Effect of different carbon sources on denitrification performance, microbial community structure and denitrification genes

Study on the simultaneous removal of fluoride, heavy metals and nitrate by calcium precipitating strain Acinetobacter sp. H12

The removal properties and mechanisms of fluoride (F^-) and nickel (Ni²⁺) were studied by biomineralizing bacteria (Acinetobacter sp. H12). The results showed that the removal ratio of F^-, Ca²⁺ and Ni²⁺ reached 75% (0.031 mg·L^-1·h^-1), 84.96% (2.123 mg·L^-1·h^-1), and 56.67% (0.024 mg·L^-1·h^-1) after 72 h, respectively. The removal ratio of nitrate (NO₃^-) reached 100% (0.686 mg·L^-1·h^-1) after 24 h. SEM and XRD images indicated that bioprecipitation of CaF₂, Ca₅(PO₄)₃F, Ca₅(PO₄)₃(OH), NiCO₃, CaCO₃ and Ni were formed, and some of these precipitation used bacteria as nucleation sites to form biological crystal seeds. N₂ was the primary product in gas chromatography analysis. Meanwhile, both the fluorescence spectroscopy and fourier transform near-infrared spectroscopy analysis proved that strain H12 had good ability to remove fluoride and nickel ions simultaneously.

Multi-omics analysis reveals structure and function of biofilm microbial communities in a pre-denitrification biofilter

The highly complex microbial communities in biofilm play crucial roles in the pollutant removal performance of wastewater treatment plants (WWTPs). In the present study, using multi-omics analysis, we studied microbial structure, key enzymes, functional traits, and key metabolic pathways of pre-denitrification biofilter in an urban WWTP in China. The analysis results of metagenomic and metaproteomic showed that Betaproteobacteria and Flavobacteriia were dominant in biofilms. The integrated metagenomic and metaproteomic data showed that the expression of nitrogen metabolism genes was high, and the high proportion of denitrification module indicating that denitrification was the main nitrogen removal pathway. The most abundant denitrifying bacterial genera were: Dechloromonas, Acidovorax, Bosea, Polaromonas, and Chryseobacterium. And microorganisms with denitrification potential may not be able to denitrify in the actual operation of the filter. The integrated analysis of metaproteomic and metabolomic showed that there was a correlation between biofilm microorganisms and metabolites. Metabolomic analysis indicated that metabolic profiles of biofilms varied with layer height. This study provides the first detailed microbial communities and metabolic profiles in a full-scale pre-denitrification biofilter and clarifies the mechanism of denitrification.

Optimization of nitrate and selenate reduction in an ethanol-fed fluidized bed reactor via redox potential feedback control

Electron donors are a major cost-factor in biological removal of oxyanions, such as nitrate and selenate from wastewater. In this study, an online ethanol dosing strategy based on feedback control of oxidation-reduction potential (ORP) was designed to optimize the performance of a lab-scale fluidized bed reactor (FBR) in treating selenate and nitrate (5 mM each) containing wastewater. The FBR performance was evaluated at various ORP setpoints ranging between -520 mV and -240 mV (vs. Ag/AgCl). Results suggested that both nitrate and selenate were completely removed at ORPs between -520 mV and -360 mV, with methylseleninic acid, selenocyanate, selenosulfate and ammonia being produced at low ORPs between -520 mV and -480 mV, likely due to overdosing of ethanol. At ORPs between -300 mV and -240 mV, limited ethanol dosing resulted in an apparent decline in selenate removal whereas nitrate removal remained stable. Resuming the ORP to -520 mV successfully restored complete selenate reduction. An optimal ORP of -400 mV was identified for the FBR, whereby selenate and nitrate were nearly completely removed with a minimal ethanol consumption. Overall, controlling ORP via feedback-dosing of the electron donor was an effective strategy to optimize FBR performance for reducing selenate and nitrate in wastewater.

