Journal of Environmental Sciences 2010, 22(5) 777 783
An autotrophic nitrogen removal process: Short-cut nitrification
combined with ANAMMOX for treating diluted effluent
from an UASB reactor fed by landfill leachate
Jie Liu1,2, Jian e Zuo1,", Yang Yang1, Shuquan Zhu2,
Sulin Kuang3, Kaijun Wang1
1. Environmental Simulation and Pollution Control State Key Joint Laboratory, Department of Environmental Science and Engineering,
Tsinghua University, Beijing 100084, China. E-mail: [e-mail]
2. School of Chemical and Environmental Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
3. Liulitun Sanitary Landfill, Beijing 100094, China
Received 30 July 2009; revised 27 November 2009; accepted 01 December 2009
Abstract
A combined process consisting of a short-cut nitrification (SN) reactor and an anaerobic ammonium oxidation upflow anaerobic
sludge bed (ANAMMOX) reactor was developed to treat the diluted effluent from an upflow anaerobic sludge bed (UASB) reactor
treating high ammonium municipal landfill leachate. The SN process was performed in an aerated upflow sludge bed (AUSB) reactor
(working volume 3.05 L), treating about 50% of the diluted raw wastewater. The ammonium removal efficiency and the ratio of NO2--
Nto NOx--N in the effluent were both higher than 80%, at a maximum nitrogen loading rate of 1.47 kg/(m3·day). The ANAMMOX
process was performed in an UASB reactor (working volume 8.5 L), using the mix of SN reactor effluent and diluted raw wastewater at a
ratio of 1:1. The ammonium and nitrite removal efficiency reached over 93% and 95%, respectively, after 70-day continuous operation,
at a maximum total nitrogen loading rate of 0.91 kg/(m3·day), suggesting a successful operation of the combined process. The average
nitrogen loading rate of the combined system was 0.56 kg/(m3·day), with an average total inorganic nitrogen removal efficiency 87%.
The nitrogen in the effluent was mostly nitrate. The results provided important evidence for the possibility of applying SN-ANAMMOX
after UASB reactor to treat municipal landfill leachate.
Key words: landfill leachate; short-cut nitrification; anaerobic ammonia oxidation; autotrophic nitrogen removal
DOI: 10.1016/S1001-0742(09)60176-5
Introduction leachate is quite low, which makes the traditional nitrifica-
tion/denitrification process inapplicable or too expensive
Municipal landfill leachate represents a special case of (Cema et al., 2006; Fux et al., 2004; Strous et al., 1997).
high-strength wastewater. It is a complex mix of many A complete autotrophic nitrogen removal process, the
kinds of organic and inorganic contaminants generated anaerobic ammonium oxidation (ANAMMOX) process
through the decomposition of municipal solid wastes has been newly developed, in which the ammonium is
during landfill and is further supplemented by rainwater oxidized directly with nitrite, without the requirement of
percolating through the waste material (Ganigue et al., any organic carbon matters, thereby this process is con-
2007). This leachate has extremely high environmental sidered an one of the most promising biological treatment
pollution potential, due to its high concentrations of or- process for nitrogen removal, which may provide a novel
ganics, ammonium, and inorganic salts, including, in some alternative solution to the nitrogen removal from leachate.
cases, heavy metals (Horan et al., 1997). The ANAMMOX process was first observed in an
Compared with organic contaminants in landfill autotrophic denitrification fluidized bed reactor fed by the
leachate, the high concentration ammonium is more dif- effluent of an anaerobic reactor containing some ammoni-
ficult to be treated. Nitrogen removal from wastewaters um (Mulder et al., 1995). It is actually an anoxic process,
is traditionally performed by a conventional biological in which the ammonium is oxidized by nitrite instead
nitrification/denitrification process (Munch et al., 1996). of oxygen in the traditional nitrification process as the
However, complete nitrogen removal can be limited by electron acceptor, and the nitrite is reduced into nitrogen
the availability of biodegradable organic carbon sources gas by ammonia instead of organic carbon matter in the
(Puig et al., 2004). The ratio of C/N in municipal landfill traditional denitrification process as the electron donner
(van de Graaf et al., 1996). ANAMMOX is an autotrophic
* Corresponding author. E-mail: [e-mail]
778 Jie Liu et al. Vol. 22
nitrogen removal process performed by the ANAMMOX 1 Materials and methods
bacteria, which are characterized by an extremely slow
growth rate (doubling time of 11 days) (Strous et al., 1998). 1.1 Raw wastewater
This makes the start-up period longer compared to other
The raw wastewater studied was obtained from the
nitrogen removal technologies.
