ACCUTEK DSADASA

Desalination 240 (2009) 160 169
*
Domestic wastewater treatment with membrane
two years experience
filtration
A. Blst’akova, I. Bodík*, L. Dancova, Z. Jakubcova
Faculty of Chemical and Food Technology, Institute of Chemical and Environmental Engineering,
Slovak University of Technology Bratislava, Radlinskeho 9, 812 37 Bratislava, Slovak Republic
Tel. +421 252935 384; Fax +421 25249 5243; email: igor.bodik@stuba.sk
Received 27 August 2007; revised 18 December 2007; accepted 25 December 2007
Abstract
This study tested domestic wastewater treatment membrane filtration without external cleaning in sustained
long term operation. Domestic wastewater treatment plant monitoring was performed at the municipal wastewater
treatment plant Devínska Nova Ves, Bratislava between February 2005 and July 2007. Two membrane modules
were tested by immersion in the domestic wastewater treatment plant. The flat sheet membrane module was
operated without external cleaning at a flux of 2060 L/m2 h for 6 months. The hollow fiber membrane module
was operated for 4 months without external cleaning with a flux of 2045 L/m2 h. Parallel operation of flat sheet
and hollow fiber membrane modules showed similar results in effluent water quality. Both membrane modules
were able to effectively remove organic matter (as much as 91%) and more than 97% of /NHþ
4 --N. Nitrogen
removal via denitrification was observed during the short periods with low oxygen concentration. Treated water
contained suspended solids under measurable limits.
Keywords: Domestic wastewater treatment plant; Immersed membrane modules; Sewage; Long term operation;
Nitrogen removal
1. Introduction
European legislation on wastewater effluent
discharge has led to a need for enhanced
treatment processes capable of removing high
percentages of BOD5, suspended solids, nitro*Corresponding author.
gen, phosphorus, bacteria, etc. One of the most
promising technologies capable of fulfilling
these requirements is the membrane filtration
process. Combining membrane technology with
biological reactors for wastewater treatment has
led to the development of membrane bioreactors
(MBRs). Ultrafiltration as a replacement for
Presented at the Third Membrane Science and Technology Conference of Visegrad Countries (PERMEA), Siofok,
Hungary, 2–6 September 2007.
0011-9164/09/$– See front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.desal.2007.12.03 9
A. Blst’
akov
a et al. / Desalination 240 (2009) 160 169
secondary sedimentation tanks in the activated
sludge process was first described in 1969 by
Ref. [1] and since then MBRs have been
successfully used worldwide in industrial and
municipal wastewater treatment in hundreds of
applications.
One of the main limitations to extensive
MBR usage in wastewater treatment is membrane fouling, because the membrane is challenged with very high total solids concentration
arising from concentrated biomass. This high
solids concentration coupled with varying levels
of colloidal and dissolved extracellular polymeric substances (EPS) are the key challenges to
the MBRs processes [24]. In the submerged
processes generally there are three strategies to
limiting fouling: (a) reducing flux, (b) increasing
membrane aeration or (c) employing physical or
chemical cleaning [2,5].
Installation and testing of MBRs in domestic
wastewater treatment plants (less than 10 m3/day
capacity) has tended toward increasing membrane aeration with the goal of long term
wastewater treatment plant (WWTP) operation
without membrane cleaning. Increasing the
aeration rate, and thus cross flow velocity,
suppresses fouling and thereby increases flux.
Recent studies carried out with submerged MBR
[2,5,6] suggest that an increase in air flow rate at
the membrane surface limits fouling. However,
Ref. [7] observed an optimum aeration rate
beyond which a further increase has no effect
on fouling suppression. Details of the phenomena occurring during air sparging have been
extensively reported in Refs. [810].
Slovak Republic entry into the European
Union resulted in a marked expansion of sewage
and municipal WWTP construction, albeit
mostly in regions with more than 10 000 PE.
However, due to inadequate experience with the
technology, MBRs are not typically considered
in designing treatment plant reconstructions. The
161
first applications of MBR in small domestic
WWTP are likely in the near future.
Czech and Slovak international cooperation
coordinated by ASIO company (CZ) together
with Slovak University of Technology Bratislava
(SK) and the Institute of Chemical Technology
Prague (CZ) has resulted in a long term pilot
plant experiments with MBR. The results from
the Prague experiments are reported in Ref. [11].
