High specific activity for anammox bacteria enriched from activated sludge at 10°C

Sustainable biochar application in anammox process: Unveiling novel pathways for enhanced nitrogen removal and efficient start-up at low temperature

This study explored the use of biochar to accelerate the establishment of anaerobic ammonium oxidation (anammox) reactors operating at 15 ± 1℃. Incorporating 10 g/L bamboo charcoal in S1 accelerated the start-up of anammox in 87 days, which was significantly shorter than 103 days in S0 (without biochar). After 140 days, S1 exhibited a 10.9 % increase in nitrogen removal efficiency due to a 28.9 % elevation in extracellular polymeric substances, bolstering anammox bacterial resilience. Predominant anammox bacteria (Cadidatus Brocadia and Cadidatus Jettenia) showed relative abundances of 3.19 % and 0.38 % in S1, respectively, which were significantly higher than 0.40 % and 0.05 % in S0. Biochar provides favorable habitats for the enrichment of anammox bacteria and accelerates the establishment of anammox at low temperatures. This finding holds promise for enhancing the efficiency of anammox in cold climates and advancing sustainable wastewater nitrogen removal.

Insights into nitrogen removal and microbial response of marine anammox bacteria-based consortia treating saline wastewater: From high to moderate and low salinities

Marine anammox bacteria (MAB) have promising nitrogen removal performance in high saline wastewater treatment. Nevertheless, the impact resulting from moderate and low salinities on MAB is still unclear. Herein, MAB were applied to treat saline wastewater from high to moderate and low salinities for the first time. Independent of salinities (35-3.5 g/L), MAB consistently exhibited good nitrogen removal performance, and maximum total nitrogen removal rate (0.97 kg/(m³·d)) occurred at 10.5 g/L salts. More extracellular polymeric substances (EPSs) were secreted by MAB-based consortia to resist hypotonic surroundings. However, a sharp EPS decrease was accompanied by the collapse of MAB-driven anammox process, and MAB granules disintegrated due to long-term exposure to salt-free environment. The relative abundance of MAB varied from 10.7% to 15.9% and 3.8% as salinity decreased from 35 to 10.5 and 0 g/L salts. These findings will provide practical implementation of MAB-driven anammox process treating wastewater with different salinities.

Starting up anammox system with high efficiency nitrogen removal at low temperatures: Performance optimization, sludge characterization and microbial community analysis

Anaerobic ammonia oxidation (anammox) has potential advantages for nitrogen removal when operating at medium temperatures, but the increased operation costs of heating limit its application. It would be advantageous to start and operate anammox at low temperatures, the feasibility of which was studied here on a lab scale. Two identical expanded granular sludge bed (EGSB) reactors were inoculated at 35 ± 1 °C (A_med) and 15 ± 3 °C (A_low). Results showed that anammox was successful after 138 d for A_low, only 7 d longer than A_med. Stable operation to 194 d in A_low, the nitrogen loading rate (NLR) increased to 1.01 kg m^-3·d^-1, giving a high nitrogen removal efficiency (NRE) of 85%, which was only slightly lower than that of A_med (90%). More extracellular polymeric substance (EPS) was produced by the microbes of A_low compared to A_med, which prevented anaerobic ammonia oxidizing bacteria (AnAOB) against low temperature stress. Microbial community revealed presence of Candidatus Jettenia in A_med with relative abundance 7.4%, while the "cold-tolerant" Candidatus Kuenenia with 4% was the dominant anammox bacteria in A_low. The anammox granules adapted well to low temperatures and demonstrated high efficiency in anammox process without heating. Therefore, constructing an energy-saving and cost-effective anammox system in high latitudes or high altitudes can be considered.

Anammox process for aquaculture wastewater treatment: operational condition, mechanism, and future prospective

Treatment of ammonia- and nitrate-rich wastewater, such as that generated in the aquaculture industry, is important to prevent environmental pollution. The anaerobic ammonium oxidation (anammox) process has been reported as a great alternative in reducing ammoniacal nitrogen concentration in aquaculture wastewater treatment compared to conventional treatment systems. This paper will highlight the impact of the anammox process on aquaculture wastewater, particularly in the regulation of ammonia and nitrogen compounds. The state of the art for anammox treatment systems is discussed in comparison to other available treatment methods. While the anammox process is viable for the treatment of aquaculture wastewater, the efficiency of nitrogen removal could be further improved through the proper use of anammox bacteria, operating conditions, and microbial diversity. In conclusion, a new model of the anammox process is proposed in this review.

Challenges, solutions and prospects of mainstream anammox-based process for municipal wastewater treatment

Anaerobic ammonia oxidation (anammox) process has a promising application prospect for the mainstream deammonification of municipal wastewater due to its high efficiency and low energy consumption. In this paper, challenges and solutions of mainstream anammox-based process are summarized by analyzing the literature of recent ten years. Slow growth rate of anammox bacteria is a main challenge for mainstream anammox-based process, and enhancement of bacteria retention has been recognized to be necessary. Compared with directly increasing sludge retention time (SRT) with membrane bioreactors or sequencing batch reactors, culturing anammox bacteria in the form of biofilm or granule sludge is more promising for its feasibility of eliminating nitrite oxidizing bacteria (NOB). Besides, adding external electron donors or conductive materials and enriching the concentration of ammonia with absorption materials have also been proved helpful to improve the activity of anammox bacteria. Other challenges include the elimination of NOB and achieving ideal ratio of NH₄⁺ and NO₂^-. To solve these problems and achieve stable partial nitrification, composite control strategies based on low SRT and limited aeration are needed based on the special characteristics of ammonia oxidizing bacteria (AOB) and NOB. When treating actual wastewater, interference of low temperature and components in the influent is another problem. Relatively high activity of anammox bacteria has been realized after artificial acclimation at low temperature and the mechanism was also preliminary explored. Different pre-treatment sections have been designed to reduce the concentration of COD and S^2- from the influent. As for the nitrate produced by the anammox reaction, coupling processes are useful to reduce the concentration of nitrate in the effluent. In brief, suitable reactor and coupling process should be selected according to the temperature, influent quality and discharge targets of different regions. The future prospects of the mainstream anammox-based process are also put forward.

On anammox activity at low temperature: effect of ladderane composition and process conditions

The application of partial nitritation-anammox (PN/A) under mainstream conditions can enable substantial cost savings at wastewater treatment plants (WWTPs), but how process conditions and cell physiology affect anammox performance at psychrophilic temperatures below 15 °C remains poorly understood. We tested 14 anammox communities, including 8 from globally-installed PN/A processes, for (i) specific activity at 10-30 °C, (ii) composition of membrane lipids, and (iii) microbial community structure. We observed that membrane composition and cultivation temperature were closely related to the activity of anammox biomasses. The size of ladderane lipids and the content of bacteriohopanoids were key physiological components related to anammox performance at low temperatures. We also indicate that the adaptation of mesophilic cultures to psychrophilic regime necessitates months, but in some cases can take up to 5 years. Interestingly, biomass enriched in the marine genus "Candidatus Scalindua" displayed outstanding potential for nitrogen removal from cold streams. Collectively, our comprehensive study provides essential knowledge of cold adaptation mechanism, will enable more accurate modelling and suggests highly promising target anammox genera for inoculation and set-up of anammox reactors, in particular for mainstream WWTPs.

Physiology of anammox adaptation to low temperatures and promising biomarkers: A review

The adaptation of bacteria involved in the anaerobic ammonium oxidation (anammox) to low temperatures in the mainstream of WWTP will unlock substantial treatment savings. However, their adaptation mechanisms have begun to be revealed only very recently. This study reviewed the state-of-the-art knowledge on these mechanisms from -omics studies, crucially including metaproteomics and metabolomics. Anammox bacteria adapt to low temperatures by synthesizing both chaperones of RNA and proteins and chemical chaperones. Furthermore, they preserve energy for the core metabolism by reducing biosynthesis in general. Thus, in this study, a number of biomarkers are proposed to help practitioners assess the extent of anammox bacteria adaptation and predict the decomposition of biofilms/granules or slower growth. The promising biomarkers also include unique ladderane lipids. Further proteomic and metabolomic studies are necessary for a more detailed understanding of anammox low-temperature adaptation, thus easing the transition to more cost-effective and sustainable wastewater treatment.

