Partial Denitrification-anammox Research Articles

Influence of hydraulic retention time on advanced synergistic nitrogen removal using internal carbon source

Hydraulic retention time (HRT) is a significant operational eter of denitrifying filter (DF). The influence of HRT on the performance and mechanism of advanced synergistic nitrogen removal (ASNR) of partial-denitrification anammox (PDA) and denitrification was investigated, consuming the hydrolytic and oxidation products of refractory organics in the secondary effluent (SE) as carbon source. When the HRT was 8, 6, 4 and 2 h, the filtered effluent total nitrogen (TN) was 1.47, 3.47, 4.17 and 4.49 mg/L, and the effluent CODcr was 8.12, 9.95, 9.40 and 9.87 mg/L, respectively. Removing 1 mg of TN actually consumed 0.87–0.96 mg CODcr, and the contribution rate of PDA to TN removal was 62.10–70.02 %. A variety of manganese oxidizing (MnOB), hydrolytic, anammox and denitrifying bacteria were identified, and their abundance was obviously affected by the HRT. The lack of carbon source was the main factor limiting the ASNR efficiency, rather than the HRT.

Influence of temperature on performance and mechanism of advanced synergistic nitrogen removal in lab-scale denitrifying filter with biogenic manganese oxides

Temperature is a significant operational parameter of denitrifying filter (DF), which affects the microbial activity and the pollutants removal efficiency. This study investigated the influence of temperature on performance of advanced synergistic nitrogen removal (ASNR) of partial-denitrification anammox (PDA) and denitrification, consuming the hydrolytic and oxidation products of refractory organics in the actual secondary effluent (SE) as carbon source. When the test water temperature (TWT) was around 25, 20, 15 and 10 °C, the filtered effluent total nitrogen (TN) was 1.47, 1.70, 2.79 and 5.52 mg/L with the removal rate of 93.38%, 92.25%, 87.33% and 74.87%, and the effluent CODcr was 8.12, 8.45, 10.86 and 12.29 mg/L with the removal rate of 72.41%, 66.17%, 57.35% and 51.87%, respectively. The contribution rate of PDA to TN removal was 60.44%∼66.48%, and 0.77–0.96 mg chemical oxygen demand (CODcr) was actually consumed to remove 1 mg TN. The identified functional bacteria, such as anammox bacteria, manganese oxidizing bacteria (MnOB), hydrolytic bacteria and denitrifying bacteria, demonstrated that TN was removed by the ASNR, and the variation of the functional bacteria along the DF layer revealed the mechanism of the TWT affecting the efficiency of the ASNR. This technique presented a strong adaptability to the variation of the TWT, therefore, it has broad application prospect and superlative application value in advanced nitrogen removal of municipal wastewater.

Rapid start-up and operational characteristics of partial denitrification coupled with anammox driven by innovative strategies

The Partial Denitrification-Anammox (PD/A) process established a low-consumption, efficient and sustainable pathway for complete nitrogen removal, which is of great interest to the industry. Rapid initiation and stable operation of the PD/A systems were the main issues limiting its engineering application in wastewater nitrogen removal. A PD/A system was initiated in a continuous stirred-tank reactors (CSTRs) in the presence of low concentration of organic matter, and the effects of organic matter types and COD/NO3−-N ratios on the performance of the PD/A system, and microbial community characteristics were explored. The results showed that low concentrations of organic matter could promote the rapid initiation of the Anammox process and then the strategy of gradually replacing NO2−-N with NO3−-N could successfully initiate the PD/A system at 70 days. The type of organic matter had a significant effect on the initiation of the Anammox and the establishment of the PD/A system. Compared to glucose, sodium acetate was more favorable for rapid start-up and the synergy among microorganisms, and organic matter was lower, with an optimal COD/NO3−-N ratio of 3.0. Microorganisms differed in their sensitivity to environmental factors. The relative abundance of Planctomycetota and Proteobacteria in R2 was 51 %, with the presence of three typical anammox bacteria, Candidatus_Brocadia, Candidatus_Kuenenia, and Candidatus_Jettenia in the system. This study provides a new strategy for the rapid initiation and stable operation of the PD/A process.

