United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S-94/001
September 1994
EPA Project Summary
Design Information on Fine
Pore Aeration Systems
Field studies were conducted over
several years at municipal wastewater
treatment plants employing line pore
diffused aeration systems. These stud-
ies were designed to produce reliable
information on the performance and
operational requirements of fine pore
devices under process conditions. The
results of the studies provided critical
input to a comprehensive treatise on
the subject entitled "Design Manual -
Fine Pore Aeration Systems." This
document, prepared by the American
Society of Civil Engineers' (ASCE) Oxy-
gen Transfer Committee, was published
in 1989 and is available to the public.
The above studies resulted in 16
separate contractor reports as part of
a cooperative research agreement with
ASCE. Abstracts of each contractor re-
port are given here.
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of field studies that are
fully documented in separate reports
(see Project Report ordering informa-
tion at back).
Introduction
In 1985, the U.S. Environmental Pro-
tection Agency (EPA) funded a coopera-
tive research agreement with ASCE 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 waste-
water treatment facilities employing fine
pore aeration, and prepare a comprehen-
sive design manual on the subject. This
manual, entitled "Design Manual - Fine
Pore Aeration Systems," was completed
in September 1989 and was first distrib-
uted at the 62nd Annual Water Pollution
Control Federation Conference in San
Francisco, CA, October 1989. Copies of
the Design Manual (EPA report no. EPA/
625/1-89/023) are available from the EPA
Center for Environmental Research Infor-
mation (CERI), Cincinnati, OH 45268. An
earlier "Summary Report - Fine Pore (Fine
Bubble) Aeration Systems" was published
in October 1985 to document the early
findings of this study and summarize the
state-of-the-art at that time. This Sum-
mary Report is also available from CERI
(EPA/625/8-85/010).
Data generated on the field studies con-
ducted at municipal wastewater treatment
plants were important sources of informa-
tion for the Design Manual. These studies
were undertaken as contracts under the
cooperative research agreement. They
were selected primarily to address techni-
cal issues and data base inadequacies
identified in the 1985 Summary Report.
The field studies were composed pri-
marily of investigations on the performance
of various fine pore diffuser generic types
in process waters (i.e., under field condi-
tions), diffuser operating characteristics
and fouling rates, and operation and main-
tenance requirements including cleaning
of partially fouled diffusers. In addition, an
interplant diffuser fouling evaluation was
carried out to relate observations and
trends to wastewater characteristics and
process operating conditions. A corollary
interplant study used microbiologically
based procedures to describe biofouling
Printed on Recycled Paper
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phenomena on fine pore aeration devices
and to determine whether biofilm charac-
teristics could be related to diffuser per-
formance parameters. Several studies
were conducted at facilities having suffi-
cient prior Information to enable case his-
tories to be developed. Finally, a survey
of European experience with fine pore rigid
porous plastic diffusers provided additional
information to supplement the North Ameri-
can data base on this class of diffusers.
Each of the above field studies resulted
in a separate contractor report. These re-
ports are referenced throughout the De-
sign Manual.
A brief abstract of each contractor field
report is given below. These abstracts are
intended to provide sufficient information
to identify those reports that may be of
individual interest as supplements to the
Design Manual.
Abstract of Reports
1. "Fine Pore Diffuser System Evalua-
tion for the Green Bay Metropolitan
Sewerage District' (EPA/600/R-94/
093) by J.J. Marx
The Green Bay Metropolitan
Sewerage District retrofitted two
quadrants of their activated sludge
aeration system with fine pore ce-
ramic disc and plasticized PVC per-
forated membrane tube diffusers to
evaluate and compare the savings
in energy use with that of the
sparged turbine aerators originally
installed. Because significant dif-
fuser fouling was expected, the two
diffuser types were closely moni-
tored over an 18-mo period. The
oxygen transfer efficiencies (OTEs)
of the full-scale systems were mea-
sured by using off-gas techniques.
The effects of diffuser fouling and
the effectiveness of diffuser clean-
ing procedures were evaluated in
the laboratory with the use of dy-
namic wet pressure (DWP) and
steady-state clean water oxygen
transfer tests.
