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Carbon-nitrogen-phosphorus removal and biofilm growth characteristics in an integrated wastewater treatment system involving a rotating biological contactor.

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ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING
Asia-Pac. J. Chem. Eng. 2009; 4: 735–743
Published online 28 June 2009 in Wiley InterScience
(www.interscience.wiley.com) DOI:10.1002/apj.329
Special Theme Research Article
Carbon-nitrogen-phosphorus removal and biofilm growth
characteristics in an integrated wastewater treatment
system involving a rotating biological contactor
Angelo H. Cabije,* Ramelito C. Agapay, and May V Tampus
Department of Chemical Engineering, University of San Carlos, Talamban, Cebu City, 6000, Philippines
Received 29 October 2008; Revised 10 March 2009; Accepted 11 March 2009
ABSTRACT: A new rotating biological contactor-packed media technology (RBC-PMT) is locally innovated using light
polyethylene Amazon screen material as disc media. A single-stage co-current fed of this type, which is connected
with a series of equalization tanks as an integrated wastewater treatment system (IWWTS), showed good carbonnitrogen-phosphorus (C-N-P) removal and unveiled biofilm growth characteristics noteworthy for treating pollutants in
wastewater.
The equalization tanks approached facultative anaerobic conditions while the RBC-PMT exhibited a completely
aerated system, both with a slightly alkaline pH, whose temperatures are ranging from 21 to 24 ◦ C, and both performed
as biological nutrient removal systems. The combined nutrient removal efficiency at high organic loading rate (HOLR)
and low organic loading rate (LOLR) showed fair chemical oxygen demand (COD) removal at 65.68 and 67.89%,
respectively. Nitrate-nitrogen removal demonstrated good removal at 79.17% at HOLR and 83.43% at LOLR. There
was excellent phosphate-phosphorus removal determined at 91.64 and 94.35% at high and low OLRs, respectively.
This indicates that increasing the organic loading rate decreases the C-N-P removal in the IWWTS.
Biofilm growth was characterized by the selection and survival of microorganisms present under aerobic
environmental conditions in the RBC-PMT system and their respective metabolism in removing C-N-P substrates.
Yeasts, coliform bacteria particularly E. coli, Cyanobacteria, and benthic diatoms were dominant microorganisms
found upon oil-immersion microscopy. Protozoans and algae including Chlorococcum, Chlorella, Diatoma, Tribonema,
Oscillatoria, Euglena, and other motile rotifiers were also dominantly found in the biofilm samples. Biofilm growth is
observed and its average thickness was measured to be 7.71 µm at HOLR and 2.81 µm at LOLR. Thicker biofilm at
HOLR has caused the reduced rate of diffusion of the microorganisms and their metabolic products as manifested by
the low C-N-P removal during HOLR.  2009 Curtin University of Technology and John Wiley & Sons, Ltd.
KEYWORDS: rotating biological contactor-packed media technology (RBC-PMT); biofilm thickness; biological
nutrient removal; organic loading rate; integrated wastewater treatment system
INTRODUCTION
Biological processes are the heart of wastewater treatment. Microorganisms have the natural tendency to
decompose the material in wastewater and are therefore
applied in the degradation and consumption of contaminants in wastewater. Because biological processes are
cost efficient (i.e. readily available inoculum and low
operation costs), they can provide effective and useful
alternatives to chemical/mechanical waste treatment.[1]
A modified rotating biological contactor (RBC)
design innovation employing packed media technology
(PMT) is now gaining reputation in the Philippines;
*Correspondence to: Angelo H. Cabije, Department of Chemical
Engineering, University of San Carlos, Talamban, Cebu City 6000,
Philippines. E-mail: anzach cab@yahoo.com
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
however, there are no sufficient research conducted
in scholarly manner to support its claim for excellent
removal of pollutants in wastewater via the biological means. The acronym PMT is attached to the RBC
name as a distinction to the Philippine patent applied by
J. V. Baring Consultants and Allied Services, manufacturer of RBC-PMT, the wastewater treatment unit that
is primarily investigated in this study.
