Start-up and long-term operation of the Anammox process in a fixed bed reactor (FBR) filled with novel non-woven ring carriers

Rapid start-up and long-term stable operation of the anammox reactor based on biofilm process: Status, challenges, and perspectives

Anammox-biofilm processes have great potential for wastewater nitrogen removal, as it overcomes the slow growth and easy loss of AnAOB (anaerobic ammonium oxidation bacteria). Biofilm carrier is the core part of the Anammox-biofilm reactor and plays a key role in the start-up and long-term operation of the process. Therefore, the research on the biofilm carrier of Anammox-based process was summarized and discussed in terms of configurations and types. In the Anammox-biofilm process, fixed bed biofilm reactor is a relatively mature biofilm carrier configuration and has advantages in terms of nitrogen removal and long-term operational stability, while moving bed biofilm reactor has advantages in terms of start-up time. Although the long-term operational stability of fluidized bed biofilm reactor is good, its nitrogen removal performance needs to be improved. Among the different biofilm carrier categories, the inorganic biofilm carrier has an advantage in start-up time, due to the enhancement of the growth and metabolic of AnAOB by inorganic materials (such as carbon and iron). Anammox-based reactors using organic biofilm carriers, especially suspension carriers, are well-established and more stable in long-term operation. Composite biofilm carriers combine the advantages of several materials, but their complex preparation procedures lead to high costs. In addition, possible research directions for accelerating the start-up and keeping the long-term stable operation of Anammox reactor by biofilm process were highlighted. It is hoped to provide a possible pathway for the rapid start-up of Anammox-based process, and references for the optimization and promotion of process.

An Advanced Synergy of Partial Denitrification-Anammox for Optimizing Nitrogen Removal from Wastewater: A Review

Anammox is a widely adopted process for energy-efficient removal of nitrogen from wastewater, but challenges with NOB suppression and NO₃^- accumulation have led to a deeper investigation of this process. To address these issues, the synergy of partial denitrification and anammox (PD-anammox) has emerged as a promising solution for sustainable nitrogen removal in wastewater. This paper presents a comprehensive review of recent developments in the PD-anammox system, including stable performance outcomes, operational parameters, and mathematical models. The review categorizes start-up and recovery strategies for PD-anammox and examines its contributions to sustainable development goals, such as reducing N₂O emissions and saving energy. Furthermore, it suggests future trends and perspectives for improving the efficiency and integration of PD-anammox into full-scale wastewater treatment system. Overall, this review provides valuable insights into optimizing PD-anammox in wastewater treatment, highlighting the potential of simultaneous processes and the importance of improving efficiency and integration into full-scale systems.

Conductive carrier promotes synchronous biofilm formation and granulation of anammox bacteria

The extracellular electron transfer capability of some anaerobic ammonium oxidation (anammox) bacteria was confirmed in recent years. However, the effect of conductive carriers on the synchronous formation of anammox biofilm and granules is rarely reported. Anammox biofilm and granules with compact and stable structures accelerate the initiation and enhance the stability of the anammox process. In this study, we found that the conductive carbon fiber brush (CB) carrier promoted synchronous biofilm formation and granulation of anammox bacteria in the internal circulation immobilized blanket (ICIB) reactor. Compared with polyurethane sponge and zeolite carrier, the ICIB reactor packed with CB carrier can be operated under the highest total nitrogen loading rate of 6.53 kg-N/(m³·d) and maintain the effluents NH₄⁺-N and NO₂^--N at less than 1 mM. The volatile suspended solids concentration in the ICIB reactor packed with conductive carrier increased from 5.17 ± 0.40 g/L of inoculum sludge to 24.24 ± 1.20 g/L of biofilm, and the average particle size of granules increased from 222.09 µm to 879.80 µm in 150 days. Fluorescence in situ hybridization analysis showed that anammox bacteria prevailed in the biofilm and granules. The analysis of extracellular polymeric substances indicated that protein and humic acid-like substances played an important role in the formation of anammox biofilm and granules. Microbiome analysis showed that the relative abundance of Candidatus Jettenia was increased from 0.18% to 38.15% in the biofilm from CB carrier during start-up stage. This study provides a strategy for rapid anammox biofilm and granules enrichment and carrier selection of anammox process.