Primary sludge as solid carbon source for biological denitrification: System optimization at micro-level

Commercial carbon source (e.g. methanol) has been frequently used to enhance heterotrophic denitrification for nitrate removal. However, this is not sustainable due to the high cost of chemical purchasing and excessive sludge production. To address these issues, this study reports an integrated denitrification system using primary sludge as solid carbon source. Complete denitrification without any nitrite accumulation achieved at the primary sludge dosage of 6.0 g VSS/g N with the maximum specific nitrate reduction rate of 6.4 mg N/g VSS/h, which was comparable with the reported soluble carbon source. More importantly, as a solid "waste" in municipal wastewater treatment plants (WWTPs), the primary sludge was simultaneously reduced by 65.3%-85.1%, and this avoids the intensive denitrification biomass generation that generally occurs in using the commercial carbon source. Ammonium, phosphate, and recalcitrant organic matter were released meantime. Interestingly, the concentration of ammonium and phosphate declined during the denitrification process. The refractory dissolved organics mainly composed of aromatic protein and microbial by-products. The detailed cycle study suggests that an appropriate denitrification cycle/duration time would largely lower the effluent organics concentration, which can be achieved by monitoring the pH turning point. This study clearly demonstrates that primary sludge is a promising alternative carbon source for biological denitrification with great economic benefits and environmental sustainability.

Effect of nickel on the comparative performance of inverse fluidized bed and continuously stirred tank reactors for biogenic sulphur-driven autotrophic denitrification

The comparative performance of an inverse fluidized bed reactor (IFBR) having high density polyethylene beads as carrier materials for biofilm formation and a continuous stirred tank reactor (CSTR), both maintaining autotrophic denitrification using biogenic sulphur (ADBIOS) in the absence and presence of nickel (Ni²⁺), was studied. The reactors were compared in terms of NO₃^--N and NO₂^--N removal and SO₄^2--S production throughout the study. A simulated wastewater with an inlet NO₃^--N concentration of 225 mg/L and a decreasing concentration of biogenic sulphur (bio-S) from 1.5 to 0.375 g/L was used. Both reactors were operated at a hydraulic retention time (HRT) of 48 h for 140 days and at an HRT of 42 h for the following 68 days. A more efficient ADBIOS was observed in the CSTR than IFBR throughout the study due to a better mixing of the feed wastewater in the bulk liquid and a higher availability of bio-S to the suspended cells. The NO₃^--N removal efficiency in the IFBR decreased by approximately 41% when the feed bio-S was reduced to 0.375 g/L, while it remained unaffected in the CSTR. Conversely, the presence of Ni²⁺ did not significantly affect NO₃^--N removal in both reactors even at a feed Ni²⁺ concentration of 120 mg/L. The highest NO₃^--N removal rates achieved were 86 and 108 mg NO₃^--N/(L·day) in the IFBR and CSTR, respectively, in the presence of 120 mg/L of feed Ni²⁺ at an HRT of 42 h. Batch studies conducted with acclimatized biomass showed that the continuous-flow operation mode in both reactors played a major role in helping the autotrophic denitrifiers to tolerate Ni²⁺ toxicity.

Low-dose Ultraviolet-A irradiation selectively eliminates nitrite oxidizing bacteria for mainstream nitritation

Nitritation is currently known as a bottleneck for mainstream nitrite shunt or partial nitritation/anammox (PN/A). Here we propose a new approach to selectively eliminate nitrite oxidizing bacteria (NOB) for mainstream nitritation by low-dose ultraviolet-A (UVA) irradiation. The results showed that mainstream nitritation was rapidly achieved within 10 days with UVA irradiation at the dose of 0.87 μE L^-1 s^-1, and nitrite accumulation ratio (NO₂^--N/(NO₂^--N + NO₃^--N) ×100%) stabilized over 80%. Microbial community analysis revealed that two typical NOB populations (Nitrospira and Ca. Nitrotoga) detected in the control reactor were suppressed efficiently in UVA irradiation reactor, whereas the Nitrosomonas genus of ammonium oxidizing bacteria (AOB) remained at similar level. Intracellular reactive oxygen species (ROS) analysis indicated that NOB-dominant sludge tends to generate more intracellular ROS compared with AOB-dominant sludge in the presence of UVA, leading to the inactivation and elimination of NOB. Additionally, amounts of microalgae found in UVA irradiation reactor could help to suppress NOB by generating ROS during photosynthesis. Briefly, the UVA irradiation approach proposed in this study was shown to be promising in NOB suppression for reliable mainstream nitritation.