The RBC is a successfully developed wastewater
microbial treatment system. It has been widely used
for the secondary treatment of domestic and industrial wastewater.[2] RBC performs effectively as a polishing step especially in terms of removing inorganic
materials,[3] treatment of meat processing wastewater,[4]
and of domestic sewage wastewater.[5] An RBC contains number of discs that are arranged along the shaft
axis of the contractor and is driven by an electrical
736
A. H. CABIJE, R. C. AGAPAY AND M. V. TAMPUS
motor. During RBC operation, biofilm forms on the
discs and the rotating motion of the equipment allows
for aeration of the biofilm and then submerges the film
into the wastewater.[6] The formation of the biofilm on
the discs as a by-product of microbial metabolism is
responsible for the biological conversions of the compounds contained in wastewater.
Biofilm composition can be described by measuring
specific constituents as exopolysaccharides and proteins. The physical properties can be estimated by the
thickness, density or mass. The substrates involved in
the biochemical reactions are transported, mainly by diffusion, into and out of the biofilm, where the reactions
take place. In aerobic processes, the oxygen required
for the reactions enters the bulk water mainly at the
water/air interface, where also gaseous products such
as carbon dioxide and methane leave the water. The
biofilm thickness is governed by the growth and decay
of the bacteria and other microorganisms, as well as the
erosion of the biofilm and the adsorption of material in
the wastewater.[7] During sloughing, detached biofilm
may be settled or kept suspended and becomes a new
source of digestible COD in the effluent stream.
The purification process is based on the metabolic
activities of complex microbial communities forming
a biofilm attached to the disk surface. Protozoa and
small metazoa are deeply involved in this process since
they contribute in the reduction of the dissolved organic
matter and the majority of dispersed bacteria contained
in wastewater.[8] The study of these microorganisms
and their interactions with the environment are of great
importance to understand biofilm ecology.[9]
The objectives of the study are: (1) to determine the
efficiency of the bioreactor in terms of percent carbonnitrogen-phosphorus (C-N-P) removal from wastewater at different organic loading rates (OLRs) and
(2) to establish the effect of different OLRs on biofilm
thickness (i.e. biofilm growth).
MATERIALS AND METHODS
The experimental RBC-PMT set-up
A single-stage rotating biological contactor-packed
media technology (RBC-PMT) using plastic Amazon
screen and supported by fiber-reinforced plastic (FRP)
ring was suited for this experiment, whose diameter is 1200 mm, fixed to rotate at 5.0 rpm with a
maximum submergence of 40%. The packing thickness of the plastic media comprising a single-stage
RBC-PMT is 300 mm. It also facilitates easier passage of the wastewater to come in contact with the
screen media. The dimension of a FRP RBC tank is
1400 mm × 500 mm × 803 mm, making a maximum
volume equivalent to 19.84 ft3 . The shafting that is
made of 16-mm-diameter stainless steel material and
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pacific Journal of Chemical Engineering
the ring are held together by arrays of bolts, nuts, and
spacer. Geared motor delivers the needed torque for the
RBC-PMT to rotate at constant speed. The geared motor
is rated at 0.1 kW and driven with a gear reducer.
In this experiment, the synthetic wastewater as influent is stored in the equalization tanks and is co-currently
fed by a peristaltic pump (Cole-Parmer 10-Model 752025, USA) into the RBC-PMT. The flow rate is expressed
in volume per unit time (i.e. millilitres per second) and
is adjusted by tuning the peristaltic pump. Both the disc
rotation and flow rate settings are checked daily. Details
of the RBC-PMT design are shown in Fig. 1 and the
actual photograph of the experimental set-up is shown
in Fig. 2.
