Desalination 185 (2005) 357 362
Treatment of landfill leachate by sequencing batch reactor
Ewa Neczaj*, Ewa Okoniewska, Malgorzata Kacprzak
Institute of Environmental Engineering, Czestochowa University of Technology, Brzeznicka 60a, 42 200
Czestochowa, Poland
Tel. �48 34 3721303; Fax �48 34 3721304; email: [e-mail]
Received 10 March 2005; accepted 10 April 2005
Abstract
The objective of this investigation was to study the effectiveness of applying ultrasound field for enhance-
ment of biological treatability of leachates generated in a typical municipal solid waste sanitary landfill. The
sonification of the leachate was carried out in static condition using the disintegrator UD-20, the field frequency
of 20 kHz and different amplitude in the range of 8 16 m. A laboratory-scale sequencing batch reactor (SBR)
was used for the examination of ultrasound application. The effect of different sonification parameters on the
efficiency of this biological treatment process was studied to optimize performance, especially for the removal of
nitrogen compounds and organic matter. Because of the high variability of the landfill leachate used in
experiment, unsteady treatment efficiency was observed.
It was found that, ultrasound pretreatment of raw leachate resulted in improvement of the treatment
efficiency. The results show significant improvement of the removal rates of COD and nitrogen compounds
in reactor operated with leachate irradiated by ultrasound. It could be explained by the fact that an ultrasound
wave in liquid causes the periodical compression and rarefaction of the medium.
Keywords: Landfill leachate; Aerobic treatment; Ultrasound, SBR reactor
1. Introduction municipal and industrial waste in landfills is the
most widespread and economical method to
Continuing industrial and commercial
waste disposal. Besides scarcity of available
growth in many countries around the world in
landfillsites, a large amount of leachate gener-
the past decades has been accompanied by rapid
ated from a landfill site poses as a major problem
increases in both the municipal and industrial
of landfill disposal of municipal solid waste
solid waste generations. Currently deposit of
(MSW). Proper treatment of the leachate has
therefore been a challenging problem
*Corresponding author.
Presented at the Conference on Desalination and the Environment, Santa Margherita, Italy, 22 26 May 2005.
European Desalination Society.
0011-9164/05/$ See front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.desal.2005.04.044
358 E. Neczaj et al. / Desalination 185 (2005) 357 362
confronting the local governments. Leachate Leachate from older, more decomposed
production is the results of rain precipitation, wastes is less amenable to biological treatment,
infiltration etc., phenomena which cause infiltra- because a higher proportion of the organic mat-
tion of water into the landfill waste and, after ter consists of relatively refractory compounds.
saturation, generation of wastewater [1]. The Due to the high concentration of non-biode-
flow rate and composition of leachate vary gradable compounds in landfill leachate, in
from site to site, seasonally at each site and this work waste ultrasound pretreatment was
depending on the age of the landfill. Young applied. For several decades, ultrasonic process
leachate normally contains high amounts of is considered as a new possibility in wastewater
volatile fatty acids. These readily degradable treatment field. It is able to remove pollutants
volatile acids account for the bulk of the chemi- through the production of radicals in the bub-
cal oxygen demand (COD) of young leachate, so ble of cavitation that can react with refractory
the ratio of biological oxygen demand (BOD) to compounds [8]. The impact of ultrasound
COD is relatively high. As the waste ages, the waves on liquid causes the periodical compres-
biodegradable fraction of organic pollutant in sion and rarefaction of the medium [9]. Cavita-
leachate decreases, as a result of the anaerobic tion occurs above a certain intensity threshold,
decomposition taking place in landfll site [2]. when gas bubbles are created which first grow
High COD and ammonium content, high in size before violently collapsing within a few
COD/BOD ratio and the presence of heavy microseconds. The violent collapse produces
metal ions present unique difficulties in biologi- very powerful hydromechanical shear forces in
cal treatment of landfill leachate [3]. Usually the bulk liquid surrounding the bubble. Cavita-
a combination of physical, chemical and biolo- tion is accomplished by high pressure gradients
gical methods are used for landfill leachate and extreme increase of the temperature inside
treatment and it is very difficult to obtain satis- the bubble. These extreme conditions can lead
factory treatment efficiencies by one of these to the thermal destruction of compounds pre-
methods alone [4,5,6]. Biological treatment is sent in the cavitation bubbles and to the gen-
mostly the first stage in a combination with eration of very reactive hydroxyl radicals. The
additional chemical physical process. Those effects that can be observed when cavitation is
treatment methods used for leachate treatment generated in aqueous solution can be summar-
are mainly aerobic, anaerobic and anoxic ized as:
processes which are used in combination [7]. High mechanical shear stress.
