2220-1 (R«». 4-77)
PREVIOUS EDITION IS OBSOLETE

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DISCLAIMER
Development of the information in this report has been
funded in part by the U.S. Environmental Protection Agency under
Cooperative Agreement No. CR812167 by the American Society of
Civil Engineers. The report has been subjected to Agency peer
and administrative review and approved for publication as an EPA
document. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.

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FOREWORD
Today's rapidly developing and changing technologies and
industrial products and practices frequently carry with them the
increased generation of materials that, if improperly dealt with,
can threaten both public health and the environment. The U.S.
Environmental Protection Agency (EPA) is charged by Congress with
protecting the Nation's land, air, and water resources. Under a
mandate of national environmental laws, the Agency strives to
formulate and implement actions leading to a compatible balance
between human activities and the ability of natural systems to
support and nurture life. These laws direct EPA to perform
research to define our environmental problems, measure the
impacts, and search for solutions.
The Risk Reduction Engineering Laboratory is responsible for
planning, implementing, and managing research, development, and
demonstration programs to provide an authoritative, defensible
engineering basis in support of the policies, programs, and
regulations of EPA with respect to drinking water, wastewater,
pesticides, toxic substances, solid and hazardous wastes, and
Superfund-related activities. This publication is one of the
products of that research and provides a vital communication link
between the researcher and the user community.
As part of these activities, an EPA cooperative agreement
was awarded to the American Society of Civil Engineers (ASCE) in
1985 to evaluate the existing data base on fine pore diffused
aeration systems in both clean and process waters, conduct field
studies at a number of municipal wastewater treatment facilities
employing fine pore aeration, and prepare a comprehensive design
manual on the subject. This manual, entitled "Design Manual -
Fine Pore Aeration Systems," was completed in September 1989 and
is available through EPA's Center for Environmental Research
Information, Cincinnati, Ohio 45268 (EPA Report No. EPA/625-1-
89/023) . The field studies, carried out as contracts under the
ASCE cooperative agreement, were designed to produce reliable
information on the performance and operational requirements of
fine pore devices under process conditions. These studies
resulted in 16 separate contractor reports and provided critical
input to the design manual. This report summarizes the results
of one of the 16 field studies.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory

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PREFACE
In 1985, the U.S. Environmental Protection Agency funded
Cooperative Research Agreement CR812167 with the American Society
of Civil Engineers to evaluate the existing data base on fine
pore diffused aeration systems in both clean and process waters,
conduct field studies at a number of municipal wastewater
treatment facilities employing fine pore diffused aeration, and
prepare a comprehensive design manual on the subject. This
manual, entitled "Design Manual - Fine Pore Aeration Systems,"
was published in September 1989 (EPA Report No. EPA/025/1-89/023)
and is available from the EPA Center for Environmental Research
Information, Cincinnati, OH 45268.
As part of this project, contracts were awarded under the
cooperative research agreement to conduct 16 field studies to
provide technical input to the Design Manual. Each of these
field studies resulted in a contractor report. A listing of
these reports is presented below. All of the reports are
available from the National Technical Information Service, 5285
Port Royal Road, Springfield, VA 22161 (Telephone: 703-487-4650) .
1.	"Fine Pore Diffuser System Evaluation for the Green Bay
Metropolitan Sewerage District" (EPA/600/R-94/093) by
J.J. Marx
2.	"Oxygen Transfer Efficiency Surveys at the Jones Island
Treatment Plants, 1985-1988" (EPA/600/R-94/094) by
R. Warriner
3.	"Fine Pore Diffuser Fouling: The Los Angeles Studies"
(EPA/600/R-94/095) by M.K. Stenstrom and G. Masutani
4.	"Oxygen Transfer Studies at the Madison Metropolitan
Sewerage District Facilities" (EPA/600/R-94/096) by
W.C. Boyle, A. Craven, W. Danley, and M. Rieth
5.	"Long Term Performance Characteristics of Fine Pore Ceramic
Diffusers at Monroe, Wisconsin" (EPA/600/R-94/097) by D.T.
Redmon, L. Ewing, H. Melcer, and G.V. Ellefson
6.	"Case History of Fine Pore Diffuser Retrofit at Ridgewood,
New Jersey" (EPA/600/R-94/098) by J.A. Mueller and P.D.
Saurer
iv

