Aerobic Granular Sludge Technology
For Wastewater Treatment
– An Overview
Nor Anuar, A.1, Ujang, Z.1, van Loosdrecht, M.C.M.2, De Kreuk, M. 2
IPASA, Faculty of Civil Engineering, University Technology of Malaysia, 81310
Skudai Johor, Malaysia.
Correspondence E-mail: email@example.com, firstname.lastname@example.org
Delft University of Technology, Kluyver Laboratory for Biotechnology, Department
of Biochemical Engineering, Julianalaan 67, NL-2628 BC Delft, The Netherlands.
Correspondence E-mail: M.C.M.VanLoosdrecht@tnw.tudelft.nl
The new aerobic granular sludge technology has the ability to contribute and to
improve the biological treatment of wastewater. Present wastewater treatment plants
have the disadvantage of a large area requirement. Moreover these processes have
to deal with a large number of conversion processes (COD-oxidation, ammonium
oxidation, nitrate reduction, biological phosphate removal etc.) Traditionally,
flocculated sludge with low settling velocities is applied and large settling tanks are
needed to separate clean effluent from the organisms. Besides large settling tanks,
separate tanks are needed to accommodate the different treatment processes.
Conventional processes need many steps for organic carbon (COD), nitrogen (N)
and phosphorus (P) removal, with large recycle flows and a high total hydraulic
retention time. Surplus sludge from a municipal wastewater plant needs different
steps to dewater (e.g. thickening and filterpressing) before it can be processed. To
overcome the disadvantages of a conventional wastewater treatment plant, biomass
has to be grown in a compact form, like aerobic granular sludge. Simultaneous
biological organic and nutrient removal was investigated with aerobic granular sludge
in an anaerobic/aerobic sequencing batch reactor (SBR). This system showed a very
stable removal performance. The average removal rate for organic carbon, total
nitrogen and phosphorus reached 100%, 95% and 94 % respectively.
Keywords: Aerobic granular sludge, Sequencing Batch Reactor (SBR),
simultaneously COD, Nitrogen and Phosphorus removal
Alternatives for conventional activated sludge system
The need for more compact reactors and short high retention time (HRT) directed
the research towards the development of systems with high biomass concentrations
and thus high volumetric conversion capacities. High biomass concentrations can be
obtained in biofilm systems. Previous research on biofilm growth mainly focused on
continuously fed systems (Tijhuis et al., 1994c; Gjatelma et al., 1995;Van Benthum
et al., 1996; Kwok et al., 1998; Picioreanu et al, 2000). In the Biofilm Airlift
Suspension (BAS) reactor for example (Tijhuis et al, 1994c; Frijters et al, 1997), the
biomass grows as biofilm on small suspended basalt particles. These systems have
successfully been applied at full scale (Heijnen et al., 1990). The additional
advantage of these systems is that they produce less sludge than the conventional
wastewater treatment systems. However, these biofilm systems have a complex
design. In particular this applies to the three-phase separator which is needed to
separate solids, liquid and gas. These systems are continuously fed systems. For
many applications a discontinuously operated system is more advantageous, since
wastewater streams usually are not constant in flow rate and in composition (Irvine
et al.,1997). Therefore, an investigation to a more simple, compact, discontinuously
fed, reactor design is needed.
Why Aerobic Granular Sludge Technology ?
Recently, SBR technology has been widely applied and demonstrated in small scale
and large scale (Wilderer et al., 2001; Irvine et al., 1997). To achieve more strict
effluent demand, i.e. better effluent quality in not only COD but also nutrients
removal (Nitrogen and Phosphorus), SBRs are mostly operated under alternating of
anaerobic and aerobic reaction in practice when treating domestic sewage. For SBR,
an important and hot research topics is the formation and development of aerobic
granular sludge in reactor (Beun et al., 1999; Morgenroth et al., 1997). Compared to
conventional activated flocs, aerobic granular sludge has a regular, dense and
strong physical structure, good settling ability, high biomass retention, and the ability
to withstand shock loading rate (Lin et al., 2003). In addition, as a result of the
diffusion gradient of oxygen, aerobic zones, anoxic zones and anaerobic zones exist
in aerobic granular sludge simultaneously (de Kreuk et al., 2004).