A new technology for simultaneous calcium-nitrate and fluoride removal in the biofilm reactor

In this study, a biofilm reactor containing Acinetobacter sp.H12 was established to investigate the simultaneous denitrification, the removal of calcium and fluoride performance. The main precipitation components in the reactor were determined by SEM, XPS and XRD. The effects of HRT (6 h, 9 h and 12 h), pH (6.0, 7.0, 8.0), influent F^- concentration (3 mg/L, 5 mg/L, 10 mg/L) on synchronously removal of nitrate and F^- and Ca²⁺ during reactor operation were studied. Optimum operating conditions were achieved with a nitrate removal ratio of 100%, F^- removal ratio of 81.91% and Ca²⁺ removal ratio of 67.66%. Nitrogen was the main gaseous product analyzed by gas chromatography. Extracellular polymers (proteins) were also identified as sites for biological precipitation nucleation by fluorescence spectroscopy. Moreover, microbial distribution and community structure analysis showed that strain H12 was the dominat strain in the biofilm reactor. And combined with the performance prediction of the reactor, strain H12 played a major role in the process of simultaneous denitrification, F^- and Ca²⁺ removal.

Comparative analysis of denitrification performance, denitrifying community and functional genes to oxytetracycline exposure between single and hybrid biodegradable polymers supported solid-phase denitrification systems

Biodegradable carrier are vital for the solid-phase denitrification (SPD) systems for treating nitrate-rich water. Two solid-phase denitrification reactors were developed with both 200 g L^-1 of single (polycaprolactone, PCL) (R1) and hybrid solid carbon sources (PCL/polylactic acid (PLA) /polyhydroxyalkanoates (PHA)) (R2) to examine the denitrification performance, denitrifying community and functional genes to various oxytetracycline (OTC) exposure in this study, respectively. Complete denitrification performance was achieved in the both SPD systems at low stress of OTC (1 mg L^-1), but then dramatically reduced to less than 20% of nitrate reduction efficiency after one-month high OTC stress (10 mg L^-1), and rapidly recovered to stable nitrate removal rates of 76.77 ± 5.48% (R1) and 40.68 ± 4.40% (R2) after the next day of no OTC stress. However, the reactor R1 with single PCL carriers acquired more efficient nitrate removal rate than that of reactor R2 at the high OTC stress and recovery phase with OTC stress, mainly due to the more organics availability from the single PCL carriers. The richness and diversity of nirK and nirS deintrifiers significantly declined at high OTC stress, and much more of those occurred in biofilm R1 with more organics availability. Besides, biofilm R1 achieved much more abundant periplasmic nitrate reductase, nitrite reductase genes and tetracycline resistance genes after high OTC stress, which explained the potential resistance to OTC and rapid recovery efficiency after no stress of OTC. Thus, the organics availability played an important role in assuring SPD system to be efficient under high OTC stress.

Soil conditioners effects on hydraulic properties, leaching processes and denitrification on a silty-clay soil

Agricultural landscapes are often affected by groundwater quality issues due to fertilizers leaching. To address this worldwide problem several agricultural best practices have been proposed, like limiting the amount of fertilizers and increasing soil organic matter content. To evaluate if these practices may promote groundwater quality enhancement, vadose zone retention time and complex biogeochemical processes must be known in detail. In this study, sequential undisturbed column experiments were performed to determine the amount of nutrients and heavy metals leached after simulated stormwater events. The column was amended with urea then flushed for two pore volumes, then straw residuals were incorporated and flushed for two pore volumes and finally compost was incorporated and flushed for six pore volumes. Dissolved ions, major gasses and heavy metals were determined in leachate samples. Nitrate and nitrite were leached in the urea treatment producing the highest concentrations, followed by compost and straw residuals. The redox conditions were aerobic in all treatments and pH was circumneutral or slightly basic. Denitrification was low but increased with the addition of straw residuals and compost. Heavy metals were all at very low concentrations except for lead and cadmium, which slightly exceeded threshold limits (10 and 1 μg/L, respectively) in all the treatments. The compost treatment, after three pore volumes, was affected by clay swelling due to sodium dispersion, which in turn provoked a reduction of porosity and hydraulic conductivity.

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.

