Resilience of anammox application from sidestream to mainstream: A combined system coupling denitrification, partial nitritation and partial denitrification with anammox

Comparation on the responses and resilience of single-anammox system and synergistic partial-denitrification/anammox system to long-term nutrient starvation: Performance and metagenomic insights

Starvation disturbance was a common problem in biological sewage treatment processes. However, understanding about the responses and resilience of different active anammox biomass in autotrophic and heterotrophic systems to long-term nutrient starvation remains limited. This study compared responses and potential recovery mechanisms of autotrophic single-Anammox and heterotrophic synergistic partial-denitrification/anammox (PD/anammox) systems to prolonged starvation (31-40 days). After starvation, total inorganic nitrogen (TIN) removal efficiency of single-Anammox and synergistic PD/anammox systems decreased to 62.16 % and 78.52 %, respectively, of their original level. After the nutrient resupply, the performance of both systems gradually recovered to a similar-to-pre-starvation level at the rate of 1.26 %/day and 1.89 %/day, respectively. Compared with single-Anammox system, complex synergistic relationship of microorganisms and effective quorum sensing (QS) regulation strategies might mitigate the negative influences were caused by starvation and ensure the performance quickly return of synergistic PD/anammox system. This study would contribute to promote the application of Anammox technology.

Unique ecology of biofilms and flocs: Bacterial composition, assembly, interaction, and nitrogen metabolism within deteriorated bioreactor inoculated with mature partial nitrification-anammox sludge

This work unraveled discrepant ecological patterns between biofilms and flocs in a deteriorated bioreactor inoculated with mature partial nitrification-anammox (PN/A) sludge. Based on 16S rRNA analysis, a comprehensive evaluation of neutral and null models, along with niche width, delineated that the bacterial community assembly in biofilms and flocs was dominantly driven by the stochastic process, and dispersal limitation critically shaped the community assembly. Co-occurrence network analysis revealed that environmental stress caused decentralized and fragmented bacterial colonies, and anammox bacteria were mainly peripheral in biofilms network and less involved in interspecific interactions. Simultaneous PN/A and partial denitrification-anammox (PD/A) processes were identified, whereas PN and PD process primarily occurred in the biofilms and flocs, respectively, as evidenced by metagenomics. Collectively, these outcomes are expected to deepen the basic understanding of complex microbial community and nitrogen metabolism under environmental disturbance, thereby better characterizing and serving the artificial ecosystems.

Enhanced and robust nitrogen removal using an integrated zeolite and partial denitrification anammox process

Anammox has received increased attention due to its enhanced and cost-efficient approach to nitrogen removal. However, its practical application is complicated by strict influent NO2--N to NH4+-N ratio demands and an 11% nitrate production from the anammox process. This study was the first known research to propose and verify a system of zeolite integrated with partial denitrification and anammox (Z-PDA) in an up-flow anaerobic sludge bed (UASB) reactor. The enhanced and robust nitrogen removal resulted in an ultra-high nitrogen removal efficiency (NRE, 93.0 ± 2.0%). Zeolite adsorption and biological desorption of ammonium contributed to robust nitrogen removal with fluctuating influent NO2--N to NH4+-N ratios. Applying 16S rRNA gene sequencing found that Candidatus Brocadia and Thauera were the key bacteria responsible for anammox and partial denitrification (PD), respectively. Zeolite also acted as a biological carrier. This significantly enriched anammox bacteria with a higher relative abundance of Candidatus Brocadia, reaching 49.2%. Metagenomic analysis demonstrated that the multiple functional genes related to nitrogen removal (nrfA/H, narG/H/I) and the metabolic pathways (Biosynthesis of cofactors, the Two-component system, the Biosynthesis of nucleotide sugars, and Purine metabolism) ensured the resilience of the Z-PDA system despite influent fluctuations. Overall, this study provided novel insights into the impacts of zeolite in the PDA system. It described the fundamental mechanism of zeolite based on adsorption and biological desorption, and demonstrated a meaningful application of the anammox process in sewage treatment.

