United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-88/060 Feb. 1989
x°/EPA Project Summary
Demonstration and
Evaluation of the CAPTOR
Process for SewageTreatment
Paul F. Cooper
The sanitary engineering field has
demonstrated substantial interest in
recent years in the potential benefits
of high blomass wastewater
treatment. For the most part, this
interest has focused on processes
that use various forms of support
media that have the ability to
colonize high concentrations of
aerobic bacterial growth. One such
concept is the CAPTOR process*
developed Jointly by the University of
Manchester Institute of Science and
Technology (UMIST) and Simon-
Hartley, Ltd., in the United Kingdom.
This high biomass approach uses
small reticulated polyurethane pads
as the bacterial growth medium. The
pads are added to standard activated
sludge aeration tankage, and the
system is operated without sludge
recycle, essentially converting a
suspended growth process to a fixed
film process. Excess growth is
removed from the pads by
periodically passing them through
specially designed pressure rollers.
The Water Research Centre (WRC)
and Severn-Trent Water Authority
conducted a full-scale evaluation of
the CAPTOR process for uprating the
activated sludge plant at the
Freehold Sewage Treatment Works
(near Stourbridge in the West
Midlands area of England) to achieve
year-round nitrification. The pro-
cess suffered initially from several
* Mention of trade names or commercial products
does not constitute endorsement or recommen-
dation for use
major design and operational prob-
lems. The report describes how
resolution of these problems was
achieved in pilot-scale studies at
the WRC's Stevenage Laboratory
before implementing the design and
operating changes so determined on
the two full-scale CAPTOR trains at
Freehold.
Whereas the pilot-scale studies
were successful in providing solu-
tions to basic design and operational
flaws, they were not able to develop
techniques for improving CAPTOR
process effluent quality. CAPTOR
performance was adversely affected
throughout the project by high levels
of suspended solids in the process
effluent in both pilot- and field-
scale studies. These high solids
levels prevented the uprated system
at Freehold from achieving nitrifica-
tion.
This Project Summary was devel-
oped by EPA's Risk Reduction Engi-
neering 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 CAPTOR process originated from
research work on pure systems in the
Chemical Engineering Department of
UMIST. Single strands of stainless steel
wire were woven into a knitted formation
and then crushed into a sphere of about
6 mm (0.25 in.) diameter. These particles
of known surface area were used for
-------
modeling liquid-fluidized bed systems.
From this work derived the idea of using
porous support pads for growing
biomass at high concentrations that
could be used in wastewater treatment
systems. The idea was jointly developed
and patented by UMIST and their
industrial partner Simon-Hartley, Ltd.
The present form of the CAPTOR
process uses 25 mm x 25 mm x 12 mm
(1 in. x 1 in. x 0.5 in.) reticulated
polyether foam pads containing pores
nominally of about 0.5 to 0.9 mm (0.02 to
0.035 in.) diameter and 94% free space.
Simon-Hartley, Ltd. conducted pilot-
plant work that indicated it was possible
to achieve
• biomass concentrations of 7,000 to
10,000 mg/L,
• waste sludge concentrations of 4% to
6% dry solids using a special pad
cleaner,
• improved oxygen transfer efficiencies,
and
• high BOD volumetric removal rates
In 1982, WRC and Severn-Trent
Water Authority agreed to jointly evaluate
the CAPTOR process at the Freehold
Sewage Treatment Works near
Stourbridge, West Midlands. The Free-
hold plant did not achieve any
nitrification in the winter and only partial
nitrification in the summer. Freehold's
activated sludge system consisted of five
trains equipped with tapered fine bubble
dome diffusers arranged in a grid (floor
coverage) configuration. The system was
modified as shown in Figure 1 to split the
wastewater flow into two equal volumes.
Half went to two trains that were modified
by adding CAPTOR pads to the first
quarter of two aeration basins, and the
other half went to two trains that
remained unaltered and served as a
control The CAPTOR modified trains
were each equipped with a CAPTOR pad
cleaner (Figure 2), and the CAPTOR
pads were prevented from escaping into
the remainder of the experimental
system aeration basins by screens
placed at the effluent ends of the
CAPTOR zones.
