Partial Nitrification Process Research Articles

Integrated thiosulfate-driven denitrification, partial nitrification and anammox process in membrane-aerated biofilm reactor for low-carbon, energy-efficient biological nitrogen removal

Combining multiple bioprocesses in a single membrane-aerated biofilm reactor (MABR) unit for wastewater treatment is an emerging research focus. This study investigated the feasibility of coupling thiosulfate-driven denitrification (TDD) with partial nitrification and anammox (PNA) in a MABR for the treatment of ammonium-containing wastewater. The integrated bioprocess was tested over a continuous operation period (>130 d) in two MABRs: one with a polyvinylidene fluoride membrane (MABR-1), and the other with micro-porous aeration tubes covered with non-wovenpolyester fabrics (MABR-2). After start-up, the MABR-1 and MABR-2 based on the TDD–PNA process achieved satisfactory total nitrogen removal efficiencies of 63% and 76%, with maximum oxygen utilisation efficiencies of up to 66% and 80% and nitrogen removal fluxes of 1.3 and 4.7 gN/(m2·d), respectively. Predictions from the AQUASIM-model verified the integrated bioprocess. These lab scale findings confirmed the applicability of MABR technology for simultaneous sulfur and nitrogen removal, promising for pilot-scale application.

Start-up and maintenance of indigenous microalgae-bacteria consortium treating toilet wastewater through partial nitrification and nitrite-type denitrification

Microalgae-bacteria consortium (MBC) provides an alternative to sustainable treatment of human toilet wastewater (TWW) and resource recovery. This study compared the conventional activated sludge system and wastewater indigenous MBC system (IMBC) for nitrogen removal in TWW through the coupled partial nitrification (PN) and nitrite-type denitrification process. PN was firstly established by alternating FA and FNA. Subsequently, the successful PN maintenance with the nitrite accumulation rate ranging between 90.1–95.3% was achieved using two strategies: light irradiation with the appropriate specific light energy density at 0.0188–0.0598 kJ/mg VSS and the timely nitrite-type denitrification with the algae-secreted organics as the carbon source, eventually resulting in the nitrite accumulation rate ranging between 90.1–95.3%. In the IMBC-PN system, bacterial metabolism contributed to 91.5% of nitrogen removal and the rest was through microalgal assimilation. This study offers a sustainable hybrid IMBC-PN process for high NH4+-N strength wastewater treatment (e.g., TWW), which theoretically saves 23.5% aeration and 34.2% carbon source as well as reduces 17.0% sludge production.

End-to-end autonomous and resilient operability strategy of full-scale PN-SBR system: From influent augmentation to AI-aided optimal control and scheduling

This study developed an artificial intelligence (AI)-driven autonomous resilient operation of partial nitrification (PN) process to enhance the performance of a two-stage PN-anammox process by ensuring a specific NO2/NH4 ratio under varying influent conditions before the wastewater enters the subsequent anammox process. First, a mathematical model representing PN process was developed in a full-scale sequencing batch reactor (PN-SBR). That model was then calibrated using AI-driven multi-objective optimization targeting NH4, NO2, and NO3 using a comprehensive rank-based global sensitivity analysis framework to identify the biological kinetic and stoichiometric parameters that has high affection on the PN process. After validating the PN-SBR model with real-time measurements of the PN process, an AI-driven optimal aeration strategy (AI-OpAS) was developed for the targeted PN-SBR. The influent characteristics were augmented using the oversampling method and then clustered using varying influent conditions. The AI-OpAS used iterative approximate dynamic programming (iADP) to determine the optimal aeration length scheduling and optimal dissolved‑oxygen control policy to maintain autonomously the NO2/NH4 ratio while reducing aeration energy under diverse influent conditions. The results show that the proposed AI-OpAS can operate the PN-SBR process by achieving the proposed NO2/NH4 ratio of 1.1 and reducing overall aeration energy consumption by up to 31.38 % under varying influent conditions; furthermore, this AI-aided strategy of resilient operation can be extended to the other variables such as pH for autonomous and sustainable PN-SBR system simultaneously.