Using an innovative umbrella-shape membrane module to improve MBR for PN-ANAMMOX process

Membrane fouling has been a key factor limiting the applications of membrane bioreactor (MBR). In this study, a novel umbrella-shape membrane module was applied to construct two MBRs for two-stage partial nitrification-anaerobic ammonia oxidation (PN-ANAMMOX) process. After 55 days operation, the ANAMMOX process was started and the PN process was well controlled. Then, the ANAMMOX and PN process were successfully coupled to run the PN-ANAMMOX process. On 103 days, the best nitrogen removing effect was achieved with the maximum nitrogen loading rate (NLR) of 0.4 kg N·(m³·d)^-1 and the corresponding maximum total nitrogen removal rate (TNRR) of 75.23%. The umbrella-shape membrane module in both reactors only needed to be cleaned once during the operation for 105 days, indicating that the membrane module had better resistance to membrane fouling. The functional bacteria were cultivated in suspension state; moreover, the cell densities of ammonia oxidizing bacteria (AOB) and ANAMMOX bacteria (AnAOB) reached 58.32 × 10¹² copies/g sludge and 28.39 × 10¹² copies/g sludge. Their abundances reached 73.25% and 57.80% of the total bacteria, respectively. MBR improved by umbrella-shape membrane module could realize the rapid start-up of ANAMMOX process, effective control of PN process, and stable operation of PN-ANAMMOX process. This study provided a novel approach to control membrane fouling by optimizing the membrane module shape and widened applications of MBRs in PN-ANAMMOX process.

A critical review of exogenous additives for improving the anammox process

Anammox achieves chemoautotrophic nitrogen removal under anaerobic and anoxic conditions and is a low-carbon wastewater biological nitrogen removal process with broad application potential. However, the physiological limitations of AnAOB often cause problems in engineering applications, such as a long start-up time, unstable operation, easily inhibited reactions, and difficulty in long-term strain preservation. Exogenous additives have been considered an alternative strategy to address these issues by retaining microbes, shortening the doubling time of AnAOB and improving functional enzyme activity. This paper reviews the role of carriers, biochar, intermediates, metal ions, reaction substrates, redox buffers, cryoprotectants and organics in optimizing anammox. The pathways and mechanisms of exogenous additives, which are explored to solve problems, are systematically summarized and analyzed in this article according to operational performance, functional enzyme activity, and microbial abundance to provide helpful information for the engineering application of anammox.

Biofilm carriers for anaerobic ammonium oxidation: Mechanisms, applications, and roles in mainstream systems

The anaerobic ammonium oxidation (ANAMMOX) process was proposed as the most promising nitrogen removal process. Biofilm carriers were demonstrated to effectively enhance the anaerobic ammonium oxidating bacteria (AnAOB) retention. This paper reviews the effect of carrier properties on the AnAOB biofilm development according to the biofilm development process and the application state-of-art of three major kinds of conventional carriers, organic-based, inorganic-based carriers, and gel carriers, from the view of system performance and functional microorganisms. The carrier modification methods and purpose are thoroughly summarized and classified into three categories corresponding to various carrier defects. Four important aspects of the desirable carrier for the mainstream ANAMMOX process were proposed, including providing spatial configuration, enhancing the biomass retention, reinforcing the activity, and improving the growth environment, which needs to combine the advantages of organic and inorganic materials. Eventually, the future application directions of novel carriers for the ANAMMOX-based process were also highlighted.

Layered inoculation of anaerobic digestion and anammox granular sludges for fast start-up of an anammox reactor

Layered inoculation of anaerobic digestion (AD) and anammox granular sludges was performed for fast start-up of anammox using an expanded granular sludge bed (EGSB) reactor (R1) with the cell lysis phase and the lag phase being shortened. The maximum nitrogen loading rate (NLR) and nitrogen removal rate (NRR) of R1 were 11 kg N/m³ d and 9.9 kg N/m³ d on day 42, respectively. The domesticated AD granular sludge on the upper layer was collected to another EGSB reactor (R2) to investigate its anammox activity. The results showed that AD granular sludge in R1 had anammox activity and could be cultured into anammox granular sludge. Adsorption, interception and domestication enhanced the biomass of anammox bacteria in R1, accelerating the start-up of the reactor. The findings of this work were expected to solve the problem of fast start-up of an anammox reactor with insufficient anammox seeding sludge in industrial application.