A temperature-resilient anammox process for efficient treatment of rare earth element tailings wastewater via synergistic nitrite supply of partial nitritation and partial denitrification

Rare earth elements result in substantial tailings wastewater with high ammonium and nitrate during extraction. In this study, a temperature-resilient Anammox process was employed for efficient treatment of rare earth element tailings wastewater through implementing synergistic nitrite supply by partial nitritation (PN) and partial denitrification (PD). Enhancing temperature resilience of Anammox process relies on dynamic management of DO and COD inputs to shift the dominant nitrite supplier from PN to PD, stable PD (NAR ≥ 90 %) can boost nitrogen removal by Anammox to 97.8 %. The nitrogen removal rate and nitrogen removal efficiency at 10.6 °C could maintain at 0.12 kgN/m3·d-1 and 92.5 %, respectively. Microbial analysis reveals that Nitrosomonas, Thauera, and Candidatus_Kuenenia are the predominant genera responsible for nitrite supply and nitrogen removal, localized within the gas channels of granules, flocs, and micro-granules, respectively. Keeping the influent C/NO3--N ratio below 1.7 is ideal to prevent overgrowth of Thauera and maintain system stability.

Piezo-photocatalytic reduction of nitrates to N2 over silver dispersed on BaTiO3@TiO2

This communication first achieved piezo-photocatalytic reduction of nitrates to N2 through designing an Ag2O/BaTiO3@TiO2 core-shell catalyst. The built-in electric field induced by piezoelectric polarization suppresses photoexcited carrier recombination, and simultaneously causes energy band tilting, leading to the generation of electrons with higher reducibility to directly trigger the NO3- reduction to ˙NO32-, even without hole scavengers.

Novel and innovative approaches to partial denitrification coupled with anammox: A critical review

The partial denitrification (PD) coupled with anaerobic ammonium oxidation (Anammox) (PD/A) process is a unique biological denitrification method for sewage that concurrently removes nitrate (NO3--N) and ammonium (NH4+-N) in sewage. Comparing PD/A to conventional nitrification and denitrification technologies, noticeable improvements are shown in energy consumption, carbon source demand, sludge generation and emissions of greenhouse gasses. The PD is vital to obtaining nitrites (NO2--N) in the Anammox process. This paper provided valuable insight by introduced the basic principles and characteristics of the process and then summarized the strengthening strategies. The functional microorganisms and microbial competition have been discussed in details, the S-dependent denitrification-anammox has been analyzed in this review paper. Important factors affecting the PD/A process were examined from different aspects, and finally, the paper pointed out the shortcomings of the coupling process in experimental research and engineering applications. Thus, this research provided insightful information for the PD/A process's optimization technique in later treating many types of real and nitrate-based wastewater. The review paper also provided the prospective economic and environmental position for the actual design implementation of the PD/A process in the years to come.

Robustness of the anammox process at low temperatures and low dissolved oxygen for low C/N municipal wastewater treatment

Low water temperatures and ammonium concentrations pose challenges for anammox applications in the treatment of low C/N municipal wastewater. In this study, a 10 L-water bath sequencing batch reactor combing biofilm and suspended sludge was designed for low C/N municipal wastewater treatment. The nitrogen removal performance via partial nitrification anammox-(endogenous) denitrification anammox process was investigated with anaerobic-aerobic-anoxic mode at low temperatures and dissolved oxygen (DO). The results showed that with the decrease of temperature from 30 to 15℃, the influent and effluent nitrogen concentrations and nitrogen removal efficiencies were 73.7 ± 6.5 mg/L, 7.8 ± 2.8 mg/L, and 89.4 %, respectively, with aerobic hydraulic retention time of only 6 h and DO concentration of 0.2-0.5 mg/L. Among that, the stable anammox process compensated for the inhibitory effects of the low temperatures on the nitrification and denitrification processes. Notably, from 30 to 15℃, the anammox activity and relative abundance of the dominant Brocadia genus were increased from 39.7 to 45.5 mgN/gVSS/d and 7.3 to 12.0 %, respectively; the single gene expression level of the biofilm increased 9.0 times. The anammox bacteria showed a good adaptation to temperatures reduction. However, nitrogen removal by anammox was not improved by increasing DO (≥ 4 mg/L) at 8-4℃. Overall, the results of this study demonstrate the feasibility of the mainstream anammox process at low temperatures.