The Simon-Hartley design predicted
that, with a concentration of 40 pads/L,
an annual average removal of 75% of the
BOD5 coming into the plant could be
achieved in the CAPTOR zones, resulting
in a reduced food-to-microorganism
(F/M) loading on the follow-on activated
sludge stage of 0.08 kg BOD5/day/kg
MLSS. With the reduced load, it was
predicted that the modified system would
achieve year-round nitrification with an
effluent ammonia nitrogen concentration
of 5 mg/L or less.
Full-Scale Plant Initial Results
The Freehold modified CAPTOR/
activated sludge system was put in
operation in September 1982 and
immediately encountered a major pro
lem. The CAPTOR pads floated on tl
surface of the tanks and would n
become incorporated into the tank liqu<
A solution was found in November whi
three of the seven longitudinal rows
fine bubble diffusers in the CAPTC
aeration basins were removed. This w,
done to create a spiral roll in the tan
Return Sludge
Secondary
Clarifier
Control Effluent
Primary Effluent
CAPTOR Effluent
Figure 1.
Return Sludge
Schematic of Freehold Sewage Treatment Works showing incorporation of
CAPTOR/nitrification trains
1 Air-Lift Pump
2 Conveyor Belt
3 Presqueeze Roller
4 Squeeze Rollers
5 Drive Gear
6 Sludge Discharge
7 Pad Discharge
Figure 2. Diagram of CAPTOR pad cleaner
-------
because it was known that coarse bubble
diffusers had been used in the previous
work done by Simon-Hartley. Coarse
bubble diffusion leads to areas of rising
and falling liquid with quite large
channels down which the pads can fall.
In the existing fine bubble grid system,
the falling zones were much smaller and
did not allow the pads to fall and then
recirculate. The spiral roll modification
provided the necessary falling zone and
produced complete mixing of the
CAPTOR pads.
Another problem that occurred at this
time was maldistribution of the pads. The
flow of wastewater tended to push the
CAPTOR pads to the outlet of their
zones, resulting in concentrations of the
order of 50 to 60 pads/L at that end and
only 10 to 20 pads/L at the inlet end.
One other disturbing feature was the
rapid deterioration in the CAPTOR pads.
The CAPTOR pads used initially were
black and were wearing at such a rate
that they would not have lasted for more
than 3 yr (making the process non-
economic).
It had also become evident by this
time that with the Freehold wastewater it
would be possible to achieve the
concentration of 200 mg biomass/pad
predicted by Simon-Hartley. However, it
was found that if the biomass was
allowed to grow beyond 180 mg/pad, the
biomass in the center of the pad became
anaerobic. The control of pad biomass
was difficult because the pad cleaners
provided were not reliable and were
situated at the CAPTOR zone inlets while
most of the pads gravitated to the outlet
ends of the zones.
During the period November 1982 to
May 1983, while the- above problems
were being tackled on the full-scale
plant, there were some occasions when
the effluent from the CAPTOR units was
reasonable (BOD5 removals of 40% to
50%), but BOD5 removal never
approached the average of 75%
predicted by Simon-Hartley based on
their pilot-plant results. Poor BODs
removals were being experienced
because the suspended solids concen-
tration in the effluent was always high
(>80 mg/L). Operating conditions and
performance results for these early runs
are summarized in Tables 1 and 2,
respectively.
By July 1983, it was obvious that the
CAPTOR process was not sufficiently
developed for the Freehold project to be
regarded as just an evaluation. A change
was then made from an evaluation to a
development project wherein pilot-scale
Table 1. Initial Freehold Operating Conditions
11/22
6/1 -
9/15-
Period
- 12/31/82
7/7/83
- 1 114183
Wastewater
Flow/ Train (mgd)
1.50
1.38
1.35
First-Stage
CAPTOR HRT (min)
43
48
47
Second-Stage
Activated Sludge
System HRT (min)
127
137
143
Table 2. Initial Freehold Performance Results
Experimental System
Parameter
(mg/L)
11/22- 12/31/82
BOD5
SS
NH4-N
Oxidized-N
6/1/-7/7I83
BODS
SS
NH4-N
Oxidized-N
9/15-11/4/83
eoDs
SS
NH4-N
Oxidized-N
Primary
Effluent
114.
