International Biodeterioration & Biodegradation xxx (2014) 1e7 Contents lists available at ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod Application of a partial nitritation and anammox system for the old landfill leachate treatment Phan The Nhat a, Ha Nhu Biec a, Nguyen Thi Tuyet Mai a, Bui Xuan Thanh b, *, Nguyen Phuoc Dan a a Faculty of Environment and Natural Resources, Ho Chi Minh City University of Technology, Building B9, 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City, Viet Nam Division of Environmental Engineering and Management, Ton Duc Thang University, No 19 Nguyen Huu Tho Street, Tan Phong Ward, District 7, Ho Chi Minh City, Viet Nam b a r t i c l e i n f o a b s t r a c t Article history: Received 15 January 2014 Received in revised form 29 May 2014 Accepted 30 May 2014 Available online xxx This study shows high nitrogen removal efficiency of a combination of partial nitritation and Anaerobic Ammonium Oxidation (anammox) process for old landfill leachate treatment A lab-scale experiment including partial nitritation using a sequencing batch reactor (PN-SBR) followed by a anammox hybrid reactor (HAR), which consists of suspended biomass layer in the bottom part and bio-carrier bed in the upper part run at the influent total ammonia concentrations (TAN) of 500 mg N/L and 1000 mg N/L The result of PN-SBR experiment showed that the NO2eN:NH4eN ratio achieved about 1.22 and 1.02 at HRT of 12 h (influent TAN of 500 mg N/L) and HRT of 19 h (influent TAN of 1000 mg N/L), respectively Simultaneously, the HAR was operated at the nitrogen loading rate (NLR) of 4.2 and 8.3 kg N/m3.d, corresponding to influent TAN of 500 mg N/L and 1000 mg N/L, respectively The effluent of the system containing 9.7 ± 3.5 mg NH4eN/L, 1.7 ± 0.4 mg NO2eN/L and 23 ± mg NO3eN/L (equivalent to 35 ± mg TN/L) at NLR of 1.02 for PN-SBR and NLR of 4.2 kg N/m3.d for HAR This effluent quality was good enough to meet Vietnamese treated landfill leachate quality The system obtained TN removals of 93 ± 1% and 81 ± 1.2% at NLRs of 4.2 kg TN/m3.d (phase I) and 8.3 kg TN/m3.d (phase II), respectively The total biomass of HAR including attached biomass and suspended one was maintained up to 20,400 mgVSS/L at the end of the experiment when the removal rate of anamnox biomass obtained 0.4 kg TN/kgVSS.d While, PN-SBR was kept at 2300 mg MLVSS/L and SRT of 10e12 days at NLR of 4.2 kg TN/m3.d, which the nitrogen conversion rate of AOB was 0.53 kg TAN/kgVSS.d In terms of COD removal, it is found that PN-SBR removed only 14% of influent COD, whereas HAR removed 30% of COD © 2014 Published by Elsevier Ltd Keywords: Partial nitritation Old landfill leachate SBR and hybrid anammox reactor Introduction Sanitary landfill is the most common municipal solid waste disposal in Vietnam Leachate generated from the landfills has caused serious water pollution due to high concentrations of ammonia and slowly or non-biodegradable organic matter High total ammonia concentration (TAN) results in high toxicity by free ammonia which inhibits anaerobic degradation of solid wastes and increases dissolved oxygen depletion in the receiving water The ammonia concentration in the leachate varies with the age of the landfill and it is in the range of 100e5500 mg N/L (Sri Shalini and Joseph, 2012) In Vietnam, all leachate treatment plants have not met the leachate quality standards (QCVN 25:2009/BTNMT) in * Corresponding author E-mail addresses: phanthenhat@gmail.com (P.T Nhat), bxthanh@tdt.edu.vn, bxthanh@hcmut.edu.vn (B.X Thanh), npdan@hcmut.edu.vn (N.P Dan) terms of the allowable ammonia (25 mgN/L) and total nitrogen concentrations (60 mg N/L) (Monre, 2009) In Vietnam, the current leachate treatment plants use mainly the conventional nitrification-denitrification