Desalination 278 (2011) 281–287

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Performance of ANAMMOX-EGSB reactor

Tingting Chen a, Ping Zheng a,⁎, Chongjian Tang a, Sheng Wang b, Shuang Ding a

a Department of Environmental Engineering, Zhejiang University, Hangzhou 310029, Chinab Department of Geography and Environmental Engineering, The Johns Hopkins University, Baltimore, MD 21218, USA

⁎ Corresponding author. Tel./fax: +86 571 86971709E-mail address: pzheng@zju.edu.cn (P. Zheng).

0011-9164/$ – see front matter © 2011 Elsevier B.V. Aldoi:10.1016/j.desal.2011.05.038

a b s t r a c t

a r t i c l e i n f o

Article history:Received 31 December 2010Received in revised form 14 May 2011Accepted 16 May 2011

Keywords:ANAMMOX-EGSB reactorANAMMOX granulesPerformance

The nitrogen pollution has caused serious environmental problems. The main aims of the present study wereto remove the nitrogen from wastewater through ANAMMOX (ANaerobic AMMonium OXidation) process,and let the effluent meet the discharge standard which was significant and advance in the field of ANAMMOXapplication which was also very important to the environmental protection and water recycling. This studyreports the performance of ANAMMOX-EGSB (Expanded Granular Sludge Bed) reactor after feeding withsynthetic wastewater. The results showed that the effluent ammonium concentration was 11.90 mg N/L andthe nitrogen remove efficiency (NRE) reached up to 94.68% when the volumetric nitrogen loading rate (NLR)and volumetric nitrogen removal rate (NRR) were as high as 27.31 and 25.86 kg N/(m3·d), respectively. Theeffluent ammonium concentration meets the Chinese integrated wastewater discharge standard (GB8978-1996) in which the ammonium concentration should be lower than 15 mg N/L. The maximum ammonium,nitrite and nitrogen conversion rates (qmax) by the ANAMMOX granular sludge in the reactor were 907.13,841.76, 1810.10 mg N/(g VSS·d) and half saturation constants (KS) were 2.69, 0.44, 3.11 mg N/L, respectively.

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© 2011 Elsevier B.V. All rights reserved.

1. Introduction

The discharge of nitrogen-containing wastewater contributes a lot tothewaterpollutionandecological deterioration.According to the report of“the state of the environment in China (2009)”, the ammonium emissionwas up to 1.23 million tons per year. Nitrogen pollution (N-pollution)causes serious environmental problems. The water blooms and red tidesfrequently occurred and seriously disturbed the balance of aquaticecosystem. Furthermore, N-pollution not only harms the sustainabledevelopment of agriculture, fishery and tourism etc., but also threatensthe living environment of human beings. Thus, it is necessary to removenitrogen from wastewater. Moreover, due to the shortage of waterresource, thenitrogen concentration in thedischargedwastewater shouldmeet the discharge standard after N-removal treatment. According to thefirst class discharge standard in the Chinese integrated wastewaterdischarge standard (GB8978-1996), the effluent ammonium concentra-tion should be lower than 15 mg N/L.

ANAMMOX (ANaerobic AMMonium OXidation) process is a noveland promising alternative in that the aeration and carbon-sourcedemand reduces by over 50% and 100%, respectively compared toconventional nitrification and denitrification processes [1]. The firstfull-scale ANAMMOX reactor was constructed by the Dokhaven–Sluisjesdijk wastewater treatment plant in Rotterdam in 2002,treating sludge dewatering effluent from the Sharon (single reactor

high activity ammonia removal over nitrite) process. Its maximumnitrogen removal rate (NRR) reached 9.5 kg N/(m3·d)[2], which wasfar higher than the maximum NRR obtained from the conventionalnitrification–denitrification process (lower than 0.5 kg N/(m3·d))[3].The estimated treatment cost of ANAMMOX – 0.75 Euro/kg N –was verylow compared to 2–5 Euro/kg N that was calculated from another pilot-scale test for nitrogen removal from sludge digestion liquors[4]. Gut et al.(2006) [5] also investigated the performance of a semi-industrialANAMMOX system (2 m3), i.e. an ANAMMOX moving-bed biofilmreactor, and achieved an average nitrogen removal efficiency of 84%. Dueto its cost-effectiveness and high efficiency, ANAMMOX process hasdrawn considerable attention. Now, the ANAMMOX process is widelyused in many occasions and has a good prospect for the application.