The purpose of this Slovak part of the study was
to investigate the long term operation of a
domestic WWTP with immersed membrane
modules without backwashing or chemical
cleaning.
2. Materials and methods
2.1. Description of the domestic wastewater
treatment plant with membrane filtration
A commercially operated domestic WWTP
(ASIO, Czech Republic) with immersed membrane was used for this study. The chosen site
was a municipal domestic WWTP Bratislava Devínska Nova Ves (ca. 35 000 PE) with a total
working volume of 1.55 m3. The wastewater was
pumped after passing through fine screens
(6 mm) into the pilot plant in amounts of 450
700 L/day (discontinuous in the eight time
intervals per day). In the first plant treatment
step sedimentation tank with a volume 0.7 m3 *
the particular suspended solids (SS) were settled
and accumulated on the bottom of the sedimentation tank. The pretreated wastewater was
passed into the biological activated sludge tank
equipped with an immersed membrane module
(MM) and with a fine-bubble aerator used
activated sludge aeration as well as aeration
cleaning of the MM. Treated water was pumped
through the membrane using a small (12 W)
pump with maximum flux capacity of
100 L/m2 h. A schematic of the treatment system
with MM is shown in Fig. 1. Table 1 shows the
basic experimental conditions and Table 2 shows
A. Blst’
akov
a et al. / Desalination 240 (2009) 160 169
162
3. Results and discussion
3.1. The first phase (February 2005 June 2005)
Fig. 1. Schematic of the treatment system with MM.
specifications of the MMs. The long term test of
the MBR included five phases.
2.1. Analytical methods
The pilot-scale experiments with MBRs were
running from February 2005 to July 2007.
During the experiment, basic influent and effluent parameters * temperature, pH, COD,
BOD5, SS, ammonium nitrogen (NHþ
4 N),
nitrite nitrogen (NO
N)
and
nitrate
nitrogen
2
(NO
3 N) as well as the activated sludge parameters * were monitored. All these parameters
were analyzed using the standard methods [12].
The photometric semimicromethod [13] was
used for COD analysis.
/
/
/
The flat sheet membrane module (FSMM)
was installed in domestic WWTP pilot plant
with operation commencing on 14 February
2005. The pilot plant was not inoculated by
activated sludge (by agreement with the operator). During the first phase after start-up, it was
concluded that rapid clogging of the FSMM
could be related to sludge inoculation. Most
likely, microscopic, colloid or high-molecular
weight particles in raw municipal wastewater
caused preterm clogging of the membrane. The
freely moving small particles in the activated
tank rapidly entered the membrane pores. If the
particles are in an environment with higher
sludge concentration, it would initiate slower
membrane plugging or it would be completely
reduced because there would be physical or
physicalchemical reactions among particles
and sludge flocks. Despite the technical problems, samples were analyzed during the entire
first phase. The COD values in the effluent were
12.4124.3 mg/L (average value is 64.4 mg/L)
Table 1
Basic experimental conditions
Phase
Time period
Inflow rate
(L/day)
Main phase goal
First
Feb 2005 Jul 2005
360
Second Jul 2005 Sep 2005
450
Start-up without seed
Flat sheet module
sludge
Start-up with seed sludge, Flat sheet module
long term operation
Third
Sep 2005 Jan 2006
Mar 2006 May 2006
700
480
Fourth
Fifth
May 2006 Oct 2006
Feb 2007 Jul 2007
Feb 2007 May 2007
700
800
7000/103
Parallel operation of two
types of membranes
Test of external aeration
Test of external aeration
in the real WWTP
Used membrane type
HRT in aeration
tank (day)
1.87
1.6
1.1
Flat sheet module
1.6
parallel with hollow
fiber module
1.1
Hollow fiber module 1.0
Hollow fiber module 0.5
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akov
a et al. / Desalination 240 (2009) 160 169
163
Table 2
Specifications of the MMs
Phase
First
Second
Third
Fourth
Fifth
Membrane
producer
Martin
Systems (D)
Martin
Systems (D)
Martin
Systems (D)
Anonymous
(CZ)
Anonymous
(CZ)
Anonymous
(CZ)
Module
configuration
Material of membrane
Pore size (mm)
Surface area of
membrane
module (m2)
Place of installed
membrane
Flat sheet
Flat sheet
Flat sheet
Hollow fiber
Hollow fiber
Hollow fiber
Organic
polymers
~ 0.04
6
Organic
polymers
~ 0.04
6
Organic
polymers
~ 0.04
6
Organic
polymers
B/0.1
4
Organic
polymers
B/0.1
8
Organic
polymers
B/0.1
48
Activated
sludge tank
of domestic
WWTP
Activated
sludge tank
of domestic
WWTP
Activated
sludge tank
of domestic
WWTP
Activated
Activated
Activated
sludge tank
sludge tank
sludge tank
of domestic
of domestic
of WWTP
WWTP
WWTP
DNV
/
3.2. The second phase (July 2005 January
2006)
After the experiences from the first phase, the
second phase was started with sludge inoculation. Fig. 2 shows sludge concentration and flux
during the second phase.
