Mainstream Anammox Research Articles

Polystyrene nanoparticles regulate microbial stress response and cold adaptation in mainstream anammox process at low temperature

Nanoplastic pollution has become one of the most pressing environmental issues, and its bioaccumulation in aquatic environment also causes a great difficulty in treatment. Therefore, this work investigated the microbial dynamics of mainstream anaerobic ammonia oxidizing (anammox) process to treat the wastewater containing typical nanoplastics, as well as the fate and regulation mechanism of polystyrene nanoparticles (PS-NPs) with different concentrations. The results showed that 0.1–0.5 mg L-1 of PS-NPs had no significant effect on the nitrogen removal efficiency (NRE). When the concentration of PS-NPs increased from 0.5 mg L-1 to 2 mg L-1, the NRE of R1 with PS-NPs decreased from 94.9 ± 2.3 % to 77.0 ± 1.6 %, while the control reactor R0 maintained a stable NRE. Notably, the relative abundance of Ca. Kuenenia decreased from 17.4 % to 14.8 %, and that of Ca. Brocadia slightly decreased from 5.9 % to 5.0 % in R1. In addition, PS-NPs induced oxidative stress in anammox consortia, leading to the significant increase in reactive oxygen species (ROS) and lactate dehydrogenase (LDH) as well as cell membrane damage. PS-NPs also downregulated the content of heme c and further inhibited anammox activity. Based on the molecular docking simulation and western blotting, cold shock proteins (CSPs) could bind to PS-NPs and reduce the performance of anammox processes at low temperatures.

Pure water and resource recovery from municipal wastewater using high-rate activated sludge, reverse osmosis, and mainstream anammox: A pilot scale study

In response to the escalating global water scarcity and the high energy consumption associated with traditional wastewater treatment plants, there is a growing demand for transformative wastewater treatment processes that promise greater efficiency and sustainability. This study presents an innovative approach for municipal wastewater treatment that integrates high-rate activated sludge with membrane bio-reactor (HRAS-MBR), reverse osmosis (RO) and partial nitrification-anammox (PN/A). With an influent of 8.4 m³/d, the HRAS-MBR demonstrated a removal efficiency of approximately 85 % for chemical oxygen demand (COD), with over 70 % of it being recovered for energy production. The RO system achieved a recovery rate of 75 % for the influent, producing pure water with an electrical conductivity of 50 μS/cm. Concurrently, it concentrated ammonia, thereby enhancing the effectiveness of the PN/A process for nitrogen removal in the mainstream, resulting in a removal efficiency exceeding 85 %. Notably, the HRAS-MBR achieved significant phosphorus removal without chemical additives, attributed to the presence of influent calcium and magnesium ions. Overall, this integrated system reduced the net energy consumption for reclaimed water production by about 26 % compared to conventional methods. Additionally, the new process produced a revenue of 0.75 CNY/m³, demonstrating considerable economic and environmental benefits. This pilot-scale study offers a viable alternative for wastewater treatment and water reuse in water-scarce regions, contributing to sustainable water resource management.

Effects of different substrate ratios on the enrichment of anammox bacteria at low substrate concentration

Anammox bacteria (AnAOB) can be easily enriched under high temperatures and high substrate concentrations, while the application of the mainstream anammox process in low substrate municipal sewage is still relatively uncommon. Therefore, this study investigated the enrichment of AnAOB under conditions of low ammonia nitrogen and nitrite concentration at 25 °C. Results showed that using inoculated aerobic sludge, four ASBRs (R1, R2, R3 and R4) were successfully initiated with different influent substrate (NO2−-N/NH4+-N) ratios of 1.2, 1.32, 1.4 and 1.5, respectively, with reactor start-up times were 162, 150, 120 and 134 days, respectively. The values of ΔNO2--N/ΔNH4+-N in reactors were stable at 1.17, 1.32, 1.43 and 1.53 respectively. The increase in influent substrate ratios resulted in improved TN removal rates and accelerated consumption of chemical oxygen demand (COD) during the initial start-up stage. The maximum TN removal rates achieved in the four reactors were 76.09%, 79.24%, 82.82% and 82.63%, respectively. The color of sludge gradually changes from yellowish-brown to reddish-brown. Furthermore, the surface of sludge exhibited a porous mineral structure, with crater-like cavities. The dominant anammox species in the system was identified as Candida Brocadia (3.04%). According to qPCR, the abundance of hzsB in the system is 1.65 × 1012 copies/g VSS, confirming the effective enrichment of AnAOB.