Synthetic wastewater
Synthetic wastewater is used in this so that it is not
affected by variable shock loading rates and fluctuating nutrient concentrations that are inherent in natural
wastewater. The formulation of synthetic wastewater
that mimics domestic wastewater for RBC-PMT experiments is adopted from the study of Tampus et al .[10]
Synthetic wastewater used as influent contained the following: CH3 COONa · 3H2 O 6.25 mm (400 mg/l COD);
yeast extract 0.001 g/l; NH4 Cl 1.50 mm; NaNO3 8.00
mm (112 mg/l N); KH2 PO4 0.48 mm; MgSO4 .7H2 O
0.34 mm; and trace elements 10 ml/l.
Microbial seeding and process run
In this study, inoculation is done by pouring about
500 ml (0.1% inoculum with respect to the physical
volume of RBC-PMT) of actual septic tank effluent
and putting four (4) capsules polyseed (InterMed, USA)
containing a mixture of natural microorganisms into the
trough of the RBC-PMT unit, while it is preliminarily
filled with synthetic wastewater. The mixed microorganisms are allowed to grow, then forming biofilm.
The non-sterile integrated RBC-PMT system is run
continuously until theoretical steady-state condition is
reached and is stopped after massive sloughing of the
biofilm, which is an indication that biomass wash-out
has occurred. From previous RBC studies, the duration
of RBC-PMT process run is designed at a maximum
24-h HRT at a corresponding OLR[11] and at least,
32 days to investigate C-N-P removal and biofilm
growth.[12]
RBC operation and performance monitoring
The rotation speed was predetermined from the design
of the experimental RBC-PMT unit. The setting of
Asia-Pac. J. Chem. Eng. 2009; 4: 735–743
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
C-N-P REMOVAL AND BIOFILM GROWTH CHARACTERISTICS
A
B
(a)
C
D
E
I
0.703m
0.830m
H
0.194m
0.803m
0.010m
(b)
0.010m
0.080m
0.225m
0.010m
F
I
G
Figure 1. A pilot scale RBC-PMT. (a) Front view and (b) side view. A: 10-mm stainless steel tertiary
shafting with nut and washer; B: 1.2-m ø fiber reinforced plastic ring; C: 0.036-m ø stainless steel
secondary shafting with nut and washer D: pillow block; E: 0.1-kW drive motor F: 13-mm mesh
amazon; G: fiber reinforced plastic RBC tank; H: 0.013-m ø influent port; I: 0.013-m ø effluent
port.
on RBC-PMT prior to this biofilm growth experiments.
The OLR was computed based on total surface area of
the discs (ATSA = 11.33 m2 ), theoretical COD of the
synthetic wastewater formulation (400 mg/l COD when
analytical grade chemicals are used), 24-h HRT, and
respective flow rates. Table 1 shows the summary of
operational parameters of the RBC-PMT system.
On-site monitoring and laboratory testing
Laboratory testing of samples is based on standard
methods for the analysis of water and wastewater.[13]
These were done at the Chemical Engineering Research
Figure 2. Photograph of integrated wastewater treatment
involving RBC-PMT.
5.0 flow-rate was based on the measured revolution
per minute (rpm) of the discs using a stop watch
with respect to motor and shaft capacity. The HRT
and flow rate settings were based on the residence
time distribution (RTD) tracer experiment conducted
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Table 1. Operational parameters of the RBC-PMT unit.
Parameter
Low OLR
High OLR
Disc rotation
HRT
Flow rate, Q
OLR
Feed flow
5.0 rpm
24 h
1.30 ml/s∗
3.96 g/m2 /day
Co-current
5.0 rpm
24 h
4.20 ml/s∗
12.71 g/m2 /day
Co-current
∗
Values are set within range of flow rate in 24-h HRT.
Asia-Pac. J. Chem. Eng. 2009; 4: 735–743
DOI: 10.1002/apj
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A. H. CABIJE, R. C. AGAPAY AND M. V. TAMPUS
Laboratory and at the Biology Research Laboratory of
the University of San Carlos. Test kits were also used
for daily on-site analysis of monitored parameters. pH
is monitored using pH meter, dissolved oxygen (DO)
with DO meter, and temperature is checked using a
calibrated glass-filled thermometer.