Although significant fouling was
encountered on both types of dif-
fusers, cost-effective cleaning pro-
cedures were developed. The
ceramic disc diffusers provided bet-
ter long-term performance with pe-
riodic cleaning than did the
plastidzed PVC membrane tube dif-
fusers, which irreversibly lost OTE
with time in use. Collectively, the
fine pore diffuser systems provided
a 30% savings in electrical power
use compared with that of the origi-
nal sparged turbine aerators.
2. "Oxygen Transfer Efficiency Sur-
veys at the Jones Island Treatment
Plants, 1985-1988" (EPA/600/R-94/
094) by R. Warriner
Ceramic plate diffusers were
among the earliest forms of fine
pore diffusers used for oxygen
transfer in activated sludge treat-
ment. They have been successfully
used for over 60 yr in the Jones
Island West Plant of the Milwaukee
Metropolitan Sewerage District
(MMSD) and in the MMSD Jones
Island East and MMSD South Shore
Plants since 1935 and 1974, re-
spectively. Results of off-gas sam-
pling surveys carried out at the
original Jones Island West Plant,
which was scheduled for rehabilita-
tion in 1988-90, and in the newly
rehabilitated East Plant are re-
ported. Twenty-one (21) basin sur-
veys were carried out in the West
Plant and 30 in the East Plant.
For the West Plant basins,
equipped with the original ceramic
plate diffusers installed in 1923 and
1924, the median value of stan-
dardized oxygen transfer efficiency
under field conditions, aF(SOTE),
was 11.8% at 15 ft of submergence.
For the East Plant basins, which
contained new plate diffusers in-
stalled in 1983, the median value
of «F(SOTE) was 15.3% at a sub-
mergence of 14 ft.
Cleaning history was noted for
each basin at the time of each off-
gas survey. A relationship between
time-in-service since cleaning and
OTE was not established in these
surveys; however, a short-term im-
provement in OTE following clean-
ing was indicated in the East Plant.
Because alpha was unknown and
varied widely between surveys, and
possibly during surveys, it was dif-
ficult to separate alpha effects from
fouling effects on OTE. For the most
part, extended periods of basin op-
eration had no measurable effect
on performance.
3. "Fine Pore Diffuser Fouling: The
Los Angeles Studies" (EPA/600/R-
94/095) by M.K. Stenstrom and G.
Masutani
Fine pore diffuser evaluations
conducted at three different waste-
water treatment plants located in
the greater Los Angeles area are
described. The overall goal of the
study was to evaluate the perfor-
mance of fine pore diffusers by us-
ing selected cleaning methods for
extended periods of time at selected
treatment plants. The major part of
this study was conducted at the
Whittier Narrows Water Reclama-
tion Plant, operated by the Los An-
geles County Sanitation Districts.
This study evaluated fine pore ce-
ramic disc and dome aeration sys-
tems using HCI acid gas cleaning
and a ceramic dome aeration sys-
tem without acid gas cleaning over
a 25-mo period. A second study,
smaller in scope and effort, was
conducted at the Valencia Water
Reclamation Plant (also operated
by the Districts). This study evalu-
ated fine pore rigid porous plastic
disc diffusers over a 13-mo period.
A third study, also smaller in scope
and effort than the Whittier Nar-
rows study, was conducted at the
Terminal Island Wastewater Treat-
ment Plant, operated by the City of
Los Angeles. In this study, the per-
formance of a perforated membrane
tube system and a parallel nonrigid
porous plastic tube system was
evaluated over a 12-mo period.
The principal indicator of the per-
formance of the different aeration
systems was OTE, as measured
by off-gas analysis. For the Whittier
Narrows study, changes in diffuser
characteristics were also reported.
The fine pore ceramic disc aera-
tion system at Whittier Narrows,
which was acid gas cleaned, per-
formed better than both the ceramic
dome system that was acid gas
cleaned and the control ceramic
dome aeration system that received
no cleaning. Part of the differences
in performance between the disc
system and the two dome systems
was attributable to mechanical prob-
lems with the domes. The cleaned
and uncleaned dome systems had
comparable OTEs during the study.
Relatively consistent performance
was observed for the rigid porous
plastic disc system at Valencia over
the 13-mo study period. The tube
systems at Terminal Island exhib-
ited high variability because of op-
erational differences, and one tube
system experienced significant foul-
ing over a relatively brief period.
