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BODIK et al. 1999 Application of Anaerobic Filterpdf
The Application of Anaerobic Filter for Municipal Wastewater
Treatment*
a
a
a
b
I . B O D Í K * * , B . HERDOVÁ, and K . K R A T O C H V Í L
Department of Environmental Sciences, Faculty of Chemical Technology,
Slovak University of Technology, SK-812 37 Bratislava
e-mail: [email protected]
b
ASIO SK, SK-014 01 Bytča
Received 14 June 1999
This paper presents results of the lab-scale anaerobic filter and pilot-scale units of anaerobic
baffled filter used for municipal wastewater treatment by low temperature. The lab-scale reactor
3
had a volume of 1.7 dm , being operated at hydraulic retention time (HRT) of 12 h and 24 h. The
wastewater temperature was adjusted at 23 °C, 15 °C, and 9°C, respectively. After almost one year
of continuous monitoring, the lab-scale upflow anaerobic filter system produced very good results in
terms of COD and BOD5 removal, and also very low solids concentration in the final effluent. The
average results of COD and BOD5 removal varied from 41 to 95 % in dependence on temperature
and values of hydraulic retention time.
The pilot-scale experiments were realized in anaerobic baffled filter with total volume of 2 m 3 .
This reactor was installed on wastewater treatment plant (WWTP) Bratislava-Petrzalka and was
fed with raw wastewater under HRT of 24 h. The start-up and operation of anaerobic filter was
executed under winter climate condition (September 1998—March 1999). The observed COD and
BOD5 removal efficiency was in average 66 % and 68 %, respectively. Very high efficiency was
achieved for suspended solids removal - 95 %.
From total 2871 settlements in Slovakia, only 400
of t h e m (these represent ca. 53 % of the country popu­
lation) have own W W T P . Nearly all bigger cities and
towns have W W T P ; the biggest lack of t h e m is in
small settlements. However, in these small communi­
ties live quite a large percentage of the population
(people living in 1952 settlements with less t h a n 2000
inhabitants represent ca. 30 % of the country pop­
ulation). Therefore, it is obvious t h a t there will be
a demand to build up a couple of hundreds of small
W W T P s . Such situation is valid also for the other
Central and Eastern E u r o p e a n countries.
For the purpose to find economically and tech­
nologically suitable W W T P , our research was aimed
also at the use of anaerobic reactors for t r e a t m e n t
of municipal wastewater. This technology has been
used quite often in recent years mainly in regions
with warmer climate. For example, Mexico, Columbia,
India, and China have built up a couple of larger
W W T P s of this type [1—4].
T h e development of high-rate reactors redounded
to the application of anaerobic t r e a t m e n t of di­
luted substrates, for example, domestic and municipal
wastewater. T h e key concept of high-rate reactors is
based on three fundamental aspects [5]:
- accumulation of biomass by means of settling,
a t t a c h m e n t to solids (fixed or mobile) or by recircula­
tion. Such systems allow t h e retention of slowly grow­
ing microorganisms by ensuring t h a t t h e mean solids
retention time becomes much longer t h a n the mean
hydraulic retention time,
- improved contact between biomass and wastewa­
ter, overcoming problems of diffusion of substrates and
products from t h e bulk liquid to biofilms or granules,
- enhanced activity of t h e biomass, due to adapta­
tion and growth.
To this reactor technology belong, for example,
anaerobic contact process, anaerobic filter, downflow
stationary fixed-film reactor, upflow anaerobic sludge
blanket reactor, fluidized bed reactor, expanded bed
reactor, anaerobic baffled reactor, etc.
Anaerobic filter (AF) is filled out with a support
material arranged in sheet, ring or sphere conforma­
tion which provides t h e best conditions for microbial
a t t a c h m e n t in biofilm form. T h e reactor may be oper­
ated in upflow or downflow feed mode. Upflow anaero-
*Presented at the 26th International Conference of the Slovak Society of Chemical Engineering, Jasná - Demänovská
dolina, 24—28 May 1999.