This technology indicated the development of simple, cost-efficient and compact
wastewater treatment systems, based on the formation of aerobic granular sludge in
sequentially operated batch reactors without a carrier (Granular Sludge Batch
Reactor). Sequential operation allows a settling phase as part of the cyclic process
and thus avoiding the need for the complex and expensive internal settlers in the
reactor. It’s also solve the problem of sludge handling, since this reactor produce
high settling capacity of the granules which result less sludge production than the
conventional activated sludge system. Simultaneous COD, N, and P removal which
can be done as well by an aerobic granule were advantageous of this system to
produce a high quality effluent. These were proved by experimental results indicated
MATERIALS AND METHODS
Reactor set-up and operation
The experimental works were carried out in Kluyver Laboratory for Biotechnology,
Delft, Netherlands using Sequencing Batch Airlift Reactor (SBAR) (refer Figure 1).
The airlift reactor had a working volume of 3.0 L. The internal diameter of the down
comer was 6.25 cm. The riser was 90 cm in height, had an internal diameter of 4 cm,
and was put at a distance of 1.25 cm from the bottom of the down comer. Air was
introduced by a fine bubble aerator at the bottom of the reactor at a superficial air
velocity of 4Ls-1. A massflow controller controlled the airflow rate. The temperature of
the reactor was maintained at 200C using a water jacket and thermostat bath, the pH
was maintained between 6.8 to 7.2 using 1M NaOH and 1M HCl. The reactor was
operated in successive cycles of 3 hours each. One cycle consisted of 60 minutes
anaerobic phase (concentrated influent quickly added into reactor in 1 minutes), 112
minutes aeration (aerobic phase), 3 minutes settling and 5 minutes effluent
withdrawal. Effluent was withdrawn at 50 cm from the bottom of the reactor. The
settling time was chosen such that only particles with a settling velocity larger than
20m/h were effectively retained in the reactor. Activated sludge from a conventional
nutrient removal wastewater treatment plant was used as inoculums.
Reactor Offgas CO 2-analyser
cooling cooling air out
Offgas recirculation Air mixing vessel
mfc air in
mfc N2 gas in
riser DO control
effluent pH-electrode + pH control
Figure 1 The experimental set-up of Sequencing Batch Airlift Reactor
The synthetic wastewater was used for this experiment which consists of two (2)
media, namely medium A (65.1 mM NaAc ; 3.7 mM MgSO4.7H2O; 4.8 mM KCl) and
medium B (36.2 mM NH4; 4.4 mM K2HPO4; 2.2 mM KH2PO4 and 10ml/L trace
element solution according to Vishniac and Santer, 1975).
During the experiment sampling, the reactor was well mixed and highly turbulent with
nitrogen gas during anaerobic phase and with low oxygen concentration (20%
oxygen saturation) during aerobic phase. Acetate (CH3C00-C), ammonium (NH4-N),
nitrate (NO3-N) and phosphate (PO4-P) were measured occasionally during one
cycle to determine the cyclic profiles. CH3C00-C concentration of filtered samples
(filtrated using a MILLIPORE membrane syringe-filter 0.45 um) was measured by
gas chromatography ;NH4-N, NO3-N and PO4-P concentrations of filtered samples
were measured using Dr. Lange’s CADA50S spectrophotometer.
RESULTS AND DISCUSSIONS
The COD and P removal process throughout one cycle
Figure 2 shows the profiles of CH3COO-C, NH4-N, NO3-N and PO4-P in a typical
cycle of the SBR process in phase. As shown in Figure 2, when the concentrations
CH3COO-C and PO4-P in the influent (t=0) were at 438.70 mg/L (3.20 mM) and
11.34 mg/L, respectively, carbon substrate was rapidly depleted and PO4-P was
sharply released after the anaerobic phase started. At the end of the anaerobic
phase, the concentrations of PO4-P increased to around 104.80 mg/L and the
concentrations of CH3COO-C decreased to around 5.47 mg/L (0.04 mM). This was a
result that phosphate accumulating organisms (PAO’s) took up organic carbon
substrates and stored them as Poly-B-Hydroxybutyrate (PHB) and released ortho-
phosphate to the bulk liquid. In addition, as can be seen from Figure 1, the released
PO4-P during the anaerobic phase was taken up luxuriously in the aerobic phase and
PO4-P could be detected in lower concentration (6.14 mg/L) at the end of aeration.
The concentration of CH3COO-C decreased lightly from 5.47 mg/L at the end of the
anaerobic phase to 0 mg/L at the end of aerobic phase. This result clearly indicated
that intracellular PHB was used as the energy sources for PO4-P uptake in the
aerobic phase, which would be beneficial for phosphorus removal if the available
amount of carbon source in wastewater is limited. During this cycle, the removal rate
for CH3COO-C and PO4-P reached almost 100% and 91% respectively.