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7.	"Oxygen Transfer Efficiency Surveys at the South Shore
Wastewater Treatment Plant, 1985-1987" (EPA/600/R-94/099)
by R. Warriner
8.	"Fine Pore Diffuser Case History for Frankenmuth, Michigan"
(EPA/600/R-94/100) by T.A. Allbaugh and S.J. Kang
9.	"Off-gas Analysis Results and Fine Pore Retrofit Information
for Glastonbury, Connecticut" (EPA/600/R-94/101) by R.G.
Gilbert and R.C. Sullivan
10.	"Off-Gas Analysis Results and Fine Pore Retrofit Case
History for Hartford, Connecticut" (EPA/600/R-94/105) by
R.G. Gilbert and R.C. Sullivan
11.	"The Measurement and Control of Fouling in Fine Pore
Diffuser Systems" (EPA/600/R-94/102) by E.L. Barnhart and
M. Collins
12.	"Fouling of Fine Pore Diffused Aerators: An Interplant
Comparison" (EPA/600/R-94/103) by C.R. Baillod and K.
Hopkins
13.	"Case History Report on Milwaukee Ceramic Plate Aeration
Facilities" (EPA/600/R-94/106) by L.A. Ernest
14.	"Survey and Evaluation of Porous Polyethylene Media Fine
Bubble Tube and Disk Aerators" (EPA/600/R-94/104) by D.H.
Houck
15.	"Investigations into Biofouling Phenomena in Fine Pore
Aeration Devices" (EPA/600/R-94/107) by W. Jansen, J.W.
Costerton, and H. Melcer
16.	"Characterization of Clean and Fouled Perforated Membrane
Diffusers" (EPA/600/R-94/108) by Ewing Engineering Co.
v

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ABSTRACT
Laboratory analyses were conducted on plasticized PVC
perforated membrane tube diffusers after varying periods in
service at two different municipal wastewater treatment
facilities. One set of diffusers from Cedar Creek, NY, was in
service for 26 months. The other set from the Green Bay
Metropolitan Sewerage District facility was in service for
approximately 47 months. Tests on the membranes included dynamic
wet pressure (DWP), flow uniformity, weight, dimensions, tensile
modulus of elasticity, hardness, and standard oxygen transfer
efficiency (SOTE).
Results of this brief study indicate a significant increase
in DWP and decrease in flow uniformity and SOTE after service.
Following membrane cleaning, there was a nonrecoverable reduction
in DWP below that of a new membrane; an increase in specific
gravity, durometer hardness, and circumferential modulus of
elasticity; and a decrease in weight, length, and strain at
failure. These findings were in good agreement with other field
tests performed with these diffusers.
This report was submitted in partial fulfillment of
Cooperative Agreement No. CR812167 by the American Society of
Civil Engineers under subcontract to Ewing Engineering Co. under
the partial sponsorship of the U.S. Environmental Protection
Agency. The work reported herein was conducted over the period
of 1988-1989.
vi

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CONTENTS
Foreword 	iii
Preface 	iv
Abstract 	vi
Tables 	viii
Introduction 	1
Methods 	1
Results 	2
Conclusions 	3
vii

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TABLES
Number	Page
1.	Characteristics of Parkson Membrane Tube
Diffusers - Cedar Creek, NY (After 26 Months
in Service)	4
2.	Characteristics of Parkson Membrane Tube
Diffusers - Green Bay, WI (After 24 and
41 Months in Service, as Noted)	6
3.	Record of DWP and Steady-State SOTE -
Green Bay, WI	7
viii

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INTRODUCTION
In the comprehensive study of fine pore diffusion systems by
the U.S. Environmental Protection Agency, which resulted in the
publication "Design Manual - Fine Pore Aeration Systems"
(EPA/625/1-89/023), the subject of changes in characteristics of
elastomeric diffusers as a function of time in service was
discussed. The results are tabulated in Table 3-6 of that
manual. In the final stages of preparation of the design manual,
additional data on this topic became available from two sites,
one at Green Bay, WI, the other at Cedar Creek., NY.
Results of the Cedar Creek investigation by Mueller and
Bauer and the Green Bay investigation by Marx were included in
the Design Manual as References 37 and 31 of Chapter 3,
respectively. Subsequent evaluation of changes in diffuser
characteristics at those two sites were conducted and are
reported in this paper.
METHODS
In both studies, new diffusers, representative of those in
service, were available. At Cedar Creek, the Parkson Flex-A-Tube
diffusers were put in service in June 1986 and were removed and
sent to Ewing Engineering Co. for testing in August 1988 after a
period of approximately 26 months in service. The Green Bay
Parkson Flex-A-Tube diffusers, believed to be of the same
materials and manufacture, were installed in approximately
January 1986 and were removed and similarly evaluated
periodically over a period of approximately 41 months.
1