Towards mainstream partial nitritation/anammox in four seasons: Feasibility of bioaugmentation with stored summer sludge for winter anammox assistance

The strong effect of low temperatures on anammox challenges its mainstream application over the winter in temperate climates. Winter bioaugmentation with stored summer surplus sludge is a potential solution to guarantee sufficient nitrogen removal in winter. Firstly, the systems for which nitrogen removal deteriorated by the temperature decrease (25 °C → 20 °C) could be fully restored bioaugmenting with granules resp. flocs stored for 6 months at 118 resp. 220% of the initial biomass levels. Secondly, the reactivation of these stored sludges was tested in lower temperature systems (15.3 ± 0.4/10.4 ± 0.4 °C). Compared to the activity before storage, between 56% and 41% of the activity of granules was restored within one month, and 41%-32% for flocs. Additionally, 85-87% of granules and 50-53% of flocs were retained in the systems. After reactivation (15.3 ± 0.4/10.4 ± 0.4 °C), a more specialized community was formed (diversity decreased) with Candidatus Brocadia still dominant in terms of relative abundance. Capital and operating expenditures (CAPEX, OPEX) were negligible, representing only 0.19-0.36% of sewage treatment costs.

Adaptation of anammox bacteria to low temperature via gradual acclimation and cold shocks: Distinctions in protein expression, membrane composition and activities

Anammox bacteria enable efficient removal of nitrogen from sewage in processes involving partial nitritation and anammox (PN/A) or nitrification, partial denitrification, and anammox (N-PdN/A). In mild climates, anammox bacteria must be adapted to ≤15 °C, typically by gradual temperature decrease; however, this takes months or years. To reduce the time necessary for the adaptation, an unconventional method of 'cold shocks' is promising, involving hours-long exposure of anammox biomass to extremely low temperatures. We compared the efficacies of gradual temperature decrease and cold shocks to increase the metabolic activity of anammox (fed batch reactor, planktonic "Ca. Kuenenia"). We assessed the cold shock mechanism on the level of protein expression (quantitative shot-gun proteomics, LCHRMS/MS) and the structure of membrane lipids (UPLCHRMS/MS). The shocked culture was more active (0.66±0.06 vs 0.48±0.06 kg-N/kg-VSS/d) and maintained the relative content of N-respiration proteins at levels consistent levels with the initial state, whereas the content of these proteins decreased in gradually acclimated culture. Cold shocks also induced a more efficient expression of potential cold shock proteins (e.g. ppiD, UspA, pqqC), while putative cold shock proteins CspB and TypA were upregulated in both cultures. Ladderane lipids characteristic for anammox evolved to a similar end-point in both cultures; this confirms their role in anammox bacteria adaptation to cold and indicates a three-pronged adaptation mechanism (ladderane alkyl length, introduction of shorter non-ladderane alkyls, polar headgroup). Overall, we show the outstanding potential of cold shocks for low-temperature adaptation of anammox bacteria and provide yet unreported detailed mechanisms of anammox adaptation to low temperatures.

Effect of the form of granular sludge and temperature on anammox immobilized fillers: From performance to microbial community analysis

The immobilized carrier was prepared with complete anaerobic ammonia oxidation granular sludge (AnGS) and crushed AnGS, respectively. We evaluated the effects of granular form and continuous temperature changes on nitrogen removal by immobilized anaerobic ammonium oxidation (anammox) filler. The results showed that the rate of nitrogen removal of crushed and encapsulated AnGS was 20% higher than that of direct encapsulated AnGS. However, the latter had higher thresholds of tolerance to Fe²⁺ and Cu²⁺. In addition, the immobilization reduced the activation energy of anammox. Above 12.5 °C, the immobilized filler was efficient at removing nitrogen removal through the dual adjustment of temperature-hydraulic retention time. From 12.5 °C to 23 °C, the temperature had a greater influence on the nitrogen removal effect than the HRT. In contrast, HRT had a dominant influence from 23 °C to 32 °C. Anammox activity was severely inhibited below 12.5 °C. High-throughput sequencing analysis showed that the community structure migrated with the changes in temperature. The anammox functional bacteria Candidatus Kuenenia (18.31-39.73%) were the dominant genus at medium and high temperatures, and it was replaced by Chryseobacterium (24.19%) at 8.5 °C. In addition, an RDA analysis showed that Candidatus Brocadia was more adaptable to low temperatures than Candidatus Kuenenia. In addition, Bellilinea was more sensitive to temperature than Candidatus Kuenenia. Thus, the temperature could be appropriately lowered to avoid overbreeding. The results of this study optimized the operation of an anammox immobilized system and promote its further application.

Robustness of mainstream anammox activity at bench and pilot scale

New technologies and processes, such as mainstream anammox, aim to reduce energy requirements of wastewater treatment and improve effluent quality. However, in municipal wastewater (MWW) anammox system are often unstable due to process control disturbance, influent variability, or unwanted nitrite oxidizing bacteria (NOB). This study examines the anammox system by focusing on anammox activity and its robustness in a mainstream environment. An 8 m³ pilot-scale sequencing batch reactor (SBR) receiving pretreated MWW (with external nitrite addition) was seeded with pre-colonized carriers. Within six months at 12-20 °C an anammox activity of 200 gN·m^-3·d^-1 was achieved. After the startup an anammox activity of 260 ± 83 gN·m^-3·d^-1 was maintained over 450 days. The robustness of the anammox activity was analyzed through three disturbance experiments. Anammox biofilm on carriers were exposed to dissolved oxygen (DO = 1.6 mg·L^-1, intermittent aeration), organic loading rate (OLR, C/N increased from 2:1 to 5:1) and temperature disturbances (20 °C to 12 °C) in triplicate 12 L bench scale reactors. The anammox activity and microbial community was monitored during these disturbances. The DO and OLR disturbance experiments were replicated at pilot scale to investigate upscaling effects. Bench and pilot scale anammox activity were unaffected by the DO disturbance. Similarly, an increase in OLR did not deteriorate the bench and pilot scale anammox activity, if nitrate was available. When, at bench scale, the reactor temperature was reduced from 20 °C to 12 °C overnight, anammox activity decreased significantly, this was not the case for the slow seasonal temperature changes (12-25 °C) at pilot scale where no strong temperature dependency was detected in winter. Metagenomic analysis revealed a broad range of Brocadiaceae species with no single dominant anammox species. Anammox thrive under mainstream conditions and can withstand typical process disruptions.

Adaptation of anammox granules in swine wastewater treatment to low temperatures at a full-scale simultaneous partial nitrification, anammox, and denitrification plant

In the anammox process, maintaining a high anammox activity at low water temperatures for stable nitrogen removal is a challenge. In this study, to verify the adaptability of anammox to low water temperatures, we investigated effects of annual temperature fluctuations on nitrogen removal in a full-scale swine wastewater treatment plant, where anammox bacteria accumulated. Annual quarters were defined as L-1 (November-January), L-2 (February-April), H-1 (April-July), and H-2 (July-October). The total nitrogen removal rate was stable at 0.08-0.11 kg-N/m³/d, even during temperature fluctuations. Removal efficiencies of biochemical oxygen demand and total nitrogen were consistently high at 95-99% and 69-81%, respectively. The anammox activity and abundance of anammox bacteria were highest in granule L-1 and lowest in granule H-2. The optimal temperature for anammox activity shifted from 35 °C in granules H-1 and H-2 to 30 °C in granules L-1 and L-2, while the latter maintained a moderate activity compared to the former at low temperature. Candidatus Jettenia asiatica was predominant, especially in granule L-2, accounting for up to 54% of the microbial community composition at the genus level. The high specific anammox activity in granule L-2 was considered to be due to the abundance of anammox bacteria and the adaptation of Ca. Jettenia asiatica to low temperature. The anammox granules adapted well to low temperatures and demonstrated high efficiency in the simultaneous partial nitrification anammox and denitrification process without heating. Thus, constructing an energy-saving and cost-effective nitrogen removal system can be considered.

