SURVEY AND EVALUATION OF POROUS POLYETHYLENE
MEDIA FINE BUBBLE TUBE AND DISK AERATORS
by
Daniel H. Houck
D.H. Houck Associates, Inc.
Silver Spring, Maryland 20901
Cooperative Agreement No. CR812167
Project Officer
Richard C. Brenner
Water and Hazardous Waste Treatment Research Division
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
F, r^ °f the inf°rmation in this report has been
funded zn part by the U.S. Environmental Protection Agenc? under
Cooperative Agreement No. CR812167 by the American Societ? of
^ H EngineerS: The rep°rt has been subjected to Agenby^eL
and administrative review and approved for publication S Sn EPA
coS^ff; MSSti0n °f trade names or commercial prodSSts dSes not
constitute endorsement or recommendation for use «
11
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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.
xn
As part of these activities, an EPA cooperative agreement
was awarded to the American Society of Civil Engineers (ASCE) i
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
111
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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/725/1-89/023)
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. In addition to
quality assurance/quality control (QA/QC) data that may be
included in these reports, comprehensive QA/QC information is
contained in the Design Manual. 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) byC.R. Baillod and K.
Hopkins i -
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
Historically, while alternative media materials have been
employed 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 plastic porus media were
installed in secondary treatment plants in Europe, primarily in
Finland and Sweden. In order to document operation and
maintenance experience with porous plastic media diffusers ,
plants in Europe were visited to observe and report on their
experiences.
This report discusses these observations and reviews on-
site, long-term operating and maintenance information. The
conclusions, in general, were that plastic porous media diffusers
were performing satisfactorily. It was also concluded that the
use of ferrous sulphate for co-precipitation.was the most adverse
fouling condition encountered by the porous plastic media
systems. The most effective cleaning method for this type of
fouling was found to be strong chemical treatment followed by an
air/water backwash with specialized equipment. The effectiveness
of similar cleaning for bio-fouling was inconclusive. .The
application and design of aeration basins with porous plastic
media diffusers appeared to be similar to those for ceramic media
diffusers.
This report was submitted in partial fulfillment of
Cooperative Agreement No. CR812167 by the American Society of
Civil Engineers under subcontract to D.H. Houck Associates, Inc.
under the partial sponsorship of the U.S. Environmental
Protection Agency. The work reported herein was conducted over
the period of 1986-1987.
VI
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CONTENTS
Foreword ................................. .
Preface ...................... ................................ ^v
Abstract ............................................ \ ; ....... vi
Figures [[[ viii
Tables [[[ ix
I . Introduction . ............................................ ]_
II . Conclusions ................ ....................... ....... 3
III . Recommendations ........ ........................ . .......... 6
IV. Study Approach .................................... ....... 7
V. Description of Studied Aeration Equipment ......... ! ....... 10
VI. Discussion of Results .......... •. ........... ....... ....... 20
Bibliography ............................................ ^i
Appendix A - Plant Summaries
United Kingdom
Canterbury ........................................ ....... 32
Finland
Degero ............... . ................ . ........... ....... 36
Kaarina . . . . . ..... . ................................. ; ^ ^ 40
Kylasaari . . .......... ......... ....... . . . . ......... ..... -.- 41
Suomenoja ......................................... ..... 43
Tampere .............. ................ . , .......... 4g
Turku ............. ... ...................... ....... 50
Vaasa ........................................... _ 54
Sweden
Henriksdal . ....................................... _ _ 5g
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FIGURES
Number
Page
5-1 Typical Installation of Nokia Tube Diffusers n
5-2 Typical Installation of Nokia Disk Diffusers 11
5-3 Nokia Diffusers ; 12
5-4 Tube Diffuser Test Arrangement ; 14
5-5 Disk Diffuser Test Arrangement 15
5-6 GSS Test Results, Nokia Tubes 15
5-7 GSS Test Results, Nokia Disks 16
5-8 Clean Water O2 Transfer Test Results From
Valencia --
A-l Canterbury Site Plan ^ 3o
A-2 Degero Site Plan 3o
A-3 Kylasaari Site Plan 44
A-4 Suomenoja Site Plan ' -45
A-5 Vaasa Site Plan 5g
A-6 Diffuser Cleaning Machine At Vaasa 58
A-7 Henriksdal Site Plan 61
A-8 Roping Site Plan 67
vnx
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TABLES
Number
Page
6-1 Surveyed Plant Characteristics 21
6-2 Design Data Summary . 22
6-3 Clarifier Loading Conditions ; 23
6-4 Process Data Summary 25
6-5 Maintenance Summary 27
A-l Canterbury Design Data , 34
A-2 Degero Design Data 37
A-3 Kaarina Design Data 40
A-4 Kylasaari Design Data 43
A-5 Sumenoja Design Data 45
A-6 Tampere Design Data 49
A-7 Turku Design Data 51
A-8 Vaasa Design Data 55
A-9 Henriksdal Design Data 60
A-10 Nokia Tube Energy Efficiency at Henriksdal ' 63
A-ll Himmerfjarden Design Data 64
A-12 Roping Design Data 66
IX
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SECTION I
INTRODUCTION
Fine bubble aeration, using grids of ceramic dome or disk
diffusers on the floor of an activated sludge basin, has become
well established in the U.S. and Canada during the last four
years. This technology is frequently the first choice for new
municipal wastewater treatment plants and also is being used with
increasing frequency to retrofit existing coarse bubble aerated
systems. The original ceramic dome technology, developed in the
United Kingdom and introduced to North America in the mid 1970's
has been broadened by the introduction of home-grown competina
equipment. v *y
.In 1978, a detailed field survey was conducted on dome
diftuser installations.located abroad (1). Several years later
the number of installations in North America had expanded to the
point where it was useful to conduct a similar survey to deter-
mine how well the new technology of aeration was faring here
(2) . The latter study included not only the original dome
difJ:user technology imported from the United Kingdom, but also a
number of designs of more recent vintage from North American
suppliers. The most notable of these replaced the dome, with its
center retainer bolt and rounded edges, with a slightly larger
ceramic disk configuration which is fastened to the supportina
dish using a peripheral retaining ring.
The ceramic diffuser element has several inherent disadvan-
tages relating to cost, weight, and cleanability. The ceramic
stones are heavy and often will break when dropped, are fairly
costly, and sometimes difficult to clean when fouled. iThese
disadvantages, and the commercial impetus to develop similar yet
competitive aeration products, have stimulated interest in the
use of porous plastic aeration media on both sides of the
Atlantic. As discussed in greater detail in Section 5 of this
report, several U.S suppliers and one European supplier currently
provide aeration equipment using plastic media. The diffusers
are configured as plates, tubes or disks.
The most experienced supplier of porous plastic diffusers
with some installations dating back more than 16 years, is the'
Nokia Company, located in Vantaa, Finland. Installations of the
Company's porous plastic tube and disk diffusers are spread over
much of Europe, with the oldest systems located in Scandinavia
The purpose of this study was to observe, first-hand, the perfor-
mance and operation and maintenance (O&M) requirements of porous
-1-
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plastic diffuser technology, both spiral-roll tube and floor
coverage disk applications. In total, 11 plants were visited in
the period from mid September to early October, 1986. Seven of
the plants were located in Finland, 3 in Sweden, and one in the
United Kingdom. Six plants were equipped with floor coverage
disks, five had sidemounted tubes, usually in a wide-band
(diffusers on both sides of a T-manifold) configuration.
The primary focus of the study was on gathering long-term
maintenance information, including data on successful cleaning
techniques. Several plants were able to provide data which could
be used for rough estimates of energy efficiency (using the
method of references 1 and 2), and several other plants made
available data from their own energy consumption studies.
The basic design practices used at the visited plants were
also noted and are discussed in this report. Most Scandinavian
wastewater treatment plants are designed for secondary treatment
only (i.e., without separate tertiary treatment units), much like
plants in North America. Addition of ferrous sulphate (FeSO4-
.7HijO) directly into primary or secondary treatment units, for
pre- or post-precipitation of phosphorus is quite common in
Sweden and nearly universal in Finland.
The principal conclusions and recommendations from this
study are given in Section 2 and 3 respectively. Section 4
summarizes the study methodology and recaps the method used for
estimating energy efficiency. Section 5 provides some;detail on.
the Nokia aerators that were installed in the study plants.
Section 6 summarizes the observations from the plant visits and
suggests design approaches for the use of this technology. The
Appendix of the report provides background data and summaries for
each of the plants that were visited. Where available; site
plans are also provided.
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SECTION 2
CONCLUSIONS
Although most of the study plants were using process
technology and loading conditions similar to those used in North
America the Widespread usage of ferrous sulphate for preSipi-
tation of phosphorous in primary or secondary treatment units
made direct comparison of maintenance requirements difficult
several plants had tried unsuccessfully to use ceramic tube
diffusers with ferrous sulphate addition into either primary or
secondary treatment units. The same plants were able to use the
6
Based on direct observations and technical discussions with
"* ^in^* ' the Allowing conclusions
1. In general, the porous plastic dif fusers are performing
satisfactorily even under adverse conditions of
accelerated fouling due to the use of ferrous sulphate
for phosphorus precipitation.
2. The most effective cleaning technique appears to be a
combination of aggressive chemical treatment and
air/water backwashing using equipment developed for
this purpose.
3. The available energy efficiency data does not allow
direct comparisons of porous plastic and ceramic
dif fusers. Based on tests conducted by the Los Angeles
County Sanitation District No. 32 (LACSD) , the Nokia
diffusers may be somewhat less efficient than ceramic
domes owing to the lower active surface area of the
former when compared to the latter. When equal active
dif f user areas are compared, the performance of the two
types of diffusers appears to be similar.
4. After a few early problems, which have been corrected
by the manufacturer, the structural elements of the
Nokia system appear to be performing quite satisfac-
torily. Very few problems such as piping, strap or
hold-down failures were observed. The dif f user
elements hold up well even when cleaned using verv
rigorous techniques.
-3-
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5. The formic acid in-situ cleaning system appears to be
effective if (a), it is operated frequently; and (b) ,
the size of the individual aeration grids is not too
large. All of the study plants which have such a
system except two (Canterbury, U.K. and Koping,
Sweden) also co-precipitate phosphorous. Thus, it
could not be determined how effective the system would
be strictly for bio-fouling versus a combination of
chemical and bio-fouling. Canterbury is a fully
nitrifying activated sludge plant without any chemical
addition. When used every several weeks, this par-
ticular cleaning system appears to keep the diffusers
clean. However, there has been no direct verification
of its cleaning effectiveness. Similar experiences
were reported by plant staff at Koping.
6. The Nokia porous plastic diffusers use a dual-media
diffuser in which the thickness of the fine porosity
layer is about one-third of the total thickness. In
theory, a thinner fine-pore layer superimposed on a
coarser matrix might make the diffuser more cleanable
as the thickness of the fine-pore layer to be cleaned
is much less than for uniform-porosity diffusers.
Based strictly on visual observation by the Author, the
dual-medial configuration appears to facilitate the
air/water backwashing process used on both tubes and
disks. However, this observation needs to be verified
by rigorous testing before any concrete conclusions can
be drawn.
7. Addition, of ferrous sulphate to the waste stream prior
to aerated grit removal appeared to diminish severity
of diffuser fouling in the activated sludge basins and
allowed for less frequent cleaning schedules. Con-
versely, addition of ferrous sulphate directly before
or into the aeration basin seemed to promote more rapid
diffuser fouling.
8. The^formic acid-based cleaning system is simple in
design and operation. Operators noted that they found
it safe and easy to use. The use of unpressurized
liquid treatment may offer a safety advantage over one
U.S. technology (in-situ ceramic diffuser cleaning
using hydrochloric acid gas, patented by the Water
Pollution Control Corporation of Milwaukee, Wisconsin)
which is based on pressurized hydrochloric acid gas.
However, this study did not establish the comparative
efficiency between formic and hydrochloric systems.
Before concluding that formic acid treatment is as
effective as hydrochloric acid gas treatment, further
study is needed. ;
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Once the correct number of diffusers has been determin-
ed by oxygen transfer testing, it appears that the
Inann^ PlaStlC diffusers «e appliefin much the lame
JSTS," Ce™m*C di"users. The Author expect! t£at
the basic principles of application discussed in
earlier studies of ceramic systems (1,2) will also
apply to the porous plastic diffusers when they are
arranged in grids on the floor of an aerltion balin
futh^V* th6 StUdy installations appeared So the
the eauiLenf6-6^-1^3 than °ptimal ^Plication of
«?!n? fment' in similar manner to ceramic'diffuser
plants observed in earlier studies (1,2).
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SECTION 3
RECOMMENDATIONS
Several questions relating to performance and O&M considera-
tions were raised as a result of this study. It is likely that
most of these questions will be addressed as a result of commer-
cial activity and competition between Nokia and suppliers of
other types of fine-pore diffusers. Specifically:
1. Better comparative oxygen transfer performance data needs to
be developed. Oxygen transfer tests by the Los Angeles
County Sanitation District (LACSD) suggest that the Nokia
disks cannot be equated on a one-to-one basis with the
ceramic dome (in this case supplied by Norton Company,
Worcester, Massachusetts). Comparison between the Nokia
disk and larger disk diffuser supplied by U.S. manufacturers
would also be useful.