Rapid establishment of municipal sewage partial denitrification-anammox for nitrogen removal through inoculation with side-stream anammox biofilm without domestication

Mainstream partial denitrification anammox was achieved through inoculation of side-stream mature partial nitritation anammox biofilm without domestication. The contribution of anammox to nitrogen removal was 29.4 %. Moreover, prolonging anoxic hydraulic retention time and introducing side-stream nitrite under different carbon/nitrogen ratios enriched anammox bacteria. The abundance of anammox bacteria increased by ∼ 10 times ((2.19 ± 0.17) × 1012 copies gene / g dry sludge) with a total relative abundance of 18.51 %. During 258 days of operation, the contribution of anammox to nitrogen removal gradually increased to 68.8 %. The total nitrogen in the effluent decreased to 8.84 mg/L with a total nitrogen removal efficiency of 76.4 % under a carbon/nitrogen ratio of 3. This paper proposes a novel way to rapidly achieve mainstream partial denitrification anammox via inoculation with side-stream mature partial nitritation anammox biofilm. This method achieves advanced nitrogen removal from municipal wastewater, even under low carbon/nitrogen ratios.

Interactions and coupling mechanisms between Anammox, partial denitrification (PD) and hydroxyapatite (HAP) biomineralization in a PD/A-HAP system

In this study, hydroxyapatite (HAP) crystallization was introduced into a partial denitrification/Anammox (PD/A) process to develop PD/A-HAP granules and achieve simultaneous removal of nitrogen and phosphorus from wastewater. During the formation of PD/A-HAP granules, an unbalanced relationship between the biomass growth and phosphorus crystallization was observed, which resulted in a mass transfer inhibition inside the system. PD and Anammox activities were both impacted by the impeded nutrient contact, and PD process was revealed to be more susceptible to inhibition. Through the regulation of COD and NO3–-N, a dynamic balance between microbial proliferation and phosphorus crystallization was achieved. As a result, high nitrogen removal efficiency (NRE) was attained at 97.8±1.2 % in the final stage of operation, accompanied by a phosphorus removal efficiency (PRE) of 59.4±2.9 %. Furthermore, the recovered phosphorus was transformed into HAP crystals and encapsulated by the PD/A biomass to form granules, which greatly promoted the settling performance of the sludge. This study underlines the importance of reconciling biomass and HAP growth for a strengthened PD/A granular sludge and an enhanced nitrogen removal system. The constructed PD/A-HAP process will expand the application of PD/A with its ability to remove phosphorus while efficiently removing nitrogen.

Improving nitrogen removal performance from rare earth wastewater via partial denitrification and anammox process with Fe(II) amendment

Treating rare earth wastewater which contains low concentration of nitrogen with little chemical oxygen demand (COD) is an increasing demand. In this study, a partial-denitrification/anammox (PD/A) process with Fe(II) amending for rare earth wastewater treatment was proposed and stably operated for 218 days. The total nitrogen removal efficiency (TNRE) reached up to 89.32 % for actual rare earth wastewater treatment. Continuously Fe(II) addition stimulated more secretion of extracellular polymeric substance (EPS), furthering enhancing the aggregation ability of microbial and adhesion of hydrophobic bacteria. The enrichment of denitrification genera Denitratisoma, Ignavibacterium, Thauera and Limnobacter provided sufficient nitrite substrate from nitrate reduction for subsequent anammox reaction, which was primarily carried out by Candidatus Brocadia (with relative abundance of 5.86 %). Metagenomic analysis indicated the relative abundance of genes hzo, hzsA/B/C and hdh responsible for anammox process increased by 12.84 %, 9.00 %, 9.25 %, 4.21 %, 1.32 %, respectively, which was significantly facilitated nitrogen removal performance of PD/A process.

