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
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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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