Partial Nitrification-anammox Research Articles

Start-up of mainstream anammox process through inoculating nitrification sludge and anammox biofilm: Shift in nitrogen transformation and microorganisms

The feasibility of starting up mainstream single-stage partial nitrification-anammox (SPNA) system by inoculating nitrification sludge and anammox biofilm was investigated. The SPNA system treating low-strength synthetic wastewater was rapidly started up with TN removal efficiency of 88.5 ± 1.8% and effluent nitrate concentration of 7.2 ± 1.2 mg/L. Both the abundance and maximum activity of nitrite oxidizing bacteria (NOB) in flocs decreased obviously. Interestingly, the abundance of anaerobic ammonium oxidizing bacteria (AnAOB) in flocs increased from 0.213% to 0.346% despite the sludge retention time (SRT) of flocs decreased to 60 days, the AnAOB in biofilm was 0.434%. That meant AnAOB gradually enriched in flocs and accounted for a fairly high proportion. The inhibition of NOB, partial denitrification and increased aerobic_chemoheterotrophy function in flocs might be the main reasons for AnAOB enrichment. The possibility of simultaneous fermentation, partial denitrification and anammox reaction was predicted in biofilm, further improving the stability of the system.

Nitrogen Removal from Mature Landfill Leachate via Anammox Based Processes: A Review

Mature landfill leachate is a complex and highly polluted effluent with a large amount of ammonia nitrogen, toxic components and low biodegradability. Its COD/N and BOD5/COD ratios are low, which is not suitable for traditional nitrification and denitrification processes. Anaerobic ammonia oxidation (anammox) is an innovative biological denitrification process, relying on anammox bacteria to form stable biofilms or granules. It has been extensively used in nitrogen removal of mature landfill leachate due to its high efficiency, low cost and sludge yield. This paper reviewed recent advances of anammox based processes for mature landfill leachate treatment. The state of the art anammox process for mature landfill leachate is systematically described, mainly including partial nitrification–anammox, partial nitrification–anammox coupled denitrification. At the same time, the microbiological analysis of the process operation was given. Anaerobic ammonium oxidation (anammox) has the merit of saving the carbon source and aeration energy, while its practical application is mainly limited by an unstable influent condition, operational control and seasonal temperature variation. To improve process efficiency, it is suggested to develop some novel denitrification processes coupled with anammox to reduce the inhibition of anammox bacteria by mature landfill leachate, and to find cheap new carbon sources (methane, waste fruits) to improve the biological denitrification efficiency of the anammox system.

Enhanced Nitrogen Removal in Partial Nitrification-Anammox (Pna) Suspended Sludge System for Real Municipal Wastewater Treatment at Extremely Low Carbon to Nitrogen Ratio

Enhanced Nitrogen Removal in Partial Nitrification-Anammox (Pna) Suspended Sludge System for Real Municipal Wastewater Treatment at Extremely Low Carbon to Nitrogen Ratio

Robustness of the partial nitrification-anammox system exposing to triclosan wastewater: Stress relieved by extracellular polymeric substances and resistance genes

The partial nitrification-anammox (PN/A) process is a promising method for the treatment of municipal wastewater. It is necessary to clarify the responses of PN/A system to antimicrobial agent triclosan (TCS) widely existed in the influent of wastewater treatment plants. In this study, it was found that PN/A system was robust to cope with 0.5 mg/L TCS. Specifically, the control reactor reached 80% total nitrogen removal efficiency (TNRE) on day 107, while the reactor feeding with 0.5 mg/L TCS reached the same TNRE on day 84. The results of the activity test, high-throughput sequencing and DNA-based stable isotope probing showed that 0.5 mg/L TCS did not impede the performance of ammonia oxidizing archaea, ammonia oxidizing bacteria (Nitrosomonas) and anammox bacteria (Candidatus Brocadia and Ca. Kuenenia), but significant inhibited the nitrite oxidizing bacteria (Nitrospira and Ca. Nitrotoga) and denitrifying bacteria. The influent TCS led to the increase of EPS content and enrichment of four resistance genes (RGs) (intI1, sul1, mexB, and tnpA), which might be two principal mechanisms by which PN/A can resist TCS. In addition, functional bacteria carrying multiple RGs also contributed to the maintenance of PN/A system function. These findings improved the understandings of antimicrobial effects on the PN/A system.

