CLONIC
CLOSING THE NITROGEN CYCLE FROM URBAN
LANDFILL LEACHATE BY BIOLOGICAL NITROGEN
REMOVAL OVER NITRITE AND THERMAL TREATMENT
M.T. VIVES*, J. COLPRIM**, H. LÓPEZ**, R. GANIGUÉ**, M. RUSCALLEDA**, A. SÀNCHEZ***, X. VILA***, R. LÓPEZ****,
MªJESÚS LLORENS****, M. SALAMERO****, E. GONZÁLEZ*, E. JIMÉNEZ*, M.D. BALAGUER**, M. ELORDUY*.
* CESPA G.R, Technical Department, Av. Catedral 6-8, 08002 Barcelona, Spain. E-mail:{teresa.vives, e.gonzalez,
e.jimenez, m.elorduy}@cespa.es
**LEQUIA-UdG, Institute of Environment, University of Girona, Campus Montilivi s/n, 17071- Girona, Catalonia, Spain. E-mail:
{J.Colprim, helio, ramon, mael, marilos}@lequia.udg.cat
*** Laboratory of Molecular Microbial Ecology, Institute of Aquatic Ecology, Universitat de Girona
****FUNDACIÓN AGBAR, Edifici Can Serra, Ctra. Sant Joan Despí 1, 08940 Cornellà de Llobregat, Barcelona. Email:{msalamero,mllorens,rlopez}@agbar.es
Urban landfill leachates are characterized by high ammonium concentrations, high amounts of organic matter
with very low biodegradable fraction and high salinity. Treatments based on a partial biological autotrophic
oxidation of ammonium to nitrite (PANI-SBR process), followed by an autotrophic anaerobic ammonium oxidation
via nitrite (Anammox process), were studied as a more sustainable and cheaper alternative for the nitrogen
removal from urban landfill leachates. After that, thermal drying treatment using biogas as an energy source was
applied in order to keep all the salinity in the dry powder produced. This innovative biological treatment allowed
the reduction of 98% of initial ammonium from leachate. Then, after drying the effluent obtained from this
process, the full process showed an environmental cost reduction of 48% in relation with conventional processes.
Both combined technologies, PANI-SBR-ANAMMOX with THERMAL DRYING, represent a technical, economical
and environmental alternative for leachate treatment with important advantages of present treatments.
1. INTRODUCTION
One of the most important problems in landfill management is the difficulty of leachate treatment. T he decision of
choosing a specific leachate treatment depends on different parameter such as: the landfill site location, physical
location of the leachate treatment plant, the leachate quality, the discharge requirements and the best
technologies available. As a consequence, different landfill leachate treatments are applied in landfills such as
classical biological processes, reverse osmosis, chem ical oxidation, evaporation plus condensation processes or
ammonium stripping units. Nevertheless, up to now is not possible to solve the global problem by applying a
single technology and for this reason a combination of different physical, biological and chemical technologies
must be considered to reduce contamination levels of leachates.
Every leachate has different nature and composition. In general, leachates show high contaminant levels, mainly
due to high organic matter (commonly non-biodegradable), nitrogen and salt contents (i.e conductivity). From a
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practical and economical point of view, the biological treatment is the best available option for nitrogen
elimintation if suitable, but some of the most important problems arising from the biological nitrogen removal are:
i) a high and gradually increasing ammonium concentration during the landfill lifetime, and ii) a low biodegradable
organic carbon to nitrogen ratio (C:N), that forces the addition of external carbon sources. On the other hand, the
removal of the high salt contents from leachates has been focussed on separation processes based on filtration
technologies, generating high volumes of concentrates which require a high economic cost for further
management.
The application of innovative techniques to reduce the economical and environmental impact must be considered
and applied in leachate treatment. In such sense, looking for a continuous technical improvement and in order to
solve the above mentioned problems, was defined the CLONIC project (www.lifeleachate.com ).
