Enhanced aerobic granulation for treating low-strength wastewater in an anaerobic-aerobic-anoxic sequencing batch reactor by selecting slow-growing organisms and adding carriers

Evaluation of aerobic granulation performance bioaugmented with the auto-aggregating bacterium Pseudomonas stutzeri strain XL-2 with heterotrophic nitrification-aerobic denitrification capacity

In this study, the possibility of an auto-aggregating bacterium Pseudomonas strain XL-2 with heterotrophic nitrification-aerobic denitrification capacity for improving granulation and nitrogen removal was evaluated. The results showed that the supplementation of strain XL-2 promoted granulation, making R1 (experimental group with strain XL-2) dominated by granules at 14 d, which was 12 days earlier than R2 (control group without strain XL-2). This was attributed to the promotion of extracellular polymeric substances (EPS) secretion, particularly proteins by adding strain XL-2, thereby improving the hydrophobicity of sludge and altering the proteins secondary structures to facilitate aggregation. Meanwhile, adding strain XL-2 improved simultaneous nitrification and denitrification efficiency of R1. Microbial community analysis indicated that strain XL-2 successfully proliferated in aerobic granule sludge and might induce the enrichment of genera such as Flavobacterium and Paracoccus that were favorable for EPS secretion and denitrification, jointly promoting granulation and enhancing nitrogen removal efficiency.

Unraveling the mechanisms and responses of aniline-degrading biosystem to salinity stress in high temperature condition: pollutants removal performance and microbial community

To explore the intrinsic influence of different salinity content on aniline biodegradation system in high temperature condition of 35±1 °C, six groups at various salinity concentration (0.0%-5.0%) were applied. The results showed that the salinity exerted insignificant impact on aniline removal performance. The low-level salinity (0.5%-1.5%) stimulated the nitrogen metabolism performance. The G5-2.5% had excellent adaptability to salinity while the nitrogen removal capacity of G6-5.0% was almost lost. Moreover, high throughput sequencing analysis revealed that the g__norank_f__NS9_marine_group, g__Thauera and g__unclassified_f__Rhodobacteraceae proliferated wildly and established positive correlation each other in low salinity systems. The g__SM1A02 occupying the dominant position in G5 ensured the nitrification performance. In contrast, the Rhodococcus possessing great survival advantage in tremendous osmotic pressure competed with most functional genus, triggering the collapse of nitrogen metabolism capacity in G6. This work provided valuable guidance for the aniline wastewater treatment under salinity stress in high temperature condition.

Efficient nitrogen removal from ammonia rich wastewater using aerobic granular sludge (AGS) reactor: Selection and enrichment of effective microbial community

Anaerobically digested sludge supernatant, characterized by its high ammonia and low biodegradable chemical oxygen demand (COD) content, has raised concerns when returned to mainstream treatment lines due to potential impacts on effluent quality. Addressing this, an aerobic granular sludge (AGS) reactor adopted nitritation/denitritation with external COD addition was utilized and achieved a considerable nitrogen treatment capacity of 4.2 kg N/m3/d, reaching over 90% removal efficiencies for both ammonia and total inorganic nitrogen. This study applied progressively increased nitrogen loading to select for a microbial community that exhibited high nitrogen oxidation and reduction rates, demonstrating peak rates of 0.5 g N/g VSS/d and 3 g N/g VSS/d, respectively. The enrichment of highly efficient microbial community was achieved along with the increased biomass density peaked at 17 g/L MLVSS, with the system retaining small-sized granular sludge at 0.5 mm. The primary ammonia oxidizing bacteria was Nitrosomonas, while Thauera was the dominated denitrifiers. Quantitative polymerase chain reaction analyses reinforced the enhanced nitrogen removal capacity based on the progressively increased abundance of nitrogen cycling functional genes. The high nitrogen treatment capacity, synergistic attributes of high specific microbial activities and the substantial biomass retention, suggest the AGS's efficacy and capacity in ammonia rich wastewater treatment.

Effects of enhanced biological phosphorus removal on rapid control of sludge bulking and fast formation of aerobic granular sludge

This study investigated the effects of enhanced biological phosphorus removal (EBPR) on rapid sludge bulking control and fast aerobic granular sludge (AGS) formation by adding 20 % of EBPR activated sludge to the bulking activated sludge (BAS) reactor. The results indicate that activating EBPR activity swiftly improved BAS settleability within 16 days, thus resolving sludge bulking issues. Subsequently, a settling time-based selection was employed, resulting in the BAS granulation within another 16 days. The rapid achievement of EBPR activity improved the BAS settleability and facilitated the formation of sludge aggregates, thereby expediting BAS granulation. Inhibition of filamentous bacteria and enrichment of slow-growing organisms contributed to both sludge bulking control and aerobic granulation. Furthermore, the increase in proteins/polysaccharides ratio facilitated the granulation process. Additionally, total nitrogen removal increased from 59.4 % to 71.7 % because of the mature AGS formation. This study provided an approach to simultaneously control sludge bulking and promote aerobic granulation.