101.
22.1
142.
122.
26.3
136.
144.
26.4
CAPTOR
Zone Effluent
45.
81.
18.2
78.
90.
20.2
0.5
78.
104
20.6
2.0
Final
Effluent
13.
19.
23.5
2.2
10.
14.
24.9
3.2
12.
17
6.1
12.2
Control System
Effluent
19.
25.
24.4
3.3
22.
29.
24.9
2.7
15.
23.
6.0
11 6
studies would be used to find solutions to
the operating problems described above
before attempting further full-scale
evaluation at Freehold. Simon-Hartley
became partners, and funding was
obtained from the Department of Trade
and Industry. Each of the partners
contributed 25% of the overall costs.
Development Project
(Pilot-Scale Studies)
The development project began with
two levels of pilot-scale studies carried
out at the WRC Stevenage Laboratory:
1. Initially, small tanks (265 L = 70 gal)
were utilized to characterize CAPTOR
process performance under very
controlled conditions.
2. This was followed by larger-scale
tests in a hydraulic test rig (HTR),
volume = 30 m3 (7,930 gal), where
various inlet and outlet arrangements,
aeration patterns, and cleaning rates
could be assessed under near full-
scale plant conditions.
The results of the small-tank and HTR
studies were to be used in deciding what
modifications could be implemented on
the full-scale plant at Freehold. The
governing principle was that no major
modification could be made on the full-
scale plant until it had first been
assessed on the HTR.
At this time, it was also decided to
evaluate two variations of the CAPTOR
process. Linde AG of West Germany
was testing a process similar to CAPTOR
called the LINPOR process. LINPOR
differed from CAPTOR in that sponge
pads were placed directly into the mixed
liquor of an activated sludge aeration tank
rather than in a separate stage before the
activated sludge tank. It was decided to
test this process variation using CAPTOR
pads rather than LINPOR pads in the
265-L (70-gal) tank arrangement at
-------
Stevenage. WRC named this process
variation CAST (CAPTOR in activated
sludge treatment). A control activated
sludge pilot unit was operated in parallel
with the CAST unit.
In addition, a single aeration tank,
volume = 236 L (62 gal), filled with 40
CAPTOR pads/L, was fed effluent from
the above activated sludge control unit to
assess the potential of CAPTOR as a
second-stage nitrification process.
Neither pad cleaning nor final clarification
was necessary with this process variation
because of the low sludge yields
characteristic of nitrifier growth
Small-Tank Results
These studies were conducted using
two well-mixed CAPTOR tanks in
series. A range of loading and pad
cleaning rates were used to evaluate
process removal capabilities for
CAPTOR. The intermediate effluent was
used as a measure of process efficiency
of the primary reactor and the final
effluent for the entire system. This
permitted plotting (Figure 3) of % BOD5
removal (total and soluble) vs volumetric
organic loading rate over the range of 1
to 3.5 kg BOD5/day/m3 (62 to 218
lb/day/1,000 ft3). High and low pad
cleaning rates are differentiated in Figure
3 as >16% and <16% of the total pad
inventory/day, respectively.
Total BOD5 removal efficiency was
less than soluble BOD5 removal
efficiency because of the oxygen
demand exerted by the biomass solids
lost in the process effluent. The higher
pad cleaning rates are believed to have
contributed to the improved total and
soluble BODg removals shown in Figure
3, although low bulk liquid DO's may
have adversely affected removals on
some of the low cleaning runs. Low
cleaning rates (<16%/day) were
detrimental to soluble BOD5 removal
efficiency because of a gradual decline
in activity of the biomass remaining in
the pad. Cleaning rates greater than
24%/day, however, resulted in reduced
biomass levels in the pads and a
reduction in performance.