effluent of an UASB reactor in Liulitun municipal solid
Prior to ANAMMOX process, a short-cut nitrification
waste (MSW) sanitation landfill plant in Beijing, Chi-
(SN)-converting ammonium to nitrite-process should be
na. The NH4+-N concentration was high and C/N ratio
performed to supply enough nitrite for the ANAMMOX
(CODcr/NH4+-N) was low in the raw wastewater (Table
process. In recent years, increasing attention has been
1). Due to the high concentration of ammonium, the raw
paid to the application of this process for wastewater
wastewater was diluted with tap water to an NH4+-N
treatment, such as the supernatant from sludge and swine
concentration of about 600 900 mg/L prior entering into
wastewater digester, municipal landfill leachate. The first
the system.
full-scale ANAMMOX reactor was build up in Rotterdam,
the Netherlands, which treats up to 750 kg-N/day (load of 1.2 Experimental set-up
10.71 kg/(m3·day)) (Wouter et al., 2007). A process con-
This process consisted of two major components: a
sisting of a partial nitrification reactor and an ANAMMOX
SN reactor and an ANAMMOX reactor. In the combined
reactor, followed by two ground soil infiltration systems,
sequential process, the diluted raw wastewater was first
was applied to treat municipal landfill leachate (Liang
fed to the SN reactor for production of nitrite. The effluent
and Liu, 2008), and a quite stable operation was obtained
from this reactor was then mixed with an approximately
when the ANAMMOX load was below 0.12 kg/(m3·day).
equal quantity of the diluted raw wastewater, and this was
The long-term stability of partially nitrification of swine
then fed into the ANAMMOX reactor for total nitrogen re-
wastewater digester liquor and the subsequent treatment by
moval. The experimental flow chart and schematic diagram
ANAMMOX process were also studied, and very stable
are shown in Figs. 1 and 2, respectively.
nitrogen removal efficiency was obtained in 70 days at
a nitrogen removal loading rate of 0.22 kg N/(m3·day)
(Yamamoto et al., 2008).
In Liulitun Sanitary Landfill, Beijing, China, the munic-
ipal landfill leachate is currently treated by a full scale
upflow anaerobic sludge bed (UASB) reactor, but the
effluent from the UASB reactor still contains high concen-
trations of ammonium and relatively low concentrations
of organic carbon matter. Thus, due to lack of carbon
sources, the traditional nitrification/denitrification process
is not suitable to be applied for nitrogen removal.
In the present article, a novel complete autotrophic nitro-
gen removal process, consisting of SN and ANAMMOX,
has been developed for treating the diluted effluent from
Fig. 1 Flow chart of the SN-ANAMMOX process.
the UASB reactor fed by municipal landfill leachate. The
ammonium in about 50% of diluted raw wastewater is
1.2.1 Short-cut nitrification system and operational
completed oxidized to nitrite, then mixed with the other
scheme
50% diluted raw wastewater, and the mix is supplied to the
ANAMMOX process, thus ammonium and nitrite are re- The SN reactor, an aerated upflow sludge bed (AUSB)
reactor, was made of polymethyl methacrylate, with a
moved simultaneously. In this way, ANAMMOX process,
combined with SN process, a new SN-ANAMMOX pro- total volume of 3.05 L and a reaction zone of 1.45 L.
The aerobic activated sludge from a nitrification reac-
cess provides a completely autotrophic nitrogen removal
tor in the same laboratory was used as the inoculum
technology. Compared with the conventional biological
(initial concentration was 2.3 g MLVSS/L). During the
treatment technologies, this process may have promising
period of the previous 85 days operation, the reactor
technical and economic advantages for the treatment of
was operated with the inorganic synthetic wastewater,
landfill leachate, due to less oxygen consumption, no
which was prepared by adding ammonium (NH4HCO3),
requirement for organic carbon matter addition, and low
sludge production (Schmidt et al., 2003; Khin and Annach- KH2PO4, NaHCO3, MgSO4·7H2O, CaCl2 and trace el-
ements ((g/L) Na2EDTA·2H2O 15, ZnSO4·7H2O 0.43,
hatre, 2004).
