Low-strength Ammonium Wastewater Research Articles

Comammox Nitrospira cooperate with anammox bacteria in a partial nitritation–anammox membrane bioreactor treating low-strength ammonium wastewater at high loadings

Research has revealed that comammox Nitrospira and anammox bacteria engage in dynamic interactions in partial nitritation–anammox reactors, where they compete for ammonium and nitrite or comammox Nitrospria supply nitrite to anammox bacteria. However, two gaps in the literature are present: the know-how to manipulate the interactions to foster a stable and symbiotic relationship and the assessment of how effective this partnership is for treating low-strength ammonium wastewater at high hydraulic loads. In this study, we employed a membrane bioreactor designed to treat synthetic ammonium wastewater at a concentration of 60 mg N/L, reaching a peak loading of 0.36 g N/L/day by gradually reducing the hydraulic retention time to 4 hr. Throughout the experiment, the reactor achieved an approximately 80 % nitrogen removal rate through strategically adjusting intermittent aeration at every stage. Notably, the genera Ca. Kuenena, Nitrosomonas, and Nitrospira collectively constituted approximately 40 % of the microbial community. Under superior intermittent aeration conditions, the expression of comammox amoA was consistently higher than that of Nitrospira nxrB and AOB amoA in the biofilm, despite the higher abundance of Nitrosomonas than comammox Nitrospira, implying that the biofilm environment is favorable for fostering cooperation between comammox and anammox bacteria. We then assessed the in situ activity of comammox Nitrospira in the reactor by selectively suppressing Nitrosomonas using 1-octyne, thereby confirming that comammox Nitrospira played the primary role in facilitating the nitritation (33.1 % of input ammonium) rather than complete nitrification (7.3 % of input ammonium). Kinetic analysis revealed a specific ammonia-oxidizing rate 5.3 times higher than the nitrite-oxidizing rate in the genus Nitrospira, underscoring their critical role in supplying nitrite. These findings provide novel insights into the cooperative interplay between comammox Nitrospira and anammox bacteria, potentially reshaping the management of nitrogen cycling in engineered environments, and aiding the development of microbial ecology-driven wastewater treatment technologies.

Iron cycle-enhanced anaerobic ammonium oxidation in microaerobic granular sludge

Granule-based partial nitritation and anaerobic ammonium oxidation (PN/A) is an energy-efficient approach for treating ammonia wastewater. When treating low-strength ammonia wastewater, the stable synergy between PN and anammox is however difficult to establish due to unstable dissolved oxygen control. Here, we proposed, the PN/A granular sludge formed by a micro-oxygen-driven iron redox cycle with continuous aeration (0.42 ± 0.10 mg-O2/L) as a novel strategy to achieve stable and efficient nitrogen (N) removal. 240-day bioreactor operation showed that the iron-involved reactor had 37 % higher N removal efficiency than the iron-free reactor. Due to the formation of the microaerobic granular sludge (MGS), the bio(chemistry)-driven iron cycle could be formed with the support of anaerobic ammonium oxidation coupled to Fe3+ reduction. Both ammonia-oxidizing bacteria and generated Fe2+ could scavenge the oxygen as a defensive shield for oxygen-sensitive anammox bacteria in the MGS. Moreover, the iron minerals derived from iron oxidation and Fe-P precipitates were also deposited on the MGS surface and/or embedded in the internal channels, thus reducing the size of the channels that could limit oxygen mass transfer inside the MGS. The spatiotemporal assembly of diverse functional microorganisms in the MGS for the realization of stable PN/A could be achieved with the support of the iron redox cycle. In contrast, the iron-free MGS could not optimize oxygen mass transfer, which led to an unstable and inefficient PN/A. This work provides an alternative iron-related autotrophic N removal for low-strength ammonia wastewater.