Synergy between Nitrogen Removal and Fermentation Bacteria Ensured Efficient Nitrogen Removal of a Mainstream Anammox System at Low Temperatures.

Simultaneous partial nitrification, anammox, denitrification, and fermentation (SNADF) is a novel process achieving simultaneous advanced sludge reduction and nitrogen removal. The influence of low temperatures on the SNADF reactor was explored to facilitate the application of mainstream anammox. When temperature decreased from 32 to 16 °C, efficient nitrogen removal was achieved, with a nitrogen removal efficiency of 81.9-94.9%. Microbial community structure analysis indicated that the abundance of Candidatus Brocadia (dominant anaerobic ammonia oxidizing bacteria (AnAOB) in the system) increased from 0.03% to 0.18%. The abundances of Nitrospira and Nitrosomonas increased from 1.6% and 0.16% to 2.5% and 1.63%, respectively, resulting in an increase in the ammonia-oxidizing bacteria (AOB) to nitrite-oxidizing bacteria (NOB) abundance ratio from 0.1 to 0.64. This ensured sufficient nitrite for AnAOB, promoting nitrogen removal. In addition, Candidatus Competibacter, which plays a role in partial denitrification, was the dominant denitrification bacteria (DNB) and provided more nitrite for AnAOB, facilitating AnAOB enrichment. Based on the findings from microbial correlation network analysis, Nitrosomonas (AOB), Thauera, and Haliangium (DNB), and A4b and Saprospiraceae (fermentation bacteria), were center nodes in the networks and therefore essential for the stability of the SNADF system. Moreover, fermentation bacteria, DNB, and AOB had close connections in substrate cooperation and resistance to adverse environments; therefore, they also played important roles in maintaining stable nitrogen removal at low temperatures. This study provided new suggestions for mainstream anammox application.

Achieving nitrite shunt using in-situ free ammonia enriched by natural zeolite: Pilot-scale mainstream anammox with flexible nitritation strategy

The mainstream partial nitritation/anammox (PN/A) process represents a significant innovation in decarbonizing municipal wastewater treatment. However, its implementation is considerably hampered by the challenge of stable nitrite supply. In this study, a pilot-scale PN/A system receiving real sewage (20 m3) was operated at room temperature for nearly one year. Remarkable PN performance with relatively high nitrite accumulation ratio of 75.04 ± 10.05 % was obtained via in-situ free ammonia (FA) strategy. The ammonium concentration enriched in the zeolite increased significantly by 548.8 times compared to that in the aqueous phase by ion exchange. This substantial increase robustly inhibited nitrite-oxidizing bacteria (NOB), resulting in high relative abundance ratio of ammonia-oxidizing bacteria (AOB) to NOB of 37.93 ± 12.61 in the zeolite biofilm, compared to 10.22 ± 1.67 in suspended floc sludge. The significant differences in FA concentrations between zeolite biofilm and suspended floc sludge resulted in distinct spatial distribution disparities of AOB and NOB, which were central to achieving stable nitrite accumulation without complex multiple selective pressures. Consequently, compliant effluent with total nitrogen of 10.91 ± 4.23 mg N/L was achieved at 10.4-31.1 °C without external carbon source addition. The biocarriers in the anammox process played a key role in enhancing functional genes and electron flow, supporting anammox-dominated nitrogen removal. This study presents a flexible and adaptable strategy for mainstream nitrite shunting, highlighting its potential for large-scale implementation of mainstream anammox treatment.

