New insights into co-treatment of mature landfill leachate with municipal sewage via integrated partial nitrification, Anammox and denitratation

Rapid start-up of an innovative pilot-scale staged PN/A continuous process for enhanced nitrogen removal from mature landfill leachate via robust NOB elimination and efficient biomass retention

The start-up and stable operation of partial nitritation-anammox (PN/A) treatment of mature landfill leachate (MLL) still face challenges. This study developed an innovative staged pilot-scale PN/A system to enhance nitrogen removal from MLL. The staged process included a PN unit, an anammox upflow enhanced internal circulation biofilm (UEICB) reactor, and a post-biofilm unit. Rapid start-up of the continuous flow PN process (full-concentration MLL) was achieved within 35 days by controlling dissolved oxygen and leveraging free ammonia and free nitrous acid to selectively suppress nitrite-oxidizing bacteria (NOB). The UEICB was equipped with an annular flow agitator combined with the enhanced internal circulation device of the guide tube, which achieved an efficient enrichment of Candidatus Kuenenia in the biofilm (relative abundance of 33.4 %). The nitrogen removal alliance formed by the salt-tolerant anammox bacterium (Candidatus Kuenenia) and denitrifying bacteria (unclassified SBR1031 and Denitratisoma) achieved efficient nitrogen removal of UEICB (total nitrogen removal percentage: 90.8 %) and at the same time effective treatment of the refractory organic matter (ROM). The dual membrane process of UEICB fixed biofilm combined with post-biofilm is effective in sludge retention, and can stably control the effluent suspended solids (SS) at a level of less than 5 mg/L. The post-biofilm unit ensured that effluent total nitrogen (TN) remained below the 40 mg/L discharge standard (98.5 % removal efficiency). Compared with conventional nitrification-denitrification systems, the staged PN/A process substantially reduced oxygen consumption, sludge production, CO2 emissions and carbon consumption by 22.8 %, 67.1 %, 87.1 % and 87.1 %, respectively. The 195-day stable operation marks the effective implementation of the innovative pilot-scale PN/A process in treating actual MLL. This study provides insights into strategies for rapid start-up, robust NOB suppression, and anammox biomass retention to advance the application of PN/A in high-ammonia low-carbon wastewater.

Robust rehabilitation of anammox system by granular activated carbon under long-term starvation stress: Microbiota restoration and metabolic reinforcement

This article investigates the buffering capacity and recovery-enhancing ability of granular activated carbon (GAC) in a starved (influent total nitrogen: 20 mg/L) anaerobic ammonium oxidation (anammox) reactor. The findings revealed that anammox aggregated and sustained basal metabolism with shorter performance recovery lag (6 days) and better nitrogen removal efficiency (84.9 %) due to weak electron-repulsion and abundance redox-active groups on GAC's surface. GAC-supported enhanced extracellular polymeric substance secretion aided anammox in resisting starvation. GAC also facilitated anammox bacterial proliferation and expedited the restoration of anammox microbial community from a starved state to its initial-level. Metabolic function analyses unveiled that GAC improved the expression of genes involved in amino acid metabolism and sugar-nucleotide biosynthesis while promoted microbial cross-feeding, ultimately indicating the superior potential of GAC in stimulating more diverse metabolic networks in nutrient-depleted anammox consortia. This research sheds light on the microbial and metabolic mechanisms underlying GAC-mediated anammox system in low-substrate habitats.

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.

Characteristics variations of size-fractionated anammox granules and identification of the potential effects on these evolutions