Start-up of Anammox systems with different biochar amendment: Process characteristics and microbial community

As the 'go-to' process when it comes to biological nitrogen removal from wastewaters in recent years, the Anammox process has undergone lots of investigations in order to optimize its performance. In evaluating the effect of distinct biochar types at different concentrations on the Anammox startup process, as well as analyze their corresponding influence on the microbial community structure, three additives (coconut, peach, and bamboo) at either 5%, 10%, or 15% respectively were amended in various Anammox EGSB setups. (i). The 5% coconut biochar amendment resulted in the fastest startup of 46 days with an average ammonium removal efficiency of 96% whereas the control setup took 69 days. Thus, a more robust and cost effective Anammox process could be realized on an industrial scale. (ii) The Illumina high-throughput sequencing of the collected sludge samples indicated that the amendment with distinct biochar resulted in varied prevailing microbial communities in the respective setups. (iii) Proteobacteria was the dominant microbial community. (iv) However, two Anammox bacteria species, Candidatus Brocadia and Candidatus Jettenia were identified, with relative abundances of 0-4.72% and 0-6.23% respectively. The results from this study illustrate the correlation between Anammox reactor performance (startup and nitrogen removal efficiency), type and concentration of biochar amendment employed, as well as microbial community succession.

Fatigue of anammox consortia under long-term 1,4-dioxane exposure and recovery potential: N-kinetics and microbial dynamics

Long-term exposure of anammox process to 1,4-dioxane was investigated using periodic anammox baffled reactor (PABR) under different 1,4-dioxane concentrations. The results generally indicated that PABR (composed of 4 compartments) has robust resistance to 10 mg-dioxane/L. The 1^st compartment acted as a shield to protect subsequent compartments from 1,4-dioxane toxicity through secretion of high extracellular polymeric substance (EPS) of 152.9 mg/gVSS at 10 mg-dioxane/L. However, increasing 1,4-dioxane to 50 mg/L significantly inhibited anammox bacteria; e.g., ~ 93% of total nitrogen removal was lost within 14 days. The inhibition of anammox process at this dosage was most likely due to bacterial cell lysis, resulting in the decrease of EPS secretion and specific anammox activity (SAA) to 105.9 mg/gVSS and 0.04 mg N/gVSS/h, respectively, in the 1^st compartment. However, anammox bacteria were successfully self-recovered within 41 days after the cease of 1,4-dioxane exposure. The identification of microbial compositions further emphasized the negative impacts of 1,4-dioxane on abundance of C. Brocadia among samples. Furthermore, the development of genus Planococcus in the 1^st compartment, where removal of 1,4-dioxane was consistently observed, highlights its potential role as anoxic 1,4-dioxane degrader. Overall, long-term exposure to 1,4-dioxane should be controlled not exceeding 10 mg/L for a successful application.

Calcium nitrate as a bio-stimulant for anaerobic ammonium oxidation process

This study explored the role of calcium nitrate as a bio-stimulant for anaerobic ammonium oxidation (anammox) process. The anaerobic sequencing batch reactor was firstly inoculated with malodorous river sediment and only fed with calcium nitrate until no marked endogenous release of ammonium in effluent (Phase 1). Subsequently, nitrite and ammonium were supplied to test the performance of anammox process (Phase 2). During the operation of Phase 1, the effluent ammonium increased firstly and then decreased. Additionally, continuous nitrite (about 1.54 mgN/L) was observed in the effluent. The microbial analysis showed the simultaneous increase of the relative abundance of heterotrophic denitrifier Denitratisoma and sulfur autotrophic denitrifier Thiobacillus from 0.15% to 5.37% and 0.21% to 4.19%, respectively. Besides, ¹⁵N isotopes trace and qPCR results showed that the contribution of anammox to total nitrogen (TN) removal increased from 3.07% to 27.6%, and that the anammox functional gene hzsB increased from 1.37 × 10⁵ to 2.90 × 10⁶ copies/g. These results indicated that calcium nitrate may induce partial mixotrophic denitrification (heterotrophic and sulfur autotrophic denitrification) to provide nitrite as electron acceptor for anammox, thus promoting the occurrence of anammox. In Phase 2, rapid ammonium and TN removal were accomplished in the initial operation with the reduction efficiency of 80.1% and 90.0%, respectively. The relative abundance of anammox bacteria Candidatus_Brocadia significantly increased from 0.01% to 7.15% during the operation of Phase 2. These findings further confirmed the above deduction. Taken together, calcium nitrate can be a promising bio-stimulant for anammox process by promoting the coupling of mixotrophic denitrification with anammox.