The chemical oxygen demand (COD) spectrometric determination at an absorbance of 600 nm was
made using Hach’s Closed-Reflux method employing
a spectrophotometer (Hach DR 2010, USA) set at an
absorbance of 540 nm. Nitrate-nitrogen was determined
at 400 nm absorbance while phosphate-phosphorus was
determined using the same spectrophotometer model at
890 nm absorbance. A blank (de-ionized water) calibrated at CAL ZERO on the display was used to correct
all spectrophotometric measurements.
The measurement of biofilm thickness is an adoption and modification of the procedures employed by
Venkatamaran and Ramanujam.[14] The film is carefully
pierced through using flat aluminum strips smeared with
red chalk powder. The depth of its penetration into the
film is recorded by wetting, staining, and removal of
chalk powder on which a thin line is marked by the
sharp tool. The wetted marking on the tip of the aluminum strip was viewed and measured in a stereoscope
(S2-PT Olympus Stereoscope, Japan) with grid calibration in micrometer. Biofilm thickness examination is
conducted at the Marine Biology Research Laboratory
of the university.
Biofilm sampling was based on the procedures made
by Cereceda et al .[9] Sampling of biofilm was made
during the attainment of theoretical steady-state condition (i.e. after experimental run period) of the RBCPMT. Biofilm samples are streaked both as fresh and/or
stained using Lugol I solution and were examined using
a compound microscope (InMedTech BM-100FL) and
actual footages are taken for standard morphological
and physiological comparison.
Asia-Pacific Journal of Chemical Engineering
while anoxic nitrification/denitrification processes are
progressing inside the oxygen-depleted tanks.[15]
In contrast, the RBC-PMT is practically aerated by
the disc rotation mechanism of the treatment equipment. The actual DO level in the RBC tub ranges
from 6.0–9.8 mg/l and temperature ranges from 22 to
25 ◦ C. A sudden shift on the condition of the influent from anaerobic to aerobic state was noted. The
freshly prepared synthetic wastewater registered a pH
range of 7.4–7.6, a slightly alkaline condition, in all
experimental runs at the start of operation. As time
increases, pH climbed up to 9.0, which is an alkaline
condition, accounting to microbiological proliferation,
both in wastewater storage and in RBC-PMT tub. Fishy
odor is also common for all experimental runs in RBCPMT trough, starting at second day and intensifies until
the first week operation. The odor is minimized and
then dissipated normally on the third week of operation,
while biofilm growth becomes more evident. It is also
common to all experimental runs that biofilm growth
appears to be generally brownish green to dark green
color, though there were also few clusters of biofilm
that are brown, black, and red in color.
Biofilm growth was not visible on the first 3 days
of operation, however, a fishy odor is present at that
time and suspended biomass was observed aggregating in the wastewater that was contained in the tub.
At this point, there is an occurrence of survival of
anoxic microorganisms because during start-up operation, DO is low and microorganisms are feeding more
on the oxygen contained in nitrate components of the
wastewater. Such biochemical reaction liberates ammonia, which is responsible for the fishy odor. As the
system becomes more aerated, nitrification followed
by denitrification succeeds the reaction, whereby the
ammonium is reduced to nitrate and further to nitrite.
Some nitrogen-fixing microorganisms such as algae also
consume nitrite and convert it into nitrogen. The selection and survival of the microorganisms explain the
appearance and dissipation of fishy odor as observed.
