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Feb 20, 2013 (4 years and 8 months ago)

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Nitrifier decay and recovery in a
Moving Bed Biofilm

Reactor
(MBBR)

treating reverse osmosis concentrate


Liu Ye*, Shihu Hu*, Yvan Poussade**, ***, Jurg Keller* and Zhiguo Yuan*
٭

* Advanced Water Management Centre (AWMC), The

University of Queensland, St Lucia, Brisbane, QLD 4072,
Australia

**
Veolia Water Australia, Level 15, 127 Creek Street,
Brisbane, QLD 4000

***
Seqwater, 240 Margaret Street,
Brisbane, QLD 4000


Email addresses:
zhiguo@awmc.uq.edu.au
;

*Corresponding author. Tel: +61 07 33654374; Fax: +61 07
33654726;

Abstract

A two
-
stage moving bed biofilm reactor (MBBR)
is

applied at the Bundamba
advanced water treatment plant (AWTP) (Queensland, Australia) to treat the reverse

osmosis concentrate (ROC) for inorganic nutrient removal. One of the operation
al

challenges for MBBR is to cope with the large fluctuations of the ROC flow. This
study investigated the decay
rates of
ammonia
-
oxidiz
ing bacteria

(
AOB
)

and
nitrite
-
oxidiz
ing
bacteria (
NOB
)

and biofilm detachment
in MBBR
during starvation
for up to
one month
. A
n
intermittent

aeration strategy of 15 min

aeration

every 6 hr

was
applied. This study

also evaluated the activity recovery of
both AOB and NOB

after
normal operation
wa
s

resumed. The results showed that t
he activity loss of AOB and
NOB was relatively minor (< 20%) within 10 days of starvation, which ensured
relative quick recovery of ammonium removal when normal operation resume
d
. In
contrast, the AOB and NOB activit
y

los
s reached 60
-
80% when the starvation time
was longer than 20 days, resulting in slower recover
y

of ammonium removal
after
starvation
. Starvation

for

less than 20 days
didn’t

result in an apparent biomass
detachment from carriers.


Keywords
:
AOB; NOB
;
decay;
MBBR; starvation; ROC



Introduction


Large fluctuations of wastewater flow and composition inherent to the industry
activities is one of the big challenges to a lot of wastewater treatment plants
(WWTPs). It’s crucial to maintain the biomass viab
ility and activity during the long
idle or starvation periods due to the interruptions of wastewater flows (E.g. annual
maintenance or seasonal production variations) to the WWTPs for weeks and even
months.

The Bundamba Advanced Water Treatment Plant (AWTP
), located in Queensland,
Australia,
played a key role in the delivery of
purified recycled water
supply to the
south east Queensland region
. Reverse Osmosis (RO) membrane is used to provide
purified recycled water to secure water supply for the rapidly gr
owing
S
outheast
Queensland region. The Reverse Osmosis Concentrate (ROC) is treated for
inorganic nutrient removal before its discharge to the Brisbane River. The ROC
treatment train includes nitrification in a two
-
stage Moving Bed Biofilm Reactor
(MBBR),
denitrification through anoxic sand filters, and chemical precipitation for
phosphate removal.
However, the ROC flow to the MBBR
is

sometimes interrupted
due to varying demand for water production.

A lot of studies have been done to investigate the
impacts

of starvation on the
bacterial population and activities of activated sludge. It has been well
-
demonstrated
that nitrifiers decayed at a higher rate under aerobic conditions than under anoxic or
anaerobic conditions (Nowak et al., 1994; Siegrist et

al., 1999;

Morgenroth et al.,
2000; Lee and Oleszkiewicz, 2003;
Manser et al., 2006;
Salem et al., 2006
; Hao et
al., 2009
).

In a recent study, Munz et al. (2011) further demonstrated that
t
he aerobic
decay
rate of nitrifiers
increase
d

with
the dissolved
o
xygen

concentration.

S
l
ower decay rates of nitrifiers have

also

been
observed

under
alternating
anaerobi
c, anoxic and aerobic condition
s

(Roslev and
King
, 1996;
Morgenroth et al.,
2000;
Yuan et al., 2000;
Lee and Oleszkiewicz, 2003
; Yilmaz et al., 2007).

