Partial Nitrification-anammox Process Research Articles

Effect of sludge redistribution strategy on stability of partial nitrification-anammox process: Further exploration of the potential value of sludge

The stability of the two-stage partial nitrification-anammox (PN/A) system was compromised by the inappropriate conversion of insoluble organic matter. In response, a sludge redistribution strategy was implemented. Through the redistribution of PN sludge and anammox sludge in the two-stage PN/A system, a transition was made to the Anammox-single stage PN/A (A-PN/A) system. This specific functional reorganization, facilitated by the rapid reorganization of microbial communities, has the potential to significantly decrease the current risk of suppression. The results of the study showed that implementing the sludge redistribution strategy led to a substantial enhancement in the total nitrogen removal rate (TNRR) by 87.51%, accompanied by a significant improvement of 34.78% in the chemical oxygen demand removal rate (CRR). Additionally, this approach resulted in a remarkable two-thirds reduction in the aeration requirements. High-throughput sequencing revealed that the strategy enriched anammox and ammonia-oxidizing bacteria while limiting denitrifying bacteria, as confirmed by quantitative polymerase chain reaction analysis. Furthermore, the principal component analysis revealed that the location and duration of aeration had direct and indirect effects on functional gene expression and the evolution of microbial communities. This study emphasizes the potential benefits of restructuring microbial communities through a sludge redistribution strategy, especially in integrated systems that encounter challenges with suppression.

DOM and DON transformation in full-scale wastewater treatment plants: Comparison of autotrophic and heterotrophic nitrogen removal units

There is limited knowledge regarding the differences and relationships in molecular composition between dissolved organic matters (DOM) and dissolved organic nitrogen (DON) in autotrophic and heterotrophic nitrogen removal processes. In this study, the composition of DOM and DON during two full-scale wastewater treatment plants (WWTPs), an autotrophic nitrogen removal with partial nitrification-anammox process (PN/A) and a heterotrophic nitrogen removal with anaerobic/anoxic/oxic process (A2O), were systematically investigated by using ultraviolet–visible spectroscopy, Excitation-Emission Matrix (EEM) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results indicated that both PN/A and A2O resulted a decrease in molecular diversity and bio-availability of DOM. However, there were distinct variations in DON between the two processes. In PN/A, transformation of DOM and DON was found to be coupled, while there was a lack of correlation observed between DOM and DON in A2O. Pearson correlation analysis revealed that transformation of DOM and DON in WWTPs was associated with microbial roles. During biotreatment, PN/A exhibited a higher metabolic capacity for degrading high bio-available and high aromatic compounds compared to A2O. The autotrophic nitrogen removal unit in PN/A resulted in an increase in molecular weight (MW) of DON, as well as a decrease in bio-availability and unsaturation degree of DON. Therefore, autotrophic nitrogen removal unit may have a positive influence on control of eutrophication and disinfection by-products (DBPs) formation. This study improved the understanding of molecular composition and relationship between DOM and DON, as well as microbial roles on DON transformation within autotrophic and heterotrophic nitrogen removal processes.

Nitrogen removal from mature landfill leachate through enhanced Partial Nitrification-Anammox process in an innovative multi-stage fixed biofilm reactor

In the current integrated PN/A method/process for mature landfill leachate treatment, microbial inhibition and low nitrogen removal capacity are the big barriers due to high ammonia concentration and low C/N. This study aimed to evaluate the performance of a high-rate nitrogen removal lab-scale reactor, which combines pre-denitrification and Partial Nitrification-Anammox (PN/A) in a multi-stage fixed biofilm reactor (MFBR), for mature landfill leachate treatment. A nitrogen removal efficiency (NRE) of 90.43 % and an average nitrogen removal rate (NRR) of 0.94 kg/m3·d were observed at an influent NH+ 4-N concentration of 2274.39 mg/L during the last operational phase. The nitrogen mass balance showed that the nitrogen concentration gradually decreases along the course, and nitrogen was mainly removed in the aerobic chambers, in which Anammox contributed to 86.4 % of the removed nitrogen, while the front anoxic chamber is mainly used to remove NO- 3-N from the recirculation. Redundancy analysis showed that the variation in NH+ 4-N concentration along the course was the main factor affecting microbial community succession, which shows that the reactor configuration enables efficient cooperation and distribution of different microorganisms. Moreover, economic analysis of MFBR process showed that the energy consumption and carbon addition were reduced by 58.9 % and 100 %, respectively. Therefore, the MFBR established in this study, with its new configuration, achieves efficient treatment of landfill leachate in a single reactor and is environmentally friendly, and could be considered as a reference for full-scale landfill leachate treatment.