Effect of long-term dosage of hydrazine on mainstream anammox process: Biofilm characteristics and microbial community

The impact of the long-term trace hydrazine (N2H4) exogenous supplementation on activity of the anaerobic ammonium oxidation (anammox) biofilm was investigated in a moving bed biofilm reactor (MBBR) for mainstream wastewater treatment. The results of this study demonstrated that the addition of 2–5 mg/L N2H4 enhanced anammox biofilm activity, as evidenced by the augmented nitrogen removal rate (NRR), which increased from 113.4 g/(m3·d) to 126.7 g/(m3·d) with the introduction of 2 mg/L N2H4. However, a higher concentration of N2H4 (10 mg/L) suppressed anammox activity, leading to a reduced NRR of 91.5 g/(m3·d). Bioindicators revealed that the long-term addition of 2 mg/L N2H4 fostered the accumulation of anammox bacteria (AnAOB) biomass, elevating the volatile suspended solids (VSS) content by 12%. Moreover, the structural composition of extracellular polymeric substances (EPS) within the biofilm was altered, resulting in enhanced biofilm strength within the reactor. The protective mechanism of the biofilm was activated, and EPS secretion was stimulated by the continuous N2H4 supplementation. The introduction of an excess dosage of N2H4 led to alterations in the microbial communities, ultimately resulting in a decline in the performance of the reactor. These findings collectively illustrate that N2H4, as an intermediate product, can effectively enhance anammox activity within the MBBR for mainstream wastewater treatment. This study contributes to the understanding of the optimization strategies for anammox processes in wastewater treatment systems.

Feasibility of simultaneous optimization of Anammox start-up and nitrogen removal performance by intermittent dosing of nanoscale zero-valent iron

The long acclimation period and sensitivity to environmental conditions of Anammox are the bottlenecks for its promotion and application. An innovative strategy was adopted to accelerate functional microbial enhancement and improve nitrogen removal performance by inoculating cryopreserved Anammox sludge and activated sludge with intermittent dosing of nanoscale zero-valent iron (nZVI). The acclimation time was shortened by 76 days with nitrogen removal efficiency (NRE) reaching up to 91.07 %. Anammox, NDFO (nitrate/nitrite-dependent Fe(II) oxidation), Feammox (Fe(III) reduction coupled with anaerobic ammonium oxidation) and abiotic reactions were coupled in the system with nZVI, contributing to 69.79 %, 15.14 %, 9.84 % and 0.25 % of nitrogen removal, respectively. Further microbial analysis demonstrated significant enrichment of functional microorganisms, such as Candidatus Jettenia, Acidovorax and Comamonas. High-efficient nitrogen removal was attribute to the increase of functional genes involved in Anammox, electronic transfer, heme C synthesis and iron metabolism. This work provides an inspiring idea for the mainstream Anammox application.

Exploring transformation of dissolved organic matters and dissolved organic nitrogen in full-scale anammox wastewater treatment: Temperature and microbial roles

Variation of dissolved organic matters (DOM) in mainstream anammox process has received limited attention. This study systematically characterized DOM and dissolved organic nitrogen (DON) in a full-scale mainstream anammox wastewater treatment plant (WWTP) using spectroscopy and Fourier transform-ion cyclotron resonance mass spectrometry. Roles of bacterial community structures related with temperatures on DOM and DON transformations were analyzed. Results indicated that the WWTP removed highly bioavailable, S-containing DOM while producing more unsaturated, aromatic, and N-containing DOM. Higher relative abundances of Proteobacteria and Chloroflexi at low temperature resulted in greater removal rates of proteins, SMP-like and humic acid-like substances. At high temperature, higher relative abundance of Actinobacteriota increased lignin production. Principal component analysis revealed that temperature significantly impacted DOM characteristics compared to DON. These findings are crucial for understanding DOM and DON transformation during mainstream anammox WWTP.