The variability in performance of
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the several aeration systems dur-
ing day-to-day changes in plant load
and operating mode was an impor-
tant finding of the study.
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
Field studies at the Madison Met-
ropolitan Sewerage District facilities
were conducted over a 3-yr period
to obtain long-term data on the per-
formance of fine pore aeration
equipment in municipal wastewater
service. The studies were con-
ducted on several basins in the East
Plant containing ceramic domes in-
stalled in 1977 and two sets of first-
pass basins in the West Plant
containing newly installed ceramic
discs.
The performance of the domes
was excellent even after 10 yr of
service. This conclusion was based
on OTE as measured by off-gas
analysis, alpha calculations, and dif-
fuser characterization. Reasons for
excellent performance included rou-
tine maintenance of the diffusers
and the use of high quality ceramic
diffusers and hardware. Evidence
was presented for this plant that
operation at high solid retention
times (SRTs), i.e., low food-to-mi-
croorganism loadings, which pro-
duced complete nitrification,
resulted in higher aF(SOTE) val-
ues than did operation at low SRTs.
Results of studies on the impact of
diffuser cleaning and hydraulic flow
patterns on performance are also
reported.
The ceramic discs in the West
Plant were monitored for 800 days.
In that period, no perceptible de-
crease in diffuser performance was
observed based on aF(SOTE)
measurements. The mean first-pass
«F(SOTE) values over 800 days
were about 11.5% at a submer-
gence of approximately 15 ft. The
mean-weighted «F(SOTE) for all
three passes ranged from 12.1% to
15.3%. The West Plant aeration
system was operated at high SRT
values to achieve complete nitrifi-
cation. As seen in the East Plant,
some evidence of improved aera-
tion performance [aF(SOTE)] with
increased SRT was noted. Brief ex-
aminations of diffusers in these low-
loaded basins suggested that
fouling was not a problem in this
plant.
5. "Long-Term Performance Charac-
teristics of Fine Pore Ceramic Dif-
fusers at Monroe, Wisconsin" (EPA/
600/R-94/097) by D.T. Redmon, L
Ewing, H. Melcer, and G. V. Ellefson
A study of the fine pore aeration
system at the Monroe, Wl, Waste-
water Treatment Facility was con-
ducted over a 2-yr period to monitor
the OTE and fouling tendencies of
ceramic discs with four different
permeabilities. The plant, which
treats a mixture of municipal and
industrial wastewaters, consisted of
three two-pass aeration tanks, each
containing two independent aera-
tion grids per pass. In 10 of the 12
passes, disc diffusers with a spe-
cific permeability of 26 were em-
ployed. The remaining two grids
contained disc diffusers with spe-
cific permeabilities of 38 and 50.
OTE was monitored by off-gas
analysis. Fouling tendencies and ef-
fectiveness of cleaning were deter-
mined by using diffusers obtained
from separate pilot test headers,
which were then analyzed in the
laboratory.
Results of this study indicated
that the clean diffuser bubble re-
lease vacuum (BRV) and its coeffi-
cient of variation were better
measures of effective pore size of
ceramic diffusers than was perme-
ability. Although OTE increased with
decreasing permeability (increasing
clean diffuser BRV) in clean water,
the operating conditions of the plant
and its wastewater characteristics
appeared to influence aF(SOTE)
more than did effective pore size.
Although fouling was visually ob-
served on the ceramic discs under
certain operating conditions, it had
little apparent effect on a F(SOTE),
BRV, or DWP. Little correlation was
shown between fouling tendencies
and permeability at this plant over
the range of permeabilities tested.
Inexpensive cleaning procedures
were used in the laboratory. These
involved a combination of high pres-
sure water spraying with or without
liquid acid treatment and/or brush-
ing, followed by additional spray-
ing. Laboratory cleaning resulted in
nearly complete restoration of the
diffusers' original characteristics.