Advanced nitrogen and phosphorus removal in pilot-scale anaerobic/aerobic/anoxic system for municipal wastewater in Northern China

Removing nitrogen and phosphorus from low ratio of chemical oxygen demand to total nitrogen and temperature municipal wastewater stays a challenge. In this study, a pilot-scale anaerobic/aerobic/anoxic sequencing batch reactor (A/O/A-SBR) system first treated 15 m3/d actual municipal wastewater at 8.1-26.4 °C for 224 days. At the temperature of 15.7 °C, total nitrogen in influent and effluent were 45.5 and 10.9 mg/L, and phosphorus in influent and effluent were 3.9 and 0.1 mg/L. 16 s RNA sequencing results showed the relative abundance of Competibacter and Tetrasphaera raised to 1.25 % and 1.52 %. The strategy of excessive, no and normal sludge discharge enriched and balanced the functional bacteria, achieving an endogenous denitrification ratio more than 43.3 %. Sludge reduction and short aerobic time were beneficial to energy saving contrast with a Beijing municipal wastewater treatment. This study has significant implications for the practical application of the AOA-SBR process.

Insight into the role of chitosan in rapid recovery and re-stabilization of disintegrated aerobic granular sludge

The disintegration and instability of aerobic granular sludge (AGS) systems during long-term operation pose significant challenges to its practical implementation, and rapid recovery strategies for disintegrated AGS are gaining more attention. In this study, the recovery and re-stabilization of disintegrated AGS was investigated by adding chitosan to a sequencing batch reactor and simultaneously adjusting the pH to slightly acidic condition. Within 7 days, chitosan addition under slight acidity led to the re-aggregation of disintegrated granules, increasing the average particle size from 166.4 μm to 485.9 μm. Notably, sludge volume indexes at 5 min (SVI5) and 30 min (SVI30) decreased remarkably from 404.6 mL/g and 215.1 mL/g (SVI30/SVI5 = 0.53) to 49.1 mL/g and 47.6 mL/g (SVI30/SVI5 = 0.97), respectively. Subsequent operation for 43 days successfully re-stabilized previous collapsed AGS system, resulting in an average particle size of 750.2 μm. These mature and re-stabilized granules exhibited characteristics of large particle size, excellent settleability, compact structure, and high biomass retention. Furthermore, chitosan facilitated the recovery of COD and nitrogen removal performances within 17-23 days of operation. It effectively facilitated the rapid aggregation of disintegrated granules by charge neutralization and bridging effects under a slightly acidic environment. Moreover, the precipitated chitosan acted as carriers, promoting the adhesion of microorganisms once pH control was discontinued. The results of batch tests and microbial community analysis confirmed that chitosan addition increased sludge retention time, enriching slow-growing microorganisms and enhancing the stability and pollutant removal efficiency of the AGS system.

Rapid start-up strategy and microbial population evolution of anaerobic ammonia oxidation biofilm process for low-strength wastewater treatment

The implementation of the anaerobic ammonium oxidation (anammox) process in treating low-strength wastewater is limited by the difficulty in enriching anammox bacteria (AnAOB). Here, the first enrichment of AnAOB at a high nitrogen (N) loading rate (NLR) as a strategy was proposed to achieve the rapid start-up of the anammox biofilm process treating low-strength wastewater. The long-term stability of the anammox biofilm process after start-up operating at a low NLR of 0.2-0.4 kg N/(m3⋅d) was evaluated. Results showed that the N removal efficiency was up to 75 % under a low NLR of 0.2 kg N/(m3⋅d) condition. Low-strength organic matter promoted the metabolic coupling between partial denitrifying bacteria (PDB) and AnAOB. The genus Candidatus Brocadia as AnAOB (18 %-27 %) can coexist with Limnobacter (PDB, 9 %-12 %) for efficient N removal. This study offers a rapid start-up strategy of anammox biofilm process in treating low-strength wastewater.

Rapid static feeding combined with Fe2+ addition for improving the formation and stability of aerobic granular sludge in low-strength wastewater

Aerobic granular sludge (AGS) needs a long start-up time and always shows unstable performance when it is used to treat low-strength wastewater. In this study, a rapid static feeding combined with Fe2+ addition as a novel strategy was employed to improve the formation and stability of AGS in treating low-strength wastewater. Fe-AGS was formed within only 7 days and showed favorable pollutant removal capability and settling performance. The ammonia nitrogen (NH4+-N) and chemical oxygen demand (COD) concentration in the effluent were lower than 5 mg/L and 50 mg/L after day 23, respectively. The sludge volume index (SVI) and mixed liquid suspended solids (MLSS) was 37 mL/g and 2.15 g/L on day 50, respectively. Rapid static feeding can accelerate granules formation by promoting the growth of heterotrophic bacteria, but the granules are unstable due to filamentous bacteria overgrowth. Fe2+ addition can inhibit the growth of filamentous bacteria and promote the aggregation of functional bacteria (eg. Nitrosomonas, Nitrolancea, Paracoccus, Diaphorobacter) by enhancing the secretion of extracellular polymeric substances (EPS). This study provides a new way for AGS application in low-strength wastewater treatment.