Metabolic characteristics and the cross-feeding of Bacillus and Ca. Brocadia in an integrated partial denitrification-anammox reactor driven by glycerol

Integrated partial denitrification-anammox (PD/A) process was considered as a novel strategy for low ammonia wastewater treatment, but the potential roles of the functional bacteria were still unclear. In this study, metagenomic binning analysis coupling with metatranscriptomic analysis was used to reveal the metabolic patterns in a stable operating PD/A system driven by glycerol. The cross-feeding between Bacillus and Candidatus Brocadia, the two dominant functional bacteria that contributed 81.1 % of the total gene expression, was constructed. Bacillus exhibited high nitrite production potential in the assimilatory nitrate reduction pathway instead of partial denitrification. And Bacillus was the main glycerol utilizer capable of synthesizing intracellular glycogen and polyhydroxybutyrate, which was also the potential branched-chain amino acids and B-vitamins supplier. Candidatus Brocadia as an anammox bacteria surprisingly expressed the activity of 3-phosphate glycerol (obtained from Bacillus) degradation. This study provided a new understanding of the metabolic patterns and interactions in PD/A system.

Reactivation performance and sludge transformation after long-term storage of Partial denitrification/Anammox (PD/A) process

This study explores the startup of innovative Partial denitrification/Anammox (PD/A) process using long-term stored sludge (>2 years at 4 °C). Results indicate a swift recovery performance, characterized by a progressive increase in the activity of functional microorganisms with improved nitrogen volumetric loading rate during operation. Stable nitrogen removal efficiency of 99.6 % was attained at 14.2 °C under influent nitrate and ammonium of 120 and 100 mg/L, respectively. A distinctive transformation was observed as the initially black seeding sludge transitioned to brownish-red, accompanied by rapid sludge granulation with size notably increased from 263.1 μm (day 4) to 1255.0 μm (day 128), significantly contributing to the rapid PD/A performance recovery. Microbial community analysis revealed substantial increases in functional bacteria, Thauera (0.09 %–10.4 %) and Candidatus Brocadia (0.003 %–1.98 %), coinciding with enhanced nitrogen removal performance. Overall, this study underscores the viability of long-term stored PD/A sludge as a seed for rapid reactor startup, offering useful technical support to advance practical PD/A process implementation.

Iron-modified carriers accelerate biofilm formation and resist anammox bacteria loss in biofilm reactors for partial denitrification-anammox

The slow formation of anammox biofilms presents a bottleneck for resolving anammox bacterial loss and achieving stable performance in biofilm-based partial denitrification-anammox (PD-A) processes. This study utilized iron-modified (K1/Fe3O4 NPs) carriers, which were prepared and used for the first time in PD-A processes. Parallel moving bed biofilm reactors (MBBRs) indicated that iron-modified carriers facilitated the formation of biofilms at a faster rate than K1 carriers, consequently improving the nitrogen removal performance of the process by over 40 %. 16S rDNA analysis showed that anammox bacteria were approximately four times more abundant in the iron-modified carrier biofilm than in the K1 carrier biofilm. XPS and zeta potential analysis suggested that the improved microbial affinity of the iron-modified carrier surface caused this. As a result, the iron-modified carriers facilitated the formation of anammox biofilms and enhanced PD-A performance.

Stimulating extracellular polymeric substances production in integrated fixed-film activated sludge reactor for advanced nitrogen removal from mature landfill leachate via one-stage double anammox

Introducing carbon sources to achieve nitrogen removal from mature landfill leachate not only increases the costs and carbon emissions but also inhibits the activity of autotrophic bacteria. Thus, this study constructed a double anammox system that combines partial nitrification-anammox (PNA) and endogenous partial denitrification-anammox (EPDA) within an integrated fixed-film activated sludge (IFAS) reactor. In this system, PNA primarily contributes to nitrogen removal pathways, achieving a nitrite accumulation rate of 98.23%. The production of extracellular polymer substances (EPS) in the IFAS reactor is stimulated by introducing co-fermentation liquid. Through the utilization of EPS, the system effectively achieves EPDA with the nitrite transformation rate of 97.20%. Under the intermittent aeration operation strategy, EPDA combined with PNA and anammox in the oxic and anoxic stages enhanced the nitrogen removal efficiency of the system to 99.70 ± 0.12%. The functional genus Candidatus kuenenia became enriched in biofilm sludge, while Thauera and Nitrosomonas predominated in floc sludge.