CoCl2·6H2O 0.24, MnCl2·4H2O 0.99, CuSO4·5H2O 0.25,
Table 1 Raw wastewater characteristics (effluent from UASB reactor fed by landfill leachate)
CODcr BOD5 NH4+-N Alkalinity PO43--P TOC pH
(mg/L) (mg/L) (mg/L) (CaCO3) (mg/L) (mg/L) (mg/L)
1900 2200 160 200 1900 2400 11000 13000 3 5 215 574 8.0 8.4
No. 5 An autotrophic nitrogen removal process: Short-cut nitrification combined with ANAMMOX for treating diluted effluent······ 779
start-up and stable running, with ammonium and nitrite
removal efficiencies of over 95% and the total nitrogen
loading rate of 0.59 kg N/(m3·day). From day 261, the
ANAMMOX reactor was operated with the mixture of
the raw wastewater and the effluent of the SN reactor,
at the beginning of the operation, the NH4+-N removal
efficiency reduced to about 64%, while the NO2--N re-
moval efficiency still kept above 95%, which indicate that
the ammonium was overdosed. Afterwards, the ratio of
raw wastewater to the effluent of SN reactor was strictly
controlled, then the removal efficiency of NH4+-N soon
risen to above 93%. The desired loading rate was attained
by adjusting the ammonium and nitrite concentration in
influent. Temperature in the reactor was maintained at (31
Ä… 1)°C by a hot water jacket. The pH value in the reactor
Fig. 2 Schematic diagram of SN-ANAMMOX process. (1) SN reactor;
was controlled in the range of 7.5 8.0 by dosing sodium
(2) ANAMMOX reactor; (3) influent; (4) peristaltic pump; (5) air pump;
(6) gas separator and collector; (7) hot water bath; (8) nitrogen gas; (9)
bicarbonate into the influent. The HRT of the reactor was
effluent; (10) hot water jacket; (11) mix tank.
maintained at 17 hr.
1.2.3 Analytic methods
NaMoO4·2H2O 0.22, NiCl2·6H2O 0.19, Na2SeO3 0.08,
and H3BO3 0.02) to tap water under the operating condi-
The analytic methods and equipments used for nitrogen
tions of temperature 25°C, pH 7.8 8.0, dissolved oxygen
(NH4+-N, NO2--N, NO3--N), pH, DO, chemical oxygen
(DO) 1.5 3mg/L, and hydraulic retention time (HRT) 18
demand (COD) and temperature are shown in Table 2.
hr. At the end of the operation, the ammonium removal
efficiency and ratio of NO2--N to NOx--N in the effluent
Table 2 Analytic methods and equipments
were both more than 90% at a loading rate of 0.82 kg
Analytic method and equipment
N/(m3·day). From day 86, the SN reactor was fed with
the diluted raw wastewater, HRT was about 14 hr and the
NH4+-N Nesster s reagent colorimetric method
nitrogen loading rate was about 1 kg TN/(m3·day), at the NO2--N N-(1-Naphthyl)-ethylenediamine spectrophotometry
NO3--N UV spectrophotometry
beginning, the pH and DO concentration were controlled
pH Orion828 acidometer
at 7.4 and 3.5 mg/L respectively, result in the decrease of
DO Thermo 810A dissolved oxygen meter
ratio of the NO2--N to NOx--N in effluent. Then the pH
COD The standard method of potassium dichromate*
Temperature Alcohol thermometer (0 50°C)
and DO were adjusted to 8 and 1.5 mg/L, respectively,
and the SN process was achieved soon afterwards. The
* Monitoring and Analyzing Methods of Water and Wastewater (4th ed.).
required ammonium nitrogen-loading rate was acquired by Environmental Protection Agency of China.
adjusting the influent flow and influent ammonium con-
centration. The reactor was performed at room temperature
(about 25°C). The pH value and alkalinity were regulated
2 Results and discussion
by the addition of sodium bicarbonate to the influent.
2.1 Short-cut nitrification process
1.2.2 ANAMMOX system and operational scheme
The concentration of NH4+-N, NO2--N, NO3--N of
The ANAMMOX reactor was an UASB reactor made
the SN reactor and the corresponding NH4+-N removal
of polymethyl methacrylate with a total volume of 8.45
L, and a reaction zone of 6.05 L. Due to the long dou- efficiency and ratio of NO2--N to NOx--N in the effluent
are presented in Fig. 3. Since an 85-day operation with the
bling time of the ANAMMOX bacteria, BMTM biofilm
synthetic wastewater was prior to the combined process,
carriers (Õ12×10 mm for each cube of carrier, Dalian
the results of the SN reactor are presented from day 85.