**The author to whom the correspondence should be addressed.
Chem. Papers 54 (3) 159—164 (2000)
159
I. BODÍK, B. HERDOVÁ, К. KRATOCHVÍL
T a b l e 1. Experimental Results Obtained in Municipal and Diluted Wastewater Treatment
General parameters
Efficiency0
Influent
V
0
HRT
Bv
pCOD
p BOD5
p ss
m3
°C
h
kg m ~ 3 d _ 1
mg d m - 3
mg d m - 3
mg d m - 3
%
0.01
0.016
3.0
10
16
102
_
18—35
11—25
15—20
22—24
10—25
17
24
20—33
2.5—10.5
8.6—37
12—18
130—340
60—543
63—213
200—250
62—114
34—40
73
-
44—573
176—221
60—220
150—220
132—390
-
-
28—64
0.05—0.54
0.2
0.05—0.61
-
690—890
77—1170
T)COD
-
„BOD5
^SS
%
%
-
59—64
73
75
70
43—63
81—87
57
70—83
91—97
80
Ref.
[И]
[9]
[7]
[10]
[12]
[12]
a) The efficiency evaluated from nonfiltered influent and nonfiltered effluent values.
bic reactor (UAF) is the oldest type of packed reactor
first described by Young and McCarty [6].
The advantages of AF are as follows [7, 8]:
- The method is suitable for the treatment of lowstrength soluble organic wastewater;
- sludge is not returned in difference to the anaer­
obic activated sludge process;
- the amount of produced sludge is smaller and
settleability of the sludge is good;
- the solid retention time can be increased so that
an efficient treatment can be performed at low water
temperatures;
- relatively good load fluctuation resistance;
- maintenance and management are easy.
The disadvantages of AF are as follows [5, 8]:
- Channelling, i.e. formation of preferential paths
of liquid flow through reactor;
- dead-zone formation caused by sludge com­
paction or clogging of matrix interstitial spaces by
solids;
- clogging of poorly designed distribution systems.
The efficiency of AF treating municipal and domes­
tic wastewater and the biomass production depends on
the character of substrate (character of pollutants and
their concentration, suspended solids concentration),
temperature, and the characteristic of support mate­
rial like the specific surface, porosity, and the shape.
Since a little biogas is produced in the treatment
process of such diluted substrate, it is economically
not effective to use this small amount of biogas for
heating, in particular for small WWTPs. This is the
reason why it is important to realize the treatment
under climate condition.
Some experimental results obtained in the labora­
tory and pilot scale by treating municipal wastewater
are summarized in Table 1.
EXPERIMENTAL
The study of treatment abilities of anaerobic filter
was performed in two scales: in the lab-scale and in
the pilot-scale models.
160
•>
4
F i g . 1. Laboratory model of upflow anaerobic filter. 1. Influent,
2. support material for biomass growth, 3. effluent, 4.
biogas.
In the lab-scale model, an upflow anaerobic filter
(UAF) was used with volume 1.72 dm 3 (Fig. 1). A
plastic material (cut isolating tubes of diameter 2 cm
and a length of 2—3 cm) filled out the whole volume of
the reactor. We studied the treatment abilities under
different temperatures (9°C, 15°C, and 23°C) and two
different HRT values (24 h and 12 h).
The pilot-scale reactor was a baffled reactor with
3
total volume of 2 m (Fig. 2). Because of the relatively
high content of suspended solids (SS) and possibility
of clogging of the filling material, the first part of reac­
tor was established like a settler. Here the undissolved
organic and inorganic particles were settled down. The
accumulated sludge was stabilized here, too. The next
four chambers were filled out by plastic filling (0.7 m 3 ).
The size of the plastic filling was changed through the
reactor. The wastewater was passing through the re­
actor alternatively up and down.
During both these experiments we monitored influ­
ent and effluent parameters - temperature, pH, COD,
BOD 5 , SS, volatile fatty acids (VFA), NH+, P-PO^".
These parameters were analyzed using the standard
methods [13].
Chem. Papers 54 (3) 159—164 (2000)
ANAEROBIC FILTER FOR WASTEWATER
F i g . 2. The pilot-scale reactor at the W W T P in BratislavaPetržalka.
RESULTS
Lab-Scale E x p e r i m e n t s
The UAF was inoculated with a municipal anaerobic digested sludge and the start-up of the reactor was
realized at the temperature of about 23 °C, HRT of 24
h. A mixture of synthetic substrate (acetate and Dglucose) and raw municipal wastewater from WWTP
Bratislava-Petržalka was used as a substrate. The parameters of influent and effluent are summarized in
Table 2.