External redox couple enhanced anammox sludge activity at low temperature: Insight into intracellular resource synthesis

Anaerobic ammonium oxidation (anammox), an energy-efficient deamination biotechnology, faces operational challenges in low-temperature environments. Enhancing the metabolic activity of anammox bacteria (AnAOB) is pivotal for advancing its application in mainstream municipal wastewater treatment. Inspired by the metabolic adaptability of AnAOB and based on our previous findings, this work investigated the enhancement of intracellular ATP and NADH synthesis through the exogenous supply of reduced humic acid (HAred) and H2O2 redox couple, aiming to augment AnAOB activity under low-temperature conditions. Our experimental setup involved continuous dosing of 0.0067 μmol g-1 volatile suspended solid of H2O2 and 10 mg g-1 volatile suspended solid of HAred into a mainstream anammox reactor operated at 15 °C with an influent TN content of 60 mg/L. The results showed that HAred / H2O2 couple succeeded in maintaining the effluent TN at 10.72 ± 0.91 mg l-1. The specific anammox activity, ATP and NADH synthesis levels of sludge increased by 1.34, 2.33 and 6.50 folds, respectively, over the control setup devoid of the redox couple. High-throughput sequencing analysis revealed that the relative abundance of Candidatus Kuenenia after adding HAred / H2O2 couple reached 3.65 % at the end of operation, which was 5.14 folds higher than that of the control group. Further metabolomics analysis underscored an activation in the metabolism of amino acids, nucleotides, and phospholipids, which collectively enhanced the availability of ATP and NADH for the respiratory processes. These findings may provide guidance on strategy development for improving the electron transfer efficiency of AnAOB and underscore the potential of using redox couples to promote the mainstream application of anammox technology.

Bibliometric analysis of wastewater treatment processes based on anaerobic ammonia oxidation process

In the realm of water treatment, the anaerobic ammonia oxidation (anammox) process stands out as one of the most innovative breakthroughs. Bibliometrics is an effective method for the evaluation of scientific results and the development of research trends in a particular field of study. Employing VOSviewer and CiteSpace, this study comprehensively analyzed scholarly articles and research trends related to anammox water treatment from 2014 to 2023. The findings revealed a total of 1225 articles in this domain, exhibiting an increasing trend every year in the world, while China emerges as the foremost contributor with close collaborations with the United States, Australia, and other nations. The examination of keyword co-occurrence and cluster network showcases coupled anammox-based reactor startup and opefrational strategies, nitrogen removal studies, nitrous oxide investigations and microbial community analyses are long-term academic endeavors. Furthermore, keyword burst and temporal network analysis,the operational control conditions, driving processes and analysis of microbial macrogenes for mainstream anammox in wastewater treatment plants need more research in the future to improve the feasibility of this technology in engineering applications. Additionally, a meticulous scrutiny of the top 20 landmark and highly cited research articles over the past decade underscores a few persistent intriguing themes, such as “mainstream anammox,” “biological nitrogen removal,” and “16 S rRNA genes,” In summary, this study contributes a nuanced understanding of the contemporary landscape and development trends within the field of anammox water treatment, which will shed light on the future research efforts.

Mixotrophic Metabolism and Oxygen Detoxification Mitigate Antibiotic Stress in Mainstream Anammox Process Under Microaerobic Condition

Mixotrophic Metabolism and Oxygen Detoxification Mitigate Antibiotic Stress in Mainstream Anammox Process Under Microaerobic Condition

Advanced nitrogen removal from municipal wastewater by autotrophy-heterotrophy coupled anammox system in a novel simultaneous microaerobic/limited-oxygen SBR: Interspecific correlation network