Organics Recovery from Waste Activated Sludge In-Situ Driving Efficient Nitrogen Removal from Mature Landfill Leachate: An Innovative Biotechnology with Energy Superiority

The sustainable recovery and utilization of sludge bioenergy within a circular economy context has drawn increasing attention, but there is currently a shortage of reliable technology. This study presents an innovative biotechnology based on free nitrous acid (FNA) to realize sustainable organics recovery from waste activated sludge (WAS) in-situ, driving efficient nitrogen removal from ammonia rich mature landfill leachate by integrating partial nitrification, fermentation, and denitrification process (PN/DN–F/DN). First, ammonia ((1708.5 ± 142.9) mg·L−1) in mature landfill leachate is oxidized to nitrite in the aerobic stage of a partial nitrification coupling denitrification (PN/DN) sequencing batch reactor (SBR), with nitrite accumulation ratio of 95.4% ± 2.5%. Then, intermediate effluent (NO2−–N = (1196.9 ± 184.2) mg·L−1) of the PN/DN-SBR, along with concentrated WAS (volatile solids (VSs) = (15 119.8 ± 2484.2) mg·L−1), is fed into an anoxic reactor for fermentation coupling denitrification process (F/DN). FNA, the protonated form of nitrite, degrades organics in the WAS to the soluble fraction by the biocidal effect, and the released organics are utilized by denitrifiers to drive NOx− reduction. An ultra-fast sludge reduction rate of 4.89 kg·m−3·d−1 and nitrogen removal rate of 0.46 kg·m−3·d−1 were realized in the process. Finally, F/DN-SBR effluent containing organics is refluxed to PN/DN-SBR for secondary denitrification in the post anoxic stage. After 175 d operation, an average of 19 350.6 mg chemical oxygen demand organics were recovered per operational cycle, with 95.2% nitrogen removal and 53.4% sludge reduction. PN/DN–F/DN is of great significance for promoting a paradigm transformation from energy consumption to energy neutral, specifically, the total benefit in equivalent terms of energy was 291.8 kW·h·t−1 total solid.

Achievement and microbial profiles of non-aerated partial nitrification in photo sequencing batch and continuous flow reactors

Nitrite accumulation could be achieved in algal-bacterial consortia without energy-intensive aeration, which could be a sustainable alternative for wastewater treatment. However, few studies focused on the achievement of partial nitrification in different non-aerated algal-bacterial systems and the related microbial mechanisms are still unclear. Here two different algal-bacterial systems (photo-sequencing batch reactor (PSBR) and up-flow sludge blanket bioreactor (PUSB)) were operated for anaerobic effluent treatment and the non-aerated partial nitrification was evaluated. Results showed that the nitrite accumulation rates in the PSBR and PUSB were 92.70 ± 7.81 % and 81.44 ± 11.28 %, respectively, which was constant with microbial activities. Denser algal-bacterial granules were observed in the PSBR, whereas looser algal-bacterial flocs were in the PUSB. Phormidium and Leptolyngbya (i.e., two filamentous cyanobacteria) were enriched in the PSBR and PUSB, respectively, and the higher enrichment of Nitrosomonas and complete inhibition of Nitrospira contributed to better partial nitrification of PSBR. The PUSB had more intensive interspecific interactions and more cooperative behavior in microbial network. Metagenomic analysis revealed that partial denitrification might partially contribute to the nitrite accumulation in the PUSB owing to higher nitrate reductase gene expressions. Overall, this study advances our understandings of the partial nitrification process and nitrite accumulation by algal-bacterial consortia.

