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441
Paper No. 731
PERFORMANCE EVALUATION OF BENCH SCALE MEMBRANE
BIOREACTOR (MBR) SYSTEMS
Aman Ahmad, Babar Abbas, Rasikh Habib, Humayun Khan, Sher Jamal Khan
442 Aman Ahmad, Babar Abbas, Rasikh Habib, Humayun Khan, Sher Jamal Khan
Centenary Celebration (1912 – 2012) 443
PERFORMANCE EVALUATION OF BENCH SCALE MEMBRANE
BIOREACTOR (MBR) SYSTEMS
By:
Aman Ahmad1, Babar Abbas1, Rasikh Habib1, Humayun Khan1, Sher Jamal Khan1
Abstract:
Water is a precious resource for the survival of mankind, but we are losing it every day. We can
replenish our ground water by treated wastewater recharge. The conventional methods to treat
the wastewater are not meeting the recent discharge standards. Membrane bioreactor is the
efficient way of treating wastewater by the combination of biological process and membrane
technology eliminating the process of sedimentation. Three membrane bioreactors (MBR) were
installed at bench scale and the performance parameters were investigated to access the
efficiency of MBR technology and to evaluate the quality of treated wastewater for reuse
purposes. The activated sludge from I-9 Sewage Treatment Plant, Islamabad was acclimatized
with synthetic wastewater for a period of 30 days in MBR along with plastic (Kaldnes) media.
Medium strength wastewater was prepared synthetically in the laboratory having a chemical
oxygen demand (COD) of 500mg/L and COD:N:P of 100:10:2. The degradation of synthetic
wastewater at a hydraulic retention time (HRT) of 8 hours was studied in three separate
reactors which included 1) Conventional MBR (C-MBR), 2) Moving Biofilm MBR (MB-MBR) and
3) Anoxic-oxic Growth MBR (A/O-MBR). The aeration provided to SG-MBR and AG-MBR was
5-6 mg/L while 1-2 mg/L was provided in anoxic compartment and 5-6 mg/L in aerobic portion of
the A/O-MBR. A pH of 7 to 8 was maintained by using Sodium Bicarbonate (NaHCO3). Sludge
retention time (SRT) was maintained at 30 days which resulted in mixed liquor suspended solids
(MLSS) concentration between 6000 and 8000 mg/L. The COD removal efficiency above 97%
was obtained in all the three MBRs. The Total Nitrogen (TN) removal efficiencies of C-MBR,
MB-MBR and A/O-MBR were obtained as 59.81%, 68.82% and 83.18% respectively. Total
phosphorous (TP) removal efficiencies of C-MBR, MB-MBR and A/O-MBR were recorded as
46.48%, 59.46% and 69.74%, respectively. Based on these results the performance of A/O-
MBR was found efficient in terms of nutrients removal over the other two MBRs due to the
production of heterogenic bacteria which are responsible for nitrification, de-nitrification as well
as phosphorous removal.
Keywords: Membrane bioreactor (MBR), Kaldnes media, Nutrients removal, Nitrification, De-
nitrification, Heterogenic bacteria.
INTRODUCTION
Water is vitally important and precious commodity for the survival of mankind. Every living thing
needs it to live and it is a key component in determining the quality of our lives. The increasing
demand of water usage has resulted in water scarcity in Pakistan. Population growth,
associated water-related pollution and public health problems are major areas of concern. The
critical subject is whether the developing world should follow the advance wastewater treatment
technology or there is an alternative “Sustainable Sanitation” (Harleman and Murcott, 2001)
Pakistan’s urban areas have a need to develop water reuse applications from the existing
wastewater sources to overcome the increasing water scarcity and degradation of water
sources. Meanwhile water demand is exponentially increasing in urban development and
1 Institute of Environmental Sciences and Engineering, School of Civil and Environmental Engineering, National
University of Science and Technology Islamabad, Pakistan
444 Aman Ahmad, Babar Abbas, Rasikh Habib, Humayun Khan, Sher Jamal Khan
becoming dependent upon availability of high quality water. It is estimated within the next 15 to
25 years a number of cities will face limited fresh water to meet increasing demand for
horticulture (Hastuti et al., 2011). We can replenish this precious resource by treating our
wastewaters efficiently. The principal objective of wastewater treatment is generally to allow
municipal and industrial effluents to be disposed off without danger to human health or
unacceptable damage to the natural environment. Irrigation with treated wastewater is both
disposal as well as effective form of utilization.
