partial nitrification and nutrient removal in intermittently aerated sequencing batch reactors...

ORIGINAL PAPER

Partial nitrification and nutrient removal in intermittently aeratedsequencing batch reactors treating separated digestate liquidafter anaerobic digestion of pig manure

Mingchuan Zhang • Peadar G. Lawlor •

Guangxue Wu • Brendan Lynch • Xinmin Zhan

Received: 1 December 2010 / Accepted: 19 May 2011 / Published online: 5 June 2011

� Springer-Verlag 2011

Abstract The performance of an intermittently aerated

sequencing batch reactor (IASBR) technology was inves-

tigated in achieving partial nitrification, organic matter

removal and nitrogen removal from separated digestate

liquid after anaerobic digestion of pig manure. The

wastewater had chemical oxygen demand (COD) concen-

trations of 11,540 ± 860 mg/L, 5-day biochemical oxygen

demand (BOD5) concentrations of 2,900 ± 200 mg/L and

total nitrogen (TN) concentrations of 4,041 ± 59 mg/L,

with low COD:N ratios (2.9) and BOD5:COD ratios (0.25).

Synthetic wastewater, simulating the separated digestate

liquid with similar COD and nitrogen concentrations but

BOD5 of 11,500 ± 100 mg/L, was also treated using the

IASBR technology. At a mean organic loading rate of

1.15 kg COD/(m3 d) and a nitrogen loading rate of

0.38 kg N/(m3 d), the COD removal efficiency was 89.8%

in the IASBR (IASBR-1) treating digestate liquid and 99%

in the IASBR (IASBR-2) treating synthetic wastewater.

The IASBR-1 effluent COD was mainly due to inert

organic matter and can be further reduced to less than

40 mg/L through coagulation. The partial nitrification

efficiency of 71–79% was achieved in the two IASBRs and

one cause for the stable long-term partial nitrification was

the intermittent aeration strategy. Nitrogen removal effi-

ciencies were 76.5 and 97% in IASBR-1 and IASBR-2,

respectively. The high nitrogen removal efficiencies show

that the IASBR technology is a promising technology for

nitrogen removal from low COD:N ratio wastewaters. The

nitrogen balance analysis shows that 59.4 and 74.3% of

nitrogen removed was via heterotrophic denitrification in

the non-aeration periods in IASBR-1 and IASBR-2,

respectively.

Keywords Intermittent aeration � Nitrogen removal �Partial nitrification � Pig manure �Separated digestate liquid

Introduction

In the European Union (EU), pig farming is a major agri-

cultural industry and large pig farms are now the norm [1].

The pig production sector in Ireland contributes 6% to the

gross agricultural output and is the third most important

agricultural sector [2]. It is estimated that 3,167,100 m3 of

pig manure (PM) is produced in Ireland annually, con-

taining 13,041 tonnes of nitrogen (N) and 2,484 tonnes of

phosphorus (P). Pig manure contains high total volatile

solids ranging 1–10%, total Kjeldahl nitrogen, ammonium

nitrogen (NH4?-N), and chemical oxygen demand (COD).

The normal method of recycling PM is to land spread it

for its fertilizer value. In Ireland, the Nitrates Directive

Action Plan (S.I. No.378/2006) and the European Com-

munities Good Agricultural Practice for the Protection of

Waters 2009 (S.I. No.101 of 2009) has imposed immense

restrictions on the use of PM on grassland and cereals. It

regulates that the maximum amount of animal manure that

M. Zhang � X. Zhan (&)

Civil Engineering, College of Engineering and Informatics,

National University of Ireland, Galway, Ireland

e-mail: xinmin.zhan@nuigalway.ie

M. Zhang � P. G. Lawlor � B. Lynch

Teagasc, Pig Development Department, Animal and Grassland

Research and Innovation Centre, Moorepark, Fermoy, Co. Cork,

Ireland

G. Wu

Research Center for Environmental Engineering

and Management, Graduate School at Shenzhen,

Tsinghua University, Shenzhen 518055, China

123

Bioprocess Biosyst Eng (2011) 34:1049–1056

DOI 10.1007/s00449-011-0556-5

can be applied to land every year is equivalent to

170 kg organic N/ha. Many spread-lands are no longer

suitable for land spreading of PM because organic nitrogen

loading from grazing livestock is already at or approaching

the 170 kg N/ha limit [3].