RESULTS AND DISCUSSION
On-site RBC-PMT monitoring and observations
The reduction profile of measured COD
concentrations
In the absence of constant mixing, the condition of
the dispensed wastewater from the equalization tank
as influent of the RBC-PMT unit was approaching
anaerobic condition. Obligate and facultative anaerobic microorganisms (DO approaching 1.0 mg/l) thrived
inside the non-sterile equalization tanks. This has been
clearly manifested by the black discoloration in stored
wastewater and by the development of distinct rottenegg and obnoxious fishy smell. The rotten-egg odor is
distinct for hydrogen sulfide formation caused by anaerobic sulfate-reducing bacteria (SRB), while the obnoxious fishy smell is an indicator of liberated ammonia
For all experimental runs, a reduction in COD was
observed both at the influent and effluent streams of the
RBC-PMT. Hence, the integrated reduction of COD is
attributed both from the equalizing tank and RBC-PMT.
The differences in the values of the originally measured
COD of the freshly prepared synthetic wastewater and
the COD value of the influent account for the reduction
of COD at the equalization tanks. The percent COD
reduction at the RBC-PMT is calculated by dividing
the differences of the averaged values both of the
influent and effluent sides by influent COD data in timeseries. Succeeding COD data at steady-state conditions
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. 2009; 4: 735–743
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
C-N-P REMOVAL AND BIOFILM GROWTH CHARACTERISTICS
were considered in the calculations of aggregate percent
COD removal of the integrated wastewater treatment
system (IWWTS).
At high organic loading rate (HOLR) during steadystate condition, the average percent COD removal at the
equalization tanks is 34.73% while the further percent
removal at the RBC-PMT is 47.42%. The aggregate
percent removal of the IWWTS at HOLR is 65.68%
(i.e. the sum of initial removal at 34.73% by the equalization tanks and the product of the remaining fraction
of the volume that is treated at removal efficiency of
47.42% by the RBC). Figure 3 presents the COD profile
at HOLR.
In the same manner as above, the averaged COD
reduction at low organic loading rate (LOLR) is computed both for equalization tanks and RBC-PMT systems. The equalization tanks registered a reduction
of 31.09% while the RBC-PMT further reduced the
COD of the influent to 53.39%. The aggregate COD
reduction for the IWWTS at LOLR is 67.89%, which
is a little bit higher when compared with the COD
reduction at HOLR. This result has a similar implication to the work of Torkian et al .[16] wherein higher
COD reductions are observed when OLR is low.
Figure 4 shows the average COD reduction profile at
LOLR.
Figure 4. COD profile of the integrated wastewater
treatment system at low organic loading rate.
The nitrate-nitrogen (NO−
3 -N) reduction profile
Both the equalization tanks and the RBC-PMT reduced
nitrate at respective percentage removal. At HOLR,
the equalization tanks reduce nitrate-nitrogen up to
41.70%, while at LOLR, it was able to remove
nitrate-nitrogen at about 46.43%. During LOLR, dispensing of wastewater from the equalization tanks
slows down, thus allowing extended hydraulic and
sludge retention times. This is then complementary
Figure 5.
Nitrate-nitrogen profile of the integrated
wastewater treatment system at high organic loading rate.
to more nutrient removal as wastewater stays longer
in the anaerobic reactor. The RBC-PMT has also
a higher nitrate-nitrogen removal at 69.08% during
LOLR than during HOLR, which only registered a
64.28% reduction. Overall, the IWWTS has a higher
aggregate nitrate-nitrogen reduction at 83.43% during LOLR, than 79.17% aggregate reduction during
HOLR. Figures 5 and 6 show the graphical profiles
of nitrate-nitrogen reduction at high and low OLRs,
respectively.
The phosphate-phosphorus (PO4 −3 -P)
reduction profile
Figure 3. COD profile of the integrated wastewater
treatment system at high organic loading rate.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Compared with COD and nitrate reduction profiles,
the phosphate reduction profile is more intensely
described to be almost consuming the available nutrient.
Asia-Pac. J. Chem. Eng. 2009; 4: 735–743
DOI: 10.1002/apj
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A. H. CABIJE, R. C. AGAPAY AND M. V. TAMPUS
Figure 6.
Nitrate-nitrogen profile of the integrated
wastewater treatment system at low organic loading rate.