Analyzing the nitrogen removal performance and cold adaptation mechanism of immobilized cold-acclimation ANAMMOX granules at low temperatures

To improve the treatment performance of anaerobic ammonium oxidation (ANAMMOX) processes at low temperatures, the immobilized cold-acclimation ANAMMOX granules (R3) were prepared and their low-temperature nitrogen removal ability as well as the cold adaptation mechanism were analyzed. The results indicated that the total inorganic nitrogen (TIN) removal efficiency of R3 was significantly higher than that of R2 (cold-acclimation granules without immobilization) and R1 (common granules), especially at 11 ± 2 and 7 ± 2°C (68% and 54%). These were attributed to the remarkable biomass retention capacity of R3, high up to 4.3-4.9 mg/gVSS even at 5-18°C. Besides, higher protein (PN) content of tightly bound extracellular polymeric substances (TB-EPS) also facilitated microbial aggregation in R3. Meanwhile, R3 granules retained higher ANAMMOX activity and heme c content at 5-25°C. The original dominant ANAMMOX genus (Candidatus Kuenenia) in R3 kept higher abundance (49%-57%) at 23 ± 2 and 16 ± 2°C, whereas Candidatus Brocadia became the dominant ANAMMOX genus (25%-32%) in R3 at 11 ± 2 and 7 ± 2°C. Notably, different ANAMMOX genera in R3 may adapt to cold environment by regulating the expression of cold-stress proteins (CspA, CspB, PpiD, and UspA). PRACTITIONER POINTS: Immobilized cold-acclimation ANAMMOX granules showed higher nitrogen removal efficiency at 23°C → 5°C. Immobilization method effectively retained biomass (Candidatus Kuenenia and Candidatus Brocadia). Immobilization facilitated TB-EPS release and biological aggregation in cold-acclimation granules. Expression of cold-stress proteins in immobilized cold-acclimation granules was more active.

Insights into current bio-processes and future perspectives of carbon-neutral treatment of industrial organic wastewater: A critical review

With the rise of the concept of carbon neutrality, the current wastewater treatment process of industrial organic wastewater is moving towards the goal of energy conservation and carbon emission reduction. The advantages of anaerobic digestion (AD) processes in industrial organic wastewater treatment for bio-energy recovery, which is in line with the concept of carbon neutrality. This study summarized the significance and advantages of the state-of-the-art AD processes were reviewed in detail. The application of expanded granular sludge bed (EGSB) reactors and anaerobic membrane bioreactor (AnMBR) were particularly introduced for the effective treatment of industrial organic wastewater treatment due to its remarkable prospect of engineering application for the high-strength wastewater. This study also looks forward to the optimization of the AD processes through the enhancement strategies of micro-aeration pretreatment, acidic-alkaline pretreatment, co-digestion, and biochar addition to improve the stability of the AD system and energy recovery from of industrial organic wastewater. The integration of anaerobic ammonia oxidation (Anammox) with the AD processes for the post-treatment of nitrogenous pollutants for the industrial organic wastewater is also introduced as a feasible carbon-neutral process. The combination of AnMBR and Anammox is highly recommended as a promising carbon-neutral process for the removal of both organic and inorganic pollutants from the industrial organic wastewater for future perspective. It is also suggested that the AD processes combined with biological hydrogen production, microalgae culture, bioelectrochemical technology and other bio-processes are suitable for the low-carbon treatment of industrial organic wastewater with the concept of carbon neutrality in future.