Anaerobic ammonium oxidation (anammox) granulation which contributed to system stabilization and performance improvement has great potential in the field of wastewater nitrogen removal. The researchers fractionated anammox granules into small-size (0.5-0.9 mm), medium-size (1.8-2.2 mm), and large-size (2.8-3.5 mm) categories to examine their properties and mechanisms. Various analyses, including high-throughput sequencing, determination of inorganic elements and extracellular polymeric substances (EPS), and microbial function prediction, were conducted to characterize these granules and understand their impact. The results revealed distinct characteristics among the different-sized granules. Medium-size granules exhibited the highest sphericity, EPS content, and anammox abundance. In contrast, large-size granules had the highest specific surface area, heme c content, specific anammox activity, biodiversity, and abundance of filamentous bacteria. Furthermore, the precipitates within the granules were identified as CaCO3 and MgCO3, with the highest inorganic element content found in the large-size granules. Microbial community and function annotation also varied with granule size. Based on systematic analysis, the researchers concluded that cell growth, chemical precipitation, EPS secretion, and interspecies interaction all played a role in granulation. Small-size granules were primarily formed through cell growth and biofilm formation. As granule size increased, EPS secretion and chemical precipitation became more influential in the granulation process. In the large-size granules, chemical precipitation and interspecies interaction, including synergistic effects with nitrifying, denitrifying, and filamentous bacteria, as well as metabolic cross-feeding, played significant roles in aggregation. This interplay ultimately contributed to higher anammox activity in the large-size granules. By fully understanding the mechanisms involved in granulation, this study provides valuable insights for the acclimation of anammox granules with optimal sizes under different operational conditions.

Response of partial nitritation and denitrification processes to high levels of free ammonia in a pilot mature landfill leachate treatment system: Stability and microbial community dynamics

The high levels of free ammonia (FA) challenge the application of partial nitritation (PN) and denitrification (DN) in the treatment of ammonia-rich wastewater. This study explored the impact of high levels of FA on the PN and DN stability and microbial community dynamics. By reducing reflux and increasing influent load, the concentrations of FA in PN and DN reactors increased from 28.9 mg/L and 140.0 mg/L to 1099.8 mg/L and 868.4 mg/L, respectively. During this process, the performance of PN and DN remained stable. The microbial analysis revealed that the Nitrosomonas exhibited strong tolerance to high levels of FA, and its relative abundance was positively correlated with amoABC (R2 0.984) and hao (R2 0.999) genes. The increase in microbial diversity could enhance the resistance ability of PN against the FA impact. In contrast, high levels of FA had scant influence on the microbial community and performance of DN.

Enhanced nitrogen removal from rural domestic sewage via partial nitrification-anammox in integrated vertical subsurface flow constructed wetland

This study aimed to improve the removal of nitrogen treating rural domestic sewage by developing a novel strategy for achieving partial nitrification-anammox (PNA) in an integrated vertical subsurface flow constructed wetland (VSFCW). The influent ammonia was oxidized to nitrite in the partial nitrification VSFCW (VSFCWPN), and 5 mg/L of hydroxylamine was added under the appropriate dissolved oxygen concentration level (1.2 ± 0.2 mg/L) to stabilize the average nitrite accumulation rate at 88.24% and maintain the effluent NO2--N/NH4+-N ratio at 1.26 ± 0.15. The effluent from VSFCWPN was introduced to the following chamber (VSFCWAN), where ammonia and nitrite were removed by the autotrophic anammox process. This implementation achieved high removal efficiencies for chemical oxygen demand, total nitrogen, and PO43--P, reaching 86.26%, 90.22%, and 78.94%, respectively, with influent concentrations of 120.75 mg/L, 60.02 mg/L, and 5.05 mg/L. Substrate samples were collected from 10 cm height (PN1, AN1) and 25 cm height (PN2, AN2). Microbial community analysis showed that Nitrosomonas dominated the community composition in VSFCWPN, with an increase from 1.61% in the inoculated sludgePN to 16.31% (PN1) and 12.09% (PN2). Meanwhile, Ca. Brocadia accounted for 44.81% (AN1) and 36.50% (AN2) in VSFCWAN. These results confirm the feasibility of the proposed strategy for establishing PNA and efficiently treating rural domestic sewage in an integrated VSFCW.

Effect of free ammonia on partial denitrification: Long-term performance, mechanism, and feasibility of PD/Anammox-FBBR for mature landfill leachate treatment