Long-term effects of phosphorus deficiency on one-stage partial nitrification-anammox system and recovery strategies

Long-term treatment of phosphorus-deficient wastewater using a one-stage partial nitrification-anammox (PNA) process may affect the growth of functional bacteria. A 650-day experiment on reject water with total phosphorus (TP)≤0.2 mg/L was conducted, using a lab-scale PNA system. The experiment found that long-term phosphorus deficiency led to a significant decrease in nitrogen removal efficiency (NRE) (91.0–28.3%), a high sludge volume index (SVI) of 157.6 mL/g-MLSS and sludge bulking. The abundance of hzsA in flocs decreased from 3.18 ± 0.05 × 106 to 1.10 ± 0.10 × 106 copies/mg-VSS. The biofilm had an advantage in resisting phosphorus deficiency with hzsA abundance being 3.78 ± 0.04 × 106 copies/mg-VSS at its lowest. According to batch test results, 0.2 mg/L PO43--P was added to the reactor. After 50 days, nitrogen removal rate (NRR) achieved up to 0.35 kg-N/(m3-d) at nitrogen load rate (NLR) of 0.4 kg-N/(m3-d) (NRE: 87.8%), and sludge bulking disappeared (SVI was 98.8 mL/g-MLSS). This experiment can serve as a reference for PO43--P dosing when using the PNA process to treat phosphorus-deficient wastewater.

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.

Start-up and optimization of a one-stage partial nitrification-anammox (PN-A) process treating low ammonium concentration wastewater: experimental results and modeling investigation.

Although the partial nitrification-anammox process (PN-A) has achieved great success in nitrogen removal for the high ammonium concentration wastewater, its application is still limited in low ammonium concentration wastewater treatment due to its instability and low nitrogen removal efficiency. In this study, a sequencing batch reactor (SBR) with continuous aeration was employed to enrich ammonia oxidation bacteria (AOB) and suppress nitrite oxidation bacteria (NOB) first; then, the SBR was operated intermittently aerated SBR (IASBR), to which the anammox granular sludge (AMX) was added to achieve complete autotrophic nitrogen removal under low influent ammonium concentration of 100mg/L. A mathematical model was used to optimize the IASBR aeration strategy to achieve sub-optimal nitrogen removal. The experimental results showed that high nitrite accumulation efficiency (above 80%) in the SBR and a fast start-up within 100days and a stable TN (total nitrogen) removal efficiency of 70% were achieved in the IASBR. Meanwhile, the simulation results indicated that keeping aeration duration at 4h, kLa (oxygen transfer coefficient) at 50day-1, or aeration duration at 2.5h, kLa at 80day-1 could obtain a higher total nitrogen removal efficiency (TNR) (TNR > 80%), and the TN removal could also be improved by increasing hydraulic retention time (HRT) under the optimal oxygen supply rate.

Stable enhanced nitrogen removal from low COD/N municipal wastewater via partial nitrification-anammox in the traditional continuous anoxic/oxic process through bio-augmentation of partial nitrification sludge under decreasing temperatures

The application of partial nitrification-anammox (PNA) in continuous flow processes for treating low COD/N (C/N) sewage remains a critical challenge. Here, a traditional continuous anoxic/oxic (A/O) process was operated to investigate nitrogen removal from municipal wastewater by the bio-augmentation of partial nitrification sludge combined with the inoculation of biocarriers under decreasing temperatures. Stable enhanced nitrogen removal via PNA was achieved. The average total inorganic nitrogen in influent and effluent was 44.3 and 7.1 mg N/L under a low C/N ratio (3.4) and a short hydraulic retention time (8.2 h). The bio-augmentation of partial nitrification sludge enhanced the PNA process under low temperatures (16.9 ± 0.6 °C). The nitrogen removal efficiency remained stable at 83.3 ± 5.7 % as the temperature decreased from 29.1 to 16.3 °C, and the relative abundance of Ca. Brocadia in carrier biofilms increased from 2.22 % to 4.31 % and 3.27 % in two aerobic chambers after 70 days of operation.