HTR Results
The problem of maldistribution of
CAPTOR pads in the aeration tank (i.e.,
crowding of pads into the effluent end of
the tank when operated in plug flow
fashion as at Freehold) was solved in the
HTR by modifying the flow pattern to
transverse flow (across the width of the
tank rather than down the length). When
implemented later at Freehold, this
100-
so-
so-
70-
5
s 60-
I 50.
3
3 4°-
3
30
20
70
0
/Vofe. 7 lb/day/1,000 ft3 =
0.16 kg/day/m3
—-c Total BOD 5 - High Cleaning
* Total BOD5 - Low Cleaning
+ Soluble BODs - High Cleaning
M Soluble BODs - Low Cleaning
—i—
25
Figure 3.
50 75 100 125 150 175 200
Volumetric Organic Loading Rate (lb/day/1,000 ft3)
Small tank CAPTOR total and soluble BOD;, removals at high and low pad
cleaning rates
225 250
Table 3. HTR Operating Conditions and Process Performance
Period
Parameter
10/8-12/7/84
12/12/84-2/21/85
Volumetric loading (Ib BOD 5I day 11, 000 ft3)'
HRT (hr)
Pads/L
Biomass/pad (mg)
Equivalent MLSS (mg/L)
F/M loading (kg BOD5/day/kgMLSS)
SRT(days)
DO (mg/L)
113
232
40
121
4,840
0.37
323
4.2
213
1.52
40
126
5.040
0.68
1 72
4.7
Total BOD5 (mg/L)
Soluble BOD5 (mg/L)
SS (mg/L)
Total BOD5 removal (%)
Soluble BOD5 removal (%)
SS removal (%)
In
175
86
116
Out
93
24
120
216
85
178
Out
129
33
160
47
72
- 3
40
61
10
"1 lb/day/1,000 rfl = 0.016 kg/day/m3
pattern resulted in a fourfold decrease in
flow velocity.
Several mixing intensities and diffuser
arrangements were tried to decrease
biomass shedding into the process
effluent. It became obvious, however,
that production of effluent biomass solids
was not significantly affected by changes
in mixing intensity or diffuser arrange-
ment. High effluent suspended solids
proved to be far more dependent on pad
cleaning rate, biochemical activity of the
biomass, and biomass growth directly
the liquor.
Using the transverse flow scheme ai
a regular pad cleaning regimen, HI
CAPTOR process performance w;
similar to that experienced in the sm
tanks. Operating parameters and proce
performance are summarized in Table
for two different volumetric loading rates
Respiration studies conducted usir
pads taken from the HTR indicated th
biomass held within the pads respires
-------
Table 4. Operating Conditions and Performance Results - CAST vs Activated Sludge
System
Parameter
Volumetric loading (Ib BOD5/day/l,000 ft3)"
HRT (hr)
Pads/L
Biomass/pad (mg)
Equivalent MLSS in pads (mg/i)
MLSS in suspension (mg/L)
Total MLSS (mg/L)
F/M loading (kg BOD5/day/kg total MLSS)
SRT, based on total MLSS (days)
DO (mg/L)
Total BOD5 (mg/L)
Soluble BOD5 (mg/L)
SS (mg/L)
Total BOD5 removal (%)
Soluble BOD5 removal (%)
SS removal (%)
CAST
148
1.8
34
116
3,930
3,720
7,650
031
3.6
25
In. Out
178 12
101 5
121 15
93
95
88
Activated Sludge
148
1.8
—
—
-
6,030
6,030
039
3.0
3.0
ln_
178
101
121
89
96
81
Out
20
4
23
"1 Ib/day/1,000 ft3 = 0.016 kg/day/m3
up to 40% to 50% less than equivalent
biomass in free suspension. Any
increase in net biomass concentration
achieved in a CAPTOR reactor above
that in a conventional activated sludge
reactor may not produce noticeable
benefits, therefore, due to the lower
specific activity. These observations
suggest that diffusion limitations were
occurring in the CAPTOR pads.