An Innovative Process for Mature Landfill Leachate and Waste Activated Sludge Simultaneous Treatment Based on Partial Nitrification, In Situ Fermentation, and Anammox (PNFA).

An innovative partial nitrification, in situ fermentation, and Anammox (PNFA) system was developed to achieve mature landfill leachate and waste activated sludge simultaneous treatment. Three separate sequencing batch reactors (SBRs) were used for partial nitrification (PN-SBR), integrated fermentation-denitrification (IFD-SBR), and partial nitrification-Anammox (PNA-SBR). After 200 days of continuous operation, a satisfactory nitrogen removal efficiency (NRE) of 99.2 ± 0.1% was obtained, with an effluent total nitrogen (TN) of 15.2 ± 3.2 mg/L. In IFD-SBR, the volatile fatty acids generated from fermentation drove efficient denitrification, obtaining sludge and nitrogen reduction rates of 4.2 ± 0.7 and 0.61 ± 0.04 kg/m3·day, respectively. Furthermore, unwanted fermentation metabolites (134.1 mg/L NH4+-N) were further treated by PNA-SBR using a combination of step-feed and intermittent aeration strategies. In PNA-SBR, Anammox significantly contributed to 82.1% nitrogen removal, and Anammox bacteria (Candidatus Brocadia, 2.3%) mutually benefited with partially denitrifying microorganisms (Thauera, 4.2%), with 66.3% of generated nitrate reduced to nitrite and then reutilized in situ by Anammox. Compared with the conventional nitrification-denitrification process, PNFA reduced oxygen energy consumption, external carbon source dosage, and CO2 emission by 21.3, 100, and 38.9%, respectively, and obtained 50.1% external WAS reduction efficiency.

Sulfidation forwarding high-strength Anammox process using nitrate as electron acceptor via thiosulfate-driven nitrate denitratation

A single up-flow thiosulfate-driven nitrate denitratation coupled with the sulfurized Anammox (TDSA) with the core–shell structure (S0@ Anammox granules) provided a chemical/energy-saving way for the removal of high-content ammonium with nitrate as electron acceptor. Approximately 83.66% total nitrogen removal efficiency (TNRE) could be achieved by the sulfurized Anammox encrusted by S0/Sn2− at a high loading rate (2.6 kg-N/(m3·d)) via resisting high concentration of free ammonia (FA) (22.35 mg/L), mainly through S2O32−, S0/Sn2− -driven partial denitrification-Anammox (PDN-Anammox) process. Moreover, S0/Sn2−-PDN-Anammox was largely restricted when intermittently aerated, but still resulting in 74.47% TNRE due to the partial nitrification-Anammox (PN-Anammox). The sequencing analysis revealed that Anammox bacterium (Candidatus_Kuenenia) and sulfur-oxidizing bacterium (Thiobacillus) coexisted, in which Anammox process occurred mainly via NO instead of NH2OH. This study provided a new perspective for high concentration nitrogen wastewater removal in engineering applications.