Achieving deep autotrophic nitrogen removal from low strength ammonia nitrogen wastewater in aeration sponge iron biofilter: Simultaneous nitrification, Feammox, NDFO and Anammox

Partial nitrification and anammox process is considered to be a good choice for nitrogen removal. Nevertheless, it is difficult to achieve in low ammonia wastewater because of the need to control further oxidation of nitrite. Nitrification combined with Feammox (anaerobic ammonia oxidation coupled to Fe (III) reduction) and NDFO (nitrate/nitrite-dependent Fe (II) oxidation) can achieve autotrophic removal of low ammonia. And sponge iron can avoid the disadvantage of continuously adding iron sources in this process. Therefore, a sponge iron biofilter (SIBF) treating low ammonia wastewater under aeration was explored in this study. The optimal operating conditions for SIBF were hydraulic retention time (HRT) of 9 h and gas–water ratio (R) of 9:1, at which the total inorganic nitrogen removal efficiency was up to 77.2 %, and effluent ammonia and total inorganic nitrogen concentrations were less than 5 mg/L and 15 mg/L, respectively. This met the 1A discharge standard of municipal wastewater in China. Stable ratio isotope results indicated that Feammox, NDFO and Anammox resulted in high nitrogen loss in SIBF. And different nitrogen transformation contribution tests indicated NDFO had the dominant contribution, which accounted for 55.7 %. Besides, the production of N2O was minimum under HRT of 9 h and R of 9:1, in which the N2O emission factor was 0.7 %. Stable isotope tracing analysis showed that 92.8 % of N2O was derived from ammonia and the dominant production pathway was nitrifier denitrification. The results of microbial community showed that the nitrification bacteria-Nitrosomonas, Nitrotoga, Nitrospira, Feammox bacteria-Dechloromonas, NDFO bacteria-Thiobacillus and anammox bacteria-Brocadia played major roles in SIBF. Therefore, SIBF shows superior performance and application potential in autotrophic nitrogen removal from low-ammonia nitrogen wastewater under aeration.

Development of Fouling-Control Strategy for Ceramic Membrane Bioreactor Applied in Partial Nitrification Process

A lab-scale ceramic membrane bioreactor (MBR) with active membrane-fouling control system was developed for the partial nitrification (PN) process. The in situ membrane cleaning method was applied to remove the contaminants on the surface of the membrane with no interruption of the wastewater treatment. The results showed that the device increased critical flux and reduced gel layer resistance (Rg) and internal resistance (Ri) of the flat-sheet ceramic membrane by inhibiting the formation of the cake layer. In long-term experiments, nitrite oxidizing bacteria (NOB) was successfully suppressed, and nitrite accumulation rate (NAR) was achieved at a high level, up to 90.09%; the effluent NO2−-N/NH4+-N was maintained in balance dynamically with an average ratio of ~1.30, which would be beneficial to the proliferation of Anammox bacteria and the following autotrophic nitrogen removal (ANR) process. Moreover, with the assistance of in situ cleaning, energy input from aeration was significantly reduced, while over aeration was avoided for more stable PN performance.

Evaluation of the Combined C/N ratio, DO Set Point, and HRT Influence on Nitrogen Removal Rate in One-Stage Reactor Through Partial Nitrification Anammox Process During Treatment of Synthetic Digestate of Poultry Litter Wastewater

Highlights A one-stage reactor PN/A process was developed and evaluated. The highest TN removal rate was 87.3% for the PN/A process to treat synthetic wastewater containing poultry litter at room temperature. Bacterial composition of mature sludge community of wastewater was investigated in this study. Adjusted parameters controlled the growth of AOB and NOB. Abstract. Anammox is an increasingly common process used for the treatment of municipally rejected water and even mainstream wastewater due to its low oxygen demand. However, anammox is not commonly utilized in the treatment of poultry litter because of its high organic content, which would inhibit the anammox process. One-stage partial nitrification and anammox (PN/A) process was developed and evaluated for removing total nitrogen (TN) content from synthetic digestate of poultry litter using a sequencing batch biofilm reactor (SBBR). Independent variables including carbon to nitrogen ratio (C/N) at 1, 2, and 3, dissolved oxygen level (DO, mg/L) at 0.2, 0.35, and 0.5, and hydraulic retention time (HRT, h) at 24, 48, and 72 were examined using Central Composite Design (CCD) coupled with Response Surface Methodology (RSM) to optimize the TN removal rate. Results showed that the one-stage PN/A process achieved an optimal TN removal rate of 87.3% and an optimal NH4+-N removal rate of 100% when C/N, DO, and HRT were 1, 0.5 mg/L, and 72 h, respectively. The quadratic regression model developed (p = 0.0018) perfectly fitted the nitrogen removal efficiency of the SBBR. The uncertainty analysis showed an error range of 0.12% to 0.96% for the model's accuracy within the DO, C/N ratio, and HRT ranges tested. The bacterial consortium analysis suggested that the control of the growth of ammonium oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was achieved. Keywords: Anammox, Comammox, Nitrospira, Partial nitrification, Poultry litter wastewater.

