United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
*
Research and Development
EPA/600/S2-S6/019 Apr. 1986
SEPA Project Summary
Status of Porous Biomass
Support Systems for
Wastewater Treatment: An
Innovative/Alternative
Technology Assessment
William C. Boyle and Alfred T. Wallace
A study was conducted to assess the
emerging wastewater treatment tech-
nology of porous biomass support sys-
tems (PBSS). These systems use large
numbers of small, open-cell or reti-
culated polyurethane foam pads to
support high concentrations of biomass
in an aeration basin. The technology is
being marketed by Simon-Hartley Ltd.
in England (CAPTOR) and Linde AG
(Unpor) in West Germany.
Visits were made to laboratories of
the original process developers in the
United Kingdom and in West Germany.
Data were gathered through interviews
with academic and commercial investi-
gators in both countries and through a
review of all available literature and
data, both published and unpublished.
The study concluded that PBSS tech-
nology does not presently qualify as a
fully developed technology, but that it
does offer some attractive potential
benefits and very little risk for some
intended applications. Thorough pilot-
plant and full-scale studies are needed
to answer many remaining questions
about the process and to provide design
data and guidance.
This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati, OH, to announce
key findings of the research project that
Is fully documented In a separate report
of the same title (see Project Report
ordering Information at back).
Introduction
The Clean Water Act of 1977 and the
Municipal Construction Grant Amend-
ments of 1981 include provisions that
encourage the use of innovative and alter-
native (I/A) wastewater treatment tech-
nologies. One emerging technology is
the use of porous biomass support sys-
tems (PBSS) for biological wastewater
treatment. These systems use large
numbers of small, open-cell or reticulated
polyurethane foam pads to provide sur-
face area for high concentrations of
biomass growth in the aeration basin. As
the pads move through the wastewater,
the wastewater also moves through the
pads, bringing nutrients, oxygen, and
paniculate matter into contact with the
biological growth, which may either be
attached to the pad material or entrapped
within the pores.
The basic technology has been devel-
oping along two different lines. The British
developer, Simon-Hartley Ltd.,* has con-
centrated on external pad cleaning
devices to waste excess biomass and
avoid the use of secondary clarification
(the CAPTOR process). The West German
developer, Linde AG, uses no pad cleaning
and has developed their process for
secondary treatment along the lines of
conventional activated sludge using a
combination of suspended and attached
"Mention of trade names or commercial products
does not constitute endorsement or recommendation
for use.
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biomass with final clarifier'and sludge
recirculation for suspended biomass con-
trol (the Linpor process).
To evaluate this emerging technology,
visits were made to the laboratories of
the original process developers in the
United Kingdom and in West Germany,
and the status of research and develop-
ment efforts was discussed with both
academic and commercial investigators
in both countries. Several pilot- and full-
scale development projects were also
visited in the United Kingdom, West
Germany, and the United States. All
available literature, both published and
unpublished, was reviewed. The final
report is the result of these efforts, most
of which took place during the spring and
summer of 1984.
CAPTOR Process Description
CAPTOR is a proprietary process
marketed by Simon-Hartley Ltd. The
CAPTOR system uses 25- x 25- x 12.5-
mm pads of reticulated polyurethane
foam. Pore size is controlled at approxi-
mately 11.8 pores/lineal cm (30 pores/
in.), with a pad porosity of 97%. The
normal design level for pad concentration
is 40,000/m3, a volume concentration of
31 %. This concentration has been deter-
mined to be near the practical limit for
consistent mixing. Screens are used to
prevent the pads from leaving the aeration
basin. Trial and error development has
resulted in the adoption of 4-mesh
screens (5.13 mm square apertures) large
enough to limit the peak hydraulic loading
to less than 78 m3/m2' hr based on gross
submerged screen area.
Pads are withdrawn from the aeration
basin as desired, and most of the ac-
cumulated biomass is removed by a pad
cleaner (Figure 1). As the pads move up
the conveyor, some interstitial water
drains by gravity. Additional water is
removed by a pre-squeeze roller followed
by a tight squeeze between two rollers,
which removes the biomass as a con-
centrated waste stream.
Aeration system design has proved to
be a critical element. The development
work has shown the necessity of pro-
ducing discrete upward and downward
currents that are strong enough to ensure
adequate mixing and keep the pads
suspended and moving through the liquid.
These currents are critical where fine
bubble aeration systems are used and in
aeration basins of high aspect ratios.