Advanced nitrogen removal from landfill leachate via a two-stage combined process of partial nitrification-Anammox (PNA) and partial denitrification-Anammox (PDA)

In this study, a two-stage combined process of partial nitrification-Anammox (PNA) and partial denitrification-Anammox (PDA) was established achieving advanced nitrogen removal from landfill leachate. The PNA sludge used to treat reject water adapted to the leachate in 37 days, resulting in fast start-up of the PNA process with a nitrogen removal rate (NRR) of 0.22 kgN/(m3·d). Partial denitrification (PD) was induced using sodium acetate and proceeded in a stepwise manner using sludge fermentation liquid (SFL), achieving a NO3−-N to NO2−-N transformation ratio (NTR) of 52.1 ± 1.1% within 16 days. PDA was established via the addition of mature Anammox biofilms. The nitrogen removal efficiency (NRE) of this system was 97.6 ± 1.5%, of which PNA and PDA contributed 74.8 ± 4.0% and 18.7 ± 4.1%, respectively. Nitrosomonas (2.6% in PNA), Thauera (16.0% in PDA) and Candidatus Brocadia (23.0% in PNA, 1.4% in PDA) were dominant in the two-stage system. This study provides valuable and novel insights, supporting the practical application of PNA-PDA processes in landfill sites.

Ozone-based advanced oxidation of biologically treated landfill leachate: Oxidation efficiency, mechanisms, and surrogate-based monitoring for bulk organics

Landfill leachate effluent obtained from partial nitrification-Anammox (PNA) biological treatment still contains various recalcitrant organics. In this study, ozone-based oxidation processes (O3 and O3/H2O2) were applied to treat PNA leachate effluent. The oxidation efficiency and mechanisms were investigated by measuring chemical oxygen demand (COD), biochemical oxygen demand (BOD5), molecular size, fluorescence, UV–vis absorbance, and electron-donating capacity (EDC). Given the challenge of efficient ozone dosing, a surrogate-based monitoring approach was proposed and evaluated. Results show that leachate variability caused significant variation in the ozone utilization efficiency (O3E) for COD removal. The O3E of O3 and O3/H2O2 ranged between 0.32 and 0.47 mgCOD/mgO3, and between 0.43 and 0.73 mgCOD/mgO3, respectively. Compared to O3, O3/H2O2 was more effective to remove COD, to degrade the high molecular fraction, and to enhance biodegradability. The two-stage pseudo-first-order model (R2 > 0.90) can well describe the degradation of COD, fluorophores, UVA330, UVA254, and EDC during O3 and O3/H2O2 treatment, and the degradation rate can be ordered as follows: fluorophores > UVA330 > EDC > UVA254 > COD. Particularly, COD reduction was correlated well with surrogate reductions (i.e., fluorophores, UVA330, EDC, and UVA254) in an exponential function (R2 > 0.90), while exhibiting different steepness depending on the degradation kinetics of surrogates. The increased BOD5 showed a trend from rising and decline when presented as a function as surrogate reductions. The above correlations demonstrate the potential of surrogates to replace the conventional parameters for oxidation optimization and control. Overall, this research enriches the knowledge in the oxidation of recalcitrant organics in leachate and provides a reference for efficient ozone dosing.

Advances in Studies on Microbiota Involved in Nitrogen Removal Processes and Their Applications in Wastewater Treatment.

The discharge of excess nitrogenous pollutants in rivers or other water bodies often leads to serious ecological problems and results in the collapse of aquatic ecosystems. Nitrogenous pollutants are often derived from the inefficient treatment of industrial wastewater. The biological treatment of industrial wastewater for the removal of nitrogen pollution is a green and efficient strategy. In the initial stage of the nitrogen removal process, the nitrogenous pollutants are converted to ammonia. Traditionally, nitrification and denitrification processes have been used for nitrogen removal in industrial wastewater; while currently, more efficient processes, such as simultaneous nitrification-denitrification, partial nitrification-anammox, and partial denitrification-anammox processes, are used. The microorganisms participating in nitrogen pollutant removal processes are diverse, but information about them is limited. In this review, we summarize the microbiota participating in nitrogen removal processes, their pathways, and associated functional genes. We have also discussed the design of efficient industrial wastewater treatment processes for the removal of nitrogenous pollutants and the application of microbiome engineering technology and synthetic biology strategies in the modulation of the nitrogen removal process. This review thus provides insights that would help in improving the efficiency of nitrogen pollutant removal from industrial wastewater.