To let the ammonium concentration in the effluent reach the emissionlimit value, not only the tested reactor should have high nitrogen removalperformance, but also the ANAMMOX granular sludge in the reactorshould possess high specific conversion rate and substrate affinity. Sincethe EGSB reactor has been successfully applied in anaerobic processes, itwas introduced to develop the ANAMMOX processes in this study. Thispaper reports the performance of ANAMMOX-EGSB reactor and theproperties of the ANAMMOX granular sludge.

2. Materials and methods

2.1. Synthetic wastewater

Ammonium and nitrite were supplemented to a mineral medium asneeded in the formof NH4Cl andNaNO2, respectively. The composition of

282 T. Chen et al. / Desalination 278 (2011) 281–287

themineralmediumwas (g/L except for trace element solution): KH2PO4,0.01; CaCl2•2H2O, 0.18; MgSO4•7H2O, 0.30; KHCO3, 1.250; EDTA, 0.005;FeSO4, 0.00625, and 1 ml/L of trace element solution. The trace elementsolution contains (g/L): EDTA, 15; H3BO4, 0.014; MnCl2•4H2O, 0.99;CuSO4•5H2O, 0.25; ZnSO4•7H2O, 0.43; NiCl2•6H2O, 0.19; CoCl2•6H2O,0.24;NaMoO4•2H2O, 0.22; NaSeO4•10H2O, 0.21 and NaWO4•2H2O, 0.05(adapted from [6]).

2.2. ANAMMOX inoculum

Inoculum was taken from a lab-scale ANAMMOX reactor. Thesuspended solids (SS) and volatile suspended solids (VSS) of theinoculum were 40.65 and 34.82 g/L, respectively. The lab-scaleANAMMOX reactor was initially inoculated with anaerobic granularsludge taken from a paper mill wastewater treatment plant (5000 m3,located in Zhejiang Province, China). The average diameter of theanaerobic granular sludge was 2.2 mm, and the VSS/TSS (totalsuspended solids) was 85% [7]. The reactor was successfully startedup and subsequently operated stably for 2 years before conducting theexperiments.

2.3. ANAMMOX bioreactor

The ANAMMOX-EGSB reactor system was illustrated in Fig. 1. TheEGSB reactor is an innovation of UASB reactor in which the liquid up-flow velocity is larger [8]. It was operated in an upflow and continuousmode with biomass retention. The total volume of reactor was 1.2 Lwith a working volume of 1.0 L, the reactor was covered with blackcloth to avoid inhibition caused by light [9]. The sampling ports weredistributed vertically on the reactor with the mutual distance of 250millimeters. The influent was purged with 95% Ar–5% CO2 in order tomaintain anaerobic condition. The synthetic wastewater was pumpedat the bottom of the reactor by using peristaltic pump. The effluentwas collected in the effluent tank after passing through the gas–liquid–solid separator. The granules settled at the bottom of thereactor and the gas escaped from the top of the reactor.

2.4. Experimental design

2.4.1. Nitrogen removal performance of ANAMMOX-EGSB reactorIn order to investigate the performance of EGSB reactor, nitrogen

loading rate (NLR) was elevated by means of increasing the influent

9

84

1

2

5

6

5

5

7

3

10

Fig. 1. Schematic diagram of ANAMMOX-EGSB system. (1— influent tank, 2— pump, 3—

EGSB reactor, 4 and 6 — sludge discharge pipe, 5 — sampling pipe, 7—pedestal, 8 — gas–liquid–solid separator, 9 — wet gas-flow meter, 10— effluent tank).

