Simultaneous nitrification–denitrification and microbial community profile in an oxygen-limiting intermittent aeration SBBR with biodegradable carriers

Partial nitrification and simultaneous denitrification in sequential anaerobic and aerobic reactors: performance and microbial community dynamics

ABSTRACTThe removal of organic matter and nitrogen from domestic sewage was evaluated using a system composed of two sequential reactors: an anaerobic reactor (ANR) with suspended sludge and an aerobic (AER) reactor with suspended and adhered sludge to polyurethane foams. Nitrogen removal consisted of AER operating at low dissolved oxygen (DO) concentrations; this favoured the simultaneous nitrification and denitrification (SND) process. The concentration of COD and N were 440 mgO2.L-1 and 37 mgTN.L-1, respectively. The operation was divided into three phases (P), lasting 51, 53, and 46 days, respectively. The initial DO concentrations applied in the AER were: 3.0 (PI) and 1.5 mg.L-1 (PII and PIII). In PIII, the AER effluent was recirculated to the ANR at a ratio of 0.25. Kinetic assays were performed to determine the nitrification and denitrification rates of the biomasses (ANR and AER in PIII). Changes in the microbial community were evaluated throughout phases PI to PIII by massive sequencing. In PIII, the best results obtained for chemical oxygen demand (COD) and total nitrogen (TN-N) removal efficiencies, were close to 94% and 65%, respectively. Under these conditions, system effluent concentrations below 30 mg COD.L-1 and 15 mg TN-N.L-1 were verified. The nitritation and nitration rates were 10.5 and 6.5 mg N.g VSS-1.h-1, while the denitrification via nitrite and nitrate were 6.8 and 5.8 mg N.g VSS-1.h-1, respectively. A mixotrophic community was prevalent, with Rhodococcus, Nitrosomonas, Pseudomnas, and Porphyromonas being dominant or co-dominant in most of the samples, confirming the SND process in the AER sludge.

Application of Biofloc-Down flow hanging sponge system to remove nitrogen components in recirculating zero water exchange aquaculture system

This study presents a novel approach to sustainable aquaculture by integrating biofloc technology (BFT) with a compact down-flow hanging sponge (DHS) reactor. The integrated BFT-DHS system effectively removed nitrogen compounds while maintaining ammonia-nitrogen (NH4+-N) concentrations below 1 mg-N L-1 without water exchange. Application of this system in a tank bred with juvenile Oreochromis niloticus showed a high NH4+-N removal rate of up to 97 % and nitrite (NO2- -N) concentrations were maintained at 0.1 ± 0.1 mg-N L-1. Microbial analysis revealed Gordonia as the predominant genus in the biofloc contributing to heterotrophic nitrification, while the Peptostreptococcaceae family dominated the DHS reactor. Heterotrophic nitrification seemed to be the primary process for enhanced nitrogen removal. Pathogenic bacteria, Vibrio sp. was absent throughout the study. This study highlights the potential integration of BFT and DHS system for sustainable aquaculture practice with effective nitrogen removal.

Wastewater Treatment with Bacterial Representatives of the Thiothrix Morphotype

Bacteria of the Thiothrix morphotype, comprising the genera Thiothrix, Thiolinea and Thiofilum, are frequently encountered in domestic and industrial wastewater treatment systems, but they are usually not clearly differentiated due to the marked similarity in their morphologies. Methods ranging from light microscopy, FISH and PCR to modern high-throughput sequencing are used to identify them. The development of these bacteria in wastewater treatment systems has both advantages and disadvantages. On the one hand, the explosive growth of these bacteria can lead to activated sludge bulking or clogging of the treatment system's membranes, with a consequent decrease in the water treatment efficiency. On the other hand, members of the Thiothrix morphotype can improve the quality of granular sludge and increase the water treatment efficiency. This may be due to their capacity for sulfide oxidation, denitrification combined with the oxidation of reduced sulfur compounds, enhanced biological phosphate removal and possibly denitrifying phosphate removal. The recently obtained pangenome of the genus Thiothrix allows the explanation, at the genomic level, of the experimental results of various studies. Moreover, this review summarizes the data on the factors affecting the proliferation of representatives of the Thiothrix morphotype.

Process optimization of a moving bed bioreactor undergoing simultaneous nitrification and denitrification for wastewater in the absence of organic carbon