Nowadays, autotrophic nitrogen removal of mainstream municipal wastewater by anammox is highly promising. However, due to the lack of a long-term stable nitrite-oxidizing bacteria (NOB) inhibition strategy, the accumulation of NO3−-N byproducts severely affects the nitrogen removal efficiency (NRE). In this study, a simultaneous autotrophy-heterotrophy coupled anammox system was developed in a microaerobic/oxygen-limited SBR through the co-induction of the regulation of aeration intensity and limited organics to achieve the optimization of the mainstream Partial nitrification-anammox (PN/A) processes. The nitrogen removal system constructed by anammox and denitrification achieved the high NRE of 90.77 ± 1.82 %. Under the autotrophic-heterotrophic multiple induction of nitrite supply (PN, partial denitrification and endogenous partial denitrification), the contribution of the nitrogen removal by anammox increased to 57.93 %. The high-throughput sequencing analysis showed that the relative abundance of AnAOB increased from 0.40 % to 0.67 %. In-situ tests assay further demonstrated that the realization of multi-channel nitrite supply facilitated the enrichment of anammox bacteria (AnAOB). The endogenous denitrifying bacterial genus Candidatus (Ca.) Competibacter was significantly enriched in the system (7.98 %, P ≤ 0.001), which enhanced the deep removal of NOX−-N and organics. Correlation network analysis indicated that closer and more balanced interspecies interactions were the key to the high efficiency and stability of the autotrophy-heterotrophy coupled anammox system. Based on the nitrite recirculation and denitrification performance, the simultaneous autotrophy-heterotrophy coupled anammox system established by the novel SBR provides a potential strategy for mainstream anammox applications.

Partial denitrifying phosphorus removal coupling with anammox (PDPRA) enables synergistic removal of C, N, and P nutrients from municipal wastewater: A year-round pilot-scale evaluation

Applying anaerobic ammonium oxidation (anammox) in municipal wastewater treatment plants (MWWTPs) can unlock significant energy and resource savings. However, its practical implementation encounters significant challenges, particularly due to its limited compatibility with carbon and phosphorus removal processes. This study established a pilot-scale plant featuring a modified anaerobic-anoxic-oxic (A2O) process and operated continuously for 385 days, treating municipal wastewater of 50 m3/d. For the first time, we propose a novel concept of partial denitrifying phosphorus removal coupling with anammox (PDPRA), leveraging denitrifying phosphorus-accumulating organisms (DPAOs) as NO2− suppliers for anammox. 15N stable isotope tracing revealed that the PDPRA enabled an anammox reaction rate of 6.14 ± 0.18 μmol-N/(L·h), contributing 57.4 % to total inorganic nitrogen (TIN) removal. Metagenomic sequencing and 16S rRNA amplicon sequencing unveiled the co-existence and co-prosperity of anammox bacteria and DPAOs, with Candidatus Brocadia being highly enriched in the anoxic biofilms at a relative abundance of 2.46 ± 0.52 %. Finally, the PDPRA facilitated the synergistic conversion and removal of carbon, nitrogen, and phosphorus nutrients, achieving remarkable removal efficiencies of chemical oxygen demand (COD, 83.5 ± 5.3 %), NH4+ (99.8 ± 0.7 %), TIN (77.1 ± 3.6 %), and PO43− (99.3 ± 1.6 %), even under challenging operational conditions such as low temperature of 11.7 °C. The PDPRA offers a promising solution for reconciling the mainstream anammox and the carbon and phosphorus removal, shedding fresh light on the paradigm shift of MWWTPs in the near future.

Functional differentiation of size-fractionated biomass in the mixotrophic mainstream UASB-anammox process

The soluble organic matter in sewage is one of the major obstacles to the stable operation of mainstream anammox, which would induce the excessive proliferation of heterotrophic bacteria. Given its excellent volumetric nitrogen removal rate (>2.0 kg N m−3 d−1) in mainstream treatment at 15 °C, the physicochemical properties and microbial ecology of size-fractionated aggregates in mixotrophic anammox-UASB system were investigated to develop strategies for population management. The presence of glucose or acetate (COD/N = 1.0) decreased the contribution of anammox by approximately 30 %, thereby causing the increase of effluent TN concentrations to over 12 mg N L−1, in which NH4+-N accounted for ∼85 %. Interestingly, the relative abundance of anammox bacteria were increased from 1.0 % in flocs (<0.2 mm) to 34.9 % in big granules (>0.8 mm) of the acetate-fed reactor, while the abundance of denitrifying bacteria was decreased from 74.0 % in flocs to 12.0 % in big granules. Similar trend was also observed for the glucose-fed reactor. As a result, the expressions of anammox functional genes, specific anammox activity, extracellular polymeric substances and heme c contents were all increased with the increase of particle sizes. Notably, in contrast to the glucose-fed biomass, the acetate-fed biomass showed significant potential of denitratation. Accordingly, the screen with a size of around 0.2 mm may be an effective tool to uncouple the retention times of denitrifying bacteria and anammox bacteria. These results provided direct evidences for functional differentiation of size-fractionated biomass and would guide us to balance their functions for a satisfactory effluent quality.