2. FUNDAMENTALS OF THE PROCESSES
High nitrogen content of leachates and the low available biodegradable organic carbon are not suitable conditions
for the application of a classical heterotrophic denitrification. For this reason, the CLONIC project proposes a
biological treatment based on a partial biological autotrophic oxidation of ammonium to nitrite (PANI-SBR
process) (Ganigué et al., 2007a) followed by an autotrophic anaerobic ammonium oxidation via nitrite
(ANAMMOX) (Strous et al. 1998). Afterwards, a thermal drying system is evaluated as an option to remove the
high amount of salts contained in leachates by the use of energy recovery techniques associated to the biogas
combustion obtained in the landfill.
2.1. PANI-SBR and ANAMMOX process
The partial nitritation (PANI) of the high nitrogen level, as ammonium content, of leachates to nitrite (Equation 1)
has been studied under aerobic conditions within a sequencing batch reactor (SBR) and with special attention to
the SBR cycle definition. The main aim of the PANI-SBR process is to achieve a suitable influent for a
subsequent anammox reactor where the molar ratio between ammonium and nitrite must be adjusted to avoid
possible inhibition conditions caused by nitrite accumulation.
NH4 + + 2 HCO3− + 1 .5O2 → NO2 − + 3H 2O + 2CO2
(Equation 1)
The ANAMMOX (Anaerobic Ammonium Oxidation) process (Jetten et al. 1999) is based on an anaerobic
ammonium oxidation without the consumption of organic matter (autotrophic process) generating nitrogen gas
according to Equation 2.
NH 4+ + 1.32 NO 2− + 0.066 HCO 3− + 0.13 H + → 1.02 N 2 + 0.26 NO3− + 0.066 CH 2 O 0.5 N 0.15 + 2. 03 H 2 O
(Equation 2)
Advantages of the combination of both biological processes are: i) a substantial reduction of the aeration
requirements because only a fraction of the influent ammonium must be oxidized to nitrite and no further nitrate
formation is required, ii) both processes are conducted by autotrophic biomass, without the need of external
biodegradable carbon sources and with a substantial reduction of excess sludge production, iii) the anammox
bacteria grow at a low specific rate (0.066 d-1) with a high metabolic activity concluding with high specific nitrogen
removal rates (Fux et al. 2002).
Nevertheless, some drawbacks must be considered: i) the PANI-SBR and the Anammox process must be
conducted at high temperatures (around 35ºC) with the subsequent energy requirements, ii) the PANI-SBR
process requires some advanced control loops, iii) the slow growing anammox bacteria is an important bottleneck
during start-up periods and thus special biomass retention conditions must be considered (Strous et al. 1998).
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2.2. Thermal Drying process
Thermal Drying is an industrial process widely used in food, ceramic, pharmaceutical, chemical and polymer
industries, as in surplus sludge of wastewater treatment; to obtain from a liquid inlet a continuous solid flow rate in
the form of powder, granular or agglomerate product. This process is based on the evaporation of the water
contained into the product before being atomised throughout hot air.
Thermal Drying installations consist of a feed pump, an atomizer, a hot inlet air, an air disperser, a drying
chamber and a system to keep particles contained in the gas effluent. The characteristics of treated liquid, the
specifications of the final product and the operational parameters determine the selection of each component of
the system.
3. EXPERIMENTAL STUDY
3.1 PANI-SBR and ANAMMOX
3.1.1 Microbiological aspects
Part of the success of the CLONIC project depended on identification and enrichment of the ANAMMOX
microorganism. In this sense, several enrichment of anammox biomass in batch cultures were started using
inocula from different sources as natural environments (marine sediments, alpine freshwater lake, brackish
coastal lagoon), modified environments (constructed wetlands) and man-made systems (laboratory SBR,
WWTP’s). In parallel, techniques for microbiological detection of microorganism s with anammox activity were
defined and applied to the cultures follow up.