Linpor Process Description
The Linpor process is being developed
by Linde AG. The pads used in the Linpor
Figure 1. Diagram of CAPTOR pad cleaner.
process are more heterogeneous in size
and shape than those used in the CAPTOR
process. An average pad is a parallele-
piped with dimensions of about 12 mm x
12 mm x 12 mm. Some pads may be as
small as 10 mm, and others' may have a
dimension up to 17 mm. The pads are of
open cell type foam and have about 15 to
20 pores/lineal cm (38 to 50/in.). The
Linpor process may use a 10% to 40%
concentration of pads (by volume), with
most of the present investigations being
carried out near the 40% level. Screens
are placed across the aeration basin exit
to prevent loss of pads. The Linpor process
uses no external pad cleaning device,
relying instead on the turbulence and
shearing action in the aertion basins to
control the amount of excess biomass.
In the Linpor-C process for carbona-
ceous BOD removal, biomass is grown
both on the pads and in suspension. The
pads retain a large quantity of biomass in
the aeration basin, reducing the solids
loading on the secondary clarifier and
maintaining a higher effective mixed
liquor solids concentration. A portion of
the settled biomass is recirculated to the
aeration basin as in a conventional
activated sludge process.
The Linpor-N process for effluent
polishing and nitrification was the first
1) Conveyor Belt
2) Air Lift Tube
Presqueeze Roller
(4) Roller Box
(5) Squeeze Rollers
(§) Back Deflector
application conceived for the foam pads
Linpor-N is operated with a feed BOD ol
20 to 30 mg/L, dissolved oxygen (DO!
levels of 4 to 5 mg/L, and no final clarifier
or sludge recirculation.
CAPTOR Development Status
The early development with PBSS was
performed at the University of Man-
chester, United Kingdom. As a result ol
this early work, a patent for the CAPTOR
process was applied for and granted in
the United Kingdom and later in the
United States.
At the time of this report, CAPTOR
experience in the United States was
limited to two pilot plants and one small-
scale industrial system. The pilot units al
Marion, Illinois, had a pad concentration
of 40/L for only 2 of the 8 weeks for
which usable data exist. Pad biomass
solids during the entire period ranged
from 45 to 70 mg/pad. Total BOD re-
movals at 40 pads/L were near 50% al
loadings to the CAPTOR system of roughly
0.6 to 0.9 kg BOD/kg pad solids-day
The pilot system at Downingtown, Penn-
sylvania, contained an average of 42
pads/L and operated at a hydraulic
residence time of about 1 hr. Pad solids
averaged 71 mg/pad resulting in an ef-
fective mixed liquor suspended solids
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(MLSS) concentration of only 2990 mg/L.
Comparison of the data from the CAPTOR
section alone with those at Marion
showed a worse performance at Down-
ing town at about the same F/M loading
and strength of feed. The industrial sys-
tem was equipped with a final clarifier
because of the amount of growth antici-
pated from the 1000 to 2500 mg/L COD
in the influent wastewater. During the
period for which most of the analytical
data are available, sludge was being
recycled, and pad mixing conditions within
the reactor were very poor, with the
majority of the pads collected in a large
floating raft at the surface of the aeration
basin. Most of the treatment (except on
occasions that are not well documented)
was being accomplished by the suspended
biomass from the recycled sludge. Though
some valuable lessons can be learned
from the U.S. experience, it would be
grossly unfair to judge the potential of
the CAPTOR process on this basis alone.
The most comprehensive full-scale in-
vestigation of the CAPTOR process was
at Freehold, United Kingdom. This plant
has two two-stage CAPTOR lanes, with
CAPTOR in the first quarter, and activated
sludge in the final three quarters.
CAPTOR was intended to allow upgrading
of the existing plant to provide nitrifica-
tion. The CAPTOR units were predicted
to remove 75% of the incoming BOD of
144 mg/L, allowing the activated sludge
systems to operate at increased solids
retention times while keeping acceptable
solids loadings to the existing final clari-
fiers. The study began in September
1982, and data have been available from
early November 1983 to the time of this
report. Throughout the course of the
study, plastic strips in the incoming pri-
mary effluent have caused problems with
the pad cleaners and effluent screens.
Pad distribution within the basins was
poor, with frequent periods of large rafts
of floating pads. The CAPTOR system did
not receive the design complement of
pads (40/L) until March 1985, when the
aeration and flow patterns were modified.