Impact of COD/N on anammox granular sludge with different biological carriers

The purpose of this study is to investigate the effect of COD/N interference on mature anammox granular sludge formed by different biological carriers. Three anammox granular sludge rectors were established with no biological carriers (R1), GAC (R2) and PVA-gel bead (R3), respectively. As the COD/N ratio increased to 1:2, the activity of anaerobic ammonia oxidizing bacteria in R1 and R2 was significantly inhibited. However, the nitrogen removal effect of R3 did not decrease dramatically, and the nitrogen removal rate in this phase was 1.54 ± 0.05 kg N/m³·d. As the COD/N ratio increased to 1:1.5, the removal of NH₄⁺-N in all reactors gradually decreased. The order of COD resistance of the three reactors in this study was R3 > R2 > R1. It was found that Candidatus Brocadia might be sensitive to the presence of organic matter. The abundance of heterotrophic denitrifying bacteria increased gradually in each reactor under increased influent COD/N ratios.

Sequential hydrotalcite precipitation and biological sulfate reduction for acid mine drainage treatment

Hydrotalcite precipitation is a promising technology for the on-site treatment of acid mine drainage (AMD). This technology is underpinned by the synthesis of hydrotalcite that can effectively remove various contaminants. However, hydrotalcite precipitation has only limited capacity to facilitate sulfate removal from AMD. Therefore, the feasibility of coupling biological sulfate reduction with the hydrotalcite precipitation to maximize sulfate removal was evaluated in this study. AMD emanating from a gold mine (pH 4.3, sulfate 2000 mg L^-1, with various metals including Al, Cd, Co, Cu, Fe, Mn, Ni, Zn) was first treated using the hydrotalcite precipitation. Subsequently, biological treatment of the post-hydrotalcite precipitation effluent was conducted in an ethanol-fed fluidized bed reactor (FBR) at a hydraulic retention time (HRT) of 0.8-1.6 day. The hydrotalcite precipitation readily neutralized the acidity of AMD and removed 10% of sulfate and over 99% of Al, Cd, Co, Cu, Fe, Mn, Ni, Zn. The overall sulfate removal increased to 73% with subsequent FBR treatment. Based on 454 pyrosequencing of 16S rRNA genes, the identified genera of sulfate-reducing bacteria (SRB) included Desulfovibrio, Desulfomicrobium and Desulfococcus. This study showed that sulfate-rich AMD can be effectively treated by integrating hydrotalcite precipitation and a biological sulfate reducing FBR.

Iron-carbon galvanic cells strengthened anaerobic/anoxic/oxic process (Fe/C-A2O) for high-nitrogen/phosphorus and low-carbon sewage treatment

The treatment of sewage with high-nitrogen/-phosphorus and low-carbon remains a challenge. A novel iron-carbon galvanic cells strengthened anaerobic/anoxic/oxic process (Fe/C-A2O) was developed for high-nitrogen/-phosphorus and low-carbon sewage treatment. The cost-effective iron-scraps (ISs) was recycled as Fe(0)-source under the mediation of Fe/C galvanic cell reaction to develop effective Fe(0)-oxidizing autotrophic-denitrification and -dephosphorization. Utilizing practical high-nitrogen/-phosphorus and low-carbon sewage as target wastewater, the performance, impact factors, contribution of Fe/C galvanic cell reactions, microbial characteristics, strengthening mechanisms, and application potential of Fe/C-A2O process were investigated. The Fe/C-A2O process achieved high TN and TP removal efficiencies of 92.0 ± 1.3% and 97.2 ± 0.9% with removal loads of 0.176 ± 0.002 kg TN/(m³·d) and 0.017 ± 0.002 kg TP/(m³·d), respectively. Optimal HRT of 12 h, DO of 4.0-4.5 mg/L, and reflux-ratio of 4:1 were obtained, and no sludge-reflux was required. Autotrophic-denitrification and -dephosphorization supported by the Fe/C galvanic cell reactions contributed 63.1% and 75.3% of TN and TP removal, respectively. Microbial characterization revealed the dominance of autotrophic denitrifiers (e.g., Thiobacillus), AOB (e.g., Nitrosomonas), NOB (e.g., Nitrospira), and heterotrophic denitrifiers (e.g., Zoogloea). The mechanism analysis demonstrated that Fe/C galvanic cells strengthened nitrogen removal by raising Fe²⁺/H₂-supported autotrophic denitrification; and strengthened dephosphorization by introducing Fe³⁺-based PO₄^3--precipitation and enhancing the denitrifying phosphate-accumulation by denitrifying phosphate-accumulating organisms (DPAOs). Based on the efficiency and cost evaluation, the ISs-based Fe/C-A2O process showed significant application potential as an upgrade strategy for traditional A2O process in advanced high-nitrogen/phosphorus and low-carbon sewage treatment.