In present era the conventional wastewater treatment technologies are not meeting the effluent
discharge standards. The design of wastewater treatment plants is usually based on the need to
reduce organic and inorganic loadings to limit pollution of the environment. Pathogen removal
has very rarely been considered an objective but, for reuse of effluents in agriculture, this must
now be of primary concern and processes should be selected and designed accordingly
(Hillman, 1988). Treatment to completely remove wastewater constituents is technically
possible, but is not economically feasible. However significant progress has been made in
developing sound technical and viable economical approaches to produce high quality and
reliable water sources from reclaimed wastewater.
The Membrane bioreactors are composed of two primary parts, the biological unit responsible
for the biodegradation of the waste compounds and the membrane module for the physical
separation of the treated water from mixed liquor. The membrane component of the MBR
eliminates the need for a clarifier and is performed using low pressure membranes i.e.
Microfiltration (MF) or Ultrafiltration (UF). This technology is suitable for urban area which has
limited space for wastewater treatment and ability to remove pathogens, nutrients, and
suspended solids (Hastuti et al., 2011). MBR technology is advancing rapidly around the world
both in research and commercial applications (Meng et al., 2009). Despite the increasing
number of studies and full-scale applications of MBR systems, directions and trends in
academic research as well as commercial developments require further investigation (Yang et
al., 2006). The MBR with a submerged membrane module can be an attractive choice for the
upcoming generations of biological wastewater treatment plants providing two clear advantages,
comparatively improved and excellent effluent quality and smaller footprints with minimal
aesthetic nuisance. The core application area so far has been to improve the industrial
wastewater treatment (Sombatsompop, 2007). Moreover MBRs may actively be employed in
domestic wastewater treatment as well because MBRs are operated at high mixed liquor
suspended solids (MLSS) concentrations and inhibit the excessive sludge production, resulting
in high removal efficiency of chemical oxygen demand (COD), nutrients (NH3-N, NO2-1, NO3-1
and PO4-2) removal and bacterial disinfection (Su et al., 2007). Another useful application of
MBRs is to treat the landfill leachate (Yang et al., 2012).
Although MBRs are very efficient in treating wastewater but at the same time we need to
develop more suitable set ups for achieving further technological improvements in the system.
In this paper the performance evaluation of bench scale MBRs has been evaluated where the
treatment performance of MB-MBR using Kaldnes media A/O-MBR was compared with C-MBR.
MATERIALS AND METHODS
Experimental set-up
Three bench scale acrylic made MBRs were set up at IESE wastewater laboratory. MBRs were
categorized based on their design and operating conditions as:
1. Conventional MBR (C-MBR)
2. Moving Biofilm MBR (MB-MBR)
Centenary Celebration (1912 – 2012) 445
3. Oxic-Anoxic MBR (A/O-MBR)
The effective volume of each tank of C-MBR and MB-MBR was 12 L for the study. Perforated
plates divided the reactor into three compartments, membrane being installed in the middle one.
Perforated plates helped in mixing of the sludge in the reactor as well as maintaining proper
aeration in each compartment of the reactor. Hollow fiber (HF) membrane (Mitsubishi Rayon,
Japan) was immersed in middle compartments of both reactors having a nominal pore size of
0.1 µm and surface area of 0.2 m2. The plastic (kaldnes) media was used as moving biofilm
carrier media and it circulates within all the three compartments of MB-MBR having a dry
volume of 20%. The schematic diagram of C-MBR is shown in Figure 1.
00
00
Figure 1: Schematic diagram of C-MBR
A third laboratory scale acrylic made MBR was set up, having a 15 L volume tank for the study.
Perforated plate divided the reactor into two Compartments, with a ratio of 1:2 of the total
volume. Membrane was installed in the smaller compartment as shown in Figure 2. The plastic
(Kaldnes) media with 20% effective volume was introduced in both compartments. A
mechanical mixer (Cole-Parmer, Model 50007-25, USA) was installed in the larger compartment
to make anoxic condition as well as to keep media in suspension. The mechanical mixer was
operated in cyclic mode as 2 minutes OFF and 10 minutes ON.