Nitrogen removal and nitrous oxide emission in the partial nitritation/anammox process at different reflux ratios

The partial nitritation/anammox (PN/A) process has been widely used in wastewater treatment owing to its notable advantages, including a low aeration rate and the non-requirement of an additional carbon source. In practical implementation, nitrite accumulation affects the nitrogen-removal efficiency and the amount of N2O released during the PN/A process. By implementing wastewater reflux, the nitrite concentration can be decreased, thereby achieving a balance between the nitrogen-removal efficiency and N2O release. This study conducted the CANON process with varying reflux ratios of 0 to 300 % and ~300 mg/L ammonium in the influent. The highest removal efficiency of ammonium and total nitrogen (98.2 ± 0.8 and 77.8 ± 2.3 %, respectively) could be achieved at a reflux ratio of 200 %. Further, a reflux ratio of 200 % led to the lowest N2O emission factor (2.21 %), with a 31.74 % reduction in N2O emission compared to the process without refluxing. Additionally, the reactor at a reflux ratio of 200 % presented the highest relative abundance of anaerobic ammonium-oxidizing bacteria (30.98 %) and the lowest proportion of ammonium-oxidizing bacteria (9.57 %). This study aimed to elucidate the impact of the reflux ratio on the nitrogen-removal efficiency of the CANON process and to theoretically explain the influence of different reflux ratios on N2O release. These findings provide a theoretical framework for enhancing the nitrogen-removal efficiency and mitigating carbon emissions in practical applications of the CANON process.

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

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

The evolution of nitrogen transformation microorganism consortium under continued manganese domestication conditions

Manganese redox-stimulated bioremediation of nitrogen wastewater is receiving increasing attention. However, the nitrogen metabolic capacity and community evolution during manganese-mediated nitrogen transformation process under continued manganese domestication conditions are ambiguous. In this study, nitrogen- metabolizing microbial consortiums were incubated with synthesized Mn-humic acid complex (Mn-HA) for one month (M1), three months (M2) and six months (M3), respectively. During the Mn-HA incubation period, Bio-MnOx accompanying with bacterial consortiums (MnOB consortiums) with high TIN removal capacities were obtained. The TIN removal rates in M1, M2 and M3 were 0.220, 1.246 and 4.237 mg·L-1·h-1, respectively, which were 15.961, 90.006 and 1550.006 times higher than CK (Control Check group, no Mn-HA added group) (0.014 mg·L-1·h-1), respectively. Functional genes (amoA, AMX and narG) were most abundant in M3, which was associated with the highest nitrogen removal rate in M3. MnOB1 (bacterial consortium in M1), including Geobactor, Geothrix, Anaeromyxobacter and Bacillus, may be responsible for the Mnammox-NDMO (MnOx reduction coupled to ammonium oxidation - nitrate/nitrite-dependent low-valent Mn oxidation) process. MnOB3 (bacterial consortium in M2) enriched nitrifying bacteria Ellin6067, and denitrifying bacteria Denitratisoma, which dominated nitrogen transformation. MnOB6 (bacterial consortium in M3) enriched denitrifiers Denitratisoma, nitrifiers Ellin6067 and potential anammox bacteria SM1A02, Candidatus_Brocadia. Combined with the reduced abundance of Nitrospirae, a short-cut partial nitrification and denitrification (PND) or partial nitrification, denitrification and anammox (PNDA) could occurred in M2 and M3. It is suggested that community may have evolved into an energetically efficient short-cut nitrification, denitrification and anammox consortium to replace the full-range nitrification and denitrification community in M1 and CK under the continued manganese domestication conditions. Enhanced metabolic pathways of hydroxylamine oxidation and the nitric oxide reduction may confirm that PND or PNDA occurred in M2 and M3.