CAST Results
The CAST variation of CAPTOR was
operated in conjunction with a final
clarifier to settle the mixed liquor solids
component of the total biomass inventory
and return it to the aeration tank.
CAPTOR pads and biomass retained
therein were kept in the reactor by
screens. Operating and performance
data are compared in Table 4 for the
CAST unit and the parallel activated
sludge control unit for a 25-day period
(November 5-30, 1984) when the
volumetric loadings and hydraulic
residence times (HRT's) for both units
were identical.
Nitrification Results
Small-tank nitrification experiments
were conducted on the CAPTOR process
from November 1984 to February 1985.
Biomass concentrations per pad ranged
from 99 to 124 mg. With a pad
concentration of 40/L, equivalent MLSS
levels varied from 3,960 to 4,960 mg/L.
Liquor DO concentrations were main-
tained between 6.4 and 8.4 mg/L, and
liquor temperature ranged from 11.5° to
6.5°C.
Secondary effluent from the control
activated sludge pilot unit used in the
CAST experiments was applied to the
nitrification reactor over a range of
loading conditions. These loading con-
ditions and corresponding performance
data are summarized in Table 5.
Essentially complete nitrification was
achieved at TKN and ammonia nitrogen
loadings of approximately 0.25 kg/
day/m3 (15.6 lb/day/1,000 ft3) and 0.20
kg/day/m3 (12.5 lb/day/1,000 ft3),
respectively.
Full-Scale Plant Results after
Modifications
Following the successful testing of the
transverse mixing arrangement in the
HTR at Stevenage, the two Freehold
CAPTOR trains were modified. Modi-
fications commenced in November 1984
and were completed in mid-March
1985.
Table 5. CAPTOR Nitrification Operating Conditions and Performance Data
Parameter
HRT (hr)
TKN loading
(lb/day/1,000 ft3)"
NH4-N loading
(lb/day/1,000 ft3)"
Total BOD5 in (mg/L)
Total BOD5 out (mg/L)
SS in (mg/L)
SS out (mg/L)
TKN in (mgiL)
TKN out (mg/L)
TKN removal ("/<>)
NH4-N in (mg/L)
NH4-N out (mg/L)
NH4-N removal (%)
NO3-N out (mg/L)
1 1/08/84-
11/28/84
1.9
36.2
30.6
21.
21.
22.
14.
46.
28.
39
39.
23.
41.
5.
12/03/84-
12/20/84
46
150
125
23.
19.
27.
22.
46.
10.
78.
36.
6.
83.
29
7/03/85-
1/18/85
4.2
20.6
16.9
52.
44.
53.
52.
57.
38.
33.
44.
29
34.
13
1/21/85-
2/08/85
40
162
13.1
13
17.
21.
26.
43.
6.
86.
35.
3
94
36
2/11/85-
2/15/85
2.7
28.7
20.6
22.
16.
39.
16.
51.
15
71.
37
12
68
32
"7 lb.day/1,000 ft3 - 0.016 kg/day/m3
-------
The modifications involved
• splitting each of the CAPTOR trains,
C1 and C2, into two compartments,
C1A and C1B and C2A and C2B, as
shown in Figure 4;
• feeding influent flow along long weirs
at the side of the trains instead of at
the narrow inlet ends;
• modifying the aeration pipework to
place all three rows of dome diffusers
directly below the outlet screens
(covering about 25% of the width of
the tanks), thereby creating a spiral roll
of pads and liquid counter-current to
the flow of wastewater entering along
the weirs on the sidewalls;
• installing two extra pad cleaners so
that each CAPTOR sub-unit was
provided with a cleaner; and
• installing fine screens at the outlet
from the primary clarifiers to reduce
the quantity of floating plastic material
entering the CAPTOR units that
created problems with the cleaners
The objective of the first three
modifications was to achieve uniform
mixing of the pads in the CAPTOR units
and prevent the situation that had
occurred previously where high con-
centrations of pads (50 to 60 pads/L)
collected at the outlet end and very low
concentrations (10 to 20 pads/L) at the
inlet end. Pads were removed from the
tanks during the modifications. After the
modifications were completed, the
number of pads in each compartment
was equalized at about 35/L
The changes were completely suc-
cessful in obtaining uniform distribution
and complete mixing in of the CAPTOR
pads. A lithium chloride tracer test con-
ducted on the modified tanks indicated
that no dead zone was occurring in the
"eye" of the roll. Formation of floating
pad rafts (which had occurred at the
outlet end of the tank with the original
arrangement) was completely eliminated.