Phosphate-phosphorus is needed in cellular metabolism
of organisms and a high phosphate nutrient uptake is
a manifestation in this study. The phosphate reduction
profile for HOLR is shown in Fig. 7.
At HOLR, there is a phosphate removal of 36.39%
at the equalization tanks. At the RBC-PMT, the
removal reached to 86.85%, thus giving a combined removal efficiency of 91.64% for the integrated
wastewater system. In Fig. 8, at LOLR, the equalization tanks registered a 42.44% phosphate removal,
while the RBC-PMT listed 90.19% removal, making
an aggregate removal of 94.35% for the IWWTS.
Such a very high phosphate reduction is comparable to the results of the study conducted by Ouyang
et al .
Collectively, there is better nutrient removal (BNR) at
LOLR than at HOLR for equalization tanks and RBCPMT individually, and for the IWWTS. Final C-N-P
reduction data are summarized in Table 2.
Figure 7. Phosphate profile of the integrated wastewater
treatment system at high organic loading rate.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pacific Journal of Chemical Engineering
Figure 8. Phosphate profile for the integrated wastewater
treatment system at low organic loading rate.
Biofilm thickness at different organic loading
rates
Biofilm thickness was measured after steady-state condition, particularly those that attached to the discs’
media and frame. The measurement were made randomly on the surface area of the disc media and
the frame using displacement-wetting method. It was
observed that there are no significant differences in
thickness between that obtained from the disc’s media
and frame. Hence, biofilm thickness can just be represented by the measurements made on the disc media.
The latter’s measurement were collated and averaged
accordingly.
During HOLR, more biomass flocs were formed
and were easily stuck and compacted in RBC-PMT
discs and into the tub’s bottom. This has facilitated
biofilm support on solid surface and accommodated
biofilm growth. This mainly contributed high biofilm
growth in terms of thickness with mean = 7.71 µm,
while biofilm thickness at LOLR was measured with
mean = 2.81 µm. Biofilms were formed as byproducts of microorganisms including bacteria and protozoan during their metabolism. During mass transfer,
biofilm thickness becomes a diffusion barrier on the
physical and chemical exchanges between substrates
and the microorganisms. So far, this explanation would
give support on substrate inhibition previously established by C-N-P removal when organic loading rate
is increased, relating with biofilm thickness. Rather,
controlled conditions should be instituted to rule out
other factors influencing biofilm growth with respect to
C-N-P removal, considering the complexity in terms
of microbial diversity and their respective selection,
metabolism, and survival in a BNR system such as the
RBC-PMT.
Asia-Pac. J. Chem. Eng. 2009; 4: 735–743
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
C-N-P REMOVAL AND BIOFILM GROWTH CHARACTERISTICS
Table 2. C-N-P removal for combined BNR systems.
Equalizing tanks
Parameter
COD
NO3 −
PO4 +3
RBC-PMT
IWWTS
HOLR (%)
LOLR (%)
HOLR (%)
LOLR (%)
HOLR (%)
LOLR (%)
34.73
41.70
36.39
31.09
46.43
42.44
47.42
64.28
86.85
53.39
69.08
90.19
65.68
79.17
91.64
67.89
83.43
94.35
(a)
(b)
(c)
(d)
(e)
(f)
Figure 9. Protozoan and photosynthetic algae in biofilms. (a) Chlorococcum, Diatoma,
and biomass flocs; (b) biomass flocs with protozoan Vorticelli; (c) Chlorella, Diatoma,
and yeasts; (d) Fragilaria, Pinnularia, Chlorella, Diatoma, Navicula, Euglena, and
Chlamydomonas; (e) filamentous algae with biomass flocs and motile rotifiers; and
(f) filamentous Tribonema and Oscillatoria.