Architecture of HAP-anammox granules contributed to high capacity and robustness of nitrogen removal under 7°C

The anaerobic ammonium oxidation (anammox) process is an autotrophic nitrogen removal process with great potential as a cost-effective and highly efficient technology in the wastewater treatment field. The main challenges yet to be overcome in this new frontier technology are operating at lower temperatures and achieving a high and stable nitrogen removal efficiency. In this study, an up-flow expanded bed reactor with hydroxyapatite (HAP)-anammox granules was operated for more than 200 days at 7°C. The nitrogen loading rate (NLR) was improved from 1.0 g-N/L/d to 3.6 g-N/L/d, together with a high-level nitrogen removal efficiency of 84-92%, which is the highest to date at extremely low temperatures in a continuous experiment. Candidatus Kuenenia was revealed to be the only dominant anammox genus, with a relative abundance of 35.3-37.5%. The optimal operational temperature was around 35°C and the apparent activation energy (E_a) was calculated as 78.37 kJ/mol. The three-layers architecture and architectural evolution of HAP-anammox granules into HAP-cores and peeling biofilms with outstanding settling performance were characterized. Under 7°C, the high capacity of nitrogen removal with robust removal efficiency using HAP-anammox granules was achieved.

Pairing denitrifying phosphorus accumulating organisms with anaerobic ammonium oxidizing bacteria for simultaneous N and P removal

Coupling of denitrifying polyphosphate accumulating organisms (DPAO) with anaerobic ammonium oxidizing (Anammox) bacteria in a single treatment scheme has so far been unsuccessful but could offer substantial energy savings, minimize sludge production, while achieving simultaneous carbon, nitrogen and phosphate removal. However, both organisms compete for nitrite and have vastly different growth rates and therefore the goal of this study was to uncouple their solid retention time (SRT) by growing them in different sludge fractions and to determine their biomass specific kinetic properties. Anammox bacteria were grown in a biofilm for longer SRTs and DPAO in flocs to allow shorter SRTs. Exposure of DPAO to anaerobic conditions was accomplished by recycling the flocs to a separate reactor by which simultaneous P, N, and C removal was accomplished. The diffusion limited biofilm lowered the biomass specific nitrite affinity for Anammox (K_s^AMX = 0.091 mM), which gave DPAO a competitive edge to consume nitrite (K_s^DPAO = 0.022 mM) in the suspended floc fraction. However, DPAO are more sensitive to nitrite (K_i^DPAO = 0.377 mM) than Anammox bacteria and (K_i^AMX > 1.786 mM), and therefore the DPAO would be better suited to grow in the protective biofilm, showing that both biomass growth types (flocs and granules) have advantages (and disadvantages) depending on the setting. This work is an important steppingstone to understanding resource competition amongst Anammox and DPAO and SRT management strategies to allow their pairing in combined reactor configurations.

Enhancing the in-situ enrichment of anammox bacteria in aerobic granules to achieve high-rate CANON at low temperatures

In this study, a high-rate CANON (Complete Autotrophic Nitrogen-removal Over Nitrite) process was started up successfully by enhancing the in-situ enrichment of anammox bacteria in aerobic granules at conditions relevant for mainstream wastewater treatment. Firstly, to provide nitrite for anammox bacteria growth efficient nitrite-oxidizing bacteria (NOB) repression was rapidly achieved and stably maintained. Both low dissolved oxygen (DO) and ammonium concentrations ratio (DO/NH₄⁺ <0.15) and selective washing-out of NOB-preferred smaller particles at short hydraulic retention time (HRT, 25-15 min) contributed to the NOB repression. Then the stepwise down-regulating DO concentrations from 2.8 to 1.2 mg/L enhanced the enrichment of anammox bacteria in the aerobic granules. The enriched anammox species was dominated by Ca. Brocadia sapporoensis with the estimated growth rate of 0.008-0.013 d^-1 at 15 °C. Chloroflexi and Chlorobi-affiliated bacteria were also significantly enriched in the granules, which may benefit the anammox bacteria activity and growth. At the end of this study, the average total nitrogen removal rate and efficiency of the granular CANON process respectively reached 1.26 kg N·m^-3·d^-1 and 68% treating low-strength ammonium (∼50 mg N·L^-1) wastewater under such aggressive conditions (DO = 0.8-1.5 mg/L, HRT< 1.0 h, and T = 15 °C). Overall, the aerobic granules provided a habitable niche for the proliferation and almost complete retention of the anammox bacteria. This study provides a roadmap for in-situ starting up of high-rate CANON process for mainstream wastewater treatment with aerobic granules as inoculum.

Anammox enrichment: impact of sludge retention time on nitrogen removal

Enrichment of anammox bacteria has long been considered to be time-consuming because of the slow growth rate. This study evaluated the impact of sludge retention time (SRT) on the enrichment of anammox bacteria with a focus on nitrogen removal and specific anammox activity (SAA) in sequencing batch reactors (SBR). A total of eight different SRTs in the range of 30-1280 days at nitrogen loading rates (NLR) range from 12.1 to 122.1 mg/L-d were used to evaluate the anammox activity. SAA was negligible during the first 105 days due to denitrification and continued to increase thereafter to peak at 0.22 g N/g VSS-d on day 530 as the solids and hydraulic retention times (SRT and HRT) decreased from 120 to 80 days and 10 to 2 days, respectively. The stability of SAA (0.21 ± 0.02 g N/g VSS-d) from day 503 to day 670 indicates that anammox bacteria should be enriched at SRTs ranging from 30 to 80 days and NLR of 122.1 mg N/L-d. Moreover, the SBR achieved a maximum nitrogen removal efficiency of 86.6% at an SRT of 30 days and an NLR of 122 mg/L-d. Microbial analysis indicated that the two most abundant microorganisms accounting for 48% of the bacterial population are Anammoxoglobus followed by the heterotrophic denitrifier Rhizobiales. The maximum specific growth rate (was estimated as 0.062 d-1, consistent with typical of 0.057 d-1. The average first-order decay rate was estimated as 0.008 d-1, and the half-saturation constants (ks) averaged 16.2 mg NH4-N/L.

Adaptation of flocculent anammox culture to low temperature by cold shock: long-term response of the microbial population

Partial nitritation-anammox (PN/A) process will substantially reduce the costs for the removal of nitrogen in the mainstream of municipal sewage. However, one of the mainstream PN/A challenges is to reduce the time necessary for the adaptation of anammox bacteria to lower temperatures in mild climates. In this study, we exposed anammox flocculent culture to cold shocks [35°C → 5°C (8 h) → 15°C] and evaluated long-term cold shock response. Over a post-shock period of 40 d at 15°C, the nitrogen removal rates in the shocked culture were significantly higher compared to control, with maximum rates up to 0.082 and 0.033 kg-N/kg-VSS/d or 0.164 and 0.076 kg-N/m3/d, for shocked culture and control, respectively. In the corresponding semi-batch cycles, the shocked culture was on average 136 ± 101% more active than the control, due to the negative effect of cold shock on side populations and more active anammox cells. Per FISH, Ca. Brocadia anammoxidans and Ca. Scalindua survived the shock and remained present throughout. Thus, both anammox microorganisms seem to respond favourably to cold shocks. In sum, we provide further evidence that cold shocks accelerate the adaptation of anammox to the mainstream of municipal WWTPs. Further, for the first time, we report the long-term adaptive response of anammox to cold shocks.