Lee and
Oleszkiewicz (2003) reported that nitrifiers decayed under alternating aerobic, anoxic
conditions at a rate that
wa
s 40% lower than
that
under anoxic conditions.
Morgenroth et al. (2000) observed that there was no or little loss (
<
5%) of nitrifying

activities when activated sludge was starved under alternating aerobic,
anoxic/anaerobic conditions for a period of up to
one

week. Yilmaz et al. (2007)
evaluate
d

the effectiveness of a specific operating strategy, which create
d

alternating anaerobic, ano
xic and aerobic conditions, in maintaining the nutrient
removal capacity of activated sludge. Their stud
y

also

show
ed

that both ammonium
-
oxidizing bacteria (AOB) and nitrite
-
oxidizing bacteria (NOB) can actually survive for
weeks and recover their activity

rapidly after start
-
up.

The
MBBR

technology
is well
-
established for

wastewater treatment where bacteria
grow as a biofilm on the protect
ed

surfaces of suspended carriers

(
McQuarrie
, et al.
2011).
However,
how to operate MBBR to cope with large
fluctuations of
influent

flow

is still a big challenge for most plants, and the

alternating operation
al

strategy
has
not been demonstrated
to be effective
for biofilm

systems
yet
. Being able to operate
the MBBR

process in periods without wastewater feed,
a
mmonium

was added at the
Bundamba AWTP

to sustain the activities of AOB and NOB.

An operational strategy
without
requiring
ammonium addition
during flow interruption
is attractive f
rom

operational, environmental and economical perspectives.

The aim of this research
i
s
to monitor nitrifier decay and biofilm detachment
during starvation
with

intermittent
aeration
, also to evaluate the activity
recovery

of both AOB and NOB after normal
operation is resumed.


M
aterial
s

and
Methods

Starvation
reactor set
-
up and operation

Carriers with biomass together with wastewater were collected from the 1
st

stage
reactor of the
full
-
scale MBBR

system

at the Bundamba AWTP and were kept in a
25 L starvation reactor (R1) for starvation tests. The volumetric r
atio of carriers to the
volume of the reactor was around 40%, which was in line with the full
-
scale MBBR.
The reactor was
aerated

intermittent
ly

for

15 min every 6 hours. The biomass was
starved for 31 days. The air flow was manually adjusted to keep disso
lved oxygen
(DO) between 2
-
4 mg/L over the aeration period. Solid and liquid samples were
taken from the reactor on a daily basis (weekdays only) at the end of an aeration
period for the analysis of mixed liqu
or

suspended solid
s

(MLSS), NH
4
+
-
N, NO
2
-
-
N,
NO
3
-
-
N and PO
4
3
-
-
P. pH and DO were measured
regularly
during the period of
starvation.



Batch experiments for measuring activity loss of AOB and NOB


During the starvation period, 2L wastewater
containing 26

carriers was taken from
R1 at the end of an aeration period on Days 5, 10, 21 and 31, and transferred into
two 1 L batch reactors (B1 and B2). Batch tests
described below
were conducted to
determine the AOB and NOB activities. In addition, 2L wastewater al
ong with 26
carriers was collected from the full
-
scale MBBR for batch test on Day 0 to measure
the AOB and NOB activities of the non
-
starved biomass.


At the start of each batch test, NH
4
Cl and NaNO
2

were added to B1 and B2,
respectively, which resulted

in the initial concentrations of 15 mg/L NH
4
+
-
N and 15
mg/L NO
2
-
-
N, respectively. DO in both batch reactors was maintained at 5±0.5 mg/L
to provide a non
-
limiting DO

concentration
. pH was adjusted to around 7.0 by the
addition of 0.1 M NaOH at the beginni
ng of each test, but not controlled in the
remaining time of the test. Each batch experiment lasted for 6
-
8 hr, during which
NH
4
+
-
N, NO
2
-
-
N and NO
3
-
-
N were measured hourly. Decrease in the activities of
AOB and NOB under starvation conditions was assessed by comparing specific
ammonium uptake rates (SAUR) (mgN/carrier.hr) and specific nitrite uptake rates
(SNUR) (mgN/carrier.hr) before and after a cer
tain period of starvation.