process, which is costly due to large oxygen supply demand for nitrification and carbon source requirement for denitrification In recent years, a partial nitritation coupled with anammox process have proven as a feasible technology for nitrogen removal in comparison to the conventional nitrificationedenitrification process (Van Dongen, 2001; Fux et al., 2002; Schmidt et al., 2003) This process consumed less 50% of oxygen demand, did not use organic carbon sources, produced less sludge amount and less CO2 emission (Reginatto et al., 2005) The arrangement of partial nitritation and anammox processes was done in single reactors or in two separate reactors in series The two-step process is recommended to avoid heterotrophic growth in the anammox reactor as well as to enhance the NH4eN removal in the case of high influent TKN concentration (Van Hulle et al., 2007) http://dx.doi.org/10.1016/j.ibiod.2014.05.025 0964-8305/© 2014 Published by Elsevier Ltd Please cite this article in press as: Nhat, P.T., et al., Application of a partial nitritation and anammox system for the old landfill leachate treatment, International Biodeterioration & Biodegradation (2014), http://dx.doi.org/10.1016/j.ibiod.2014.05.025 P.T Nhat et al / International Biodeterioration & Biodegradation xxx (2014) 1e7 Table Characteristics of old landfill leachate in the study Parameter Unit Mean value ± std (n ¼ 8) pH Alkalinity TKN NH4eN (TAN) NO2eN NO3eN COD BOD5 SS mg CaCO3/L mg N/L mg N/L mg N/L mg N/L mg/L mg/L mg/L 8.4 15133 3868 3449 0.21 2.23 3621 425 59 ± ± ± ± ± ± ± ± ± 0.30 58 26 233 0.01 0.18 440 72 16 Some studies shown application of partial nitritation and anammox processes for leachate treatment were potential control for nitrogen removal (Liang and Liu, 2007; Xiao et al., 2009; Xu et al., 2010; Yapsakli et al., 2011) However, these processes only run at low nitrogen loading rates in the previous studies and it ranged from 0.17 to 0.96 kg N/m3.d (Liang and Liu, 2008; Xu et al., 2010; Rucalleda, 2011; Wang et al., 2011) Therefore, this study aimed to evaluate the feasibility of the partial nitritation followed by anammox process at high nitrogen loading rates for the old landfill leachate treatment A partial nitritation SBR and a hybrid anammox reactor were used in this study is shown in Fig The PN-SBR is a cylindrical reactor with the working volume of 66.5 L Its size is 0.6 m high and 0.42 m in internal diameter Air was supplied from the bottom of the PN-SBR through five air diffusors, and the air flow was adjusted by a manual valve to maintain the DO concentration higher than mg/L The diluted feed raw leachate stored in 300 L tank, was pumped to the PN-SBR A mechanical stirrer at 30 rpm was used to enhance the complete mixing with aeration The supernatant decanted from PN-SBR was stored in a container with volume of 90 L, and then it was pumped to the HAR The HAR was made of acrylic tube with an internal diameter of 114 mm and the ratio of height to diameter is 5.7 Its working volume was L The HAR comprised suspended biomass layer located in the bottom part, a spiral structure column that was made from stainless steel in the middle part and a fixed bio-carrier bed in the upper part The spiral column consisted of pitches to separate the nitrogen air from anammox sludge The distance between pitches was cm, the length of whole spiral column was 28 cm Slope of each pitch was 300 The biomass carrier consisted of polyester non-woven porous sheets, which have a total one-sided area of 1116 cm2, thickness of 0.5 cm and height of 31 cm (Japan Vilene, US patent 5,185,415, 1993) This carrier was designed to enhance biomass attachment and to prevent the washout of biomass from the reactor A gas collector was installed at top of HAR Materials and methods 