Generalized temperature dependence model for anammox process kinetics

Temperature is a key operational factor influencing the anammox process kinetics. In particular, at temperatures below 15 °C, the specific anammox activity (SAA) considerably decreases. This study aimed to describe the temperature dependence of the anammox process kinetics in the temperature range from 10 to 55 °C, including the specific characteristics of "cold anammox". The commonly used Arrhenius and extended and modified Ratkowsky equations were examined. The Ratkowsky equations yielded a strong correlation (coefficient of determination, R² = 0.93-0.96) between the measured and predicted data over the analyzed temperature range (10-55 °C). However, these equations could not correctly reflect the anammox temperature dependence at temperatures below 15 °C (R² = 0.36-0.48). Therefore, a new generalized temperature model was proposed. The generalized temperature equation (GTE) considered the division of the analyzed temperature range into three temperature ranges: 10-15 °C, 15-35 °C and 35-55 °C. The ranges correspond to "cold anammox", "(low) mesophilic anammox" and "thermophilic anammox". The applied approach yielded a strong correlation between the measured and predicted SAA (R² = 0.97) over the temperature range from 10 to 55 °C and over the low-temperature range from 10 to 15 °C (R² = 0.99). Overall, the GTE could enhance the predictions of the temperature dependence of the anammox process kinetics. The GTE can help examine anammox-based bioaugmentation systems operating at both high temperatures (sidestream reactors) and low temperatures (mainstream reactors).

Towards mainstream deammonification: Comprehensive review on potential mainstream applications and developed sidestream technologies

Deammonification (partial nitritation-anammox) process is a favorable and innovative process, for treatment of nitrogen-rich wastewater due to decreased oxygen and carbon requirements at very high nitrogen loadings. The bacterial groups responsible for this process are anaerobic ammonium oxidation (anammox) bacteria in symbiosis with ammonium oxidizing bacteria (AOB) which have an active role in development of nitrogen removal biotechnology in wastewater. Development and operation of sidestream deammonification processes has augmented since the initial full-scale systems, yet there are several aspects which mandate additional investigation and deliberation by the practitioners, to reach the operating perspective, set for the facility. Process technologies for treatment of streams with high ammonia concentrations continue to emerge, correspondingly, further investigation towards feasibility of applying the deammonification concept, in the mainstream treatment process is required. Mainstream deammonification can potentially improve the process of achieving more sustainable and energy-neutral municipal wastewater treatment, however feasible applications are not accessible yet. This critical review focuses on a comprehensive assessment of the worldwide lab-scale, pilot-scale and full-scale sidestream applications as well as identifying the major issues obstructing the implementation of mainstream processes, in addition to the designs, operational factors and technology advancements at both novel and/or conventional levels. This review aims to provide a novel and broad overview of the status and challenges of both sidestream and mainstream deammonification technologies and installations worldwide to assess the global perspectives on deammonification research in the recent years. The different configurations, crucial factors and overall trends in the development of deammonification research are discussed and conclusively, the future needs for feasible applications are critically reviewed.

Pilot-scale enrichment of anammox biofilm using secondary effluent as source water

Enough biomass of anaerobic ammonium oxidation (anammox) bacteria is essential for maintaining a stable partial nitrification/anammox (PN/A) wastewater treatment system. Present enrichment procedures are mainly labor-intensive and inconvenient for up-scaling. A simplified procedure was developed for enrichment of anammox biofilm by using secondary effluent as source water with no supplement of mineral medium and unstrict control of influent dissolved oxygen (DO). Anammox biofilm was successfully enriched in two pilot-scale reactors (XQ-cul and BT-cul) within 250 and 120 days, respectively. The specific anammox activity increased rapidly during the last 2 months in both reactors and achieved 2.54 g N₂-N/(m²·d) in XQ-cul and 1.61 g N₂-N/(m²·d) in BT-cul. Similar microbial diversity and community structure were obtained in the two reactors despite different secondary effluent being applied from two wastewater treatment plants. Anaerobic ammonium oxidizing bacteria genera abundance reached up to 37.4% and 43.1% in XQ-cul and BT-cul biofilm, respectively. Candidatus Brocadia and Ca. Kuenenia dominated the enriched biofilm. A negligible adverse effect of residual organics and influent DO was observed by using secondary effluent as source water. This anammox biofilm enrichment procedure could facilitate the inoculation and/or bio-augmentation of large-scale mainstream PN/A reactors.

Start-Up of Anammox SBR from Non-Specific Inoculum and Process Acceleration Methods by Hydrazine

Biological nutrient removal from wastewater to reach acceptable levels is needed to protect water resources and avoid eutrophication. The start-up of an anaerobic ammonium oxidation (anammox) process from scratch was investigated in a 20 L sequence batch reactor (SBR) inoculated with a mixture of aerobic and anaerobic sludge at 30 ± 0.5 °C with a hydraulic retention time (HRT) of 2–3 days. The use of NH4Cl, NaNO2, and reject water as nitrogen sources created different salinity periods, in which the anammox process performance was assessed: low (<0.2 g of Cl−/L), high (18.2 g of Cl−/L), or optimum salinity (0.5–2 g of Cl−/L). Reject water feeding gave the optimum salinity, with an average nitrogen removal efficiency of 80%, and a TNRR of 0.08 kg N/m3/d being achieved after 193 days. The main aim was to show the effect of a hydrazine addition on the specific anammox activity (SAA) and denitrification activity in the start-up process to boost the autotrophic nitrogen removal from scratch. The effect of the anammox intermediate hydrazine addition was tested to assess its concentration effect (range of 2–12.5 mg of N2H4/L) on diminishing denitrifier activity and accelerating anammox activity at the same time. Heterotrophic denitrifiers’ activity was diminished by all hydrazine additions compared to the control; 5 mg of N2H4/L added enhanced SAA compared to the control, achieving an SAA of 0.72 (±0.01) mg N/g MLSS/h, while the test with 7.5 mg of N2H4/L reached the highest overall SAA of 0.98 (±0.09) mg N g/MLSS/h. The addition of trace amounts of hydrazine for 6 h was also able to enhance SAA after inhibition by organic carbon source sodium acetate addition at a high C/N ratio of 10/1. The start-up of anammox bacteria from the aerobic–anaerobic suspended biomass was successful, with hydrazine significantly accelerating anammox activity and decreasing denitrifier activity, making the method applicable for side-stream as well as mainstream treatment.

Effect of biomass immobilization and reduced graphene oxide on the microbial community changes and nitrogen removal at low temperatures

The slow growth rate and high optimal temperatures for the anaerobic ammonium oxidation (anammox) bacteria are significant limitations of the anammox processes application in the treatment of mainstream of wastewater entering wastewater treatment plant (WWTP). In this study, we investigate the nitrogen removal and microbial community changes in sodium alginate (SA) and sodium alginate–reduced graphene oxide (SA-RGO) carriers, depending on the process temperature, with a particular emphasis on the temperature close to the mainstream of wastewater entering the WWTP. The RGO addition to the SA matrix causes suppression of the beads swelling, which intern modifies the mechanical properties of the gel beads. The effect of the temperature drop on the nitrogen removal rate was reduced for biomass entrapped in SA and SA-RGO gel beads in comparison to non-immobilized biomass, this suggests a ‘‘protective” effect caused by immobilization. However, analyses performed using next-generation sequencing (NGS) and qPCR revealed that the microbial community composition and relative gene abundance changed significantly, after the implementation of the new process conditions. The microbial community inside the gel beads was completely remodelled, in comparison with inoculum, and denitrification contributed to the nitrogen transformation inside the beads.

Review of characteristics of anammox bacteria and strategies for anammox start-up for sustainable wastewater resource management

Wastewater management has experienced different stages, including pollutant removal, resource recovery, and water nexus. Within these stages, anaerobic ammonia oxidation-based biotechnology can be incorporated for nitrogen removal, which can help achieve sustainable wastewater management, such as reclamation and ecologization of wastewater. Here, the physiology, metabolism, reaction kinetics and microbial interactions of anammox bacteria are discussed, and strategies to start-up the anammox system are presented. Anammox bacteria are slow growers with a high doubling time and a low reaction rate. Although most anammox bacteria grow autotrophically, some types can grow mixotrophically. The reaction stoichiometric coefficients can be affected by loading rates and other biological reactions. Microbial interactions also contribute to enhanced biological nitrogen removal and promote activities of anammox bacteria. The start-up of the anammox process is the key aspect for its practical application, which can be realized through seed selection, system stimulation, and biomass concentration enhancement.