Effects of microaeration and sludge recirculation on VFA and nitrogen removal, membrane fouling reduction and microbial community of the anaerobic baffled biofilm-membrane bioreactor in treating building wastewater

A novel anaerobic baffled biofilm-membrane bioreactor (AnBB-MBR) with microaeration of 0.62 LO2/LFeed was developed to improve VFA and nitrogen removal from building wastewater. Three different membrane bioreactor systems - R1: AnBB-MBR (without microaeration); R2: AnBB-MBR with microaeration; and R3: AnBB-MBR with integrated microaeration and sludge recirculation - were operated in parallel at the same hydraulic retention time of 20 h and sludge retention time of 100 d. The microaeration promoted greater microbial richness and diversity, which could significantly enhance the removal of acetic acid and dissolved methane in the R2 and R3 systems. Moreover, the partial nitrification and the ability of anammox (Candidatus Brocadia) to thrive in R2 enabled NH4+-N removal to be enhanced by up to 57.8 %. The worst membrane fouling was found in R1 due to high amount of protein as well as fine particles (0.5-5.0 μm) acting as foulants that contributed to pore blocking. While the integration of sludge recirculation with microaeration in R3 was able to improve the membrane permeate flux slightly as compared to R2. Therefore, the AnBB-MBR integrated with a microaeration system (R2) can be considered as promising technology for building wastewater treatment when considering VFA and nutrient removal and an energy-saving approach with low aeration intensity.

Effects of NaHCO3 Stress on Black Locust (Robinia pseudoacacia L.) Physiology, Biochemistry, and Rhizosphere Bacterial Communities

Soil salinization has become an ecological and environmental problem that cannot be ignored. Tetraploid black locust (Robinia pseudoacacia L.) is a leguminous tree with characteristics of drought and saline-alkali tolerance. Rhizosphere bacteria are the primary functional microorganisms within the plant root system, and they play a crucial role in regulating plant growth and enhancing stress tolerance. However, there is still a lack of research on the effect of saline-alkali stress on the bacterial community structure in the rhizosphere of black locusts. In this study, we applied 0, 50, 100, and 150 mM NaHCO3 stress to diploid (2×) and tetraploid (4×) black locusts for 16 days. We used 16S rDNA sequencing to investigate the changes in the rhizosphere bacterial communities. Furthermore, we evaluated soil enzyme activity and plant physiological characteristics to explore the response of rhizosphere bacteria to NaHCO3 stress. The results demonstrated that the 4× plant exhibited superior alkali resistance compared to its 2× plant counterpart under NaHCO3 stress. Simultaneously, it was observed that low concentrations of NaHCO3 stress notably increased the abundance of rhizosphere bacteria in both plant types, while reducing their diversity. The impact of stress on the rhizosphere bacterial community weakened as the stress concentration increased. The application of NaHCO3 stress caused a significant change in the composition of the bacterial community in the rhizosphere. Additionally, alkaline salt stress influences the diversity of rhizosphere bacterial communities, which are linked to soil enzyme activities. These data will help us better understand the relationship between the dominant rhizosphere bacterial community and black locust. They will also provide a reference for further improving the alkali resistance of black locust by enhancing the soil bacterial community.

Microalgae-assisted heterotrophic nitrification-aerobic denitrification process for cost-effective nitrogen and phosphorus removal from high-salinity wastewater: Performance, mechanism, and bacterial community

A microalgae-assisted heterotrophic nitrification-aerobic denitrification (HNAD) system for efficient nutrient removal from high-salinity wastewater was constructed for the first time as a cost-effective process in the present study. Excellent nutrient removal (∼100.0 %) was achieved through the symbiotic system. The biological removal process, biologically induced phosphate precipitation (BIPP), microalgae uptake, and ammonia stripping worked together for nutrient removal. Furthermore, the biological removal process achieved by biofilm contributed to approximately 55.3-71.8 % of nitrogen removal. BIPP undertook approximately 45.6-51.8 % of phosphorus removal. Batch activity tests confirmed that HNAD fulfilled an extremely critical role in nitrogen removal. Microalgal metabolism drove BIPP to achieve efficient phosphorus removal. Moreover, as the main HNAD bacteria, OLB13 and Thauera were enriched. The preliminary energy flow analysis demonstrated that the symbiotic system could achieve energy neutrality, theoretically. The findings provide novel insights into strategies of low-carbon and efficient nutrient removal from high-salinity wastewater.