As a stable and effective approach for NO2--N accumulation, partial denitrification (PD) could significantly cut down operation cost, and PD/Anammox (PD/A) is a promising nitrogen removal process in wastewater treatment. The biotoxicity of free ammonia (FA) to nitrifying bacteria and anammox bacteria has been demonstrated, while whether FA affects PD bacteria is an open question. Here, long-term operation of PD-fixed bed biofilm reactor (PD-FBBR) treating synthetic wastewater and mature landfill leachate was conducted to reveal the mechanism concerning the effect of FA on PD bacteria. Stable NO2--N accumulation was achieved with NO3--N to NO2--N transformation ratio (NTR) of 60-70% during 280-day operation with FA ranged from 0 to 20.71 ± 0.23 mg/L, while NTR decreased and maintained at ∼30% when FA reached 40.59 ± 0.19 mg/L. Specific NOx--N reduction rate improved at low FA concentration (< 12 mg/L), while high FA level (> 25 mg/L) had inhibitory effect on PD bacteria. Under FA stress, more extracellular polymeric substances (EPS) were secreted, and the glnA gene abundance, glutamine synthase concentration, and glutamine concentration in cell and EPS significantly increased, indicating the enhancement of glutamine biosynthesis in PD bacteria for ammonia assimilation played an important role in response to FA stress. Metagenomic sequencing showed that FA stimulated the upregulation of narK (NO3--N/NO2--N antiporter) gene abundance and enhanced uptake of NO3--N and extrusion of NO2--N. Comamonas, unclassified_f__Comamonadaceae and Thauera were highly enriched in biofilm, which played a key role in the stable NO2--N accumulation. Furthermore, a novel two stage PD/A-FBBR was applied to mature landfill leachate treatment, and satisfactory total inorganic nitrogen removal efficiency ranged from 81.38 ± 3.56% to 89.16 ± 1.57% was obtained at relatively low COD/NO3--N of 2.57-2.84. Overall, these findings demonstrated how PD bacteria respond to FA stress and confirmed the feasibility of PD/A process in high FA wastewater treatment.

Integration of EBPR with mainstream anammox process to treat real municipal wastewater: Process performance and microbiology

The mainstream application of anaerobic ammonium oxidation (anammox) for sustainable N removal remains a challenge. Similarly, with recent additional stringent regulations for P discharges, it is imperative to integrate N with P removal. This research studied integrated fixed film activated sludge (IFAS) technology to simultaneously remove N and P in real municipal wastewater by combining biofilm anammox with flocculent activated sludge for enhanced biological P removal (EBPR). This technology was assessed in a sequencing batch reactor (SBR) operated as a conventional A2O (anaerobic-anoxic-oxic) process with a hydraulic retention time of 8.8 h. After a steady state operation was reached, robust reactor performance was obtained with average TIN and P removal efficiencies of 91.3 ± 4.1% and 98.4 ± 2.4%, respectively. The average TIN removal rate recorded over the last 100 d of reactor operation was 118 mg/L·d, which is a reasonable number for mainstream applications. The activity of denitrifying polyphosphate accumulating organisms (DPAOs) accounted for nearly 15.9% of P-uptake during the anoxic phase. DPAOs and canonical denitrifiers removed approximately 5.9 mg TIN/L in the anoxic phase. Batch activity assays, which showed that nearly 44.5% of TIN were removed by the biofilms during the aerobic phase. The functional gene expression data also confirmed anammox activities. The IFAS configuration of the SBR allowed operation at a low solid retention time (SRT) of 5-d without washing out biofilm ammonium-oxidizing and anammox bacteria. The low SRT, combined with low dissolved oxygen and intermittent aeration, provided a selective pressure to washout nitrite-oxidizing bacteria and glycogen-accumulating organisms, as relative abundances of.

Succession of microbial communities reveals the inevitability of anammox core in the development of anammox processes

The lack of anammox seeds is regarded as the bottleneck of anammox-based processes. Although the interactions in anammox consortia have attracted increasing attention, little is known about the influence of inoculated sludge populations on the growth of anammox bacteria. In this study, four sludge of distinct communities mixed with anammox sludge (the relative abundance of Ca. Kuenenia was 1.96 %) were used as the seeds, respectively for the start-up of anammox processes. Notably, all these mixed microbial communities tend to form a similar microbial community, defined as the anammox core, containing anammox-bacteria (22.9 ± 5.9 %), ammonia-oxidizing-bacteria (0.8 ± 0.7 %), nitrite-oxidizing-bacteria (0.2 ± 0.2 %), Chloroflexi-bacteria (0.7 ± 0.4 %), and heterotrophic-denitrification-bacteria (0.3 ± 0.2 %). It also elucidated that the communities of Nitrosomonas-dominated sludge were the closest to the anammox core, and achieved the highest nitrogen-removal rate of 0.73 kg-N m^-3 d^-1. This study sheds light on the solution to the shortage of anammox seeds in the full-scale wastewater treatment application.