2. Although the manufacturer makes no claims that the formic
acid cleaning system is effective against biofouling,
observations during this study suggest that it may have some
effectiveness. The formic acid system appears to be simple,
low in cost, and relatively safe when compared to gaseous
systems which operate under pressure. A comparative
evaluation of its performance against the performance of
hydrochloric acid gas based technology used in the U.S. is
recommended.
3. The pressurized water-backwashing equipment developed at
Vaasa Finland for cleaning porous plastic tube diffusers is
effective and easy to use. Cleaning procedures based on
chemical cleaning and the use of this type of device should
be studied for rehabilitative cleaning of fine-pore dome,
disk, and tube diffusers being currently sold in the U.S.'
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SECTION 4
STUDY APPROACH
th^ sec^ion summarizes the approach used in carrying out
is imi^r ?n analyzin9 the results. Although the metholology
is similar in some respects to that used in the original "Survey
SSi !i? i°U °f Flne BUbble D°me Diffus^ Aeratio? Equipment-
study (1), budget constraints and availability of data restricted
the level of detail, study of historic data, and performance
evaluation in comparison to that earlier work. perrormance
SELECTION OF PLANTS FOR VISITATION
Age was the primary criteria used to select plants for
visitation, followed by plant size and location. Al?hougS there
treatment Plants ^ing Nokia disk diffu-
, u-
tat d r^ni-0^1^ °f S^andanavia- Budget constraints necessi-
tated a plant itinerary that would minimize travel time and
expense As a result, all of the plants with the exception of
one (Canterbury, U.K.) were located in either Sweden o? Finland
Even though most of the oldest and largest plants are locked in
,- * ^^ °f si^"i^nt tube and disk
located in France and Italy that date back to 1977.
PLANT VISITS
With the exception of Canterbury, U.K., which was a nit-r-ifv
ing system^ the visited plants used secondary activated s?Jdge Y
processes similar to those found in the U.S., and aeration basins
° ' * * PaSSeS' The ma^°^t of th tdy plan
i-vo=+-,=.^ m~.! -i j - o_~ «i
-------
Finland (cont.)
Suomenoja Disk
Tampere Tube
Turku Disk
Vaasa Tube
Sweden
Henriksdal (Stockholm) Tube/Disk
Himmerfjarden (Stockholm) Tube/Disk
Roping Disk :
Less than one day was spent at each plant in addition to
travel time. The plants selected for visit were contacted in
advance with an outline covering the type of information that
would be requested. About one-half of the plants compiled data
in advance of the visit, and the remainder was obtained during
the time of the site visit where possible. Most interviewing was
conducted through a translator.
METHOD OF EVALUATION
_ As noted earlier, most of the information gathered was
empirical in nature, obtained by direct interview, and focused
mainly on operation and maintenance. In most cases, fairly
detailed data on activated sludge process design and typical
operation was obtained and is summarized in the Appendix
However, several plants also provided data which were adequate to
allow performance estimating using the methods developed for
previous surveys (1,2). The method is based on mass balance and
approximate process oxygen consumption is computed using influent
and effluent data provided by the plant. This is then divided bv
net energy consumption to arrive at an estimate of oxygen
supplied (kg or Ibs) per unit of energy (kWh or wire hp-hour)
The estimating equations are as follows:
Oxygen Demand
Units of Oxygen Required/Unit of BODs Removed:
R = 0.75 + 0.05/FM
Where:
R - Ratio of oxygen reqd./unit of: BODo rem
(0.05
-------
Where:
GT - Total oxygen consumption per day
Bs - Aeration basin influent BOD3 (kg/day)
Be - Final clarifier effluent BODa (kg/day)
Ns - Aeration Basin influent NHs-N (kg/day)
Ne - Final clarifier effluent NH3-N (kg/day)
Ne *- Final clarifier effluent NO3-N (kg/day)
Note: This computation can also be made in terms
of pounds per day (or week, month, year, etc.) by
applying the appropriate conversion factors.
Energy efficiency:
AE = Gt (in Ibs/dav or kg/day)
Aeration Power (kWh/day or wire hp-hours/day)
Where:
AE - Energy efficiency, Ibs or kg oxygen
removed per kiloWatt-hour
It should be re-emphasized that this method is very ap-
proximate and is most useful for comparing performance ,of similar
treatment plants treating similar wastes rather than fqr es-
tablishing absolute values of energy efficiency. Currently,
routine, reliable and accurate measures of aeration energy
efficiency is best obtained from off-gas measuring techniques
\ <5 / •
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SECTION 5 ;
DESCRIPTION OF STUDIED AERATION EQUIPMENT
As noted previously, this study consisted primarily of field
visits and observations to treatment plants equipped with tube or
disk diffusers supplied by the Nokia Company, of Vantaa,
Finland. This Section provides a summary description of that
equipment. More detailed information is available from the
Muriters Corporation (U.S. licensee for Nokia), located in Fort
Myers, Florida. Some comparisons between the Nokia products and
diifusers manufactured by Sanitaire (Milwaukee, WI), Norton
(Worcester, MA), and FMC (Warminster, PA) are drawn below
Information on these products can be obtained from these suppli-
ers and is also provided in some detail in References 1 or 2.
Nokia diffusers are available as either tube diffusers
designed to be installed on fixed or swing manifolds for spiral-
flow tanks (Figure 5-1), or arranged in grids on the aeration
basin floor (Figure 5-2). The HKP and MKP series of aerators are
fine and medium bubble tubes, respectively. Disk diffusers are
designated as either HKL for fine bubble or MKL for medium bubble
porosities. Figure 5-3 depicts the two types of aerators.
Both the tube and disk diffusers use a dual-porosity poly-
ethylene diffuser media that is approximately 3/8 inch (0.95 cm)
thick. The outer fine porosity layer is about 1/8 inch (0.32 cm)
thick and the coarse porosity supporting layer is about 1/4 inch
(0.64 cm) thick. By contrast, the FMC Pearlcomb tube diffuser
(another commercially available plastic diffuser) element is
about 9/16 inch (1,43 cm) thick and of uniform porosity. The
Norton dome diffuser and the Sanitaire (Water Pollution Control
Corp.) disk diffusers are about 3/4 inch (1.9 cm) thick and also
of uniform porosity. ;
The oxygen transfer performance tests conducted for the
Valencia Water Reclamation Plant by County Sanitation District
No 32 of Los Angeles County indicate that the Nokia and Norton
aiffusers were comparable in oxygen transfer efficiency when
evaluated on an equal diffuser-area basis (4). The tests
discussed in more detail later herein, did not include develop-
ment of comparative data with the Sanitaire disk diffuser.
The diameter of a Nokia disk diffuser element is approxi-
mately 7 3/8 inches (18.7 cm) and the active area is about 7
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Figure 5-1. Typical Installation of Nokia Tube Diffusers,
Figure 5-2. Typical Installation of Nokia Disk Diffusers.
-11-
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HKP 600 or MKP 600 diffuser
OJ
HKL 215 or MKL 215 diffuser
Figure 5-3. Nokia Diff users.
inches (17.8 cm) in diameter. By contrast, the Sanitaire disk
^^^
. . ir^jK^frs^ss ; ? -
larger effective surface area than the horizonial surface aLne '
The.Nokia tube diff users have an internal perforated air
•
a
diftuser manifold female bosses (usually 3/4 or 1
3/4 inches (7
the
tu crrenly valable
the U.S. However, there are a number of substantial desian
differences from U.S. made ceramic dome or disk di?f users'?
-12-
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1. The diffuser assembly includes a PVC diffuser body
(including the diffuser, retainer ring, orifice
assembly, and baseplate) which is secured to: the pine
by a wedge piece. The diffuser unit is shipped
separately from the pipe and mounted on the pipe at the
time of assembly after the pipe has already been
mounted on the basin floor. Theoretically, this
reduces the possibility of damage to the diffuser
assemblies in shipping and handling. Also, it allows
the owner to move the diffuser assemblies to different
locations on the pipe at a later date if required.
2. Most disk and dome diffusers utilize a control orifice
between the air supply manifold and the diffuser
baseplate of fixed port diameter for which headless
(and hence energy consumption) increases with airflow
Nokia utilizes a rubber check valve arrangement in
which the effective orifice area increases with
increasing airflow (variable orifice). As discussed
further below, this characteristic has a significant
effect on the energy efficiency of the diffuser at
higher air flows. Also, if air flow is interrupted,
the check valve prevents backflow of liquid from the
diffuser into the interior of the air supply piping.
However, liquid can still backflow into the diffuser
baseplate dish (between the diffuser and control
orifice).
3. The diffuser disk is held on by a threaded retainer
ring which is similar to that used by Sanitare (though
much smaller in diameter). The gasket covers the
entire edge of the diffuser and only a small portion of
the inner and outer surfaces. It is easily installed
and fits tightly around the perimeter of the disk and
it is very difficult to install the disk in the
baseplate unless the gasket has been installed proper-
ly. This may reduce the possibility of leakage caused
by improper gasket installation.
i
4. As noted previously, the thickness of the fine-pore
layer of the Nokia diffusers (tube or disk) is much
less than that for similar fine-pore diffusers. This
might contribute to the ease of cleaning of the dif-
fusers as the thickness of fine porosity material to be
cleaned would be much less. Based on the Valencia
tests (4) the thinner fine-porosity layer design does
not appear to substantially lower the ability-of the
media to form the fine bubbles typical of this class of
device and achieve performance levels comparable to
ceramic media dome and disk diffusers when compared on
an equivalent-area basis.
-13-
-------
OXYGEN TRANSFER PERFORMANCE
Oxygen transfer performance studies on the Nokia :tubes and
disks were conducted in mid 1980 by Gerry Shell Environmental
Engineers, Inc., under contract to EPI, Inc., Nokia's licensee at
that time (5,6). The tests were conducted at three water depths
of 10, 17.5, and 25 feet (3.05, 5.33, and 7.62 m) using the clean
water unsteady state method with sodium sulfite for deoxygenation
and cobalt chloride.as the catalyst. Test results were corrected
to standard conditions of tap water at 20°C liquid temperature,
1.0 atmosphere pressure, zero dissolved oxygen and an alpha and
beta equal to 1.0.
The test tank was cylindrical, 21 feet (6.4 m) in diameter
and equipped with three sampling points. Tests were peformed in
June 1980 on the medium bubble (MKP-600) and fine bubble (HKP600)
tubes (5). In August 1980, tests were conducted on the medium
bubble (MKL-210) and fine bubble (HKL-210) disk aerators (6).
The latter are essentially the same as the HKL-215 fine bubble
disk aerators that were observed in Scandanavia and the U.K.
The tube diffuser tests were performed on 20 tubes in a
wide-band configuration on a single, centered manifold located
about 12 inches (30.48 cm) off the basin floor. The diffusers
were spaced on two foot (61 cm) centers and arranged as shown in
Figure 5-4.
TOP VIEW
Figure 5-4. Tube diffuser test arrangement.
In August 1980, tests were conducted on the disk diffusers,
which were arranged in the same tank in the floor coverage
configuration shown in Figure 5-5. In total, 108 disk diffusers
were tested. The horizontal surface of the. disks were located
-14- :
-------
11.5 inches (29.2 cm) above the floor and spacing between disks
was approximately 2 feet (61 cm). The arrangement usel for the
test is illustrated in Figure 5-5.
TOP VIEW
24
Figure 5-5. Disk,diffuser test arrangement.
tt
*
0
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CO
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fa
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Figure 5-6. GSS test results, Nokia tubes.
-15-
-------
36
32 .
28 ~
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en
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i
i
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I
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0
0-4 0.8 1.2 1.6. 2.0
Figure 5-7. GSS test results, Nokia disks.
2.4
Figures 5-6 and 5-1 are the oxygen transfer performance
curves for the medium and fine bubble tubes and disks respective-
ly, operating in 11.5 feet (5.3 m) total water depth (16.5 feet ,
5 m, submergence). At 0.6 scfm per diffuser (0.017 m3/min) , the
fine bubble tube (HKP 600) operated at a 19 percent transfer rate
into clean water. The medium bubble tube (MKP 600) at the same
air flow tranferred 13 percent.
The efficiency spread between the fine and medium bubble
disks was considerably narrower. At 1.2 scfm per diffuser (0.035
m3/min), the fine bubble disk (HKL 210) transferred at the rate
of about 29.5 percent; the medium bubble disk (MKL 210) trans-
ferred at 26.5 percent.
In response to a competitive bid by Nokia to supply diffu-
ser s for the Valencia, California, treatment plant, owned by the
County Sanitation District No. 32 of Los Angeles County, CA,
tests were conducted by the County on the Nokia HKL 210 disk
diffusers in December of 1985 (4) . The tests were conducted in
the same tank used for an earlier test program which tested a
wide variety of coarse, medium and fine bubble aerators, includ-
ing fine bubble domes (Norton) and disks (Sanitaire). By using
this facility and following essentially the same procedures used
-16-
-------
used in the earlier test program, the District could develop
direct comparison of the Norton domes and Nokia disks.