In situ startup of a full-scale combined partial nitritation and anammox process treating swine digestate by regulation of nitrite and dissolved oxygen

A challenge during the startup of the combined partial nitritation and anammox process is how to balance dissolved oxygen control and nitrite accumulation for converting partial nitritation into anammox, maintaining stable partial nitritation and promoting growth of anammox bacteria. An innovative regulation strategy of nitrite dosing and dissolved oxygen control in this study was developed to achieve the rapid startup of a full-scale combined partial nitritation and anammox reactor within 77 days and the total nitrogen removal rate of reactor was 0.097 kg N/kgMLSS·d^-1, and the activity and gene copy concentration of anammox bacteria reached 0.307 kg N/kgMLVSS·d^-1 and 7.79 × 10⁹ copies/gMLVSS, respectively. Microbial community analysis revealed that Candidatus_Kuenenia and Nitrosomonas were the dominant nitrogen transformation bacteria with an abundance of 2.49% and 14.86%, respectively. This study offers a new method for rapid startup and spreading application of the full-scale anammox process.

Anammox, biochar column and subsurface constructed wetland as an integrated system for treating municipal solid waste derived landfill leachate from an open dumpsite

This study aims to treat nitrogen-rich landfill leachate from Karadiyana open dumpsite, Sri Lanka, through an integrated treatment train consists of an anammox process, Municipal Solid Waste derived biochar column followed by a biochar embedded subsurface constructed wetland. Characterization of leachate was done and the leachate pollution index (LPI) was estimated. Meanwhile, leachate was treated through a treatment system comprising an anammox reactor having 140 mm diameter and 250 mm height, a biochar reactor having the same dimensions with 1.3 kg of MSW biochar, and a laboratory-scale constructed wetland of 1 × 0.3 × 0.45 m. The influent and effluent quality was assessed for the samples taken in 24 h intervals. The analysis indicated that the leachate was high in COD (4000-14,000 mg/L), ammonia (760-900 mg/L), nitrate (60-126 mg/L), and phosphorus (33-66 mg/L). Ammonia and nitrite were removed 94 and 99% by anammox unit, respectively. Nitrate, phosphate, COD and conductivity were significantly removed by the constructed wetland system in 78, 70, 65 and 61%, respectively, whereas biochar barricades extended support for removal of the contaminants and color. The combined treatment system demonstrated treatment efficiencies as 100% of ammonia, 98.7% of nitrite, 98.2% of nitrate, 80.9% of phosphate, 79.7% of COD, and 69.9% of conductivity. Thus, it can be concluded that the anammox, combined with biochar embedded treatment train is promising to treat landfill leachate, having a high pollutant index.

Performance of the anammox process treating low-strength municipal wastewater under low temperatures: Effect of undulating seasonal temperature variation

In the anammox process treating low-strength municipal wastewater, the effect of common seasonal temperature variation (15.1 °C-22.2 °C) on performance was studied. In autumn and winter, the nitrogen removal rate (NRR) decrement of 0.038kgN/(m³·d) (17.9 °C → 15.1 °C) was nearly threefold higher than 0.014kgN/(m³·d) (22.2 °C → 17.9 °C), which showed that lower temperature laid more negative impact on nitrogen removal. ¹⁵N isotope tracing tests confirmed that the contribution of denitrification to nitrogen removal was far less than anammox, and anammox contributed more at 15.1 °C (91.7%) than 21.9 °C (78.9%). Anammox bacteria could adapt to lower temperature after short-term acclimatization, especially the dominant genus Ca. Brocadia increased from 1.8% to 2.5% and its abundance was significantly correlated with nitrogen consumption (p < 0.05). Above findings suggest that the adaptability of Ca. Brocadia could provide the possibility to maintain nitrogen removal performance at lower temperature. In spring, the improved maximum anammox activity from 2.85 to 3.23mgNH₄⁺-N/(gVSS·h) indicated the recovered removal capacity.

Technologies for biological removal and recovery of nitrogen from wastewater

Water contamination is a growing environmental issue. Several harmful effects on human health and the environment are attributed to nitrogen contamination of water sources. Consequently, many countries have strict regulations on nitrogen compound concentrations in wastewater effluents. Wastewater treatment is carried out using energy- and cost-intensive biological processes, which convert nitrogen compounds into innocuous dinitrogen gas. On the other hand, nitrogen is also an essential nutrient. Artificial fertilizers are produced by fixing dinitrogen gas from the atmosphere, in an energy-intensive chemical process. Ideally, we should be able to spend less energy and chemicals to remove nitrogen from wastewater and instead recover a fraction of it for use in fertilizers and similar applications. In this review, we present an overview of various technologies of biological nitrogen removal including nitrification, denitrification, anaerobic ammonium oxidation (anammox), as well as bioelectrochemical systems and microalgal growth for nitrogen recovery. We highlighted the nitrogen removal efficiency of these systems at different temperatures and operating conditions. The advantages, practical challenges, and potential for nitrogen recovery of different treatment methods are discussed.

Effects of Potamogeton crispus decline in the rhizosphere on the abundance of anammox bacteria and nirS denitrifying bacteria☆

Bacteria involved with ecosystem N cycling in the rhizosphere of submerged macrophytes are abundant and diverse. Any declines of submerged macrophytes can have a great influence on the abundance and diversity of denitrifying bacteria and anammox bacteria. Natural decline, tardy decline, and sudden decline methods were applied to cultivated Potamogeton crispus. The abundance of anammox bacteria and nirS denitrifying bacteria in rhizosphere sediment were detected using real-time fluorescent quantitative PCR of 16S rRNA, and phylogenetic trees were constructed to analyze the diversities of these two microbes. The results indicated that the concentration of NH₄⁺ in pore water gradually increased with increasing distances from the roots, whereas, the concentration of NO₃^- showed a reverse trend. The abundance of anammox bacteria and nirS denitrifying bacteria in sediment of declined P. crispus populations decreased significantly over time. The abundance of these two microbes in the sudden decline group were significantly higher (P > 0.05) than the other decline treatment groups. Furthermore, the abundances of these two microbes were positively correlated, with RDA analyses finding the mole ratio of NH₄⁺/NO₃^- being the most important positive factor affecting microbe abundance. Phylogenetic analysis indicated that the anammox bacteria Brocadia fuigida and Scalindua wagneri, and nirS denitrifying bacteria Herbaspirillum and Pseudomonas, were the dominant species in declined P. crispus sediment. We suggest the sudden decline of submerged macrophytes would increase the abundance of anammox bacteria and denitrifying bacteria in a relatively short time.

Enhance the treatment of low strength wastewater at low temperature with the coexistence system of AnAOB and heterotrophic bacteria: Performance and bacterial community

The application of anammox process in mainstream wastewater treatment process is still facing challenges especially at the low temperature. To resolve this problem, the coexistence system of anaerobic ammonia-oxidizing bacteria (AnAOB) and heterotrophic bacteria (HB) was built in this study. The nitrogen removal efficiency mainly maintained at above 90% during the process of temperature reducing from 35 °C to 10 °C. The nitrogen removal rate were 0.30 g N·L^-1·d^-1 at both 25 and 15 °C and 0.10 g N·L^-1·d^-1 at 10 °C, respectively. Analysis of 16S rRNA genus sequencing revealed that as the temperature reduced to 10 °C, the Denutrotisoma genera presented a downward trend but Comamonadaceae genera showed an upward trend. At 10 °C, the contrast of anammox activities between granular and flocculent sludge in the system revealed that although the abundance of anammox genera was much lower in flocculent sludge than that in granular sludge, the anammox activities showed no significant discrepancy. And the abundance of Comamonadaceae and Chloroflexales genera were much higher in flocculent sludge than those in granular sludge, presenting their key roles to anammox activity at low temperature. The Circos diagram and Cluster of orthologous Group of protein functional predication showed that the functional abundance related to interaction among microbial communities were higher in flocculent sludge but those related to self-growth was higher in granular sludge. This result indicated the significance of the interactions based on the microbial diversity in the application of annamox process at low temperature.