Advances and challenges of mainstream nitrogen removal from municipal wastewater with anammox-based processes

Anaerobic ammonium oxidation (anammox) is a novel process of deammonification that exhibits superior ecological and economic potential compared to that of traditional heterotrophic processes. Although this process has been successfully implemented in treating high-strength nitrogen-contaminated wastewater, it still faces many challenges in treating mainstream municipal wastewater. This review aims to provide an overview of the status and challenges of mainstream anammox-based processes. The different configurations and crucial factors are discussed in this review. Finally, the future needs for feasible application are stated. PRACTITIONER POINTS: Factors restricting mainstream application of anammox-based processes are reviewed. Control strategies for selecting and maintaining anammox bacteria are discussed. Recent advances in nitrite production via partial nitrification or denitrification are summarized. Future needs for the feasible application of anammox-based nitrogen removal technology for mainstream municipal wastewater treatment are outlined.

Anammox-based processes: How far have we come and what work remains? A review by bibliometric analysis

Nitrogen contamination remains a severe environmental problem and a major threat to sustainable development worldwide. A systematic analysis of the literature indicates that the partial nitritation-anammox (PN/AMX) process is still actively studied as a viable option for energy-efficient and feasible technology for the sustainable treatment of N- rich wastewaters, since its initial discovery in 1990. Notably, the mainstream PN/AMX process application remains the most challenging bottleneck in AMX technology and fascinates the world's attention in AMX studies. This paper discusses the recent trends and developments of PN/AMX research and analyzes the results of recent years of research on the PN/AMX from lab-to full-scale applications. The findings would deeply improve our understanding of the major challenges under mainstream conditions and next-stage research on the PN/AMX process. A great deal of efforts has been made in the process engineering, PN/AMX bacteria populations, predictive modeling, and the full-scale implementations during the past 22 years. A series of new and excellent experimental findings at lab, pilot and full-scale levels including good nitrogen removal performance even under low temperature (15-10 °C) around the world were achieved. To date, pilot- and full-scale PN/AMX have been successfully used to treat different types of industrial sewage, including black wastewater, sludge digester liquids, landfill leachate, monosodium glutamate wastewater, etc. Supplementing the qualitative analysis, this review also provides a quantitative bibliometrics study and evaluates global perspectives on PN/AMX research published during the past 22 years. Finally, general trends in the development of PN/AMX research are summarized with the aim of conveying potential future trajectories. The current review offers a valuable orientation and global overview for scientists, engineers, readers and decision makers presently focusing on PN/AMX processes.

Investigation of the process stability of different anammox configurations and assessment of the simulation validity of various anammox-based kinetic models

Over the last 30 years, the successful implementation of the anammox process has attracted research interest from all over the world. Various reactor configurations were investigated for the anammox process. However, the construction of the anammox process is a delicate topic in regards to the high sensitivity of the biological reaction. To better understand the effects of configurations on the anammox performance, process-kinetic models and activity kinetic models were critically overviewed, respectively. A significant difference in the denitrification capabilities was observed even with similar dominated functional species of anammox with different configurations. Although the kinetic analysis gained insight into the feasibility of both batch and continuous processes, most models were often applied to match the kinetic data in an unsuitable manner. The validity assessment illustrated that the Grau second-order model and Stover–Kincannon model were the most appropriate and shareable reactor-kinetic models for different anammox configurations. This review plays an important role in the anammox process performance assessment and augmentation of the process control.