Moving bed bioreactors are efficient for the removal of nitrogen effluents by simultaneous nitrification and denitrification (SND), which is particularly challenging for effluents with low C/N ratio due to insufficient carbon available for denitrification. The addition of external organic carbon in such cases increases treatment costs. Endogenous degradation of biomass offers a cost-effective and persistent source of carbon. Internal carbon leads to low denitrification rates and optimizing the biomass content leads to a sustainable solution for treating such effluents. The present study aims to optimize the process of SND using endogenous carbon by investigating the effect of operational parameters like dissolved oxygen, influent ammonium (NH4-N) loading, hydraulic retention time (HRT) and carrier filling ratio (CFR). The synthetic wastewater used in the study does not inherently contain any organic carbon, thus indicating the responsible carbon for denitrification to be of internal origin. Using a novel carrier for multispecies biofilm development, initial NH4-N concentration variation showed an insignificant effect on SND efficiency. At higher loading, nitrite accumulation due to incomplete denitrification was observed. The effect of CFR was investigated in a range of 20-35%, beyond which non-homogeneous mixing was caused in the reactor. Under controlled DO and temperature of about 5 mg/L and 28 ± 2°C, respectively, an optimum filling ratio of 35% was finalised, resulting in an SND efficiency of 97.9% at 22 h HRT for high influent NH4-N concentration of 500 mg/L. Bacteriological species identification revealed the coexistence of nitrogen-fixing, aerobic nitrifying and anaerobic denitrifying bacteria in the biofilm growing on the biocarrier.Mechanism of SND occurring in aerobic moving bed bioreactors: Laboratory-scale aerobic Moving Bed Bioreactor setup for a continuous study evaluating the influence of operational parameters on SNDOccurrence of aerobic and anoxic zones in biofilm grown on the surface of novel carriers due to diffusional gradient of dissolved oxygen.

Partial nitrification-denitrification and enrichment of paracoccus induced by iron-chitosan beads addition in an intermittently-aerated activated sludge system

Insufficient carbon source has become the main limiting factor for efficient nitrogen removal in wastewater treatment. In this study, an intermittently-aerated activated sludge system with iron-chitosan (Fe-CS) beads addition was proposed for nitrogen removal from low C/N wastewater. By adding Fe-CS beads, partial nitrification-denitrification (PND) process and significant enrichment of Paracoccus (with ability of iron reduction/ammonium oxidation/aerobic denitrification) were observed in the reactor. The accumulation rate of NO2--N reached 81.9 %, and the total nitrogen removal efficiency was improved to 93.9 % by shortening the aeration time. The higher activity of ammonium oxidizing bacteria and inhibited activity of nitrite-oxidizing bacteria in Fe-CS assisted system mediated the occurrence of PND. In contrast, the traditional nitrification and denitrification process occurred in the control group. The high-throughput sequencing analysis and metagenomic results confirmed that the addition of Fe-CS induced 77.8 % and 54.9 % enrichment of Paracoccus in sludge and Fe-CS beads, respectively, while almost no enrichment was observed in control group. Furthermore, with the addition of Fe-CS beads, the expression of genes related to outer membrane porin, cytochrome c, and TCA was strengthened, thereby enhancing the electron transport of Fe(Ⅱ) (electron donor) and Fe(Ⅲ) (electron acceptor) with pollutants in the periplasm. This study provides new insights into the direct enrichment of iron-reducing bacteria and its PND performance induced by the Fe-CS bead addition. It therefore offers an appealing strategy for low C/N wastewater treatment.

Nitrogen removal characteristics of heterotrophic nitrification-aerobic denitrification bacterium Acinetobacter ZQ-A1 and community characteristics analysis of its application in pig farm wastewater

A heterotrophic nitrifying aerobic denitrifying (HN-AD) strain ZQ-A1 with excellent denitrification performance, identified as Acinetobacter, was isolated from simultaneous nitrification and denitrification (SND) craft. ZQ-A1 was capable of removing NH4+, NO2-, and NO3-; the 21-hour removal rates were 84.84%, 87.13%, and 92.63%. ZQ-A1 has the ability to treat mixed nitrogen sources. In addition, ZQ-A1 can be well applied to actual sewage. According to the analysis of microbial community characteristics, the relative abundance of Acinetobacter in the experimental group increased from 0.06% to 2.38%, which is an important reason for the removal rate of NH4+ exceeding 99% within 30 days. The results of KEGG function prediction showed that with the addition of ZQ-A1, the relative abundance of pathways related to bacterial metabolism, such as tricarboxylic acid cycle metabolism, was higher. The research expanded the thinking of HN-AD bacteria in actual production and laid a foundation for its application in sewage treatment.

Cold-resistant performance and the promoted development of functional community with flexible metabolic patterns in a Biofilm Bio-Nutrient Removal (BBNR) system amended with supplementary carbon source for phosphorus recovery

The need for recovery of phosphorus (P) from wastewater has accelerated the retrofitting of existing bio-nutrient removal (BNR) processes into bio-nutrient removal-phosphorus recovery processes (BNR-PR). A periodical carbon source supplement is needed to facilitate the P-recovery. But the impact of this amendment on the cold resistances of the reactor and the functional microorganisms (for nitrogen and phosphorus (P) removal/recovery) are still unknown. This study presents the performances of a biofilm BNR process with a carbon source regulated the P recovery (BBNR-CPR) process operating at different temperatures. When the temperature was decreased from 25 ± 1 °C to 6 ± 1 °C, the system total nitrogen and total phosphorus removals and the corresponding kinetic coefficients decreased moderately. The indicative genes of the phosphorus-accumulating organisms (e.g., Thauera spp. and Candidatus Accumulibacter spp.) increased significantly. An increase of Nitrosomonas spp. genes aligned to polyhydroxyalkanoates (PHAs), glycine, and extracellular polymeric substance synthesis were observed, which was probably related to cold resistance. The results provide a new vision for understanding the advantages of P recovery-targeted carbon source supplementation for constructing a new type of cold-resistant BBNR-CPR processes.