Long-term stability of partial nitritation-anammox for treatment of municipal wastewater in a moving bed biofilm reactor pilot system

Nitrogen removal from the mainstream of municipal wastewater with partial nitritation-anammox (PNA) would be highly beneficial with regard to the uses of energy and organic carbon. However, the challenges of process instability, low nitrogen removal rates (NRR) and unwanted aerobic nitrite oxidation need to be solved to reach large-scale implementation. Here, we have operated pilot-scale moving bed biofilm reactors (MBBRs) for mainstream treatment, together with sidestream treatment of sludge liquor from anaerobic digestors, for over 900 days to investigate process stability, reactor performance and microbial community structure at realistic conditions. The MBBR biofilm contained stable and high relative abundances of anammox bacteria (10-32%) consisting of two major Brocadia sp. populations, and several populations of aerobic ammonia-oxidising bacteria (AOB) within Nitrosomonas sp. (0.2-3.1%), as assessed by 16S rDNA amplicon sequencing. In addition, nitrite-oxidising bacteria (NOB) consisting of Nitrospira sp. (0.4-0.8%) and Nitrotoga sp. (up to 0.4%) were present. Nitrogen was removed at a peak rate of 0.66 g N m^-2 d^-1 (0.13 kg N m^-3 d^-1) with a nitrate production over ammonium consumption of 15% by the NOB, at operation with continuous aeration at 15 °C. However, during most periods with continuous aeration, the NRR was lower (≈ 0.45 g N m^-2 d^-1), with larger relative nitrate production (≈40%), presumably due to problems to maintain stable residual ammonium concentrations during wet-weather mainstream flows. Changing reactor operation to intermittent aeration decreased the NRR but did not help in suppressing the NOB. The study shows that with MBBRs, stable mainstream PNA can be attained at realistic NRR, but with need for post-treatment of nitrate, since effective NOB suppression was hard to achieve.

Nitrogen loss by anaerobic ammonium oxidation in a mangrove wetland of the Zhangjiang Estuary, China

Anaerobic ammonium oxidation (anammox), a microbial process in which NH₄⁺ is oxidized to N₂ gas, is considered a significant nitrogen cycle process, but its significance in mangrove wetland sediments, particularly its depth- and genus-specific distribution and activity have remained uncertain. Here we report the vertical distribution, abundance, activity and role of anammox bacteria in mangrove sediments of Zhangjiang Estuary, China. We used stable isotope-tracer techniques, 16S rRNA and anammox bacterial functional gene (Hydrazine synthase B: hzsB) clone libraries and quantitative polymerase chain reaction (qPCR) assays, along with an assessment of nutrient profiles of sediment core samples. We observed a widespread occurrence of anammox bacteria at different depths of mangrove sediments. The abundance of anammox bacterial 16S rRNA and hzsB genes ranged from 0.41×10⁷ to 9.74×10⁷ and from 0.42×10⁶ to 6.44×10⁶ copies per gram of dry soil and peaked in the upper layer of mangrove sediments. We also verified the co-occurrence of different genera of anammox microorganisms in mangrove sediments, with Candidatus Scalindua and Candidatus Kuenenia being the dominant genera. Potential anammox rates ranged from 4.83 to 277.36 nmolN₂·g^-1·d^-1 at different depths of sediment cores, and the highest rates were found in the deeper layer (70-100cm) of mangrove sediments. Scaling our findings up to the entire mangrove system, we estimated that anammox hotspots accounted for a loss of 751 gN·m^-2·y^-1, and contributed to over 12% of the nitrogen lost from the deeper layer of mangrove sediments in this region.

Effective nitrogen removal in a two-stage partial nitritation-anammox reactor treating municipal wastewater - Piloting PN-MBBR/AMX-IFAS configuration

A novel partial nitritation-anammox (PNA) reactor configuration was piloted for 250 days. Primary effluent from full-scale municipal wastewater treatment plant was treated in a two-stage biofilm system incorporating innovative process control for cold partial nitritation. Partial nitritation was combined with carbon removal in a moving bed biofilm reactor (MBBR) to achieve high-rate treatment and nitritation was obtained with dissolved oxygen to total ammonium nitrogen (DO/TAN) ratio control and free ammonia (FA) for inhibition of nitratation. Effluent from MBBR was directed to an integrated fixed-film activated sludge (IFAS) reactor where nitrogen was removed via anammox. MBBR achieved partial nitritation at 2.0 ± 0.3 g-N m^-2 d^-1 and nitrogen removal in the IFAS reactor reached 0.45 ± 0.1 g-N m^-2 d^-1 (55 g-N m^-3 d^-1). The process performed well at 19 ± 3 °C with an average effluent total inorganic nitrogen (TIN) concentration of 11 ± 4 mg L^-1.

Controlling cold temperature partial nitritation in moving bed biofilm reactor

Mainstream partial nitritation was studied at 10 °C in a moving bed biofilm reactor treating synthetic wastewater containing both nitrogen (≈40 mg L^-1) and organic carbon at COD/N ratio ranging from 1.3 to 2.2. Three different control strategies were investigated to achieve partial nitritation. Initially, biofilm age was controlled by incorporating a media replacement strategy. Next, separately from the media replacement, oxygen limited conditions were investigated and finally pH control was incorporated together with oxygen limitation. Successful partial nitritation was achieved only by combining oxygen limitation with pH control. The average NH₄-N concentration was equal to 16.0 ± 1.6 mg L^-1 and average NO₂-N concentration was equal to 15.7 ± 2.4 mg L^-1 during steady state partial nitritation. The average residual NO₃-N concentration was equal to 2.6 ± 2.2 mg L^-1. The results obtained from this study prove for the first time that partial nitritation can be successfully controlled in a biofilm reactor treating wastewater with low nitrogen concentration, relatively high COD/N ratio and at low temperature. An algorithm for dynamic process control of partial nitritation has been also developed.

Impacts of solids retention time and antibiotic loading in activated sludge systems on secondary effluent water quality and microbial community structure

Solids retention time (SRT) is one of the most important factors in designing and operating activated sludge systems for biological wastewater treatment. Longer SRTs have been shown to alter the structure and function of microbial communities, thereby leading to improved treatment efficacy with respect to bulk and trace organics, nutrient removal, and membrane fouling. Research has also shown that longer SRTs and/or higher influent antibiotic concentrations may lead to increased prevalence of antibiotic resistance. However, it is unclear whether elevated, yet subclinical, concentrations of antibiotics also impact the overall microbial community. The purpose of this study was to characterize changes in microbial community structure in a laboratory-scale activated sludge system as a function of SRT (2-20 days) and influent concentrations (1×-100× ambient) of ampicillin, sulfamethoxazole, tetracycline, trimethoprim, and vancomycin. Changes in microbial community structure were evaluated based on 16S rRNA gene sequencing, and microbial community function was evaluated based on changes in effluent water quality, including attenuation of bulk and trace organics. The results confirmed that longer SRTs-but not antibiotic loadings-had a significant impact on microbial community structure and effluent water quality. Therefore, moderate spikes in influent antibiotic concentrations are not expected to adversely impact biological wastewater treatment. PRACTITIONER POINTS: Longer SRTs lead to changes in microbial community structure, including alpha and beta diversity and relative abundance of various taxa. Enhanced TOrC attenuation at longer SRTs may be linked to biomass abundance rather than changes in microbial community structure. Moderate spikes in influent antibiotic concentrations do not impact activated sludge performance or microbial community structure. The phyla Proteobacteria and Bacteroidetes comprise a majority of the microbial community in primary effluent and mixed liquor.