Recovery tests and reactor operation


1.5 L wastewater together with 20 carriers was taken from R1 at the end of an
aeration period on Day 5, 10, 21 and 31, respectively, and transferred to another
reactor (R2, recovery reactor
) for recovery tests.

R2 was continuously fed with real ROC wastewater collected weekly from the
Bundamba AWTP. Samples were analyzed on the day of collection for its NH
4
+
-
N
concentration. Extra NH
4
Cl was added to the ROC water to maintain the influent
le
vel of NH
4
+
-
N at an approximate level of 5
-
7 mg
N
/L

(wastewater collected
sometimes contained very low levels of ammonium, e.g. < 2

mg
N
/L
, which was not
ideal for activity tests
)
.
The
hydraulic retention time (HRT) was maintained at 1.5 hr
and DO controlled

by a programming logic controller in the range of 2
-
4 mg/L
,
mimic
king

the
operation at the

Bundamba AWTP
.
The DO controller was an on/off
controller with aeration turned on and off when DO reached
2

and
4

mg/L,
respectively.
During the recovery period, am
monium in the reactor was analysed
every 4 hours during daytime

for 5 days
. DO and pH were monitored continuously
over the whole recovery period
. O
xygen uptake rate (OUR)

was determined
as the
slopes of the DO profiles

in period when aeration was turned o
n.


Analytical Methods

The ammonium (N
-
NH
4
+
), nitrate (N
-
NO
3
-
), nitrite (N
-
NO
2
-
) and orthophosphate (P
-
PO
4
3
-
) concentrations were analyzed using a Lachat QuikChem8000 Flow Injection
Analyzer (Lachat Instrument, Milwaukee, Wisconsin).

Total and soluble
chemical
oxygen demand (CODt and CODs, respectively), total Kjeldahl nitrogen (TKN), total
phosphorus (TP), MLSS and MLVSS were analysed according to the standard
methods (APHA, 1995).


Time (day)
0
5
10
15
20
25
30
NH
4
+
-N, NO
2
-
-N, PO
4
3-
-P (mg/L)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
NO
3
-
-N (mg/L)
0
5
10
15
20
25
30
PO
4
3-
-P
NH
4
+
-N
NO
2
-
-N
NO
3
-
-N
Figure 1
The variation of nutrient concentrations in the
starvati
on
reactor
over

the
starvation

period


Time (day)
0
5
10
15
20
25
30
MLSS (mg/L)
0
100
200
300
400
Figure 2

T
he variation of stripped biomass concentration in the
starvation
reactor during the starvation period

Results and Discussion

Performance of the starvation reactor


Figure 1 shows the nutrient concentration

profile
s measured during the starvation
period

from R1
. The concentration of phosphorus increased gradually, which could
have resulted from cell lysis. Similarly, the rise in the level of nitrate was observed,
which could be attributed to the oxidation of NH
4
+
released by bacterial decay.

Ammonium was undetec
table, indicating all ammonium released as a result of decay
was oxidized by nitrifiers, which provided energy source to nitrifiers to some extent.

The growth of nitrifiers

during aerobic period utilising the ammonia released through
the decay of heterotrophic bacteria can largely compensate for the reduction of
nitrifying activity caused by the decay of nitrifiers (Morgenroth et al., 2000).

However,
the ROC feed to the full
-
scale MBBR
contained limited amount

of organic carbon (<
50

mgCOD/L), and hence
the amount of heterotrophic biomass in the biofilms was
expected to be low (not determined).
















During the whole starvation period, pH in the starvation reactor increased
gradually, from 7.1 on Day 0 to 8.0 at Day 31.













The MLSS profile
i
s shown in Figure 2. MLSS didn’t change significantly within the
first 20 days of starvation and had an average concentration of approximate 200
mg/L, suggesting negligible detachment of biofilm f
rom carriers during that period.
After that, during Day 20
-
31, MLSS increased and reached a concentration of 270
mg/L at the end of starvation. This revealed that biofilm detachment occurred after
25 days of starvation.

After a long time starvation, the in
creased depletion of nutrient
supply to the bacterial growth or maintenance may have resulted in an increase in
the
detachment rates

(
Sawyer

et al., 1998)
.