Performance evaluation of moving bed bioreactor for simultaneous nitrification denitrification and phosphorus removal from simulated fertilizer industry wastewater

With increasing demand for agricultural production, chemical fertilizers are now being intensively manufactured and used to provide readily available nutrients in larger quantities, which often leach out and contaminate the groundwater source. At the same time, effluents from fertilizer plants also pollute water bodies, when disposed of without proper treatment. The present study evaluates nitrogen and phosphorus removal efficiencies in a single-stage aerobic moving bed bioreactor (MBBR) from diammonium phosphate (DAP)-spiked wastewater containing no organic carbon. To date, no similar study has been undertaken that treats fertilizer plant effluent or agricultural runoff without the aid of external carbon, where organic carbon is hypothesized to be supplied from endogenous degradation of biomass. Both denitrification and phosphorus removal occurs in the anoxic zones of deeper layers of the biofilm. The present investigation demonstrates the feasibility of the processes with the requirement of a two-stage MBBR for effective simultaneous nitrification, denitrification, and phosphorus removal (SNDPr) together with a polishing technology to bring down the phosphorus concentration within limits. A novel bio-carrier designed for efficient SND was used in the study, with a carrier filling ratio of 35% that supported the formation of deep biofilms creating anoxic zones in the inner surface. Identification of the bacterial species reflects the occurrence of simultaneous nitrification, denitrification, and phosphorous removal (SNDPr) in the reactor. A maximum ammonium nitrogen removal efficiency of 98% was recorded with 95% total nitrogen removal, 69% phosphorus removal, and 85% SND efficiency, indicating the applicability of the process with a tertiary phosphorus removal unit to lower the nutrient concentration of effluents prior to disposal.

Simultaneous nitrification-denitrification in biofilm systems for wastewater treatment: Key factors, potential routes, and engineered applications

Simultaneous nitrification-denitrification (SND) is an advantageous bioprocess that allows the complete removal of ammonia nitrogen through sequential redox reactions leading to nitrogen gas production. SND can govern nitrogen removal in single-stage biofilm systems, such as the moving bed biofilm reactor and aerobic granular sludge system, as oxygen gradients allow the development of multilayered biofilms including nitrifying and denitrifying bacteria. Environmental and operational conditions can strongly influence SND performance, biofilm development and biochemical pathways. Recent advances have outlined the possibility to reduce the carbon and energy consumption of the process via the "shortcut pathway", and simultaneously remove both N and phosphorus under specific operational conditions, opening new possibilities for wastewater treatment. This work critically reviews the factors influencing SND and its application in biofilm systems from laboratory to full scale. Operational strategies to enhance SND efficiency and hints to reduce nitrous oxide emission and operational costs are provided.

A divided flow aerobic-anoxic baffled reactor for simultaneous nitrification-denitrification of domestic wastewater

A novel aerobic-anoxic baffled reactor is designed for the effective denitrification of real domestic wastewater without an external carbon source. The flow is divided between two inlets at the beginning of each zone to provide a carbon source for the denitrifying bacteria. The effects of operating parameters such as the ratio of chemical oxygen demand to nitrogen (COD/N), flow division ratio, and hydraulic retention time (HRT) on the nitrogen removal were investigated. The optimum values of COD/N and HRT were estimated using response surface methodology (RSM) coupled with a central composite experimental design. The addition of porous biomass support media considerably improved the denitrification and removal of COD. Furthermore, the aerobic-anoxic system showed high stability against sudden HRT and COD/N ratio changes. The microbial analysis showed that Alcaligenes, Achromobacter, and Bordetella were the dominant denitrifying bacteria in the anoxic zone, whereas other species coexisted in the aerobic zone.

Investigation of an intermittently-aerated moving bed biofilm reactor in rural wastewater treatment under low dissolved oxygen and C/N condition

An intermittently-aerated moving bed biofilm reactor (MBBR) was proposed for nitrogen and carbon removal from low C/N synthetic rural wastewater. In purposes of low energy consumption and costs, the intermittent aeration modes were changed and the dissolved oxygen was reduced gradually during the operation. The results showed that effluent concentrations of ammonia nitrogen and chemical oxygen demand were lower than 15 and 50 mg/L, respectively, even under microaerobic condition (0.1-1.0 mg/L). Meanwhile, the simultaneous nitrification-denitrification was achieved by intermittent aeration. The activity of functional bacteria was still high and the proportion of autotrophic biomass increased significantly under intermittent micro-aeration mode, which improved the nitrification performance. Aerobic denitrifier Hydrogenophaga, anoxic denitrifier Thiothrix, and heterotrophic nitrifier such as Rhodobacter were enriched in the intermittently micro-aerated MBBR, which will provide an applicable solution for rural wastewater treatment under low C/N and costs.