Advanced nitrogen removal from municipal sewage via partial nitrification-anammox process under two typical operation modes and seasonal ambient temperatures

A novel two-stage partial nitrification-anammox (PN-A) process was developed, achieving nitrogen removal from low carbon/nitrogen ratio municipal sewage under two typical operational modes and seasonal ambient temperatures. When complete nitritation-anammox was performed at temperatures greater than 19.4 °C, the effluent concentration of total inorganic nitrogen (TIN) was 4.1 mg/L, corresponding to a nitrogen removal efficiency (NRE) of 94.3 %. In contrast, when partial nitritation-anammox was performed at temperatures below 19.4 °C, the effluent TIN was 12.3 mg/L, corresponding to a NRE of 83.6 %. The relative abundance of Nitrosomonas and Nitrosomonadaceae increased from 0.02 % to 0.28 %, while Ca. Brocadia decreased from 1.85 % to 1.30 %, with the contribution of anammox to nitrogen removal being highest under low temperatures (19.4℃ to 13.8℃), at 59.0 %. This novel two-stage PN-A process provides a new approach for the stable operation of wastewater treatment plants (WWTPs) under low ambient temperatures.

Advanced treatment of landfill leachate through combined Anammox-based biotreatment, O3/H2O2 oxidation, and activated carbon adsorption: technical performance, surrogate-based control strategy, and operational cost analysis

The complexity of landfill leachate makes it difficult to treat it with a single biological/ physical/chemical process. Moreover, the dynamic leachate characteristics pose a challenge for effective process control. Therefore, a combined treatment, consisting of a one-stage partial nitrification-Anammox process, an O3/H2O2 process, and a granular activated carbon filtration (GAC) process, was investigated. Meanwhile, a novel surrogate-based ozone dose control strategy for O3/H2O2 process was evaluated. Results show that this three-stage process offers high removal of total nitrogen (> 90%), COD (chemical oxygen demand, 60–82%), and micropollutants (atrazine, alachlor, carbamazepine, and bisphenol A, > 96%), satisfying discharge requirements. In the combined post-treatment, ozone dosing for COD removal can be real-time controlled by UVA254 reduction monitoring, based on a specific correlation between COD and UVA254 changes. On the other hand, O3/H2O2 pre-treatment controlled at a 50% UVA254 reduction shows to be the optimal point, when adsorption is designed as the main step for COD removal. Cost analysis shows that post-treatment with low (high) organic load i.e., COD ≤ (≥)540 mg/L, a combination with O3/H2O2 (GAC) as the main step appears to be more cost-effective. Therefore, a dynamic operation strategy in response to the leachate change is recommended.

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.

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%.

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.

Linking organic matter removal and biogas yield in the environmental profile of innovative wastewater treatment technologies

Wastewater treatment plants (WWTPs) need to abandon the linear concept and adapt to the circular philosophy integrating standards of technological performance but also environmental, economic and social indicators. However, this change cannot be made by merely replacing one technology, but integrated solutions need to be applied. In this framework, a new strategy of treatment has gained strength in recent years, which consists of recovering organic matter (OM) in the primary treatment and implementing partial nitrification-anammox process as secondary treatment.In this study, three different schemes based on this approach were evaluated from an environmental and economic perspective and compared with a conventional wastewater treatment plant. The three proposed schemes are: i) upflow anaerobic sludge blanket (UASB) + integrated fixed film activated sludge (IFAS); ii) high rate activated sludge (HRAS) and IFAS, and finally, rotating belt filter (RBF) + chemical enhanced primary treatment (CEPT) followed by an IFAS unit. Even though the technological and operational complexity is noteworthy in the schemes based on this strategy, lower environmental impacts were estimated for the first two configurations. However, the consumption of chemicals in the third alternative was detrimental for the environmental performance of the plant, even with higher impacts than those of the conventional scheme for the toxicity-related categories. In this regard, the consumption of energy and chemicals are the main barriers for its successful implementation.

Autotrophic nitrogen removal by partial nitrification-anammox process in two-stage sequencing batch constructed wetlands for low-strength ammonium wastewater

In this study, partial nitrification-anammox process was established in two-stage sequencing batch constructed wetlands (SBCWs) to achieve autotrophic nitrogen removal for low-strength ammonium wastewater treatment. The operational parameters of the partial nitrification process were investigated and optimized, for the subsequent anammox process. The results indicated idle time and reaction time had significant influences to partial nitrification SBCW (WPN). In the WPN with optimal condition (idle time = 7.5 h, reaction time = 16 h), the effluent nitrite to ammonium ratio (NO2−-N/NH4+-N) remained stable at 1.24 ± 0.09, which favored the anammox process. The anammox SBCW (WAmx) was established rapidly within 61 d. The two-stage SBCWs showed high-efficient nitrogen removal capacity, with effluent total nitrogen (TN) concentration of 3.89 ± 0.62 mg/L and TN removal rate of 81.11 ± 2.92 %. Moreover, high-throughput sequencing revealed that Nitrosomonas (37.5 %) was dominant under optimal condition in WPN and responsible for partial nitrification process. Candidatus Brocadia (26.5 %) was enriched in WAmx, undertaking anammox process with synergism of flanking bacteria. This study provides a sustainable alternative for low-strength wastewater treatment.