2.2 Experimental set-up and operational conditions 2.2.2 Enrichment of sludge 2.2.2.1 AOB sludge The seed sludge was activated sludge from an aeration tank of the Go Cat leachate treatment plant An enrichment of AOB was conducted in PN-SBR 546 g TSS of the seed sludge was seeded into the reactor to obtain VSS concentration of 1500 mg/L The ratio of VSS and TSS was 0.25 AOB sludge was enriched using the leachate diluted with tap water to achieve NH4eN concentration of 500 mg N/L The PN-SBR run at DO higher than mg/L and HRT of 21 h for 45 days Enrichment of AOB was completed until the conversion efficiency of NH4eN to NO2eN reached more than 90% The effluent NO2eN and NO3eN concentration after enrichment were 486 mg N/L and 15 mg N/L, respectively 2.2.1 Experimental set-up A lab-scale partial nitritation-anammox system including a PNSBR followed by HAR was used in this study The schematic diagram 2.2.2.2 Anammox sludge The HAR was inoculated with g MLVSS of anammox sludge, which was taken from the current polyester non-woven carrier reactor (PNBCR) (Nhat et al., 2012) The 2.1 Feed leachate Landfill leachate used in the study was collected from Go Cat municipal solid waste landfill in Ho Chi Minh city, Vietnam, which was closed in 2007 Its characteristics are shown in Table Table indicates that the typical characteristics of old landfill leachate contained high NH4eN concentration and low BOD5:COD ratio (Kjeldsen et al., 2002) Feed leachate was diluted with tap water to obtain the influent ammonia concentration ranging from 500 to 1000 mg N/L HAR (b) Effluent Influent 28 cm 20 cm cm Supernatant tank ( 90 L) 28 cm 12 cm 31 cm PN-SBR (a) Sludge (1)Influent pump; (2) feed raw leachate tank; (3) stirrer; (4) air pump; (5) gas collector; (6) polyester non-wovenbiomasscarrier; (7)spiral column and (8) suspended anammox blanket Fig Schematic diagram of the lab-scale PN-SBR and HAR system Please cite this article in press as: Nhat, P.T., et al., Application of a partial nitritation and anammox system for the old landfill leachate treatment, International Biodeterioration & Biodegradation (2014), http://dx.doi.org/10.1016/j.ibiod.2014.05.025 P.T Nhat et al / International Biodeterioration & Biodegradation xxx (2014) 1e7 into PN-SBR effluent tank to reduce DO less than 0.5 mg/L Amount of 20 mg Na2SO3 was used to reduce about mg DO Influent pH was adjusted in the range of 6.8e7.1 by HCl 20% solution Operational conditions of the experiment show in Table Table Operational conditions of PN-SBR and HAR system Time (days) I 1ste45th II 45the90th HRT (h) The influent TAN concentration (mg N/L) 500 1000 TAN loading rate (kg/m3.d) PN-SBR HAR PN-SBR HAR 19 15 12 19 21 0.7 0.8 1.0 1.3 1.2 4.2 2.3 Analytical methods 8.3 dominant bacterial species in the consortium was identified as the anammox Candidatus Kuenenia stuttgartiensis and uncultured anoxic sludge bacterium KU2 (Nhat et al., 2012) The enriched anammox biomass was adapted with synthetic wastewater (NH4Cl 215 mg N/ L, NaNO2 248 mg N/L, KHCO3 125 mg/L, KH2PO4 54 mg/L) Trace element solutions were added based on the previous studies (Van de Graff et al., 1996) The HAR run at the nitrogen loading rate of kg N/m3/d during the enrichment of 60 days The enrichment was completed when the nitrogen the TN removal efficiency was above 90%, corresponding to the obtained removal rate (NRR) of 7.2 kg N/ m3/d Then, the influent of HAR was switched to the effluent of PNSBR fed with the real leachate 2.2.3 Operational conditions 2.2.3.1 Partial nitritation-Sequencing batch reactor (PN-SBR) PN-SBR was operated with 10 of feed, 45 of settle and of decant The adjustment of the aerobic reaction time of reactor depended on the effluent NO-2eN to NHỵ -N ratio HRT was determined by the aerobic reaction time, total