Process Biochemistry 40 (2005) 177–182
Wastewater treatment with combined upflow anaerobic fixed-bed and
suspended aerobic reactor equipped with a membrane unit
B. Kocadagistan a , E. Kocadagistan a,∗ , N. Topcu b , N. Demircioǧlu a
a
Faculty of Engineering, Department of Environmental Engineering, University of Ataturk, Erzurum, Turkey
b Faculty of Education, University of Celal Bayar, Manisa, Turkey
Received 14 August 2003; accepted 29 November 2003
Abstract
A combined upflow anaerobic fixed-bed (UAF-B), using pumice as a biofilter material, and a suspended aerobic activated sludge bioreactor
(SAR) equipped with a microfiltration (MF) unit has been designed. This system exhibited high performance on the removal of organic matter.
COD removal efficiencies were in the range of 94–98.7% with organic loading rates (OLR) of 3.67–16.56 kg COD m−3 per day. Phosphorous
and nitrogenous materials were removed from the wastewater as well as COD. High PO4 -P removal efficiencies (96–97%) were achieved
in this study. NO2 -N and NO3 -N concentrations in the effluent of MF were less than 1.0 mg l−1 through most experiments. Suspended solid
concentrations measured in the effluent were below the detectable levels. Biofilm development and microbial communities were investigated
using scanning electron microscopy (SEM).
© 2004 Elsevier Ltd. All rights reserved.
Keywords: Pumice; Membrane; Upflow anaerobic fixed-bed (UAF-B); Biofilter; Phosphate removal
1. Introduction
Fixed-film anaerobic reactors have been widely used for
the treatment of high strength wastewaters. In fixed-film
anaerobic reactors, large amount of biomass remains in the
filter to secure solid retention despite a short hydraulic retention times. These reactors have several advantages over
aerobic and anaerobic reactors such as higher organic loadings, lower hydraulic retention times and smaller reactor
volumes. Lower sludge and suspended solid quantities can
also be achieved in these reactors.
Many different materials have been studied as filter support media including baked clay [1], RPF sheets [2], plastic
tubes with diameter of 2 cm and length of 1.5–2 cm [3], PVC
Raschig rings with a diameter of 2 cm and a specific surface
area of 228 m2 /m3 [4], ceramic Raschig rings, wind ball and
circular pipes [5]. The surface state of filter bed material,
the pore size and the media geometries have been found to
be important factors in treatment efficiencies of anaerobic
∗ Corresponding author. Tel.: +90-442-231-4808;
fax: +90-442-231-4808.
E-mail address: [email protected] (E. Kocadagistan).
0032-9592/$ – see front matter © 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.procbio.2003.11.055
fixed-bed reactors [6–9], while specific surface area and media porosities have been only minor [10–12].
Several studies have been performed by anaerobic filters
for the treatment of high strength industrial wastewaters
from the dairy, fermentation and sugar refining industries [12–14]. All these reports have shown that anaerobic
fixed-film reactors were capable of treating high strength
wastewaters.
Furthermore, for the biological removal of nitrogenous,
phosphorous and carbonaceous matter, combined systems
should be used including anaerobic–aerobic fixed-bed and
anaerobic expanded-bed reactors [15]. For this purpose
many different treatment systems have been used.
A combined anaerobic–aerobic fixed-film bioreactor has
been tested for organic matter removal for 133 days and 92%
removal efficiencies of organic matter removal achieved at
an average of 0.39 kg COD/m−3 per day organic loading
rates [16].
A bioreactor integrated to a membrane module system is
usually referred to as a membrane bioreactor (MBR) [17].
Because MBRs have several advantages over conventional
biological reactors, they have been found as convenient for
water and wastewater treatment in the last decade. The MBR
processes can be especially suitable for reuse and recycling
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of wastewater owing to their high-quality and disinfected
effluents [17].
This article is focused on treatment of a synthetically prepared, high strength wastewater with a combined laboratory
scale system consist of an anaerobic fixed-bed reactor filled
with pumice as a filter bed media and an aerobic suspended
sludge activated sludge bioreactor equipped with a crossflow
microfiltration membrane unit.