Advanced nitrogen removal from municipal wastewater through partial nitrification-denitrification coupled with anammox in step-feed continuous system

Combined partial nitrification-denitrification/anammox (PN-PD/A) processes have attracted great attention from researchers in recent years to achieve high nitrogen removal from low carbon /nitrogen (C/N) municipal wastewater. In this context, a step-feed anoxic/oxic (A/O) process was conducted in this study through the combination of the partial nitrification-anammox (PN/A) and partial denitrification-anammox (PD/A) to remove N from municipal wastewater with low C/N. The enhancement of the PN-PD/A process resulted in N removal efficiency of 85.6% at C/N of 2.8. The contributions of the anammox reached 36.4 and 8.8% in the anoxic and oxic chambers, respectively. The biocarriers added to the anoxic and oxic chambers increased the relative abundance of the anammox bacteria in biofilms from 0.61% to 1.51% and 1.02%, respectively. This study demonstrated that employing the step-feed A/O process can create optimal conditions for the anammox bacteria growth, thereby ensuring advanced N removal from low C/N municipal wastewater.

Study on rapid start-up and stable nitrogen removal efficiency of carrier enhanced continuous flow PD/A granular sludge system

Anaerobic ammonia oxidation (anammox) is a vital process for nitrogen removal, but challenges like slow start-up and unstable operation persist. To tackle these issues and assess carrier efficiency in improving the partial denitrification/anammox (PD/A) process’s start-up and stability under low nitrogen loading rates (NLR) (0.11–0.19 kg/(m3·d)), two continuous flow PD/A systems were set up: one with self-immobilized granular sludge (R1) and the other with carrier-based granular sludge (R2). The results showed that R2 achieved over 70% total nitrogen (TN) removal within 45 days, 16 days shorter than R1. Scanning electron microscope (SEM) characterization revealed that the ecological maturity of biofilm granular sludge was approximately 14 days earlier in R2 than in R1. Comparative analysis of protein/polysaccharide (PN/PS) ratios within extracellular polymeric substances (EPS) and volatile suspended solids/suspended solids (VSS/SS) demonstrated that carrier-based granular sludge exhibited superior settling characteristics and structural stability compared to self-immobilized granular sludge. Moreover, nitrogen removal stability within the R2 reactor system was superior to R1 under diverse operating conditions, highlighting carrier reinforcement’s efficacy in enhancing the PD/A process’s operational stability. The increased abundance of anammox bacteria Candidatus_Kuenenia in R2 ensured complete nitrogen removal in the PD/A coupling process, elucidating the microscopic mechanism of carrier-enhanced nitrogen removal. The hydrophilic porous biological carrier not only expedited the PD/A system’s start-up in the upflow sludge bed (USB) reactor but also enhanced the enrichment and collaboration of effective functional microorganisms. This study provides technical reference and theoretical evidence for rapid start-up and long-term stable operation of PD/A process.

Performance optimization and nitrogen removal mechanism of up-flow partial denitrification/anammox process

This study aimed to remediate the problems of sludge floating and uneven mass transfer in up-flow partial denitrification/anammox (PDA) reactors and dissect the nitrogen removal mechanism. Two up-flow PDA reactors were operated, whereby in R1 combined biological carriers were added, while in R2 mechanical stirring was applied, the reactors were inoculated with PD sludge and anammox sludge. Results showed the TN removal rates at the end of the operation were 89% (R1) and 92% (R2). The addition of both strategies suppressed the occurrence of sludge upwelling and deterioration of settling performance, even when the granule diameter of the granular zone in R1 and R2 reached 1.921 and 2.006 mm, respectively. 16SrRNA sequencing revealed R1 had a higher abundance of anammox bacteria (AAOB, 14.53%-R1, 9.06%-R2, respectively), and R2 had a higher quantity of denitrifying bacteria (61.92%-R1, 67.11%-R2, respectively). And the nitrogen removal was contributed by anammox and denitrification in combination, with contributions of 82.17%, 17.83% (R1), and 85.07%, 14.93% (R2), respectively. In summary, both strategies prevented sludge flotation and uneven nitrogen mass transfer. However, mechanical agitation had a more substantial positive effect on the performance of PDA than the addition of biocarriers because it achieved a more adequate mass transfer.