cycle time and volume exchange ratio pH of the influent was controlled at 7.5 ± 0.2 by adding HCl 20% solution DO in the reactor was maintained higher than mg/L The study was operated at the influent total ammonia concentration (influent TAN) of 500 and 1000 mg N/L The study aimed to determine a proper HRT of reactor at every influent TAN concentration in order to obtain the suitable NO-2eN to NHỵ eN ratio for anammox process Operational conditions were presented in Table 2.2.3.2 Hybrid anammox reactor (HAR) The experiment was run under dark condition by using a black plastic sheet enclosing fully the reactor body to prevent algal growth Na2SO3 salt was added pH and DO were measured by using pH meter (HI 8314, Hanna) and DO meter (InoLab 740 with terminal 740 WTW, Germany), respectively Total suspended solids (TSS), volatile suspended solids (VSS), COD, NH4eN, NO2eN and NO3eN and alkalinity were measured according to Standard Methods for examination of Water and Wastewater (APHA, 1998) Sample filtration was done using Whatman filter papers with pore size of 0.45 mm Results and discussion 3.1 Partial nitritation SBR (PN-SBR) After 45 days of enrichment, NH4eN was converted to NO2eN over 90% at the influent NH4eN concentration of 500 mg N/L and HRT of 21 h To get suitable influent for anammox process, the partial nitritation should be run to reach to the stoichiometric NO2eN:NH4eN ratio of 1.32 HRT of SBR was adjusted at values less than 21 h (19 h, 15 h and 12 h) At HRT of 19 h, NO2eN: NH4eN ratio was still high (2.75 ± 0.87, n ¼ 4) under steady-state condition At the loading rate of 0.7 kg TAN/m3.d, the mean effluent TAN and NO2eN concentrations were 142 ± 35 mg N/L and 370 ± 28 mg N/L, respectively The ratio decreased to 1.53 ± 0.05 (n ¼ 6) at HRT of 15 h (NLR of 0.8 kg TAN/m3.d) The steady state condition reached after 03 days of running at HRT of 12 h The obtained NO2eN: NH4eN ratio was 1.22 ± 0.1 (n ¼ 5) that was close to the stoichiometric ratio for anammox process The mean effluent TAN and NO2eN concentrations were 224 ± and 274 ± 14 mg N/L, respectively In this phase, the effluent NO3eN concentration was low (15 ± mg N/L), equivalent to 3% of influent TAN It means that the partial nitritation which run at long HRT (15 h) and at NLR of 1.0 kg TAN/m3.d did not exist nitrate accumulation In phase II, the influent TAN concentration was increased to 1000 mg N/L From 45th to 54th day, the NO2eN: NH4eN ratio was low 0.67 ± 0.02 (n ¼ 4) at HRT 19 h (Fig 2) It may be due to the short HRT (19 h) coupled with high NLR (1.3 kg TAN/m3.d) that AOB were not able to convert 50% of TAN to nitrite As HRT increased up 4.0 Nitrogen Concentration (mg N/L) 1200 Phase II Phase I 1000 3.0 2.75 800 600 1.53 400 2.0 1.22 1.02 1.0 NO2-N:NH4-N ratio Phase 0.67 200 0.0 19 Inf N-NH4 Eff N-NO3 15 12 19 Nitrogen Loading Rate (kgN/m3.day) Eff N-NH4 Eff NH4:NO2 ratio 21 Eff N-NO2 Stoichiometrical ratio Fig Conversion of TAN and the effluent NO2eN to NH4eN ratio at the various HRTs in the PN-SBR experiment Please cite this article in press as: Nhat, P.T., et al., Application of a partial nitritation and anammox system for the old landfill leachate treatment, International Biodeterioration & Biodegradation (2014), http://dx.doi.org/10.1016/j.ibiod.2014.05.025 P.T Nhat et al / International Biodeterioration & Biodegradation xxx (2014) 1e7 Table shows the biomass concentration and sludge retention time in both phases At NLR of 1.22 kg TAN/m3.d, the nitrogen conversion rate of AOB was 0.53 kg TAN/kg MLVSS.d It is found that scum happened in Phase I (SRT of 20 days), whereas it insignificantly occurred in Phase II The average effluent SS after 45 of settling was 19 ± mg/L that shown a good settling ability of AOB at SRT of 12 days Table Biomass