substrate concentrations or shortening the hydraulic retention time(HRT) while all the other operational parameters were held constant.TheEGSB reactorwasoperated at35±1 °C. InfluentpHwas always keptin the range of 6.8–7.0 by dosing hydrochloric acid [10]. During thecontinuous operation, stop increasing the influent substrate concentra-tions (ammonium or nitrite) when it is around 230 mg N/L, and thenelevate the NLR by decreasing the HRTs. The reactor was runwith shortHRT and low substrate concentrations to enrich ANAMMOX granularsludge with high conversion rate and substrate affinity. When theammoniumconcentration in the effluentmet the emission limit valueof15 mg N/L in the Chinese integrated wastewater discharge standard(GB8978-1996), the nitrogen removal performance of EGSB reactorwassupposed to be good. Then continue elevating NLR, or else, stopelevating NLR and calculated the corresponding NRR to estimate theperformance of ANAMMOX-EGSB reactor.

2.4.2. ANAMMOX granular sludge propertiesFive completely-mixed reactors were used to study the properties of

ANAMMOX granular sludge. The granular sludge was taken from theANAMMOX-EGSB reactor on day 55. The operation conditions of thisexperiment including the temperature and influent pH were the sameas those of the ANAMMOX-EGSB reactor. The reactors used for thisexperiment had the same shape, but different volume (100 mL) withtheANAMMOX-EGSB reactor. In this experiment, theHRTwasfixed, thesubstrate concentrations were elevated until the specific conversionrates did not increase. The parameters qmax and KS were determined torepresent the specific conversion rate and substrate affinity of theANAMMOX granular sludge. The qmax and KS could be obtainedaccording to Monod model (Eq. 1) [11].

q =dS=dtð Þu

X=

Q S0−Seð ÞVX

=qmaxSKS + S

ð1Þ

where: q, qmax— specific substrate conversion rate, maximal substrateconversion rate (1/d); Q-the influent flow (L/d); V — the reactorvolume (L); X — the concentration of biomass in reactor (mg/L); KS —

half saturation constant (mg/L); S — the substrate concentrations(mg/L).

2.5. Analytical methods

The influent and effluent sampleswere collected everyday andwereanalyzed immediately. Wastewater samples and VSS were analyzedaccording to the standardmethods [12]. The analyzed parameters of thewastewater samples included ammonium concentration, nitrite con-centration, nitrate concentration and pH value.

3. Results

3.1. The nitrogen removal performance of ANAMMOX-EGSB reactor

The EGSB reactor was seeded with 0.6 L inoculum, the initial HRTwas set at 6 h and the initial influent concentrations of ammonium andnitrite were 98 and 112 mg N/L, respectively. The reactor presentsANAMMOX reaction at the first day with the initial NLR of0.84 kg N/(m3·d). Keeping other operational parameters (temperature,influent pH) at constant level, the NLR was elevated either by increasingthe influent substrate concentrations or shortening of HRT. Aftercontinuous operating for about 50 d, the influent concentrations ofammonium and nitrite were increased to 191.63 and 229.64 mg N/L,respectively, and the HRT was shortened to 0.6 h (Table 1). The resultsindicated the ammonium concentration in the effluent was13.67 mg N/L which was lower than 15 mg N/L when the NLR andNRR were as high as 16.85 and 16.26 kg N/(m3·d), and the correspond-ing removal efficiency of ammonium and nitrite reached 92.87% and

Table 1The performance of ANAMMOX-EGSB reactor at different substrate concentrations and HRTs (average values).