The initial objective was to determine the equivalent number
of Norton domes and Nokia disks. This would then be used to
specify the number of the latter that would be required to
satisfy the requirements of the Valencia specification. It was
determined in the previous tests that the effective operating
surface area of the Norton dome at 1.0 scfm (0.029 m3/min) air
flow is 48.5 square inches (312 cm2). The active area of the
flat Nokia disk was computed to be 37.94 in2 (245 cm2) based on
an exposed surface diameter (not including areas covered by
retainer ring or gasket) of 6.95 inches (17.6 cm). If the two
diffuser systems are compared on an equivalent area basis, this
suggested that 107 Norton domes and 137 Nokia disks would perform
similarly in the same test tank using the same (clean water) test
procedures assuming that the ceramic and porous polyethylene
diffuser materials are equivalent in performance. The actual
test was conducted on 136 Nokia diffusers as the manifold
configuration would not, allow equal distribution of 137 disks.
The test results, a sample of which is shown in Figure 5-8,
appear to support the hypothesis of equivalent performance based
on equivalent areas. Although the Nokia diffuser has a larger
pore size and a lower bubble release pressure, it appears to
perform very much like the Norton diffuser. The Nokia aeration
efficiency was found to be slightly higher at the upper end.of
STANDARD WIRE AERATION EFFICIENCY vs. WIRE POWER UTILIZATION
(for Nokia & Norton with equal areaf
I
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1-4
13
12
11
10
a
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(1.00 scfm per Norton diffuser,
0.78 scfm per Nokia diffuser)
Test Basin Wire Power Utilization (whp)
M system * Nokia results prorated
+Norton dome system from 135_137 diffuser
_. . _ . , configuration
Figure 5-8. Clean water O2 transfer test results from Valencia
-17-
-------
a.-xr £lo-w range. This was attributed by LACSD to the lower
orifice loss of the Nokia diffuser at high air flows. At the low
end of the air flow range, the Norton diffuser was slightly more
efficient. No explanation was given for this observation.
The implication of the District's testing is that the porous
polyethylene material used by Nokia will perform similarly to
ceramic diffuser materials, when compared on an equivalent area
basis, at least in clean water tests. At the design air flow per
diffuser, 1.28 Nokia diffusers would thus be required for every
Norton diffuser. Equivalency under "dirty water" conditions was
not determined as part of the District's evaluation.
DIFFUSER TESTS AT LAKEVIEW, ONTARIO, CANADA
In 1982, testing was conducted at the Lakeview, Ontario,
Canada (Ministry of Ontario Region of South Peel) treatment
plant, located in Mississauga, Ontario, to evaluate the potential
for biofouling of fine bubble diffusers in activated sludge
treatment (7). The waste stream at this plant includes a strong
industrial effluent from corn-starch manufacture, plus an
internal recycle stream from sludge heat treatment. As a result,,
the waste has a high soluble-BOD content when compared to typical
domestic sewage.
The test reactor was tubular, 14 feet high, 1.15 feet in
diameter, and fitted with a single test diffuser at the bottom.
Tested diffusers included a ceramic dome, a ceramic disk, and a
Nokia disk. The test reactor was located adjacent to the
activated sludge basins and dosed with settled sewage and return
activated sludge to stimulate various conditions at the inlet of
the proposed complete-mix aeration tanks.
The first series of tests determined that rapid biofouling
was likely for all test runs of ceramic domes. Only minor slime
growth was reported on the Nokia disk diffuser. However,
pressure drop across the Nokia diffuser increased significantly
and when the diffuser was removed and examined, a slurry of water
and solids was found on the air-side of the disk and it had
assumed a convex shape. Apparently, some leakage had occurred
which allowed mixed liquor from the reactor vessel to infiltrate
the diffuser.
A second test run relocated the reactor to allow it to draw
influent wastes that did not include the heat treatment liquor
recycle stream. The Nokia disk diffuser was not retesjted, but
biofouling of the ceramic diffusers was considerably reduced as a
result of removing the heat treatment liquor stream.
Further tests focused on tests of tubes manufactured by FMC
(Pearlcomb) and two other suppliers (Hut, Mizpe). Test headers
of tube diffusers were fabricated and inserted into an activated
sludge basin. This particular portion of the process includes
-18-
-------
addition of ferrous and ferric chlorides. Although little
bioJ:puling was observed on the tubes, a buildup of oxidized iron
products in the tube material was observed. It was concluded
that this buildup was the source of increased backpressure (7).
Separate tests of Nokia tubes and disks were also carried
out in a basin without iron salt addition. The tubes were tested
uder similar conditions as the tube tests summarized above. The
disks were installed in two of the cylindrical reactors used in
the first series of tests. Biofoulants built up rapidly on the
tubes but were removed fairly effectively with formic acid
dosing. Under conditions of aeration tank influent soluble BOD
averaging 77 mg/1, only small amounts of bio-fouling were noted
on both test disk diffusers. The buildup did not increase
significantly over a 6 week test period. Formic acid was
injected five times over the disk test period, but no improvement
was observed, as there was little bio-growth on the diffusers.
The results of these tests indicate the possibility that the
Nokia disk might have been less s.ubject to biofouling than
ceramic diffusers. In a written comment on this test (8), Nokia
cited another reference (9) as providing explanation of this
observation. In particular, the uniformity of air distribution
of the diffuser and the higher air flow rates per diffuser used
by Nokia when designing for systems with bio-fouling potential
were cited as the reason for the apparently superior performance
of the Nokia disk in this test.
Further substantiation of the results of this test, and the
claims made by Nokia, are required before any conclusions could
be drawn. In particular, if reduced bio-fouling can be obtained
by designing and operating Nokia diffusers at higher air flow
rates, it is quite possible that similar results might be
obtained by subjecting ceramic fine-pore diffusers to similar
operating conditions. Indeed, "flushing" of ceramic dome and
disk diffusers by subjecting them to elevated air flow rates for
periods of several hours is one maintenance strategy used for
these systems. It is possible that the Lakeview tests are simply
verifying that elevated air flow rates can impact the rate of
bio-fouling on fine-pore diffusers as a class of device.
-19-
-------
SECTION 6
DISCUSSION OF RESULTS
As noted in the Introduction, this study focused on first
hand observation of operating Nokia tube and disk installations
and direct interviews of operating personnel to assess the O&M
performance of the equipment. No formal effort was made to
obtain efficiency data on the equipment, although some informa-
tion was obtained during the plant visits.
Summarized below are the observations and findings resulting
from the site visits. Suggestions for improved application of
this equipment are also included where appropriate.
DESCRIPTION OF VISITED PLANTS
In total, 11 plants were visited, 7 in Finland, 3 in Sweden
and one in the United Kingdom. Six plants were equipped with
floor coverage Nokia disks, five had sidemounted Nokia tubes
usually in a wide-band {diffusers on both sides of a T-manifold)
configuration. Most of the tube diffuser installations were of
the M-series (medium bubble); all of the disk installations used
H-series (fine bubble) media. Appendix A provides a plant-by-
plant summary of the site visits. Tables 6-1 and 6-2 summarizes
design data for each of the plants.
With the exception of the Canterbury, U.K., treatment plant,
a nitrifying system, most of the study plants provided secondary
treatment only for biological contaminant removal and were quite
similar to U.S. treatment plants in design. However, most of the
scandanavian plants added ferrous sulphate (FeSO<•7H2O) for
co-precipitation of phosphorous. As discussed later herein this
has a. marked impact on inorganic fouling of fine and medium
bubble diffusers. Diffusers at all installations using ferrous
sulphate are cleaned frequently, sometimes 3-4 times per year
Thus, biofouling could not be observed or differentiated from"
inorganic fouling during this study.
Physically, the Scandinavian plants are designed much like
plants in the U.S. Step-feed aeration basins, usually dual-pass
are used. The basins are equipped for optional plug-flow
operation. Length/width ratios are relatively low (Table 6-2)
when compared to many plants in the United Kingdom (1) and very
similar to U.S. plants (2). Wide band, spiral-roll diffuser
systems predominate. Usually, but not always, diffusers are
mounted on swing headers. ,
-20- •
-------
TABLE 6-1
SURVEYED PLANT CHARACTERISTICS
Plant Name,
Location
Description of Aeration System
Flow
(mgd)
United Kingdom
Canterbury
Finland
Degero
Kaarina
Kylasaari
Suomenoja
Tampere
Turku
Vasisa
Sweden
Henriksdal
Himmerfjarden
Roping
Four single-pass disk aerated tanks, 5.3
nitrifying process, disk diffusers -with
uniform diffuser layout.
Three two-pass step feed tanks, tube 0.72
diffusers in uniform wide-band layout,
ferrous sulfate addition to aeration.
Six two-pass step feed tanks, tube 2.6
diffusers in uniform wide-band layout,
ferrous sulfate added.
Twelve two-pass step feed tanks, now 32.0
equipped with Inka tubes, being con-
verted to disk diffusers in tapered
configuration. Ferrous sulfate added.
Six two-pass step feed tanks, disk 19.0
diffusers in uniform layout except
for last grid, sodium aluminate and
ferrous sulfate added.
Six two-pass step feed tanks, tube 5.3
diffusers in uniform wide-band layout,
ferrous sulfate added.
Five two-pass step feed tanks, disk 17.3
diffusers in uniform layout, in-situ
cleaning system, ferrous sulfated added.
Five two-pass step feed tanks, tube 5.8
diffusers in uniform wide-band layout,
ferrous sulfate added.
Eleven two-pass aeration tanks, 10 81.0
with tubes, one with disks, ferrous
sulfate added, in-situ cleaning.
Eight two-pass aeration tanks, 7 30.4
with tubes, one with disks, ferrous
sulfate added.
Two dual-pass step feed tanks, disk 5.0
aerated, tapered configuration, in-
situ cleaning system.
-21-
-------
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Air Flow Average Mixing
Per Diff. Air Input
(scfm) (scfm/1000 ft3)
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Primary clarifiers in the plants visited in Scandinavia were
similar in design and loading conditions to U.S. plants.
Detention times typically ranged from 2-3 hours and surface
loading rates ranged from 590 to as high as 2000 gpd/ft2 (Turku,
Finland), though a high of 1200 gpd/ft2 was more usual. The
primary clarifiers at Canterbury was typical of U.K. plants, with
a surface loading rate of 437 gpd/ft2 and detention time of 6
hours.
Secondary clarification practices at many Scandinavian
plants were found to be similar to U.S. practices in terms of
loading conditions though several plants had relatively high
loading rates on the secondary clarifier system. Again, the
Canterbury plant featured very low clarifier loading rates
typical of U.K. treatment plants. Most of the Scandinavian
plants visited used rectangular clarifers.
Table 6-3 summarizes clarifier loading conditions at the
visited plants.
TABLE 6-3
CLARIFIER LOADING CONDITIONS
Plant Name
United Kingdom
Canterbury
Finland
Degero
Kaarina
Kylasaari
Suomenjoa
Tampere
Turku
Vasisa
Sweden
Henriksdals
Himmerf jarden
Koping
Primary Clarifiers
Rise Rate DT
(gpd/ft2) (hrs)
437
590
None
1000
710
670
650
470
None
1180
1060
900
6.0
2.4
None
1.7
.1-2. ...
2.1
3.7
3.4
None
1.8
1.7
1.6
Secondary Clarifiers
Rise Rate '' DT
(gpd/ft* ) (hrs)
400
1000
360*
650
530
470
355
. 590
440
440
1030
830
1100
8.0
1.6
6.0*
2.9
. , . ' . 3 . 9
2.9
7.2
3.7
3.6
4.7
3.0
2.8
2.0
* Calculated at mean annual flow, 3 units in operation.
-23-
-------
Virtually all of the study plants were equipped with
positive displacement blowers of the Roots type. Himmerfjarden
had recently installed HV-Turbo variable speed blowers, manufac-
tured by Helsingtfr Vaerfta/s of Denmark. These single stage
units are variable over a wide range, 45-100 percent, with a
nearly flat efficiency curve averaging 80 percent (see appen-
dix) . Plant operators reported that the blowers perform very
well and are particularly well suited to fine bubble systems with
dissolved oxygen control systems.
Air filtration is usually provided using disposable cart-
ridge filters or dry electrostatic collectors, similar to units
used in the U.S. However, those plants using medium bubble tubes
generally provided only single stage, relatively coarse, air
filtration. Plant operators noted this appeared adequate to
protect against diffuser air-side fouling. None of the plants
visited reported problems from excessive air filter maintenance.
PROCESS CONDITIONS
Table 6-4 summarizes basic process parameters observed at
the study plants. With the exception of Canterbury, which
resembled other U.K. plants visited during an earlier study (1),
plant process conditions are similar to those in U.S. secondary
treatment plants, in terms of process loading conditions,
aeration basin geometry, and mixed-liquor solids levels.
Nitrification is the exception rather than the rule in Scan-
dinavia though it is expected to be more widely practiced in the
future.
As noted previously, most of the study plants add ferrous
sulfate for co-precipitation of phosphorous. This chemical is a
waste byproduct of metal industries in Scandinavia and is
available at low cost. A high degree of phosphorous removal is
achieved with this treatment, though plant operators reported
that it imposed a significant additional maintenance cost on
plant operations, mainly in the form of jliffuser maintenance and
accelerated corrosion of metallic components.
Two Swedish plants, Henriksdals and Himmerfjarden, are
testing the use of anoxic pretreatment and single-stage nitrifi-
cation, as demonstrated at the Ryemeads, U.K., treatment plant.
Early indications at both plants are that the process functions
properly, reduces energy consumption, and achieves 30-40 percent
denitrification. It is planned to test the process at both
plants for 1-2 years and convert all aeration units to this
process if the test is successful.