Under these circumstances, several technologies are

exploited for disposal of PM. Available technologies

include anaerobic digestion (AD), aerobic treatment using

suspended-growth activated sludge and fixed-growth bio-

film processes, air stripping, etc. [4–6]. Among them, AD

is a sustainable technology. Through AD, methane gas is

recovered with the achievement of COD removal of

60–90%. However, after AD, most of NH4?-N in PM, up to

800–4,000 mg NH4?-N/L, still remains in the digestate [7,

8]. In practice, the digestate containing high NH4?-N can

be used as fertilizer. However, considering the constraints

of the nitrates directive regulations, further treatment to

remove nitrogen and organic matter from the digestate is

necessary before discharge into water bodies or land-

spreading.

Conventional biological nitrogen removal (BNR) con-

sists of two successive steps: (1) autotrophic nitrification in

which NH4?-N is oxidized to nitrite (NO2

--N) and then

nitrate (NO3--N) by nitrifiers under aerobic conditions;

and (2) heterotrophic denitrification in which NO3--N is

reduced to nitrogen gas (N2) by heterotrophic denitrifiers

under anoxic conditions with organic carbon as the electron

donor. Efficient nitrogen removal via conventional BNR is

achieved at COD:N ratios of above 5–6 [9]. COD:N ratios

in digestate after AD are much lower. For the digestate

liquid used in the present study, the COD:N ratio was 2.9

and 5-day biochemical oxygen demand (BOD5):N ratio

was only 0.7. External carbon sources, like methanol, can

be added in the denitrification step to achieve efficient

nitrogen removal [10, 11]; however, this increases the

operational cost for pig farms.

BNR can also be achieved without provision of organic

carbon sources through anaerobic ammonium oxidation

(ANAMMOX). Autotrophic ANAMMOX microorganisms

oxidize NH4?-N (electron donor) to N2 with NO2

--N as

the electron acceptor [12]. As for the ANAMMOX process,

stable nitrite accumulation is the prerequisite step. Using

partial nitrification followed by ANAMMOX for BNR

saves 25% of the aeration cost in nitrification and does not

require the addition of external organic carbon in the

denitrification step. Efficient partial nitrification has been

observed in intermittently aerated sequencing batch reac-

tors (IASBRs) treating wastewater [13, 14]. It is reported

that IASBRs treating slaughterhouse wastewater achieved a

NO2--N level of up to 96% of the total oxidized nitrogen

(TON, NO2--N and NO3

--N), in addition to COD and

total nitrogen (TN) removals from wastewater of more than

94 and 92%, respectively [15, 16].

In this study, the efficiency of long-term partial nitrifi-

cation in IASBRs treating separated liquid after anaerobic

digestion of PM was investigated in addition to the per-

formance of IASBRs in COD and nitrogen removal.

Nitrogen in the treated wastewater from the IASBR reac-

tors could be further reduced in an ANAMMOX reactor

before discharge.

Materials and methods

Intermittently aerated sequencing batch reactors

Two identical laboratory-scale IASBRs were constructed in

the Environmental Lab, National University of Ireland,

Galway (Fig. 1). One reactor (IASBR-1) treated the sepa-

rated digestate liquid after anaerobic digestion of PM and

the other (IASBR-2) treated synthetic wastewater simu-

lating the digestate. The reactors were made from trans-

parent Plexiglas, each having an effective volume of 10 L

with an inner diameter of 194 mm and a height of 400 mm.

Each reactor was stirred with a rectangular mixing paddle

(100 mm 9 80 mm). The air was supplied using aquarium

air pumps through air diffusers installed at the bottom of

the reactors, and the air flow rate was controlled by air flow

meters. The air flow rate during the aeration period was

0.8–0.9 L air/min. The temperature of the two IASBRs

was controlled at 26 ± 1 �C, simulating the digestate

temperature after AD and separation. MasterFlex L/S

peristaltic pumps were used to feed the influent wastewater

into the reactors and withdraw the treated wastewater.

Programmable timers (Samson Electric Wire, Germany)

were used to control the operation of the IASBRs.

The IASBRs were operated in 8-h cycles. The opera-

tional phases in a cycle are shown in Fig. 2. After 1 h non-

aeration period in which the fill phase lasting 5 min was

included, the reactors were intermittently aerated with four

successive 50-min aeration/30-min non-aeration periods.

Then, after the fifth 50-min aeration, the settle phase lasted

40 min. The effluent was withdrawn in the last 10 min.