(b)
(a)
Figure 1. (a) Batch culture enrichment (b) DGGE (Denaturing Gradient Gel Electrophoresis) molecular technique used for the
detection and identification of anammox microorganism.
3.1.2 Pilot plants
During the project, two pilot plants were built. In a first stage, a laboratory plant with two reactors of 20 L each
was used in order to start-up and study both biological processes (Figure 2a). Afterwards, once PANI-SBR and
ANAMMOX processes were well known, a pilot plant consisting of two reactors of 250 L each was built (Figure
2b).
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(a)
(b)
Figure 2. Pilot plants of 20 L and 250 L in LEQUIA-UdG installations.
Figure 3 shows a scheme of the plants configuration, which were equipped with a monitoring and control system
that allowed the process control thanks to the continuous acquisition data by means of specific developed
software.
1
7
6
5
PC
4
10
8
9
3
2
1 STORAGE TANK
5 pH CONTROL
2 INFLUENT PUMP
6 PROBES (ORP, DO, T, pH)
3 JACKETED SBR
7 STIRRER
8 DISCHARGE VALVE
9 GAS (DO or N2) VALVE
10 CONTROL PANEL
4 THERMOSTATIC BATH
Figure 3. Pilot plants descriptions used for the PANI_SBR and Anammox reactors. The Anammox SBR was operated with
initial nitrogen gas addition while the PANI-SBR was aerated by compressed air diffusion.
3.1.3. Experimental procedure with pilot plants
Table 1 presents the main operational parameters of the SBRs. All the operational cycles were designed with an
8 hour length and a volumetric exchange ratio (VEX) defined as the ratio between the volume treated per cycle to
the maximum reactor volume.
Table 1. Main operation conditions of the SBRs during the experimental study.
Process
Units
PANI-SBR
Anammox SBR
Vmax
litres
20
16
Vmin
litres
9.7
13
VEX
0.225
0.103-0.188
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Temperature
ºC
36±1
36±0.3
Operation
Feed-batch & Step-Feed
Feed-batch
PANI -SBR
Feed -Batch
0
60
120
180
240
Time (min)
300
360
420
480
0
60
120
180
240
Time (min)
300
360
420
480
120
180
240
time (min)
300
360
420
480
Step-Feed
Anammox SBR
Feed -Batch
0
60
N2 gas addition
MixedFeeding
Reaction
Settling
Draw
Figure 4. Operational cycles for the SBRs.
The cycle definitions are depicted in Figure 4. The PANI-SBR, responsible for the partial nitritation process, was
operated under two filling strategies in order to identify the most stable effluent composition and stability (Ganigué
et al., 2007b). The anammox reactor was operated at different loading rates in order to obtain suitable enrichment
conditions for the initial growing of the anammox bacteria.
3.2 Thermal Drying Process
3.1.1. Pilot plants
A thermal drying plant, with a capacity of 500 kg/h of masse or influent
treated with a solid concentration of 3%, was installed in a landfill site
located on the Mediterranean coast of Spain (Alcora, Castelló). Two were
the innovations of this application. On one hand, the use of leachate as
influent and on the other hand, the plant was operated using the landfill
biogas as its energy source, whose design consumption was around 108
Nm3/h of biogas with a methane enrichment of 50%.
Figure 5. Semi-industrial thermal drying plant installed in Alcora (Castelló)
3.1.2. Experimental Procedure
During the running period, around two years, the operational conditions were established according to the
modifications carried out by adapting the plant to the innovative application with leachate. Three operational
periods were carried out to study thermal drying technology in leachate treatment: i) Period 1, starting up and
adjust of the plant with an unique kind of leachate; ii) Period 2, technical assessment with three different
leachates and iii) Period 3, test the effluent treated in PANI-SBR-ANAMMOX processes.
For each period, three complete analytical tests were done to determine chemical characteristics and physical
parameters of liquid influent, as well as solid and gaseous emissions. Each sample was collected by two official
laboratories with the aim of com paring results.