2. Materials and method
2.1. Wastewater
The wastewater, employed in this study, was prepared
synthetically at various COD concentrations in the range between 250 and 5000 mg COD l−1 . The initial concentration
of phosphorous and nitrogenous materials were also modified by altering the composition of wastewater (Table 1).
2.2. Reactors
The experimental system is given in Fig. 1. It was composed of an up flow anaerobic fixed-bed reactor, a suspended
aerobic activated sludge reactor (SAR) equipped with an MF
unit. The synthetic wastewater was fed to the bottom of the
Table 1
Composition of synthetic wastewater
Chemical
Amount (mg l−1 )
C6 H12 O6
CO(NH2 )2
MgSO4
CaCl2
KH2 PO4
K2 HPO4
FeCl3
COD
1000
227
100
7.5
52.7
107
0.5
1007
Fig. 1. Schematic view of experimental system.
Table 2
The authentic characteristics of pumice used in this study [18]
Parameters
Values
Chemical compound (%)
SiO2
AlO2
Fe2 O3
Na2 O
K2 O
TiO2
Uniformity coefficient (D60 /D10 )
Effective grain size, D10 (mm)
Porosity (%)
Density (0.5–1.0 mm grain size) (g cm−3 )
72.07
13.50
1.21
1.60
11.27
0.35
1.35
0.59
69.24
0.689
UAF-B reactor. The UAF-B reactor was a circular polyester
column with an inner diameter of 10 cm and a total height of
100 cm. The working volume of this reactor was varied from
1 to 5 l depending on the hydraulic retention time. During
the experiments nitrogen gas was used in the UAF-B reactor to strip oxygen and maintain anaerobic conditions. The
dissolved O2 (DO) concentrations of UAF-B were measured
as 0.1 mg l−1 during the experiments. This reactor was filled
with pumice, which was supplied by Ercis, Turkey, as filter
bed material.
Pumice is used as a biofilm support material in water and
wastewater treatment because of its high porosity and large
surface area. It is a light and porous volcanic rock material
formed during explosive eruptions. Pumice is riddled with
pores of irregular or oval shape, which are usually not connected to each other. Italy, is the biggest pumice producer
in the world (% 44 in total) and Turkey is the second (9%
in total) [18].
The chemical composition of the pumice, obtained from
an Electron Probe Microscopic Analyzer (EPMA), is given
in Table 2. The SEM picture of pumice, before use in the
UAF-B reactor, is shown in Fig. 2.
Effluent, taken from the upper level of the UAF-B reactor, then passed to the SAR and aerated for achieving
Fig. 2. SEM picture of pumice before filling to the reactor (upsizing:
400×).
B. Kocadagistan et al. / Process Biochemistry 40 (2005) 177–182
aerobic digestion and phosphorus uptake with an airflow of
40–60 l h−1 [19].
The SAR has similar construction properties to the
UAF-B and operated according to the principles of suspended growth activated sludge reactors. Because adequate
mixing occurred in the SAR by the recycled water of the
membrane unit (retentate), no mixing was applied to this
reactor. While the UAF-B was operated under mesophilic
conditions (35 ± 1 ◦ C) the SAR temperature was kept in the
range between 18 and 20 ◦ C. Both the reactors were jacketed and temperature controlled by a Lauda thermostatic
water bath.
The SAR contents then taken from the bottom and recycled to the upper side of the reactor after passing through
the crossflow MF unit with the aid of a circulating pump
(1400 d min−1 , 0.75 kW centrifuge pump). The MF unit permeate is the effluent of the entire system. The influent rates
were adjusted as equal to the MF permeate rate (in the range
of 1–5 ml min−1 ) during all experiments, hence the wastewater inlet pump (Masterflex, L/S model peristaltic pump)
was turned on after the permeate reached a stationary flow
rate. Consequently, the working volumes of both UAF-B and
SAR were fixed to required levels. A denitrified wastewater recycle line was placed to the UAF-B from the SAR to
accomplish denitrification in the UAF-B reactor (1–4 times
influent flow).