Over the last 30 years, the successful implementation of the anammox process has attracted research interest from all over the world.

Effect of external hydrazine addition on anammox reactor start-up time

Hydrazine is an intermediate product of the anaerobic ammonium oxidation (Anammox) process where both ammonium and nitrite in wastewater are converted to nitrogen gas by bacteria. In this study the effect of external hydrazine addition (5, 10, 15, and 20 mg/L) on the start-up period of the Anammox process was studied using sequencing batch reactors (SBRs). The SBR with an addition of 10 mg/L hydrazine took only 7 weeks to stabilize and achieve the maximum removal of ammonium and nitrite, whereas the SBR without the addition of hydrazine took 12 weeks. The amount of Heme C extracted from the biomass indicated that externally added hydrazine accelerated the growth of Anammox bacteria and reduced the release of nitrous oxide gas from the reactors.

Physico-chemical and microbial characterization of compartment-wise profiles in an anammox baffled reactor

In this study, compartment-wise investigation of an anammox baffled reactor (AnBR) was performed. The AnBR achieved steady-state conditions after a start-up period of ∼50 days and achieved NH₄ and NO₂ conversion percentages of 88.5 and 99.3%, respectively. Examination of the nitrogen mass balance revealed that an AnBR with a two-compartment configuration was sufficient for nitrogen loading rates (NLRs) ranging from 0.125 to 1.975 kg N/m³/d and resulted in a nitrogen removal efficiency (NRE) of 86.7-93.7%. Higher NLRs (4.04-5.05 kg N/m³/d) required four compartments to achieve an NRE of 82.2-87.1%. Further, an overall NLR increase of up to 5.93 ± 0.23 kg N/m³/d resulted in complete AnBR failure. The maximum nitrogen removal rate was consistently recorded in the 1^st compartment for all NLRs examined; as a result, this compartment exhibited the highest bacterial activity. Biomass concentration, specific anammox activity, extracellular polymeric substances, and average granule diameter in the 1^st compartment with an overall NLR of 0.05 kg N/m³/d were estimated to be 11.2 g_VSS/L, 0.03 mg N/g_VSS/h, 84.3 mg/g_VSS, and 0.65 mm, respectively. These values increased to 26.1 g_VSS/L, 11.80 mg N/g_VSS/h, 242.1 mg/g_VSS, and 2.31 mm, respectively, when the overall NLR was incremented to 4.04 kg N/m³/d. However, a gradual reduction in bacterial activity was observed from the 1^st to the 5^th compartment. The microbial community analysis indicated that the dominant phyla in the 1^st compartment (NLR of 0.252 kg N/m³/d) with the highest nitrogen removal were Chloroflexi (38.13%), Planctomycetes (22.62%), and Proteobacteria (14.75%).

Fast start-up of anammox process with mixed activated sludge and settling option

In this study, successful start-up of the anaerobic ammonium oxidation (anammox) process in a sequencing batch reactor (SBR) was achieved by seeding mixed activated sludge which included aerobic sludge, anaerobic sludge, simultaneous partial nitrification, anammox and denitrification (SNAD) sludge, and anammox sludge with low activity at a 2200:2100:5:2 volume ratio. On day 15, the effective anammox activity was attained in SBR, with the specific total nitrogen removal rate (SRR) of 0.214 gNg^-1 VSSd^-1. The total nitrogen removal rate (NRR) increased to 230 gNm^-3 d^-1 by gradually reducing the setting time to 10 min. With the nitrogen loading rate (NLR) up to 506 gNm^-3 d^-1, the total NRR of the SBR reached 433 gNm^-3 d^-1 during stationary phase. Candidatus Brocadia was detected as predominant functional microbes in the anammox SBR. The results demonstrated the feasibility of seeding mixed activated sludge to start-up an anammox SBR by settling option.