The start-up sludge concentration was 0.6 g/L.
During the second phase, solids accumulation
and biomass growth led to an almost constant
sludge concentration 3.03.5 g/L. After three
months of relatively stable sludge concentration
in the activated sludge tank, the pilot plant
influent was increased from 450 L/day to 700 L/
day (September 2005). This influent increase
caused slow but continually increased sludge
concentration in the activated sludge tank with
values up to 1213 g/L. One of the reasons for
increasing sludge concentration in the system
was overflow of primary sludge from the
sedimentation tank. This sludge was accumulated
and digested in the sedimentation tank during the
summer season and was not removed from the
system. The flux showed relatively stable values
of 60 L/m2 h and did not change during the first
three months of operation. Similarly, as observed
by sludge concentration measurements, the measured flux decreased significantly after the
increase in influent wastewater. This decrease
was probably caused by significant overflow of
70
14
60
12
50
10
40
8
30
6
20
4
10
2
0
2.7.2005
21.8.2005
10.10.2005
Date
29.11.2005
Sludge concentration (g/L)
/
Flux (L/m2 . h)
which represents 85% process efficiency. Nitrification was limited (the values of NHþ
4 N were
approximately 33 mg/L during long term operation) and the increase of NO
3 N was not
significant.
0
18.1.2006
Flux FSMM
Sludge concentration
Fig. 2. Sludge concentration and flux FSMM during the
second phase.
A. Blst’
akov
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164
Table 3
Water qualities of the influent, outflow from sedimentation tank and effluent treated wastewater during the second phase
Concentration
(mg/L)
COD
BOD5
SS
þ
/NH --N
4
Ntotal
Influent (raw municipal
waste water)
Outflow (sedimentation
tank)
Effluent (flat sheet membrane
module)
Average
Scope
Average
Scope
Average
Scope
h (%)
787.8
327.4
383.1
68.6
156.7
502.7 1419
227.2 420.1
60 976.7
33.5 134.1
91.5 259.5
157.6
188.5
120.2
77.1
158.5
145.6 663.7
80.5 333.7
83.0 203.3
42.3 164.3
88.5 291.2
45.6
5.8
B/3
1.5
29.0
12.4 86.9
2.8 12.2
0.2 14.1
2.4 46.0
94.2
98.2
f100.0
97.1
81.4
digested primary sludge into the activated sludge
tank. This sludge had a consistency that was
relatively too sticky for efficient membrane
filtration. In the next experimental phases, digested sludge was regularly withdrawn from the
sedimentation tank.
The main parameters measured to assess
influent, outflow from the sedimentation tank
and treated wastewater effluent quality are
summarized in Table 3. Average influent COD
concentration was 787.8 mg/L and average effluent COD was 45.6 mg/L. Parameter COD
values in the effluent were relatively high
compared with values reported elsewhere [14].
Analysis of COD by the photometric semimicromethod at low COD concentrations is believed to be highly accurate with low
susceptibility to error (high precision). During
operation of the second phase, there was no
excess sludge withdrawal from the system and
soluble components of the decayed sludge were
slowly released. The elevated effluent measurements could have resulted due to this change in
the pilot plant operation.
Nitrification occurred without any problems.
High total nitrogen (Ntotal) concentrations in the
influent were caused by grab sampling. In
addition, wastewater sampling occurred in the
morning when urea concentrations are highest;
the efficiency of NHþ
4 N removal was 97.1%.
Nitrogen removal as Ntotal was relatively efficient.
/
This high efficiency was caused by denitrification
in those parts of activated sludge tank which were
not sufficiently aerated. Considering the high
sludge concentrations and long retention times,
denitrification was relatively successful.