Low C/N promotes stable partial nitrification by enhancing the cooperation of functional microorganisms in treating high-strength ammonium landfill leachate

Partial nitrification is an effective process for treating high-strength ammonium landfill leachate with low C/N ratio, for the cooperation with denitrification can save almost 40% carbon addition in biological nitrogen removal. However, high ammonia loading often causes the instability of partial nitrification process. Less carbon addition can promote the stability of partial nitrification and increase the nitrite accumulation ratio (NAR). Nevertheless, the microbial mechanisms within remain further elusive. In this study, two laboratory-scale sequencing batch reactors were constructed and operated for 125 days, which were fed with ammonia synthetic wastewater with C/N of 0.6 (CN system) and C/N of 0.0 as the control (N system). CN system performed more stably and had the highest NAR of 100%. Extracellular polymeric substances (EPS) generated from carbon source provided spatial and nutrient niches to tighten the cooperation of functional microorganisms, thus, enhanced the stability and efficiency of partial nitrification. Thauera was the dominant denitrifier in CN system. Nitrosomonas was one of the most important autotrophic ammonia oxidizing bacteria, while Paracoccus and Flavobacterium were the main heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria in CN system. The enrichment of HN-AD bacteria outcompeted nitrite oxidizing bacteria (NOB), therefore leaded to higher nitrite accumulation in CN system. The findings of this study may be conducive to increasing the understanding of the microbial collaboration mechanisms of partial nitrification, thereby provides theoretical support for the improvement of biological nitrogen removal technology.

Efficient partial nitrification with hybrid nitrifying granular sludge based on a simultaneous fill/draw SBR mode

In this study, a simultaneous fill/draw SBR was applied to investigate the feasibility of partial nitrification process with inoculation of matured aerobic granular sludge. The system operated stably over 120 days with the relatively high ammonium removal efficiency (≥ 98.83%) and nitrite accumulation rate (≥ 89.60%). Moreover, a hybrid flocs/granules system was formed stably after long-term operation. The nitrite-oxidizing bacteria (NOB) was suppressed effectively because of the combined effect of simultaneous fill/draw mode and intermittent aeration conditions. Furthermore, batch tests were separately tested with isolated granules (> 200 μm) and flocs (< 200 μm), showing that the specific ammonia oxidation rate of granules and flocs were 15.94 ± 2.85 and 66.77 ± 0.83 mg N/(g MLSS·h), respectively. Correspondingly, the abundance of Nitrosomonas as a typical AOB in granules (6.24%) and flocs (11.94%) was obtained via the microbial diversity analysis, while NOB was almost hardly detected in granules and flocs.