Process research of one‐stage partial nitrification‐anammox (S‐PN/A) technology in toilet water treatment and related kinetic simulation

AbstractBACKGROUNDToilet water is a typical wastewater that is abundant and has a low organic carbon‐to‐nitrogen ratio; therefore, it is necessary to explore an economical and efficient treatment option. Partial nitrification‐anammox (PN/A) technology is characterized by low aeration energy consumption and a high nitrogen removal rate. As a process technology that has emerged in recent years, PN/A technology involves operating conditions that require further study.RESULTSIn this work, two one‐stage partial nitrification‐anammox (S‐PN/A) reactors were operated to achieve nitrogen removal from toilet water. The total nitrogen removal rate of the two reactors reached 85%. The hydraulic nitrogen load of the first reactor was only 0.03 kg N m–3·d–1, while the hydraulic nitrogen load of the second reactor reached 0.09 kg N m–3·d–1. Nitrosomonas and Candidatus Kuenenia in the reactor were the main functional bacteria for partial nitrification and anammox. Kinetic simulations were performed using AQUASIM 2.0 software. The results showed that, in the partial nitrification system, the higher the (sludge retention time) SRT , the lower the effluent ammonia nitrogen concentration; the optimal operating condition's sludge retention time (SRT) was 10 days and dissolved oxygen (DO) was 0.2 mg L–1. The higher the SRT in the anammox system, the lower the concentration of ammonia and nitrite nitrogen in the effluent; in addition, the SRT should be greater than 60 days to ensure that as much nitrogen was removed as possible.CONCLUSIONIn summary, the research results confirm that it is feasible to use PN/A technology to remove nitrogen from toilet water. © 2021 Society of Chemical Industry (SCI).

Enhanced nitrogen removal by partial nitrification-anammox process with a novel high-frequency micro-aeration (HFMA) mode: Metabolic interactions among functional bacteria

A novel high-frequency micro-aeration (HFMA) mode with aeration frequency of 15 times/h and DO concentration lower than 0.5 mg/L was proposed. Advanced partial nitrification-anammox (PN-A) performance was achieved in a two-stage sequencing batch reactor-integrated fixed-film activated sludge reactor with the HFMA mode. When treating wastewater with carbon/nitrogen ratio of 3, the abundance of NO2−-N oxidation related genes decreased, and the genes carried out NO3−-N reduction and carbon source consumption were up-regulated. These variations in microbial metabolism brought more NO2−-N substrate for the subsequent anammox process, and consumed part of the accumulated organic matter and NO3−-N. Thus, the HFMA conditions eventually promoted the expression of anammox bacteria with NH2OH as an intermediate metabolite and the substance exchange activity of anammox bacteria. The changes in microorganisms lead to increase in the nitrite accumulation rate, nitrogen removal efficiency and abundance of anammox bacteria (16.34%, 18.71% and 5.92%, respectively).

Removal of nitrogen components, bulk organics, and fluorophores during one-stage partial nitrification-Anammox treatment of landfill leachate