The modifications, however, had no
effect on the high level of suspended
solids present in the liquor.
The performance of the modified
CAPTOR system and the parallel
activated sludge train was monitored
from April 1 to July 23, 1985. The
average volumetric loading rate to
each train was 1.24 kg BODs/day/mS (77
lb/day/1,000 ft3), and the average HRT in
each train (excluding sludge recycle) was
2.55 hr. The results of these tests are
presented in Table 6.
Before Modifications
Screens
oo
XXX
Primary
Effluent
X X X X X X
/Spiral
Roll
xxxxxxxxxxx
C2 f
\
>^j Activated
I Sludge
Walkway \
Primary
Effluent
| X X X
X X X X X X
. \ ' /
C1 f \i Activated
j ^1 Sludge
xxxxxxxxxxxxxj f
Aeration Pipework and Domes Covering 25% of Area
50.2 ft
After Modifications
Screen
xxxxxxxxxxx
C2A
n,'< 11 m 1111
Primary
Effluent
Flow Splitter
Box
X X X X X
-J
Activated
Sludge
iTimmm
Screens
C1A
X X X X X X
Spiral
1C X X X X
'xxxxxxx*xxxx
1111t t t t*t 111
=•••7
Activated
Sludge
Full Length Weir
Aeration Pipework
and Domes Covering
25% of Area
Note: 1 ft = 0.305 m
Figure 4. Modifications to Freehold CAPTOR system flow pattern.
Clearly, the modified CAPTOR unit
was less effective in removing BOD and
suspended solids than the parallel
control activated sludge system at the
same volumetric loading rate, despite the
fact that it carried a higher overall
biomass concentration (4,830 vs 2,623
mg/L). The interstage values in Table 6
show that the CAPTOR portion of the
modified trains had higher effluent
suspended solids levels than the primary
effluent.
Throughout the experiments, problems
were encountered in keeping all the
CAPTOR pad cleaners in operation. The
Mark II pad cleaners developed by
Simon-Hartley were an improvement on
the Mark I units, but still suffered from
blockages and breakdowns.
The CAST variation of the CAPTO
process, which had exhibited somewh
better performance than convention
activated sludge in the small tar
experiments, was also field evaluated
Freehold. The CAPTOR trains wei
further modified so that return sludc
could be introduced to the CAPTO
zones (35 pads/L), providing an activate
sludge component throughout the entii
aeration tanks, not just in the nitrificatic
stage. CAPTOR pads were not added
the nitrification stages as this would ha\
required substantial additional tar
modifications.
The full-scale CAST system we
operated in parallel with the activate
sludge control trains from August 1
October 31, 1986. The averag
-------
volumetric organic loadings and HRT's
(excluding sludge recycle) for each
system were 1.11 kg BOD5/day/m3 (69
lb/day/1,000 ft3) and 3.40 hr, respec-
tively.
Performance data summarized in
Table 7 indicate that, contrary to the
small tank results, the CAST system
effluent was of poorer quality than that of
the conventional activated sludge
system. In addition, difficulties were
experienced in supplying sufficient air to
the CAPTOR units. The maximum air
supply had been sized for the CAPTOR
pads alone, and this was not enough at
times to satisfy the oxygen demand
created by the biomass on the pads and
the biomass of the mixed liquor.