6. "Case History of Fine Pore Diffuser
Retrofit at Ridgewood, New Jersey"
(EPA/600/R-94/098) byJ.A. Mueller
and P.O. Saurer
In April 1983, the Ridgewood, NJ,
Wastewater Treatment Plant was
partially retrofitted from a coarse
bubble to a fine pore ceramic dome
diffused aeration system. The pro-
cess was also modified from a con-
tact stabilization to a tapered
aeration activated sludge treatment
regime. A case history of plant and
aeration system performance from
1981-1986 is presented. Extensive
aeration studies were conducted on
the fine pore system in 1985 and
1986 to observe changes in OTE
with time and evaluate cleaning fre-
quency requirements to maintain
efficiency at a viable level. An eco-
nomic evaluation including bid
prices, maintenance costs, and pay-
off period based on power savings
is included. Over the 6 yr of study,
the coarse bubble system exhib-
ited an average aF(SOTE) of 4.8%
(at a submergence of approximately
13 ft) with an average «F value of
0.55. Over 3.75 yr of operation, the
fine pore dome diffusers produced
an average aF(SOTE) of approxi-
mately 9.5% (at a submergence of
approximately 14 ft) during normal
operation with an average a F value
of 0.4. A significant improvement in
effluent quality with respect to nitri-
fication in the summer months was
observed with the fine pore system
when compared with the coarse
bubble system, which achieved no
nitrification.
7. "Oxygen Transfer Efficiency Sur-
veys at the South Shore Wastewa-
ter Treatment Plant, 1985-1987"
(EPA/600/R-94/099) by R. Warriner
Ceramic plate diffusers were
among the earliest forms of fine
pore diffusers used for oxygen
transfer in activated sludge treat-
ment. They have been successfully
used for over 60 yr in the Jones
Island West Plant of the Milwaukee
Metropolitan Sewerage District
(MMSD) and in the MMSD Jones
island East and MMSD South Shore
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Plants since 1935 and 1974, re-
spectively. Twenty basin off-gas
sampling surveys were carried out
at the South Shore Plant, yielding
a median aF(SOTE) value of
18.9% at a submergence of 15 ft.
When evidence of nitrification was
present, aF(SOTE) values were
higher than on other survey dates.
A diffuser cleaning history was ob-
tained at the time of each off-gas
survey; however, no correlation be-
tween the number of months-in-ser-
vice since cleaning and aF(SOTE)
could be identified.
8. "Fine Pore Diffuser Case History
for Frankenmuth, Michigan" (EPA/
600/R-94/100) by T.A. Allbaugh and
SJ. Kang
In 1986, the Frankenmuth, Ml,
Wastewater Treatment Facility,
which treats a mixture of municipal
and industrial wastewaters, was ret-
rofitted with fine pore ceramic discs.
Significant flows received by the
plant from a brewery and a large
restaurant produced high soluble or-
ganic loadings on the aeration
tanks. Off-gas tests were conducted
over a 1-yr period on 13 different
days to determine the effects of
acid gas cleaning and operation at
elevated airflow rates on the per-
formance of the fine pore system.
The rate of diffuser fouling at the
plant was significant. Acid gas
cleaning was typically initiated when
the DWP reached 16 to 18 in. (wa-
ter gage). Gas cleaning was effec-
tive in controlling the DWP at this
plant, but little effect was observed
on OTE.
9. "Off-Gas Analysis Results and Fine
Pore Retrofit Information for
Glastonbury, Connecticut" (EPA/
60Q/R-94/101) by R.G. Gilbert and
R.C. Sullivan
The Town of Glastonbury, CT,
retrofitted one of its two aeration
tanks in 1983 with rigid porous plas-
tic tube fine pore diffusers in a spi-
ral roll configuration. These tubes
were placed on existing swing arms
used for the original coarse bubble
spargers. An extensive aeration
system performance evaluation us-
ing off-gas analysis was conducted
involving six separate investigations
over a 35-mo period. The
ccF(SOTE) measurements aver-
aged 6.6.% at a submergence of
approximately 12 ft; this represents
a 57% increase in OTE compared
with the average 4.2% aF(SOTE)
value estimated for the original
coarse bubble spargers. The retro-
fit simple payback period was less
than 18 mo.
10. "Off-Gas Analysis Results and Fine
Pore Retrofit Case History for Hart-
ford, Connecticut' (EPA/600/R-94/
105) by R.G. Gilbert and R.C.