Shengyuan Water Treatment Equipment Development
Co., Ltd., China) were used to immobilize the anaero- After the diluted raw wastewater was used as the influent,
the pH value and the DO concentration in the reactor
bic microorganisms. Prior to the operation with mixture
were maintained at 7.4 and 3.5 mg/L, respectively, at the
of the diluted raw wastewater and the effluent of the
beginning of the operation, while the HRT was 14 hr and
SN reactor, the reactor was operated with the synthetic
the temperature was 25°C. The NH4+-N removal efficiency
wastewater, which was prepared by adding NH4HCO3,
was maintained at around 90%, the ratio of NO2--N to
NaNO2, KH2PO4, NaHCO3, MgSO4·7H2O, CaCl2, trace
NOx--N in the effluent fluctuated around 50% between day
elements I ((g/L) EDTA 5, FeSO4 5) and trace elements
85 and day 97. From day 91, the pH value in the reactor
II ((g/L): EDTA 15, H3BO4 0.014, MnCl2·4H2O 0.99,
was increased to about 8.0, the DO concentration in the
CuSO4·5H2O 0.25, ZnSO4·7H2O 0.43, NiCl2·6H2O 0.19,
reactor was adjusted to about 1.5 mg/L, and the ratio of
NaSeO4·10H2O 0.21, NaMoO4·2H2O 0.22) to a mineral
NO2--N to NOx--N in the effluent increased to 86% and
medium for 260 days, under the operating conditions of
maintained at about 90% after day 102. This suggested that
temperature 31°C, pH 7.6, HRT 17 hr. At the end of the
at certain HRT and temperature conditions, the pH and DO
experiment, the ANAMMOX reactor achieved a successful
780 Jie Liu et al. Vol. 22
the effluent of the SN reactor was mixed with the other
about 50% of the diluted raw wastewater and then fed
to the ANAMMOX reactor. Compared with the report-
ed SHARON-ANAMMOX process, the SN-ANAMMOX
process has some obvious advantages. First, the DO con-
centration is not necessary to be controlled to the limited
level, and a higher nitrogen loading rate of the reactor may
be maintained. Second, a proper ratio of ammonium to
nitrite in the influent of the ANAMMOX reactor can be
easily controlled only by changing the ratio of the diluted
raw wastewater to effluent of the SN reactor according
for a operational situation of the SN reactor, the nitrite
concentration and the ratio of ammonium to the nitrite
in the influent of the ANAMMOX reactor are the most
important parameters for a stable performance of the
ANAMMOX process. Third, the sludge in the AUSB SN
reactor can be cultivated to granule sludge, and this makes
a relative higher sludge concentration in the SN reactor,
then results in a higher nitrogen loading rate. The operation
of AUSB SN reactor is much easier and simpler, owing to
the dynamic operation strategy for stable operation of the
Fig. 3 Performance of short-cut nitrification reactor. (a) NH4+-N re-
short-cut nitrification process (Yang et al., 2007), in which
moval efficiency and NH4+-N concentrations in influent and effluent; (b)
some operational parameters, including temperature, pH
NO2--N concentrations in influent and effluent, and the ratio of NO2--
value, DO, and total ammonia concentration, etc., could
N/NOx--N in effluent.
affect the growth rate of ammonium oxidizing bacteria
(AOB) and nitrite oxidizing bacteria (NOB) in different
concentration in the reactor are two important parameters
ways. A non-linear mathematic dynamic model (based on
for obtaining a higher ratio 90% of NO2--N to NOx--
the modified Monod equations), including all these param-
N in the effluent. An the end of the operation, with an
eters, was proposed and certified for a stable operation
average nitrogen loading rate of about 1.4 kg/(m3·day), the
of SN process. According to this model, stable operation
NH4+-N removal efficiency and the 90% ratio of NO2--
of the SN reactor should be achieved by controlling the
N to NOx--N in the effluent could be still maintained,
operating conditions, under which the growth rate of AOB
suggesting a successful operation of the SN reactor fed
(µAOB) is greater than that of the NOB (µNOB). For instance,
by the diluted raw wastewater at room temperature (about
in the present article, process conditions were controlled as
25°C) conditions.