Analyzing the effect of organic carbon on partial nitrification-anammox process based on metagenomics and quorum sensing.

The effects of adding organic carbon on the performance of different partial nitrification-anammox (PNA) process (the activated sludge process and biofilm process) were studied, especially nitrogen removal, functional microbial activity, and microbial community structure. The potential influences of quorum sensing (QS) on the nitrogen metabolism were also analyzed. The results showed that the addition of organic carbon in biofilm systems could reduce total nitrogen (TN) removal percentages, while in activated systems it could increase TN removal percentages. The TN removal percentages in SBBR-CN (the biofilm system with addition of organic carbon) and SBR-CN (the activated sludge system with addition of organic carbon) were 15% and 45%, respectively, and those in SBBR-N (the biofilm system without addition of organic carbon) and SBR-N (the activated sludge system without addition of organic carbon) were 75% and 21%, respectively. Batch experiments have proved that organic carbon inhibited the activities of nitrite-oxidizing bacteria (NOB) and anaerobic ammonia oxidation (anammox) bacteria, and organic carbon could promote the activity of denitrifying bacteria in activated sludge systems. Compared with activated sludge systems, biofilm systems could protect the activity of anammox bacteria. The relative abundances of ammonia oxidizing bacteria (AOB) and anammox bacteria were decreased, while the relative abundances of denitrifying bacteria (Thauera) were increased with the addition of organic carbon. The biofilm systems were more conducive to the growth of anammox bacteria. Metagenomics revealed that the same bacteria might be involved in different nitrogen metabolism, and nitrogen metabolism was achieved through the complex cooperation among functional bacteria. Besides, functional bacteria involving in the nitrogen metabolism had genes related to QS, indicating that QS might affect the nitrogen metabolism by regulating the functional bacteria activity. PRACTITIONER POINTS: PNA was achieved through SBBR and complete nitrification was achieved through SBR under the low ammonia nitrogen concentration condition. The effect of organic carbon on biofilm and activated sludge PNA process was different under the low ammonia nitrogen concentration condition. QS and QQ may affect the nitrogen removal performance by regulating the expression of nitrogen metabolism-related genes.

Optimizing of operation strategies of the single-stage partial nitrification-anammox process

To achieve efficient and stable nitrogen removal and low N2O emission in the single-stage partial nitrification (PN)-anaerobic ammonium oxidation (anammox) process, a sequence batch reactor (SBR) was operated for 223 days, the optimal operation strategies were investigated. Aeration rate control was applied to achieve the synergy between anammox and partial nitrification. The variation of specific anammox activity (SAA), specific ammonia oxidizing bacteria activity (SAOA), and specific nitrite oxidizing bacteria activity (SNOA) revealed that the anammox process was a rate-limiting step under low-strength ammonium loading condition. With the long-term acclimation, the anammox process showed more tolerance to substrate variation, in contrast, the inhibitory threshold concentration of partial nitrification to ammonium was decreased. The evolution of specific activities and substrate tolerance abilities of the functional microbes verified the changes in the nitrogen removal performance and proved that the aeration control strategy was efficient for operating a low nitrogen loading PN-anammox reactor. The nitrous oxide (N2O) isotopic composition analysis revealed that 73% of N2O was produced via the nitrifier denitrification pathway. N2O production could be mitigated by increasing the SAA in the PN-anammox process. The reveal of the synergy effect between functional microbes and the N2O pathway provide a guidance for operating a PN-anammox system for treating low nitrogen loading wastewater.