Every day, 660 mL of mixed liquor was discharged from

each reactor immediately before the settle phase, to

maintain a sludge retention time of 15 days.

Separated digestate liquid and the synthetic wastewater

The separated digestate liquid was taken from a mesophilic

pig manure digester on a pig farm in Co. Kerry, Ireland. A

centrifuge, in addition with alum and polyacrylamide

(PAM), was used to reduce solids from the digestate. The

separated digestate liquid was delivered to the lab, and

stored in a refrigerator at 4 �C until use. The wastewater

was fed to IASBR-1 at loading rates of 1.15kg

1050 Bioprocess Biosyst Eng (2011) 34:1049–1056

123

COD/(m3 d) and 0.38 kg NH4?-N/(m3 d). Table 1 lists

the average water quality of the separated digestate liquid.

It can be seen that the COD:N ratio was 2.9 and NH4?-N

was up to 94.2% of TN. BOD5 was only 25.1% of COD,

indicating a low proportion of readily biodegradable

organic matter in the wastewater.

To understand influence of the low level of easily bio-

degradable organic matter on nitrogen removal, organic

matter removal and partial nitrification in the IASBR

technology, synthetic wastewater which had similar COD,

TN and NH4?-N levels as in the separated digestate liquid

was treated in IASBR-2. The average volatile fatty acids

(VFA) concentration in the separated digestate liquid was

2,330 mg/L. Thus, the synthetic wastewater contained

2.8 g/L sodium acetate. The other components of the

synthetic wastewater included 10 g/L glucose, 17.6 g/L

(NH4)2SO4, 1.2 g/L KH2PO4, 20 g/L NaHCO3, 100 mg/L

NaCl, 200 mg/L MgCl2, 20 mg/L FeCl2, 20 mg/L MnSO4

and 2 g/L yeast. The synthetic wastewater had a much

higher BOD5 level than the separated digestate liquid.

The two IASBRs were seeded with activated sludge

taken from a local municipal wastewater treatment plant

(WWTP). The initial biomass concentrations in the IAS-

BRs after seeding were 2.4 g SS/L, and the volatile sus-

pended solids (VSS)/SS ratio was 92%.

Analytical methods

COD, BOD5, SS and VSS were tested in accordance with

the standard APHA methods [17]. Soluble COD was

measured after centrifuging samples for 3 min at

14,000 rpm. 1.2 lm pore size GC/F filter papers (What-

man, UK) were used for SS and VSS measurement. NH4?-

N, NO2--N and NO3

--N concentrations were measured

Influenttank

Influentpump

Effluenttank

Effluentpump

Mixer

Heater

Airpump

Flowmeter

Timer

Reactor

pH

DO

Datarecorder

Fig. 1 Schematic diagram of

the IASBR systems

Operation

Draw

0 30 60 110 140 190 220 270 300 330 380 430 470 480Time(min)

Fill

Non-aeration Aeration Settle draw+idle

Fig. 2 A complete operational cycle of IASBR systems

Table 1 Characteristics of the real and synthetic wastewater treated in IASBRs

COD (mg/L) BOD5 (mg/L) NH4?-N (mg/L) TN (mg/L) COD:N BOD5:N

Digestate 11,540 ± 860 2,900 ± 200 3,808 ± 98 4,041 ± 59 2.9:1 0.7:1

Synthetic wastewater 12,000 ± 200 11,500 ± 100 3,810 ± 25 4,015 ± 90 3.0:1 2.9:1

Bioprocess Biosyst Eng (2011) 34:1049–1056 1051

123

with a Konelab nutrient analyzer (Konelab 20, Thermo,

USA). TN was measured with Hach TN kits (Hach, USA).

A pH probe (pH 320, WTW, Germany) and dissolved

oxygen (DO) sensor (Unisense, Denmark) were used for

pH and DO measurement, respectively.

The nitrite accumulation efficiency (g) is a term used to

describe the performance of IASBRs in partial nitrification:

g ¼ SNO2

SNO2þ SNO3

� 100% ð1Þ

where, SNO2and SNO3

are the concentrations of NO2--N

and NO3--N in the effluent, respectively.