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4. RESULTS
4.1. Microbiological aspects
Several of the batch enrichments showed anammox activity, which was first confirmed by the monitorization of
nitrogen compounds and afterwards using PCR (Polymerase Chain Reaction) and FISH (Fluoresc ense In Situ
Hybridization) molecular techniques. Final identification of the microorganism was carried out by means of the
combination of PCR, DGGE (Denaturing Gradient Gel Electrophoresis) and Sequencing, which lead to the
determination of Candidatus Brocadia Anammoxidans as the responsible of anammox activity in all studied
enrichments.
4.2 PANI-SBR
The main goal of a partial nitritation process, as a previous step of an anammox reactor, is the production of an
effluent with a suitable ammonium to nitrite ratio on a stable way. Initially a SHARON (Single reactor system for
High Ammonium Removal Over Nitrite) was chosen, but showed as instability to influent loading shocks. Thus,
experiments have been conducted on a Partial Nitritation-Sequencing Batch Reactor (PANI-SBR) using two
different configuration cycles (feed-batch and step-feed), in order to evaluate them in terms of performance and
stability.
In Run A, the PANI-SBR was operated for more than 250 days in a feed-batch strategy. The reactor was
inoc ulated with nitrifying sludge from a urban WWTP and it was acclimated to the landfill leachate wastewater by
a progressive increase of the ammonium loading rate and the percentage of leachate in the feed. This start-up
period (about 190 days) concluded when stable conditions were reached treating raw urban landfill leachate
(results not shown). Figure 6a and 6b present the performance of PANI-SBR during 80 days subsequent to the
start–up period.
Concerning Run B, the reactor was operated for more than 160 days in a step-feed strategy, reaching a raw
leachate feeding 75 days after the start-up period (results not shown), a shorter time period than in Run A.
Results of the Run B during 85 days of stable performance treating raw urban landfill leachate are presented in
Figure 6c and 6d.
As can be seen in Figure 6, it was possible to partially nitritate the influent ammonium, avoiding further nitrification
of nitrite to nitrate. Looking in more depth the results, it can be observed (Figure 6a) that in Run A (feed-batch
strategy) the PANI-SBR performance presented a fluctuating behaviour, ranging the nitritation percentage from
30 to 55%. In contrast, the performance of Run B, presented in Figure 6c, demonstrated a higher stability treating
an influent ammonium concentration of 2500 mg N-NH4+•L-1, higher than the 1500 mg N-NH4+•L-1 treated in Run
A.
The nitritation performance is hardly dependent on the available alkalinity. Thus theoretically an influent HCO3:NH4+ molar ratio of about 1.14 is necessary to get a suitable feed for an anammox reactor. From Figure 6b and
6d it can be seen that Run B shows a more stable NH4+:NO2- molar ratio and, in addition, values obtained were
closer to the theoretical ones. Thus, if properly adjusting the influent HCO 3-:NH4+ molar ratio, the PANI-SBR will
produce an effluent with the desired composition (0.77 moles of NH4+ per mol of NO2-).
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Run B: Step-feed operation
Run A: Feed-batch operation
3000
a)
Nitrogen (mg N·L - 1)
2500
c)
Influent ammonium
Effluent ammonium
Effluent nitrite
Effluent nitrate
2000
1500
1000
500
b)
d)
NH4+ :NO2- effluent molar ratio
+
HCO :NH influent
3
4
2.5
molar ratio
Molar ratio
2.0
1.5
1.0
0.5
0.0
190
200
210
220
230
240
250
260
Time (days)
80
90
100
130
140
150
Time (days)
Figure 6: Influent and effluent evolution of the main chemical parameters. a) concentration of nitrogen compounds in Run A;
b) effluent NH4+:NO2- and influent HCO3 -:NH4+ molar ratio in Run A; c) concentration of nitrogen compounds in Run B; d)
effluent NH4+:NO2 - and influent HCO3-:NH4+ molar ratio in Run B.