Effective enrichment of anaerobic ammonia oxidation sludge with feast-starvation strategy: activity, sedimentation, growth kinetics, and microbial community

To address the issue of floating and loss of floc sludge caused by gas production in anaerobic ammonia oxidation (anammox) reactors, this study proposes a limited nitrite supply strategy to regulate gas production during the settling and enhance sludge retention. Results indicate that the effluent suspended solids in the anammox reactor can be reduced to as low as 0.11 g/L under specific feast-starvation conditions. Even under long-term intermittent nitrite-starvation stress, the maximum growth rate of Candidatus_Kuenenia can still reach 0.085d-1, with its abundance increasing from 0.47% to 8.83% within 69 days. Although the combined effects of starvation and sedimentation would lead to a temporary decrease in anammox activity, this reversible inhibition can be fully restored through substrate intervention. The limited nitrite supply strategy promotes the sedimentation of anammox sludge without significantly affecting its growth rate, and effective sludge retention is crucial for enriching anammox sludge during initial cultivation.

Comprehensive review on recent production trends and applications of biochar for greener environment

The suitability of biochar as a supplement for environmental restoration varies significantly based on the type of feedstocks used and the parameters of the pyrolysis process. This study comprehensively examines several aspects of biochar's potential benefits, its capacity to enhance crop yields, improve nutrient availability, support the co-composting, water restoration and enhance overall usage efficiency. The supporting mechanistic evidence for these claims is also evaluated. Additionally, the analysis identifies various gaps in research and proposes potential directions for further exploration to enhance the understanding of biochar application. As a mutually advantageous approach, the integration of biochar into agricultural contexts not only contributes to environmental restoration but also advances ecological sustainability. The in-depth review underscores the diverse suitability of biochar as a supplement for environmental restoration, contingent upon the specific feedstock sources and pyrolysis conditions used. However, concerns have been raised regarding potential impacts on human health within agricultural sectors.

Enhanced denitrification performance of granular sludge for the treatment of waste brine from ion exchange resin process

Ion exchange resin process is a widely used process in wastewater treatment plants, but its waste brine is characterized by high salinity and nitrate concentration, leading to costly treatment. This study innovatively explored the use of an up-flow anaerobic sludge bed (USB) for the treatment of waste brine from ion exchange resin process, following a pilot-scale ion exchange resin process. Specifically, the D890 ion exchange resin was employed for nitrate removal from secondary effluent, with resin regeneration using 4% NaCl solution. The USB was inoculated with anaerobic granular sludge and acclimated under various single-factor conditions, which revealed the optimal pH range of 6.5-9, salt concentration of 2%, hydraulic retention time of 12 h, C/N ratio of 3.3, and up-flow velocity of 1.5 m/h for reactor operation. This study provides a novel approach for the cost-effective treatment of waste brine from ion exchange resin process. The study found that the denitrification efficiency was highest when the NO3--N concentration was around 200 mg/L, with NO3--N and TN removal rates exceeding 95% and 90%, respectively, under optimal operating conditions. Characterization of the granular sludge during different phases of the operation revealed a significant increase in proteobacteria and gradually became the dominant species over time. This study presents a novel, cost-effective approach to treat waste brine from ion exchange resin process, and the long-term stable operation of the reactor offers a reliable option for resin regeneration wastewater treatment.

Insights on pretreatment technologies for partial nitrification/anammox processes: A critical review and future perspectives

For almost 20 years, partial nitrification-anammox (PN/A) has been the subject of intensive study and development. Pretreatment of wastewater for PN/A is crucial because the inhibitory substances in the influent may reduce the performance of PN/A. In this review, the current PN/A pretreatment technologies are comprehensively summarized. The selection of pretreatment technology for PN/A depending on the source of the wastewater and its main characteristics (high-strength wastewater or municipal wastewater, organic matters, suspended solids). Comparison of pretreatment technologies through multiple perspectives including wastewater characteristics, the objectives of the wastewater treatment (treating requirement, energy and resource recovery demand), reactor configuration of PN/A. Based on the discussion, two integrated processes, HRAS + one-stage PN/A and advanced AD + two-stage PN/A, are recommended as the preferred processes for treating municipal wastewater and wastewater with a high-strength ammonium, respectively. This review aims to provide guidance for future research and development of PN/A.