Nitrite accumulation in activated sludge through cyclic anaerobic exposure with acetate

Achieving nitrite accumulation still remains challenging for efficient short-cut biological nitrogen removal in municipal wastewater treatment. To tackle the problem of insufficient carbon in incoming wastewater for biological nutrient removal, a return activated sludge (RAS) fermentation method has been proposed and demonstrated to enable producing supplemental volatile fatty acids (VFAs) and enhance biological phosphorus removal via sludge cycling between mainstream and a sidestream anaerobic reactor. However, the impacts of long anaerobic exposure with acetate on nitrifying bacteria, known as the aerobic chemoautotrophic microorganisms, remains unexplored. In this study, the activated sludge underwent a cyclic anaerobic treatment with the addition of acetate (Ac), the effects on nitrification rate, abundance and microdiversity of nitrifying communities were comprehensively assessed. Firstly, batch activity tests proved the direct addition of high acetate (above 1000 mg/L) could cause inhibition on the nitrification rate, moreover, the inhibitory effect was stronger on nitrite-oxidizing bacteria (NOB) activity than that of ammonia-oxidizing bacteria (AOB). Then, a sequencing batch reactor (SBR) was applied to test the nitrogen conversion performance for low-strength ammonium wastewater. Nitrite accumulation could be achieved via the cyclic anaerobic exposure with 1000–5000 mg Ac/L. The maximum effluent concentration of nitrite was 40.8 ± 3.5 mg N/L with nitrite accumulation ratio (NAR) of 67.6 ± 3.5%. The decrease in NOB activity (72.7%) was greater than AOB of 42.4%, promoting nitrite accumulation via nitritation process. Furthermore, the cyclic anaerobic exposure with acetate can largely reshape the nitrifying communities. As the dominant AOB and NOB, the abundance of Nitrosomonas and Nitrospira were both decreased with species-level microdiversity in the nitrifying communities. However, the heterotrophic microorganism, Thauera, were found to be highly enriched (from 0 to 17.3%), which may act as the potential nitrite producer as proved by the increased nitrate reduction gene abundance. This study can provide new insights into achieving mainstream nitrite accumulation by involving sidestream RAS fermentation towards efficient wastewater treatment management.

Genome-centered metagenomics illuminates adaptations of core members to a partial Nitritation-Anammox bioreactor under periodic microaeration.

The partial nitritation-anaerobic ammonium oxidation (anammox; PN-A) process has been considered a sustainable method for wastewater ammonium removal, with recent attempts to treat low-strength wastewater. However, how microbes adapt to the alternate microaerobic-anoxic operation of the process when treating low ammonium concentrations remains poorly understood. In this study, we applied a metagenomic approach to determine the genomic contents of core members in a PN-A reactor treating inorganic ammonium wastewater at loading as low as 0.0192 kg-N/m3/day. The metabolic traits of metagenome-assembled genomes from 18 core species were analyzed. Taxonomically diverse ammonia oxidizers, including two Nitrosomonas species, a comammox Nitrospira species, a novel Chloroflexota-related species, and two anammox bacteria, Ca. Brocadia and Ca. Jettenia, accounted for the PN-A reactions. The characteristics of a series of genes encoding class II ribonucleotide reductase, high-affinity bd-type terminal oxidase, and diverse antioxidant enzymes revealed that comammox Nitrospira has a superior adaptation ability over the competitors, which may confer the privileged partnership with anammox bacteria in the PN-A reactor. This finding is supported by the long-term monitoring experiment, showing the predominance of the comammox Nitrospira in the ammonia-oxidizing community. Metagenomic analysis of seven heterotrophs suggested that nitrate reduction is a common capability in potentially using endogenous carbohydrates and peptides to enhance nitrogen removals. The prevalence of class II ribonucleotide reductase and antioxidant enzymes genes may grant the adaptation to cyclically microaerobic/anoxic environments. The predominant heterotroph is affiliated with Chloroflexota; its genome encodes complete pathways for synthesizing vitamin B6 and methionine. By contrast, other than the two growth factors, Nitrospira and anammox bacteria are complementary to produce various vitamins and amino acids. Besides, the novel Chloroflexota-related ammonia oxidizer lacks corresponding genes for detoxifying the reactive oxygen species and thus requires the aid of co-existing members to alleviate oxidative stress. The analysis results forecast the exchanges of substrates and nutrients as well as the collective alleviation of oxidative stress among the core populations. The new findings of the genomic features and predicted microbial interplay shed light on microbial adaptation to intermittent microaeration specific to the PN-A reactor, which may aid in improving its application to low-strength ammonium wastewater.