OPERATION AND MAINTENANCE
Basic maintenance procedures observed are summarized in
Table 6-5. Because most of the study plants add ferrous sulfate
to the aeration process to co-precipitate phosphorous, the O&M
-24- ' :
-------
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requirements of the diffuser systems were quite extensive.
Usually, operators at plants with tube diffusers find it neces-
sary to remove and clean the diffusers as frequently as twice per
year. Degero reported the longest tube diffuser cleaning cycle
of two years. Interestingly, ferrous sulfate is added into the
aerated grit chambers at this plant rather than the more typical
practice of addition to the aeration basins. Possibly, this
earlier addition may reduce the fouling of the tube diffusers.
In all cases, plant operators report that the foulant is
inorganic in nature, appearing as a rust-red scale. None of the
plants reported problems with organic foulants. Procedures which
involved the use of strong chemicals and/or steamcleaning, or
air/water backwash were typically used to clean the tubes (see
Appendix, plant writeups for Tampare,Turku, Vaasa). The most
successful and easy to apply procedure appeared to be that used
at Vaasa, where a cleaning "machine" has been developed. After
soaking the tube diffusers in a strong solution (10 percent) of
potassium hydroxide for one week, the diffusers are air/water
cleaned using the hydraulic cleaning machine. The cleaning
process requires 10-15 seconds per tube, including installation,
cleaning and removal on the machine. The cleaning procedures
used at Vaasa were clearly the most effective from the standpoint
of minimizing operator labor and exposure to dangerous chemi-
cals. A cleaned diffuser sample from this plant was tested for
bubble release pressure (by Ewing Engineers, Milwaukee, WI) and
found to be relatively clean when compared to a new diffuser.
Review of plants with disk diffusers generally revealed few
problems. Operators reported excellent performance at both
Roping and Suomenoja. Problems at Turku appear to be related to
the relatively large size of the aeration grids, and some
inattention to repair of line breaks. It appears that the acid
cleaning system cannot successfully keep the diffusers clean on
the perimeter of the large grids at Turku. Also, several major
line leaks were observed during the plant visit.
All of the Scandinavian plants removed phosphorous from
their effluents. Only Roping did so in a separate stage,
following the activated sludge process. Roping was also equipped
with an in-situ liquid formic acid cleaning system for its disk
diffusers. Ferrous sulfate was not present as a diffuser
foulant, and the activated sludge process used is fairly typical
of that used in the U.S. Hence, Roping may represent a good
example of how the disk diffusers and the cleaning system might
function in a similar U.S. plant.
Operators at Roping report that dosing of the diffusers on a
twice per year basis using the formic acid cleaning system
appears to keep them fully clean and functional. Visual observa-
tions during the site visit confirmed an even, fine bubble
aeration pattern. The cleaning system has been operated over six
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Plant Name
TABLE 6-5. MAINTENANCE SUMMARY
Summary of Maintenance Procedures
And Results
United Kingdom
Canterbury
Finland
Degero
Kaarina
Kylasaari
Suomenoja
Tampere
Turku
Vaasa
Original disk diffusers failed due to blower
air supply malfunction. Current system has
formic acid cleaning system, installed in '
1984. Diffusers are dosed weekly with 1 0
gram of formic acid per diffuser over a 10
minute period. System reported as function-
ing satisfactorily.
Tube diffusers are cleaned every 2 years by
soaking for 1-2 days in a 10 percent solution
of strong hydrochloric (HC1) acid, followed
by air/water backwash.
Every 6 months, tubes are washed and coated
in-place with strong HC1 solution, left for
several hours, then washed again. Every 3
years, the diffusers are removed and acid
treated and scrubbed inside and outside.
New system, no maintenance observations.
Due to an air line failure, an initial manual
cleaning of the tube diffusers needed. An in-
situ formic acid cleaning system was in-
stalled in 19.82, operated 3 times per year
System reported functioning satisfactorily.
Tubes are removed annually and soaked for 12
hours in a hot cleaning solution of potassium
hydroxide (KOH) . Solution is made up from
diluting 6.4 percent KOH with water in the
ratio of 1:10 and adding a strongly basic
commercial cleaning agent. Diffusers are
steam then cleaned inside and outside.
Disk diffusers are cleaned using in-situ
formic acid cleaning system which is operated
based on blower back-pressure readings
System does not appear to be fully cleaning
diffusers due to improper operation and
overly large aeration grids.
fine bubble tubes changed to medium
bubble tubes in 1981. New tubes cleaned
twice yearly by soaking for one week in a
strong solution (29 percent) of KOH, followed
by air/water backwashing in a cleaning unit
-27-
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Plant Name
SUMMARY
Summary of Maintenance Procedures
And Results
Sweden
Henriksdal
Himmerf jarden
Tube diff users are mechanically renewed by
cutting 0.04-0.08 inches (1-2 nun) off the
°f the tube Usin9 a ^the.
YStem in Tank X1 WiPPed with
acid cleaning system.
Test basin (No. 8) equipped with disks and
irSS.J0?1^ aCld Cleanin3 syst^. System
is operated about every 4 months. Plant
staff reported that system is effective
agaznst inorganic foulants but appears to
impact organic fouling very little.
Disk diff user system equipped with in-situ
formic acid cleaning system. Cleaning system
is operated twice yearly for about one hour
on each individual aeration grid (see
and
Similar observations were reported by olant *t-*ff **
=
DESIGN DISCUSSION
'" l^^*^^^^^—^ ""•
plants Ba"r°n C0mpoundf) Present in most of the ----
-28-
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Ho-weveir, this possibility needs further investigation.
Where possible, it is suggested that the disk diffuser
system be designed such that the individual aeration grids
have 300 or fewer diffusers. This may help avoid the
problem of incomplete cleaning of diffusers along the
periphery of the grid, as observed at Turku.
Porous polyethylene tube diffuser systems can also be
equipped with formic acid in-situ cleaning. Each drop
header should be equipped with an individual acid solution
injection port. Observations from this study do not
indicate that formic acid cleaning is as effective for tube
diffusers as it is for disks.
2. Application of porous polyethylene or ceramic diffusers in
wastes having high soluble BOD is not recommended without
pilot testing. Pilot testing should include evaluation of
the formic acid in-situ cleaning system as well as hydro-
chloric acid based systems offered by at least one ceramic
diffuser supplier.
3. The rigorous operating conditions caused by the use of
ferrous sulfate in most of the study plants have fostered
the development of effective techniques and equipment for
cleaning porous polyethylene tubes and disks in Scan-
danavia. The dual-media construction of the diffuser
element might make it more suitable for cleaning than
uniform porosity ceramic or plastic diffusers. Possibly,
the reduced thickness of the fine porosity layer may
facilitate cleaning. However, this possibility needs to be
investigated further.
A complete O&M manual which details chemical/mechanical
cleaning procedures should be provided for all types of fine
bubble diffusers. Depending on the size of the project and
the type of diffuser specified, appropriate cleaning tools
should also be provided or the cost/availability of cleaning
or replacement should be included in the economic analysis
for the project.
4. The design of the Nokia disk diffuser allows the entire
diffus'er unit (baseplate, control orifice, diffuser element)
to be relocated after installation, or added quickly to an
existing pipe grid. Installing a new diffuser assembly on
an existing grid is done by drilling the air pipe and
wedging the diffuser assembly on the pipe. Field gluing is
not required. A diffuser assembly can be relocated by
tapping the wedge bracket loose, plugging the hole in the
pipe, and reinstalling the assembly in the desired location.
Spare diffusers can be stored until needed rather than
installed on the air distribution lines initially. Also,
this feature may allow the designer to provide adequate
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backup with fewer spare diffusers as additional diffuser
units can be purchased and installed if and when needed.
Design procedures relating to provision of spare diffusers
for currently available ceramic diffuser products might need
to be modified if the Nokia disk diffuser is used for
retrofit.
5. The control orifice design of the Nokia disk diffuser may
offer several important benefits over that used in some
other current fine bubble dome/disk designs. Firstly, the
orifice also acts as a check valve to limit backflow of
liquids from the aeration tank into air supply lines during
blower shutdown and loss of air flow. Secondly, the orifice
offers variable resistance to air flow. At high air flows,
the resistance of the variable orifice may be significantly
less than that of most fixed-orifice fine bubble diffusers.
This might permit the diffuser to be used at higher air flow
rates with some reduction in oxygen transfer. This charac-
teristic may in turn allow the use of fine bubble diffusion
in applications of moderate to high bio-fouling potential
where design and operation at elevated air flow rate could
reduce this problem.
6. Other than as noted above, the tube and disk diffusers
studied during this project appear to be applied much like
other similar fine bubble aeration equipment available in
the U.S. Having determined the correct number of tubes or
disks based on oxygen transfer and mixing considerations,
the Nokia equipment are subject to most if not all of the
design and O&M considerations discussed in earlier studies
(1,2). These considerations include waste characteristics,
process type, and aeration basin geometry.
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BIBLIOGRAPHY
1. Houck, D. H. and A. G. Boon. Survey and Evaluation of Fine
Bubble Dome Diffuser Aeration Equipment. U.S. EPA Municipal
Environmental Research Laboratory, EPA-600/2-81-222,
September 1981.
2. Houck, D.H. Survey and Evaluation of Fine Bubble Dome
Diffuser Aeration Equipment in North America. U.S. EPA
Municipal Environmental Research Laboratory, pending
publication.
3. Boyle, W. C., Ed. Proceedings: Seminar Workshop on
Aeration System Design, Testing, Operation and Control.
U.S. EPA Water Engineering Research Laboratory, EPA
600/9-85-005, January 1985. :
4. Yunt, F.O. and T. Hancuff. Analysis of Shop Performance
Tests On The Air Diffusion Equipment For The Valencia Water
Reclamation Plant Stage Three. County Sanitation District
No. 32 of Los Angeles, California, 1955 Workman Mill Road,
Whittier, California 90601, January 1986.
5. Gerry Shell Environmental Engineers Inc. Oxygen Transfer
and Headless Characteristics of the Nokia MKP-600 and
HKP-600 Tube Diffusers, June 1980.
6. Gerry Shell Environmental Engineers Inc. Oxygen Transfer
and Headless Characteristics of the Nokia HKL-210 and
MKL-210 Disk Diffusers, September 1980.
7. G. Addison. Slime Growth On Fine Bubble Diffusers. Gore &
Storrie Limited Consulting Engineers, Toronto, Ontario,
Canada, 1984.
8. T. Laukkarinen, Nokia Inc. Letter to G. Addison commenting
on "Slime Growth On Fine Bubble Diffusers. April 4, 1984.
9. Boyle, W.C. and D. T. Redmon. Biological Fouling of Fine
Bubble Diffusers: State-of-Art. ASCE Journal of Environ-
mental Engineering, Vol. 10-9, No. 5, October 1983, pp. 991-
1005.
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APPENDIX A
PLANT SURVEY SUMMARIES
CANTERBURY, ENGLAND
Background
The^Canterbury sewage treatment plant is located northeast
of the City of London. Sewage treatment was first installed in
Canterbury in 1868, when the sewage was filtered through beds of
charcoal. This method was found to be too costly and ineffec-
tive, and three subsequent attempts to develop practical waste-
water treatment on the site proved to be similarly futile. In
1916, a successful treatment plant, designed around biological
trickling filters, was installed. This facility was operated
until growth of the town and its industries caused severe
overloading, at which time the first phase of the current
activated sludge treatment facility was constructed onithe site
and commissioned in 1969 at a cost of 540,000 Pounds (1968 cost)
and included complete secondary activated sludge treatment using
mechanically aerated (Kessener Brush) activated sludge aeration
basins.
In 1973 the plant was expanded to its present configuration,
shown on Figure A-l, with the construction of additional secon-
dary treatment facilities and improved sludge management. The
current system is comprised of two parallel plants, one mechan-
ically aerated and capable of treating 8,000 m3/day, and a fine
bubble aerated system which can treat 24,000 m3/day. Total rated
plant capacity is 24,000 m3/day. Current served population
equivalent is about 50,000 and flows are averaging 20,000 m3/day.
Plant Description
The activated sludge treatment plant at Canterbury includes
comminution and screening, degritting, primary sedimentation,
activated sludge treatment in parallel mechanical and fine bubble
aerated systems, final sedimentation, sludge conditioning and
pressing. Table A-l provides design parameters for the major
plant elements.
The four diffused aeration channels, each measuring 8 m wide
by 33 m long are each equipped with 500 Nokia HKL 215 fine bubble
disk aerators. The original system was installed in 1977 as a
replacement for the original ceramic dome aeration system. The
diffusers are arranged in two grids per tank. Each grid has 9
-32-
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Commi'nutors *•
Main Work*
Pumpinq Station
Mactralor Chambtr
0< 1/74 or-
C
frimaru
Sludy*. Pumping
•- . *^1 .
Study* fr*ft\
Budding I
5(uofy«
Pumplncj Station
Figure A-l. Canterbury Site Plan.