Dynamic pulse approach to enhancing mainstream Anammox process stability: Integrating sidestream support and tackling nitrite-oxidizing bacteria challenges

Nitrite-oxidizing bacteria (NOB) seriously threaten the partial nitritation and Anammox (PN/A) process, hindering its mainstream application. Herein, a one-stage PN/A reactor was continuously operated for 245 days under nitrogen loading rate lifted from 0.4 g N/L/d to 0.6 g N/L/d and 0.8 g N/L/d with the nitrogen removal efficiency of 71 %, 64 %, and 41 %, respectively. Furthermore, the NOB species over time was identified as Nitrospira_sp._OLB3, exhibiting an increase of the relative abundance from 0.9 % to 4.3 %. The hydroxyapatite (HAP) granules gradually lost their microbiological function of Anammox bacteria then aged, leading to NOB dominance. Therefore, one “pulse therapy” was introduced and combined with “continuous enhancement” of Anammox sludge supported by sidestream to competitively limit the NOB dynamics. The treatment's effect persisted for around two months. The strategy that returning at least 50 % of the impaired HAP granular sludge to the sidestream for recultivation could fulfill the bottlenecks of mainstream PN/A.

How to Provide Nitrite Robustly for Anaerobic Ammonium Oxidation in Mainstream Nitrogen Removal.

Innovation in decarbonizing wastewater treatment is urgent in response to global climate change. The practical implementation of anaerobic ammonium oxidation (anammox) treating domestic wastewater is the key to reconciling carbon-neutral management of wastewater treatment with sustainable development. Nitrite availability is the prerequisite of the anammox reaction, but how to achieve robust nitrite supply and accumulation for mainstream systems remains elusive. This work presents a state-of-the-art review on the recent advances in nitrite supply for mainstream anammox, paying special attention to available pathways (forward-going (from ammonium to nitrite) and backward-going (from nitrate to nitrite)), key controlling strategies, and physiological and ecological characteristics of functional microorganisms involved in nitrite supply. First, we comprehensively assessed the mainstream nitrite-oxidizing bacteria control methods, outlining that these technologies are transitioning to technologies possessing multiple selective pressures (such as intermittent aeration and membrane-aerated biological reactor), integrating side stream treatment (such as free ammonia/free nitrous acid suppression in recirculated sludge treatment), and maintaining high activity of ammonia-oxidizing bacteria and anammox bacteria for competing oxygen and nitrite with nitrite-oxidizing bacteria. We then highlight emerging strategies of nitrite supply, including the nitrite production driven by novel ammonia-oxidizing microbes (ammonia-oxidizing archaea and complete ammonia oxidation bacteria) and nitrate reduction pathways (partial denitrification and nitrate-dependent anaerobic methane oxidation). The resources requirement of different mainstream nitrite supply pathways is analyzed, and a hybrid nitrite supply pathway by combining partial nitrification and nitrate reduction is encouraged. Moreover, data-driven modeling of a mainstream nitrite supply process as well as proactive microbiome management is proposed in the hope of achieving mainstream nitrite supply in practical application. Finally, the existing challenges and further perspectives are highlighted, i.e., investigation of nitrite-supplying bacteria, the scaling-up of hybrid nitrite supply technologies from laboratory to practical implementation under real conditions, and the data-driven management for the stable performance of mainstream nitrite supply. The fundamental insights in this review aim to inspire and advance our understanding about how to provide nitrite robustly for mainstream anammox and shed light on important obstacles warranting further settlement.