A novel simultaneous partial nitrification, anammox, denitrification and fermentation process: Enhancing nitrogen removal and sludge reduction in a single reactor

This study verified the feasibility of simultaneous partial nitrification, anammox, denitrification and fermentation process under intermittent aeration in a single reactor, and explored the impact of dissolved oxygen (DO) on the synergy between fermentation and nitrogen removal. An advanced nitrogen removal efficiency of 92.8 % and a low observed sludge yield of 0.0268–0.1474 kgMLSS/kgCOD were achieved. In-situ test showed that nitrate and ammonium decreased synchronously in the absence of organic matter, indicating the possibility of simultaneous partial denitrification, anammox and fermentation. Additionally, the abundance of functional genes for acetate production was 66,894 hits, while the key genes relevant to methanogenesis were only 348 hits, which suggested that fermentation might stop at the acid-producing stage and promote partial denitrification-anammox reaction, achieving simultaneous sludge reduction and advanced nitrogen removal performance. When DO increased from 0.1–0.3 to 0.4–0.6 mg/L, the nitrogen removal efficiency was increased (63.9 %→92.8 %) while sludge reduction was negatively affected.

Applying response surface methodology to optimize partial nitrification in sequence batch reactor treating salinity wastewater

In this study, the operation parameters of a partial nitrification process (PN) treating saline wastewater were optimized using the Box–Behnken design via the response surface methodology (BBD-RSM). A novel strategy based on the control of the carbon/nitrogen ratio (C/N), alkalinity/ammonia ratio (K/A), and salinity in three stages was used to achieve PN in a sequence batch reactor. The results demonstrated that a high and stable PN was completed after 50 d with an ammonia removal efficiency (ARE) of 98.37 % and nitrite accumulation rate (NAR) of 85.93 %. Next, BBD-RSM was applied, where ARE and NAR were the responses. The highest responses from the confirmation experiment were 99.9 % ± 0.04 and 95.25 % ± 0.32 when the optimum C/N, K/A, and salinity were identified as 0.84, 2, and 5.5 (g/L), respectively. The results were higher than those for the nonoptimized reactor. The developed regression model adequately forecasts the PN performance under optimal conditions. Therefore, this study provides a promising strategy for controlling the PN process and shows how the BBD-RSM model can improve the PN performance.

Coupling of partial nitrification and aerated vertical flow constructed wetland for enhancing nitrite removal and reducing nitrous oxide

High nitrous oxide (N2O) and nitrite (NO2--N) emission limit the application of the partial nitrification (PN) technology. A novel aerated vertical flow constructed wetland (VFCW) using waste gas from PN process was designed to enhance nitrogen removal and reduce N2O and NO2--N in PN process. Compared with unaerated VFCW, NH4+-N and TN removal efficiencies in aerated VFCW were significantly improved by 118.48% and 78.14%, respectively. Furthermore, the aerated wetland mode can effectively eliminate the problem of high NO2--N and N2O pollution. After VFCW purification, the NO2--N concentration was reduced from 17.07 mg/L to 0.34 mg/L. Meanwhile, the N2O removal rate could reach 88.72%. Microbial analysis showed that the higher microbial community abundance and more fully nitrification and denitrification process were found in aerated VFCW, led to its reduced NO2--N and N2O emission.

Comparison of the Start-up and Long-term Operation Characteristics of floc sludge and biofilm Integrated Anammox Reactors

&lt;p&gt;Integrated anammox process has competitive advantages of low energy and carbon consumption in nitrogen removal. Because of the coupling of partial nitrification and anammox process, complex physicochemical and biological interactions occur in integrated anammox reactors, and long-term operation might change the characteristics which is seldom reported in previous studies. In this study, a floc sludge bioreactor and a MBBR reactor were investigated for more than 450 days and compared from the startup to stable operation. The results showed that flocs aggregated into biofilms first and granulated after being detached artificially in the suspended sludge system, which provided solid evidence that the sludge granulation can be achieved by operational control in a continuous flow reactor. In the MBBR reactor, inhibiting Nitrate Oxidizing Bacteria (NOB ) was more difficult due to biofilm protection, and the total nitrogen removal rate was restricted by aeration. The biofilm and granular sludge samples in the reactors were analyzed by metagenomic sequencing, and the results revealed that the abundance of anammox was higher in the biofilm, while the NOB was inhibited greater in the granular sample. This study provides an in-depth understanding the mechanism of anammox process and broaden the feasibility of its application.&lt;/p&gt;&#x0D;

Long-Term Performance of Nitrogen Removal and Microbial Analysis in an Anammox MBBR Reactor with Internal Circulation to Provide Low Concentration DO.