Conclusions
1. When the CAPTOR process was
installed at the Freehold Sewage
Treatment Works, several problems
were immediately evident:
a. There were major problems with
respect to pad mixing, suspension,
and distribution.
b. The Mark I pad cleaners were not
reliable.
c. Performance was adversely af-
fected by the high level of
suspended solids in the CAPTOR
stage effluent.
The problems of pad mixing and
distribution were solved by pilot-
and full-scale development work.
The Mark II pad cleaners produced by
Simon-Hartley were a considerable
improvement over the Mark I cleaners,
but minor problems remained to be
resolved.
2 The performance of the CAPTOR
process was still adversely affected
by the high level of suspended solids
in the CAPTOR stage effluent after
correction of the pad mixing, sus-
pension, and distribution problems.
This prevented the achievement of
nitrification in the follow-on activated
sludge stage.
3 The presence of CAPTOR pads in the
tank liquid did not improve oxygen
transfer efficiency.
4. The durability of the CAPTOR pads
was solved by switching to different
pads. The original black pads (made
by ScotFoam, Inc., USA) deteriorated
rapidly as did the yellow CAPTOR
, pads provided by Recticel (Belgium),
Table 6. Full-Scale Performance Results - Modified CAPTOR Activated Sludge System vs
Conventional Activated Sludge
Experimental System
Parameter
(mg/L)
Total BOD5
Soluble BOD5
SS
NH4-N
Oxidized-N
Primary
Effluent
728.
40.
138.
24.0
—
CAPTOR
Zone Effluent
(C2A & C2B)
122.
28.
754.
24.9
-
Final
Effluent
22.
4.
32.
24.4
0.6
Control
System
Effluent
76.
3.
23.
22.5
2.0
Table 7. Full-Scale Performance Results - CAST vs. Conventional Activated Sludge
Parameter
(mg/L)
Total BOD5
Soluble SO05
SS
NH4-N
Oxidized-N
Primary Effluent
738.
56.
720.
26.7
-
CAST
System Effluent
16.
2
27.
17.2
3.7
Control
System Effluent
W.
2
75.
77.4
7.8
but the orange pads made by
ScotFoam, Inc., were very durable.
5 The peak biomass concentration in
the pads is unpredictable. It does not
appear to be related to the BOD
concentration of the wastewater.
There were indications in the various
studies, however, that the frequency
of pad cleaning (and, hence, the
biomass/pad concentration) was
critical to the performance of the
process. Regular pad cleaning is
essential to prevent anaerobic
conditions from developing m the
pads.
6. It is possible to raise the biomass
concentration in a CAPTOR stage to
6,000 to 8,000 mg/L, but the
respiration rate of the biomass in the
pads is lower than the respiration of
the same biomass if freely suspended
and less than that of normal activated
sludge. These data suggest that the
geometry of the CAPTOR pads results
in diffusion limitations, which severely
restrict the potential for economic
utilization of the CAPTOR process in
wastewater treatment.
7. The CAST variation of the CAPTOR
process performs well, but it is
doubtful if it is economic.
8. CAPTOR may have some potential as
an add-on package for tertiary nitri-
fication. However, this process varia-
tion may not be cost competitive.
9. The use of CAPTOR as a roughing
treatment (followed by interstage
clarification) was estimated to be less
cost effective than using conventional
nitrifying biological filters for uprating
Freehold to complete year-round
nitrification. The CAPTOR option,
however, was projected to be more
cost effective than extending the
activated sludge plant for the same
purpose.
The full report was submitted in
fulfillment of Cooperative Agreement No.
CR810911 by the Water Research Centre
of Stevenage, England, under the partial
sponsorship of the U.S. Environmental
Protection Agency.
-------
Paul F. Cooper is with the Water Research Centre, Stevenage, Hertsfordshire SG1
1TH, United Kingdom.
Richard C. Brenner is the EPA Project Officer (see below).
The complete report, entitled "Demonstration and Evaluation of the CAPTOR
Process for Sewage Treatment," (Order No. PB 89-118 665/AS; Cost: $21.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-88/060
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