-33-
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TABLE A-l. CANTERBURY DESIGN DATA
Stormwater Holding Tank
1 Circular Tank
Diameter:
Depth:
Primary Sedimentation Tanks
2 Circular Tanks
Diameter:
Depth:
SLR:
DT:
Mechanical Aeration Plant
4 Rectangular Tanks, Kessener Brush Aerated
Width:
Length:
Depth:
DT:
Diffused Aeration Plant
4 Rectangular Tanks, Nokia Disk Aerated
Width:
Length:
Depth:
DT:
Disks/Tank:
Final Sedimentation Tanks
4 Circular Tanks (Mechanical Plant)
Diameter:
Depth:
SLR:
DT:
2 Circular Tanks (Diffused Air Plant)
Diameter:
Depth:
SLR:
DT:
29 m;
8.25!m
28 .6 m
3 m
0.74 m/hr
6 hr ;@ DWF*
11 m
12 m
4 m
8 hr @ DWF*
8 m
33 m
4 m ,
8 hr @ DWF*
500 i
20 m
3.5 m:
0.68 m/hr
8 hr @ DWF*
25 m
3.5 m;
16.3 m/d
8 hr @ DWF*
* Dry weather flow.
rows of diffusers and the overall floor arrangement is uniform-
there is no tapering. The current average influent flow of
-34-
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of air flow at 8.5 psi and 1700 rpm. The blowers are
modulated «-infl a pHOX dissolved oxygeS
C?ntrois air fl°* to maintain 2.0*2™! DO at
by
.
an
d- eos-as f
axd. There 1S also a 6200 scfm capacity stand-by air filter
es
^tubing. The formic acid is purchased in
system is located in a small enclosure ad
aeration tanks.
Performance
the oS^SJE.?;*:.^:.'*;"* ln an ear"er ^-^ •*«*.
by USmSn 6 ment/ySJem at Cant^bury is moderatly lode
* and*chiev" relatively high rates of removal
SroSSSJ System1whi^ Pl«Wd the diffuSer/on the air s?de
Problems have also been experienced with loss of power on the
site with resulting blower shut-down. As a result of both
problems the diffuser elements became badly plugged anfan
attempt to clean them using a 5 percent hydrochloric acid
solution was not successful. At the time of the site
-35-
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the formic acid system about twice per year. Since the new
diffusers have been installed, the aeration tanks have been
drained and the diffusers have been spray washed and inspected
and found relatively clean. Plant staff report no discernible
pressure buildup and the aeration pattern was quite uniform and
fine bubble in appearance at the time of the plant visit except
for slight coarse bubbling in the vicinity of the feed zones.
Plant maintenance personnel reported that the original
diffusion system required some maintenance. The original pipe
hold-down straps, which secure the air piping to the floor
stands, began to fail shortly after installation and had to be
completely replaced between 1979 and 1981. Nokia reports that
the original strap material, PVC, was replaced with polypropy-
lene. Also, a number of the disk retainer rings broke and were
replaced. When the disks were replaced in 1984, it was necessary
to replace the rubber disk gaskets as well, at considerable
expense, since the original rings had expanded. Nokia reports
that the original gaskets were made from a rubber strip by
vulcanizing the ends together to form a circle. This approach
was not satisfactory and was replaced by continous molding of
butyl rubber. Since the last disk change, during which any other
obvious repairs were also made, the system has functioned well
and there have been no significant hardware problems.
The formic acid system is operated quite frequently. Each
diffusion grid is dosed for 10 minutes weekly. The dosage rate
of the formic acid is 1.0 gram per diffuser over 10 minutes
doscige time.
The plant receives tannery and slaughterhouse wastes in
addition to domestic sewage. Consequently, waste strength is
relatively high, with BOD5 (ATU)* averaging about 350 mg/1 raw and
about 150 mg/1 to the aeration basin. Effluent BOD averages 10
mg/1 or less. In the diffused aeration system, MLSS is main-
tained at about 3500 mg/1, resulting in an F/M of 0.13. Influent
ammonia levels are quite high as well, but the plant produces a
nitrified effluent, removing about 35 mg/1 per day of ammonia in
the aeration process and discharging 2 mg/1 or less at; the
outfall. The diffused air system consumes on average 110,000
m3/day of airflow at an average power draw of 100 kW. Using the
methodology outlined in Section 4, apparent efficiency of the
system is estimated at 1.8 kg/kWh (wire). This is somewhat lower
than the performance levels of the most efficient plants surveyed
in earlier studies (1,2). Air flow per diffuser averages 38
1/min (80.5 scfm).
DEGERO (LAAJASALO), FINLAND
Background
The Degero treatment plant, part of the City of Helsinki,
* Nitrification-inhibited BODs test.
-36-
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Finland waste management system, was commissioned in 1966 to
serve a design population of 20,000 generating a flow of 8,000
m3/day. The plant treats primarly domestic wastes with a minor
(3-4 percent) contribution from local industries in this bedroom
suburb. The industries are primarily involved in some type of
metal finishing or processing.
The plant is currently handling flows from a population of
about 11,000, at an average per capita flow rate of 250 I/day,
dry weather flow. As part of a centralization of Helsinki's
wastewater treatment operations, this plant will be shut down
within about 3 years.
Plant Description
Treatment at Degero includes screening, degritting, primary
sedimentation, aeration, and secondary sedimentation. Primary
and waste activated sludge is digested and dewatered on drying
beds. Table A-2 provides process sizing based on design DWF.
Figure A-2 is a site plan of the treatment plant.
TABLE A-2. DEGERO DESIGN DATA
Primary Sedimentation Tanks
2 Circular Tanks
Diameter:
Depth:
SLR:
DT:
Diffused Aeration Plant
23 m
1.65 m
1.0 m/hr
2.4 hr @ DWF*
Three Dual Pass Rectangular Tanks, Nokia Tube Aerated
Width: 3.7 m/pass
Length: 10.7 m
Depth: 2.6 m
DT: 1.0 hr @ DWF*
' Tubes/Tank: 38
Final Sedimentation Tanks
6 Rectangular Tanks
Width:
Length:
Depth:
SLR:
DT:
5 m
10.7 m
5.1 m (max)
1.7 m/hr
1.6 hr @ DWF*
* Dry weather flow.
-37-
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1. Sludge Handling System
2. Screening and Degritting
Primary Settling
Aeration Basins
Secondary Setting Tanks
Splitter Box
Sludge Digestion
Sludge Drying
9. Splitter Box
10. Flow Metering
11. Overflow
12. Chlorination
Figure A-2. Degero Site Plan,
-38-
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a
The six aeration tanks are arranged into three two-pass
process units, each pass equipped with 38 Nokia MKP medium-bubble
tube diffusers. The Nokia diffusers were installed in 1977 as a
replacement for the original Chicago Pump tube diffuser system
The diff users are set at a depth of 2.6 meters, or 1.1 meters
above the tank floor. The aeration basins are step fed through
series of slots along the tank wall. The process is relatively
high-rate; it is not designed for nitrification. However, most
of the influent phosphorous is removed by co-precipitation in the
aeration process by chemical addition. The chemical used is
ferrous sulfate (FeSO4 • 7H2O), a waste product from the manufac-
ture, of titanium dioxide in Finland. The chemical is added to
the grit removal system at a dosage of about 200 mg/1.
Process air is supplied by two positive displacement,
varialble speed blowers which supply 30-88 Nm3/min of air. The
blowers were manufactured in West Germany and are driven by
Siemens 74 kW motors. Air filtration is provided by metal mesh
prefilters followed by a plate filter unit. There are 4 paper
cartridge plates, providing a total surface area of 2m2. Each
plate is 50 x 100 cm and is 1.5 cm thick. The filter system is
rated at an air flow of 30-86 m3/min.
Performance
A review of 1984 data for this plant indicates that flow
averaged about one-half of DWF, or about 4,000 m3/day, resulting
in an aeration detention time of about 2 hours. Operators
maintained MLSS levels of 2500-3000 mg/1, yielding an f/m loading
of 0.4-0.45. Power consumption analyses conducted by Helsinki
treatment system staff indicate that the aeration basin consumed
2.0 -3.75 kWh/kg BOD? removed, or 0.27-0.5 kg BOD?/kWh (actual
operating conditions, no DO residuals given). Stated in terms of
BODs , at a ratio of BOD? = 1.14 x BODs (per plant staff),
aeration basin energy consumption averaged 0.23-0.44 kg/kWh. A
comparison of this plant with other plants in the Helsinki system
indicates that it is relatively inefficient, using 2-3 times as
much power per unit of BOD? removed as other plants. Air flow
per diffuser averages 0.21-0.39 m3/min. No attempt is made to
control aeration DO and plant operators report that it tends to
be high.
The diffusers are cleaned relatively infrequently by
comparison with some of the other plants visited in Finland.
Every two years, the diffusers are soaked in a 10 percent
solution of strong hydrochloric acid. Afterwards, they are
washed with a combination of water and'air. The plant staff have
developed a cleaning jig onto which the diffuser is fitted for
cleaning. Using the jig, the air/water backwash is injected into
the inside of the diffuser and forced through to the outside.
Plant staff have conducted some investigations into the use of
alternative chemicals and methods for cleaning both the Nokia
tubes as well as ceramic tubes. They found that ultrasonic
-39-
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cleaning in conjunction with an oxalic acid cleaning solution was
effective on the ceramic tubes but not on the plastic tubes.
KAARINA, FINLAND
Background
The Kaarina plant is an older facility which was modernized
in 1975. A local brewery is the main industrial contributor .to
the plant, accounting for 60 percent of the organic load and 40
percent of the flow. Annual mean flow is 10,000 m3/day. There
is extensive infiltration as dry weather flow averages 5,000
m3/day. The sewer system in the City of Kaarina is currently
being rehabilitated to reduce infiltration/inflow.
Plant Description
The treatment process at Karrina includes influent screen-
ing, aerated grit removal, secondary aeration and settling, and
polishing in an existing oxidation pond. There is no primary
settling in the system. Table A-3 summarizes some design data
for the plant. The six aeration tanks are two-pass; three of the
TABLE A-3. KAARINA DESIGN DATA
Diffused Aeration Plant
6 Dual Pass Rectangular Tanks, Nokia Tube Aerated
Width: 3.15 m/pass
Length: 24 m
Depth: 4m
DT: 8.7 hr @ mean
flow*
Tubes/Tank: 68
Final Sedimentation Tanks
6 Rectangular Tanks
Width: 6.5m
Length: 37 m
Depth: 3.5 m
DT: 12.1 hr 8 mean
flow
SLR: • 0.3 m/hr @
mean flow*
* Assumes all units in service. In practice, as few as two
lines may be in service at one time.
tanks were part of the plant moderization in 1975. The plant was
originally equipped with Nokia HKP fine bubble tubes; these were
-40-
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changed to MKP medium bubble tubes in 1979 owing to rapid tube
Tn^relLf IF ferr?"S ^lfate addition *or phosphorous PremovaJ.
There are six aeration drops per pass. In the first pass each
is equipped with 7 tubes; in the second, the first drop Sas 6
Performance
mnn Typically' the aeration system is operated at an MLSS of
1000 mg/1 or less to suppress nitrification. A test was run to
llnlTJr thVn?rgy efficiency of the system in early 1985. Four
lines (four dual-pass aeration tanks + four final clairifers)
were operated during the test. Minimum air flow to the system
with four lines operating is 70 m3/min, or 0.26 m'/min/tube.
Power consumption was estimated at 1.35 kWh per kg of BOD7
removed in a limited study by plant personnel earlier this year
ne a"J?matically «d ranges from 2-3 mg/1 according
ng
Efficiency drops to 1 . 0 kWh per kg when only two
r*™ h are °perated' due to higher air flow rates
through the diff users.
Relatively simple cleaning procedures appear to suffice for
diffuser maintenance at Kaarina. Every six months, working with
w^hdJ HUSerVn ?nl dual-pass tan* at a time, the diffuse?s are
washed down, brushed with strong hydrochloric acid, left for
several hours, then washed down again. Every three years the
d^USer!!-are ?'emoy'rd f°r a more th°rough cleaning which includes
acid soaking, brushing and washing of interior surfaces Plant
operators report that these procedures appear to renew the
wM ih^Vr1"1^17- ThS N°kia tubes "placed sock diffusers
difi'iculty6 qU1Ckly and could only be cleaned with great
KYLASAARI (HELSINKI) , FINLAND
Background
The Kylasaari treatment plant is the largest of eight
treatment plants serving the greater Helsinki area. Long range
plans call for shutting down most of the other plants in the
system and piping all Helsinki area wastes to Kylasaari The
principal rationale for this is that treatment can be most
efficiently and effectively carried out on a single site Also
a major outfall tunnel to convey sewage effluents through the '
?Ut t0-the °pen sea wil1 be Constructed to pick
^*^7l+SafriJaS °f finally constructed in 1932 as a secondary
treatment plant serving a design population of 20,000. At that
E^?h^ti-PrSVided SGFeenin9- degritting, primary sedimentation in
Emscher tanks, aeration, secondary sedimentation, digestion and
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sludge drying on beds. In 1969, the plant was expanded to serve
a population of 300,000 and the decision was made to begin
centralizing sewage treatment operations on the site. In 1984,
work began on expanding and upgrading the aeration system and on
improving energy recovery from digester gas.
Plant Description
The current treatment process as Kylasaari includes screen-
ing, degritting, preaeration, primry sedimentation, aeration,'
secondary sedimenation, sludge digestion, centrifugation and land
disposal, Table A-4 provides design data for the plant. Figure
A-3 is a site plan of the plant. There are 12 dual-pass step
feed aeration tanks, each equipped with 55 Inka aerators. These
are currently being changed to Nokia disk diffusers. Air is
provided by three Suomen Puhallintehdas positive displacement air
blowers of capacity 100,000 ms/hour and driven by 350 kW electric
motors. Ferrous sulphate is fed into the plant influent channel
in a dosage of about 80 mg/1 to precipitate phosphorous. The
Inka aerators will be replaced with 805 Nokia HKL 215 disks per
tank as the plant is converted to fine bubble aeration.