4.3 ANAMMOX SBR
A 20 L reactor was inoculated with a mixture of different activated sludges, which previously had shown
anammox activity. The anammox SBR was operated for one year on an 8-hour cycle treating high nitrogen
content synthetic wastewater, without biodegradable organic matter. The SBR was operated at different nitrogen
load rate (NLR) and influent nitrite to ammonium ratios divided into three periods: start-up, enrichment and growth
(Table 2). During all the periods, a continuous supervision of SBR performance was done by following on-line and
analytical data as well as a microbiological supervision by molecular techniques.
Table 2. Anammox SBR operational, influent conditions and performance during experimental periods.
Days
Influent NO2--N/NH4+-N ratio
NLR applied (Kg N·m-3·d -1)
Influent NH4+-N (mg N·L-1)
Influent NO2--N (mg N·L-1)
Influent NO3--N (mg N·L-1)
Ammonium removal (%)
Nitrite removal (%)
HRT average (days)
pH range (pH units)
Start-up
0-78
0.76
0.01-0.02
14.9-24.5
9.6-20.9
200.6-31.8
0-53
0-56
2.93
7.5-8.1
Enrichment
79-225
1.00
0.02-0.26
21.9-250.0
22.2-263.1
34.8-28.2
53-79
56-96
2.06
7.4-8.4
Growth
226-365
1.32
0.26-1.60
272.0-1268.0
340.0-1661.4
27.0-0
79-99
96-99
1.88
7.2-8.6
During the whole experimental period, different operational parameters were studied, as for example, different
inlet nitrogen load rates (NLR ) which was gradually increased from 0.01 to 1.6 Kg N·m -3·d-1 (Figure 7), or
different nitrite-ammonium ratio in the influent (between 0.72 and 1.32 mol·mol-1). This figure also shows relation
between the nitrogen load rate (NLR, Kg N·m -3·d-1) and nitrogen discharge rate (NDR, Kg N·m -3·d-1) calculated
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from SBR discharge. Also, right axis represents the evolution of nitrogen removal rate (NRR, Kg N·m -3·d-1) with a
natural log axis.
-
+
Influent NO2 -N:NH4 -N molar ratio
0.76
1.00
1.32
e3
1.8
e2
NRR=0.0014·e0.0225·t
r2=0.9824
1.4
e1
e0
1.2
e -1
1.0
e -2
0.8
e -3
e -4
0.6
-3
-1
NRR (Kg N·m ·d )
-3
-1
NLR & NDR (Kg N·m ·d )
1.6
e -5
0.4
e -6
0.2
e -7
e -8
0.0
0
30
Oct-05
60
90
120
150
180
Dec-05
210
240
270
300
330
May-06
360
Oct-06
time (d)
NLR (NH4 +-N + NO2- -N)
NDR (NH 4+ -N + NO 2--N)
NRR (natural log)
Figure 7. Evolution of nitrogen loading rate (NLR), nitrogen discharge rate from the SBR (NDR) and the nitrogen removal
rate (NRR) presented in natural log axis.
In parallel, a 2 L SBR reactor was operated treating an influent consisting of the effluent of a PANI-SBR process,
diluted with tap water, which had treated raw leachate. The same operational conditions than in the 20 L SBR
were applied and after 60 days of operation the process showed anammox activity showing. As total nitrogen in
the influent was increased, it was also increased nitrogen removal in the outlet achieving efficiencies of more than
98%. It was also seen that 80% of nitrogen removal was due to anammox activity, while the other 20% was due
to heterotrophic activity.
With these results, a 250 L SBR Anammox reactor was started up using a raw leachate treated with PANI-SBR
with NO dilution influent.