Activity loss of AOB and NOB


B
atch tests

revealed that

both the NH
4
+
-
N and NO
2
-
-
N oxidation rates decreased
with starvation time, which implied
a loss of activity

of both AOB and NOB. The
decline in both SAUR and SNUR
was

less than 20% in the first 10 days of starvation
(shown in
Figure.3). However, decreases of 42% and 67% in SAUR occurred after
21 and 31 days of starvation, respectively. SNUR followed the same trend, with a fall
of 40% and 53%, respectively, over the same starvation periods. The average decay
rates of AOB and NOB

were determined to be 0.044 d
-
1

and 0.033 d
-
1
, respectively,
through fitting an exponential decay model. Both AOB and NOB had a relatively slow
decay rate.















The decay rates of both AOB and NOB observed in this study were much lower
than those reported in literature. The AOB decay rate in many studies,
as
summarized by Salem et
al.(2006), ranged between 0.15

0.21, 0.025

0.06 and
0.05

0.2d
-
1
, respectively, for activated sludge systems at 20 °C (similar to the
temperature used in this study) under aerobic, anaerobic and anoxic conditions. The
NOB decay rates under the
se

conditions were 0.21, 0.06 and 0.12d
-
1

under aerobic,
anaerobic and anoxic conditions, respectively (Salem et al., 2006). It further
confirmed that the
intermittent aeration strategy
(
15 min

aeration

every 6 hr
)

is a
suitable strategy for maintaining nitr
ifier activity during starvation.
Yilmaz et al. (2007)
reported that, w
ith th
is

operation
al

strategy, the AOB and NOB decay rates

of
a
Fig
ure 3

SAUR and SNUR measured after 0, 5, 10, 21 and 31 days
of starvation. The
regression line
s

were obtained

with an

exponential

decay model


Exponential decay
model (SAUR)

Exponential decay
model (SNUR)

sludge treating abattoir wastewater

were even lower,
being

0.017d
-
1

and 0.004d
-
1
,
respectively. The weekly extra addition

of ammonium and nitrite into the starvation
reactor
during

batch test
s

in
the
Yilmaz

et al. (2007)
study
likely
provided more
electron
donors

and therefore
partially
compensated
for
the nitirifier decay.

In this
study, the batch tests were not carried out in the parent reactor, but in
separate
batch reactors.




Activity recovery after starvation
























Figure 4 shows the ammonium removal in the recovery reactor following 5, 10, 21

and 31 days of starvation. After normal operational conditions were resumed, the
ammonium consumption quickly improved when the starvation was less than 10
days. Compared with the ammonium removal in the full
-
scale plant (data shown in
Figure 5), where th
e results showed the performance of the two
-
stage MBBR rather
than just the first stage, it is regarded that NH4+
-
N removal efficiency recovered to
the original level in 24
-
48 hr when the starvation was less than 10 days, and all
ammonium oxidised was conv
erted to nitrate after 48
-
72 hr recovery. In contrast, the
Figure
4

Ammonium removal

rate

in the recovery

process

after starvation for 5, 10, 21 and 31 days


Fig
ure

5

Ammonium removal in the

f
ull
-
scale two
-
stage MBBR plant in the last quarter of 2010.
Note that the removal was achieved by two stages. No data were available for the first stage for
direct comparison.


ammonium removal recovery was slow in the cases of 21 and 31 days starvation.
These results again suggested that a starvation period of less than 10 days is
preferable, supporting the results obtai
ned for decline in SAUR and SNUR.


Figure
6

presents

the results of
OUR during the recovery
period
after starvation for
0, 5, 10, 21 and 31 days, respectively.
In the cases of

5 and 10 day starvation
,

OUR
increased to around 0.006
-
0.008 mgO
2
L
-
1
min
-
1

carr
ier
-
1

(OUR observed on Day 0)
after
a
recovery
period
of

1
-
2 days. However,
in

the 21 and 31 day cases
, OUR

went
up

slowly and didn’t reach the same
value

within

the 5 day recovery period
, which
further

confirmed our previous conclusion
that a starvation period shorter than
10

days is desirable.