Anaerobic-aerobic treatment of wastewater and leachate: A review of process integration, system design, performance and associated energy revenue

Hybrid anaerobic-aerobic biological systems are an environmentally sustainable way of recovering bioenergy during the treatment of high-strength wastewaters and landfill leachate. This study provides a critical review of three major categories of anaerobic-aerobic processes such as conventional wetland, high-rate and integrated bioreactor systems applied for treatment of wastewaters and leachate. A comparative assessment of treatment mechanisms, critical operating parameters, bioreactor configurations, process control strategies, efficacies, and microbial dynamics of anaerobic-aerobic systems is provided. The review also explores the influence of wastewater composition on treatment performance, ammonium nitrogen removal efficacy, impact of mixing leachate, energy consumption, coupled bioenergy production and economic aspects of anaerobic-aerobic systems. Furthermore, the operational challenges, prospective modifications, and key future research directions are discussed. This review will provide in-depth understanding to develop sustainable engineering applications of anaerobic-aerobic processes for effective co-treatment of wastewaters and leachate.

Discovering dominant ammonia assimilation: Implication for high-strength nitrogen removal in full scale biological treatment of landfill leachate

Landfill leachate containing high-strength nitrogen is generated in domestic waste landfilling. The integration of anoxic and aerobic process (AO) based on nitrification and denitrification, has been a mainstream process of biological nitrogen removal (BNR). But the high-strength organics as well as aerobic effluent reflux might change the biochemical environment designed and operated as AO. In view of the nitrogen balance in a full scale landfill leachate treatment plant with two-stage AO, we found that approximately 90% removal of total nitrogen (TN) and ammonia (NH₄⁺-N) focused on primary anoxic and aerobic stage. Meanwhile, the less nitrate and nitrite in the aerobic effluent were incapable of sustaining denitrification or anaerobic ammonia oxidation (anammox). The high reflux flow from aerobic to anoxic process enabled the similar microbial community and functional genes in anoxic and aerobic process units. However, the functional genes involving ammonia assimilation in all process units showcased the highest abundance compared to those correlated with other BNR pathways, including nitrification and denitrification, assimilatory and dissimilatory nitrate reduction, nitrogen fixation and anammox. The ammonia assimilation dominated the removals of TN and NH₄⁺-N, rather than other BNR mechanism. The insight of dominant ammonia assimilation is favorable for illustrating the authentic BNR mechanism of landfill leachate in AO, thereby guiding the optimization of engineering design and operation.

Continuous plug-flow anammox system for mature landfill leachate treatment: Key zone for anammox pathway

This study established the one-stage partial nitrification coupled anammox and partial denitrification coupled anammox process in an anoxic/oxic continuous plug-flow system and operated for 465 days to treat mature landfill leachate. 97.9 %-98.1 % of inorganic nitrogen was removed when the nitrogen loading rate was maintained at 0.33-0.36 kg N/m³/d, and a high anammox contribution to nitrogen removal (89.8 %-92.4 %) was achieved. The long-term in-situ free ammonia (FA) anoxic treatment contributed to the stable performances of partial nitrification and in-situ fermentation. The employed integrated fixed-film activated sludge technology favored the enrichment of hzsA, hzsB, hdh, amoA, hao, narG, and napA functional genes. The oxic zone, particularly oxic biofilm, was the key zone for anammox pathway, where Candidatus_Kuenenia (from 1.6 % to 8.3 %) with high tolerance to FA and salinity stress outcompeted Candidatus_Brocadia (from 18.3 % to 0.1 %) as the dominant anammox bacteria. This study could provide guidance for anammox-mediated landfill leachate treatment in practical projects.