The intrinsic relevance of nitrogen removal pathway to varying nitrate loading rate in a polycaprolactone-supported denitrification system

Up to date, the intrinsic association of nitrate loading rate (NLR) with treatment performance of solid-phase denitrification (SPD) systems is still ambiguous. To address this issue, three continuous up-flow bioreactors were configured. They were packed with polycaprolactone (PCL) under a filling ratio of 30%, 60% or 90% and were operated under a varying NLR of 0.34 ± 0.01-3.99 ± 0.12 gN/(L·d). Results showed that the denitrification efficiency was high (RE > 96%) and stable except the case with the highest NLR, which was mainly attributed to the lack of available carbon sources. At the phylum or genus level, most of the detected dominant bacterial taxa were either associated with organics degradation or nitrogen metabolism. The difference in bacterial community structure among the three stages was mainly caused by NLR rather than the filling ratio. Moreover, as the NLR got higher, the Bray-Curtis distance between samples from the same stage became shorter. By the results of gene or enzyme prediction performed in PICRUSt2, the main nitrogen metabolism pathways in these reactors were denitrification, dissimilatory nitrate reduction to ammonium (DNRA), assimilatory nitrate reduction to ammonium (ANRA) and nitrogen fixation. Moreover, aerobic and anaerobic nitrate dissimilation coexisted in the systems with the latter playing a dominant role. Finally, denitrification and DNRA occurred under both high and low NLR conditions while nitrogen fixation and ANRA preferred to occur under low NLR environments. These findings might help guide practical applications.

Elevated Atmospheric CO2 Modifies Mostly the Metabolic Active Rhizosphere Soil Microbiome in the Giessen FACE Experiment

Elevated levels of atmospheric CO2 lead to the increase of plant photosynthetic rates, carbon inputs into soil and root exudation. In this work, the effects of rising atmospheric CO2 levels on the metabolic active soil microbiome have been investigated at the Giessen free-air CO2 enrichment (Gi-FACE) experiment on a permanent grassland site near Giessen, Germany. The aim was to assess the effects of increased C supply into the soil, due to elevated CO2, on the active soil microbiome composition. RNA extraction and 16S rRNA (cDNA) metabarcoding sequencing were performed from bulk and rhizosphere soils, and the obtained data were processed for a compositional data analysis calculating diversity indices and differential abundance analyses. The structure of the metabolic active microbiome in the rhizospheric soil showed a clear separation between elevated and ambient CO2 (p = 0.002); increased atmospheric CO2 concentration exerted a significant influence on the microbiomes differentiation (p = 0.01). In contrast, elevated CO2 had no major influence on the structure of the bulk soil microbiome (p = 0.097). Differential abundance results demonstrated that 42 bacterial genera were stimulated under elevated CO2. The RNA-based metabarcoding approach used in this research showed that the ongoing atmospheric CO2 increase of climate change will significantly shift the microbiome structure in the rhizosphere.

Performance and bacterial community of bio-electrochemical system treating simulated domestic wastewater containing low concentration of cephalosporin antibiotics

This study investigated the effects of five cephalosporin antibiotics (ceftazidime, ceftriaxone, cefdinir, cefixime and cefepime) on performance and bacterial community structure in bio-electrochemical systems (BES) and sequencing batch biofilm reactor (SBBR). The results showed that the external electric field had no significant effect on the removal of COD and ammonia nitrogen in water. The removal rates of five antibiotics in BES increased by 28.5%, 20.0%, 9.1%, 21.0%, and 11.5%, respectively. High-through sequencing showed that microbial membrane-growing process increased species diversity, and antibiotics had a significant inhibitory effect on the initial biofilm of the reactor. As time progressed, the inhibitory effect was weakened, and the microorganism were tolerated and re-enriched. The increase in the type and concentration of antibiotics and the applied electric field had a significant effect on the microorganisms in the reactor. The dominant microorganisms for antibiotic removal in the SBBR were Luteococcus, Cloacibacterium, Dysgonomonas, and Ottowia. The dominant bacteria in the BES were Ottowia and Tahibacte. The abundance of these strains increased significantly during antibiotic acclimation. The abundance of Ottowia, Tahibacter, and Nakamurella were significantly higher than SBBR. Thus the BES system had a good antibiotic degradation effect. The BES can effectively treat simulated domestic sewage containing multiple antibiotics, laying a theoretical foundation for the actual wastewater treatment.

Denitrification performance and microbial community of bioreactor packed with PHBV/PLA/rice hulls composite

In this study, a novel biodegradable PHBV/PLA/rice hulls (PPRH) composite was applied and tested as biofilm attachment carrier and carbon source in two bioreactors for biological denitrification process. The denitrification performance, effect of operational conditions and microbial community structure of PPRH biofilm were evaluated. The batch experiment results showed that PPRH-packed bioreactor could completely remove 50 mg L^-1 of NO₃^--N at natural pH (ca. 7.5) and room temperature. The continuous flow experiments indicated that high NO₃^--N removal efficiency (77%-99%) was achieved with low nitrite (<0.48 mg L^-1) and ammonia (<0.81 mg L^-1) accumulation, when influent NO₃^--N concentration was 30 mg L^-1 and hydraulic retention time was 2-6 h. Furthermore, the microbial community analysis indicated that bacteria belonging to genus Diaphorobacter in phylum Proteobacteria were the most dominant and major denitrifiers in denitrification. In summary, PPRH composite was a promising carbon source for biological nitrate removal from water and wastewater.