Conclusion


T
he activity loss of both AOB and NOB
under

starvation

conditions

and the
recovery of their activities after resum
ing

normal operation
were evaluated. The
following conclusions can be drawn.



The activity loss of AOB and NOB
is relatively minor (
< 20%) within 10 days
of
starvation, which ensures relative quick recovery o
f ammonium removal when
normal operation resumes;



The AOB and NOB activities loss
is substantial (
reach
ing

60
-
80%
)
when the
starvation time
is

longer than 20 days, resulting in slower recover
y

of
ammonium removal when normal operation resumes;



The intermit
tent aeration strategy of 15 min
aeration
every 6 hr is a suitable
strategy for maintaining nitrifier activity
of MBBR systems
during starvation;
Starvation less than 20 days does not result in an apparent biomass
detachment from carriers.




Fig
ure

6

Oxygen uptake rates in the
recovery

reactor after 0, 5, 10, 21 and 31 days of starvation

Acknowledgments

This work
wa
s financially supported
by
Seqwater
, Australia. Mr. Jason Krzciuk is
acknowledged to the on
-
site help.



References:


APHA, 1995. Standard Methods for the Examination of Water and Wastewater. American
Public Health Association
,Washington, DC.

Hao, X., Wang, Q., Zhang, X., Cao, Y. and Mark Loosdrecht, C.M.v. (2009) Experimental
evaluation of decrease in bacterial activity due to cell death and activity decay in activated
sludge.
Water Research

43
(14), 3604
-
3612.

Lee, Y. and
Oleszkiewicz, J.A. (2003) Effects of predation and ORP conditions on the
performance of nitrifiers in activated sludge systems.
Water Research

37
(17), 4202
-
4210.

Manser, R., Gujer, W., Siegrist, H.
(2006)

Decay processes of

nitrifying bacteria in biologica
l
wastewater treatment systems.
Water Reserach

40
(12), 2416

2426.

McQuarrie, J.P. and Boltz, J.P. (2011) Moving Bed Biofilm Reactor Technology: Process
Applications, Design, and Performance.
Water Environment Research

83
(6), 560
-
575.

Morgenroth, E., Oberma
yer, A., Arnold, E., Bruhl, A., Wagner, M. and Wilderer, P.A. (2000)
Effect of long
-
term idle periods on the performance of sequencing batch reactors, pp. 105
-
113.

Munz, G., Lubello, C. and Oleszkiewicz, J.A. (2011) Modeling the decay of ammonium
oxidizing

bacteria.
Water Research

45
(2), 557
-
564.

Nowak, O., Schweighofer, P. and Svardal, K. (1994) Nitrification inhibition
-

a method for
the estimation of actual maximum autotrophic growth rates in activated sludge systems.
Water Science and Technology

30
(6),
9
-
19.

Roslev, P. And
King, G.M.
(
1995
)

Aerobic and anaerobic starvation

metabolism in
methanotrophic bacteria.
Applied and Environmental Microbiology

61

(4), 1563

1570.

Salem, S., Moussa, M.S. and van Loosdrecht, M.C.M. (2006) Determination of the decay ra
te
of nitrifying bacteria.
Biotechnology and Bioengineering

94
(2), 252
-
262.

Siegrist, H., Brunner, I., Koch, G., Phan, L.C. and Le, V.C. (1999) Reduction of biomass
decay rate under anoxic and anaerobic conditions.
Water Science and Technology

39
(1), 129
-
1
37.

Sawyer, L.K. and Hermanowicz, S.W. (1998) Detachment of biofilm bacteria due to
variations in nutrient supply.
Water Science and Technology

37
(4
-
5), 211
-
214.

Yuan, Z., Bogaert, H., Leten, J. and Verstraete, W. (2000) Reducing the size of a nitrogen
rem
oval activated sludge plant by shortening the retention time of inert solids via sludge
storage.
Water Research

34
(2), 539
-
549.

Yilmaz, G., Lemaire
, R., Keller, J. and Yuan, Z. (2007) Effectiveness of an alternating
aerobic, anoxic/anaerobic strategy for maintaining biomass activity of BNR sludge during
long
-
term starvation.
Water Research

41
(12), 2590
-
2598.