The main task of the leachate biological process Radical reactions: creation of OH and H
is the reduction of the organic biodegradable radicals; chemical transformation of
compounds and nitrogen in order to minimize substances.
secondary treatment cost. The most popular Thermal breakdown of volatile substances.
biological treatment of landfill leachate is In this study the effect of ultrasound
the sequencing batch reactor (SBR) method. pretreatment on leachate degradability
The SBR process strategy is characterized by was investigated using ultrasound at a
a controlled periodic change of process condi- frequency of 20 kHz and high acoustic inten-
tions such as concentration of oxygen, and sities. Leachate needed to be diluted with
availability other biological reactants. These synthetic wastewater in order to reach bio-
environmental conditions are controlled using mass-non inhibiting concentration. The aim
fill and draw operations at distinct time of the research was to evaluate the maximum
intervals. percentage of leachate that can be
E. Neczaj et al. / Desalination 185 (2005) 357 362 359
biologically treated without any inhibition of monitored by the relevant probes. The initial
microbiological activity and examine the volume of the culture in the tank was 1 l
effect of leachate ultrasound disintegration which was completed to 4 l with the addition
on the efficiency of the aerobic digestion of 3 l leachate at the beginning of each cycle.
process. During these investigations each SBR cycle
consisted of the following phase:
Aerobic fill (0.15 h).
2. Materials and methods
Aerobic react (2.0 h).
The laechates used in the research came Anoxic react (1.0 h).
from the urban solid wastes landfill of Sobuc- Settle (0.30 h).
zyna. This is an old landfill and leachates from Draw (0.08 h).
this tip present relatively low COD values and Samples were withdrawn from the reactor at
low ratio of BOD/COD compared with COD the beginning and at the end of each cycle for
values from young landfills. The production of analysis. On such samples (after filtration
leachate was estimated at around 70 m3/day. on GF-C filters) the following parameters
The leachate samples used for the SBR con- were measured: COD, TKN, N-NH4�, Ptot,
tained (average values for whole experimental N-NO2, N-NO3, MLSS, MLVSS concentration
period): 800 mg/l N-NH4, 3500 mg/l COD and [10]. At the end of each SBR operation,
high pH value (approximately 8.3). Ammonia- the organisms were settled for 30 min and 3 l
cal nitrogen content was on the medium level, is of the treated wastewater was removed. Settled
typically higher for leachate from old tip. organisms were used for the next treatment
The disintegration of leachate was carried operation. A fraction (1/10) of the culture
out in static conditions using disintegrator was removed from the reactor before sedimen-
UD 20 with a   Sandwich  concentrator tation every day to adjust the sludge age to 10
(TECHPAN Warsaw). The sonification of days.
the leachate was carried out in static condi- The SBR systems were operated at feeding
tion using the disintegrator UD-20. The field condition of leachate dilution of 5, 10, 15, 20,
frequency of 20 kHz and different amplitude 25, 30, 35, and 40% by volume with a syn-
in the range of 8 16 m and the sonification thetic wastewater and with 4 g/l sludge
time of 120 s was applied. concentration.
For the laboratory experiments a SBR was
used, with cylindrical shape and total volume
3. Results and discussion
of 5 l, constructed from plexiglass. Peristaltic
pump was employed for influent feed, waste In the first phase of this study the maximum
sludge and effluent draw. The reactor content percentage of leachate in the influent was eval-
was mixed with a magnetic stirrer, while suf- uated. Performances with leachate addition of
ficient aeration was provided by a compressor 5, 10, 15, 20, 25, 30, 35, and 40% (v/v) were
connected to porous stone located close to investigated to evaluate biodegradability of
the bottom of the reactor. The compressor leachate in the same conditions (Fig. 1). COD
was used only during the aerobic period to removals over 85% were maintained with
ensure an oxygen concentration equal to addition of leachate up to 10% (v/v) and gra-
2 mg/l. Temperature, pH, dissolved oxygen dual decrease in organic compounds removals
(DO) and oxidation-reduction potential was observed as leachate percentage increased
(ORP) of nutrient medium were continuously from 15 to 40% (v/v). Therefore, lecheate
360 E. Neczaj et al. / Desalination 185 (2005) 357 362
90 90 95 95
85 85 90 90
80 80 85 85
75 75 80 80
70 70 75 75
65 65 70 70
60 60 65 65
55 55 60 60
50 50 55 55
45 45 50 50
0 5 10 15 20 25 30 35 40 45
40 40
0 5 10 15 20 25 30 35 40 45
Leachate percentage (%, v/v)
leachate percentage (%, v/v)
&
Fig. 3. COD ( ) and ammonia (*) removal at
&
Fig. 1. COD ( ) and ammonia (*) removal at
increasing leachate percentage. (amplitude 10 m).