Simultaneous nitrification and denitrification in continuous flow MBBR with novel surface-modified carriers

ABSTRACTMoving-Bed Biofilm Reactor (MBBR) process is an ideal preference for simultaneous nitrification and denitrification (SND) attributing to the longer sludge age and aerobic/anoxic microenvironment along biofilm. However, conventional carriers generally exhibit negative charge and surface hydrophobicity, which are unbeneficial for biofilm formation. In this study, novel surface-modified carriers with favourable hydrophilicity (surface contact angle dropped to 60.2 ± 2.3°) and positive surface charge (+11.7 ± 1.1 mV, pH 7.0) were prepared via polymer blending and implemented for SND in continuous flow MBBR system. Results indicated SND started up quickly with more biomass in MBBR filled with surface-modified carriers. At the operation condition of low dissolved oxygen level (0.75 ± 0.25 mg/L), pH of 7.5 ± 0.5, 23 ± 2°C and C/N ratio of 7, COD, NH₄⁺-N and TN removal efficiencies were 90.5%, 88.6% and 76.6% respectively in MBBR filled with surface-modified carriers, which ensured the effluent met the first grade A of the Discharge Standard of China. On the contrary, COD, NH₄⁺-N and TN removal efficiencies were 89.7%, 82.3% and 60.4% respectively in the control reactors filled with conventional polyethylene carriers. The worse performance of the control reactor was mainly attributed to the less biomass and lower functional bacteria abundance developed on conventional carriers. Moreover, novel carriers provided a favourable niche for more types of functional bacteria, of which autotrophic nitrification, anoxic denitrification, heterotrophic nitrification and aerobic denitrification co-existed and participated in nitrogen removal.

Recent advancements in the biological treatment of high strength ammonia wastewater

The estimated global population growth of 81 million people per year, combined with increased rates of urbanization and associated industrial processes, result in volumes of high strength ammonia wastewater that cannot be treated in a cost-effective or sustainable manner using the floc-based conventional activated sludge approach of nitrification and denitrification. Biofilm and aerobic granular sludge technologies have shown promise to significantly improve the performance of biological nitrogen removal systems treating high strength wastewater. This is partly due to enhanced biomass retention and their ability to sustain diverse microbial populations with juxtaposing growth requirements. Recent research has also demonstrated the value of hybrid systems with heterogeneous bioaggregates to mitigate biofilm and granule instability during long-term operation. In the context of high strength ammonia wastewater treatment, conventional nitrification-denitrification is hampered by high energy costs and greenhouse gas emissions. Anammox-based processes such as partial nitritation-anammox and partial denitrification-anammox represent more cost-effective and sustainable methods of removing reactive nitrogen from wastewater. There is also growing interest in the use of photosynthetic bacteria for ammonia recovery from high strength waste streams, such that nitrogen can be captured and concentrated in its reactive form and recycled into high value products. The purpose of this review is to explore recent advancements and emerging approaches related to high strength ammonia wastewater treatment.

Long-term operation of bio-catalyzed cathodes within continuous flow membrane-less microbial fuel cells

Microorganisms were observed to facilitate cathodic oxygen reduction and enhance cathode performance of microbial fuel cells (MFCs). However, the long-term activity and stability of bio-catalyzed cathode needs to be explored. This study evaluated the long-term performance of bio-catalyzed cathode and iron(II) phthalocyanine (FePc)-catalyzed cathode MFCs through effluent water quality, electricity production and electrochemical impedance spectroscopy (EIS) analysis under different scenarios, including conventional wastewater treatment and energy harvesting using a power management system (PMS). During the continuous operation, both systems demonstrated high chemical oxygen demand and ammonium removal, but bio-catalyzed cathode MFCs could achieve significantly better total nitrogen removal than FePc-catalyzed cathode MFCs. The FePc-coated cathode showed constant cathode potential during the entire operation period, but the biocathode showed varied but step-wise increased cathode potential to achieve more than 500 mV versus the standard hydrogen electrode, likely due to the gradual enrichment of biocathode biofilm. EIS analysis revealed that biocathode had higher ohmic resistance than bare carbon felt cathode but the microbial biofilm could largely decrease polarization resistance of cathode material. Microbial community analysis has shown the presence of nitrifying and denitrifying bacteria in the bio-catalyzed cathode biofilm. When connecting PMS, both bio-catalyzed cathode and FePc-catalyzed cathode MFCs successfully charged a capacitor, but the bio-catalyzed cathode MFC voltage significantly dropped to less than 100 mV after charging for 91 h, and gradually recovered when disconnecting PMS. This study has demonstrated the potential application of oxygen reduction bio-catalyzed cathode MFCs for continuous wastewater treatment and energy harvesting for long period of time.