Nitric oxide removal from flue gas with ammonium using AnammoxDeNOx process and its application in municipal sewage treatment

A novel AnammoxDeNOx process was designed to simultaneously remove NOx in flue gas and ammonium wastewater, with the aim of exploring the possibility of using NO as a long-term and stable electron acceptor for anammox bacteria. The performance of the AnammoxDeNOx process indicated a NOx removal efficiency from simulated flue gas (including CO₂, SO₂, O₂ and NO₂) of 87-96% using simulated ammonium wastewater. With municipal wastewater, the removal efficiencies for NOx were 70-90%, total nitrogen 40-70%, and COD 80-90% (NO concentration: 100-500 ppm). The anammox genus underwent considerable changes from the dominant Candidatus Kuenenia in the stage of domestication to the predominant Candidatus Brocadia, which then became the dominant species in the simulated flue gas and actual municipal wastewater stages.

Microbial community dynamics in an ANAMMOX reactor for piggery wastewater treatment with startup, raising nitrogen load, and stable performance

Bacterial community dynamics of the ANAMMOX reactor of an integrated “UASB + SHARON + ANAMMOX” system for treating piggery wastewater were investigated using the Illumina MiSeq method with samples obtained at ~ 2-week intervals during a 314-day period. With aerobic activated sludge as seeds and low content artificial wastewater (NH₄⁺–N 50 mg/L; NO₂⁻–N 55 mg/L) as influent for the ANAMMOX reactor, nitrogen removal was initially observed on day 38 with a removal rate 1.3 mg N L⁻¹ day⁻¹, and increased to 90.4 mg N L⁻¹ day⁻¹ on day 55 with almost complete removal of ammonia and nitrite, indicating a successful startup of the reactor. Increasing influent load stepwise to NH₄⁺–N 272.7 mg/L/NO₂⁻–N 300 mg/L, nitrogen removal rate increased gradually to 470 mg N L⁻¹ day⁻¹ on day 228, and maintained a stable level (~ 420 mg N L⁻¹ day⁻¹) following introduction of SHARON effluent since day 229. Correlation between microbial community dynamics and nitrogen removal capability was significant (r = 0.489, p < 0.001). Microbial community composition was determined by influent ammonia, influent nitrite, effluent nitrate and some undefined factors. Anammox bacteria, accounting for ~ 98.7% of Planctomycetes, became detectable (0.03% relative abundance) since day 38 and increased to 0.9% on day 58, well consistent with nitrogen removal performance of the reactor. Relative abundance of anammox bacteria gradually increased to 38.4% on day 140 with stepwise increased influent load; decreased to 0.4% on day 169 because of nitrite inhibition; increased to 19.24% on day 233 when the influent load was dropped; kept at ~ 9.0% with SHARON effluent used as influent and dropped to 3.3% finally. Anammox bacteria, only Candidatus Brocadia and Ca. Kuenenia detected, were the most abundant at genus level. Ca. Brocadia related taxa were enriched firstly under low load and detectable during the entire experimental period. Three main groups represented by Ca. Brocadia related OTUs were enriched or eliminated at different loads, but Ca. Kuenenia related taxa were enriched only under high load (NO₂⁻–N > 300 mg/L), suggesting their different niches and application for different loads. These findings improve the understanding of relationships among microbial community/functional taxa, running parameters and reactor performance, and will be useful in optimizing running parameters for rapid startup and high, stable efficiency.

Using low frequency and intensity ultrasound to enhance start-up and operation performance of Anammox process inoculated with the conventional sludge

A lab-scale ultrasound enhancing Anammox reactor (R1) was established and irradiated once a week by ultrasound with the optimal parameter (frequency of 25 kHz, intensity of 0.2 W cm^-2 and exposure time of 3 min) obtained by batch experiments. R1 and the controlled Anammox reactor (R2) without exposure to the ultrasound were operated in parallel. The start-up period of Anammox process (53 days) in R1 was shorter than that (61 days) in R2. The nitrogen loading-enhancing period (day 53-day 135) in R1 was also shorter than that (day 61-day 151) in R2. At the end of the nitrogen loading-enhancing period, NLR (0.76 kg N m^-3 d^-1) and NRR (0.68 kg N m^-3 d^-1) of R1 were both higher than NLR (0.66 kg N m^-3 d^-1) and NRR (0.56 kg N m^-3 d^-1) of R2. Moreover, The stability of Anammox process in R1 was better than that in R2. The results demonstrated that the periodical irradiation of ultrasound enhanced the start-up and operational performance of Anammox reactor. Microbial community analysis indicated that the ultrasound accelerated the microbial succession from some other bacteria to Anammox bacteria so that shorten the start-up period of Anammox process from the conventional activated sludge. It also indicated that the ultrasound strengthened the competitive advantage of Candidatus Kuenenia stuttgartiensis in Anammox bacteria of the mature sludge so as to enhance the nitrogen removal performance of the Anammox reactor under the operation condition of high nitrogen loading.