3.3. The third phase (March 2006 September
2006)
In the third phase, the pilot plant experiment
started with sludge inoculation. Two different
membrane modules were inserted in the activated sludge tank. As shown in Fig. 4, during the
third phase the sludge concentration continually
increased from 0.6 g/L to 12 g/L. The flux values
were measured in both MMs. For the FSMM, the
starting flux value was 60 L/m2 h and for the
hollow fiber membrane module (HFMM), the
starting flux value was 45 L/m2 h. After the startup of operation, moderate flux decrease was
observed. However, in the entire 6 months of
operation a relatively constant flux was observed
with a value of more then 45 L/m2 h for the
FSMM and more than 35 L/m2 h for the HFMM.
During the entire third phase, the FSMM was
neither mechanically nor chemically cleaned. On
3 August 2006, the HFMM was cleaned by air
back-flush because a significant flux decrease
was observed (see Fig. 3). At the end of the third
phase, a greater volume of digested primary
sludge again entered into the activated sludge
70
14
60
12
50
10
40
8
30
6
20
4
10
2
0
3.3.2006 12.4.2006 22.5.2006 1.7.2006 10.8.2006
Date
0
Sludge concentration (g/L)
Flux (L/m2 . h)
A. Blst’
akov
a et al. / Desalination 240 (2009) 160 169
Flux FSMM
Flux HFMM
Sludge concentration
165
operation, kept relatively higher flux values,
thereby showing good operational efficiency.
During the 6-month test period, different cleaning requirements were observed for both membrane systems. For the HFMM, membrane
cleaning was necessary after 4 months of
operation, while the FSMM performed well for
the entire 6 months test period without needing
cleaning.
During the entire third phase, relatively high
NHþ
4 N concentrations (average 68 mg/L) in
influent (raw municipal wastewater) were measured (see Table 4). As discussed previously,
these high values were caused by grab sampling
and by high morning urea concentrations in the
wastewater. Despite the high NHþ
4 N concenþ
trations in the influent, NH4 N concentrations
in the effluent were relatively low. After the
start-up phase, during the stabilized period of
operation, NHþ
4 N concentrations were measured below 1 mg/L (Fig. 4). Until the first
membrane clogging (on 3 August 2006), the
NHþ
4 N removal efficiency was 98%. In the
period when the primary sludge started to overflow (after 18 July 2006), NHþ
4 N concentrations of about 2.5 mg/L were measured. Pilot
plant nitrification occurred without problems.
Effluent NO
3 N concentrations were relatively
high because the pilot plant was not well adapted
to denitrification. During operation, the NO
3 N
concentration gradually increased, and after
/
Fig. 3. Sludge concentration and flux FSMM and
HFMM during the third phase.
tank, which caused a significant flux decrease in
both membranes. At this occurrence, third phase
experiments ceased.
Tables 4 and 5 show water quality of the
influent, outflow from sedimentation tank and
effluent treated wastewater. Average influent
COD was 644.4 mg/L. The effluent COD concentration from the FSMM and HFMM was
56.3 mg/L and 51.6 mg/L, respectively. The
effluent COD concentration and the organic
matter removal efficiency were approximately
identical in both MMs. The effluent NHþ
4 N
concentration in both MMs was 0.91.1 mg/L.
During this phase nitrification was stabilized.
Parallel operation of FSMM and HFMM produced quite similar results in effluent quality. We
confirmed that the FSMM, under long term
/
/
/
/
/
/
/
/
Table 4
Water quality of the influent and outflow from sedimentation tank during the third phase
Concentration (mg/L)
COD
BOD5
SS
þ
/NH --N
4
Ntotal
Influent (raw municipal waste water)
Outflow (sedimentation tank)
Average
Scope
Average
Scope
644.4
239.4
247.5
67.5
149.1
247.9 1163.9
110.0 450.0
100.0 480.0
28.8 147.6
88.8 268.2
347.8
88.3
104.4
58.6
119.6
156.5 617.3
35.0 180.0
10.0 321.4
28.1 102.9
75.5 177.3
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166
Table 5
Water quality of the effluent treated wastewater FSMM and HFMM during the third phase
Concentration (mg/L)
COD
BOD5
SS
þ
/NH --N
4
Ntotal
Effluent (flat sheet membrane module)
Effluent (hollow fiber membrane module)
Average
Scope
h (%)
Average
Scope
h (%)
56.3
3.1
B/3
0.9
30.8
14.9-109.9
0.8-8.4
0.1-4.5
10.4-66.7
91.3
98.7
f100.0
98.7
79.3
51.6
4.1
B/3
1.1
31.9
17.8-118.6
0.8-8.8
0.3-3.6
12.9-71.1
91.9
98.3
f100.0
98.4
78.6
some time, stable concentrations at about 30 mg/L
were observed (Fig. 4).