Carbon availability shifts the nitrogen removal pathway and microbial community in biofilm airlift reactor

This study investigated the response of nitrogen removal performance and microbial community to different carbon composites in biofilm airlift reactors for wastewater treatment. Three reactors were filled with poly (butylene succinate) and bamboo powder composite at the blending ratio of 9:1, 1:1 and 1:9. Increasing the component of bamboo powder in the carrier reduced the carbon availability and had an adverse effect on nitrate removal efficiency. However, bamboo powder improved the ammonia removal rate which mainly through autotrophic nitrification. Three reactors exhibited distinct microbial compositions in both bacterial and fungal diversity. High inclusion of bamboo power decreased the relative abundance of denitrifiers Denitromonas and increased the relative abundance of nitrifiers, including Nitromonas, Nitrospina and Nitrospira. Moreover, correlation network revealed a competitive interaction between the taxa responsible for ammonia removal and nitrate removal processes. Those results indicated the feasibility of steering nitrogen removal pathway through carrier formulation in wastewater treatment.

Dynamics of denitrification performance and denitrifying community under high-dose acute oxytetracycline exposure and various biorecovery strategies in polycaprolactone-supported solid-phase denitrification

Solid-phase denitrification (SPD) is a promising technology for nitrate-rich water purification. This study aimed to examine the variation in denitrification performance and denitrifying community under high-dose acute oxytetracycline (OTC) exposure and various biorecovery strategies. The denitrification performance was impaired significantly after one-day OTC shock at 50 mg L^-1 in a continuous-flow SPD system supported by a polycaprolactone (PCL) carrier but could rapidly recover without the addition of OTC. When 50 mg L^-1 OTC stress was applied for a longer time in the batch tests, a natural recovery period of more than 20 days was required to reach more than 95% nitrate reduction. Under the same conditions, the addition of both mature biofilm-attached PCL carrier and fresh biofilm-free PCL carrier significantly shortened the recovery time for efficient nitrate reduction, mainly due to the increase in organic availability from the PCL carriers. However, the composition of the microbial community notably changed due to the effects of OTC according to high-throughput sequencing and metagenomic analysis. Genes encoding NAR and NIR were much more sensitive than those encoding NOR and NOS to OTC shock. Tetracycline resistance gene (TRG) enrichment was 15.86% higher in the biofilm that experienced short-term OTC shock than in the control biofilm in the continuous-flow SPD system.

Removal of bisphenol A by waste zero-valent iron regulating microbial community in sequencing batch biofilm reactor

The removal of bisphenol A (BPA) by waste zero-valent iron (ZVI) regulating microbial community in sequencing batch biofilm reactor (SBBR) was investigated. Compared with SBBR_-BPA, the acclimation time of microorganisms in the presence of waste ZVI and BPA (SBBR_-ZVI+BPA) decreased from 56 d to 49 d. During stable operation period, BPA was removed completely at 150th min and 100th min in the SBBR_-BPA and SBBR_-ZVI+BPA, respectively. The optimal initial pH and BPA concentration in the SBBRs were respectively 8.0 and 10 mg/L. The composition and content analysis of extracellular polymeric substances (EPS) using fluorescence spectrometer showed that the yield of EPS was enhanced by the addition of ZVI. The analysis of microbial community structure in the SBBRs using Illumina Miseq sequencing method indicated that the indexes of ACE, Chao1 and Shannon were higher and Simpson index was lower in the SBBR_-ZVI+BPA. Moreover, the abundance of BPA biodegradation strains was increased in the presence of ZVI. This study provided a promising method with low cost of effectively removing BPA from wastewater.

The influence mechanism of temperature on solid phase denitrification based on denitrification performance, carbon balance, and microbial analysis

In this work, the influence mechanism of temperature on solid phase denitrification (SPD) was investigated using a pilot-scale reactor supported with polycaprolactone (PCL). The results showed that under nitrate loads of ~31.5 mg N/(L·h), as temperature decreased from 30 °C to 13 °C, the nitrate removal efficiency declined from 94% to 57%. Furthermore, denitrification rate constants were input into Arrhenius equation and the resulting temperature coefficient was 1.04. Significantly nitrite accumulation and less effluent COD residue occurred at low-temperatures. Via stoichiometry, the sludge yield coefficient and COD demand for nitrate removal both increased as a function of increasing temperature; and were calculated at 20 °C as 0.069 g MLVSS/(g COD·d) and 3.265 g COD/g N, respectively. Carbon balance analysis indicated that the COD release rate (υ) at 30 °C was twice that at 13 °C. LEfSe analysis demonstrated that Desulfomicrobium, Desulfovibrio, and Meganema were abundant at low-temperature, while Simplicispira, Aquabacterium, and Acidovorax were enriched at high-temperature. Besides, carboxylesterase (PCL depolymerase) was more abundant at high-temperature, implying an association with a fast υ. Moreover, nar was enriched at low-temperature, while nir was depleted, which led to nitrite accumulation. These results provide reference for SPD design parameter estimation and/or optimal operation strategy.