Anammox-based processes have been intensively studied for the nitrogen removal from leachate, but less attention was paid to monitoring the evolution of leachate organics. In this study, fluorescence Excitation-Emission Matrix (EEM) measurement coupling with Parallel Factor Analysis (PARAFAC) analysis was used to supplement the routine monitoring in order to reveal more insights into pollutants removal during the leachate treatment by a one-stage partial nitrification-Anammox process (PNA). During this PNA process, up to 96% of total nitrogen and 43% of COD were removed, indicating the potential of PNA process to simultaneously remove nitrogen and organics. Fluorescence intensities and ratios clearly showed the dynamics of influent fluorophores during seasonal variations, where a high amount of protein-like compound was observed during summer months. Protein-like compound was preferentially removed (43–63%) in the PNA process, whereas humic/fulvic-like compounds exhibited recalcitrance to biodegradation. The increase of oxygen supply promoted protein-like compound degradation, which could be associated with the aerobic oxidation pathway. Furthermore, the protein-like compound removal was linearly correlated with the reduction of NH4+-N at limited oxygen conditions (i.e., air flow rate ≤1.6 Lgas/h/Lreactor) (r = 0.97, n = 65). The fluorescence directly extracted at Ex/Em:230 nm/345 nm was strongly correlated with the biodegradable chemical oxidation demand (BCOD) (r = 0.92, n = 204), showing its high potential as an indicator for biodegradable organics. Given the relatively weak correlation between fluorescence parameters and COD, EEM coupled with multivariate partial least squares (PLS) modeling was proposed and exhibited good predictive power for COD, as exemplified by a mean error of 4.5%.

Highly efficient and synchronous nitrogen removal from ammonia-rich wastewater and domestic wastewater via a novel anammox coupled with double-nitrite-shunt process at low temperature

Anaerobic ammonium oxidation (anammox) has been widely accepted as an energy-efficient approach for nitrogen removal from high-strength sidestreams. However, insufficient nitrogen removal due to the excessive NO3–-N residue represents the major challenge, especially at low temperature. In this study, highly efficient and synchronous nitrogen removal from ammonia-rich wastewater and real domestic wastewater was achieved via a novel anammox-mediated treatment by coupling with double-nitrite-shunt process in two-stage sequencing batch reactors. Stable partial nitrification/anammox (PNA) was successfully developed, while the total nitrogen (TN) removal efficiency was limited to 86.9 % due to excessive NO3–-N accumulation. Significantly, integration with partial denitrification (NO3–-N → NO2–-N) coupling anammox (PDA) process offered an efficient solution, which transformed the overproduced NO3–-N of PNA to NO2–-N and subsequently completely removed with NH4+-N via anammox pathway by mixing with real domestic wastewater (NH4+-N of 69.0 mg/L, COD of 203.6 mg/L). Excellent nitrogen removal performance with average TN removal efficiency of 98.4 % and high-quality effluent with average TN of 4.9 mg/L was maintained despite the temperature dropping to 13.0 ℃. 16S rRNA gene sequencing unveiled the different community of anammox bacteria cooperating stably with AOB and denitrifiers in the two systems. Compared with conventional nitrification/denitrification methods, the novel PNA-PDA process not only enabled 60% saving in aeration energy and 95.5% saving in organic carbon for ammonia-rich wastewater treatment, but also required no aeration energy for domestic wastewater treatment. Overall, this study provides a promising application with simple-control strategy for cost-effective and synchronous nitrogen removal from sidestreams and mainstreams.

Two-stage partial nitrification-Anammox process for nitrogen removal from slaughterhouse wastewater: Evaluation of the nitrogen loading rate and microbial community analysis

The production of inputs for animal feed using slaughterhouse byproducts is a predominant waste valorization route of the meat industry. This practice generates complex effluents containing high concentrations of organic matter and nutrients. The partial nitrification process followed by the Anammox process (PN/A) has been shown to be a viable technology for nitrogen removal from wastewaters with high concentrations of ammonia and low COD/N ratios, as found in Upflow Anaerobic Sludge Blanket (UASB) effluent from animal feed inputs industries. However, its application has not been assessed for slaughterhouse byproducts processing wastewaters. This work aimed at evaluating the influence of the nitrogen loading rate (NLR) on the removal of total nitrogen (TN) of a PN/A process treating real animal feed industry wastewater. The NLR in the Anammox reactor varied from 1.3 to 6.3 g N L−1.d−1, with a constant COD/N ratio of 0.5 ± 0.1 mg COD.mg N−1. An average removal efficiency of TN of 84.2 ± 9.8% was observed throughout 440 days of operation. Microbiological analyses of the granular Anammox sludge performed before and after the operation revealed an increase in the population of heterotrophic denitrifying bacteria, while the relative abundance of Anammox species decreased. It was demonstrated that although both microbial groups can coexist synergistically, the presence of organic matter contributed to the growth of heterotrophic denitrifying species and impaired the growth of Anammox bacteria, without affecting system performance.