Time(d) HRT (h) Inf. concentration(mg N/L) Eff. concentration (mg N/L) Removal efficiency (%) NLR[kgN/(m3·d)]

NRR[kgN/(m3·d)]

Ammonium Nitrite Ammonium Nitrite Ammonium Nitrite

1–4 6 96.24 118.90 37.05 0.07 60.69 99.84 0.85 0.705–8 6 118.96 179.88 3.01 0.06 97.47 99.97 1.20 1.189–11 6 161.50 206.16 3.59 0.23 97.78 99.89 1.47 1.4612–16 6 212.13 232.86 0.00 1.90 100.00 99.18 1.78 1.7717–21 4.8 172.50 206.16 4.43 2.55 97.43 98.76 1.89 1.8622–24 4 213.52 227.30 0.93 5.10 99.56 97.76 2.64 2.6125–27 3.4 213.99 219.51 0.00 1.16 100.00 99.47 3.06 3.0528–30 3 192.54 217.66 0.00 1.58 100.00 99.27 3.28 3.2731–33 2.4 218.56 209.43 3.68 1.79 98.32 99.15 4.28 4.2334–38 2 195.92 196.15 5.36 0.79 97.26 99.60 4.70 4.6339–41 1.7 200.70 198.75 13.05 1.44 93.50 99.28 5.64 5.4342–43 1.5 212.04 237.56 9.65 0.22 95.45 99.91 7.19 7.0444–46 1.2 178.90 233.41 4.31 0.44 97.59 99.81 8.25 8.1547–49 0.9 199.78 224.74 10.22 0.14 94.88 99.94 11.32 11.0450–52 0.6 191.63 229.64 13.67 1.06 92.87 99.54 16.85 16.2653–55 0.3 209.70 255.67 59.20 34.50 71.77 86.51 37.23 29.73

283T. Chen et al. / Desalination 278 (2011) 281–287

99.54%, respectively. The NRR was quite high compared to thoseobtained from previous researches [2,9,10,13–15].

3.2. ANAMMOX granular sludge properties

3.2.1. Conversion properties of ammoniumThe information given in Table 2 demonstrated the specific

ammonium conversion rates of ANAMMOX granular sludge. The datafittingwithMonodmodel (Eq. (1))was shown in Fig. 2. The informationpresented in Fig. 2 suggested that the Monod model is very suitable tocharacterize the ammonium conversion properties of ANAMMOXgranular sludge with correlation coefficients of 0.931, 0.915 and 0.980,respectively. When the HRTs were 1.2, 0.7 and 0.2 h, the qmax and KS ofammonium (qA, KSA) were 281.40 mg N/(g VSS·d), 32.85 mg N/L;293.34 mg N/(g VSS·d), 2.69 mg N/L and 907.13 mg N/(g VSS·d),20.06 mg N/L, respectively.

3.2.2. Conversion properties of nitriteTable 3 presented the specific nitrite conversion rates of ANAMMOX

granular sludge. The analytical results were shown in Fig. 3. It is evidentfrom Fig. 3, thatMonodmodel was reliable to describe nitrite conversionproperties with correlation coefficients of 0.911, 0.956 and 0.952,

Table 2The specific ammonium conversion rates of ANAMMOX granular sludge (average values).

HRT (h) Inf. concentration(mg N/L)

Eff. concentration(mg N/L)

Ammonium removalefficiency (%)

Volumetric ammrate(NLRA) [kgN

1.2 93.20 0.70 99.25 1.49207.13 20.21 90.24 3.31301.35 51.50 82.91 4.82443.17 76.08 82.83 7.09479.30 114.60 76.09 7.66

0.7 125.48 1.19 99.05 4.76243.69 24.49 89.95 9.24343.79 49.24 85.68 13.04435.08 79.35 81.76 16.50494.38 145.40 70.59 18.75

0.2 109.90 11.90 89.17 13.19149.30 22.20 85.13 17.92175.30 27.10 84.54 21.04248.90 45.90 81.56 29.87320.70 108.20 66.26 38.48

a qA=NRRA/X.

respectively. When the HRTs were 1.2, 0.7 and 0.2 h, the qmax, KS fornitrite (qN, KSN) were 203.62 mg N/(g VSS·d), 2.81 mg N/L;322.96 mg N/(g VSS·d), 0.44 mg N/L and 841.76 mg N/(g VSS·d),0.18 mg N/L, respectively.