Advanced nitrogen removal from mature landfill leachate based on novel step-draining partial nitrification-denitrification and Anammox process: Significance of low volume exchange ratio

To save external carbon source dosage and simplify NH4+ to NO2- ratio control strategy, this study established a novel step-draining based partial nitrification-denitrification and Anammox (PND-AMX) system for advanced nitrogen removal from mature landfill leachate. Separation of partial nitrification and denitrification was realized based on step-draining, achieving 74.8 % nitrogen removal. 25 % was the optimal volume exchange ratio for synergistic removal of organics and nitrogen, allowing full use of carbon source. NH4+ to NO2- ratio was easily controlled by varying the volume ratio of the first and second effluent of PND reactor. Brocadia, Kuenenia and Jettenia collectively accounted for 13.61 % in AMX reactor, contributing 21.0 % of nitrogen removal. Nitrogen removal efficiency and nitrogen removal rate reached 98.3 ± 1.2 % and 3.07 ± 0.09 kgN/(m3∙d), respectively. Partial Anammox process based on step-draining was easier to realize and of practical significance for application in treatment of landfill leachate.

Purposely Development of the Adaptive Potential of Activated Sludge from Municipal Wastewater Treatment Plant Focused on the Treatment of Landfill Leachate

Biological treatment is a key technology in landfill leachate treatment However, often its efficiency is not high enough due to the pollutants in concentrations above the critical ones. The present study aimed to investigate the adaptive responses that occur in activated sludge (AS) during landfill leachate purification. A model process with AS from a municipal wastewater treatment plant and landfill leachate in increasing concentrations was constructed. The data showed that when dilutions 25 and 50 times had been applied the structure of the AS was preserved, but the COD cannot be reduced below 209 mg O2/L. The feed of undiluted leachate destroyed the AS structure as SVI was reduced to 1 mL/g, biotic index to 1, floc size was greatly reduced and COD remained high (2526 mg O2/L). The dominant group of protozoa was changed from attached to free-swimming ciliates. An increase of the bacterial groups responsible for the xenobiotics elimination (aerobic heterotrophs, genera Pseudomonas, Acinetobacter, Azoarcus, Thauera, Alcaligenes) was registered. This was accompanied by a significant increase in free bacteria. The obtained data showed that for optimal treatment of this type of water it is necessary to include a combination of biological treatment with another non-biological method (membrane filtration, reverse osmosis, etc.).

Intermittent pH control strategy in sludge anaerobic fermentation: Higher short-chain fatty acids production, lower alkali consumption, and simpler control

The pH control to promote short-chain fatty acids (SCFAs) production during anaerobic alkaline fermentation basically focused on constant pH control. In this study, a simple and consumption-reducing intermittent pH control strategy at moderate temperature (23 ± 2 °C) was investigated with adjusting pH to 10 when naturally reduced to 8. The intermittent pH control strategy could alleviate the inhibition of acid-producing bacteria by strong alkaline and high FA concentration. Meanwhile, microbial diversity promoted by 6% and 69% while the relative abundance of acid-producing bacteria increased by 36% and 61% compared to blank and constant pH fermenters. The relative genes abundance related to amino acid metabolism and fatty acid production were mostly promoted and led to enhanced SCFAs production. In the long-term fermenter, the intermittent pH control strategy could result in a 68% reduction in alkali consumption and a 37% increase in SCFAs production compared to that of the constant pH at 10.

Nitrogen Advanced Treatment of Urban Sewage by Denitrification Deep-Bed Filter: Removal Performance and Metabolic Pathway

This study aimed to explore the performance of denitrification deep-bed filter (DN-DBF) to treat municipal sewage for meeting a more stringent discharge standard of total nitrogen (TN) (10.0 mg L-1). A lab-scale DN-DBF was conducted to optimize operation parameters and reveal the microbiological mechanism for TN removal. The results showed that more than 12.7% TN removal was obtained by adding methanol compared with sodium acetate. The effluent TN concentration reached 6.0-7.0 mg L-1 with the optimal influent carbon and nitrogen ratio (C/N) and hydraulic retention time (HRT) (3:1 and 0.25 h). For the nitrogen removal mechanism, Blastocatellaceae_Subgroup_4 and norank_o_JG30-KF-CM45 were dominant denitrification floras with an abundance of 6-10%. Though large TN was removed at the top layer of DN-DBF, microbial richness and diversity at the middle layer were higher than both ends. However, the relative abundance of nitrite reductase enzymes (EC1.7.2.1) gradually increases as the depth increases; conversely, the relative abundance of nitrous oxide reductase gradually decreased.