Ultra-high nitrogen removal from real municipal wastewater using selective enhancement of glycogen accumulating organisms (GAOs) in a partial nitrification-anammox (PNA) system

Integrating endogenous denitrification (ED) into partial nitrification-anammox (PNA) systems by adequately utilizing organics in municipal wastewater is a promising approach to improve nitrogen removal efficiency (NRE). In this study, a novel strategy to inhibit phosphorus-accumulating organisms (PAOs) by inducing phosphorus release and exclusion was adopted intermittently, optimizing organics allocation between PAOs and glycogen-accumulating organisms (GAOs). Enhanced ED-synergized anammox was established to treat real municipal wastewater, achieving an NRE of 97.5±2.2% and effluent total inorganic nitrogen (TIN) of less than 2.0 mg/L. With low poly-phosphorus (poly-P) levels (poly-P/VSS below 0.01 (w/w)), glycogen accumulating metabolism (GAM) acquired organics exceeded that of phosphorus accumulating metabolism (PAM) and dominated endogenous metabolism. Ca. Competibacter (GAO) dominated the community following phosphorus-rich supernatant exclusion, with abundance increasing from 3.4% to 5.7%, accompanied by enhanced ED capacity (0.2 to 1.4 mg N/g VSS /h). The enriched subgroups (GB4, GB5) of Ca. Competibcater established a consistent nitrate cycle with anammox bacteria (AnAOB) through endogenous partial denitrification (EPD) at a ∆NO2−-N/∆NH4+-N of 0.91±0.11, guaranteeing the maintenance of AnAOB abundance and performance. These results provide new insights into the flexibility of PNA for the energy-efficient treatment of low-strength ammonium wastewater.

Inhibition of Nitrospira and Nitrotoga by paracetamol achieved the rapid start-up and long-term stable operation of partial nitrification for low-strength ammonium wastewater

Achieving stable partial nitrification (PN) are the basic guarantee of anaerobic ammonia oxidation (anammox) process. However, there is no recognized feasible method for rapidly achieving stable PN in municipal wastewater, and further research is necessary. In this study, paracetamol was proved as an effective nitrite oxidation inhibitor through long-term experiment lasting 392 days in three systems (floc sludge, granular sludge, biofilm). PN of low-strength ammonium wastewater was rapidly achieved within 28 days and maintained for about 80 days after paracetamol dose, whereas PN recovered again within 10 days and sustained over 150 days under paracetamol dose combined with low dissolved oxygen strategy. The inhibition effect of paracetamol on NOB was almost not affected by biomass growth modes. QPCR and high-throughput sequencing showed that Nitrospira (Oligotype 1) was inhibited by paracetamol, and PICURSt2 analysis indicated its key enzyme NXR was significantly downregulated after paracetamol treatment, which were the key reasons of PN start-up in three systems. The emergence and adaptation of Nitrotoga was the main reason for the instability of PN. This study proved that paracetamol could be used as a novel nitrite oxidation inhibitor, and provided a possibility to achieve the mainstream PN and anammox for treating wastewater with low-strength ammonium.

Solid retention time regulates partial nitrification by algal-bacterial consortia in wastewater treatment: Performance and mechanism

Partial nitrification in algal-bacterial consortia is a promising approach for low-strength ammonia wastewater treatment without mechanical aeration. However, the effects of solid retention times (SRTs) on microbial communities and interactions in algal-bacterial partial nitrification systems remain unclear. In this study, light-driven partial nitrification bioreactors were designed and operated at different SRTs (5, 10, 20, and 40 d) for over 140 d. An SRT of 10 d was found ideal for stable nitrite accumulation owing to the increased activity of ammonium oxidizing bacteria (AOB) and inhibited activity of nitrite oxidizing bacteria (NOB). However, longer SRTs (20 and 40 d) produced more nitrate due to a higher NOB activity and abundance. SRTs were found to be strongly associated with microbial diversity, which was mainly driven by the specific nitritation rates and nitrate concentrations. Accordingly, the functional microorganisms of SRT for 10 d were strongly correlated with AOB activity and nitrite accumulation, whereas those for 20 and 40 d ultimately correlated with NOB activity and nitrate production. Based on co-occurrence patterns and metagenomic analysis, enhanced microbial competition and higher network complexity associated with higher species richness and more connected pairs at SRT of 10 d promoted the formation of stable communities and thus ensured more efficient partial nitrification. Overall, this study provides the possibility of optimizing the configuration/process and operation of mainstream wastewater nitrogen removal by exploring the response mechanism of the algal-bacterial partial nitrification system to varying SRTs.