follows: temperature was about 25°C, pH value was about
As the electron acceptor of the ANAMMOX process, the
8, DO concentration was about 1.5 mg/L, total ammonia
NO2--N concentration in influent is one of key parameters
(NH4+ and NH3) concentration in the reactor was about
to the combined SN-ANAMMOX system. Compared to
80 mg/L. The calculation of the model showed that under
previously reported SHARON-ANANMMOX process, the
the above condition, the µAOB is about 0.57 day-1, and the
strategy for obtaining NO2--N in this article was somewhat
µNOB is about 0.0050 day-1. That means the AOB will
different (Fig. 4b), in which about 50% of the diluted
grow faster than the NOB in this reactor, i.e., the stable
raw wastewater was fed into the SN reactor first, and
performance of the SN reactor can be achieved in this
more than 90% of NH4+-N was oxidized into NO2--N,
Fig. 4 Flow chart of two NO2--N obtaining strategies. (a) Reported NO2--N obtaining strategy of SHARON-ANAMMOX process; (b) NO2--N
obtaining strategy of SN-ANAMMOX system used in this article.
No. 5 An autotrophic nitrogen removal process: Short-cut nitrification combined with ANAMMOX for treating diluted effluent······ 781
reactor, so a SN process was achieved. During that period, tain higher nitrogen removal efficiency in the ANAMMOX
the maximum nitrogen load was 1.47 kg/(m3·day) and both reactor. Subsequently, the NH4+-N and NO2--N removal
the ammonium removal efficiency and the ratio of NO2-- efficiency stabilized above 93% and 95%, respectively,
Nto NOx--N in the effluent of the SN reactor were both with a maximum influent nitrogen loading rate of about
more than 90%. 0.91 kg/(m3·day).
The average ratio of the removed NO2--N to NH4+-N
2.2 ANAMMOX process
was 1.41 : 1, which was similar to the value reported (1.32
The concentration of NH4+-N, and NO2--N of the : 1) reported by other researchers (Strous et al., 1998).
ANAMMOX reactor, the corresponding NH4+-N and This suggested that the organic matter in raw wastewater
NO2--N removal efficiency, and the ratio of removed did not result in a bloom of denitrification bacteria, most
NO2--N to the removed NH4+-N are presented in Fig. 5. of nitrogen removed in ANAMMOX reactor was removed
The pH value and temperature were maintained around by ANAMMOX bacteria. Meanwhile, the average COD
7.6 and (31 Ä… 1)°C, respectively, while the HRT was removal efficiency was less than 18%, suggesting that the
maintained at 17 hr. As the reactor had been operated organic matter remained in raw wastewater was mostly
with synthetic water for 260 days prior to the operation non-biodegradable; thus, its effect on ANAMMOX bacte-
with the diluted raw wastewater and the effluent of the ria was limited.
SN reactor, the results of the ANAMMOX reactor is Due to strict anaerobic environments are required for
presented from day 260. The NH4+-N removal efficiency the growth of ANAMMOX bacteria, an oxygen removal
fluctuated around 75% during day 260 to day 279, due to process for influent, in which ammonium and nitrite
an inappropriate ratio of the diluted raw wastewater to the concentration were both about 50 mg/L, was applied
effluent of the SN reactor. Therefore, the mix ratio was during the start-up period. After 103-day operation, the
strictly controlled from day 279 on, then the NH4+-N and removal efficiency of ammonium and nitrite were both
NO2--N removal efficiency subsequently reached above above 90%, suggesting a successful start-up. In addition,
95%. This suggests that an appropriate ratio of the raw the application of BMTM biofilm carriers in ANAMMOX
wastewater to the effluent of the SN reactor is crucial to ob- reactor favored better the growth of ANAMMOX bacteria
on the surfaces and pores of carriers. Except plenty of
biofilm attached to the carriers, in the lower part of the
ANAMMOX reactor, some granular sludge can be found
at the end of the operation, which can contribute to the
nitrogen removal in the reactor.
On the basis of the above results, a novel combined
SN and ANAMMOX process was proven to be a feasible
process to treat the diluted effluent of a UASB reactor
fed by landfill leachate. When the combined system is
practically applied, the effluent of the system could be
used to dilute raw wastewater, so that a proper influent
ammonium concentration and loading rate can be applied
to the SN reactor. In addition, a proper influent ammonium
and nitrite concentrations and total nitrogen loading rate
can be applied to the ANAMMOX reactor.