Simultaneous partial nitrification, denitrification, and phosphorus removal in sequencing batch reactors via controlled reduced aeration and short-term sludge retention time decrease

Simultaneous bio-treatment processes of organic carbon (C)-, nitrogen (N)-, and phosphorus (P)-containing wastewater are challenged by insufficient carbon sources in the effluent. In the present study, two parallel anaerobic/aerobic sequencing batch reactors (R-1 and R-2) treating low C/N (≤4) wastewater were employed using different partial nitrification start-up strategies, controlled reduced aeration, and decreased sludge retention time. Advanced removal efficiencies for NH4+-N (≥96%), total nitrogen (TN, ≥86%), PO43--P (≥95%), and CODintra (≥91%) were realized, with TN and PO43--P effluent concentrations of 10.0 ± 3.5 and 0.11 ± 0.3 mg/L in R-1 and 9.28 ± 4.0 and 0.11 ± 0.1 mg/L in R-2, respectively. Higher nitrite accumulation rate (nearly 100%) and TN (121.1 ± 0.7 mg TN/g VSS·d) and P (12.5 ± 0.6 mg PO43--P/g VSS·d) removal loadings were obtained in R-2 by a thorough elimination of nitrite-oxidizing bacteria. Moreover, different microbial structures and nutrient removal pathways were identified. Denitrifying glycogen-accumulating organisms (Candidatus Competibacter) and phosphorus-accumulating organisms (PAOs) (Tetrasphaera) removed N and P with partial nitrification-endogenous denitrification pathways and aerobic P removal in R-1. In R-2, aerobic denitrifying bacteria (Psychrobacter) and PAOs ensured N and P removal through the partial nitrification-aerobic denitrification and aerobic P removal pathways. Compared to R-1, R-2 offers greater efficiency, convenience, and scope to further reduce carbon-source demand.

Ball-milled magnetic sludge biochar enables fast aerobic granulation in anoxic/oxic process for the treatment of coal chemical wastewater

Coal chemical wastewater (CCW) containing toxic and hazardous matters requires to be treated prior to discharge. Promoting the in-situ formation of magnetic aerobic granular sludge (mAGS) in continuous flow reactor process has a great potential for CCW remediation. However, long granulation time and low stability limit the application of AGS technology. In this study, Fe₃O₄/sludge biochar (Fe₃O₄/SC) with biochar matrix derived from coal chemical sludge were applied to facilitate the aerobic granulation in two-stage continuous flow reactors, containing separated anoxic and oxic reaction units (abbreviated as A/O process). The performance of A/O process was evaluated at various hydraulic retention times (HRTs) (42 h, 27 h, and 15 h). Magnetic Fe₃O₄/SC with porous structures, high specific surface area (BET = 96.69 m²/g), and abundant functional groups was successfully prepared by ball-milled method. Adding magnetic Fe₃O₄/SC to A/O process could promote aerobic granulation (85 days) and the removal of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N)_, and total nitrogen (TN) from CCW at all tested HRTs. Since the formed mAGS had high biomass, good settling ability, and high electrochemical activities, mAGS-based A/O process had high tolerance to the decrease of HRT from 42 h to 15 h for CCW treatment. The optimized HRT for A/O process was 27 h, at which Fe₃O₄/SC addition can result in the increase of COD, NH₄⁺-N and TN removal efficiencies by 2.5 %, 4.7 % and 10.5 %, respectively. Based on 16S rRNA genes sequencing, the relative abundances of genus Nitrosomonas, Hyphomicrobium/Hydrogenophaga and Gaiella in mAGS accounting for nitrification, denitrification as well as COD removal were increased during aerobic granulation. Overall, this study proved that adding Fe₃O₄/SC to A/O process was effective for facilitating aerobic granulation and CCW treatment.

Understanding the impacts of intermittent electro field on the bioelectrochemical aniline degradation system: Performance, microbial community and functional enzyme

On account of the lack of a sustainable electron donor source and the inhibitory effect of aniline on denitrogenation make it tough to achieve simultaneous removal of aniline and nitrogen. Herein, the strategy of adjusting electric field mode was applied to the electro-enhanced sequential batch reactors (E-SBRs: R1 (continuous ON), R2 (2 h-ON/2 h-OFF), R3 (12 h-ON/12 h-OFF), R4 (in the aerobic phase ON), R5 (in the anoxic phase ON)) to treat aniline wastewater. Aniline removal rate reached approximately 99% in the five systems. Decreasing electrical stimulation interval from 12 to 2 h significantly improved the electron utilization efficiency for aniline degradation and nitrogen metabolism. The total nitrogen removal was achieved from 70.31% to 75.63%. Meanwhile, the hydrogenotrophic denitrifiers of Hydrogenophaga, Thauera, and Rhodospirillales, enriched in reactors of minor electrical stimulation interval. Accordingly, the expression of functional enzyme related to electron transport was incremental with the proper electrical stimulation frequency.