Comammox Nitrospira Bacteria Are Dominant Ammonia Oxidizers in Mainstream Nitrification Bioreactors Emended with Sponge Carriers.

Complete ammonia oxidation (i.e., comammox) is a newly discovered microbial process performed by a subset of the Nitrospira genus, and this unique microbial process has been ubiquitously detected in various wastewater treatment units. However, the operational conditions favoring comammox prevalence remain unclear. In this study, the dominance of comammox Nitrospira in four sponge biofilm reactors fed with low-strength ammonium (NH4+ = 23 ± 3 mg N/L) wastewater was proved by coupling 16S rRNA gene amplicon sequencing, quantitative polymerase chain reaction (qPCR), and metagenomic sequencing. The results showed that comammox Nitrospira dominated in the nitrifying guild over canonical ammonia-oxidizing bacteria (AOB) constantly, despite the significant variation in the residual ammonium concentration (0.01-15 mg N/L) under different sets of operating conditions. This result indicates that sponge biofilms greatly favor retaining comammox Nitrospira in wastewater treatment and highlights an essential role of biomass retention in the comammox prevalence. Moreover, analyses of the assembled metagenomic sequences revealed that the retrieved amoA gene sequences affiliated with comammox Nitrospira (53.9-66.0% read counts of total amoA gene reads) were always higher than those (28.4-43.4%) related to β-proteobacterial AOB taxa. The comammox Nitrospira bacteria detected in the present biofilm systems were close to clade A Candidatus Nitrospira nitrosa.

Establishment and optimization of partial nitrification/anammox/partial nitrification/anammox (PN/A/PN/A) process based on multi-stage ammonia oxidation: Using response surface method as a tool

The presence of nitrite-oxidizing bacteria (NOB) when treating low-strength ammonia wastewater was a challenge in the application of the PN/A process. The partial nitrification/ANAMMOX/partial nitrification/ANAMMOX (PN/A/PN/A) process based on multiple oxidations of ammonia was proposed to solve this problem. The influence of independent variables such as nitrite concentration was analyzed based on the response surface method (RSM). The model showed that nitrite concentration has an adverse impact on ammonia removal efficiency and nitrite accumulation rate. The model provided optimal parameters for the PN/A/PN/A process: the dissolved oxygen concentration was 0.60 mg/L, and the cycle duration was 90 min. Advanced nitrogen removal was achieved by maintaining the nitrite concentration below 10.0 mg/L. The nitrogen removal efficiency was 81.44 ± 4.15 %, and the nitrogen removal rate was 0.18 ± 0.02 kg N/(m3⋅d). Potential functions of microorganisms were analyzed by functional annotation of prokaryotic taxa (FAPROTAX) and the correlation network analysis was performed.

Coexistence and competition of the nitrifying and anammox bacteria in SMBBR reactor with partial nitritation/anammox process treating synthetic low-strength ammonium wastewater

The nitrite-oxidizing bacteria (NOB) suppression largely restricts the implementation of partial-nitritation and anammox (PN/A) process for low-strength ammonium wastewater treatment. The main goal of the present study was to verify the feasibility of sequencing moving bed biofilm reactor (SMBBR) treating synthetic low-strength ammonium wastewater and the influence of operating conditions and microbial competitions on NOB suppression. The reactor was operated in sequencing batch reactor (SBR) mode with influent ammonium of 50 mg/L, in which the seeded biofilm harvested from an existing similar PN/A reactor treating high-ammonium synthetic wastewater. After increasing the dissolved oxygen (DO) from 0.50 to 1.25 mg/L-with hydraulic retention time (HRT) gradually decreasing from 15 to 5 h-stable nitrogen removal through PN/A was obtained. The long-term operation results showed nitrogen removal efficiencies of 66.23 ± 7.78 % were stably obtained at a relatively low filling ratio of 25 %. The reactor operated in SBR mode allowed NOB suppression and low effluent ammonium due to the ammonium gradient created in cycles. Further, the activity of NOB was controlled at a low level at medium DO concentration. Both ammonium-oxidizing bacteria (AOB) competition acting as DO-cut and anaerobic ammonium-oxidizing bacteria (anammox, AMX) competition acting as nitrite-sink were found to be essential for NOB suppression, and DO-cut played a dominated role. A simple hypothetical microstructure of one-stage PN/A biofilm, assuming AOB layered in the surface of the biofilm while AMX and NOB in the interior, was proposed to define the mechanism of DO-cut and Nitrite-sink. The obtained results demonstrated SMBBR could be regarded as an alternative guideline for successful operation of mainstream PN/A as compared to the integrated fixed film activated sludge (IFAS) systems.