Performance
As the retrofitted system was not yet in and operating at
the time of the plant visit, no performance data was available at
this plant. However, discussions were held with Helsinki staff
who have been directly involved in the development and; testing of
the Nokia disk diffusers and gas cleaning system. They offered
the following comments:
1. There may be a direct correlation between air flow and
inorganic fouling. Operation of the diffusers at a higher
air flow rate appears to retard buildup of inorganic
material.
2. It is important to operate the gas cleaning system as soon
as pressure begins to increase. Waiting until pressure is
much higher and the diffusers are coarse bubbling may result
in incomplete cleaning.
3. The aeration grids should not be too large and each grid
should be cleaned separately. Overly large grids can cause
a problem in that the diffusers at the periphery may not
have enough gas flow to clean them, allowing them:to plug up
over a period of time.
4. The diffuser material does not appear to degrade signifi-
cantly when exposed to the common cleaning agents. The
cleaning procedures of soaking in strong mineral acid and
air/water backwashing, such as used at Vaasa (described
later in this section) appear to remove oxide buildup
resulting from the use of ferrous sulphate for phosphorous
precipitation.
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5. Mineral addition for phosphorous precipitation should be
made at the beginning of the plant, before the primary
sedimentation and preaeration steps, to minimize buildup of
foulants on the diffusers. This can result in greatly
reduced diffuser maintenance.
TABLE A-4. KYLASAARI DESIGN DATA
Primary Sedimentation Tanks
24 Rectangular Tanks
Width: 6 m
Length: 40.5m
Depth: 2>4 m
SLR: 1.5 m/hr
DT: 1.7 hr @ DWF*
Diffused Aeration Plant
12 Dual Pass Rectangular Tanks, Inka Tube Aerated
Width: 6 in/pass
Length: 42.3 m
Depth: 4>0 m
DT: 3.0 hr @ DWF*
Final Sedimentation Tanks
24 Rectangular Tanks
Width: 6 m
Length: 55.5 m
Depth: 3.4 m
SLR: 1.1 m/hr
DT: 2.9 hr @ DWF*
* Dry weather flow.
SUOME:NOJA (ESPOO) , FINLAND
Background
The Suomenoja sewage treatment plant serves the towns of
Espoo and Kauniainen, plus flows from the western part of the
town of Vantaa. Primary treatment was initiated on the site in
1969, followed by chemically assisted primary treatment in 1974
and secondary treatment in 1980. The current facility is
o™1™6'1 t0 treat a flow °f 108,000 mVday from a population of
280,000. Flows in 1984 ranged from a high of 135,360 m?/day in
April to a low of 52,300 m«/day in August, averaging 71,930
ma/day on an annual basis. The sewage is largely domestic in
origin; only 7 percent is classified as industrial. The treated
effluent is discharged to the sea via a 7.5 km long rock tunnel.
-43-
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Plant Description
The treatment process at Suomenoja includes screening,
pumping, aerated grit removal, primary sedimentation, secondary >
aeration and sedimentation, phosphorous removal and provision for
effluent chlorination. Sludge is digested and dewatered before
being land disposed. The plant's anaerobic digestion process
/
i.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Influent Sewers
Preliminary Treatment & Control Bldg,
Ferrous Sulfate Dosing
Influent Pumping Station
Preaeration Basins
Primary Sedimentation
Aeration
Final Sedimentation
Maintenance & Blower Room
Effluent Channel
—rji
<>-- -
Sludge Thickening
Sludge Digesters
Digested Sludge Storage
Sludge Dewatering Plant
Dewatered Sludge Storage1
Gas Holder ]•
Gas.Beating Plant
Excess Gas Burner
Figure A-3. Kylasaari Site Plan.
-44-
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provxdes sufficient energy for building heat plus surplus gas
which is burned in a nearby municipal power plant. Figure A-4 is
a flow chart for the plant. Table A-5 summarizes the design of
the major secondary plant elements.
Figure A-4. Suomenoja Site Plan.
-45-
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TABLE A-5. SUOMENOJA DESIGN DATA
Primary Sedimentation Tanks
12 Rectangular Tanks
width: 5 m (6 tanks)
6 m (6 tanks)
Length: 60 m
• Depth: 2.2/2.4 m
SLR: 1.2 m/hr
DT: 2.0 hr @ DWF*
Diffused Aeration Plant
6 Dual-Pass Rectangular Tanks
Width: 6.8 in/pass
Length: 40 m
Depth: 4.6 p, (1_3)
3.5 M (4-6)
_. , , DT: 3.9 hr @ DWF*
Disks/Tank: 896
Secondary Sedimentation Tanks
12 Rectangular Tanks
Width: 6.8 m
Length: 60 m
Depth: 3.5 m
SLR: . 0.9 m/hr
DT: 3.9 hr @ DWF*
=====:===================================r===========:==:==:=:=:==:==__.__
* Dry weather flow.
The aeration tanks are equipped with Nokia HKL 215 disk
diffusers that were installed new in 1980. Each tank was
originally equipped with 960 diffusers, arranged in a uniform
configuration with two grids per pass, each having 8 lines of
diffusers. To reduce excessive dissolved oxygen in the last part
of the last pass, 64 diffusers were removed from the final grid
in each of the second-pass tanks. The in-situ cleaning system
was installed in 1982.
A total of six, positive displacement blowers are installed
at the plant. Four are two speed, 8200/4900 m3/hr and two are
single speed 8200 m3/hr units. Process DO is monitored with
DanFoss on-line DO monitors, but control is manual. There are
two separate EuropAir air filter units equipped with 18 sets of
replaceable air filter cartridges.
A combination of sodium aluminate and ferrous sulfate is
added for phosphorous precipitation, with dosages ranging from
80-100 mg/1 for the ferrous sulphate and about 19 mg/1 for sodium
-46-
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alumanate. The combination of chemicals is used as a result of
testing which showed that the two chmicals were more effective
than ferrous sulfate alone.
Performance
The diffuser system was installed and started up in 1980 and
operated for two years without any cleaning. In 1982, a major
air line failure resulted in apparent fouling of the aeration
system. The diffusers in one aeration tank were completely
renewed by dismantling and cleaning the piping and replacing the
diffuser elements with spares. These were then cleaned by
soaking in strong hydrochloric acid for four days and then
pressure washed with a high pressure hose. These diffusers were
then used for rehabilitating the next tank, and so on until all
six tanks had been worked over. At this time, the in-situ gas
cleaning system was also installed. Since that time, the
cleaning system has been operated about three times per year,
depending on measurements of DO versus air flow to the tanks.
At the time of the plant visit, the system appeared to be
functioning well. Plant staff indicated that their own evalua-
tions appear to show that the diffusers are effectively cleaned
by the in-situ cleaning system. They also provided detailed
performance and power consumption data for 1984, along with the
results of DO profiling before the system was altered to reduce
the number of diffusers in the second pass. Before the change
DO would average less than 2 mg/1 in the first pass, and rise to
over 4 mg/1 at the outlet. After the change, the profile was
somewhat flatter, but effluent DO still tends to exceed average
DO in the first pass by up to 2 mg/1.
In 1984, the plant treated an average flow of 72,000 m3/day
having a BOD7of 160 mg/1. The treatment process removed about 90
percent of the influent BOD and 8 mg/1 of ammonia. F/m loading
was relatively low, ranging from 0.15-0.2/day (BOD7 basis, this
equates to 0.13-0.17 on a BODs basis). Power consumption for
secondary aeration only ranged from a low of 116,880 kWh in April
to a peak of 206,100 kWh in September, averaging 146,115 kWh per
month on an annual basis. With 35 percent removal of BOD? in the
primary process, average system efficiency for 1984 can be
estimated as follows:
O2 Demand = (R) (Q) (BODsin - BODoout) (10-3 )
(kg/day) + {10~3 x Q)(4.3)(NP - Ne )
Where: R = 0.75 + 0.05/(f/m)
For Suomenoja:
R = 0.75 + 0.05/0.15
= 1.08
-47-
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O2 Demand
(kg/day)
(1.08 x 10~ 3 ) (72 , 000) (90)
+ (10- 3 ) (72 , 000) (4. 3) (8)
9475
1
of DO
0 5 and 1 2
05 and 1.2
rfrmnce
On an annual basis, there are 30.4 days per month, thus average
?hTLMnTS 10n dailY ±S 146'13-5/30.4 or 4806 kWh/day. Eencl ,
94?5/2s ot or 1 a*?rage JnergY Sf f iciency o* this system in 1984 Is
°J ~ygen •"«*"«* per kWh. in the absence
? " fSPOrt that aeration DO ranges between
would appear to be a fairly efficient
Air flo« to the diffusion system avlraged
- o« o e fusion system avra
yie g " average air flow rat* per diffuser of
0 028
TAMPERE, FINLAND
Background
•4-u Treatment began on the site of the Tampere plant in 1961
with the installation of the original "old" plan? in ?970 the
system was upgraded and rated at a capacity of 8,000 m'/day A
annual flow is 13,000
Plant Description
Treatment at Tampere includes screening, aerated grit
removal, primary sedimentation, secondary activated sludge and
sedimentation, and provision for chlorination. Sludge il
thickened and anaerobically digested before land disposal. The
S?:?i5 ^V^ US6d t0 °perate the m^ aeration blower. As
"old"" oLn? Inll ^ ', ***** ^ tW° UnltS ±n each *>rocess of the
old plant and 4 units in each process of the "new" plant The
newer plant has slightly larger sedimentation units and slightly
smaller aeration tanks as compared to the old plant. ; Y
hiS PJ°V^ded ?sin3 Nokia MKP medium bubble tube
The old plant is equipped with 104 tubes on 6 drops
in each pass, for a total of 208 tubes per tank. The Nokia tubes
were installed in late 1971. The new plant has 140 tubes on
seven drops in each pass, for a total of 280 tubes for each
plants. 1S n° tapering of Aerators in either the new or old
is supplied by an Aerzener blower, rated at 58 2
-— pressure. The blower is direct-coupled to an 8
cylinder |as engine. The system is backed up by two motor driven
,... , , lowers wnich are normally not operated.
iltered in two stage FinnFilter OY units. The fine
s of the disposable paper cartridge type. These are
on three year intervals. The current filters are of
pore size than the originals. The change was made based
chano
changed
coarser
-48-
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TABLE A-6. TAMPERE DESIGN DATA
Primary Sedimentation Tanks
Old System:
2 Rectangular Tanks
Width:
Length:
Depth:
SLR:
DT:
New System:
4 Rectangular Tanks
Width:
Length:
Depth:
SLR:
DT:
Diffused Aeration Plant
Old System:
2 Dual-Pass Rectangular Tanks
Width:
Length:
Depth:
DT:
Tubes/Tank:
New System:
4 Dual-Pass Rectangular Tanks
Width:
Length:
Depth:
DT:
Tubes/Tank:
Secondary Sedimentation Tanks
Old System:
2 Rectangular Tanks
Width:
Length:
Depth:
SLR:
DT:
New System:
4 Rectangular Tanks
Width:
Length:
Depth:
SLR:
DT:
6 m
24.5 m
2.35 m
1.13 m/hr
2.1 hr @ DWF*
4.5m
25.8 m
4 m
1.1 m/hr
3.7 hr @ DWF*
2.8 m/pass
32.5 m
4 m
4.3 hr @ DWF*
208
2.25 m/pass
28.5 m
4 m
4.1 hr @ DWF*
280
6 m
32.5 m
2.5 m
0.8 m/hr
2.9 hr @ DWF*
6 m
36.5 m
4.1 m
0.6 m/hr
7.2 hr @ DWF*
* Dry Weather Flow.
-49-
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on the usage of medium bubble diffusers which it is believed
require less filtration.
Performance
Tampere has extensive experience in the operation and
maintenance of the tube diffusers. The original tubes were
cleaned annually and replaced after ten years of service when
they no longer could be cleaned. Cleaning is determined by
visual observation of the aeration pattern on the surface
Cleaning is accomplished by removing the tubes and soaking them
for 12 hours in a hot (60-80°C) cleaning solution of potassium
hydroxide solution made up from diluting 6.4 percent KOH in the
ratio of 1:10 plus a strongly basic commercial cleaning agent.
They are then steam cleaned internally and externally using a
high pressure steam cleaner. As a last resort, the surface layer
of the diffuser is cut away using a lathe. This is only done
once; when the diffusers cannot be cleaned further by chemical
?S X°^' ^JJ are replaced. Experience at the plant indicates
that the diffusers will last about 10 years in this application
The principal foulant is oxidized ferrous sulfate, which is added
into the aeration process for co-precipitation of phosphorous.
27 m3/ ^ the system averages 93,600 m'/day, divided into
27 m'/min into the old system and 38 m« /min into the new system.
Air flow per diffuser averages 0.27 m^/min. Dissolved oxygen is
continuously monitored by DO probes located at the end of the
first pass of each aeration system. These are coupled to an
automated control system which was out of order at the time of
the plant visit. DO is maintained at a level of 1.5-2.0 ma/1
manually or by the plant's automated DO control system.