AOR and NOR were measured using batch experi-

ments modified from the one used by Kim et al. [18]: All

batch experiments were carried out in 1 L beakers where

air diffusers were installed at the bottom. Washed acti-

vated sludge was added into the beakers, with the addition

of tap water to reach the effective volume of 800 mL, and

the SS concentrations in the beakers were close to those

inside the reactors. When measuring AOR, NH4Cl was

added in the beakers to obtain specified NH4?-N con-

centrations which were closed to NH4?-N concentrations

in one operational cycle in the two reactors. Then, the

aeration commenced and liquid samples were taken from

the reactors at intervals for the measurement of NH4?-N,

NO2--N and NO3

--N concentrations. The reduction rates

of NH4?-N at various initial NH4

?-N concentrations were

calculated. The half-saturation constant (KS) and the

maximum specific oxidation rates (rmax) were simulated

using the Monod equation [19]. When measuring NOR,

the procedure applied was the same as mentioned above,

but NaNO2 was added into the beakers rather than NH4Cl.

AOR and NOR was measured at two aeration strategy:

DO concentrations of 4 or 1.2 mg/L by controlling the

aeration rate.

Results and discussion

Overall performance of IASBRs in removals of organic

matter and nitrogen

The two reactors were operated for 5 months. Figure 3

shows the performance of the two IASBRs in removing

COD. The average COD removal efficiency in IASBR-1

was 89.8%, while it was over 99% in IASBR-2. Since the

BOD5:COD ratio was only 25.1% in the separated dige-

state liquid, the results clearly show that the IASBR tech-

nology was capable of removing slowly biodegradable

organic matter under a long hydraulic retention time

(HRT), which was around 10 days. IASBR-1 effluent was

added to flasks in addition with activated sludge taken from

the reactor, and then air was continuously provided for

8 days; there was no evident decrease in COD, indicating

that most of the remaining COD in IASBR-1 effluent was

inert organic matter. The high COD removal in IASBR-2

was understandable as the synthetic wastewater contained a

much higher concentration of easily biodegradable organic

matter compared with the separated digestate liquid.

The remaining COD in IASBR-1 effluent can be further

reduced by means of coagulation. A series of standard jar

tests were carried out. Using 200 mg/L FeCl3 as the

coagulant and 10 mg/L PAM as the coagulant aid, the

COD level was reduced to less than 40 mg/L and BOD5

was close to zero. Therefore, IASBR-1 effluent can be

further treated by means of coagulation to the COD levels

acceptable for discharge.

Nitrite accumulation appeared immediately in both

IASBRs (Fig. 4). However, the effluent NH4?-N level rose

and the nitrification efficiency worsened from Day 3.

During this period, a serious pH decrease was observed in

IASBR-1: the pH value was decreased from 7.9 to 6.2 in

the first 10 days (Fig. 5). The average alkalinity in the pig

digestate was 21.6 g/L, which was not sufficient to sustain

stable pH because nitrification of high concentrations of

NH4?-N consumed alkalinity [9]:

80:7NHþ4 þ 114:55O2 þ 160:4HCO�3! C5H7NO2 þ 79:7NO�2 þ 82:7H2Oþ 155:4H2CO3

ð2Þ

134:5NO�2 þ NHþ4 þ 62:25O2 þ HCO�3 þ 4H2CO3

! C5H7NO2 þ 134:5NO�3 þ 3H2O: ð3Þ

If the nitrogen removal efficiency was around 77–83%,

the addition of 4.1–5.3 g/L of alkalinity into the waste-

water was required to sustain stable pH. An additional 7 g/L

of alkalinity was added to the digestate from Day 13. The

decrease in pH value was immediately reversed and pH

0

20

40

60

80

100

0

200

400

600

800

1000

1200

1400

1600

0 40 80 120 160

CO

D r

emov

al (

%)

Eff

luen

t C

OD

(m

g/L

)

Duration (d)

Fig. 3 Performance of COD removal in IASBRs (filled squareeffluent COD in IASBR-1; open square effluent COD in IASBR-2;

filled triangle COD removal efficiency in IASBR-1; open triangleCOD removal efficiency in IASBR-2)

1052 Bioprocess Biosyst Eng (2011) 34:1049–1056

123

was increased to 8.0 on Day 32. After Day 32, the amount

of alkalinity added was decreased from 7 to 4.5 g/L. After

pH adjustment, the NH4?-N oxidation rate (AOR)

increased, and the effluent NH4?-N concentration dropped

to below 10 mg/L from Day 30. The increase in the

effluent NH4?-N concentration on Day 99 and Day 106

was due to the error with the programmable timer, which

disrupted aeration. The effluent NH4?-N level in IASBR-2

was higher than in IASBR-1, due to the facts as follow: (1)

high levels of biodegradable organic matter existed in

IASBR-2; and (2) there was a relatively lower DO in

IASBR-2 operational cycles and DO was not above 1 mg/L

until the end of the fifth aeration period (Fig. 6). The

activity of autotrophic bacteria in IASBR-2 was inhibited.