Achieving partial nitrification and high lipid production in an algal-bacterial granule system when treating low COD/NH4–N wastewater

Partial nitrification-Anammox process is an efficient and energy-saving method for nitrogen removal from low C/N wastewaters. In this study, partial nitrification was achieved in an algal-bacterial granular sludge system when treating low COD/NH4–N (309.4 mg L−1/213.6 mg L−1) wastewater under sunlight irradiation (RS). Sunlight irradiation, algae growth and free nitrous acid (FNA) decreased the activity of ammonia oxidizing bacteria (AOB) by 25.7% and completely inhibited the activity of nitrite oxidizing bacteria (NOB), resulting in a NH4–N removal efficiency of ≥99% and a nitrite accumulation efficiency of 96.5% in Rs. Compared with the control without sunlight irradiation (RC), the algal-bacterial granules in RS produced 34.7% and 13.1% more proteins and polysaccharides, respectively, and exhibited a higher structure stability. The lipid content in the algal-bacterial granules was 68.7 mg g-SS−1, which was about 2.1 times higher than that in the granules from RC, making the algal-bacterial granule a value-added biomass. Meanwhile, the content of unsaturated fatty acid methyl esters increased remarkably due to the growth of algae (Stigeoclonium, Scenedesmus and Navicula). The combined stress of sunlight irradiation, algae growth and high FNA in RS only slightly lowered the relative abundance of Nitrosomonadaceae (AOB family) from 7.5% to 5.8%, while Nitrospiraceae (NOB family) was severely inhibited and became undetectable.

Two-step partial nitrification-anammox process for treating thermal-hydrolysis anaerobic digester effluent: Start-up and microbial characterisation

Abstract Although the thermal hydrolysis has been proven to be an effective pre-treatment method for anaerobic digestion (AD), the ammonium-rich anaerobic digester effluents are unavoidably produced by thermal hydrolysis pre-treatment AD (THP-AD). In this study, a two-step partial nitrification-anammox (PN-A) process was conducted for the anaerobic digester effluents. By combining control of the solid retention time (SRT), dissolved oxygen (DO) and hydraulic retention time (HRT) (SRT 20 d, DO concentration 0.5–0.8 mg/L, HRT 11 h), start-up of the PN reactor was achieved with a total nitrogen loading rate of 2.34 kg N/(m3·d), generating an NH4+-N/NO2−-N molar ratio of around 1.0–1.4 in the effluent. The anammox reactor was then successfully started by feeding the effluent of the PN reactor, with a total nitrogen removal rate of 1.25 kg N/(m3·d). The system became unstable after 100 days of operation, and surface analyses of the anammox sludge particles suggested that the main reason was the adsorption of microsized suspended organic flocs in the influent onto the anammox sludge particles. Further study showed that the microsized suspended organic flocs contained large quantities of bacteria, which can compete with anammox bacteria. In addition, analyses of the microbial community reveal that Nitrosomonas and Candidatus brocadia were the main ammonium-oxidising bacteria and anammox bacteria in this study, respectively. The trends of their relative abundance during the PN-A system process confirmed the successful start-up of the PN-A reactors and the effectiveness of the start-up operations. These findings are expected to provide references for the treatment of anaerobic digester effluents from THP-AD via the biological removal of nitrogen.

Start-up of oxygen-limited autotrophic partial nitrification-anammox process for treatment of nitrite-free wastewater in a single-stage hybrid bioreactor

ABSTRACT This study presents effective ammonium removal from nitrite-free ammonium-rich synthetic wastewater through combined partial nitrification (PN) and anammox processes in a multi-zone hybrid airlift bioreactor (BioCAST). Removal efficiencies of ammonia-nitrogen and total nitrogen up to 85.6% and 81.2%, respectively, were achieved shortly after the start-up of bioreactor treating the nitrite-free ammonium-rich synthetic wastewater with ammonium concentrations of 10–350 mg/L. The hybrid (containing suspended and attached biomass) and multi-zone design of the bioreactor with different dissolved oxygen levels, along with the inoculation with anammox-containing sludge were the main factors in the successful start-up of the bioreactor. Nitrate accumulation problem due to the fast growth of nitrite-oxidizing bacteria in the bioreactor was controlled by two operating strategies including lowering the HRT from 4 days to 2 days and controlling the dissolved oxygen concentration in the aerobic zone of the bioreactor between 0.9 and 1.2 mg/L. Moreover, the 16S rRNA gene analysis confirmed that the partial nitrification of ammonia to nitrite occurred by Nitrosomonas sp. primarily in the suspended biomass in the aerobic zone, while the conversion of nitrite to N2 occurred by Candidatus Brocadia species in the anoxic zone. This study showed the effective removal of ammonium from a nitrite-free wastewater by providing a proper HRT, controlling the DO concentration between 0.9 and 1.2 mg/L in the aerobic zone, and preventing biomass loss using both suspended and attached microbial cultures in different zones of the bioreactor.