Increasing carbon to nitrogen ratio promoted anaerobic ammonia-oxidizing bacterial enrichment and advanced nitrogen removal in mainstream anammox system

The effects of fluctuating organic carbon to nitrogen (C/N) ratios on mainstream simultaneous partial nitrification, anammox, and denitrification (SNAD) process were studied over 376-day period. The nitrogen removal efficiency decreased from 85.0 ± 6.6 % to 75.8 ± 2.8 % as C/N ratio decreased (3.4 → 1.7), but increased to 82.0 ± 1.9 % when C/N ratio raised to 2.9 and to 78.4 ± 3.0 % when C/N ratio decreased again (2.9 → 2.1), indicating that high C/N ratios promoted nitrogen removal. As C/N ratio raised (1.7 → 2.9), anaerobic ammonia-oxidizing bacteria (AnAOB) abundance increased from 1.3 × 109 to 2.0 × 109 copies/L, which explained the improved nitrogen removal. With an elevated C/N ratio, partial nitrification and endogenous partial denitrification reactions were enhanced, providing more nitrite for AnAOB. Additionally, the aerobic_chemoheterotrophy function and particle sizes increased, forming more stable anoxic microenvironment for AnAOB. Overall, increasing C/N ratio promoted the stability of mainstream SNAD.

Efficient reactivation of anammox sludge after prolonged storage using a combination of batch and continuous reactors.

Due to the slow growth rate of anammox bacteria, enriched sludge is required for the rapid start-up of anammox-based reactors. However, it is still unclear if long-term stored anammox sludge (SAS) is an effective source of inoculum to accelerate reactor start-up. This study explored the reactivation of long-term SAS and developed an efficient protocol to reduce the start-up period of an anammox reactor. Although stored for 13months, a low level of the specific anammox activity of 28mg N/g VSS/d was still detected. Experimental Phase 1 involved the direct application of SAS to an upflow sludge bed reactor (USB) operated for 90 d under varying conditions of hydraulic retention time and nitrogen concentrations. In Phase 2, batch runs were executed prior to the continuous operation of the USB reactor. The biomass reactivation in the continuous flow reactor was unsuccessful. However, the SAS was effectively reactivated through a combination of batch runs and continuous flow feed. Within 75days, the anammox process achieved a stable rate of nitrogen removal of 1.3g N/L/day and a high nitrogen removal efficiency of 84.1 ± 0.2%. Anammox bacteria (Ca. Brocadia) abundance was 37.8% after reactivation. These overall results indicate that SAS is a feasible seed sludge for faster start-up of high-rate mainstream anammox reactors.

Migration of microorganisms between nitrification–denitrification flocs, anammox biofilms and blank carriers during mainstream anammox start-up

To solve the shortage of inoculum, the feasibility of establishing simultaneous partial nitrification, anammox, and denitrification (SNAD) reactor through inoculating nitrification–denitrification sludge, anammox biofilm and blank carriers was investigated. Advanced nitrogen removal efficiency of 91.2 ± 3.6 % was achieved. Bacteria related to nitrogen removal and fermentation were enriched in anammox biofilm, blank carriers and flocs, and the abundance of dominant anaerobic ammonia oxidizing bacteria (AnAOB), Candidatus Brocadia, reached 3.4 %, 0.5 % and 0.3 %, respectively. Candidatus Competibacter and Calorithrix became the dominant denitrifying bacteria (DNB) and fermentative bacteria (FB), respectively. The SNAD system was successfully established, and new mature biofilms formed in blank carriers, which could provide inoculum for other anammox processes. Partial nitrification, partial denitrification and aerobic_chemoheterotrophy were existed and facilitated AnAOB enrichment. Microbial correlation networks revealed the cooperation between DNB, FB and AnAOB that promoted nitrogen removal. Overall, the SNAD process was started up through inoculating more accessible inoculum.

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.