The pH value in IASBR-2 was in the range of 7.6–7.7,

which was very stable from the commencement of the

experiment. The reasons were: (1) there was efficient

denitrification in IASBR-2, with nitrogen removal of 97%,

causing the recovery of alkalinity [9]:

0:57C18H19O9Nþ 3:73NO�3 þ 3:73Hþ

! 1:65N2 þ 5:26CO2 þ 3:80H2Oþ C5H7NO2 ð4Þ

and (2) nitrification was not as efficient as in IASBR-1.

After Day 80, an extra 1.2 g/L alkalinity was added to the

synthetic wastewater. The pH value was increased to above

8, but there was no increase of the nitrification efficiency.

On average, nitrogen removal of 76.5% was achieved in

the stable period in IASBR-1. The nitrite accumulation

efficiency was very stable, at 77–79%. There were several

factors contributing to the efficient and stable partial

nitrification. One was high pH in IASBR-1. The pH values

in the two IASBRs ranged 7.7–8.3. When pH is above 7.5,

it may inhibit the growth and activity of nitrite oxidizing

bacteria (NOB). Ciudad et al. [20] reported that partial

nitrification was achieved in the pH range of 7.5–8.6 and

Sinha and Annachhatre [21] have concluded that pH in the

0

20

40

60

80

100

0 40 80 120 160

Duration (d)

NH

4+-N

(mg/

L)

0

20

40

60

80

100

0

200

400

600

800

1000

0 40 80 120 160

Nit

rite

acc

umul

atio

n ef

fici

ency

(%

)

Duration (d)

TO

N (

mg/

L)

(a)

(b)

Fig. 4 Performance of IASBRs in nitrogen removal and partial

nitrification (filled square effluent NH4-N in IASBR-1; open squareeffluent NH4-N in IASBR-2; filled triangle nitrite accumulation

efficiency in IASBR-1; open triangle nitrite accumulation efficiency

in IASBR-2; filled circle TON concentrations in IASBR-1; opencircle TON concentrations in IASBR-2)

6

6.5

7

7.5

8

8.5

0 40 80 120 160

pH

Duration (d)

Fig. 5 Profiles of pH in the IASBRs (filled circle IABSR-1; opencircle IABSR-2)

Fig. 6 Profile of DO and FA in a typical cycle (filled square DO in

IASBR-1; open square DO in IASBR-2; filled triangle FA in IASBR-

1; open triangle FA in IASBR-2)

Bioprocess Biosyst Eng (2011) 34:1049–1056 1053

123

range of 7.5–8.5 is suitable for inhibition of NOB activity.

The second factor was presence of free ammonia (FA) in

the two reactors. The FA level was from 0.5 to 27.5 mg/L

in IASBR-1, and 2.3 to 18.9 mg/L in IASBR-2 (Fig. 6). FA

concentrations in the range of 0.1–150 mg/L can benefit

partial nitrification [22].

Another factor might be the intermittent aeration strat-

egy used in the IASBR technology. Li et al. also observed

efficient partial nitrification in their IASBRs treating

slaughterhouse wastewater [23].

To confirm that the intermittent aeration strategy was an

important factor for partial nitrification, batch experiments

were carried out at two aeration strategies: (1) 30 min non-

aeration before aeration, and (2) direct aeration. In batch

experiments, activated sludge taken from the reactors

(IASBRs) was washed with tap water and added into 0.5 L

beakers (effective volume of 400 mL), in addition with

NaNO2 solutions with the NO2--N concentration of

50 mg/L. Air was provided with air pumps through air

diffusers located at the bottom of the beakers. For the first

aeration strategy, there was no aeration (the mixed liquor

was quiescent in the beakers) for 30 min before the aera-

tion was turned on. For the second aeration strategy, the

aeration commenced immediately when the experiment

commenced. Water samples were taken from the beakers at

intervals for the measurement of NO2--N and NO3

--N

concentrations. Under the first aeration strategy, after

commencement of aeration, the increase in NO3--N was

retarded for 16–18 min (the amount of NO2--N supply was

ample) (Fig. 7), indicating that NO2--N oxidation was not

activated immediately after the aeration started and the lag

time was 16–18 min. Tappe et al. [24] attributed the lag

time of NO3--N oxidation to the different mechanisms of

ammonium oxidizing bacteria (AOB) and NOB in main-

tenance energy demand and starvation recovery dynamics;

AOB can be resuscitated more easily than NOB. The batch

experiment result clearly shows that the intermittent aera-

tion strategy can benefit partial nitrification.