Evaluation of the economic and environmental benefits of partial nitritation anammox and partial denitrification anammox coupling preliminary treatment in mainstream wastewater treatment

Anaerobic ammonium oxidation (anammox) technology is considered the best alternative for current wastewater treatment to improve resource recovery and energy efficiency. Evaluation of the economic and environmental benefits of partial denitrification anammox (PDA) and partial nitritation anammox (PNA) from a plant-wide perspective, which are the two most common mainstream anammox processes, is crucial for guiding the development direction of anammox, but research is still lacking. In this study, two plant-wide processes with chemically enhanced primary treatment-PDA (CEPT-PDA) and high rate activated sludge-PNA (HRAS-PNA) as the core units respectively, were firstly proposed and analysed, and life cycle assessment (LCA) was conducted to assess environmental impacts (EIs). The results of energy and economic analysis showed that the net energy consumption of CEPT-PDA and HRAS-PNA was 0.11 kwh/m3 and 0.16 kwh/m3 respectively; however, the operating cost of CEPT-PDA was 16.54% higher than that of HRAS-PNA due to the requirement for more chemicals. Compared with CEPT-PDA, the total EIs of HRAS-PNA decreased by 14.80%. The EI categories related to human toxicity and ecotoxicity contributed greatly to total EIs, accounting for 95.81% in CEPT-PDA and 96.75% in HRAS-PNA. Major environmental impacts were attributed to coagulant and energy consumption in two processes. In addition, improving the iron recycling efficiency was more beneficial for CEPT-PDA and further narrowed the gap between CEPT-PDA and HRAS-PNA on EIs. This study identifies that CEPT-PDA is competitive in the engineering application of mainstream anammox but reducing iron addition is a prerequisite.

New insights into the effects of wetland plants on nitrogen removal pathways in constructed wetlands with low C/N ratio wastewater: Contribution of partial denitrification-anammox.

Nitrogen (N) removal in constructed wetlands (CWs) was often challenged by limited denitrification due to the lack of carbon source, and wetland plants would be more important in carbon (C) and N cycling in CWs with influent of low carbon to nitrogen (C/N) ratio. In this study, the underlying mechanisms of nitrate nitrogen (NO3--N) removal under different low C/N ratios were revealed by constructing microcosm CWs, and the unplanted group was set as the control to explore the role of plants in N removal. The results showed that plants and the concentration of influent carbon significantly affected NO3--N and total nitrogen (TN) removal (p < 0.05). The presence of plants significantly increased the concentration of DO and wetland plant-derived DOM (p < 0.05). The enhanced NO3--N and TN removal with increased C/N ratio attributed to high denitrification activity reflected in the abundance of denitrification microbes and genes. However, the contribution of partial denitrification-anammox (PDN/AMX) to N removal in CWs decreased from more than 75.3% at the C/N ratio of 0 to 70.4% and 22.3% with the C/N ratio increased to 1.5 and 3, respectively. Furthermore, the PDN/AMX process was negatively correlated with favorable oxygen environment in the planted group and plants roots carbon secretion, but the overall N removal efficiency of the CWs was enhanced by increased abundance of N removal-related functional genes in the presence of plants. Abovementioned results provided new insights to explain the mechanism of N removal in CWs under low C/N ratio.