Response of denitrifying community, denitrification genes and antibiotic resistance genes to oxytetracycline stress in polycaprolactone supported solid-phase denitrification reactor

The coexistence of nitrate and antibiotics in wastewater is a common problem. The study aimed to explore the response of denitrifying community, denitrification genes and antibiotic resistance genes (ARGs) to oxytetracycline (OTC) stress in polycaprolactone (PCL) supported solid-phase denitrification (SPD) reactors. Complete nitrate reduction (greater than99%) was achieved in SPD system with OTC stress of 0, 0.05, 0.25 and 1 mg L^-1 during three-month operation, while it significantly declined by about 5% at a further increased OTC level of 5 mg L^-1. The efficient denitrification strongly related with a rich diversity of denitrifiers, while the abundances of which dramatically reduced as the OTC concentration reached ≥0.25 mg L^-1, which caused significant decline of denitrification genes, especially for narH, narJ, narI nirD, nosZ, and norB. Tetracycline resistance genes were a major type of promoted ARGs by different OTC stress, mainly related with the increase of tet36, tetG, tetA, tetM and tetC.

Simultaneous nitrification and denitrification process using novel surface-modified suspended carriers for the treatment of real domestic wastewater

Moving-bed biofilm reactor (MBBR) is a well-established technology for simultaneous nitrification and denitrification (SND). In MBBR, biofilm development and pollutant removal performance are strictly governed by the physico-chemical properties of the carriers. In this study, novel surface-modified carriers with enhanced hydrophilicity (surface contact angle of 60.2 ± 2.3°) and positively-charged surfaces (+11.7 ± 1.1 mV, pH 7.0) had been prepared successfully via polymer blending, and they had also been implemented in SND system for the treatment of real domestic wastewater. Results showed that accelerated startup of SND with more biomass on the carriers was observed in MBBR system filled with surface-modified carriers. At low DO level (0.6-0.8 mg L^-1) and low C/N ratio (≤5), highly efficient organics removal and SND performance could be achieved with COD removal, TN removal and SND efficiencies of 79.3-85.7%, 62.0-75.9% and 58.5-71.8%, respectively. The efficient performance of SND in MBBR system filled with surface-modified carriers was mainly attributed to the coexistence of enriched mixtrophic nitrifiers and denitrifiers like autotrophic nitrifers (Nitrosomonas, Nitrospira, Nitrobacter), heterotrophic nitrifers (Rudaea), aerobicdenitrifiers (Dokdonella, Terrimonas), anoxic denitrifiers (Gemmobacter, Ottowia, Methyloversatilis, Thermomonas) and N₂O producer (Mesorhizobium).

Coupling ammonia nitrogen adsorption and regeneration unit with a high-load anoxic/aerobic process to achieve rapid and efficient pollutants removal for wastewater treatment

In this study, an ammonium nitrogen (NH₄⁺-N) adsorption and regeneration (AAR) was constructed by a zeolite-packed column and NaClO-NaCl regeneration unit, and coupled with an anoxic/aerobic (AO) system to achieve efficient removal of carbon, nitrogen and phosphorus under short hydraulic retention time (HRT) and sludge retention time (SRT). Compared to conventional anaerobic/anoxic/aerobic (AAO) process, the proposed AO-AAR process achieved more efficient and stable nitrogen removal with greatly shorter HRT (5.6 h) and SRT (8 d) at 10.4 °C, with NH₄⁺-N and total nitrogen in the effluent below 1.5 and 8.0 mg/L, respectively. The AO-AAR also obtained efficient phosphorus removal (<0.5 mg/L) by dosing aluminum in aerobic tank. High load and short SRT deteriorated sludge settleability and dewaterability, but enhanced methane production by improving sludge biodegradability. Dosing aluminum made the AO operating module more stable with improved settleability and dewaterability, and further enhanced methane production. Short HRT and SRT also resulted in the thriving of filamentous bacteria (Thiothrix) and heterotrophic nitrifiers (Acinetobacter, Pseudomonas and Rhodobacter) in the AO module, which helped in enhancing denitrification potential and nitrification efficiency under low temperature. Long-term operation showed that exchange capacity and physicochemical properties of zeolite were unchanged under NaClO-NaCl regeneration by introducing the tail gas from aerobic tank into the used regenerant to remove Ca²⁺ and Mg²⁺ exchanged from effluent of the AO module. Techno-economic analysis showed that the AO-AAR process is attractive and sustainable for municipal wastewater treatment by significantly improving nitrogen removal, greatly reducing land occupancy, enhancing methane production and achieving efficient reduction of carbon dioxide emission.