Comparison of inoculum sources for long-term process performance and fate of ANAMMOX bacteria niche in poly(vinyl alcohol)/sodium alginate gel beads

The process performance and microbial niche of anaerobic ammonia oxidation (ANAMMOX) bacteria were compared in two identical bioreactors inoculated with different inoculum sources (i.e., pre-cultured ANAMMOX bacteria: PAB and activated sludge: AS) entrapped in poly(vinyl alcohol)/sodium alginate (PVA/SA) gel beads for a long-term period (i.e., 1.5 years). The start-up period with AS was longer than that with PAB; however, both bioreactors were successfully operated over the long-term with stable ANAMMOX activity. After long-term operation, the 16S rRNA gene concentration of ANAMMOX bacteria in both bioreactors was significantly increased, and thereby became comparable. In addition, Candidatus Jettenia sp. became the dominant ANAMMOX species in both bioreactors. Our results suggested that the ANAMMOX performance and microbial niche of ANAMMOX bacteria became nearly identical during long-term operation despite the use of different inoculum sources. Therefore, the use of PVA/SA gel beads entrapping AS appears to be a relevant option for constructing an ANAMMOX process in places where a full-scale ANAMMOX process has never been done previously.

Impact of substrate concentration on anammox-UBF reactors start-up

Two up-flow blanket filter (UBF) reactors were employed to treat synthetic wastewater with different substrate concentrations and nitrogen load rates (NLR) for 178days. During days 0-60, higher influent NLR of R₂ (0.21-0.58kg·m³·d) slowed down the formation of anammox sludge compared with the lower NLR of R₁ (0.18-0.31kg·m³·d). Difference in sludge color and nitrogen conversion rate indicated greater anammox activity of R₂ than R₁. During days 61-178, R₁ and R₂ achieved the maximum nitrogen removal rates (NRR) of 1.213 and 1.684kg/(m³·d) under the NLRs of 1.924 and 2.502kg/(m³·d), respectively. Furthermore, high-throughput sequencing showed that R₂ (43.5%) had a higher proportion of anammox bacteria than R₁ (37.8%) and less species. These results showed that after going through a higher NLR acclimation process during start-up period, stronger resistant capability against high impact nitrogen load and greater anammox activity were obtained by R₂.

Coupling ARB-based biological and photochemical (UV/TiO2 and UV/S2O82-) techniques to deal with sanitary landfill leachate

The aim of this study was to provide an alternative way to remove bio-refractory organics and ammonical-nitrogen from mature municipal solid waste (MSW) landfill leachate by combining biological and photochemical processes. To achieve this objective, the effectiveness of anoxic aged refuse-based bioreactor (ARB) for biological leachate pretreatment followed by Advanced Oxidation Processes (AOPs) by heterogeneous photocatalysis (TiO₂/UV) and persulfate (S₂O₈^2-) oxidation were tested. The results obtained after ARB based pre-treatment demonstrated a mean 72%, 81% and 92% degradation of COD, NH₄N and TN, respectively. However, this treated leachate cannot be discharged without another treatment; hence, it was further treated by UV-mediated TiO₂ photocatalysis and S₂O₈^2- oxidation. An average 82% of COD was abated at optimum condition (1gL^-1 TiO₂; pH 5) whereas, using an optimum 1.5gL^-1 persulfate at pH 5, 81% COD reduction occurred. Acidic and alkaline pH favored COD and NH₄N removal respectively. The results of this study demonstrated that coupling ARB with AOPs is potentially applicable process to deal with bio-recalcitrant compounds present in mature landfill leachate.