Tritium and Carbon-14 Contamination Reshaping the Microbial Community Structure, Metabolic Network, and Element Cycle in the Seawater Environment

The potential ecological risks caused by entering radioactive wastewater containing tritium and carbon-14 into the sea require careful evaluation. This study simulated seawater's tritium and carbon-14 pollution and analyzed the effects on the seawater and sediment microenvironments. Tritium and carbon-14 pollution primarily altered nitrogen and phosphorus metabolism in the seawater environment. Analysis by 16S rRNA sequencing showed changes in the relative abundance of microorganisms involved in carbon, nitrogen, and phosphorus metabolism and organic matter degradation in response to tritium and carbon-14 exposure. Metabonomics and metagenomic analysis showed that tritium and carbon-14 exposure interfered with gene expression involving nucleotide and amino acid metabolites, in agreement with the results seen for microbial community structure. Tritium and carbon-14 exposure also modulated the abundance of functional genes involved in carbohydrate, phosphorus, sulfur, and nitrogen metabolic pathways in sediments. Tritium and carbon-14 pollution in seawater adversely affected microbial diversity, metabolic processes, and the abundance of nutrient-cycling genes. These results provide valuable information for further evaluating the risks of tritium and carbon-14 in marine environments.

Synergetic effects of pyrrhotite and biochar on simultaneous removal of nitrate and phosphate in autotrophic denitrification system

In the trend of upgrading wastewater treatment plants, developing advanced treatment technologies for more efficient nutrient removal is crucial. This study prepared a pyrrhotite-biochar composite (Fe_x S_y @BC) to investigate its potential for simultaneous removal of nitrate and phosphate under autotrophic denitrification conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to characterize the novel composite of Fe_x S_y @BC, which exhibited 9.2 mg N/(L·d) NO₃ ^- -N reduction rate, 97.3% N₂ production, and 81.8 mmol N/(kg·d) NO₃ ^- -N material load with small solid/liquid ratio (0.008). The NO₃ ^- -N removal with Fe_x S_y @BC was 1.2-2.2 times higher than that with pure iron sulfides or biochar or their mixtures, whereas the Δn(S)/Δn(N) of Fe_x S_y @BC was the lowest (1.80). Moreover, the PO₄ ^3- -P reduction rate of Fe_x S_y @BC reached 3.23 mg P/(L·d), as high as that of pure pyrite or pyrrhotite. Thiobacillus was the most dominant denitrifying bacterium. Fe_x S_y @BC exhibited great promise for enhancing nutrient removal from secondary effluent without additional carbon source. PRACTITIONER POINTS: FexSy@BC enhanced nitrate and phosphate removal simultaneously. First-order kinetics and Monod model were fitted for denitrification with FexSy@BC. FexSy@BC had smaller molar ratio of sulfate release to nitrate removal. Thiobacillus was the dominant bacterium in FexSy@BC autotrophic denitrification. Synergistic effects on nutrients removal existed between biochar and pyrrhotite.

Synergistic effects of simultaneous coupling ozonation and biodegradation for coking wastewater treatment: Advances in COD removal, toxic elimination, and microbial regulation

Coking wastewater contains high concentrations of cyanide, phenols, pyridine, quinoline, and polycyclic aromatic hydrocarbons. Its high toxicity and low biodegradability leads to long hydraulic retention time of biological process and high cost of advanced oxidation process. In this study, the simultaneous combination of ozonation and biodegradation (SCOB) was proposed to treat coking wastewater. Through this process, ozonation breaks the refractory organics, and the biodegradable intermediates are rapidly mineralized by microorganisms protected by porous carriers. Thus, the performances of SCOB, individual biodegradation and ozonation systems were compared. The long-term stability of the SCOB system was evaluated, the contributions of ozonation and biodegradation were analyzed, and their synergistic mechanisms were elaborated. Results showed that biological activity was inhibited in the biodegradation system, and chemical oxygen demand (COD) removal was only 27.6% for the ozonation system. COD and total phenol removal of SCOB system reached 48.5% and 79.3%, respectively, and its kinetic degradation constant of COD was 55.6% higher than that of the ozonation system. Ozonation contributed to the oxidation of organics with unsaturated functional groups as well as soluble microbial products (SMPs), causing the effluent toxicity and chroma to decrease by 82.7% and 270 times, respectively. The higher abundances of microorganisms and functions were enriched in the core of carrier, which became dominant region for biodegradation. Consequently, COD removal of the SCOB system stabilized at >80% for real coking wastewater treatment, confirming its promising potential for the treatment of highly polluted industrial wastewater.