Rapid initiation of a single-stage partial nitritation-anammox process treating low-strength ammonia wastewater: Novel insights into biofilm development on porous polyurethane hydrogel carrier

Media-supported biofilm is a powerful strategy for growth and enrichment of slow-growing microorganisms. In this study, a single-stage nitritation-anammox process treating low-strength wastewater was successfully started to investigate the biofilm development on porous polyurethane hydrogel carrier. Suspended biomass migration into the carrier and being entrapment by its internal interconnected micropores dominated the fast initial colonization stage. Both surface-attached growth and embedded growth of microbes occurred during the following accumulation stage. Fluorescence in situ hybridization analysis of mature biofilm indicated that ammonium-oxidizing bacteria located at the outer layers featured a surface-attached growth, while anammox microcolonies housed in the inner layers proliferated as an embedded-like growth. In this way, the growth rate of anammox bacteria (predominated by Candidatus Kuenenia) could be 0.079 d-1. The anammox potential of the biofilm reactor reached 1.65 ± 0.3 kg/m3/d within two months. This study provides novel insights into nitritation-anammox biofilm formation on the porous polyurethane hydrogel carrier.

Utilization of three-layered polyvinyl alcohol gel cubes for treating low-strength ammonium wastewater in a single-stage autotrophic nitrogen removal process

This study examined the feasibility of using a three-layered polyvinyl alcohol (PVA) gel cube for low-strength ammonium wastewater (<50 mg-NH4+-N/L) treatment in a single reactor. The outer layer of this three-layered PVA gel cube was composed of immobilized nitrifying bacteria, while the inner layers were composed of anaerobic ammonium oxidation (anammox) bacteria. A single-stage autotrophic nitrogen removal (SANR) reactor containing these three-layered PVA gel cubes was operated at 35 °C for 197 days, with intermittent aeration. Although the activity of nitrite-oxidizing bacteria (NOB) was incompletely inhibited under a narrow range of dissolved oxygen (DO) concentrations (0.1–1.1 mg-O2/L), a nitrogen removal efficiency (NRE) of 71.9% was achieved at 35 °C. At this temperature, the high NRE was achieved due to the coexistence of anammox and denitrifying bacteria. After decreasing the temperature to 20 °C, the NRE was maintained at a similar level (69.8%) for 53 days. The change in the structure of the bacterial community was insignificant with decreasing temperature. The 16S rRNA high-throughput sequencing analysis revealed that Planctomycetes (46.8–53.4%) was the most abundant phylum, wherein anammox bacteria accounted for 45.4–51.9% of the relative biodiversity abundance. Candidatus Jettenia asiatica disappeared for the operation of 187 days, while Candidatus Brocadia sinica was abundant. After 220 days, the relative abundances of ammonium-oxidizing bacteria (AOB) and NOB doubled and tripled, respectively. The abundant AOB were Nitrosomonas aestuarii and Nitrosomonas ureae, while the dominant NOB was Nitrospira moscoviensis. Nitrate produced by undesirable NOB activity was converted to nitrite by Denitratisoma oestradiolicum, which led to the abundance of anammox bacteria.