Before this time, one lane operated with
28 pads/L, and the other operated with
only 16/L.
The BOD removal correlation developed
by Simon-Hartley Ltd. from previous
pilot-scale work was as follows:
Percent BOD Removal =
100exp(-0.67F/M)
This correlation has appeared in several
of their publications, but the effluent BOD
values represent BOD remaining after 1
hr of settling, which is not indicative of
CAPTOR operation without a final clarifier.
Linpor Development Status
The first application of PBSS by Linde
AG was for the purpose of nitrification in
a 1-m3 reactor receiving secondary ef-
fluent from a domestic wastewater treat-
ment process. These studies did not use
final clarification or sludge return, and
they achieved a substantial degree of
nitrification at hydraulic residence times
of less than 2 hr. Other pilot studies to
assess nitrification of secondary effluent
at Poing, West Germany, have shown
that dissolved oxygen (DO) played an
important role, probably because of dif-
fusional limitations. DO values below 5
mg/L were observed to affect nitrification
rates.
Pilot-plant studies have also been con-
ducted with the Linpor-C process at
several treatment facilities in West
Germany. Biomass growth and attrition
within the pads reached equilibrium with
good biomass activity, as measured by
the specific oxygen uptake rate within
the pads. Visual examination of the pads
during the site visits revealed that the
particle biomass was fresh and dark
brown throughout the particle volume,
with no signs of anaerobosis within the
pad structure. Parallel tests in activated
sludge units with and without pads re-
vealed lower sludge volume indices and
improved effluent quality in two different
pilot studies at 30% and 40% pad volumes.
Currently, at least two full-scale studies
using Linpor-C are being conducted in
West Germany. At Freising, Linpor pads
(25% by volume) have been added to one
tank for the primary purpose of reducing
sludge volume index. Other research at
Munich I is being conducted in both pilot
plants and full-scale tanks. Results of
this work were not available at the time
this assessment was written.
Conclusions
Visits to operating facilities and a re-
view of the available data indicated that
PBSS technology is not fully developed.
The manufacturers and suppliers of this
technology would not recommend instal-
lation of a system at present without
thorough pilot-plant investigation to pro-
vide design data and guidance. The pro-
mising applications of this technology
appear to include:
a) Pretreatment systems for high-
strength waste,
b) Upgrading of overloaded activated
sludge plants, especially those that
are habitually plagued by fila-
mentous bulking, and
c) Additions to existing systems to
produce nitrification without the
need for additional clarifiers.
A tremendous number of questions
about PBSS technology remain. Funda-
mental research questions on the char-
acteristics of the PBSS biomass exist.
Evaluation of the effect of pad cleaning
rates on biomass physiology, specific
substrate uptake, sludge yields, sludge
dewaterability, biomass hold-up, and free
suspended solids would yield further in-
sights into CAPTOR performance. Both
CAPTOR and Linpor require extra atten-
tion to the quality and reliability of pre-
liminary and primary treatment processes
to avoid severe operation and mainten-
ance problems with the pad cleaners
(CAPTOR) and retaining screens (both
processes). Furthermore, design require-
ments to ensure proper pad mixing and
distribution need to be better defined.
Linpor-C is almost ready to become
classified as one of the regular members
of the available spectrum of treatment
systems capable of consistently meeting
secondary treatment requirements. The
CAPTOR process, used as the sole bio-
logical process without final clarifiers, is
not ready to become so classified. PBSS
should be treated as an innovative tech-
nology with a degree of risk that varies
with the specific application. PBSS pro-
jects receiving consideration for I/A
funding should be those for which the
risks are minimized through careful con-
sideration of the specific details of the
project. As the technology continues to
evolve and be better understood, it should
be possible to attempt some projects with
higher risk factors, provided that high
potential benefits are possible as well.
The full report was submitted in partial
fulfillment of Contract No. 68-03-3130
by Dynamac Corporation under the spon-
sorship of the U.S. Environmental Protec-
tion Agency.
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William C. Boyle is with the University of Wisconsin, Madison, Wl 55706; and
Alfred T. Wallace is with the University of Idaho, Moscow, ID 83843.
James A. Heidman is the EPA Project Officer (see below).
The complete report, entitled "Status of Porous Biomass Support Systems for
Wastewater Treatment: An Innovative/Alternative Technology Assessment,"
(Order No. PB 86-156 965/AS; Cost: $16.95, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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