3.2.3. Conversion properties of nitrogenThe specific nitrogen conversion rates of ANAMMOX granular

sludge were shown in Table 4. The analytical results of the data werepresented in Fig. 4. Fig. 4 suggested that the Monod model wassuitable choice to describe the nitrogen conversion properties withcorrelation coefficients of 0.958, 0.936 and 0.971, respectively. Whenthe HRTs were 1.2, 0.7 and 0.2 h, the qmax, KS for nitrogen (qT, KST)were 404.42 mg N/(g VSS·d), 24.88 mg N/L; 605.71 mg N/(g VSS·d),3.11 mg N/L and 1810.10 mg N/(g VSS·d), 16.43 mg N/L, respectively.

3.2.4. The morphology of the granular sludgeThemorphology of the granular sludgewas presented in Fig. 5. First,

the color of granular sludge at HRT 6 h (on day 1) and 0.3 h (on day 55)was different. At HRT 6 h, the granular sludge was brown, but at HRT0.3 h, the granular sludge turned into red. Second, the anammoxosomein which the ANAMMOX took place was obviously different. The

onium loading/(m3·d)]

Volumetric ammonium removalrate(NRRA) [kg N/(m3·d)]

Specific ammonium conversionrate (qA)a [mgN/(gVSS·d)]

1.48 42.492.99 85.874.00 114.775.87 168.635.84 167.534.26 112.397.52 198.22

10.10 266.3512.20 321.6811.97 315.5711.76 339.0015.25 439.6717.78 512.6524.36 702.2225.50 735.08

0 20 40 60 80 100 120 140 1600

100

200

300

400

500

600

700

800 HRT=1.2h HRT=0.7h HRT=0.2h

q A(m

gN/(

gVS

S.d

))

SA(mg/L)

r2=0.931,qmax

=218.40,KS=32.85

r2=0.915,qmax

=293.34,KS=2.69

r2=0.980,qmax

=907.13,KS=20.06

Fig. 2. The ammonium conversion properties of ANAMMOX granular sludge.

0 20 40 60 80 100 1200

200

400

600

800

1000 HRT=1.2h HRT=0.7h HRT=0.2h

q N(m

gN/(

gVS

S.d

))

SN(mg/L)

r2=0.911,qmax

=203.62,KS=2.81

r2=0.956,qmax

=322.96,KS=0.44

r2=0.952,qmax

=841.76,KS=0.18

Fig. 3. The nitrite conversion properties of ANAMMOX granular sludge.

284 T. Chen et al. / Desalination 278 (2011) 281–287

anammoxosome of the cell at HRT 0.3 h was more compact and darkercompared to the cell at HRT 6 h.

4. Discussion

4.1. The performance of ANAMMOX-EGSB reactor

The reactor performance under different influent substrateconcentrations and HRTs were shown in Table 1. Under the conditionof the ammonium concentration in the effluent lower than 15 mg N/L,the NLR and NRR of the reactor were 16.85 and 16.26 kg N/(m3·d),respectively.

The ANAMMOX-EGSB reactor has good adaptability to substrateconcentrations. When the influent ammonium concentrations were inthe range of 96.24 to 218.56 mg N/L, the effluent ammonium concen-trationwas able tomeet the emission limit value inGB8978-1996 as longas the HRTs were properly adjusted in the range of 0.6–6.0 h.

The results from the ANAMMOX granular sludge properties suggestthat when the NLR and NRR were as high as 27.31 and25.86 kg N/(m3·d), respectively, the corresponding effluent ammoni-um concentration was 11.90 mg N/L and NRE was 94.68%. Tsushima(2007) [13] reported very high NRRwas achieved in a fixed-bed biofilmcolumn reactor. Although the NRR was up to 26 kg N/(m3·d) in this

Table 3The specific nitrite conversion rates of ANAMMOX granular sludge (average values).