Denitrification performance and microbial communities of solid-phase denitrifying reactors using poly (butylene succinate)/bamboo powder composite

This study explored the denitrification performance of solid-phase denitrification (SPD) systems packed with poly (butylene succinate)/bamboo powder composite to treat synthetic aquaculture wastewater under different salinity conditions (0‰ Vs. 25‰). The results showed composite could achieve the maximum denitrification rates of 0.22 kg (salinity, 0‰) and 0.34 kg NO3--N m-3 d-1 (salinity, 25‰) over 200-day operation. No significant nitrite accumulation and less dissolved organic carbon (DOC) release (<15 mg/L) were found. The morphological and spectroscopic analyses demonstrated the mixture composites degradation. Microbial community analysis showed that Acidovorax, Simplicispira, Denitromonas, SM1A02, Marinicella and Formosa were the dominant genera for denitrifying bacteria, while Aspergillus was the major genus for denitrifying fungus. The co-network analysis also indicated the interactions between bacterial and fungal community played an important role in composite degradation and denitrification. The outcomes provided a potential strategy of DOC control and cost reduction for aquaculture nitrate removal by SPD.

Deciphering the toxic effects of antibiotics on denitrification: Process performance, microbial community and antibiotic resistance genes

The extensive application of antibiotics, and the occurrence and spread of antibiotic resistance genes (ARGs) shade health risks to human and animal. The long-term effects of sulfamethoxazole (SMX) and tetracycline (TC) on denitrification process were evaluated in this study, with the focus on nitrogen removal performance, microbial community and ARGs. Results showed that low-concentration SMX and TC (<0.2 mg L^-1) initially caused a deterioration in nitrogen removal performance, while higher concentrations (0.4-20 mg L^-1) of both antibiotics had no further inhibitory influences. The abundances of ARGs in both systems generally increased during the whole period, and most of them had significant correlations with intI1, especially efflux-pump genes. Castellaniella, which was the dominant genus under antibiotic pressure, might be potential resistant bacteria. These findings provide an insight into the toxic effects of different antibiotics on denitrification process, and guides future efforts to control antibiotics pollution in ecosystems.

Combined heterotrophic and autotrophic system for advanced denitrification of municipal secondary effluent in full-scale plant and bacterial community analysis

Total nitrogen (TN) removal is the major technical challenge for wastewater treatment plants to meet the more stringent discharge standard. In this study, lab- (0.05 m³/d), pilot- (1000 m³/d) and full-scale (10,000 m³/d) combined heterotrophic and autotrophic denitrification reactors (HARs) were designed and operated to treat municipal secondary effluent. During the 110-day stable operation, the effluent TN was reduced below 2.5 mg/L without secondary pollution causing by the excessive addition of organics, close to Class IV of Environmental Quality Standards for Surface Water. The bacterial richness and diversity increased with the expansion of reactor scale. Denitrifying bacteria (DB) dominated in all reactors, however, Thiomonas (12.42%), Methylotenera (6.35%), Thiobacillus (20.62%), Methyloverstatilis (5.44%) and Thauera (8.21%) were the main genera in lab-, pilot- and full-scale reactors respectively. The denitrification efficiency temporarily deteriorated at the later stage, and redundancy analysis (RDA) indicated the obviously increased sulfate reducing bacteria (SRB) and sulfide were main contributors. Sludge supplement rapidly recovered the reactors performance in five days. This study suggests that HARs could be a promising technique for advanced denitrification of the municipal secondary effluent.