concentration and sludge retention time in the experiment Phase SRT, days SS, mg/L MLSS, mg/L MLVSS, mg/L SVI, mL/g VSS I 20 days II 10e12 days 23 ± (n ¼ 6) 19 ± (n ¼ 13) 7712 ± 750 (n ¼ 6) 5583 ± 570 (n ¼ 7) 3479 ± 244 (n ¼ 6) 2298 ± 133 (n ¼ 7) 34 ± (n ¼ 6) 43 ± (n ¼ 7) NLR, NRR kgN/m3.day) to 21 h at NLR of 1.2 kg TAN/m3.d, NO2eN: NH4eN ratio of 1.02 ± 0.18 (n ¼ 12) was obtained The effluent TAN and NO2eN concentrations were 469 ± 58 mg N/L and 516 ± 40 mg N/L, respectively The effluent NO3eN concentration was low (20 ± 7) mg N/L The result of this study was similar to that of Taichi Yamamoto et al (2008), who used successfully partial nitritation reactor for swine wastewater digester liquor at TAN loading rate of 1.0 kg N/m3.d With the above result, it is expected that PN-SBR may run effectively at higher influent TAN concentration at longer HRT and at NLR which should be kept by 1.2 kg TAN/m3.d However, increase of influent TAN concentration may result in rise of free ammonia (FA) in SBR as well as rise of alkalinity demand as carbon sources for AOB Some previous studies claimed that nitritation process running at the NLRs over kg TAN/m3.d was inhibited AOB growth at FA concentration of about 150 mg N/L (Anthonisen et al., 1976; et al., 2012) In this study, the Kurniawan et al., 2006; Ganigue average FA concentration in the PN-SBR was less than 20 mg N/L that did not inhibited AOB 10.0 3.2 Hybrid anammox reactor (HAR) In enrichment, the HAR was run with the synthetic wastewater at 8.0 kg TN/m3.d After two months, the obtained TN removal rate was 7.9 kg TN/m3/d The HAR was then run with the effluent from PN-SBR High nitrogen removal rate (3.6 kg TN/m3/d) was obtained at NLR of 4.0 kg TN/m3.d after 45 days of run This presented that the components of the leachate with TN of 500 mg N/L from PNSBR did not cause negative impact on anammox bacteria Fig 3a,b shows the time courses of TN (TAN ỵ NO2eN) removal efciency and TN removal rate of the HAR during 90 days of experiment The obtained TN removals were 93 ± 1% and 81 ± 1.2% at NLRs of 4.3 kg TN/m3.d (phase I) and 8.3 kg TN/m3.d (phase II), respectively At NLR of 4.0 kg N/m3.d, the effluent TAN, NO2eN, and NO3eN of HAR were 9.7 ± 3.5 mg N/L, 1.7 ± 0.4 mg N/L and 23 ± mg N/L, respectively This effluent quality was good enough to meet QCVN 25:2009/BTNMT At NLR of 8.3 kg N/m3.d (HRT of h and influent TN concentration of 1000 mg N/L), the effluent TAN, NO2eN, NO3eN and TN Phase II Phase I 8.0 6.0 4.0 NLR 2.0 NRR 0.0 (a) Nitrogen concentration (mg N/L) 1200 1000 Phase II Phase I 800 600 400 200 12 18 24 30 36 42 48 54 60 66 81 90 Operating time (day) Inf TAN (PNSBR) Eff NO3 (PNSBR) Eff NO3 (HAR) Eff NH4 (PNSBR) Eff NH4 (PNSBR) Eff NO2 (PNSBR) Eff NO2 (HAR) (b) Fig Time courses of the whole system: (a) Nitrogen loading rate (NLR) and nitrogen removal rate (NRR); (b) Nitrogen concentration Please cite this article in press as: Nhat, P.T., et al., Application of a partial nitritation and anammox system for the old landfill leachate treatment, International Biodeterioration & Biodegradation (2014), http://dx.doi.org/10.1016/j.ibiod.2014.05.025 P.T Nhat et al / International Biodeterioration & Biodegradation xxx (2014) 1e7 Ammonia removal (%) concentrations were 76 ± 11 mg N/L, 80 ± mg N/L, 39 ± mg N/L and 196 ± 12 mg N/L, respectively This effluent quality was not met threshold values of the leachate quality standards It is expected that the effluent nitrogen concentration may reach the QCVN 25:2009/BTNMT as the HAR is run at lower NLR, corresponding to longer HRT The produced NO3eN was about 10% of influent TN in anammox process (Furukawa et al., 2009) In the anammox process, the stoichiometric ratio of NH4eN and NO2eN consumption and the NO3eN production (molar NH4:NO2:NO3 ratio) is 