Advanced nitrogen removal from low C/N municipal wastewater by combining partial nitrification-anammox and endogenous partial denitrification-anammox (PN/A-EPD/A) process in a single-stage reactor

In this study, an innovative partial nitrification-anammox (PN/A) and endogenous partial denitrification-anammox (EPD/A) process was developed in a single-stage integrated fixed film activated sludge sequencing batch reactor (IFAS-SBR) treating real municipal wastewater with C/N ratio below 3.2. Enhanced efficiency of total nitrogen (TN) removal reached 90.1% with low HRT of 12 h and DO of 0.4 ± 0.1 mg/L. Detailed nitrogen removal mechanism analysis of typical cycle revealed that 89.9% of TN was eliminated through anammox pathway. Anammox bacteria (Candidatus Brocadia) and endogenous denitrifying bacteria (Candidatus Competibacter) were abundant both in biofilms and suspended sludge, meanwhile ammonium-oxidizing bacteria has outcompeted nitrite-oxidizing bacteria, which all favored the synergistic effect of anammox with PN and EPD and contributed to the improvement of nitrogen removal. Overall, the above results confirmed that combined PN/A and EPD/A process is a reliable and efficient alternative for mainstream anammox process.

Pre-anaerobic treatment enhanced partial nitrification start-up coupled with anammox for advanced nitrogen removal from low C/N domestic wastewater

A modified two-stage partial nitrification/anammox (PN/A) process with short aerobic HRT of 5.7 h was established and realized advanced nitrogen removal from domestic wastewater. The first process was partial nitrification in the PN-SBR, the initiation and stable maintenance of partial nitrification was achieved by pre-anaerobic treatment without inoculation or addition of inhibitor, nitrite accumulation rate was over 90% and maintained over 200 days, meanwhile pre-anaerobic improved the storage of endogenous carbon sources to enhance the nitrogen removal efficiency. The second process was anammox in the AMX-SBR, which was fed with the effluent of PN-SBR, the effluent total inorganic nitrogen was below 5 mgN/L, nitrogen removal efficiency reached 92.06%. Furthermore, Candidatus-Brocadia was enriched after treating domestic sewage with low ammonia from 0.02% to 0.23%.This study demonstrated the feasibility of starting and maintaining partial nitrification by pre-anaerobic treatment and the feasibility of nitrogen removal by coupling simultaneous-nitrification–denitrification with anammox to treat actual municipal sewage.

Anammox bacteria enrichment in fixed biofilm successfully enhanced nitrogen removal of domestic wastewater in a sequencing biofilm batch reactor (SBBR)

The feasibility of enhancing anammox enrichment in sewage treatment through fixed biofilm was investigated in this study. Two reactors were used to treat real domestic sewage and operated in an identical mode: one is a sequencing biofilm batch reactor (SBBR) with blank carriers and the other is a sequencing batch reactor (SBR) without carriers. After anammox sludge inoculation and 160 days' operation, the abundance of the anammox bacteria increased to 2.58 × 109 gene copies/g dry sludge in the biofilm of SBBR, but decreased to 8.18 × 107 gene copies/g dry sludge in the activated sludge of SBR. The nitrogen removal efficiency (NRE) of SBBR and SBR was 79.3% and 57.9%, respectively. Further analysis suggests that the partial nitrification was stabilized in SBBR due to the addition of carriers and the dominating nitrogen removal pathway was the anammox reaction. In general, the fixed biofilm effectively maintained and enriched the anammox bacteria, which benefitted the start-up and steady operation of the sewage partial nitrification anammox (PNA) process.