From the nitrogen balance (Table 5), we
conclude that Ntotal removal efficiency was
relatively high and obtained 70% efficiency.
For a short period after high COD wastewater
was pumped into the pilot plant, the oxygen
concentration sharply decreased to below 1 mg/L
(Fig. 5) and this caused reduction of NO
3 N in
the activated sludge tank.
/
3.4. The fourth phase (February 2007 July
2007)
On 28 February 2007, the fourth test phase
with immersed HFMM was started. The surface
area of the membrane increased to 8 m2 in
comparison with the third test phase which
operated with a surface area of 4 m2. The module
consisted of 10 organic polymer hollow fiber
bunches fixed on supporting constructions. The
module was situated adjacent to an aerated
element. Membrane cleaning occurred with
additional compressed air injection and aeration.
The compressed air cleaning of the membrane
was first used in the second half of the fourth
phase (the first membrane clogging was on 26
March 2007). The pilot plant was inoculated by
activated sludge obtained from the previously
discussed third test phase. The starting sludge
concentration in the activated sludge tank was
nearly 3.2 g/L. Table 6 shows the water quality
of the influent and effluent during the fourth
phase.
At the start of the fourth phase a compressor
with compressed air was not used and the HFMM
was not subjected to additional (supplemental)
70
10
40
8
30
6
20
4
10
2
0
3.3.2006 12.4.2006 22.5.2006 1.7.2006 10.8.2006
Date
0
+
NO3-N effluent HFMM
NH4-N effluent HFMM
þ
Fig. 4. /NO
3 --N and /NH4 --N concentrations in the
effluent during the third period.
7
Oxygen concentration (mg/L)
12
50
NH4 –N effluent (mg/L)
–
NO3 –N effluent (mg/L)
14
60
6
5
4
3
2
1
0
0
15
30
45
60
75
90 105 120 135 150 165 180
Minute
Fig. 5. Oxygen concentration during the three-hourly
cycle pumping of the influent (raw municipal wastewater) during the third phase.
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167
Table 6
Water quality of the influent and the effluent of treated wastewater HFMM during the fourth phase
Concentration (mg/L)
COD
BOD5
pH
SS
þ
/NH N
4
Ntotal
Influent (raw municipal wastewater)
Effluent (hollow fiber membrane module)
Average
Scope
Average
Scope
h (%)
595.9
291.6
8.1
500
54.1
139.5
248.7 1037.9
255 330
7.5 8.5
160 530
23.2 76.6
114.3 200
46.9
3.6
7.4
B/3
1.5
27.4
14.9 78.2
2.9 8.6
6.9 7.7
0.4 2.6
3.5 45.3
92
99
1
f100.0
97
80
10
9
8
7
6
5
4
3
2
1
0
25
Flux (L/m2 . h)
20
15
10
5
0
28.2.2007
9.4.2007
19.5.2007
Date
Sludge concentration (g/L)
aeration (only to aeration by the standard diffuser
placed besides the HFMM). After start-up of the
fourth phase, the flux was 20 L/m2 h and gradually the flux decreased to the minimal value of
0.4 L/m2 h at the end of March (see Fig. 6).
On 26 March 2007 the MM was completely
clogged and the activated sludge overflowed the
pilot plant. The membrane was subsequently
cleaned and regenerated by backwashing with
dilute NaOCl and by blowing. Additional injected air aeration of the membrane occurred for
a duration of 10 s at 10-min intervals. The
module was repeatedly started-up and the flux
was held at stabilized values of about 20 L/m2 h
until the end of the experiment.
28.6.2007
Flux HFMM
Sludge concentration
Fig. 6. Sludge concentration and flux HFMM during the
fourth phase.
The decreased flux gradually increased the
sludge concentration to a maximum value of
8.4 g/L (Fig. 6) at the time of total membrane
clogging. After membrane regeneration, sludge
concentrations were stabilized. By the end of the
fourth phase (last month), sludge concentration
did not change significantly. The average sludge
concentration value was about 6 g/L. Despite the
high age of activated sludge, its organic portion
generated an average of 70% of suspended
solids. The sludge index values during the entire
fourth phase were about 70 mL/g.