Figure 8. Anammox biomass
4.4. Thermal Drying Process
Analytical results of the three operational periods are shown in Talbe 3. Chemic al characterisation of the leachate
for the two first operational periods was ranged between 13.690 and 81.400 µS/cm of Conductivity, 4.660 and
24.300 mg/L of COD, 137 and 3.930 mg/L N as Ammonia, 11.428 and 82.000 mg/L Dry Matter, 330 and 31.276
mg/L Chlorides, 2,2 and 282 mg/L Sulphides, and pH between 6,6 and 8,4. The higher values of contaminants
were found in the concentrate of reverse osmosis.
After thermal drying treatment, all contaminants remained immobilized in the dry powder, meanwhile the rest
appeared in atmospheric emissions, which were kept under allowed legal limits (Real Decreto 833/1975, BOE
num 290) as it is shown in Table 3.
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Table 3: Atmospheric emissions produced by thermal dry plant during the whole operational periods.
Atmospheric Emissions
Sulphide acid (Kg H2S/h)
Ammonia (Kg N-NH3/h)
Chloride (Kg Cl/h)
VOCs (Kg C/h)
Odour Units (UOE/Nm3)
Period 1
Test 1
0,0023
0,4444
0,0024
0,0130
9.713
Test 2
0,0054
0,9765
0,0056
0,0006
7.510
Test 3
0,0143
1,4569
0,0081
0,0026
7.610
Period 2
Test 4
0,0019
0,0156
0,0094
0,0006
2.150
Test 5
0,0409
0,1043
0,0102
0,0006
380
Test 6
0,0223
0,4433
0,0115
0,0001
1.140
Period 3
Effluent
0,0000
0,0182
0,0000
0,0004
1.375
Legal
Limit
100
No limit
1
10
Otherwise, ignition and explosive point of dry powder were determined to avoid some disposal risk. All samples
showed no explosive behaviour and only tests 5 and 6 showed a minimum ignition temperature for a layer layout
at 350ºC and 270ºC respectively.
In Period 3, the effluent coming from PANI-SBR-ANAMMOX processes, basically composed by salts, must be
dried. As the biological process was still not able to generate enough effluent to be dried in the thermal plant, the
effluent obtained was analysed and characterized and then, a similar effluent coming from classical biological
nitrification and denitrification treatment was found and used. After thermal dry treatment, all contaminants
remained again in the dry powder, which will be disposed in an appropriate landfill. Atmospheric emissions,
presented as an average of three analytical tests in Table 3, were kept lower than the values obtained in periods
1 and 2 and under allowed legal limits, as it is shown in Table 3.
4.5 Environmental and Economic Analysis
An environmental analysis was carried out in order to evaluate and compare environmental and economical costs
of a conventional leachate treatment, consisting of OHP plus NH 4 Stripping, versus CLONIC treatment (PANISBR+Anammox+ Thermal Drying). Thus, FLEXRIS methodology was used, which is based on two methods:
Benefit Transfer method, for obtaining means values for each pollutant cost; and Statistical probabilistic method,
for parameter estimation (mean and standard deviation) and to establish the confidence level of obtained results.
Results showed an environmental cost of 0,02566 €/L for the conventional treatment and 0,013315 €/L for the
CLONIC treatment, that is to say, that the CLONIC process achieves an environmental improvement of 48%.
5. CONCLUSIONS
This project has demonstrated the effectiveness and the environmental interest of the leachate treatment with the
PANI-SBR-ANAMMOX and thermal dry processes. During the whole operational running, the viability of PANISBR applied to leachates directly followed by Anammox process has been demonstrated obtaining a nitrogen
removal of 98%. Whereas, Thermal Dry technology has been shown as an effective process for salinity influents,
because all salts remained in the solid powder produced, having lower concentrations in the atmospheric
emissions than environmental requirements. Furthermore, the operational parameters to treat landfill leachates
have been defined for both technologies.
Both combined processes, PANI-SBR-ANAMMOX with THERMAL DRYING, represent a technical, economical
and environmental alternative for leachate treatment with important advantages in relation to present treatments.
Application of both processes allows landfills to avoid external treatment of leachates, closing the cycle at the
same landfill and reducing environmental impact.
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