CLONIC CLOSING THE NITROGEN CYCLE FROM URBAN LANDFILL LEACHATE BY BIOLOGICAL NITROGEN REMOVAL OVER NITRITE AND THERMAL TREATMENT

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1 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, 0800 Barcelona, Spain. {teresa.vives, e.gonzalez, e.jimenez, m.elorduy}@cespa.es **LEQUIA-UdG, Institute of Environment, University of Girona, Campus Montilivi s/n, Girona, Catalonia, Spain. {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, Cornellà de Llobregat, Barcelona. E- mail:{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 1/9

2 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 ( ).. 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., 007a) 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..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. + NH + HCO + 1.5O NO + 3H O + CO 4 3 (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. + + NH NO HCO H 1.0 N NO CH O N H O (Equation ) 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. 00). 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). /9

3 .. 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 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. (a) (b) Figure 1. (a) Batch culture enrichment (b) DGGE (Denaturing Gradient Gel Electrophoresis) molecular technique used for the 3.1. Pilot plants detection and identification of anammox microorganism. During the project, two pilot plants were built. In a first stage, a laboratory plant with two reactors of 0 L each was used in order to start-up and study both biological processes (Figure a). Afterwards, once PANI-SBR and ANAMMOX processes were well known, a pilot plant consisting of two reactors of 50 L each was built (Figure b). 3/9

4 (a) (b) Figure. Pilot plants of 0 L and 50 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 PC STORAGE TANK 5 ph CONTROL 8 DISCHARGE VALVE INFLUENT PUMP 6 PROBES (ORP, DO, T, ph) 9 GAS (DO or N) VALVE 3 JACKETED SBR 7 STIRRER 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 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 V max V min V EX Temperature Operation Units litres litres - ºC PANI-SBR ±1 Feed-batch & Step-Feed Anammox SBR ±0.3 Feed-batch 4/9

5 PANI-SBR Feed-Batch Time (min) Step-Feed Time (min) Anammox SBR Feed-Batch time (min) N 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., 007b). 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. Thermal Drying Process 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) 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, 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. 5/9

6 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. 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 50 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 500 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- :NH 4+ 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 + :NO - molar ratio and, in addition, values obtained were closer to the theoretical ones. Thus, if properly adjusting the influent HCO3 - :NH4 + molar ratio, the PANI-SBR will produce an effluent with the desired composition (0.77 moles of NH4 + per mol of NO - ). 6/9

7 a) Run A: Feed-batch operation Influent ammonium Effluent ammonium Effluent nitrite Effluent nitrate c) Run B: Step-feed operation Nitrogen (mg N L -1 ) b) NH :NO effluent molar ratio - + HCO :NH influent molar ratio 3 4 d).5.0 Molar ratio Time (days) Time (days) Figure 6: Influent and effluent evolution of the main chemical parameters. a) concentration of nitrogen compounds in Run A; b) effluent NH4 + :NO - and influent HCO3 - :NH4 + molar ratio in Run A; c) concentration of nitrogen compounds in Run B; d) effluent NH4 + :NO - and influent HCO3 - :NH4 + molar ratio in Run B. 4.3 ANAMMOX SBR A 0 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 ). 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. Anammox SBR operational, influent conditions and performance during experimental periods. Start-up Enrichment Growth Days Influent NO--N/NH4+-N ratio NLR applied (Kg N m-3 d -1) Influent NH4+-N (mg N L-1) Influent NO--N (mg N L-1) Influent NO3--N (mg N L-1) Ammonium removal (%) Nitrite removal (%) HRT average (days) ph range (ph units) 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 0.7 and 1.3 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 7/9

8 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 NO - -N:NH 4 + -N molar ratio e 3 NLR & NDR (Kg N m -3 d -1 ) NRR= e 0.05 t r =0.984 e e 1 e 0 e-1 e - e -3 e -4 e -5 e -6 NRR (Kg N m -3 d -1 ) 0. e Oct-05 Dec-05 May-06 Oct-06 time (d) NLR (NH + 4 -N + NO - -N) NDR (NH + 4 -N + NO - -N) NRR (natural log) e -8 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 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 0 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 0% was due to heterotrophic activity. With these results, a 50 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 and µs/cm of Conductivity, and mg/l of COD, 137 and mg/l N as Ammonia, and mg/l Dry Matter, 330 and mg/l Chlorides,, and 8 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 90) as it is shown in Table 3. 8/9

9 Table 3: Atmospheric emissions produced by thermal dry plant during the whole operational periods. Period 1 Period Period 3 Legal Atmospheric Emissions Test 1 Test Test 3 Test 4 Test 5 Test 6 Effluent Limit Sulphide acid (Kg HS/h) 0,003 0,0054 0,0143 0,0019 0,0409 0,03 0, Ammonia (Kg N-NH3/h) 0,4444 0,9765 1,4569 0,0156 0,1043 0,4433 0,018 No limit Chloride (Kg Cl/h) 0,004 0,0056 0,0081 0,0094 0,010 0,0115 0, VOCs (Kg C/h) 0,0130 0,0006 0,006 0,0006 0,0006 0,0001 0, Odour Units (UOE/Nm3) 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 70ºC 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 and under allowed legal limits, as it is shown in Table 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 NH4 Stripping, versus CLONIC treatment (PANI- SBR+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 0,0566 /L for the conventional treatment and 0, /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 PANI- SBR 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. 9/9