Advanced nutrient removal and external sludge reduction: Demonstration in a pilot-scale sequencing batch reactor

Although the addition of excess sludge fermentation products to improve nutrient removal from sewage is cost-effective, its application has rarely been demonstrated. In this study, the external sludge was first collected and fermented under a sludge retention time of 10 days, then introduced into SBR with a 1:15 sewage ratio. The results revealed a gradual increase in the nitrite accumulation ratio to 34.7% in the SBR at the end of the oxic stage after 64 days of adding fermented sludge products. In addition, the average effluent total nitrogen and phosphorous decreased to 7.3 and 0.5 mg/L, corresponding to removal efficiencies of 86.7% and 95.5%, respectively. On the other hand, the use of the fermented sludge products as external organic carbon sources in the SBR increased the external sludge reduction ratio to 42.5%. High-throughput sequencing demonstrated that the increase in the endogenous denitrifier community, polyphosphate-accumulating organisms, and fermentation bacteria were the main factors contributing to the increase in nutrient removal and excess sludge reduction. The economic evaluation indicated that the operational cost of the pilot-scale system saves 0.011$/m³ of sewage treated. PRACTITIONER POINTS: Fermented sludge addition effectively enhanced nutrient removal in pilot-scale SBR. Average effluent TN and PO₄ ^3- -P decreased to 7.3 and 0.5 mg/L, respectively. Highest external sludge reduction rate was 42.5% in pilot-scale reactor. Sewage treatment cost can save 0.011$/m³ under advanced nutrient removal.

Enhanced biological phosphorus and nitrogen removal by high-concentration powder carriers: extracellular polymeric substance, microbial communities, and metabolic pathways

In this study, diatomite, activated carbon, and iron-carbon (Fe-C) were used as biological carriers for the integrated fixed-film activated sludge process. Biomass, pollutant removal efficiency, and extracellular polymer were tested, and the effect of nitrogen and phosphorus removal, enzyme activity, and microbial diversity were studied after the sludge retention time was changed. The mechanism of carrier enriching microorganism and promoting pollutant degradation was studied. The results showed that the addition of these three carriers contributed to the enrichment of nitrifying bacteria in the system, and the NH₄⁺-N removal efficiency was above 98%. Diatomite and Fe-C could improve pollutant removal by increasing the activity of the electron transfer system. The abundance of denitrogenation-related reductases and the enzymes synthesizing poly-β-hydroxybutyrate was increased in activated carbon. The addition of Fe-C increased the abundance of denitrifying phosphate-accumulating organisms by approximately 25% and the removal efficiency of total phosphorus by 12.61-14.88% at the end of the long-term operation.

Discovering dominant ammonia assimilation: Implication for high-strength nitrogen removal in full scale biological treatment of landfill leachate

Landfill leachate containing high-strength nitrogen is generated in domestic waste landfilling. The integration of anoxic and aerobic process (AO) based on nitrification and denitrification, has been a mainstream process of biological nitrogen removal (BNR). But the high-strength organics as well as aerobic effluent reflux might change the biochemical environment designed and operated as AO. In view of the nitrogen balance in a full scale landfill leachate treatment plant with two-stage AO, we found that approximately 90% removal of total nitrogen (TN) and ammonia (NH₄⁺-N) focused on primary anoxic and aerobic stage. Meanwhile, the less nitrate and nitrite in the aerobic effluent were incapable of sustaining denitrification or anaerobic ammonia oxidation (anammox). The high reflux flow from aerobic to anoxic process enabled the similar microbial community and functional genes in anoxic and aerobic process units. However, the functional genes involving ammonia assimilation in all process units showcased the highest abundance compared to those correlated with other BNR pathways, including nitrification and denitrification, assimilatory and dissimilatory nitrate reduction, nitrogen fixation and anammox. The ammonia assimilation dominated the removals of TN and NH₄⁺-N, rather than other BNR mechanism. The insight of dominant ammonia assimilation is favorable for illustrating the authentic BNR mechanism of landfill leachate in AO, thereby guiding the optimization of engineering design and operation.

Positive effects of magnetic Fe3O4@polyaniline on aerobic granular sludge: Aerobic granulation, granule stability and pollutants removal performance

The magnetic material has been determined to have a positive effect on sludge granulation and wastewater treatment performance. In this study, the effect of magnetic Fe₃O₄@polyaniline (Fe₃O₄@PANI) on aerobic granulation, granule stability, and pollutants removal performance was evaluated by adding it into a sequencing batch reactor to cultivate aerobic granular sludge (AGS). The results indicated that the composite combined the advantages of PANI and Fe₃O₄ to promote the formation of AGS during the granulation period. The Fe₃O₄@PANI stimulated the granules to secrete extracellular polymeric substances with a higher proteins/polysaccharides ratio, thus enhancing the stability of the AGS. In addition, microbial community analysis revealed that the great performance of the AGS on denitrification and phosphorus removal could be attributed to the enrichment of denitrifying bacteria, phosphorus accumulating organisms (PAO), and denitrifying PAO by Fe₃O₄@PANI. Thus, Fe₃O₄@PANI has been demonstrated to have a positive effect on the formation and stability of AGS.