increasing leachate percentage.
COD removal efficiency achieved over 90%
addition of 10% seems to be a practical upper
for 5, 10 and 15% leachate addition (Fig. 3).
limit for SBR process.
Ammonia removal efficiency gradually
In the next step of this study the influence
decreased as leachate concentration in influent
of ultrasound pretreatment of leachate on
decreased. It was very low for 35 and 40%
pollutans biodegradability was investigated.
leachate addition and in that cause achieved
The results obtained for amplitude 8 m of
value of 50%.
ultrasound filed was shown on Fig. 2.
High COD removal, over 90% was observed
The sonification of raw leachate leads to
in SBR process when amplitude of 12 mwas
enhancement of COD and ammonia removal
applied (Fig. 4). It was on the same level up to
at all leachate percentage addition in influent
25% leachate addition, and then gradually
as compare to experiment without ultrasound.
decreasing of organic meter was observed.
Over 85% removal of organic compounds was
Ammonia removal efficiency was almost 70%
observed up to 15% leachate addition. When
for leachate concentration in influent of 5, 10
ultrasound amplitude of 10 m was applied
100 100
90 90
85 85
90 90
80 80
75 75
80 80
70 70
65 65
70 70
60 60
55 55
60 60
50 50
45 45
50 50
0 5 10 15 20 25 30 35 40 45 0 5 10 15 20 25 30 35 40 45
Leachate percentage (%, v/v) Leachate percentage (%, v/v)
& &
Fig. 2. COD ( ) and ammonia (*) removal at Fig. 4. COD ( ) and ammonia (*) removal at
increasing leachate percentage (amplitude 8 m). increasing leachate percentage. (amplitude 12 m).
+
4
+
4
NH removal (%)
COD removal (%)
COD removal (%)
NH removal (%)
+
4
+
4
NH removal (%)
COD removal (%)
NH removal (%)
COD removal (%)
E. Neczaj et al. / Desalination 185 (2005) 357 362 361
100 100
4. Conclusion
In this study, ultrasonic pretreatment of
90 90
landfill leachate was examined in order to
80 80 improve the SBR process. The most impor-
tant results are:
70 70
Ultrasonic pretreatment enhances the sub-
sequent aerobic digestion resulting in a
60 60
better degradation of landfill leachate.
The sonification of raw leachate leads to
50 50
enhancement of COD and ammonia
0 5 10 15 20 25 30 35 40 45
removal at all leachate percentage addition
Leachate percentage (%,v/v)
in influent as compare to experiment with-
&
Fig. 5. COD ( ) and ammonia (*)removal at
out ultrasound.
increasing leachate percentage. (amplitude 14 m).
High COD removal was observed in SBR
process when amplitude of 12 m was
100 100
applied. It was over 90% up to 25% lea-
chate addition, and then gradually
90 90
decreasing of organic meter was observed.
Ammonia removal efficiency was almost
80 80
70% for leachate concentration in influent
of 5, 10 and 15%. Decreasing of leachate
70 70
addition caused gradually decrease of
NH4� removal.
60 60
Increase of amplitude over 12 m did not
cause increase of SBR process efficiency.
50 50
0 5 10 15 20 25 30 35 40 45
Additional researches are required in order
Leachate percentage (%,v/v)
to optimize the SBR process.
&
Fig. 6. COD ( ) and ammonia (*) removal at
increasing leachate percentage. (amplitude 16 m). References
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+
4
NH removal (%)
COD removal (%)
+
4
NH removal (%)
COD removal (%)
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