HRT(h) Inf. concentration(mg N/L)

Eff. concentration(mg N/L)

Nitrite removalefficiency (%)

Volumetric nitrit(NLRN) [kgN/(m3

1.2 87.07 1.70 98.05 1.39209.48 1.24 99.41 3.35282.48 4.33 98.47 4.52432.58 19.15 95.57 6.92522.73 109.06 79.14 8.36

0.7 133.95 0.23 99.83 5.08261.77 3.35 98.72 9.93307.58 1.77 99.4 11.66365.33 17.16 95.30 13.85468.57 82.37 82.42 17.77

0.2 117.70 0.21 99.82 14.12159.50 0.26 99.84 19.14219.50 10.10 95.40 26.34294.20 21.00 92.86 35.30328.00 89.20 72.80 39.36

a qN=NRRN/X.

reactor, the NRE was only 44.44%. Compared the NLR and NRR with thehigh-rate lab-scale ANAMMOXreactors in theworld (Table 5), we couldconclude that the NLR and NRR were at a high level. And moreover,when theNRRwas almost the same, theNRE in this studywas very highcompared to those reported in the literature [13,15–20].

4.2. ANAMMOX granular sludge prosperities

4.2.1. Specific conversion rateThe maximum specific conversion rates of ANAMMOX sludge on

ammonium, nitrite and nitrogen were 907.13, 841.76 and1810.10 mg N/(g VSS·d), respectively, which are higher than thereported values (qA: 38.65–297.2 mg N/(g VSS·d)[10,21,22], qN:202.96 mg N/(g VSS·d)[21], qT: 300–1800 mg N/(g VSS·d)[13,23,24]).The high specific conversion rates of ANAMMOX granular sludge in thiswork might be the possible reasons that ensure the ANAMMOX-EGSBrector possesses higher NRR.

4.2.2. Substrate affinityThe minimum KS of ANAMMOX granular sludge on ammonium,

nitrite and nitrogen were 2.69, 0.44 and 3.11 mg N/L, which are lowerthan 48.41–87.1 (KSA) [21,25], 6.55–15.39 (KSN) [21,25]and 84.37 mg/L(KST) [26]. Stours et al. (1999) [27] reported that the KSA and KSN were

e loading rate·d)]

Volumetric nitrite removal rate(NRRN) [kgN/(m3·d)]

Specific nitrite conversion rates(qN)a [mgN/(gVSS·d)]

1.37 39.223.33 95.664.45 125.776.61 189.926.62 190.034.59 120.928.86 233.68

10.49 276.5411.94 314.8413.24 349.2314.10 406.4219.11 550.8425.13 724.3632.78 945.0628.66 826.06

Table 4The specific nitrogen conversion rates of ANAMMOX granular sludge (average values).

HRT(h) Inf. concentration(mg N/L)

Eff. concentration(mg N/L)

Nitrogen removalefficiency (%)

Volumetric nitrogen loadingrate(NLRT) [kg N/(m3·d)]

Volumetric nitrogen removalrate(NRRT) [kg N/(m3·d)]

Specific nitrogen conversionrates(qT)a [mgN/(gVSS·d)]

1.2 180.27 2.40 98.67 2.88 2.85 81.71416.61 21.45 94.85 6.67 6.32 181.53583.83 55.83 90.44 9.34 8.45 242.55875.75 95.23 89.13 14.01 12.49 358.55

1002.03 223.66 77.70 16.03 12.45 357.560.7 259.43 1.42 99.45 9.84 8.85 233.31

505.46 27.84 94.49 19.17 16.38 431.90651.37 51.01 92.17 24.70 20.59 542.89800.41 96.51 87.94 30.35 24.14 636.52962.95 227.77 76.35 36.52 25.21 664.80

0.2 227.60 12.11 94.68 27.31 25.86 745.43308.80 22.46 92.73 37.06 34.36 990.51394.80 37.20 90.58 47.38 42.91 1237.01543.10 66.90 87.68 65.17 57.14 1647.28648.70 197.40 69.57 77.84 54.16 1561.14

a qT=NRRT/X.