Effects of sponge iron dosage on nitrogen removal performance and microbial community structure in sequencing batch reactors

The application of sponge iron (SI) carriers can improve the biochemical treatment performance of sequencing batch reactors (SBR) during wastewater treatment. This study used SBR reactors to explore the effects of SI dosage on the nitrogen removal performance and reactor stability and microbial community structure under low temperature and ultra-low load. In contrast to conventional SBR, the average removal rate of total nitrogen (TN) in the biological sponge iron system (BSIS) was increased by 5.38 % for 45 g/L, 18.93 % for 90 g/L, and 13.52 % for 135 g/L, respectively. The nitrogen removal performance and reactor stability showed the best performance under the SI dosage of 90 g/L. The addition of SI formed the anaerobic-anoxic-aerobic microenvironments, which facilitate the propagation of denitrifying bacteria (Saccharimonadales, Hydrogenophaga) and iron bacteria (Rhodoferax and Acinetobacter) in the BSIS. This study provides a new insight on the application of SI in the wastewater treatment.

Effect of flow regime on mass transfer diffusion and stability of aerobic granular sludge (AGS) in view of interfacial thermodynamic

Aerobic granular sludge (AGS) technology has been widely studied as "The Next Generation Wastewater Treatment technology". The effect of hydraulic conditions on the structural stability of AGS has been widely studied. However, the function of flow regime on the AGS stability, especially dissolved oxygen (DO) mass transfer, is still unknown. In this study, we used the Reynolds number (Re) to quantify the flow regime and selected different stages of AGS as experimental subjects. Results showed that the relatively suitable Re (Re = 150) could create lower DO mass transfer limitation (Lc = 27.4 μm) and increase protein (PN) contents and the abundance of hydrophobic functional groups in AGS. At this condition (Re = 150), the interfacial Gibbs free energy of sludge-water (ΔG_LS^a) was at a lower state (-129.75 ± 2.15 mJ·m^-2), which favored the stability of AGS. Principal component analysis (PCA) and correlation analysis indicated that the response of ΔG_LS^a was affected by Lc, PN, and hydrophobic groups. In addition, results obtained for unstable AGS further verified that suitable Re regulates the structural stability of AGS. This study deepens the understanding of Re as an important hydraulic parameter for structural stability of AGS, which is also of great significance for energy saving of sequential batch reactors (SBRs) with agitation in practical engineering.

Nitrogen removal performance and microbial characteristics during simultaneous chemical phosphorus removal process using Fe3

To evaluate the effect of Fe³⁺ on nitrogen (N) removal and associated microbial characteristics during simultaneous chemical phosphorus (P) removal, a sequencing batch reactor was used to analyze the changes in the microbial community and metabolic pathways caused by Fe³⁺ addition. Results demonstrated that Fe³⁺ promoted ammonia nitrogen (NH₄⁺-N) removal and inhibited denitrification process, and increased the sludge particles (D50) and the biomass per sludge particle size. Furthermore, the abundances of denitrifying bacteria (Haliangium and Terrimonas) and biological phosphorus removing bacteria (Halaingium, norank_f_Saprospiraceae and SM1A02) were decreased. On the contrary, the increase of nitrifying bacteria abundance and the coding genes of nitrification-related enzymes confirmed the promotion for nitrification with Fe³⁺ addition. Besides, Fe³⁺ inhibited the interspecific relationship between denitrifying bacteria genera and other genera to reduce denitrification efficiency.

Fate, toxicity and effect of triclocarban on the microbial community in wastewater treatment systems

Triclocarban (TCC), one of the typical antimicrobial agents, is a contaminant of emerging concern commonly found in high concentration in water environments. However, the fate and toxicity of TCC in wastewater treatment systems remain poorly understood. Here, we investigated how TCC impacts chemical oxygen demand and inorganic nitrogen transformation in a hydrolytic anaerobic-anoxic/oxic process. In the anaerobic section, the transformation of TCC was dominated by reductive dechlorination and supplemented by two amid bonds hydrolysis. In the anoxic and oxic sections, the hydrolysis of amid bonds dominated. The toxicity was reduced after the treatment (IC₅₀ from 0.09 to 0.54). TCC inhibited NH₄⁺-N removal in the anaerobic section and led to the NO₃^--N accumulation (2.84-4.13 mg/L) after treatment, with the abundance of N-removal bacteria decreased by 6%. Furthermore, the original ecological niche was gradually replaced by TCC-resistant/degradative bacteria, formating new microbial modules to resist the TCC stress. Importantly, fourteen genera including Methanosaeta, Longilinea, Dokdonella and Mycobacterium as potential bioindicators warning TCC and its intermediates were proposed. Overall, this study provides new insights into the fate of TCC in biological wastewater treatment systems and suggests a great importance for TCC control to ensure the health and resilience of ecosystems.