0
Figure 2:Schematic diagram of A/O-MBR
Air Diffusers
Feed Tank
Solenoid Valve
Relay Unit
Level Sensor
Control Tank
Water Trap
Digital manometer
Peristaltic Pump
Effluent
Air Diffusers
Feed Tank
Solenoid Valve
Relay Unit
Level Sensor
Control Tank
Water Trap
Digital manometer
Peristaltic Pump
Effluent
Mechanical Mixer
446 Aman Ahmad, Babar Abbas, Rasikh Habib, Humayun Khan, Sher Jamal Khan
Acclimatization of sludge and media with synthetic wastewater
Wastewater was prepared synthetically in the laboratory having a COD of 500 mg/L and
COD:N:P of 100:10:2. To maintain a pH of 7-8, NaHCO3 was used as pH buffer. The activated
sludge from I-9 Sewage Treatment Plant, Islamabad was acclimatized with synthetic
wastewater for a period of 30 days in MBR along with Kaldnes media.
Table 1: Chemical Composition of Synthetic waste water
Chemicals Formula Quantity (mg/L)
Hydrated Glucose C6H12O6.H2O 500
Ammonium Chloride NH4Cl 191
Potassium Di-Hydrogen Phosphate KH2PO4 54.85
Calcium Chloride
Magnesium Sulphate
Ferric Chloride
Manganese Chloride
CaCl2
MgSO4.7H2O
FeCl3
MnCl2.4H2O
5
5
1.5
1
pH buffer NaHCO3 142.5
The specific properties of the Kaldnes media used during the research study are as listed in
Table 2.
Table 2: Specific Properties of Plastic (Kaldness) Media
Properties Description
Dimensions 1 cm dia.
Dry Volume 20 %
Wet Volume 8 %
Material K3 Type Plastic
Membrane characteristics
The main features of the membrane modules used in the MBRs are presented in Table 3.
Centenary Celebration (1912 – 2012) 447
Table 3: Hollow-fiber (HF) membrane characteristics
Item Characteristic
Manufacturer Mitsubishi Rayon Engineering Co. Ltd., Japan
Membrane
material Polyethylene
Pore size 0.1 μm
Filtration area 0.2 m
2
MLSS 5,000-12,000 mg/L recommended (3,000 - 15,000
mg/L)
Filtration flow rate Constant
Suction pressure 5-30 kPa
Intermittent
suction Operating time ≤ 13 min; relaxing time ≥ 2 min
Temperature 15-35oC
MBR operational conditions
• Peristaltic Pump (Master Flex, Cole-Parmer, USA) was used to periodically draw
permeate at a cycle of 10 min filtration, 2 min relaxation, maintaining HRT of 8 hrs.
Sludge retention time (SRT) was set to 30 days and nitrogen loading rate (NLR) of 0.15
Kg/m3/d organic loading rate (OLR) was kept at 1.5 Kg/m3/d.
• Air pumps provided sufficient air flow rate to keep the media in suspension, scour the
membrane fibers along with maintaining dissolved oxygen (DO) concentration of 5-6
mg/L except the anoxic zone of A/O-MBR where DO concentration was maintained at 2
mg/L.
• Diffused aeration was provided in the reactor by the help of air diffusers.
• Flow meter was used to monitor the aeration rate at 7 L/min. (3 L/min in the membrane
compartment and 4 L/min in the side compartments in C-MBR and MB-MBR). Similarly 3
L/min aeration rate was maintained in the membrane compartment of A/O-MBR.
• Trans-membrane pressure (TMP) was recorded using Data logging manometer (Sper-
Scientific 840099, Taiwan) as indicator of membrane fouling tendency. The membranes
were operated till the TMP reached to a limit of 30 KPa.
The MBR set up was operated for 140 days under the following conditions:
448 Aman Ahmad, Babar Abbas, Rasikh Habib, Humayun Khan, Sher Jamal Khan
Table 4: Operating conditions
Parameter Condition
SRT 30 days
HRT 8 hours
OLR 1.5 Kg/m3/d
NLR 0.15 Kg/m3/d
F/M 0.2
pH 6-7
MLSS 6-8 g/L
Analytical Methods
The parameters that were investigated, the technique adopted to determine each parameter
and the equipment/material used are reported in Table 5
Parameter Method Equipment/Material Reference
MLSS/
MLVSS Filtration-
Evaporation 1.2 μm (GF/C, Whatman); 105oC oven
(MLSS); 550oC Muffle Furnace (MLVSS) APHA , 2005
COD Close reflex COD tube/vial; 150oC oven APHA , 2005
NH4+-N,
NO2--N,
NO3--N
Hach Reagents
Spectrophotometer (DR 2010, Hach) APHA , 2005
PO-4-P Molybdovanadate Spectrophotometer (DR 2010, Hach) APHA , 2005
Table 5: Analytical Parameters, Methods and Equipment
RESULTS AND DISCUSSION
The previous studies (Jamal et al., 2011) and (Jamal et al., 2012) have already evaluated the
performance of MBRs. These studies proved MBR technology’s capability to treat the
wastewater for reuse purposes. Previously, the studies by Jamal et al. (2011) were carried out
with sponge media as biofilm carrier having 20% dry volume of the reactor. In the present study,
the sponge media was replaced by plastic (Kaldnes) media and A/O-MBR was introduced.