285T. Chen et al. / Desalination 278 (2011) 281–287

equal to or less than 0.1 mg N/L when the ANAMMOX sludge withdiameter less than 50 μm was used. In this study, the diameters ofANAMMOX granular sludge were at millimeter scale, and the KS valueswere slightly higher than that reported by Stours et al. (1999) [27]. Allthese illustrate that the ANAMMOX granular sludge obtained from theANAMMOX-EGSB reactor has high substrate affinity which guaranteesthe nitrogen concentration in the effluent meet the discharge standard.

The emission limit value of ammonium concentrations is15 mg N/L, the KSA is 2.69 mg N/L. The permissible emission concen-tration of ammonium is 5.58 times higher than the KSA. It means thatthe ANAMMOX granular sludge is still able to reach their maximumconversion rates even though the ammonium concentrations in theeffluent reach the emission limit value.

4.2.3. The morphology of the granular sludgeThe hydroxylamine oxidoreductase and hydrazine oxidoreductase

are two key enzymes of the ANAMMOX metabolic pathway. Both ofthese enzymes are rich in heme c, which endows the granular sludgewith the carmine color [28,29]. It was also reported that the color ofANAMMOX granules at high loading rate were uniquely carmine andthe hemewas presumed to play a key role to attribute the carmine colorof ANAMMOX sludge [30]. In this study, the color of the granular sludge

0 50 100 150 200 2500

200

400

600

800

1000

1200

1400

1600

1800

HRT=1.2h HRT=0.7h HRT=0.2h

q T(m

gN/(

gVS

S.d

))

ST(mg/L)

r2=0.958,qmax

=404.42,KS=24.88

r2=0.936,qmax

=605.71,KS=3.11

r2=0.971,qmax

=1810.10,KS=16.43

Fig. 4. The nitrogen conversion properties of ANAMMOX granular sludge.

atHRT0.3wasmuch fresher than the color of granular sludge atHRT6 h.The NRR at HRT 0.3 h was higher than the NRR at HRT 6 h, whichindicated that along with the increase of NRR, the ANAMMOX granularsludge gradually turned into red. The similar phenomenon wasobserved by other researchers [30].

TEM performed on the granular sludge taken from the EGSB reactorrevealed that the dominant cells in both granular sludge displayedtypical ultrastructural features of ANAMMOX bacteria. In the cell, thereis an intracellular compartment bounded by a single membrane; themembrane is in a curved configuration which is a typical feature ofanammoxosome [31]. As evident from Fig. 5, the granular sludgedominated byANAMMOXcells. Themorphology of theANAMMOX cellsin the granular sludge showed some differences of the anammoxosomein which the ANAMMOX reaction takes place. The membrane of theanammoxosome contains ladderane lipids which provide a densemembrane around anammoxosome [32]. Molecularmodeling indicatedthat the ladderane lipids surrounding the anammoxosome are tightlypacked [32]. The compact and darker anammoxosome of the cell at HRT0.3 h might be due to the ANAMMOX reaction was more active and theNRR was higher at HRT 0.3 h.

4.3. The feasibility of the ANAMMOX-EGSB reactor in the industry

The first full-scale ANAMMOX reactor in the world was started inRotterdam [2]. And the maximum NRR was 9.5 kg N/(m3·d) which isextremelyhighcompared to the conventionalnitrification–denitrificationprocess (lower than 0.5 kg N/(m3·d))[3]. Up to now, many ANAMMOXreactors in pilot or full scales are applied all over the world (Table 5)[5,33–36]. Overall, the NRR of most of them are around 0.6–2 kg N/(m3·d),however themaximumvaluesare limitedby theavailableinfluent load and are not amaximumNRR of ANAMMOX reactor. TheNRRand NRE of the ANAMMOX-EGSB reactor in this study were high.Furthermore, the ANAMMOX granular sludge has high specific conver-sion rate and low KS, the high specific conversion rate could guarantee theANAMMOX-EGSB reactor had high removal rate which have the potentialdecrease volume requirements and electrical energy, this is verybeneficial to the engineering application, in themeantime, the low KS

could ensure the ammonium concentration in the effluent was able tomeet thedischarge standardwhichwas conducive to the environmentalprotection and water resource recycling.