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

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

Hydroxylamine metabolism in mainstream denitrifying ammonium oxidation (DEAMOX) process: Achieving fast start-up and robust operation with bio-augmentation assistance under ambient temperature

Nitrogen removal from mainstream wastewater via DEnitrifying AMmonium OXidation (DEAMOX) is often challenged by undulated actual temperature and high loading rate. Here, we discovered NH₂OH addition (HA) and bio-augmentation (BA) tactics on start-up and operation performance of DEAMOXs (R1 and R2) under ambient temperature (11.3-31.7 °C). Over 340-day operation suggested that R2 received 10 mg/L HA and 1:25 BA ratio (v/v, anammox/partial denitrification sludge) achieved desirable nitrogen removal efficiency (NRE) of 97.22% after 145-day, while R1 under higher BA ratio of 1:12.5 without HA obtained lower NRE (90.86%) after 184-day. Batch tests revealed that nitrate-nitrite transformation ratio reached 98.64% at low COD/NO₃^--N of 2.6 with HA. Significantly, compared with R2, R1 recovered quickly with satisfactory effluent total nitrogen of 4.21 mg/L despite nitrogen loading rate greater than 0.15 kg N/m³/d and temperature decreased to 14.6 °C. The abundant narG represented high nitrate reduction potential, hzsA and hdh were extensively detected as the symbolisation of anammox metabolism. Thauera, Denitratisoma and unclassified f Comamonadaceae dominated nitrite accumulation. Ca. Brocadia as the dominant anammox bacteria, and its population maintained stable against low temperature and load shocks by NH₂OH intensification. Overall, this study offers an opportunity for the wide-applications of DEAMOX treating mainstream wastewater.

Improving stability of mainstream Anammox in an innovative two-stage process for advanced nitrogen removal from mature landfill leachate

This study presents an innovative mainstream Anammox based on multiple NO₂^--N supplement pathways to treat actual mature landfill leachate over 180 days. Desirable effluent quality of 11.8 mg/L total nitrogen (TN) and nitrogen removal efficiency of 98.8% were achieved despite fluctuation conditions of 1.5-fold influent substrates and 8.0-fold dissolved oxygen overload. Nitrogen mass balance confirmed Anammox was the dominant nitrogen removal pathway, contributing up to 87.9%. Functional genes of ammonia monooxygenase (amoA), hydrazine synthase (hzsB), and ratio of nitrate/nitrite reductase were highly detected. Anammox genera, Candidatus_Kuenenia (4.1%) and Candidatus_Brocadia (5.3%) were dominant in two functional systems, respectively, due to the different affinity of nitrite, oxygen, and organic carbon. As an economical and sustainable technology, the innovative process enabled a 95.1% decrease in organic carbon demand, a 61.5% reduction in aeration energy consumption, and 77.6% lower biomass production compared with traditional nitrification-denitrification process.

Achieving synergetic treatment of sludge supernatant, waste activated sludge and secondary effluent for wastewater treatment plants (WWTPs) sustainable development

A novel process that combines partial nitrification, fermentation and Anammox-partial denitrification (NFAD) was proposed to co-treat ammonia rich sludge supernatant (NH₄⁺-N = 1194.1 mg/L), external WAS (MLSS = 22092.6 mg/L) and WWTP secondary effluent (NO₃^--N = 58.6 mg/L). Three separated reactors were used for partial nitrification (PN-SBR), integrated fermentation and denitrification (IFD-SBR) and combined Anammox-partial denitrification (AD-UASB), respectively. The process resulted in excellent nitrogen removal efficiency (NRE) of 98.7%, external sludge reduction efficiency (SRE) of 44.6% and external sludge reduction rate of 4.1 kg/m³ after 200 days of continuous operation. IFD-SBR and AD-UASB contributed towards 89.4% and 9.2% nitrogen removal, respectively. In AD-UASB, cooperation between Anammox bacteria (4.1% Candidatus Brocadia) and partial denitrifying bacteria (3.2% Thauera) resulted in significant stability of Anammox pathway, which contributed up to 84.1% nitrogen removal in the combined Anammox-partial denitrification process. NFAD saved up to 100% organic resource demand and 25% of aeration consumption compared with the traditional nitrification-denitrification process.