In IASBR-2, the TN removal efficiency was 97%,

higher than that in IASBR-1 due to more easily biode-

gradable organic matter in the synthetic wastewater.

However, even in IASBR-2, the COD:N ratio was 3.0 and

BOD5:N was 2.9, much lower than the optimal COD:N

range, above 5–6, for the conventional BNR process [9].

This shows that the IASBR technology is a promising

technology for nitrogen removal from low COD:N ratio

wastewaters. The nitrite accumulation efficiency was 71%,

and it was lower relative to that in IASBR-1.

With regard to the biomass in IASBR-1 and IASBR-2,

the half-saturation coefficients for substrates (KS) for

NH4?-N oxidation and NO2

--N oxidation were calculated

as 10 and 6.7 mg NH4?-N/L, 1.3 and 2.7 mg NO2

--N/L,

respectively. The maximum specific NH4?-N and NO2

--N

oxidation rates (NOR) (rmax) were calculated as 13.8 mg

NH4?-N/(g VSS h) and 3.0 mg NO2

--N/(g VSS h) in

IASBR-1, and 9.3 mg NH4?-N/(g VSS h) and 4.4 mg

NO2--N/(g VSS h) in IASBR-2, respectively. The ratios of

the NH4?-N oxidation rate to the NO2

--N oxidation rate

were 4.27 and 2.18 when DO was 4 mg/L (in the last

aeration period) in IASBR-1 and IASBR-2, respectively.

When DO was less than 1.2 mg/L (in the first four aeration

periods), the AOR:NOR ratios were as high as 5.44 and

2.77 in IASBR-1 and IASBR-2, respectively.

Figure 6 showed that DO levels rose sharply in the two

reactors in the last aeration period (from 380 to 430 min).

This indicates end of nitrification. If aeration would be

terminated before the sharp increase, the energy input

would be saved [15]. In addition, since the AOR:NOR

ratios at DO of 4 mg/L were higher than those at DO of

1.2 mg/L, maintaining the operation of the IASBR reactors

at lower DO levels would benefit partial nitrification.

Cycle performance and nitrogen balance

The cycle performance of the IASBR system was investi-

gated in a few operational cycles, and a typical cycle

performance on Day 135 was presented. In both IASBRs,

COD reduction was completed within five aeration periods

(Fig. 8). The difference was that, COD degradation was

accomplished in the last aerobic period in IASBR-2; while

in IASBR-1, the COD reduction rate was very low in the

third aeration period and the COD concentration did not

change notably in the remaining period of the cycle.

After 5-min fill, total oxidized nitrogen (TON) linearly

decreased via denitrification (Fig. 9). The denitrification

rates were 29 mg N/(L h) and 36.9 mg N/(L h) in IASBR-

1 and IASBR-2, respectively. It was higher in IASBR-2

due to a sufficient supply of easily biodegradable organic

matter. The denitrification rates decreased gradually. In the

third aeration period in IASBR-1 and the fifth aeration

period in IASBR-2, when most bio-degradable organic

0

1

2

3

4

5

6

0 5 10 15 20 25 30

NO

3- -N c

once

ntra

tion

(m

g/L

)

Time from the commencement of aeration (min)

direct aeration

30 min non-aeration before

Fig. 7 Effects of the aeration strategy on partial nitrification

1054 Bioprocess Biosyst Eng (2011) 34:1049–1056

123

matter was consumed while there was 25 mg NH4?-N/L

remaining, the specific NH4?-N utilization rates were

13.4 NH4?-N/(g VSS h) and 8.5 NH4

?-N/(g VSS h),

respectively.