The performance efficiency of the system could not be
estimated because the direct-driven blower provides virtually all
of the plant's air requirement for at least 8-10 months per
year. In 1983, the plant treated an average flow of 12,930
ms/day of sewage, removing over 90 percent of the 288 mg/1
average influent BOD7 . Plant operators stated that the use of
snn nnnS^r 2&S driven blower saved the plant the purchase of
800,000 kWh of power per year.
TURKU,. FINLAND
Background
•,0
-------
Industrial effluents from a brewery, several dairies and small
food processors provide about 30 percent of the treated flow and
phosphorous is precipitated by adding about 70 mg/1 of ferrous
sulfate. In 1984, the new stage treated an average daily flow of
65,540 m3/day, ranging from an hourly mean of 3280 m3/hr to an
hourly maximum of 8000 m3/hr.
Plant Description
The 1979 plant extension, which is equipped with Nokia HKL
210 fine bubble disk diffusers, has 5 two-pass aeration tanks
each equipped with 1050 diffusers, two grids of 525 per tank on
one main air drop pipe which splits below the water line. Each
grid has eight rows of diffusers. Diffuser submergence is 5.6 m
and total aeration volume is 14,000 m3. There are five Aerzener
positive displacement blowers, three of capacity 116 m3/min and
two of capacity 51 m3/min at a rated output pressure of 70
kiloPascals. One of the smaller blowers can be run at one half
speed. Air filtration is provided using replaceable two-stage
filters. The coarse filter is changed annually, the fine filter
is changed every two years. Table A-7 summarizes design data for
the new secondary plant.
TABLE A-7. TURKU DESIGN DATA
Primary Sedimentation Tanks
4 Circular Tanks
Diameter:
Depth:
SLR:
DT:
Nokia Aerated Diffused Aeration Plant
38 m
4 m
0.8 m/hr
3.4 hr @ DWF*
5 Rectangular Two-Pass Tanks, Nokia Disk Aerated
Width: 7.5 m/pass
Length: 65 m
Depth: 5.9 m
„. , , DT: 4.1 hr @ DWF*
Disks/Tank: 1050
Final Sedimentation Tanks
5 Rectangular Tanks
Width:
Length:
Depth:
SLR:
DT:
7 m/pass
50 m
3.75 m (avg)
1.0 m/hr
3.7 ;hr @ DWF*
* Dry weather flow.
-51-
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Performance
1Q™ Thf aeration system was placed in service in November of
1979 and by April of 1982 it was observed that the back pressure
in the blower lines had increased from the original 0.56 bar to
0 62 bar This caused a safety valve on one of the two operating
blowers to open. It was noted that as many as 8 power failures
may have occurred during the 2.5 year service period of the
diffusers. Nokia recommended that in-situ cleaning using Formic
SoJ?^ Vn^^V In May 1982' the air drop into one tink was
modified by installing an acid injection nipple and nozzle
!?r;X«;SiV?Bi/^eCteS ±nt° the 1±ne USing a paint spray "pump
at a rate of 3 1/min. In total, 13 cans of 35 kg each of 85
percent formic acid (technical grade) was used, equivalent to
0.43 kg of acid per diff user.
Problems with the pump at the beginning resulted in acid
transfer at a slow pace. It was observed that the aeration in
the center of the two grids became noticeably improved; however,
the cleaning effect was mainly restricted to a narrow area in the
middle of the tank close to the drop pipe. At this point, 70 kg
of acid had been used. The pump was repaired and the remaining
11 containers of acid were pumped in at a much more rapid rate
It was then observed that the cleaning effect appeared to spread
to the remainder of the grid. The pressure in the air main
decreased from 0.62 to 0.605-0.610 bar. Based on the results of
this cleaning, it was decided to clean the diff users in the other
tanks as well.
On May 18, the next two tanks, having a total of 2100
Si^r^MnRnV^;3^ US±ng 12 Cans (35 kg each) of formic acid
per tank (1050 diffusers, 0 . 42 kg/dif fuser) . Addition of acid
was spread over 2 hours per tank. After these two tanks were
cleaned, line pressure dropped to 0.585 bar. On May 19 the
remaining 2 tanks were treated in the same manner and line
original level when the system
Energy consumption was also monitored during the cleaning
period. Daily power consumption was 7450 kWh/day before cleaning
and this dropped to 6550 kWh/day after all of the tanks were
cleaned, a 12 percent reduction. The additional energy cost of
the clogged diffusers was estimated at FIM 200 ($40) per day
The cost of the formic acid treatment was also tabulated, as"
shown below:
Acid, 85 percent formic, 2135 kg FIM 8 850
Labor, 30 hr @ FIM 50/hr FIM I'soo
Pump rental FIM ' 660
Air main modification
TOTAL FIM Ilf770
(US $2,354)
-52-
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Thus, payout on the cleaning was under 60 days. The cost per
diffuser was FIM 2.24 (US $0.45).
During and after the cleaning, the plant staff monitored
treatment process parameters and performance efficiency closely
They concluded that the acid treatment had no effect on the pH or
on biological treatment efficiency. It was concluded that the
acid was largely neutralized in removing the inorganic foulant,
?JofiPaiiy ir°n °X*de' and the remainder biodegraded or neutral-
ized by the alkalinity of the wastewater.
iin> ^ aerati°n efficiency and fouling has been definitely
linked to the problem of repeated power failures at this facili-
ry«U J™3 W£ltten !!ummary of experience with diffuser fouling and
cleaning, the plant manager observed that during an extended
power failure the headless will increase 0.01-0.02 bars, and that
the aeration system will require acid cleaning after 3-4 black-
outs of extended duration. During the summer of 1982,: several
long-lasting blackouts occurred due to failure of plant electri-
DjLs2riP?Jnn'fioTKe P°Wer fa>-lures lead 'to a major increase in
pre&sure to 0.62 bar, requiring acid cleaning. Because the
clogging was uneven, the total amount of acid (1505 kg) was
diJ™b*Jed af?ng ^ aeration tanks in accordance with observed
«!? , £ fouling. Tanks 1 and 2 were each dosed with 315 kg of
Sa^rf ?£ waVnit*ally do^ed with 280 kg of acid and further
treated the next day with an additional 105 kg of acid. Tanks 4
and 5 were treated with 245 kg of acid. After the treatment,
which occurred on two successive days, line pressure dropped to
discerned a^ain' n° impact on biological treatment could be
A?, a?afysis of aeration efficiency was provided for a full
o?a~J T I } ^ 5y Plant Staff " Xt was Performed for both the
older, Inka aerated system and the Nokia aerated 1979 extension
The results tabulated below indicate that the Nokia system was
about 25 percent more efficient.
Inka Aerated Nokia Aerated
Annual Air Flow (m") 13,738,910 23,985,910
BOD7 removed 1,128,960 1,949,045
kg BOD7/ni»-day 0.42 0.45
Energy Consumed, kWh 1,879,060 2,415,000
kWh/kg BOD7 1.66 1 24
(kWh/kg BOD3) (1.43) {i;o7)
Using the method of Section 4, these results can be restated to
reflect the energy efficiency of the system in terms of total
-53-
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1982' avera^ f/m was 0.19 on a BOD7
, which translates to 0.16 on a BODS basis. Hence:
R = 0.75 + 0.05/(f/m)
= 0.75 + 0.05/0.16
R = 1.06
02 (kg/yr) = 1.06 x 1 ,128,960/1.16 + 4.3 x 788,400 x 0.5 x 0.6*
— A , Uflo ,O/U
kg 02/kWh = 2,048,670/2,415,000
= 0.85
* NOTE: It was stated that the plant
achieves about 50 percent nitrifi-
cation. This computation corrects
the total nitrogen load figure for
this removal and for the fact that
the Nokia equipped plant treats
about 60 percent of the flow.
It would appear that the energy efficiency of this system is
h?i?i 1Y l0?' althou^h the computation must be regaled as
atgtne tiSrS"1^6 a*d SU*J?Ct t0 err°r- However, 2bs2rv«Son.
iL ?! t*me°f the Slte visit would seem to support a relatively
low level of performance at that time. Apart from the aDDareJt
problems with the aeration system, there was excessive cufr^nf
* v°ne of *h* °Perating blowers. The aeration pattern in
"?" WaS ?ig?lY irre^lar and one tank had a major air"
h -4PParent.PlUgging °f the diff users along the perimeter of
the diffuser grids was observed. Most of the air flow was
?hat°tne -,diffUSerS Cl°?eSt t0 the dr°P P^e- " is p
that the cleaning operations have been more successful in
cleaning the diffusers nearest to the drop pipes? InteJestinalv
blower back pressure was only slightly elevated. PoSsibly '
effectiveness of the aeration system is reduced by the laroe
number of diffusers on a single air drop. 9
VAASA, FINLAND
Background
^Vaasa sewage treatment plant is currently serving a
fv-™ -T —'°P° myday- There is substantial industrial*^ low*
from a large local brewery, accounting for about 14 percent of
s^v^f^110-10^^ ab°Ut 2° Perc^t of the organic loaS. The
J«2? % lncludes older Portions of Vaasa which are served by
combined sewers. Hence, wet weather flows are quite hiah
exceeding 2000.»-/hr at which point excess flowSarJ bypassed
-54-
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Plant Description
plant). The older plant uses aerated grit chambers
system which is not used. There are five
lime
============== ____ ™__A-8. VAASA DESIGN DATA
Diffused Aeration Plant
5 Dual-Pass Rectangular Tanks (2 old, 3 new)
Width: /i oc /
Length: ?195 m/*>ass
Depth: f3 »
DT- 3.4 m
Tubes/Tank:" 3 hr @ DWF*
Sld" 384
New- 504
Secondary Sedimentation Tanks
Old System:
6 Rectangular Tanks
Width:
Length:
Depth:
SLR:
DT:
New System:
6 Rectangular Tanks
Width:
Length:
Depth:
SLR:
DT:
5 m
41 m
2.7 m
0.75 m/hr
3.6 hr @ DWF*
Dry weather flow.
5 m
41 m
3.5m
0.75 m/hr
4.7 hr @ DWF*
-55-
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positive displacement blowers, four of which are used for process
aeration. Two of these are rated at 100 m3/min, the third is
rated at 80 m3/min, and the forth rated at 60 m3/min.' All are
driven by 110 kW motors and the variation in output is achieved
D
D
A
A - Administration Building
B - Screening/Grit Cyclones
D - Aeration Basins
E - Final Clarifiers
F - Post Chlorination
G - Aerated Grit;Chambers
H - Service Tunnel
K - Sludge Pumping
J - Thickeners .
N - Pump Station:
Figure A-5,
Vaasa Site Plan.
-56-
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by varying the sizes of the drive shieves. There is only one
Suo-^iT; ?/in;C;:ie* M°del LJ^-2-16-l-6. «anufac?Srld £y
Sucxnen Puhallin Tehdas OY. It is a single stage moving belt unit
using a labyrinth filter belt path. Figure A-5 is a layout of
e A~8 Suimnarizes the dimensional data provided
Performance
Si ?lan* repor5?d that it treated an average of 7820 kg of
36o /l /S *he *lve ^ration Basins in 1984. MLSS averged
3600 mg/1 F/M loading was 0.3 (BOD7 basis) and no appreciable
nitrification occurred. A theoretical oxygen requirement of 6500
0 sf L°o /JygSnnWaS C°!?pujed bv plant ^aff, corresponding to
0.8J kg 02/kg BOD7, or 0.96 on a BODS basis. Using the methodol-
22 ^J^dij Section 4 of this report, the same ratio is
computed as 0.94 using the BODS basis, showing good agreement
with the computations made by plant staff. All four of ?hT
aeration blowers were operated in total about 90 percent of the
time, corresponding to an power draw of approximately 1.39
million kilo-Watt hours per year, or 159 kilo-Watts per hour (100
m3/min - 70 kW for the Vaasa blowers). Aeration efficiency of
the system is estimated at 271 kg/159 kW, or 1.7 kg oxygen
supplied per kWh (DO averages 2-3 mg/1). This does not Include
the oxygen consumed in the oxidation of ferrous sulfate. On a
stoichiometric basis, 1/2 mole of oxygen would be required for
™?S* £ ferr1ous sulphate added. Hence, 6.93 mg/1 of oxygen
would be consumed when 120 mg/1 of FeSO4-7H2O is added, requiring
an additional 152.5 kg of oxygen per day at design flow. *
Plant operators at Vaasa were highly experienced in the
maintenance of the tube diff users. The original fine bubbll
S22J! ?hr; fhan«;d in /981 after ten years use to medium bubble
tubes that have been found less likely to foul as a result of the
t?mirLSUlphat\additi0n- The new tubes *™ craned about two
™ P«£ year/ based on monitoring of - backpressure at, the blower
It ?he «S prefsureexceeds.O-45 kg/cm^ . the tubes are cleaned.
kS/™? p? °? ^e^plan^ visxt' P^ssure was averaging about 0.3
kg/cm* . Plant staff noted that the tubes foul more quickly at
lower air flows and the fouling is largely caused by oxidized
fnr*??%i PhaJ6- ,A±r fl°W avera^s 230 m3/min, corresponding to
an air flow rate of 230/2280 or 0 . 1 m* /min per tube.