1:1.32:0.26 (Strous et al., 1998) The obtained molar NH4:NO2:NO3 ratios in this study were 1:1.27:0.03 at phase 1and 1:1.13:0.05 at phase The different ratios were reported by some previous researches on leachate treatment The study of Ruscalleda (2011) and Liang and Liu (2008) presented the ratio of 1: 1:42: 0:15 and 1:1.09: 0.007, respectively The significant difference between the obtained ratios in this study and the stoichiometric value is nitrate production This may be due to the presence of heterotrophic denitrifying bacteria in the HAR Indeed, nitrate reduction coupled with COD removal was found during all the operational periods Liang and Liu (2008) who used an up-flow fixed bed annamox biofilm reactor for old landfill leachate treatment shown that the obtained NRR was 0.2 kg N/m3.d at TN concentrations of 1000e1500 mg N/L The research of Furukawa et al (2009) got NRR of 4.2 kg N/m3.d for a PEG gel carrier anammox reactor used to treat anaerobic swine wastewater digester liquor at NLR of 5.3 kg N/m3.d In comparison with the above researches, an extremely high NRR (7.3 kg N/m3.d) at NLR of 8.3 kg N/m3.d was achieved in this study 100 90 80 70 60 50 40 30 20 10 Biomass concentration increased from 9000 mg/L at the beginning of enrichment to 28,960 ± 980 mg MLSS/L and 20,400 ± 1000 mg MLVSS/L at the end of the experiment The maximum total nitrogen removal rate of anamnox biomass was 0.4 kg TN/kgVSS.d The average effluent SS during the phase II was 10 ± mg/L This presents the sludge wash-out was not remarkably during the experiment It is explained that the combination between suspended growth using a spiral column and the bio-carrier enhanced the sludge wash-out Figs 4a and b presents the TAN conversion of PN-SBR, HAR and TN removal of the whole system The ammonia removal of the overall system depended much on ammonia conversion of PN-SBR In phase I, the ammonia removal of 99 ± 1% in the overall system was achieved when conversion of NH4eN of PN-SBR was 61 ± 8% Whereas, in phase II, the ammonia removal (91 ± 3%) and conversion to nitrite (49 ± 6%) of the whole system were little bit lower Fig 4b shows that the TN removal efficiency was 85 ± 7% and 81 ± 1% in Phase I and Phase II, respectively The highest TN removal of the whole system was reached at the end of the phase I when the molar NH4:NO2 ratio of PN-SBR was 1.22 Thus, control of molar NH4:NO2 ratio of PN-SBR is very important to aim to high TN removal efficiency of the overall system 3.2.1 COD Removal Fig shows the removal of COD of overall system during 100 days of experiment The COD removal efficiency of overall system in phase I and II were 50 ± 3% and 46 ± 12%, respectively The COD removal by PN-SBR was low, it was only 18 ± 4% in phase I and Phase I 12 18 Phase II 24 30 HAR 36 42 48 54 60 PN-SBR 66 81 90 Operation time (day) TN removal (%) (a) 100 95 90 85 80 75 70 65 60 55 50 Phase II Phase I 12 18 24 30 36 42 48 54 60 66 81 90 Operating time (day) (b) Fig Time course of nitrogen removal of PN-SBR and HAR system experiment: (a) Ammonia; (b) TN (TAN þ NO-2eN þ NO-3eN) Please cite this article in press as: Nhat, P.T., et al., Application of a partial nitritation and anammox system for the old landfill leachate treatment, International Biodeterioration & Biodegradation (2014), http://dx.doi.org/10.1016/j.ibiod.2014.05.025 P.T Nhat et al / International Biodeterioration & Biodegradation xxx (2014) 1e7 Inf COD (PNSBR) Eff COD (PNSBR) Eff COD (HAR) COD Concen (mg/L) 1200 Phase I 1000 Phase II 800 600 400 200 12 18 24 30 36 39 42 48 54 60 63 66 69 72 75 78 81 84 87 90 Time course (day) Fig Removal of COD in the PN-SBR and HAR system 12 ± 5% in phase II It is due to low ratio of BOD5 to COD in the raw leachate (around 0.1) The average BOD5 of leachate (425 ± 72 mg BOD5/L) was 12% of total COD BOD5 content was completely removed in the PN-SBR The result is similar to that of the study of Wang et al (2014) which presented the low COD removal (30%) and high BOD5 removal (80%) in the PN-SBR The COD removal of the HAR ranged from 14 to 46%, whereas biodegradable COD were fully removed in the PN-SBR Similarly, Liang and Liu (2008) reported that old landfill leachate treatment using anammox reactor obtained COD removal of 23e41% Bacterial community of the HAR may remove refractory organics such as fulvic-like compounds from the PN-SBR effluent Denitrifying bacteria could not directly use aquatic humic substance (AHS) in the leachate Liang and Liu (2008) indicated that some kinds of heterotrophs living in community of annamox biomass were able to degrade AHS into readily biodegradable organic matters which were then utilized by denitrifier living in the community Conclusions The system including a PN-SBR followed by a HAR was able to remove efficiently total nitrogen from the old landfill leachate The effluent quality was met the Vietnamese leachate quality standards at NLR of 1.0 kg TAN/m3/d for PN-SBR and 4.0 kg TN/m3.d for HAR The HAR obtained the extremely high NRR of 7.3 kg TN/m3/ day at NLR of 8.3 kg TN/m3/day The achievement of molar NH4:NO2 ratio of 1.2e1.4 for PN-SBR helped to enhance TN rem oval efficiency of the overall system Bacterial community of HAR was able to degrade slowly biodegradable or non-biodegradable COD Acknowledgments The Authors gratefully thank to Vietnam Brewery Ltd Company for financial support of this study References Anthoniesm, A.C., Loehr, R.C., Prakasam, T.S., et al., 1976 Inhibition of nitrification by ammonia and nitrous acid J Water Pollut Control Fed 48, 835e852 APHA, AWWA, WPCF, 1998 Standard Methods for Examination of Water and Wastewater, twentieth ed Furukawa, K., Inatomi, Y., Qiao, S., Quan, L., Yamamoto, T., Isaka, K., Sumino, T., 2009 Innovative treatment system for digester liquor using anammox process J Biotechnol 100, 5437e5443 Fux, C., Boehler, M., Huber, P., Brunner, I., Siegrist, H., 2002 Biological treatment 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Y., Zeng, G.M., Yang, Z.H., Liu, Y.S.-H., Ma, Y.H., Yang, L., Wang, R.J., Xu, ZhY., 2009 Coexistence of nitrifiers, denitrifiers and anammox bacteria in a sequencing batch biofilm reactor as revealed by PCR-DGGE J Appl Microbiol 106, 496e505 Xu, Z.Y., Zeng, G.M., Yang, Z.H., Xiao, Y., Cao, M., Sun, H.S., Ji, L.L., Chen, Y., 2010 Biological treatment of landfill leachate with the integration of partial nitrification, anaerobic ammonium oxidation and heterotrophic denitrification Bioresour Technol 101, 79e86 Yapsakli, K., Aliyazicioglu, C., Mertoglu, B., 2011 Identification and quantitative evaluation of nitrogen-converting organisms in a full-scale leachate treatment plant J Environ Manage 92, 714e723 Please cite this article in press as: Nhat, P.T., et al., Application of a partial nitritation and anammox system for the old landfill leachate treatment, International Biodeterioration & Biodegradation (2014), http://dx.doi.org/10.1016/j.ibiod.2014.05.025 ... cite this article in press as: Nhat, P.T., et al., Application of a partial nitritation and anammox system for the old landfill leachate treatment, International Biodeterioration & Biodegradation... ratio at the various HRTs in the PN-SBR experiment Please cite this article in press as: Nhat, P.T., et al., Application of a partial nitritation and anammox system for the old landfill leachate. .. press as: Nhat, P.T., et al., Application of a partial nitritation and anammox system for the old landfill leachate treatment, International Biodeterioration & Biodegradation (2014), http://dx.doi.org/10.1016/j.ibiod.2014.05.025