Results revealed that the nutrients (TN and TP) removal was more efficient in A/O-MBR due to
the production of nitrifying and denitrifying bacteria in anoxic zone of A/O-MBR. The anoxic
zone may have also facilitated the growth of phosphorous accumulating microorganisms
(PAOs).
Centenary Celebration (1912 – 2012) 449
COD Removal
All the three MBRs gave almost more than 95% COD removal for entire period. There is the
slight difference in COD removal of all three MBRs however A/O-MBR shows relatively better
COD removal among the three MBRs as shown in the following figure.
Figure 3: Influent and effluent COD
Nutrients removal
NH4-N removal
The C-MBR was able to remove 90% NH4-N from influent synthetic wastewater. The MB-MBR
gave 95% NH4-N removal due to nitrification by the biofilm developed on the plastic media. A/O-
MBR exhibits relatively high quality effluent, almost 96% removal due to nitrification followed by
de-nitrification in the anoxic zone. Nitrification converts NH4-N into NO2-1and NO3-1 i.e. low
concentration of NH4-N in A/O-MBR and MB-MBR’s effluents. Figure shows the influent and
effluent trend in all MBRs.
450 Aman Ahmad, Babar Abbas, Rasikh Habib, Humayun Khan, Sher Jamal Khan
Figure 4: Influent & effluent NH4-N of C-MBR, MB-MBR & A/O-MBR.
NO2-1 Removal
A/O-MBR gave maximum NO2-1 removal than the other two MBRs due to enhanced nitrification
process in anoxic conditions.
Figure 5: NO2-1 in effluents of all MBRs
Centenary Celebration (1912 – 2012) 451
NO3-1 Removal
AO-MBR was most efficient in terms of NO3-1 removal due to nitrification and de-nitrification in
anoxic zone. AO-MBR gave 5 mg/L of NO3-1 in effluent on average. While C-MBR and MB-MBR
effluents were found to be 12 mg/L and 10 mg/L, repectively.
Figure 6: NO3-1 in effluents of all MBRs
TN Removal
It was found that the maximum TN removal (83.2 %) was in A/O-MBR followed by 69 % TN
removal in MB-MBR while 60 % in C-MBR. Better TN removal in A/O-MBR was due to the
appropriate production of nitrifying and denitrifying bacteria.
Figure 7: TN removal in all three MBRs
452 Aman Ahmad, Babar Abbas, Rasikh Habib, Humayun Khan, Sher Jamal Khan
PO4-3 – P Removal
The PO4-3-P removal is very important parameter in wastewater treatment as it can cause
eutrophication along with NO2-1 and NO3-1.The effluent quality with least concentration of PO4-3
was found in the A/O-MBR. Phosphorous removal efficiencies of C-MBR, MB-MBR and A/O-
MBR were as 46.48%, 59.46% and 69.74% respectively on average basis. C-MBR showed
least removal efficiency because it had no anoxic zone and moving biofilm carriers in it.
Figure 8: Influent & effluent PO4-3 in all three MBR
CONCLUSIONS
This study revealed the following specific conclusions:
1. COD removal efficiency above 95% was achieved in all the three MBR systems namely
C-MBR, MB-MBR and A/O-MBR
2. NH4-N removal was found to be maximum in A/O-MBR due to effective nitrification
process in anoxic zone and biofilm carriers.
3. A/O-MBR was efficient in the removal of NO31- due to abundance of de-nitrifying bacteria
as compared to the other MBRs.
4. PO4 –P removal was highest in A/O-MBR due to anoxic zone attained by optimum
mechanical mixing and biofilm carriers. It was also better in MB-MBR due to biofilm
formation on moving biofilm carriers.
Centenary Celebration (1912 – 2012) 453
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454 Aman Ahmad, Babar Abbas, Rasikh Habib, Humayun Khan, Sher Jamal Khan