The anammox process is considered as a revolutionary new denitrification technology. In this study, the anammox process was started in a single-stage moving bed biofilm reactor (MBBR) and the mechanism of excess removal of ammonia nitrogen was studied. At stage I (day 0-51), anammox bacteria (AnAOB) was enriched by feeding synthetic sewage without adding organic carbon. The removal rate of ammonia nitrogen was maintained at about 54% and the removal rate of total inorganic nitrogen was maintained at about 62%. At stage II (day 52-91), internal circulation was added into the MBBR. After adding internal circulation, the ammonium removal efficiency reached about 96% (at day 56) and the total nitrogen removal efficiency reached about 86%. At day 90, the biofilm sample was drowned out for high-throughput sequencing. The results showed that the relative abundance of AnAOB was 23.23%. The dominant anammox genus was Candidatus Brocadia. The relative abundance of Nitrosomonas (ammonia oxidizing bacteria, AOB) was 0.63%. The excess ammonia nitrogen was removed by AOB and AnAOB through the partial nitrification and anammox (PNA) process.

An enriched ammonia-oxidizing microbiota enables high removal efficiency of ammonia in antibiotic production wastewater

High ammonia concentration hinders the efficient treatment of antibiotic production wastewater (APW). Developing effective ammonia oxidation wastewater treatment strategies is an ideal approach for facilitating APW treatment. Compared with traditional nitrification strategies, the partial nitrification process is more eco-friendly, less energy-intensive, and less excess sludge. The primary limiting factor of the partial nitrification process is increasing ammonia-oxidizing bacteria (AOB) while decreasing nitrite-oxidizing bacteria (NOB). In this study, an efficient AOB microbiota (named AF2) was obtained via enrichment of an aerobic activated sludge (AS0) collected from a pharmaceutical wastewater treatment plant. After a 52-day enrichment of AS0 in 250 mL flasks, the microbiota AE1 with 69.18% Nitrosomonas microorganisms was obtained. Subsequent scaled-up cultivation in a 10 L fermenter led to the AF2 microbiota with 59.22% Nitrosomonas. Low concentration of free ammonia (FA, < 42.01 mg L−1) had a negligible effect on the activity of AF2, and the nitrite-nitrogen accumulation rate (NAR) of AF2 was 98% when FA concentration was 42.01 mg L−1. The specific ammonia oxidation rates (SAORs) at 30 °C and 15 °C were 3.64 kg NH4+-N·kg MLVSS−1·d−1 and 1.43 kg NH4+-N·kg MLVSS−1·d−1 (MLVSS: mixed liquor volatile suspended solids). The SAOR was 0.52 kg NH4+-N·kg MLVSS−1·d−1 when the NaCl concentration was increased from 0 to 20 g L−1, showing that AF2 functioning was stable in a high-level salt environment. The ammonia oxidation performance of AF2 was verified by treating abamectin and lincomycin production wastewater. The NARs of AF2 used for abamectin and lincomycin production wastewater treatment were >90% and the SAORs were 2.39 kg NH4+-N·kg MLVSS−1·d−1 and 0.54 kg NH4+-N·kg MLVSS−1·d−1, respectively, which was higher than the traditional biological denitrification process. In summary, AF2 was effective for APW treatment via enhanced ammonia removal efficiency, demonstrating great potential for future industrial wastewater treatment.