A very quick start-up of UAF was obtained in
the lab-scale experiments. COD removal efficiency of
about 70 % was reached in the second week of the
start-up. Temperature and HRT were changed to observe influence of HRT and temperature on the treatment efficiency. Dependence of COD removal efficiency on HRT and temperature is shown in Fig. 3.
The bigger influence of HRT changing from 24 h to 12
h is demonstrated when the temperature decreases below 10°C. The decrease of reactor performance below
10°C under changing HRT can be seen in Table 2, too.
The response of the filter on lower HRT - 12 h under
23 °C is already the subject of our research. Concerning
results obtained with UAF reactor under temperature
about 15°C and HRT of 12 h (84 % COD, 70 % BOD 5
removal) and 24 h (87 % COD, 91 % BOD 5 removal)
we can suppose to achieve similar removal efficiency.
The results obtained in the first two weeks (reactor
is adapted on substrate and previously worked under
temperature about 10 °C) prove very good efficiency
of about 80 % of COD removal.
The results prove also very good efficiency in the
removal of SS, which reached approximately values of
10—40 mg d m - 3 . In the whole experiment the concentration of volatile fatty acids (VFA) and the value of
redox potential were monitored. The concentration of
VFA achieved very low values, which propose a good
neutralization capacity of the municipal wastewater.
The value of redox potential is a parameter, which
shows if the milieu of the process is anaerobic. The
monitored redox-potential values in the whole experiment were in average -250 mV. The anaerobic milieu
is defined for values below -150 mV, but the optimal
redox potential for methanogenic bacteria is -330 mV.
It is not possible to obtain the optimal condition for
the methanogenic bacteria under such low temperature and low loading rates, which results in the low
biogas production.
Pilot-Scale E x p e r i m e n t s
Concerning good results obtained with the labscale anaerobic filter, simplicity, low investment and
T a b l e 2. Experimental Results from Lab-Scale of UAF for Municipal Wastewater Treatment
Influent
в
HRT
Bv
°c
h
8
15
8
15
23
12
12
24
24
24
COD
pBOD5
pSS
kg m ~ 3 d _ 1
mg d m - 3
mg d m - 3
1.00
1.16
0.47
0.60
0.75
490
570
540
690
780
290
290
240
310
440
p
Efficiency11
Effluent
COD
pBOD5
pSS
^COD
„BODO
mg d m - 3
mg d m - 3
mg d m - 3
mg d m - 3
%
%
%
230
70
230
260
70
170
65
70
150
34
64
26
30
30
10
25
46
84
64
87
90
41
70
71
91
95
80
90
72
-
p
40
77SS
-
a) The efficiency evaluated from nonfiltered influent and nonfiltered effluent.
Chem. Papers 54 (3) 159—164 (2000)
161
I. BODIK, B. HERDOVA, К. KRATOCHVIL
x
cd
>
О
S
Q
O
u
Ü
c
100
90
80
70
60
50
40
30
20
10
0
D
D
-
D
GG
-
dB O
D
•
•
•
D
•
•.
•
D
D
•
•
D
•
T
D
G°
D
-
m
-
•
D
•
'"J"„"
D D
.úl
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D
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•
-
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•
• .
•
,
10
20
15
eľc
25
30
F i g . 3. The influence of temperature and HRT on the treatment efficiency in the lab-scale UAF reactor. D HRT = 24 h, • HRT
= 12 h.
T a b l e 3. Experimental Results from the Pilot-Scale of the Anaerobic Filter at the W W T P Petržalka
в
HRT
Bv
kg m~
Range
8—20 20—26
Average
14
24
0.24—1.38
0.55
.COD
mg dm
„BOD5
3
mg dm
Efficiency0
Effluent
Influent
n
SS
mg dm
„COD
3
224—1264 112—440 140—1098
475
229
448
mg dm
n
3
30—270
160
BOD5
mg dm
3
20—114
73
mg dm
10—46
22
3
^COD
„BOD5
„SS
%
%
%
25—88 23—91 62—99
66
68
95
a) The efficiency evaluated from nonfiltered influent and nonfiltered effluent.
operating cost, we decided for application of AF
in pilot-scale experiments. The baffled anaerobic fil­
ter was installed directly on the WWTP Petržalka.