The TN removals were 76.9 and 96.8% in IASBR-1 and

IASBR-2, respectively. To investigate how nitrogen was

removed or transformed, a nitrogen balance analysis using

Eq. 5 was conducted:

TNi ¼ TNe þ TNs þX

TNdiþ TNa þ TNo ð5Þ

where TNi: amount of nitrogen delivered into the reactor

tank in the fill phase; TNe: amount of nitrogen contained in

effluent withdrawn from the reactor tank in the draw phase;

TNs: amount of nitrogen used for biomass assimilation;PTNdi

: amount of nitrogen removed by means of deni-

trification in non-aeration stages (i = 1, 2, 3, 4, 5), which

was calculated from the reduction of oxidized nitrogen in

the non-aeration periods; TNa: amount of nitrogen removed

via air stripping of ammonia gas; and TNo: nitrogen

removed through other pathways, such as simultaneous

nitrification and denitrification in the aeration periods.

In the typical cycle, 1,347 and 1,338 mg TNi was fed

into IASBR-1 and IASBR-2, respectively. TNe was equal

to 316 and 42 mg in IASBR-1 and IASBR-2, respectively.

As for nitrogen removal through biomass assimilation, the

average nitrogen content in the biomass was measured at

98 mg N/g SS in the two IASBRs. 2.33 g and 2.49 g

sludge was wasted in this cycle, contributing to 76 and

81 mg nitrogen removed (TNs) in IASBR-1 and IASBR-2,

respectively.P

TNdiwas up to 800 and 994 mg in IASBR-

1 and IASBR-2, equal to 59.4 and 74.3% of the total

amount of nitrogen removed, respectively. The nitrogen

removal via air stripping of ammonia gas (TNa), estimated

using the method modified from that of Lei et al. [25], was

equal to 87 and 98 mg in IASBR-1 and IASBR-2,

respectively. So, TNo were 68 and 123 mg nitrogen, about

5 and 9% of total nitrogen removed in IASBR-1 and

IASBR-2, respectively, but this was difficult to quantify.

0

200

400

600

800

1000

1200

1400

1600

0 50 100 150 200 250 300 350 400 450 500

Duration (min)

CO

D in

IA

SBR

-1 (

mg/

L)

0

50

100

150

200

250

300

350

400

CO

D in

IA

SBR

-2 (

mg/

L)

NA A NA A NA A NA A NA A NAFig. 8 Profile of COD

concentrations in a typical cycle

(filled square IASBR-1; opensquare IASBR-2. NA non-

aeration duration; A aeration

duration)

0

100

200

300

400

500

600

700

800

900

1000

0 50 100 150 200 250 300 350 400 450 500

Duration (min)

TO

N c

once

ntra

tion

(m

g/L

)

0

20

40

60

80

100

120

140

160

180

200

NH

4-N

con

cent

rati

on (

mg/

L)

NA A NA A NA A NA A NA A NAFig. 9 Profile of TON and

NH4-N concentrations in the

typical cycle (filled square TON

in IASBR-1; open square TON

in IASBR-2; filled triangleNH4-N in IASBR-1; opentriangle NH4-N in IASBR-2.

NA non-aeration duration;

A aeration duration)

Bioprocess Biosyst Eng (2011) 34:1049–1056 1055

123

Conclusion

This paper studied the performance of the IASBR tech-

nology in partial nitrification, organic matter removal and

nitrogen removal from separated digestate liquid after

anaerobic digestion of pig manure. The results obtained are

as follows:

The COD removal efficiency was up to 89.8 and 99% in

IASBR-1 and IASBR-2, respectively. The effluent COD

from IASBR-1 was inert organic matter and can be further

reduced through coagulation.

Stable and long-term partial nitrification was achieved in

both IASBRs, with a nitrite accumulation efficiency of

77–79% in IASBR-1, and 71% in IASBR-2. One factor

causing and maintaining efficient partial nitrification was

the intermittent aeration strategy. Batch experiments show

that intermittent aeration provided a lag time of 16–18 min

for NOB to recover activity.

77 and 97% of nitrogen removal was achieved in IAS-

BR-1 and IASBR-2, respectively. The results clearly show

that the IASBR technology is a promising technology for

nitrogen removal from low COD:N ratio wastewaters. The

nitrogen balance analysis shows that 59.4 and 74.3% of the

total amount of nitrogen removed was via heterotrophic

denitrification in the non-aeration periods in IASBR-1 and

IASBR-2, respectively.

Acknowledgments This research was funded by Teagasc Walsh

Fellowship (Ref: 2008022).

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