A novel two-stage partial-nitritation/anammox (PN/A) process based on zeolite biological fixed bed reactor for low-strength ammonium wastewater treatment

A novel two-stage partial nitritation/anammox (PN/A) process coupled by a zeolite biological fixed bed reactor (ZBFB) and an anammox reactor were proposed for wastewater containing 30 mg/L NH4+-N by long-term operation. The cycle operational results by adsorption and biological desorption in ZBFB showed adsorption effluent NH4+-N maintained at 3.0-4.0 mg/L and the average biological desorption effluent NO2--N was 42.2 mg/L. In ZBFB, free ammonia inhibition on nitrite oxidizing bacteria was the main reason for stable nitrite accumulation performance with nitrite accumulation ratio as 88.70% during biological desorption step. Total nitrogen in the mixture of influent and biological desorption effluent of ZBFB could be removed to less than 15 mg/L by the subsequent anammox reactor. High-throughput sequencing analysis results presented the enrichment of Nitrosomonas and inhibition of Nitrobactor and Nitrospira in ZBFB, and dominance of Candidatua Kuenenia in anammox reactor. All results revealed desirable feasibility for nitrogen removal from low-strength ammonium wastewater by ZBFB combined with anammox reactor.

Strategy for Maintaining Stable Partial Nitritation of Low-Strength Ammonia Wastewater by Hydrazine

The primary objectives of this study were to identify the effectiveness of hydrazine on partial nitrification in a sequencing batch reactor when treating low-strength ammonia wastewater and to inve...

Achieving superior nitrogen removal performance in low-strength ammonium wastewater treatment by cultivating concentrated, highly dispersive, and easily settleable granule sludge in a one-stage partial nitritation/anammox-HAP reactor

In low-strength ammonium wastewater (LSAWW) treatment, the application of anammox-based process is still limited due to extreme instability and the poor nitrogen removal rate (NRR). In this work, granule sludge, comprised of functional microbes and hydroxyapatite (HAP), was inoculated and cultivated in a one-stage partial nitritation/anammox (PNA) reactor for LSAWW treatment. The results showed that at the hydraulic retention time (HRT) of about 1.0 h and the influent ammonium concentration of 63.0 mg/L, an average NRR of 1.28 kg/m3/d was achieved, which far exceeds that reported in similar studies. The main inorganic matter in sludge was identified as HAP through the X-ray diffractometer and Raman spectrum analysis. The tomographic images of wet granule created through computed tomography revealed that the interior density of the granules was uneven and many hollow structures existed in the granule interior. Combined with the Scanning Electron Microscope images of dry granules, it was found that the granules were comprised of hollow sub-granules. Since the biomass in the reactor increased with no obvious increase in the granule size, it was inferred that the hollow sub-granules had fragile connections with each other and that granules division occurred easily, resulting in the high dispersity of sludge. Florescence in situ hybridization results also showed that the ammonium-oxidizing bacteria and anammox bacteria were mainly distributed in the two sides of the sub-granule shells and the HAP in the middle. This kind of structure raised the density of granules and improved the settleability of sludge, which made it possible to achieve a high biomass in the reactor at a short HRT. Therefore, the sludge formed in the reactor was concentrated, highly dispersive and easily settleable. These factors appear to be crucial for achieving the desired nitrogen removal performance. This study marks a big leap in LSAWW treatment through the one-stage PNA process and has great potential in actual applications.

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.

Reactor performance and microbial community structure of single-stage partial nitritation anammox membrane bioreactors inoculated with Brocadia and Scalindua enrichment cultures

Partial nitritation combined with anaerobic ammonium oxidation (anammox), hereafter referred to as PNA, is a promising biological nitrogen-removal process for ammonia-rich wastewater; however, the PNA application process to low-strength ammonia wastewater (i.e., mainstream anammox) remains challenging. In this study, two single-stage PNA processes using a membrane bioreactor (MBR) inoculated with the anammox enrichment culture of Candidatus Brocadia sinica (Brocadia-MBR) or Candidatus Scalindua sp. (Scalindua-MBR) were operated for low-strength ammonia wastewater treatment. Single-stage PNA process was established in both MBRs, showing rates of total nitrogen (TN) removal from 0.58 g-N L−1 day−1 to 0.66 g-N L−1 day−1, and 81%–89% TN-removal efficiency under optimal dissolved oxygen. Microbial community analysis showed that three ammonia-oxidizing bacteria (AOB), one nitrite-oxidizing bacteria (NOB), one Candidatus Brocadia were detected in the Brocadia-MBR, whereas one AOB, no NOB, and one Candidatus Scalindua were detected in Scalindua-MBR. The operational conditions in this study resulted in the outcompetition of anammox bacteria in both MBRs.