NH4-N, NO3-N, PO4-P ( mg/L )
100.00 2.50 CH3C00-C ( mM )
0 20 40 60 80 100 120 140 160 180
NH4-N NO3-N PO4-P CH3COO-C
Figure 2 The profiles of CH3COO-C, NH4-N, NO3-N and PO4-P in a typical cycle of
the SBR process in an anaerobic/aerobic phase
N removal process throughout one cycle
As shown in Figure 2, during the anaerobic phase, the NH4-N concentration slowly
decreased, and the amount of NO3-N left over from the previous cycle was
denitrified. When the aerobic phase starts, the NH4-N concentration immediately
started to decrease faster than during the anaerobic phase. This was mainly due to
nitrification processes which NH4-N was converted to NO3-N. Therefore, the NO3-N
concentration was also increased during this period. As can be seen in Figure 2,
when the concentrations in the influent was 16.79 mg/L respectively, the effluent
concentrations (t = 180 min) could be reduced to 5.20 mg/L respectively after treated
by the SBAR. The nitrogen removal is about 95% with 100% ammonium removal.
When all NH4-N was depleted, the NO3-N concentration did not decrease but
remained constant, indicating that denitrification did not occur during aerobic phase.
The denitrification probably stopped due to full penetration of oxygen into the
granules since nitrification was completed (Beun et al., 2000). Those results
suggested that simultaneous nitrification and denitrification could happen efficiently
in the process when dissolved oxygen was controlled at low concentration (20%
oxygen saturation) during aerobic stage, which indicates that aerobic granular sludge
has an excellent performance in nitrogen removal.
This experimental results clearly demonstrated that it is possible to achieve a good
organic and nutrient removal in anaerobic/aerobic SBR system. This capability was
contributed much from the special structure of the sludge like aerobic granular
sludge. Interestingly, the use of long anaerobic feeding period allows to have
combined biological nitrogen and phosphate removal and also needed for
economically feasible full scale applications. At low oxygen saturation (20%) high
removal efficiencies were obtained; 100 % COD removal, 91% phosphate removal
and 95% total nitrogen removal (with 100% ammonia removal). As a conclusion.
aerobic granular sludge is a very promising technology for improvement of
conventional wastewater treatment plant from an engineering point of view, and
should therefore be further developed.
APHA (2002). Standard Method for the Examination of Water & Wastewater
(American Public Health Association Washington).
Beun J.J., Hendriks A., van Loosdrecht M.C.M., Morgenroth M., Wilderer P.A. and
Heijnen J.J. (1999a). Aerobic Granulation in a Sequencing Batch Reactor.
Wat. Res., 33 (10), 2283 - 2290.
Beun J.J., van Loosdrecht M.C.M., and Heijnen J.J. (2000). Aerobic Granulation.
Wat. Sci. Technol., 41 (4-5), 41 - 48.
Bishop, P.L. (1997). Biofilm Structure and Kinetics. Wat. Sci. Technol., 36 (1), 287 –
294.Conley, D.J. (2000). Biogeochemical nutrient cycles and nutrient
management strategies. Hydrobiologia, 410, 87 – 96.
Dangcong P., Bernet N., Delgenes J.P. and Moletta R. (1999). Aerobic Granular
Sludge – a Case Report. Wat. Res., 33(3), 890 – 893.
De Kreuk, M.K. and De Bruin L.M.M. (2004). Aerobic Granule Reactor Technology.
London, IWA Publishing.
Falkentoft, C., Maria (2000). Simultaneous removal of nitrate and phosphate in a
biofilm reactor; the aspect of diffusion. PhD Thesis. Technical University of
Fritjers C.T.M.J., Eikelboom D.H. and Mulder R. (1997). Treatment of municipal
wastewater in a Circox airlift reactor with integrated denitirification. Wat Sci.
Technol. 36: 173-181.
Gjaltema, A., Tijhius L., Van Loosdrecht M.C.M. and Heijnen J.J. (1995).
Detachment of biomass from suspended non-growing spherical biofilms in
airlift reactors. Biotechnol.Bioeng., 45, 258-269.
Heijnen, J.J, Mulder A., Weltevrede R., Hols P.H. and Van Leeuwen H.L.J.M. (1990).
Large Scale Anaerobic/Aerobic Treatment of Complex Industrial Wastewater
Using Immobilized Biomass in Fluidised Bed and Air-Lift Suspension
Reactors. Chem. Eng. Technol., 13, 202-208.