The OLR of the UAF-B and SAR were in the range from
3.67 to 16.56 and 0.33 to 2.92 kg COD m−3 per day, respectively, in this study. The membrane filtration unit, manufactured in-house, was a flat type module with an effective
surface area of 50 cm2 and the pore diameter of this cellulose acetate membrane sheet, produced by Schleicher &
Schuel was 0.45 ␮m. The pressure difference (P) used as
driving force was required for the formation of crossflow
regime and adjusted with two valves placed at the inlet and
outlet line of the MF unit. The pressure differences were in
the range from 0.2 to 1 kg cm−2 and the permeate fluxes obtained with this membrane module were 12 and 60 l m−2 h−1
for 1 and 5 ml min−1 effluent flow rates, respectively, in this
study.
2.3. Experimental
Samples were taken from the permeate flow of the membrane unit (the effluent of the experimental system) for evaluating the entire system performance and from the effluent
of both reactors for evaluating each reactor performance.
NO3 -N, NO2 -N, PO4 -P, COD and SS analyses were accomplished according to the Standard Methods [20]. pH, temperature and dissolved O2 were measured with a WTW, Multi
340i model multi parameter measurement apparatus. COD
analyses were made by the aid of Dr. Lange, LT100 model
thermo reactor and all of the analyses were carried out with
an UV spectrophotometer (Shimadzu UV-160 A). The pH
was manually controlled close to neutral pH by addition of
1.0 M of HCl or NaOH solutions.
179
2.4. Start-up period
The UAF-B reactor was filled with pumice which was
ground and sieved to 0.5–1 mm granule diameters. The
UAF-B was first fed with a mixture of 1 l dewatered activated sludge taken from the wastewater treatment plant of
Erzincan City of Turkey and synthetic wastewater as inoculum (1/1, volume/volume ratio). Nitrogen gas was injected
with a diffuser system to the bottom of the UAF-B to maintain anaerobic conditions. Biogas production and biofilm
formation were observed for 7 and 45 days, respectively,
after this inoculation. Biofilm formation can be seen from
the SEM picture of pumice (Fig. 3). The UAF-B reactor
OLR values were increased progressively (in the range
from 0.5 to 5 kg COD m−3 per day) to adapt the reactor microorganisms to high organic loading rates. The SAR was
also filled with the above mentioned mixture and aerated
continuously. The start-up period continued for 60 days.
3. Results and discussion
The experimental system exhibited excellent performance
for COD removal from the wastewater. 98.70% of COD removal efficiency was achieved (Fig. 4) under the following
conditions: initial COD of 1150 mg l−1 and organic loading rate for UAF-B reactor of 4.14 kg COD m−3 per day.
Because the influent COD concentrations of the SAR (effluent of the UAF-B) varied according to the treatment performance of UAF-B, the organic loading rates of SAR also
fluctuated.
When UAF-B was filled with pumice to a level of 4 l
(51 cm height of the UAF-B), 0.8 l of wastewater was able to
penetrate to the reactor and the hydraulic retention time was
determined by considering this wastewater volume, existent
in the UAF-B. Consequently, the hydraulic retention times
(HRT) were 2.66 h for UAF-B and 13.33 h for SAR (the
volume of SAR was 4 l), respectively, at 5 ml min−1 flow
rate.
As the OLR, applied to the UAF-B, was increased, there
was a slight decrease in the COD removal of the system
(Fig. 5). However, results showed that the removal rates
were higher than those of classical systems although the
OLR values increased up to the 16.56 kg COD m−3 per day.
These COD removal rates were 98.39, 98.35, 97.88 and
94.00% for 5.58, 7.20, 9.00 and 16.56 kg COD m−3 per day
organic removal rates, respectively. High removal rates at
high OLR values achieved with membrane bioreactors were
also reported by many researchers [21–23].
The PO4 -P concentrations of influent wastewater were
varied (in the range 4–84 mg PO4 -P l−1 ) with altering the
concentrations of KH2 PO4 and K2 HPO4 , in the synthetic
wastewater. Phosphate release and uptake rates in the
UAF-B and SAR are shown in Fig. 6. PO4 -P values increased from 5 to 115 mg l−1 , while the COD decreased
from 634 to 254 mg l−1 in the UAF-B. SAR COD and
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Fig. 4. COD removal performance of the reactors.
Fig. 5. The effect of OLR on COD removal efficiencies.