On 12 July, after 3 months of stable measured
values for the key parameters, the fourth phase
of module measurement ended together with the
fourth phase pilot plant test operation of the
domestic WWTP.
3.5. The fifth phase (February 2007 May 2007)
On 23 February 2007 the fifth phase started
using the HFMM with the installation of the
membrane into the activated sludge tank of the
real WWTP in Bratislava * DNV. The MM
consisted of 60 organic polymer fiber bunches
which were fixed on supporting construction. The
surface area of the MM was 48 m2. The HFMM
was placed into the activated sludge tank with
fine bubble aeration. Because it was anticipated
that the HFMM would be insufficiently cleaned
by fine bubble aeration, supplemental aeration by
168
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akov
a et al. / Desalination 240 (2009) 160 169
Table 7
Water quality of the influent and the effluent HFMM during the fifth phase
Concentration (mg/L)
COD
BOD5
pH
SS
þ
/NH --N
4
Ntotal
Influent (raw municipal wastewater)
Effluent (hollow fiber membrane module)
Average
Scope
Average
Scope
h (%)
595.9
291.6
8.1
500
54.1
135.6
248.7 1037.9
255 330
7.5 8.5
160 530
23.2 76.6
92.3 210.4
44.9
4.2
7.3
B/3
1.2
29.5
29.3 66.7
3.1 8.9
6.9 7.8
0.5 1.9
11.2 62.1
92
99
1
f100.0
98
78
injection of compressed air (analogous to the
fourth phase) was prepared for use as needed.
In the start-up of the fifth phase, the HFMM
worked without supplemental cleaning by compressed air until the first membrane clogging (16
April 2007). The flux during the first month of
operation gradually decreased from 3.5 L/m2 h to
1 L/m2 h but stabilized during the next month.
However, on 16 April 2007 total membrane
clogging was observed. The membrane was then
cleaned and on 25 April 2007 started operation
again. To prevent membrane clogging, the
HFMM was subjected to supplemental compressed air injection for a duration of 30 min at
10-min intervals. On 11 May the membrane
clogged again and its operation was ended.
Because of the relatively high surface area of
the HFMM, the supplemental compressed air
injection during the test period was inadequate to
prevent clogging. The flux values were too low
and it is concluded that the MBR process needs
advanced efficiency aeration to clean the MMs
to prevent clogging. Table 7 shows the water
quality of the influent and the effluent from
HFMM installed into the activated sludge tank
of WWTP DNV during the fifth phase.
4. Conclusions
In this study, 2 years of data collection
and operational experience were obtained for
immersed MMs in a domestic WWTP. Based on
these data and experiences the following conclusions can be drawn:
.
.
.
.
Pilot plant need activated sludge inoculation
(during the first stage), because a MM without
inoculation became clogged in short time.
Experimental testing of MMs during pilot
plant operations for several months without
external cleaning showed that measured water
quality parameters and flux were satisfactory.
The FSMM was operated without external
cleaning for 6 months with a flux of 2060
L/m2 h. The operation HFMM was operated
for 4 months without external cleaning with
flux of 2045 L/m2 h.
Short duration, short interval, external cleaning of hollow fiber membrane by an adequate
quantity of compressed air was demonstrated.
Long term operation of the activated sludge
tank without excess sludge draw off occurred
due to an effective pretreatment stage (high
HRT in the sedimentation tank).
Results of water quality analyses illustrated
that the membrane technologies can be used to
treat raw municipal wastewater to produce high
quality water. Organic matter removal in this
system was stable and efficient (up to 90%).
Under these conditions, more than 97% of
þ
NHþ
4 N was removed, and effluent NH4 N
/
/
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concentration was less then 1.5 mg/L during long
term measurement. Nitrogen removal via denitrification was observed during the short periods
with low oxygen concentration.
Based on 2 years of experiments and pilot
plant operational experience, the first Slovak
domestic WWTP (300 PE) using MBR was
designed and constructed and is now beginning
its first year of operation.
Acknowledgments
The authors are thankful to the staff of
Bratislava Water Company at the Waste water
treatment plant Devínska Nova Ves (Mr. Minarovich), to the company ASIO from Czech
Republic for providing the conditions for testing
of pilot model (Mr. Poles
nak) and to the Slovak
Grant Agency for financial support of research
(VEGA 1/0145/08).
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