2.3 Combined process
The concentration of total inorganic nitrogen in the
influent and effluent of the combined system and the
corresponding removal efficiency are presented in Fig. 6.
During the period of stable operation, the total average
Fig. 5 Performance of ANAMMOX reactor. (a) NH4+-N removal
efficiency and NH4+-N concentrations in influent and effluent; (b) NO2--
N removal efficiency and NO2--N concentrations in influent and effluent;
Fig. 6 Performance of combined SN-ANAMMOX system.
(c) ratio of removed NO2--N to NH4+-N.
782 Jie Liu et al. Vol. 22
Fig. 7 SEM photographs of sludge samples at end of operation of SN and ANAMMOX reactors. (a) SN sludge; (b) ANAMMOX sludge.
inorganic nitrogen concentration in influent was 573.6 3 Conclusions
mg/L, while the total average nitrogen concentration in
effluent was 77.3 mg/L, with NH4+-N, NO2--N and NO3-- The stable operation of SN process was achieved in an
N concentrations of 2.2 mg/L, 2.7 mg/L and 72.3 mg/L, AUSB reactor fed by diluted raw wastewater (the effluent
respectively. This suggested that NO3--N was a byproduct of UASB reactor treating landfill leachate). The maximum
of the system, which is a main factor affecting the total inorganic nitrogen load of 1.47 kg/(m3·day) resulted in an
nitrogen removal efficiency of the system. At the end of ammonium removal efficiency above 80% and about an
the operation, the average nitrogen loading rate was 0.56 over 90% of the ratio of NO2--N to NOx--N in the effluent.
kg/(m3·day), while the average inorganic nitrogen removal The successful operation of ANAMMOX was achieved
efficiency of the system was 87%. Thus, the feasibility of in an UASB reactor fed by a mixture of diluted raw
applying the SN-ANAMMOX process for treating diluted wastewater (effluent of the UASB reactor treating land-
raw wastewater was confirmed. fill leachate) and the effluent of the SN reactor, with a
maximum inorganic nitrogen loading of 0.91 kg/(m3·day)
2.4 Morphological characterization of microorganisms
and an above 93% of both ammonium and nitrite removal
in reactors
efficiency.
When the diluted raw wastewater was applied as influ- The SN-ANAMMOX combined process was confirmed
ent, the color of the sludge in SN and ANAMMOX reactors to be a feasible process for treating the diluted effluent
gradually changed from yellow and red to brown and of the UASB reactor fed by landfill leachate. The com-
grey brown, with time went on. High-magnification SEM bined process successfully achieved stable performance
showed the morphological diversity of the microorganisms for 70 days, with a maximum nitrogen loading rate of
that inhabited the SN reactor, which included spherical-, 0.63 kg/(m3·day), and a removal efficiency of ammonium
rod- and long filamentous-shaped microorganisms among and nitrite both above 93%. However, the average total
others (Fig. 7a). The configuration of the granule sludge inorganic nitrogen removal efficiency was only about 87%,
and its magnified surface from the ANAMMOX reactor are mainly due to the production of nitrate in the ANAMMOX
shown in Fig. 7b. The configuration of the granule was a process.
regular oval, while the microorganisms inhabiting on the
Acknowledgments
surface of the granule included some ANAMMOX-like
bacteria (Yang et al., 2006) and a few long filamentous- This work was financially supported by the Special Fund
shaped microorganisms. of State Key Joint Laboratory of Environment Simulation
No. 5 An autotrophic nitrogen removal process: Short-cut nitrification combined with ANAMMOX for treating diluted effluent······ 783
and Pollution Control, China (No. 08Y03ESPCT) and the Wastewater nitrogen removal in SBRs, applying a step-
feed strategy: From lab-scale to pilot-plant operation. Water
Key Projects in the National Science & Technology Pillar
Science and Technology, 50(10): 89 96.
Program in the Eleventh Five-Year Plan Period of China
Schmidt I, Sliekers O, Schmid M, Bock E, Fuerst J, Kuenen J G
(No. 2006BACl9B01).
et al., 2003. New concepts of microbial treatment processes
for the nitrogen removal in wastewater. FEMS Microbiology
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