Microorganisms identified in biofilm formation
The observable facts described and discussed previously
had manifested that the RBC-PMT system investigated
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
in this study is truly a complex system with mixed
cultures. Morphology and microscopic characteristics
were employed to describe the types of microorganisms
in the biofilm. Biofilm samples that were inoculated
Asia-Pac. J. Chem. Eng. 2009; 4: 735–743
DOI: 10.1002/apj
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A. H. CABIJE, R. C. AGAPAY AND M. V. TAMPUS
in nutrient agar formed thick mucus indicative of
fecal coliform proliferation. Upon examination under
oil-immersion microscopy, E. coli was found out in
dominance, together with yeasts, and mixed culture of
spiral-shape spirillo and comma-shape vibrio bacteria.
Coliform groups including E. coli were confirmed
when re-inoculated in lactose broth and E. coli broth,
respectively, forming gas displacement in an inverted
Dorham fermentation tube.
Coliforms, yeasts, heterocysts-anabaena (also known
as Cyanobacteria) and benthic diatoms were found
out during microscopic examination when the cultured
inoculums were stained with Lugol I solution. Colors
such as black, red and brown appearing as microbial colonies are caused by spore formation of some
microorganisms described above.
Biofilm samples collected fresh and cultured with the
same wastewater were also examined under the compound microscope. Protozoan, algae, and other motile
microorganisms were observed. These microorganisms
survived and dominated most throughout the entire
duration of experimental runs. Photosynthetic light was
also remarkably noted to be facilitating the proliferation
and dominance of blue-green and green algae in the system. These microorganisms are described according to
morphological structure and appearance as seen in the
microscope at Fig. 9.
The results and findings on microorganisms involved
in biofilm formation can be compared to some extent on
the work of Cereceda et al .[9] But, more photosynthetic
autotropes such as algae had thrived toward the end
of each experimental run. Unlike in the work of
Surampali and Baumann,[17] no evidence of Beggiatoa
was observed in the biofilm.
CONCLUSIONS AND RECOMMENDATION
Setting the co-current fed RBC-PMT at fixed disc
rotation, disc submergence, temperature, DO levels,
while varying the OLR suggested substantial carbon
and better N-P removals. The enhanced C-N-P removal
in the RBC-PMT system with primary removal at the
anaerobic equalization tanks made the IWWTS more
efficient. The RBC-PMT performance apparently may
not be quite at its best when used as primary system
for COD removal, since some effluent samples have not
reached the effluent standards. It was noted consistently
that there was better C-N-P removal when the integrated
wastewater system is set at LOLR. Contrary, the C-NP removal efficiency becomes lower when the organic
loading rate is increased. On the other hand, biofilm
thickness was greater at HOLR, a reverse phenomenon
where the microorganisms are expected with higher
growth when exposed to the feast regime.
At the end of each experimental run, the bacterial
dominance of yeast, coliform, and E. coli and the
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pacific Journal of Chemical Engineering
substantial presence of protozoan and algal autotrophes,
including Chlorella, Chlorococcum, and diatoms were
evident for biological survival, although their survival
effects on substrate removal or inhibition were not fully
investigated in the study.
The characterization, selection, and survival of
microorganisms in the biofilm and possible effects
on suspended growth metabolism can be explored to
enhance the findings and the correlation of C-N-P
removal and biofilm growth in the RBC-PMT system.
Controlling the tendency of anaerobic state environment at the influent tank by aeration can be sought
for investigating changing patterns of C-N-P removal.
Another implication on C-N-P removal and biofilm
growth can be further investigated when counter-current
fed is employed rather than the co-current RBC-PMT
system that is used in this study. Finally, mathematical models can be proposed on appropriate biochemical
kinetics corresponding to the observed conditions leading to the improvement of the RBC-PMT design and
operation.
Acknowledgement
A special thanks to the Royal Dutch Embassy through
the Water REMIND Project is extended for financing
this study.
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characteristics, treatment, involving, growth, biological, system, integrated, removal, wastewater, nitrogen, biofilm, rotating, carbon, contactors, phosphorus
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