Identification and nitrogen removal characteristics of Thauera sp. FDN-01 and application in sequencing batch biofilm reactor

A strain FDN-01 was isolated from the sequencing batch biofilm reactor (SBBR) which was seeded with wasted activated sludge from a municipal wastewater treatment plant in Shanghai. Bacterium FDN-01 was identified as Thauera sp., and Genbank Sequence_ID was KY393097. By comparing inorganic total nitrogen (TN) removal efficiency by strain FDN-01 under different conditions, the optimal initial pH, carbon source and the ratio of carbon to nitrogen were 7.5, sodium succinate and 4.0, respectively. Inorganic TN removal efficiency was 93% within 3 d while the concentration of nitrate was 100 mg/L, and the type of substrates affected extracellular polymeric substances (EPS) production and the ratio of protein to polysaccharide in the EPS. Further investigation for the application of strain FDN-01 in the SBBRs showed that anoxic ammonia oxidation occurred at room temperature, and the removal efficiencies of inorganic TN were noticeably enhanced by the augmentation of bacterium FDN-01 back into the SBBR. This study provided a promising method of TN removal requiring less carbon source in the wastewater.

Nitrogen removal from wastewater via simultaneous nitrification and denitrification using a biological folded non-aerated filter

A conventional biological filter has been shown to be a viable method for removing nitrogenous compounds from wastewater, but it still has many disadvantages. In this study, a biological folded non-aerated filter (BFNAF) was designed, and its feasibility for nitrogen-loaded wastewater treatment has been confirmed. Effects of the HRT and the COD/N ratio on the performance of BFNAF were investigated. Through response surface method, when the COD/N ratio and the HRT were 5.39 and 10.83 h, removal efficiencies of NH₄⁺, COD and TN reached maximum values of 88.62 ± 0.81%, 76.12 ± 0.57%, and 50.48 ± 1.02%, respectively. In addition, it was found that several denitrifying bacteria, such as Azoarcus, Arcobacter, Flavobacterium, along with many ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, co-existed in the community of the biofilm. All the results showed that the BFNAF could realize the simultaneous nitrification and denitrification (SND) process effectively.

Effects of 2,4,6-trichlorophenol on simultaneous nitrification and denitrification: Performance, possible degradation pathway and bacterial community structure

This study aimed to investigate the effect of different 2,4,6-trichlorophenol (TCP) concentrations on the performance of simultaneous nitrification and denitrification processes established in a sequential batch biofilm reactor. And the degradation and the possible degradation pathway of 2,4,6-TCP and microbial community structure were also explored. Results indicated that 2,4,6-TCP inhibited the nitrification with the decrease in ammonium nitrogen removal. However, 2,4,6-TCP had different effects on denitrification. Nitrate accumulation showed the tendency to decrease first and then increase, whilst nitrite accumulation showed the opposite with a small change. The adaptation and recovery time of 25 mg/l 2,4,6-TCP was longest. In addition, the process had a good degradation effect on 2,4,6-TCP. Comparing the degradation of 2,4,6-TCP under different concentrations, the result showed that 2,4,6-TCP was mainly reduced to 2,4-dichlorophenol. With the increase in 2,4,6-TCP concentration, the differences in the bacterial community in the reactor were significant.

Establishing simultaneous nitrification and denitrification under continuous aeration for the treatment of multi-electrolytes saline wastewater

Simultaneous nitrification and denitrification (SND) was established under continuous aeration (6 mgO₂ L^-1) aiming at achieving a feasible and simple operational strategy for treating multi-electrolyte saline wastewaters. Two Structured Fixed-Bed Reactors (SFBR) were used to assess SND performance with (Saline Reactor, SR) and without (Control Reactor, CR) salinity interference. Salinity was gradually increased (from 1.7 to 9 atm) based on the composition of water supplied in arid regions of Brazil. At 1.7 atm, N-NH₄⁺ oxidation and Total Nitrogen (TN) removal efficiencies of 95.9 ± 2.8 and 65.76 ± 7.5%, respectively, were obtained. At osmotic pressure (OP) of 9 atm, the system was severely affected by specific salt toxicity and OP. High chemical oxygen demand (COD) removal efficiency was achieved at all operational conditions (97.2 ± 1.6 to 78.5 ± 4.6%). Salinity did not affect microbial diversity, although it modified microbial structure. Halotolerant genera were identified (Prosthecobacter, Chlamydia, Microbacterium, and Paenibacillus).

N2O production from hydroxylamine oxidation and corresponding hydroxylamine oxidoreductase involved in a heterotrophic nitrifier A. faecalis strain NR

N₂O production from NH₂OH oxidation involved in a heterotrophic nitrifier Alcaligenes faecalis strain NR was studied. ¹⁵N-labeling experiments showed that biological NH₂OH consumption by strain NR played a dominant role in N₂O production, although chemical reaction between NH₂OH and O₂ indeed existed. Hydroxylamine oxidoreductase (HAO) from strain NR was partially purified by (NH₄)₂SO₄ fractionation and DEAE Cartridge chromatography. The maximum activity of HAO was 9.60 mU with a specific activity of 92.04 mU/(mg protein) when K₃Fe(CN)₆ was used as an electron acceptor. The addition of Ca²⁺ promoted the HAO activity, while the presence of Mn²⁺ inhibited the enzyme activity. The optimal temperature and pH for HAO activity were 30 °C and 8. Analysis of enzyme-catalyzed products demonstrated that NH₂OH oxidation catalyzed by HAO from strain NR played significant role in the production of N₂O.