Hydroxyapatite (HAP) formation in acetate-driven partial denitrification process: Enhancing sludge granulation and phosphorus removal

Partial denitrification/anammox (PD/A) processes have emerged as a promising technology for efficient nitrogen removal from wastewater. However, these processes fail to remove phosphorus (P), a key pollutant that contributes to water eutrophication. To address this issue, the potential of inducing hydroxyapatite (HAP) precipitation in PD processes to achieve simultaneous P removal was investigated for the first time. Specifically, three SBRs (R1-R3) for PD were operated with adding varying concentrations of external Ca (30, 60, and 120 mg/L, respectively). Results demonstrated significant P reduction in all three SBRs, particularly in R3 with high Ca, which achieved an 80 % removal efficiency. Notably, sludge granulation was observed during operation, with the granule size in R3 with high Ca reaching 906.1 μm during the stable period, exceeding those in R2 (788.7 μm) and R1 (707.1 μm). This led to good settle ability of the PD sludge, as demonstrated by the lowest SVI5 (20 mL/g MLSS). Moreover, the decrease in the MLVSS/MLSS ratio suggested that the inorganic content accumulated, as observed by confocal laser scanning microscopy in the interior of the granules. Elemental composition analysis suggested that PD granules contained high P and Ca, while the X-ray diffraction (XRD) results confirmed the formation of HAP. Overall, this study demonstrated that PD-HAP coupled granular sludge process has potential as a robust and efficient method for nitrite production, as well as effective P removal and recovery, thereby advancing the application of anammox processes in wastewater treatment.

A comprehensive literature mining and analysis of nitrous oxide emissions from different innovative mainstream anammox-based biological nitrogen removal processes

The biological nitrogen removal (BNR) process in wastewater treatment plants generates a substantial volume of nitrous oxide (N2O), which possesses a potent greenhouse gas effect. A limited number of studies have systematically investigated the N2O emissions of anammox-based systems with different BNR processes under mainstream conditions. Based on extensive big data statistical analysis, it had been revealed that simultaneous nitritation, anammox and denitrification (SNAD), partial nitritation anammox (PNA) and partial denitrification anammox (PDA), exhibit significantly lower N2O emission factors when compared to traditional BNR processes. The median values for N2O emission factors were determined to be 1.01 %, 1.15 % and 1.43 % for SNAD, PNA and PDA, respectively. Based on nitrogen removal data and N2O emission factors, the N2O emissions from PNA, SNAD and PDA processes were calculated to be 0.016 g·d−1, 0.037 g·d−1 and 0.008 g·d−1, respectively. Furthermore, the machine learning models (SVM and ANN) exhibited excellent predictive performance for N2O emissions in the BNR processes. However, after removing environmental factors, the R2 value of the SVM model sharply decreased. The SHAP feature analysis demonstrated the significant impact of environmental factors on the accuracy of predictive performance in machine learning models. Spearman correlation analysis was employed to investigate the relationship between N2O emissions and operational factors as well as microbial communities. The results demonstrated a negative correlation between HRT, temperature and C/N with N2O emissions. Moreover, strong associations were observed between Nitrosomonas, Nitrospira, Denitratisoma, Thauera species and N2O emissions. The contribution of N2O production via AOB pathways played a key role that was quantitatively calculated to be 93 %, 80 % and 48 % in the PNA, SNAD and PDA processes, respectively. These findings highlight the potential of these innovative BNR processes in mitigating N2O emissions.

A new sulfur bioconversion process development for energy- and space-efficient secondary wastewater treatment