K *i ThS fcf eajment Plant at Vaasa had developed what appeared to
be the most effective and efficient means of cleaning ?he tSbes?
After the tubes are removed and rough cleaned to remove surface
* * <-are • S°a!!e5 f°r °ne Week in a Stron9 (29 percent)
no <- •
an air Sa?PH rXU?-hydr°Xide- They are rem<>ved and cleaned in
a?«a 7 I backwashing machine, shown in the photographs of
«2««S • The.°Perator was able to clean one tube every 20
seconds using this machine and he was well protected from
hazardous caustic spray and slop by a movable shield. The
machine is pneumatically operated. The machine was invented and
-57-
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Figure A-6. Diffuser Cleaning Machine At Vaasa.
-58- • ;
-------
dS[ei°Ped>,by °ne °f the Plant's senior maintenance technicians
and was the only one of its kind observed during the site" studies
pLn^rarTu^na tnT^? tO ^ inventor' severaf other ^nniln
? ndifpers^r s^sg ss^'oSS^ coS11"
aieeaned dif JSS^bKTSI' sa^^bScSres^re w°hendr^L^lled
after cleaning that they exhibited when new. installed
HENRIKSDAL (STOCKHOLM), SWEDEN
Background
.T?LH^k;?ai1.'r;?J'0eni S,13"?. is the Central treatment
are housed below ground in caverns hollowed out froS^JiS rock
Plant Description
Henriksdal is equipped with a complete secondary 'treatment-
process which begins with coarse screening, dlgr?t?ing p?eal?a
S^r" primary sedimentation. Ferrous sulfate is doseSinlo
the primary system at the rate of 120 mg/1 to precipitatl
X
an of whch
The lit is onvi \areKe
-------
diffusers respectively. Dissolved oxygen in each aeration zone
is monitored by DO sensors located at the inlet and outlet of the
wh?Jh i-?«tPUVf f16 °f thS Pr°be~S is averaged by a controller
whKh^then modulates a compressor. The purpose of this experi-
m*ntMls.to determine the effectiveness and energy efficiency of
the Nokia diffusers and the anoxic process. The experiment was
designed after consultation with the British Water Research
Centre. The WRC recently completed a similar experiment that was
successful at a plant in Ryemeads, England.
TABLE A-9. HENRIKSDAL DESIGN DATA
Primary Sedimentation Tanks
13 Rectangular Tanks
Twidth: 10 m
Length: 60 m*
Depth: 3.6 m
nrn" 2*° m/hr
D^: -1.8 hr @ DWF+
* Four tanks are 70 meters in length
Diffused Aeration Plant
10 Dual Pass Rectangular Tanks, Nokia Tube Aerated
TWidth: 5 m/pass
Length: 130 m
Depth: 5.2 m
m v, /m 4.5 hr @ DWF+
Tubes/Tank: 534
1 Dual Pass Rectangular Tank, Nokia Disk Aerated
TWidl:h: 5 m/pass
Length: 130 m
DePth: ............ 5.2 m
_. .DT: " 4.5 hr @ DWF+
Disks: 1790
Final Sedimentation Tanks
11 Rectangular Tanks
Width: 10 m
Length: 80 m
Depth: 5<2 m
SJjR: 1.75 m/hr
______________ ___ _„ ________ ____ 3-0 hr @ DWF+
+ Dry weather flow.
Air supply is provided by three Aerzener positive displace
ment blowers with a capacity of 500 m^/min, one blower of 250
ms/min, and one blower of 125 m^/min. In 1980, a turbo compres
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Figure A-7. Henriksdal Site Plan.
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sor with a capacity of 600 m"/min was added to supply air to the
test tank, independently of the other 10 aeration tanks Air
filtration is provided by two-stage coarse/fine air filters.
Performance
In 1983, the Henriksdal plant treated 306,500 m3/day of
sewage averaging 153 mg/1 raw and 90 mg/1 BOD7 in strength after
primary sedimentation to a final strength of 8 mg/1 BOD7 Flow
is increasing slowly, about 7000 m'/day/year. Suspended'solids
averaged 264 mg/1 in 1983. MLSS averages about 1100 mg/1 in the
ten tube-aerated basins and 2500 mg/1 in the disk aerated basin
F/m loading on a BOD7 basis averages 0.32 in the ten tube aerated
basins. Although not designed for nitrification, the plant
achieves about 40 percent ammonia removal. The process modifica-
tion now being studied in aeration tank 11 would be used to
convert the plant to full nitrification and partial denitrifica-
tion.
Henriksdal scientific staff recently estimated the energy
efficiency of the aeration process based on a methodology which
is very similar to the one used in this report. Oxygen demand
was computed thusly:
02 Demand = {0.75 x 10- a ) (Q) (BOD5 in - BOD3out)
(kg/day) + (0.048 x 10-3)(v)(MLSS)
+ (10-3 x Q) (4.3) (NP - Ne)
+ (10-3 x Q) (2.83) [(NP - Ne ) - Ne*J
Based on this computation, the results shown in Table A-10 were
reported.
Henriksdal operators do not chemically clean the tube
diffusers using the methods used at most of the other plants
studied in this project. Rather, they mechanically clean the
diffusers by periodically cutting off 1-2 mm of the diffuser
using a lathe. This is done once during the lifecycle1 of the
diffuser, after about 4-5 years. When the diffuser fouls again
it is replaced. This procedure was developed as a result of the
plant's experiences with the'xirst set of tube diffusers that was
installed in 1974. It was determined that these original
diffusers were defective, having been incorrectly sintered in the
manufacturing process, leading to premature failure. They were
rehabilitated by machining once, when chemical treatment methods
proved to be unsuccessful,then replaced in 1979 as a matter of
routine procedure. In 1984, the tubes were all replaced again
It xs planned to replace the tubes every 5 years if required to
maintain efficiency. Studies at the plant indicate that the cost
of removing, chemically cleaning and replacing the diffusers will
be 30-40 Swedish Kroner ($3.75-$5) versus a replacement cost of
about 60 Kroner ($8). This finding is the basis for the mainte-
nance procedures that have been adopted.
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==~==—_^RATION_EFFICIENCY AT HENRIKSDAL*
Year ° ~~
1980
1981
8,650,500
9,709,000
11,826,000
10,585,000
11,205,500
SS — SB =
-------__
10,597,210
11,960,580
11,750,380
12,386,900
= — — _____ — — _ _ — __
1.09
0 99
0.90
, 0.90
.
be adversely affecting the system was also raised. it was
might not
HIMMERFJARDEN (STOCKHOLM), SWEDEN
Background :
The Himmerfjarden plant serves five suburban cities in i-h*.
SOTl^'ilWl?1 ^ f" f*Y*n ^ "f" f\f*\rV. f\ 1 * -e -*•** L-HtJ
in 1974 and the system's current user^were coniecte^oveJ^the1"6
?^^i° yej«* Jhe.p?;ant is designed to produce a high grade
tertiary effluent with phosphorous removed. it is currently
treating a flow of 115,000 m«/day on average, ranging between a
minimum of 85,000 and a maximum of 260,000 m3/day
i
Plant Description
Treatment at Himmerfjarden includes degritting, primary
f?^™?^1011' feconda^y aeration, secondary sedimentation,
flocculation, alum addition for post-precipitation, final
?« 23n5a^X2n' f!ludge thickening and digestion. Ferrous sulfate
™ *ddeLi?!°>!?:f ?.r^_Chamber.s f?r Pre-precipitation of
air ±S Provided by 4 Helsingoer Vaerft (Danish)
innn s3' The blowers c^ ^e varied between 5500 and
13,000 m3/hour. These blowers were recently installed to replace
the original positive displacement blowers. They feature a very
flat output curve between 45 and 100 percent of load, making ?nlm
well suited for automated DO control. Delbag replaceable
cartridge air filters are used for air filtration! ladh aeration
basin is equipped with two dissolved oxygen analyzers that
operate through controllers to provide air flow regulation
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Seven of the plant's aeration basins are still equipped with
the original Brandol tubes. The tubes are arranged in a" wide
band configuration with 80 tubes in the first 1/2 pass, 45 in the
next 1/2 pass, 32 in the first 1/2 of the second pass,, and 31 in
?SL J f P*SS- The ei9hth tank was reconfigured in July of
1984 to use Nokia HKL disk diffusers, and an anoxic pretreatmen?
zone (used only for denitrification process trials) patterned
after the design used at Ryemeads, England. The anoxic zone is
^nutes Detention time. Following the anoxic
disks are installed in a tapered configuration of
, which is a 33/27/19/20 percent distribution
There are respectively 8 lines, 6 lines, 5 lines and 5 lines of
diffusers in each grid. The original configuration of the
TABLE A-ll. HIMMERFJARDEN DESIGN DATA
Primary Sedimentation Tanks
8 Rectangular Tanks
Width:
Length:
Depth:
'
Diffused Aeration Plant
6 m
50 m
3 m ,
1.8 m/hr
1.7 ;hr @ DWF*
8 Dual-Pass Rectangular Tanks, One Nokia Disk Aerated
T™^: 6 m/Pass
Length: 48 ^
Depth: 5 m
DT: 2.5 :hr @ DWF*
Secondary Sedimentation Tanks
16 Rectangular Tanks
Width:
Length:
6 m
50 m
3.6 in
Final Sedimentation Tanks
16 Rectangular Tanks
Width:
====================:
* Dry weather flow.
2.0 hr @ DWF*
6 m
62. 5; m
4 m
1'4 m/hr
2.8 hr @ DWF*
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ta?ered- Initially the taper was 368/216/-
Performance
.
soon after the diffusers were installed, a pump failure
S-Jt-SL-SS^f ^S^S^^erh £? ?
system several times, with limited success as Verified b
r s? is.rsass ssi ,r;, S
problem was caused by the combination of full nitrification
the
u.
understandxng that such data is now available? but It Jal not
been made available as of March, 1988.
ROPING, SWEDEN
Background
J.y,uuu m /day. in 1984, flow averaged 13,560 m3 /dav The.
process xs secondary treatment withphosphorous removal
Plant Description
Treatment at Koping includes screening, arit removal sr>
preaeratxon, primary sedimentation, second2^cJiv«?2 JlSS
final sedimentation, flocculation for solids and phosphorous
t P°US
. Tabe
Figurl :8 Is an £J? ff°V1^ a summary of design parameters.
*iguie A 8 is an artist's rendering of the site plan.
+-K ..?he+.dual-Pass aeration tanks are step-fed at five points in
with^l? ^0 ^S ""f 2?S ^ arran ^d in *oSV?aSe"d "
v, J"v ' 5°' and 63 diffusers respectively. The final
has a hxgher number of aerators so that the DO of the mSd
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liquor will be increased somewhat just before entering the final
sedimentation tanks. The aeration system is equipped with formic
acid cleaning, with separate injectors for each grid.
Plant air is supplied by three Klein L-52 positive displace-
™!£* i?W!Sn/iS! blowers are dual speed (1450/960 rpm) units
rated at 2650/1465 m* /hour output. Air filtration is provided by
EBA~TE disposable cartridge filter rated at
Performance i
Data was provided for the year 1984. Average flow for the
TABLE A-12. ROPING DESIGN DATA
Primary Sedimentation Tanks
4 Rectangular Tanks
Width: 6 m
Length i OR a -m
£»*J * \J ill
Depth: 2.35 m
SL*: 1.52; m/hr
DT: 1.55! hr @ DWF*
Diffused Aeration Plant
2 Dual Pass Rectangular Tanks, Nokia Disk Aerated
Width: 6 m/pass
Length: 20.9m
DePth: 5.2 m
r,- , /m D,T: 2.45'hr @ DWF*
Disks/Tank: 295
Final Sedimentation Tanks
4 Rectangular Tanks
Width: 6m
Length: 21 m
Depth: 3.8 m
SL?;: 1.86 m/hr
DT: 2.0 hr @ DWF*
1
Tertiary Sedimentation Tanks
4 Rectangular Tanks
Width: 6m
Length: 21 m
DePth: 3.8 m
st;R: 1.86 m/hr
===========———I—I . 2-° hr ® DWF*
* Dry weather flow. "=
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A.
Pretreatment
Sludge Incinerator
Secondary Treatment
Administration
Figure A-8. Koping Site Plan.
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bItweenS603and°263/daY' Influent BOD7 averaged 126 mg/1, ranging
' JL S
First Grid:
Second Grid:
Third Grid:
Fourth Grid:
28 liters over 1.8 hours
17 liters over 1.1 hours
12 liters over 0.8 hours
15 liters over 1.0 hours
At the time of the site visit, the aeration pattern was well
b^nrcbf 6V^ f±ne bUbble ln ^-rance. The dSfusers nad
been cleaned the previous week. Plant operators noted that the
aeration pattern becomes much coarser as the time for cleaning
approaches After cleaning, backpressure is reduced by 0?S1 bar
(4 kPa). Air flow per diffuser averages 0.03 m'/min.
. Sufficient data was not available to estimate performance
harm?SmientS ^ 9t ^ tlme °f the Plant visitPindicSSd
that mixed liquor DO was relatively elevated. DO averaged 6-8
mg/1 in the first pass, and 3.5-4.5 mg/1 in the second. Plant
operators indicated that they do not try to "fine tune" DO levels
wjtjhfhsystein- Typically, one blower is operated on full speld
with the second run at half speed for 80-85 percent of the time
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