Sullivan
In 1986, the Hartford Water Pol-
lution Control Plant in South Mead-
ows, CT, was retrofitted from a
coarse bubble, spiral roll system to
a fine pore ceramic dome, grid-con-
figured system. Four of six aeration
tanks were involved in the retrofit.
Extensive off-gas studies were con-
ducted over 18 mo to evaluate the
performance of the new system and
to determine the effectiveness of
diffuser cleaning. The aF(SOTE)
measurements averaged 10.0%;
this is more than double the aver-
age a F(SOTE) value estimated for
the original coarse bubble, spiral
roll aeration equipment. The retrofit
simple payback period was less
than 3 yr.
11. "The Measurement and Control of
Fouling in Fine Pore Diffuser Sys-
tems" (EPA/600/R-94/102) by E.L.
Barnhart and M. Collins
The purposes of this study were
to define the efficiency of various
methods of cleaning fine pore dif-
fusers and to develop a methodol-
ogy that could be used to evaluate
the efficiency of several cleaning
techniques. Fouled ceramic dome
diffusers from the North Texas Mu-
nicipal Water District were cleaned
with these techniques, and the im-
provement in OTE was measured.
The domes were reinstalled in
the aeration tanks and withdrawn
at various time intervals thereafter.
The deterioration in OTE was then
noted. The cleaning techniques
were repeated, and the improve-
ment in transfer was recorded.
Overall, the domes from the North
Texas Plant did not exhibit severe
fouling. Low-pressure hosing ap-
peared to be as effective as any
other method in cleaning the
domes. The domes deteriorated
promptly after they were reintro-
duced into the aeration tank, and
aF(SOTE) stabilized.
The technique of using an off-
line aeration tank for studying dif-
fuser cleaning techniques provided
mixed results. The comparative ef-
fectiveness of cleaning techniques
appeared to be properly described
in this small test tank. The break-
down of slimes and fouling materi-
als during dome transportation and
handling, however, may have
caused an underestimation of the
degree of fouling.
12. "Fouling of Fine Pore Diffused Aera-
tors: An Interplant Comparison"
(EPA/600/R-94/103) by C.R. Baillod
and K. Hopkins
The objective of this study was
to assess the relative fouling ten-
dencies of fine bubble diffusers at
nine activated sludge treatment
plants. A secondary .objective was
to relate fouling to mixed liquor and
process parameters. A standardized
diffuser test header containing four
removable diffusers was installed
at each of the participating plants.
Diffusers were periodically removed
and tested for OTE, BRV, DWP,
foulant accumulation, and increase
in OTE after acid cleaning.
The results of this study showed
that an increase in BRV was gen-
erally accompanied by a decrease
in OTE, an accumulation of foulant,
and an increase in DWP loss
through the diffuser. The plants
were classified according to their
degree of fouling (as measured by
BRV). The classifications were
heavily fouling (Jones Island West,
Wl and Frankenmuth, Ml), moder-
ately fouling (Green Bay, Wl, North
Texas, TX, and Whittier Narrows,
CA), fouling (South Shore, Wl and
Portage Lake, Ml), and lightly foul-
ing (Madison, Wl and Monroe, Wl).
Observations at individual plants
suggested that high organic loads
enhanced fouling, although inter-
plant comparisons suggested a
weak association between fouling
and organic load.
13. "Case History Report on Milwau-
kee Ceramic Plate Aeration Facili-
ties" (EPA/600/R-94/106) by LA.
Ernest
Ceramic plate diffusers were
among the earliest forms of fine
pore diffusers used in activated
sludge treatment. They have been
used for 60 yr in the Jones Island
West Plant of the Milwaukee Met-
ropolitan Sewerage District (MMSD)
and in the MMSD Jones Island East
and MMSD South Shore Plants
since 1935 and 1974, respectively.
The Jones Island East Plant aera-
tion basins were completely reha-
bilitated in 1982-83, and the West
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14.
Plant basins were scheduled for re-
habilitation in 1989-90. In both
cases, alternative fine pore systems
were evaluated and ceramic plate
diffusers were again selected. Three
separate case history reviews are
presented: the Jones Island East
Plant, the Jones Island West Plant,
and the South Shore Plant.