Life cycle assessment of electrodialysis for sidestream nitrogen recovery in municipal wastewater treatment

Nitrogen is removed during municipal wastewater treatment to reduce eutrophication of waterways and preserve drinking water quality. Nitrification-denitrification and sidestream partial nitrification-anammox are state-of-the-art municipal N removal technologies, but they require energy for aeration and can release nitrous oxide as a fugitive greenhouse gas. An emerging sidestream electrodialysis technology is intended to both remove and recover N as ammonium-based fertilizer. This midpoint life cycle assessment compiles literature values to compare the state-of-the-art technologies of municipal wastewater nitrogen removal to the new electrodialysis nitrogen removal and recovery technology, accounting for the offset of Haber-Bosch-derived ammonia. Electrodialysis is projected to be environmentally favorable compared to the state-of-the-art, predicting electricity savings similar to anammox and, with the offset of industrial ammonia manufacture, net negative emissions in five of ten midpoint environmental impact categories, including global warming potential.

Adaptation of anammox granules in swine wastewater treatment to low temperatures at a full-scale simultaneous partial nitrification, anammox, and denitrification plant

In the anammox process, maintaining a high anammox activity at low water temperatures for stable nitrogen removal is a challenge. In this study, to verify the adaptability of anammox to low water temperatures, we investigated effects of annual temperature fluctuations on nitrogen removal in a full-scale swine wastewater treatment plant, where anammox bacteria accumulated. Annual quarters were defined as L-1 (November–January), L-2 (February–April), H-1 (April–July), and H-2 (July–October). The total nitrogen removal rate was stable at 0.08–0.11 kg-N/m3/d, even during temperature fluctuations. Removal efficiencies of biochemical oxygen demand and total nitrogen were consistently high at 95–99% and 69–81%, respectively. The anammox activity and abundance of anammox bacteria were highest in granule L-1 and lowest in granule H-2. The optimal temperature for anammox activity shifted from 35 °C in granules H-1 and H-2 to 30 °C in granules L-1 and L-2, while the latter maintained a moderate activity compared to the former at low temperature. Candidatus Jettenia asiatica was predominant, especially in granule L-2, accounting for up to 54% of the microbial community composition at the genus level. The high specific anammox activity in granule L-2 was considered to be due to the abundance of anammox bacteria and the adaptation of Ca. Jettenia asiatica to low temperature. The anammox granules adapted well to low temperatures and demonstrated high efficiency in the simultaneous partial nitrification anammox and denitrification process without heating. Thus, constructing an energy-saving and cost-effective nitrogen removal system can be considered.

Efficient and advanced nitrogen removal from mature landfill leachate via combining nitritation and denitritation with Anammox in a single sequencing batch biofilm reactor

A novel combined partial nitrification-Anammox and partial denitrification-Anammox (PnA/PdA) single sequencing batch biofilm reactor (SBBR) was established to realize efficient and advanced nitrogen removal from mature landfill leachate with low biodegradability. Nitrogen removal rate and nitrogen removal efficiency were increased to 2.83 ± 0.06 kgN/(m3∙d) and 98.6 ± 0.2% by stepwise increase of dissolved oxygen (DO, from 0.5 to 3.5 mg/L) and continuous carbon source feeding. Comparable activities of ammonia oxidation bacteria and Anammox bacteria were realized during aerobic period. More organic carbon was redirected from complete denitrification to partial denitrification during anoxic period. The main pathway PnA jointly synergized with PdA, which contributed to 76.04% and 19.44% nitrogen removal, respectively. Nitrosomonas, Thauera, and Kuenenia dominated in floc sludge (0.78%, 5.38%, and 1.14%, respectively) and biofilm (0.34%, 5.18%, and 0.98%, respectively). Overall, this study provides new insight into the high-efficiency treatment of landfill leachate at full-scale landfill sites.