Potential coupling effects of ammonia-oxidizing and anaerobic ammonium-oxidizing bacteria on completely autotrophic nitrogen removal over nitrite biofilm formation induced by the second messenger cyclic diguanylate

The objective of this study was to investigate the influence of extracellular polymeric substance (EPS) on the coupling effects between ammonia-oxidizing bacteria (AOB) and anaerobic ammonium-oxidizing (anammox) bacteria for the completely autotrophic nitrogen removal over nitrite (CANON) biofilm formation in a moving bed biofilm reactor (MBBR). Analysis of the quantity of EPS and cyclic diguanylate (c-di-GMP) confirmed that the contents of polysaccharides and c-di-GMP were correlated in the AOB sludge, anammox sludge, and CANON biofilm. The anammox sludge secreted more EPS (especially polysaccharides) than AOB with a markedly higher c-di-GMP content, which could be used by the bacteria to regulate the synthesis of exopolysaccharides that are ultimately used as a fixation matrix, for the adhesion of biomass. Indeed, increased intracellular c-di-GMP concentrations in the anammox sludge enhanced the regulation of polysaccharides to promote the adhesion of AOB and formation of the CANON biofilm. Overall, the results of this study provide new comprehensive information regarding the coupling effects of AOB and anammox bacteria for the nitrogen removal process.

The performance of high-loading composite anammox reactor and its long-term recovery from extreme substrates inhibition

A composite reactor combined with granule and biofilm in one single SBR was developed for high-rate anammox operation. Low activity flocculent inoculum was used as seed sludge and the nitrogen loading rate reached 10.62kgNm(-3)d(-1) after 93days' operation. Subsequently, the performance of high-loading anammox reactor under fluctuation condition was investigated. Due to the extremely short hydraulic retention time and high-strength substrates, the reactor presented dramatic substrates accumulation which resulted in severe inhibition subsequently. Nevertheless, the composite reactor presented significant recovery potential even after biomass hydrolysis caused by inhibition, mainly due to the protection and promotion supplied by biofilm. Besides, granules were gradually formed and accumulated from the flocculent sludge directly during the recovery operation, further elevating the reactor performance. The nitrogen loading rate and corresponding nitrogen removal rate achieved 20.30 and 18.01kgNm(-3)d(-1) with total nitrogen in the influent of 1500mg/l finally.

Fast start-up of Anammox process with appropriate ferrous iron concentration

In this study, three upflow column reactors were compared for anaerobic ammonium oxidation (Anammox) process start-up time with different ferrous iron concentration in feeding. Continuous experiments indicated that the start-up time of Anammox process could be shortened from 70 to 58d in R2 (0.06mM Fe(2+)) and 50d in R3 (0.09mM Fe(2+)). The Anammox activity appeared after 16days operation in R3. Quantitative PCR (q-PCR) analysis demonstrated a significant increase in quantity of Anammox bacteria in R3 compared with the other two reactors during entire operation. At the Fe(II) concentration of 0.09mM, the heme c levels inside Anammox cell and hydrazine dehydrogenase (HDH) activity increased dramatically, which could be the trigger of fast Anammox start-up.

Unprecedented development of anammox in presence of organic carbon using seed biomass from a tannery Common Effluent Treatment Plant (CETP)

This work describes development of a microbial consortium dominant in anammox in presence of organic carbon (available through cell lyses) by employing simple sequencing batch operation in 23 cycles exceeding 400days. Seed biomass from a tannery Common Effluent Treatment Plant (CETP) was enriched for anammox and attained maximum removals of NH4-N (95%) and NO2-N (98%). The anammox was confirmed by nitrogen mass balance in a controlled batch experiment and by DNA extraction-PCR-agarose gel electrophoresis. The effective anammox followed first order reaction kinetics with rate constant of 0.0141/h and half-saturation constant of 10.6mg/L. Evidence for coexistence of denitrification (99% NO2-N removal) and anammox (57.8% NH4-N removal) was demonstrated. This study opens-up possible application of microbial consortium dominant in anammox for simultaneous removal of ammonia and organic carbon from wastewaters.