Adding monochloramine to control the growth of nitrite oxidizers and complete ammonia oxidizers in nitrifying moving-bed biofilm reactor

This study investigated a new method of using monochloramine (NH2Cl) to enhance nitrite accumulation in nitrifying moving-bed biofilm bioreactor (MBBR). Firstly, two parallel MBBRs were operated - with 1 mg Cl2 L−1 of NH2Cl in MBBR-1 and without NH2Cl addition in MBBR-2. Both MBBRs oxidized ammonia completely. The NO2− accumulation efficiency increased by twofold in MBBR-1 but remained low in MBBR-2. Subsequently, the carriers from MBBR-1 and 2 were seeded into four sequencing batch reactors (SBRs) for in-situ nitrogen transformation analysis. The results showed that continuous exposure to 1 mg Cl2 L−1 of NH2Cl successfully accumulated 50 mg N L−1 of nitrite in the effluent and suppressed the growth of nitrite-oxidizing bacteria (NOB) and complete ammonia oxidizers (comammox). The finding indicated that adding NH2Cl could be a promising strategy to attain reliable nitrite accumulation for developing two-stage partial nitrification and anaerobic ammonia oxidation process in the future.

Stable and rapid partial nitrification achieved by boron stimulating autoinducer-2 mediated quorum sensing at room & low temperature.

The stable and rapid initiation of partial nitrification is a long-term interest of researchers. In this study, boron, an activator of autoinducer-2 (AI-2), was first proposed to promote partial nitrification and improve sludge properties. Two concentrations of boron were added to six laboratory-scale nitrification reactors to study the effects of boron stimulated AI-2-mediated quorum sensing on nitrification at room and low temperature. Boron could significantly increase the concentration of AI-2 in the reactor (p<0.05), and the high concentration of boron showed better performance at two temperatures. The realization of partial nitrification was mainly due to the accumulation of NO2-- N promoted by the increase of AI-2 concentration. NO2-- N accumulation occurred in all the boron-treated reactors, while no NO2-- N accumulation occurred in the reactor without boron at room temperature or the accumulation efficiency was 14% lower at low temperature. Community analysis and qPCR further confirmed that exogenous boron had no significant effect on AOB, but inhibited NOB, especially at room temperature. The changes of EPS were slightly different at the two temperatures: at room temperature, boron increased the total EPS production, while at low temperature it mainly changed the PN/PS value of EPS. It was worth noting that the effect of boron on partial nitrification depended not only on its concentration, but also on NH4+-N concentration and temperature. This study provided a new strategy for the rapid and stable initiation of partial nitrification process.

A novel vertical dual-loop reactor for rapid start-up of simultaneous partial nitrification and anammox process in treating landfill leachate: Performances and mechanisms

A novel vertical dual-loop reactor (VDLR) was developed to start and conduct a single-stage partial nitritation (PN) and anammox (PN/A) process for treating landfill leachate. Results showed that the total nitrogen (TN) removal reached 1.54 kg N/m3·d in the VDLR. It exhibited excellent mixing uniformity and buffer performance, which can increase the nitrogen removal performance up to 42.1 % via the improvement of anammox granular sludge activity (a particle size of 0.5–1 mm). Mass balance and microbial analysis indicated that the VDLR achieved efficient TN removal via anammox (99.24 %) and AOB (Nitrosomonas and Ellin6067) and anAOB (Candidatus kuenenia) played a vital role in this process.

Effect of aeration modes on nitrogen removal and N2O emission in the partial nitrification and denitrification process for landfill leachate treatment

The anoxic/multi-aerobic process is widely applied for treating landfill leachate with low carbon to nitrogen ratio. In this study, the effect of two aeration modes in the aerobic phase, i.e. decreasing dissolved oxygen (DO) and increasing DO, on nitrogen removal and N2O emission in the process were systematically compared. The results demonstrate that the aerobic phase with increasing DO mode has a positive effect on improved total nitrogen removal (78 %) under the COD/N ratio as low as 3.45 and minimized N2O emission. DO concentration higher than 1.5 mg/L in the aerobic phase reduced nitrogen removal and led to a significant high N2O emission in the process. Complete nitrite denitrification in the anoxic phase correlated with minimized N2O emission. Under efficient nitrogen removal stage, N2O emission factor was 2.4 ± 1.0 % of the total incoming nitrogen. Microbial analysis revealed that increasing DO mode increased the abundance of ammonia oxidizing bacteria and denitrifiers.