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Characteristics measured included dynamic wet pressure (DWP),
flow uniformity, weight and dimensions, tensile modulus of
elasticity, hardness, and standard oxygen transfer efficiency
(SOTE). These parameters and the methods of testing or
measurement are described in the design manual.
SOTE, DWP, and flow uniformity were measured on diffusers
under as received conditions and after cleaning. Two methods of
cleaning were employed, both recommended by Parkson Corp. The
most commonly used up to the time of testing described herein
consisted of hosing at approximately 50 psi nozzle pressure,
scrubbing, and rehosing. The nozzle had an exit orifice of 0.125
in. The other method consisted of scrubbing while simultaneously
flushing from the inside with about 5 gpm of clean water. This
was performed in addition to the same pre and post hosing.
Dimensions, weight, tensile modulus, and hardness were
determined on new and cleaned diffusers only.
RESULTS
The data obtained from the Cedar Creek diffusers are
presented in Table 1. Final characterization of the Green Bay
diffusers are shown in Table 2. Sequential DWP and SOTE tests on
diffusers as received and following cleaning are presented in
Table 3.
Although the scope of evaluation of this study was somewhat
limited, the results obtained are consistent with the
2

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investigators' experience with plasticized membrane diffusers at
other sites that were not part of this design manual project.
CONCLUSIONS
1. With few exceptions, the characteristics of both the unused
(new) diffusers and diffusers after varying periods of service
appear to be in reasonably good agreement with those that have
been obtained in other field tests of Parkson PVC membrane
diffusers.
2. Service exposure apparently produces a measurable increase
in "as received" DWP, as well as in "after cleaning" specific
gravity and durometer hardness. The after cleaning DWP indicates
a non-recoverable reduction from "new" DWP. These changes are
accompanied by a dramatic increase in circumferential tensile
modulus of elasticity.
3.	Service exposure in these tests resulted in a measurable
decrease in "as received" air flow uniformity, SOTE, and "after
cleaning" weight, length, and strain at tensile rupture.
4.	The two methods of cleaning investigated appeared to provide
similar results.
5.	The detrimental effects of service on diffuser
characteristics appeared to occur at a declining rate over the
period of observation.
6.	These detrimental effects did not appear to be progressive
beyond that period of early change.
7.	Cleaning appears to have a minor beneficial effect on the
restoration of SOTE to near original values.
3

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TABLE 1. CHARACTERIZATION OF PARKSON MEMBRANE
TUBE DIFFUSERS - CEDAR CREEK, NY
(AFTER 26 MONTHS IN SERVICE)
Date
Tested
Diffuser
No.
Condition1
Weight
(g)
PWP (in. w.g.)
Thickness
(in.)
0.75
cfm
1.00
cfm
2.0
cfm
3.00
cfm
Flow
Uniformity
(six)2
8-24-88	1	Fouled as Received
8-25-88	1	After LP HBH
111
0.0277
5.00
3.30
5.60
3.45
8.05
3.85
12.95
4.30
0.277
0.182
8-24-88	2	Fouled as Received
8-25-88	2	After FHB
4.55
3.55
4.90
3.75
7.50
4.40
10.70
5.10
0.418
0.242
8-24-88	3	Fouled as Received
8-25-88	3	After LP HBH
5.40
4.45
6.20
4.55
8.25
5.25
11.55
5.85
0.318
0.839
8-24-88	4	Fouled as Received
8-25-88	4	After FBH
112
0.0280
6.65
5.20
7.45
5.50
11.25
6.45
15.95
7.50
0.268
0.151
8-24-88	5	Fouled as Receoved
8-25-88	5	After LP HBH
101
0.0270
6.35
4.10
7.10
4.20
10.90
4.60
15.75
4.90
0.339
0.517
8-24-88	6	Fouled as Received
8-25-88	6	After FBH
8-29-88	7	New
9-16-88	7	New
10-20-88	7	New
107
118
0.0282
0.0278
5.55
4.30
5.25
5.95
4.40
5.45
8.05
4.90
6.00
10.65
5.30
6.50
0.492
0.176
0.149
'LP - Low pressure
'HBH - Hose, brush, and rehose
'FBH - Flush, brush, and hose
2Sample standard deviation/average of individual sample points
3Shore A durometer, average of five points
duplicates