PO4 -P concentrations were observed as 26 and 0.6 mg l−1 ,
respectively, at the end of the 24 h. COD and PO4 -P removal
efficiencies of the entire system were determined as 97.4
and 96.25%, respectively. Similar data were observed in all
the other experiments. PO4 -P removal efficiencies achieved
in this study are given in Fig. 7.
Nitrogenous matter removal performance of the entire system was evaluated with NO2 -N and NO3 -N concentrations
of both UAF-B and SAR. NO2 -N concentrations of SAR
Fig. 3. SEM pictures of pumice taken from UAF-B reactor after 2 months
of operation (upsizing: a, 300×; b, 400×; c, 3000×; d, 8000×).
Fig. 6. PO4 -P release and uptake together with COD removal (initial
COD = 1000 mg l−1 ; initial PO4-P = 16 mg l−1 ).
B. Kocadagistan et al. / Process Biochemistry 40 (2005) 177–182
181
4. Conclusions
Fig. 7. The effect of initial PO4 -P concentrations on the PO4-P removal
efficiencies.
(MF effluent) decreased from 1.73 to 0.38 mg l−1 , while the
concentration of UAF-B was 8.2 to 2.14 mg l−1 (Fig. 8).
NO3 -N concentrations in both UAF-B and SAR decreased
from 4.43 to 1.65 and 6.16 to 0.31 mg l−1 , respectively,
in a period of 1.25 when the recycle flow from SAR to
UAF-B was four times the influent flow rate (Fig. 8b). When
no recycle was applied to the system (Fig. 8a), the effluent NO2 -N and NO3 -N concentrations were, respectively,
1.241 and 8 mg l−1 for SAR and 0.11 and 0.412 mg l−1 for
UAF-B at the end of the same time period above. The influent nitrogen concentration was determined theoretically
from CO(NH2 )2 which was the unique nitrogen source in
the synthetic wastewater.
Biological removal of carbonaceous, phosphorous and
nitrogenous materials was investigated in a combined upflow anaerobic fixed-bed and suspended aerobic bioreactor
equipped with a membrane unit. The following conclusions
were drawn from this study.
The experimental system was capable of simultaneous removal of the carbonaceous, phosphorous and nitrogenous
materials. The COD removal efficiencies above 94% even
though the OLR values were 16.56 kg COD m−3 per day.
The best COD removal efficiency was 98%. These removal
efficiencies were achieved with short HRT in the range
2.66–13.33 h. Since a high biomass content could be held
in the UAF-B reactor, the volume of reactor was minimized
and the hydraulic retention times were short.
Phosphorous and nitrogenous materials were removed
from the wastewater with this system as well as COD.
PO4 -P removal efficiencies were obtained up to 99% and
during most experiments NO2 -N and NO3 -N concentrations
were low (in the range from 0.1 to 1 mg l−1 ) as compared
with influent theoretical nitrogen concentrations.
The recycle flow between SAR and UAF-B has an important role in the removal of nitrogen because the denitrification process cannot occur in the absence of NO3 . The
denitrified water recycle line from SAR to UAF-B was connected to the system to supply NO3 to the UAF-B reactor.
Since suspended solids and most of the bacteria cannot
pass through the membrane filter, these parameters were not
observed in the effluent (MF effluent) during the experiments.
The pumice used in this study is a very cheap and readily
available material in Turkey. Furthermore, it exhibited good
performance as a fixed-bed material for microorganisms. It
seems that, pumice is a practicable biofilter material. Consequently, it was considered that, the combined upflow anaerobic fixed-bed, formed with pumice, and suspended aerobic
activated sludge bioreactor equipped with a crossflow membrane unit designed for this study is a useful system to treat
high strength wastewaters.
Acknowledgements
This research was supported by the project (BAP-2001/43)
of the Research Fund of Ataturk University and performed
in the laboratories of Ataturk University, Engineering Faculty, Environmental Engineering Department. The authors
would like to thank to the personnel of Scanning Electron
Microscopy Laboratory of Engineering Faculty.
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Fig. 8. NO2 -N and NO3 -N concentration behaviours of the reactors without
(a) and with (b) four times of inflow rate denitrified recycle.
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