Anammox and partial nitritation in the mainstream of a wastewater treatment plant in a temperate region (Denmark)

The Marselisborg WWTP (Aarhus, Denmark) fed the mainstream nitrification/denitrification tanks with excess sludge from a sidestream DEMON tank for more than three years to investigate if anammox can supplement conventional nitrification/denitrification in a mainstream of a temperate region. To evaluate this long-term attempt, anammox and also denitrification rates were measured in activated sludge from the main- and sidestream at 10, 20 and 30 °C using ¹⁵N-labelling (stable isotope) experiments. The results show that anammox contributes by approximately 1% of the total nitrogen removal in the mainstream tanks and that anammox conversion rates there are approximately 800-900 times lower than in the DEMON. A distinct temperature dependence of both anammox and denitrification rates was also confirmed, however, results from different temperatures did not significantly alter relative shares, e.g. anammox rates in activated sludge from the nitrification/denitrification tanks are also negligible at 30 °C. This indicates that the anammox bacteria abundance in the nitrification/denitrification tanks is too low to play an important role and that an adaptation to lower temperatures had not occurred. Additional in situ measurements in the nitrification/denitrification tanks further revealed that full nitrification dominates over partial nitritation. Dominant nitritation-anammox is therefore excluded per se and also nitrite shunt activities are not particularly supported.

Short-term effects of reduced graphene oxide on the anammox biomass activity at low temperatures

Anaerobic ammonium oxidation (anammox) is an efficient process for nitrogen removal from wastewater, but its common use is limited by its relatively high optimal temperature (30 °C). One of the major bottlenecks of the implementation of mainstream PN/A process is the low activity of the anammox bacteria at low temperature. Due to this reason over the past years, numerous researchers have attempted to overcome this limitation. Recently it was shown that the reduced graphene oxide (RGO) can accelerate the anammox bacteria activity. However all these studies were performed at high temperatures (over 30 °C). Thus, in this study, supporting the anammox process at low temperatures (10-30 °C) by the RGO was investigated for the first time. The statistical analysis confirmed that RGO significantly affects the anammox activity. The stimulation effect of RGO on the anammox bacteria activity is of particular importance at low temperatures, when drastic decrease in process activity is observed at temperatures below 15 °C. The short-term experimental results demonstrated stimulation of the anammox activity at 13 °C, up to 28% by 15 mg RGO/L, but concentrations above 40 mg RGO/L caused the process inhibition, up to 30% with 50 mg RGO/L. However, the effect of RGO probably depends on the nanomaterial dose per biomass unit and the optimal range of this value was evaluated as 20 to 45 mg RGO/g VSS (volatile suspended solids).

Realizing stable operation of anaerobic ammonia oxidation at low temperatures treating low strength synthetic wastewater

The low activity of Anammox bacteria at low temperatures and competition from nitrite oxidation bacteria (NOB) when treating low strength wastewater have been major bottlenecks in implementing Anammox in mainstream wastewater treatment. By intermittent high strength feeding (IHSF) and stepwise temperature reduction, stable operation of a granular Anammox reactor was realized at low temperatures (down to 15°C) for 28days when treating low strength synthetic wastewater. The nitrogen loading rate reached 1.23-1.34kgN/m³/day, and the total nitrogen removal rate reached 0.71-0.98kgN/m³/day. The IHSF enriched the Anammox sludge in high strength cycles and compensated for sludge loss in low strength cycles, and the high concentration of ammonium in high strength cycles inhibited NOB. The 16SrRNA gene sequencing results revealed that Candidatus Kuenenia was predominant in the reactor at low temperatures.

Influence of temperature on an Anammox sequencing batch reactor (SBR) system under lower nitrogen load

The nitrogen removal performance and microbial communities of an Anammox sequencing batch reactor (SBR) was studied under varied temperatures with a lower nitrogen loading rate (NLR) about 0.28 kgN/m³/d. Results showed that the temperature could influence the nitrogen removal performance and the community structure in the Anammox SBR system. Under lower temperatures, both the nitrogen removal efficiencies and Anammox activity were in lower levels. When temperature was raised again, the Anammox activity recovered accordingly. When the temperature dropped from 33 ± 1 °C to15 °C, the dominant Anammox bacteria shifted from Ca. Brocadia to Ca. Kuenenia in the sludge. When the temperature returned over, the abundance of Ca. Brocadia recovered, while the Ca. Kuenenia was still the dominant Anammox bacteria. This indicated that Ca. Kuenenia is more adaptable to low temperature environment than Ca. Brocadia under low NLR with temperature variation.

The microbial community structure change of an anaerobic ammonia oxidation reactor in response to decreasing temperatures

In anaerobic ammonium oxidation (anammox) systems, temperature may regulate the activity of functional bacteria (e.g., anammox bacteria) and the composition of the microbial population, ultimately determining the performance of the anammox reactor. Knowledge of the dynamic changes in nitrogen removal rates and the microbial anammox community at low and/or ambient temperature is still limited. This study explored the response of an anammox sequencing batch reactor (SBR) to a gradient of decreasing temperature (33, 25, 20, 15, 10 °C), followed by recovery to 22 °C, over 360 days. Particularly, the specific anammox activity (SAA) and microbial community were assessed. The anammox reaction in the SBR remained stable and efficient at 20-33 °C, with a total nitrogen removal load of 0.4 g-N L^-1 day^-1 and an SAA of > 0.32 g-N g-VSS^-1 day^-1; 10 °C was the turning point for the anammox bacterial metabolic activity, at which the SAA decreased by 91% compared with that at 33 °C. After the temperature was returned to 22 °C, the anammox activity recovered to 0.24 g-N g-VSS^-1 day^-1. The apparent activation energy for the anammox reaction was 68.4 kJ mol^-1 at 10-33 °C and 152.9 kJ mol^-1 at 10-20 °C. High-throughput sequencing results revealed that Kuenenia was the dominant species of anammox bacteria, and Kuenenia had a higher tolerance to low temperature than Candidatus Brocadia and Candidatus Jettenia. This study clearly shows the effectiveness of anammox bioreactors for treatment of wastewater at ambient temperatures of 15-33 °C.

Fast start-up of the cold-anammox process with different inoculums at low temperature (13 °C) in innovative reactor

Three innovative reactors (CAMBR) through optimally combining with the Anaerobic Baffled reactor and Membrane bioreactor were applied to start up the cold-anammox process at low temperature (13 °C) through inoculating flocculent nitrification sludge (R1), anaerobic granular sludge (R2) and flocculent denitrification sludge (R3), respectively. Results showed that anammox process was started successfully with over 90% total nitrogen removal rate in R1, R2 and R3 after 75d, 45d, and 90d, respectively. Microbial community revealed that Ca. Brocadia and Ca. Jettenia were the dominant anammox bacteria in R1, R2 and R3, accounting for an abundance of 0.08%, 12.18%; 3.17%, 0 and 0.08%, 0.38%, respectively. Three anammox species, Ca. Brocadia caroliniensis, Ca. Brocadia sinica and Ca. Jettenia asiatica were annotated based on the phylogenetic tree, suggesting the anammox species with larger maximum growth rate contributed to the rapid start-up of the cold-anammox process. This study reinforces the potential application of mainstream anammox.

Comparing two start up strategies and the effect of temperature fluctuations on the performance of mainstream anammox reactors

Anammox cultivated with high substrate concentration (NH₄⁺-N, 150 mg/L; NO₂^--N, 200 mg/L) at 35 °C was first used as seed sludge to start up reactors at 35 (Ra), 20 (Rb) and 15 °C (Rc) with low substrate concentration (NH₄⁺-N 30 mg/L, NO₂^--N 40 mg/L). The results showed that anammox activity initially decreased in the three reactors, but that activity levels and nitrogen loading rate (NLR) increased as the bacteria gradually adapted to the new conditions (12-30 days). Temperature and concentration shift affected anammox activity jointly. In the process, the abundance of mRNA of the key functional genes of hdh and nirS, changed with time but this change did not reflect the change of anammox activity. When the reactors reached a stable state after 40 d, the effect of temperature fluctuations was tested. The results showed that anammox adapted to low temperatures as soon as temperature decreased (i.e., decreased from 35 °C to 15 °C). When temperature increased, 2-3 days were needed for activity recovery. From this result, it may be concluded that reactors with low temperatures and low substrate (mainstream) concentrations can be started up using anammox cultivated at a higher temperature (35 °C) with low substrate. Then anammox in Ra was used to start up a mainstream reactor at 15 °C and it was operated for 60 days. The results showed that the activity in Ra decreased sharply to the level as that of Rc at the stable state. After the experiment, microbiological analysis showed that the anammox was stable and that Candidatus Kuenenia was the dominant species.