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SOTE SOTE
Date	Diffuser at	at
Tested	No. 1 cfm 3 cfm
8-24-88	1
8-25-88	1
8-24-88	2
8-25-88	2
8-24-88	3
8-25-88	3
8-24-88	4
8-25-88	4
8-24-88	5
8-25-88	5
8-24-88	6
8-25-88	6
8-29-88	7
9-16-88	7
10-20-88	7
0.1342 0.1290
0.1275
0.1378 0.1301
0.1431
0.1406 0.1426
0.1802
0.1602 0.1363
0.1632
0.1476 0.1424
0.1318 0.1499
0.1363	0.1307
0.15594	0.1634
0.14264
0.1603	0.1688
0.1803
0.1781	0.1852
TABLE 1 (continued)
Tensile	Diameter	Diameter
Specific	Modulus	Estimated	at 5 in. w.g
Gravity Hardness2	(psi)	(in.)	(in.)
71.75	1287	2.343	2.404
75.25	1405	2.283	2.354
1.247 77.20	5967	2.154	2.204
77.12	4433	2.143	2.186
1.205 62.75	653	2.319	2.425

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TABLE 2. CHARACTERIZATION OF PARKSON MEMBRANE TUBE
DIFFUSERS - GREEN BAY, WI
(AFTER 24 AND 41 MONTHS IN SERVICE, AS NOTED)




DWP fin. w.s).
CWOTEused/CWOTEnew3 Flow


Tube

Tensile
Diffujer
No. Basin'
Condition2
1.0
cfm
2.0
cfm
3.0
cfm
1.0
cfm
3.0
cfm
exp.4
Uniformity
(tlx)5
Weight
(8)
Length
(in.)
Diameter
(in.)
Thickness
(in.)
Modulus Hardness6
(psi)
A-l
A-l
C
As Found
After HBH
8.1
3.7
13.2
4.1
19.2
4.7
0.68
0.75
0.77
0.91
+0.03
-0.10
0.32
0.37





A-2
A-2
C
As Found
After FB
9.8
3.3
14.6
3.7
20.1
4.3
0.74


0.51
0.33
114
25.3
2.34
0.0290
1,090 68.0
A-3
C
As Found
6.1
10.8
17.4



0.25





> >
R
As Found
After HBH
10.2
3.6
17.0
4.4
24.3
5.1
0.63
0.73
0.73
0.86
+0.05
+0.07
0.52
0.36
114
25.3
2.39
0.0290
1,350 65.0
A-5
R
As Found
9.4
15.7
22.3



0.37





A-6
A-6
R
As Found
After FB
9.9
3.8
17.5
4.7
24.5
5.8
0.71


0.41
0.34





C
Inlet
A-7
A-7
A-8
A-8
A-9
A-9
A-10 C New
A* Found
After HBH
C As Found
Middle
After HBH
C As Found
Outlet
After HBH
9.5
4.0
9.9
3.9
8.1
3.4
7.25
16.6
5.5
19.0
5.6
16.5
4.2
9.70
0.87
0.79
0.81
1.00 1.00 -0.08
0.47
0.29
0.23
0.29
0.24
105
104
104
119
24.7
24.7
24.7
26.2
2.24
*C - Contact basin
*R - Reaeration basin
2HBH = hose, brush, and rehosc
2FB > flush @ 3-5 gpm of clean water while brushing
'Ratio of small tank clean water oxygen transfer efficiencies,
CWOTEnew ® 1.0 cfm = 0.180
CWOTEnew® 3.0 cfm = 0.165
^Exponent: CWOTE = Constant x (air flow rate) exp.
^Sample standard deviation/average of individiual sample points
'Shore A durometer, average of five points
0.0310
0.0280
0.0280
0.0302
1,290	78.0
1,020	81.0
1,370	81.0
630	63.0
(mo)
~24
24
24
24
24
24
24
24
24
24
41
41
41
41
41
41
0

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TABLE 3. RECORD OF DWP AND STEADY-STATE SOTE -
GREEN BAY, WI
Date
Tested
Condition
Time In
Service (mo)
Basin
DWP (in. w.g.) DWP (in.w.g.) SOTE
Type	@1.0 elm	@ 3.0 cfrn	@ 2.0 cfm
11-86
11-86
As Received
After HBH
10
10
Contact
Contact
Grid
Grid
6.5
4.3
9.9
5.4
0.115
0.123
7-87
7-87
As Received
After HBH
19
19
Contact
Contact
Grid
Grid
6.3
2.9
12.5
4.9
0.125
0.142
12-87
12-87
5-89
5-89
As Received
After HBH
As Received
After HBH
Original
24
24
41
41
Contact
Contact
Contact-
Inlet
Contact-
Inlet
Pilot
Pilot
Grid
Grid
8.0
3.5
9.2
3.5
7.6
18.9
4.5
17.2
5.1
10.6
0.127
0.135
0.141
0.173
1 HBH - Hose, brush, and rehose

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