Conversion of full nitritation to partial nitritation/anammox in a continuous granular reactor for low-strength ammonium wastewater treatment at 20°C.

The feasibility of converting full nitritation to partial nitritation/anammox (PN/A) at ambient temperature (20°C) was investigated in a continuous granular reactor. The process was conducted without anammox bacteria inoculation for the treatment of 70mgL-1 of low-strength ammonium nitrogen wastewater. Following the stepwise increase of the nitrogen loading rate from 0.84 to 1.30kgNm-3d-1 in 320days of operation, the removal efficiency of total inorganic nitrogen (TIN) exceeded 80% under oxygen-limiting conditions. The mature PN/A granules, which had a compact structure and abundant biomass, exhibited a specific TIN removal rate of 0.11gNg-1 VSSd-1 and a settling velocity of 70.2mh-1. This was comparable with that obtained at above 30°C in previous reports. High-throughput pyrosequencing results revealed that the co-enrichment of aerobic and anaerobic ammonium-oxidizing bacteria identified as genera Nitrosomonas and Candidatus Kuenenia, which prompted a hybrid competition for oxygen and nitrite with nitrite-oxidizing bacteria (NOB). However, the overgrowth of novel NOB Candidatus Nitrotoga adapted to low temperatures and low nitrite concentration could potentially deteriorate the one-stage PN/A process by exhausting residual bulk ammonium under long-term excessive aeration.

Achieving reliable partial nitrification and anammox process using polyvinyl alcohol gel beads to treat low-strength ammonia wastewater

In this study, polyvinyl alcohol (PVA) gel beads were used to aid the partial nitrification and anammox process (PN/A) for treating low-strength ammonia wastewater. When treating synthetic and municipal wastewater, the reactor amended with PVA gel beads achieved a total nitrogen removal efficiency of 75.1 ± 8.4% and 66.6 ± 7.0% respectively, while the control reactor without PVA gel beads achieved 63.2 ± 7.8% and 28.2 ± 11.5% respectively. Dissolved oxygen (<0.5 mg O2 L−1) and substrate diffusion in porous PVA gel beads facilitated the formation of microbial stratification in the gel beads. Unclassified Candidatus Brocadiaceae (major anammox bacteria) and Ignavibacterium (major ammonia oxidizing bacteria) enriched in the inside and outside layers of PVA gel beads, which benefited the synergetic cooperation of these bacteria and protecting them from environmental fluctuations. This study provides a promising solution for achieving a reliable PN/A process in mainstream wastewater treatment.

Characteristics and formation mechanism of hollow Anammox granular sludge in low-strength ammonia sewage treatment

• Hollow Anammox granular sludge formed in low-strength ammonia wastewater. • TN removal efficiency was 80% with NRR 0.93 kg N m −3 d −1 under a short HRT (1.8 h). • Tryptophan or protein-like was the active component of PN as the main part of EPS. • Candidatus Kuenenia lived and coexisted with other bacteria under EPS shield. • The formation of bubble cavitation was one of the key steps of regranulation. Hollow anaerobic ammonium oxidation (Anammox) granular sludge formed and became the main part in the treatment of low-strength ammonia wastewater. The characteristics and formation mechanism of hollow Anammox granular sludge were investigated in a continuous stirred tank reactor (CSTR) at room temperature. Granular sludge was found to be cavitated, and Candidatus Kuenenia was the dominant bacteria that lived and coexisted with other bacteria in walls under an extracellular polymeric substance (EPS) shield. The EEM-PARAFAC analysis was applied to characterize the EPS, while EPS secretion was the expression of specific Anammox activity. Tryptophan or protein-like was the active component of proteins (PN) as the main part of EPS in granules. These results confirm that hollow Anammox granular sludge is suitable for low-strength ammonia sewage. Finally, a conceptual model of hollow Anammox granules growth and breakage was developed, and cavitation was a key step of regranulation.