Microbial community response to influent shift and lowering temperature in a two-stage mainstream deammonification process

The effects of influent shift from synthetic wastewater to anaerobically pretreated actual sewage coupling with lowering temperature on microbial community of a two-stage partial nitritation (PN)-anammox process were evaluated through high-throughput sequencing. Venn diagrams and Hill numbers showed the significantly increased bacterial diversity both in the PN and anammox reactor. However, taxonomic analysis indicated that outstanding enrichment of heterotrophic bacteria and reduction of autotrophic species mainly occurred in the PN reactor, while nearly all of the dominant bacteria in the anammox reactor only slightly decreased in abundance. Moreover, immigrant bacteria from the PN reactor to the following anammox reactor had no negative effect on the anammox function. These results implied the positive role of the first-stage PN in maintaining the stability of the following anammox community. Nitrosomonas europaea (17.9-52.9%) and one cluster (19.2-27.7%) within Candidatus Brocadia remained as the dominant functional species in the PN and anammox reactor, respectively.

Status, Challenges, and Perspectives of Mainstream Nitritation-Anammox for Wastewater Treatment

  The nitritation-anammox process is an efficient and cost-effective approach for biological nitrogen removal, but its application in treating mainstream wastewater remains a great challenge. Mainstream nitritation-anammox processes could create opportunities for achieving energy self-sufficient, or energy-generating water resource recovery facilities. Significant advancements have been achieved via pilot- and full-scale trials to overcome the major obstacles under mainstream conditions, such as repression of nitrite-oxidizing bacteria, limiting the overgrowth of denitrifiers, and effective selection and retention of ammonia-oxidizing bacteria and anammox bacteria. This review paper intends to provide a detailed update of research progress on mainstream nitritation-anammox processes, discuss metabolic interactions, and examine major challenges and possible solutions towards the future development.

Glocal assessment of integrated wastewater treatment and recovery concepts using partial nitritation/Anammox and microalgae for environmental impacts

This study explored the feasibility and estimated the environmental impacts of two novel wastewater treatment configurations. Both include combined bioflocculation and anaerobic digestion but apply different nutrient removal technologies, i.e. partial nitritation/Anammox or microalgae treatment. The feasibility of such configurations was investigated for 16 locations worldwide with respect to environmental impacts, such as net energy yield, nutrient recovery and effluent quality, CO₂ emission, and area requirements. The results quantitatively support the applicability of partial nitritation/Anammox in tropical regions and some locations in temperate regions, whereas microalgae treatment is only applicable the whole year round in tropical regions that are close to the equator line. Microalgae treatment has an advantage over the configuration with partial nitritation/Anammox with respect to aeration energy and nutrient recovery, but not with area requirements. Differential sensitivity analysis points out the dominant influence of microalgal biomass yield and wastewater nutrient concentrations on area requirements and effluent quality. This study provides initial selection criteria for worldwide feasibility and corresponding environmental impacts of these novel municipal wastewater treatment plant configurations.

Effects of temperature on anammox performance and community structure

A lab-scale anammox up-flow anaerobic sludge blanket (UASB) reactor was run to investigate the influence of temperature on anammox performance and community structure. The anammox system had a higher substrate tolerance at 13 °C than at 18 °C. The adverse effects caused by the use of a lower temperature (8 °C) could be restored. The nitrogen removal rate (NRR) decreased with decreasing in situ specific anammox activity (SAA). Interestingly, the ex situ SAA acclimated at 23 °C, when exposed to ex situ temperatures of 33 and 28 °C, was higher than for those acclimated at 33 and 28 °C. No shift was observed in the optimum temperature for ex situ SAA in the whole lowering process of anammox UASB. More extracellular polymeric substances were produced in response to cooler conditions (18 °C and 13 °C). Ca. Kuenenia became much more abundant (55.18% of the microbial community) and had a competitive advantage over other anammox bacteria (AnAOB) at 13 °C.

What is the Best Biological Process for Nitrogen Removal: When and Why?

Many different aerobic and anaerobic biological processes and treatment schemes are available for transforming organics and/or removing nitrogen from domestic wastewaters. Significant reductions in oxygen requirements and absence of a need for organics for nitrogen reduction are often indicated as advantageous for using the newer anammox organism approach for nitrogen removal rather than the traditional nitrification/denitrification method, the most common one in use today. However, treatment schemes differ, and there are some in which such suggested advantages may not hold. When nitrification/denitrification is used, an anoxic tank is now commonly used first and the nitrate formed by nitrification later is recycled back to that tank for oxidation of wastewater organics. This greatly reduces oxygen requirements and the need for adding organics. So when are such claims correct and when not? What factors in wastewater composition, regulatory requirements, and treatment flow sheet alter which treatment process is best to use? As an aid in making such judgments under different circumstances, the stoichiometry of the different biological processes involved and the different treatment approaches used were determined and compared. Advantages of each as well as imitations and potential opportunities for research to prevent them are presented.

Deterioration of the anammox process at decreasing temperatures and long SRTs

The implementation of autotrophic nitrogen removal in the mainstream of a municipal wastewater treatment plant is currently pursued. Among the crucial unknown factors are the kinetic properties of anaerobic ammonium oxidising (anammox) bacteria at low temperatures. In this study we investigated the adaptation of a fast-growing anammox culture to a lower temperature. In a membrane bioreactor a highly enriched anammox community was obtained at 30°C, 25°C and 20°C. This culture was exposed to long- and short-term temperature changes. In short-term experiments the decrease in biomass-specific activity due to decrease in temperature can be described by an activation energy of 64 ± 28 kJ mol^-1. Prolonged cultivation (months) implies that cultivation at low temperatures resulted in deterioration of biomass-specific activity (Ea^LT 239 kJ mol^-1). The growth rate and specific anammox activity in the system decreased from 0.33 d^-1 and 4.47 g NO₂-N g VSS^-1 d^-1 at 30°C to 0.0011 d^-1 and 0.037 g NO₂-N g VSS^-1 d^-1 at 20°C. The reason for the deterioration of the system was related to the required long SRT in the system. The long SRT leads to an increase of non-active and non-anammox cells in the reactor, thereby decreasing the biomass-specific activity.

Metabolomics Uncovers the Regulatory Pathway of Acyl-homoserine Lactones Based Quorum Sensing in Anammox Consortia

Acyl-homoserine lactones (AHLs)-mediated quorum sensing in bacterial communities have been extensively observed. However, the metabolic pathways regulated by AHLs in bacteria remain elusive. Here, we combined long-term reactor operation with microbiological and metabolomics analyses to explore the regulatory pathways for different AHLs in anammox consortia, which perform promising nitrogen removal for wastewater treatment. The results showed that no obvious shifts induced by exogenous AHLs occurred in the microbial community and, mainly, dosing AHLs induced changes in the metabolites. 3OC6-HSL, C6-HSL, and C8-HSL controlled the electron transport carriers that influence the bacterial activity. In contrast, only 3OC6-HSL regulated LysoPC(20:0) metabolism, which affected bacterial growth. AHLs mainly regulated the synthesis of the amino acids Ala, Val, and Glu and selectively regulated Asp and Leu to affect extracellular proteins. Simultaneously, all the AHLs regulated the ManNAc biosynthetic pathways, while OC6-HSL, OC8-HSL, and C6-HSL particularly enriched the UDP-GlcNAc pathway to promote exopolysaccharides, resulting in different aggregation levels of the anammox consortia. Our results not only provide the first metabolic insights into the means by which AHLs affect anammox consortia but also hint at potential strategies for overcoming the limitations of the long start-up period required for wastewater treatment by anammox processing.