All of the historical reviews dis-
cuss the conceptual designs and
selection processes involved for
each of the plants. The review of
the Jones Island West Plant covers
the period from the start-up of the
activated sludge plant in 1915
through the planned rehabilitation
in 1989-90. The Jones Island East
Plant history begins with start-up in
1930 and discusses in some detail
the comparisons of optional fine
pore diffuser layout patterns with
the original ridge-and-furrow full
floor diffuser coverage pattern. The
East Plant review also includes the
history of the 1982-83 retrofit to
diffuser plates installed in concrete
containers placed at right angles to
the basin flow and with the diffuser
surface flush with the floor. In the
South Shore history, the concept of
the layout and design of the con-
crete containers is discussed. The
South Shore Plant history, covers
the time from initial plant start-up in
1974 to 1988 and describes how
the results at South Shore formed
the basis for the Jones Island East
and West Plant rehabilitations.
"Survey and Evaluation of Porous
Polyethylene Media Fine Bubble
Tube and Disk Aerators" (EPA/600/
R-94/104) by D.H. Houck
Historically, although alternative
media materials have been em-
ployed over the years with varying
degrees of success, the principal
fine pore diffuser medium has been
porous ceramic. In the early to mid-
1970s, diffusers with rigid porous
plastic media were installed in sec-
ondary treatment plants in Europe,
primarily in Finland and Sweden.
To document operation and main-
tenance experiences with rigid po-
rous plastic media diffusers, 11
plants in Europe were visited.
Observations made at each site
and the review of on-site, long-term
operation and maintenance infor-
mation are discussed. In general, it
was concluded that the rigid po-
rous plastic diffusers were perform-
ing satisfactorily. It was also
concluded that the use of ferrous
sulfate for precipitation of phospho-
rus in wastewater treatment facili-
ties was the most adverse fouling
condition encountered in applica-
tions of these diffusers. The most
effective cleaning method for this
type of fouling was found to be
formic acid gas treatment followed
by an air/water backwash with spe-
cialized equipment. The effective-
ness of similar cleaning for
biofouling was inconclusive. The
design and application of aeration
systems using rigid porous plastic
media diffusers appeared to be
similar to those employing ceramic
media diffusers.
15. "Investigations Into Biofouling Phe-
nomena in Fine Pore Aeration De-
vices" (EPA/600/R-94/107) by W.
Jansen, J.W. Costerton, and H.
Melcer
Microbiologically based proce-
dures were used to describe
biofouling phenomena on fine pore
aeration devices and determine
whether biofilm characteristics could
be related to diffuser process per-
formance parameters. Fine pore dif-
fusers were obtained from five
municipal wastewater treatment
plants in Wisconsin, one in Michi-
gan, and one in California. Biofilm
thickness and carbohydrate content
were measured as was each film's
ability to retain air bubbles. Scan-
ning electron microscopy (SEM)
procedures were used 1o examine
biofilm structure. The effect of four
different laboratory cleaning proce-
dures on diffuser characteristics was
also measured. A parallel labora-
tory-scale investigation simulated
microbially induced fouling of small-
scale diffusers and the effects of
bleach and acid cleaning.
Microbial fouling of the diffusers
occurred irregularly at all seven
sites. The thickness of a biofilm
and its distribution over a diffuser
appeared to vary randomly. Highly
structured biofilms were observed
by SEM and were thought to inter-
fere with the passage of air bubbles
such that the size of the bubbles
released from a fouled diffuser sur-
face was probably not the same as
those from a cleaned and unfouled
diffuser surface. Two types of
biofoulant were observed. One ap-
peared to reduce OTE with mini-
mal impact on diffuser headless as
measured by DWP. The second
appeared to increase DWP with
minimal impact on OTE. Although
measurements of biofilm thickness
and carbohydrate content did not
appear to be directly related to mea-
surements of OTE, DWP, and BRV,
the microbiological measurements
contributed to an improved under-
standing of diffuser operation and
performance.
The laboratory investigations
showed that the progressive devel-
opment of a bacterial biofilm on the
surface of a fine bubble diffuser
could increase the size of bubbles
released from the fouled surface.
Five-percent bleach was found to
be more effective in removing the
biofilm than 14% HCI on both artifi-
cially induced and naturally occur-
ring biofilms, and a combination of
bleach followed by acid returned
the diffusers to their original condi-
tion.