Harvesting organic matter from wastewater, chemical enhanced primary treatment for instance, is widely applied to maximize energy recovery; however, it limits the applicability of secondary treatment for acceptable effluent discharge into surface water bodies. To turn this bottleneck issue into an opportunity, this study developed oxygen-induced thiosulfatE production duRing sulfATe reduction (ERATO) to provide efficient electron donor for denitrification or partial denitrification anammox in wastewater treatment. Typical pretreated wastewater was synthesized with chemical oxygen demand of 110 mg/L, sulfate of 50 mg S/L, ammonium of 30 mgN/L, and varying dissolved oxygen (DO) and was fed into a moving-bed biofilm reactor (MBBR) with a short hydraulic retention time of 40 min. The ORP maintained at − 311 mV in the bioreactor, indicating that the influent DO was vanished immediately when it enters the bioreactor. In 349 days’ continuous operation, the surface-specific sulfate reduction rate reached 0.42 g S/(m2·d). Notably, the formation rate of thiosulfate reached 0.12–0.18 g S/(m2·d) with a high thiosulfate-Sproduced/sulfide-Sproduced ratio of 38–73% when influent DO was 2.7–3.6 mg/L, much higher than 0–17% obtained in previously reported sulfate-reducing process. Then, batch tests and metabolism analysis were conducted to confirm the oxygen effect on thiosulfate formation, and to explore the mechanism of oxygen-induced thiosulfate formation in ERATO. Results examined that oxygen supply promoted the thiosulfate-Sproduced/sulfide-Sproduced ratio from 4% to 24–26%, demonstrated that S0 and sulfate were critical for thiosulfate production, and indicated that oxygen induces thiosulfate formation mainly through: sulfide first oxidized to S0 which then reacts with sulfite derived from oxygen-regulated biological sulfate reduction (S0 + SO32−→S2O32−). The proposed compact ERATO process with high thiosulfate production, supporting space- and energy-efficient secondary wastewater treatment.

Sidestream bio-P and mainstream anammox in a BNR process with upstream carbon capture.

The integration of biological phosphorus removal (bio-P) and shortcut nitrogen removal (SNR) processes is challenging because of the conflicting demands on influent carbon: SNR allows for upstream carbon diversion, but this reduction of influent carbon (especially volatile fatty acids [VFAs]) prevents or limits bio-P. The objective of this study was to achieve SNR, either via partial nitritation/anammox (PNA) or partial denitrification/anammox (PdNA), simultaneously with biological phosphorus removal in a process with upstream carbon capture. This study took place in a pilot scale A/B process with a sidestream bio-P reactor and tertiary anammox polishing. Despite low influent rbCOD concentrations from the A-stage effluent, bio-P occurred in the B-stage thanks to the addition of A-stage WAS fermentate to the sidestream reactor. Nitrite accumulation occurred in the B-stage via partial denitrification and partial nitritation (NOB out-selection), depending on operational conditions, and was removed along with ammonia by the tertiary anammox MBBR, with the ability to achieve effluent TIN less than 2mg/L. PRACTITIONER POINTS: A sidestream reactor with sufficient fermentate addition enables biological phosphorus removal in a B-stage system with little-to-no influent VFA. Enhanced biological phosphorus removal is not inhibited by intermittent aeration and is stable at a wide range of process SRTs. Partial nitritation and partial denitrification are viable routes to produce nitrite within an A/B process with sidestream bio-P, for downstream anammox in a polishing MBBR.

Ozone pretreatment combined with partial denitrification-anammox process for efficient nitrogen removal from nanofiltration concentrate of landfill leachate

Treatment of nanofiltration concentrate (NFC) from landfill leachate is challenging due to its complex composition and high concentration of refractory organic matter. This study proposed a combined process of ozone pretreatment and partial denitrification/anammox (PD/A) for treating NFC, exploring the feasibility of using ozone-oxidized NFC as a carbon source for partial denitrification. The ozone oxidation process was employed to degrade the refractory organic compounds. With an ozone flow rate of 1.2 L/min and a reaction time of 50 min, the chemical oxygen demand (COD) removal efficiency of NFC was 20.83%, and the volatile fatty acid (VFA) content reached a maximum value of 104.37 mg/L. Meanwhile, the process significantly increased the ammonia and nitrate concentrations in the NFC. Then, PD/A process was applied to remove nitrogen from the NFC. Results showed that PD/A can effectively remove nitrogen from the NFC without additional carbon source. Using VFA produced in the ozone oxidation stage as carbon source, the reactor achieved a nitrogen removal efficiency of approximately 70%, resulting in an effluent with a total nitrogen below 40 mg/L, which satisfied the relevant standards in China. This study provides new insights into the application of ozone oxidation and PD/A in treating NFC from leachate.