NLR and NRR could be elevated bymeans of increasing the influentsubstrate concentrations or shortening the HRT. Evidences fromTable 2, 3 and 4 shown that, on the premise of the ammoniumconcentration in the effluent meet the discharge standard, shorteningthe HRT was a more effective way to elevate NRR. To meet the

b

a

p

pa

1 2

3 4

a

Fig. 5. The morphology of the granular sludge. ((a), (b) — the morphology of the granular sludge at HRT 6 h and 0.3 h (on day 1 and 55), a-anammoxosome, where the ANAMMOXreaction takes place, is surrounded by a single membrane; p-paryphoplasm; the scale bar in 1 and 3=1 mm, and in 2 and 4=0.5 μm).

286 T. Chen et al. / Desalination 278 (2011) 281–287

discharge standard, the relationship between influent substrateconcentration and HRT should be taking into account.

5. Conclusions

1) The ANAMMOX-EGSB reactor has excellent performance to meetdischarge standard in terms of the effluent ammonium concen-tration. When the effluent ammonium concentration was11.90 mg N/L which is lower than 15 mg N/L, the NLR, NRR and

Table 5Overview of the NLR and NRR of ANAMMOX reactors in the world.

Reactor type Volume N

Lab scale Up-flow fixed-bed column reactor 0.8 L 58Up-flow Anammox column reactor 5.8 L 20Anaerobic up-flow granular bed anammox reactor 1.3 L 23Anaerobic biological filtrated 0.2 L 19Anammox upflow filter system 1.0 L 7.Upflow anaerobic sludge blanket 1.1 L 13Gas-lift reactor 7 L 2.EGSB 1.0 L 27

In pilot or full scale Moving bed biofilm reactor 2.1 m3 0.Rotating Biological Contactors 240 m3 NSequencing batch reactor 500 m3 NMoving bed 67 m3 NGranular sludge bioreactor 70 m3 10

NRE were 27.31 kg N/(m3·d), 25.86 kg N/(m3·d) and 94.68%,respectively. The nitrogen removal efficiency is high and theeffluent substrates concentrations are low compared to thoseobtained from past researches.

2) The ANAMMOX-EGSB reactor has good adaptability to the substrateconcentrations.When the influent ammoniumconcentrationswere inthe range of 96.24 to 218.56 mg N/L, the effluent can be controlledunder the emission limit value of ammonium in GB8978-1996 as longas the HRTs were properly adjusted in the range of 0.6 to 6.0 h.

LR [kg N/(m3·d)] NRR [kg N/(m3·d)] NRE [1](%) Country Reference

.5 26.0 44.4 Japan [13]

.5 17.5 85.37 Japan [20]

.33 14.0 60±7 Japan [15]

.1 11.5 60.21 Japan [19]34 6.11 83.24 China [18].92 11.70 84.05 China [17]0 1.76 88 Spain [16].31 25.68 94.68 China This study133 0.122 25.0–97.4 Sweden [5]ot available 1.7 Not available U.K. [33]ot available 0.6 83.9±1.8 Austria [34]ot available 1 Not available Germany [35]

9.5 90–95 Netherlands [36]

287T. Chen et al. / Desalination 278 (2011) 281–287

3) The ANAMMOX granular sludge has high specific substrateconversion rates. The qmax of ammonium, nitrite and nitrogenwere 907.13, 841.76 and 1810.10 mg N/(g VSS·d) which isextremely high compared to those reported in literatures.

4) The ANAMMOXgranular sludgehas great substrate affinity, the KS ofANAMMOX granular sludge to ammonium, nitrite and nitrogenwere 2.69, 0.44 and 3.11 mg N/L which is significantly stronger thanthat in the similar studies.

Acknowledgements

The authors wish to thank the Natural Science Foundation of China(No. 30770039), the National High-tech Research and DevelopmentProgram of China (No. 2006AA06Z332) and the National KeyTechnologies Research and Development Program of China (No.2008BADC4B05) for the partial support for this study.

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