16. "Characterization of Clean and
Fouled Perforated Membrane Dif-
fusers" (EPA/600/R-94/108) by L
Ewing and J. Kitzinger
Laboratory analyses were con-
ducted on plasticized PVC perfo-
rated membrane tube diffusers after
varying periods in service at two
different municipal wastewater treat-
ment facilities. One set of diffusers
from Cedar Creek, NY, was in ser-
vice for 26 mo. The other set from
the Green Bay Metropolitan Sew-
erage District facility was in service
for approximately 47 mo. Tests on
the membranes included DWP, flow
uniformity, weight, dimensions, ten-
sile modulus of elasticity, hardness,
and OTE.
Results of this brief study indi-
cate a significant increase in DWP
and decrease in flow uniformity and
OTE after service. Following mem-
brane cleaning, measurements in-
dicated: a nonrecoverable reduction
in DWP below that of a new mem-
brane; an increase in specific grav-
ity, durometer hardness, and
circumferential modulus of elastic-
ity; and a decrease in weight,
length, and strain at failure. These
findings were in good agreement
with other field tests performed with
these diffusers.
The full reports were submitted in par-
tial fulfillment of Cooperative Research
Agreement CR812167 by the American
Society of Civil Engineers under the par-
tial sponsorship of the U.S. Environmental
Protection Agency.
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7?7/s Project Summary was authored by The Steering Subcommittee of the ASCE
Committee on Oxygen Transfer. ASCE headquarters are in New York, NY
10017.
Richard C. Brenner is the EPA Project Officer (see below).
The complete reports are entitled:
"Fine Pore Diffuser System Evaluation for the Green Bay Metropolitan
Sewerage District," (Order No. PB94-200813; Cost: $27.00, subject to
change);
"Oxygen Transfer Efficiency Surveys at the Jones Island Treatment Plants,
1985-1988," (Order No. PB94-200821 Cost: $19.50, subject to change);
"Fine Pore Diffuser Fouling: The Los Angeles Studies," (Order No. PB94-
200839; Cost: $27.00, subject to change);
"Oxygen Transfer Studies at the Madison Metropolitan Sewerage District
Facilities," (Order No. PB94-200847; Cost: $27.00, subject to change) ;
"Long-Term Performance Characteristics of Fine Pore Ceramic Diffusers at
Monroe, Wisconsin," (Order No. PB94-200854; Cost: $27.00, subject to
change);
"Case History of Fine Pore Diffuser Retrofit at Ridgewood, New Jersey,"
(Order No. PB94-200862; Cost: $27.00, subject to change);
"Oxygen Transfer Efficiency Surveys at the South Shore Wastewater Treat-
ment Plant, 1985-1987," (Order No. PB94-200870; Cost: $17.50, subject
to change);
"Fine Pore Diffuser Case History for Frankenmuth, Michigan," (Order No.
PB94-200888; Cost: $19.50, subject to change);
"Off-Gas Analysis Results and Fine Pore Retrofit Information for Glastonbury,
Connecticut," (Order No. PB94-200896; Cost: $27.00, subject to change);
"Off-Gas Analysis Results and Fine Pore Retrofit Case History for Hartford,
Connecticut," (Order No. PB94-200938; Cost: $27.00, subject to change);
"The Measurement and Control of Fouling In Fine Pore Diffuser Systems,"
(Order No. PB94-200904; Cost: $27.00, subject to change);
"Fouling of Fine Pore Diffused Aerators: An Interplant Comparison," (Order
No. PB94-200912; Cost: $19.50, subject to change) ;
"Case History Report on Milwaukee Ceramic Plate Aeration Facilities," (Order
No. PB94-200946; Cost: $19.50, subject to change);
"Survey and Evaluation of Porous Polyethylene Media Fine Bubble Tube and
Disk Aerators," (Order No. PB94-200920; Cost: $19.50, subject to
change);
"Investigations into Biofouling Phenomena in Fine Pore Aeration Devices,"
(Order No. PB94-200953; Cost: $19.50, subject to change); and
"Characterization of Clean and Fouled Perforated Membrane Diffusers,"
(Order No. PB94-200961; Cost: $17.50, subject to change).
These reports will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
EPA/600/S-94/001
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
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