Rapid start-up and advanced nutrient removal of simultaneous nitrification, endogenous denitrification and phosphorus removal aerobic granular sequence batch reactor for treating low C/N domestic wastewater

The rapid start-up and advanced nutrient removal of simultaneous nitrification, endogenous denitrification, and phosphorus (P) removal aerobic granular sequence batch reactor (SNEDPR-AGSBR) is a challenge in the treatment of low carbon/nitrogen (C/N) domestic sewage. In this study, the feasibility of the SNEDPR-AGSBR process was examined in an exceedingly single-stage anaerobic/aerobic/anoxic sequencing batch reactor for treating low C/N ratio (3.3-5.0) domestic sewage. The initial results showed that accompanied by the rapid formation of the mature aerobic granular sludge based on the selection for slow-growing organisms, the rapid start-up (38 d) of the SNEDPR-AGSBR process was successfully realized. The formed mature aerobic granules had a dense structure with an average diameter of 667.7 μm and SVI₃₀ of 30.0 mL/g. Two conditions for achieving the competitive balance between phosphorus-accumulating organisms/denitrifying phosphorus-accumulating organisms (PAOs/DPAOs) and glycogen accumulating organisms/denitrifying glycogen accumulating organisms (GAOs/DGAOs) were revealed by the long-term operation results. First, the dissolved oxygen (DO) concentration needed to be decreased to 3.0 mg/L in the aerobic phase, and then, the aerobic and anoxic phase hydraulic retention time (HRT) should be increased to 3.0 h. Notably, high removal efficiencies for NH₄⁺-N (100%), total nitrogen (84.3%), and P (91.8%) of the SNEDPR-AGSBR process were stably obtained with a low C/N ratio of 3.9 domestic sewage. Simultaneous nitrification and endogenous denitrification (SNED) efficiency of 61.6% was achieved during a long-term operation of 142 days. Finally, microbial community analysis confirmed that GAOs (Defluviicoccus)/DGAOs (Candidatus_Competibacter) were responsible for the removal N, and PAOs (Acinetobacter, Candidatus_Accumulibacter, Hypomicrobinm)/DPAOs (Pseudomonas and Dechloromonas) ensured P removal.

The phylogeny, ecology and ecophysiology of the glycogen accumulating organism (GAO) Defluviicoccus in wastewater treatment plants

This comprehensive review looks critically what is known about members of the genus Defluviicoccus, an example of a glycogen accumulating organism (GAO), in wastewater treatment plants, but found also in other habitats. It considers the operating conditions thought to affect its performance in activated sludge plants designed to remove phosphorus microbiologically, including the still controversial view that it competes with the polyphosphate accumulating bacterium Ca. Accumulibacter for readily biodegradable substrates in the anaerobic zone receiving the influent raw sewage. It looks at its present phylogeny and what is known about it's physiology and biochemistry under the highly selective conditions of these plants, where the biomass is recycled continuously through alternative anaerobic (feed); aerobic (famine) conditions encountered there. The impact of whole genome sequence data, which have revealed considerable intra- and interclade genotypic diversity, on our understanding of its in situ behaviour is also addressed. Particular attention is paid to the problems in much of the literature data based on clone library and next generation DNA sequencing data, where Defluviicoccus identification is restricted to genus level only. Equally problematic, in many publications no attempt has been made to distinguish between Defluviicoccus and the other known GAO, especially Ca. Competibacter, which, as shown here, has a very different ecophysiology. The impact this has had and continues to have on our understanding of members of this genus is discussed, as is the present controversy over its taxonomy. It also suggests where research should be directed to answer some of the important research questions raised in this review.

Use of sponge iron as an indirect electron donor to provide ferrous iron for nitrate-dependent ferrous oxidation processes: Denitrification performance and mechanism

Sponge iron (SI) can serve as an indirect electron donor to provide Fe(II) for the nitrate-dependent ferrous oxidation (NDFO) process, producing OH^- and magnetite. The SI-NDFO system mainly uses Fe(OH)₂ as an electron donor, achieving a TN reduction rate of 0.42 mg-TN/(gVSS·h) for a period of at least 90 days. The enrichment of iron-oxidizing bacteria and the competition of iron-carbon micro-electrolysis for reaction sites on the surface of SI are the main reasons for the improvement of total nitrogen removal efficiency (TNRE). With an influent NO₃^--N concentration of 50 mg/L and a SI concentration of 50 g/L (at pH 5.0 and 30 °C), the TNRE reached a maximum level of 38.28%. In addition, reducing the pH environment was found to improve the denitrification efficiency of the SI-NDFO system, although denitrification stability was also reduced as a result. Overall, the SI-mediated NDFO process is a promising technique.