Irvine RL, Widerer PA, Flemming HC.(1997). Controlled unsteady state processes
and technologies-an overview. Wat.Sci. Technol.,35,1-10.
Jang, A., Yoon Y.H., Kim I.S. and Bishop P.L. (2003). Characterization and
Evaluation of Aerobic Granules in Sequencing Batch Reactor. J. Biotechnol.,
105 (1-2), 71 - 82.
Kwok, W.K., Picioreanu C., Ong S.L., van Loosdrecth M.C.M., Ng W.J., Heijnen J.J.
(1998). Influence of biomass production and detachment forces on biofilm
structures in a biofilm airlift suspension reactor. Bitechnol Bioeng., 58, 400 -
Lin, Y.M, Liu, Y. and Tay J.H. (2003). Development and characteristics of
phosphorus – accumulating microbial granules in sequencing batch reactors.
Appl. Microbiol. Biotechnol. 62, 430-435.
Liu, Y., and Tay J.H. (2004). State of the Art of Biogranulation Technology for
Wastewater Treatment.Biotechnology Advances, 22 (7), 533 – 563.
Liu, Q.S., Yang S.F. and Tay J.H. (2004). Improved Stability of Aerobic Granules by
Selecting Slow Growing Nitrifying Bacteria. J. Biotechnol., 108 (2), 161 - 169.
Morgenroth, E., Sherden T., van Loosdrecth M.C.M., Heijnen J.J. and Wilderer, P.A.
(1997). Aerobic Granular Sludge in a Sequencing Batch Reactor. Wat.Res.,
12, 3191- 3194.
Morgenroth, E. and Wilderer P.A. (1998). Controlled biomass removal – the key
parameter to achieve enhanced biological phosphorus removal in biofilm
systems. Microbial Ecology of Biomass : Concepts, Tools and Applications,
Lake Bluff, Illinois, USA, IAWQ.
Moy, B.Y.P., Tay J.H., Toh S.K., Liu Y. and Tay S.T.L. (2002). High Organic Loading
Influences the Physical Characteristics of Aerobic Sludge Granules. Letters in
Applied Microbiology, 34, 407 - 412.
Picioreanu, C., Van Loosdrecht M.C.M and Heijnen J.J. (2000). Effect of Diffusive
and Convective Substrate Transport on Biofilm Structure Formation : A Two -
Dimensional Modelling Study. Biotechnol. Bioeng., 69, 504 - 515.
Qin, L., Liu Y. and Tay J.H. (2004a). Effect of Settling Time on Aerobic Granulation
in Sequencing Batch Reactor. Biochemical Engineering Journal, 21(1), 47 -
Qin, L., Tay J.H and Liu Y. (2004b). Selection Pressure Is a Driving Force of Aerobic
Granulation in Sequencing Batch Reactors. Process Biochemistry, 39(5), 579
Tijhius, L., van Loosdrecht M.C.M. and Heijnen J.J. (1994c). Formation and Growth
of Heterotrophic Aerobic Biofilms on Small Suspended Particles in Airlift
Reactors. Biotechnol. Bioeng., 44, 595-608.
Van Loosdrecht M.C.M., Eikelboom D.H., Gjatelma A., Mulder A., Tijhius L., and
Heijnen J.J. (1995). Biofilm Structures. Wat. Sci. Technol., 32 (8), 35 - 43.
Van Loosdrecht M.C.M., and De Kreuk M.K. (2004). Method for the Treatment of
Waste Water with Sludge Granules. Bureau voor Industriele Eigendom. The
Netherlans, International, Techinisce Universiteit Delft.
Van Loosdrecht, M.C.M., Hooijmans C.M., Brdjanovic D. and Heijnin J.J. (1997).
Biological Phosphate Removal Processes. Appl. Microbiol. Biotechnol., 48 (3),
289 - 296.
Van Loosdrecht, M.C.M., Tijhius L., Wijdieks A.M.S. and Heijnen J.J. (1995).
Population distribution inaerobic biofilms on small suspended particles. Wat.
Sci. and Technol., 31 (1), 163-171.
Vishniac, W. and Santer M. (1975). The Thiobacili. Bacteriol.Rev., 21,195 - 213.
Wilderer, P.A., Irvine R.L. and Goronszy M.C. (2001). A Sequencing Batch Reactor
Technology. Colhester, UK, IWA Publishing.