Incoming municipal wastewater flows after passing
through the screen into the reactor. The wastewater
incoming to the WWTP is collected from one part of
Bratislava-Petržalka (ca. 120 000 inhabitants) and it
is mostly domestic wastewater with negligible fraction
of industrial wastewater.
The pilot-scale experiment started in the second
half of September 1998. The two first chambers filled
with plastic medium were inoculated with municipal
anaerobic digested sludge. The initial HRT was set
to 1 day, calculated on the volume filled with plastic
filling. The first results showed good effluent parameters approximately 40—180 mg d m - 3 COD in the
first month, when the temperature varied from 15 to
20 °C (Fig. 4).
The effluent COD values increased in the winter
1998/99 up to 130—260 mg dm" 3 due to falling temperature, reaching 8—13 °C in this year time. The
influence of temperature on the effluent parameters
is shown in Fig. 4. The temperature under 10 °C is
often mentioned in the literature as boundary temperature for psychrophilic anaerobic treatment processes. Summary of the obtained results is given in
162
Table 3. The results show very often mentioned property of filter, the very good efficiency in removing
of suspended solids even under unfavourable temperature conditions (Fig. 4). The effluent of SS-values
reached in the whole start-up concentration of 10—46
mg d m - 3 . The reactor has a very good neutralizing
capacity. pH values in the reactor were ranging between 6.7—8.2. Also the concentration of VFA was
very low in the effluent, which indicates a good stability of reactor and nonproblematic decomposition of
the pollution.
The first 200 start-up days of operation under
unfavourable temperature condition prove relatively
good results. We can expect better results in the
other months of the year, in which the temperature
of wastewater achieves 15—25°C. It can be supposed
that the reactor will provide in the next winter better
results after good adaptation of anaerobic population
on the substrate and psychrophilic condition. Results
obtained in similar research, such as the one performed
in Holland [8] verify this assumption.
The reactor response on the changing of HRT
will be very interesting. Because of the increasing requirements on effluent parameters in the future, it is
necessary to consider the possibility of aerobic posttreatment.
Chem. Papers 54 (3) 159—164 (2000)
ANAEROBIC FILTER FOR WASTEWATER
20
15
U
10
'g
ъ 1000
Q
О
U
500
• \
ř^*i'4'
» - «.
40
^ °
"s
-О
300
^
200
Q
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i
175
200
Time/d
F i g . 4. Temperature, influent and effluent of COD, BOD5, and SS concentration in the pilot-scale anaerobic filter. О Temperature,
• influent (24-h mixture), D effluent.
CONCLUSION
The presented research was focused on the real
application of anaerobic filter reactor for municipal
and/or domestic wastewater treatment. Process of
wastewater treatment was performed at ambient ternperature. The practical research was oriented to two
scales: lab-scale experiments and the pilot-scale application.
Main results obtained in the lab-scale reactor were
Chem. Papers 54 (3) 159—164 (2000)
as follows:
- Anaerobic wastewater treatment process is suitable for municipal and/or domestic wastewater;
- COD removal efficiency is dependent mainly on
temperature and hydraulic retention time. Under low
values of HRT the removal efficiency is more boldly
influenced by temperature;
- The lab-scale model was operated without any
technological problems. The start-up process was realized by 23°C and was very fast (two weeks);
163
I. BODÍK, В. HERDOVA, К. KRATOCHVIL
- Under ambient temperature it is possible to ob­
tain relatively high COD and BOD5 removal effi­
ciency.
Concerning very good experience from the labscale model, we decided for application of anaerobic
baffled filter in pilot-scale experiments. Main results
obtained in the full-scale reactor were as follows:
- Very good start-up process was observed at the
temperature of 20°C. High COD and BOD 5 removal
efficiency was obtained in the first months of operation
despite low ambient temperature (8—15 °C);
- Decrease of COD and BOD 5 removal efficiency
was observed with decreasing temperature;
- The pilot-scale reactor worked during the whole
experiments without any technological problems. No
significant changes of pH, VFA were observed in anaer­
obic reactor.
Acknowledgements. The study has been done with the sup­
port of the Grant No. 1/4204/97 of S.G.A. for biological and
environmental sciences.
164
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Chem. Papers 54 (3) 159—164 (2000)
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