Comparative Study of Denitrifying-MBBRs with Different Polyethylene Carriers for Advanced Nitrogen Removal of Real Reverse Osmosis Concentrate

Nitrogen (N) remains a great challenge in wastewater treatment while attempts to remove N has continuously been a research point for decades. In this study, the long-term performance of four identical-shape denitrification MBBRs (moving bed biofilm reactors) with four different configurations of cylindrical polyethylene as carriers (Φ25 × 12, Φ25 × 4, Φ15 × 15, and Φ10 × 7 mm) for advanced N removal of real reverse osmosis concentrate was investigated in great detail. The N of the real concentrate can be effectively removed by denitrification MBBRs when the pH, temperature, hydraulic retention time (HRT), C/N ratio, and filling rate are 7.50–8.10, 24~26 °C, 12 hours, 6.6, and 50%, respectively. The results showed that the MBBR with the Φ15 × 15 poly-carrier had the best removal efficiency on NO₃^-–N (78.0 ± 15.8%), NO₂^-–N (43.79 ± 9.30%), NH₄⁺–N (55.56 ± 22.28%), and TN (68.9 ± 12.4%). The highest biomass of 2.13 mg/g-carrier was in the Φ15 × 15 poly-carrier was compared with the other three carriers, while the genes of the Φ15 × 15 poly-carrier reactor were also the most abundant. Proteobacteria was the most abundant phylum in the system followed by Bacteroidetes and then Firmicutes. The entire experiment with various parameter examination supported that Φ15 × 15 poly-carrier MBBR was a promising system for N removal in high strength concentrate. Despite the lab-scale trial, the successful treatment of high strength real reverse osmosis concentrate demonstrated the reality of the treated effluent as possible reclaimed water, thus providing a good showcase of N-rich reverse osmosis concentrate purification in practical application.

Enhanced performance of simultaneous carbon, nitrogen and phosphorus removal from municipal wastewater in an anaerobic-aerobic-anoxic sequencing batch reactor (AOA-SBR) system by alternating the cycle times

The performance of simultaneous carbon (C), nitrogen (N) and phosphorus (P) removal was investigated by altering the cycle times in an anaerobic-aerobic-anoxic sequencing batch reactor (AOA-SBR) system. Results showed that the AOA-SBR system achieved high simultaneous C, N and P removal efficiency with a cycle time of 6 h, with average removal efficiencies for COD, TN, and TP of 96.81%, 96.32% and 94.33%, respectively. The highest anoxic removal rate of NO_X-N was 203.44 mg·g^-1- MLVSS·d^-1. Meanwhile, anaerobic release rate and aerobic, anoxic removal rate of TP reached peak values of 104.31 and 85.81 mg·g^-1- MLVSS·d^-1, respectively. Microbial community analysis demonstrated that Proteobacteria, Bacteroidetes and Candidatus Saccharibacteria at phylum level and Betaproteobacteria, Gammaproteobacteria, Sphingobacteriia, Deltaproteobacteria and Alphaproteobacteria at the class level benefited AOA-SBR performance. Functional analysis of genes indicated that the metabolic potential related to C, N and P metabolism increased under the optimal cycle time condition.

Effects of Hydraulic Retention Time and Influent Nitrate-N Concentration on Nitrogen Removal and the Microbial Community of an Aerobic Denitrification Reactor Treating Recirculating Marine Aquaculture System Effluent

The effects of hydraulic retention time (HRT) and influent nitrate-N concentration on nitrogen removal and the microbial community composition of an aerobic denitrification reactor treating recirculating marine aquaculture system effluent were evaluated. Results showed that over 98% of nitrogen was removed and ammonia-N and nitrite-N levels were below 1 mg/L when influent nitrate-N was below 150 mg/L and HRT over 5 h. The maximum nitrogen removal efficiency and nitrogen removal rate were observed at HRT of 6 or 7 h when influent nitrate-N was 150 mg/L. High-throughput DNA sequencing analysis revealed that the microbial phyla Proteobacteria and Bacteroidetes were predominant in the reactor, with an average relative total abundance above 70%. The relative abundance of denitrifying bacteria of genera Halomonas and Denitratisoma within the reactor decreased with increasing influent nitrate-N concentrations. Our results show the presence of an aerobically denitrifying microbial consortium with both expected and unexpected members, many of them relatively new to science. Our findings provide insights into the biological workings and inform the design and operation of denitrifying reactors for marine aquaculture systems.

Simultaneous Ammonium oxidation denitrifying (SAD) in an innovative three-stage process for energy-efficient mature landfill leachate treatment with external sludge reduction

High-loaded ammonia and low-strength organics mature landfill leachate is not effectively treated by conventional biological processes. Herein, an innovative solution was proposed using a three-stage Simultaneous Ammonium oxidation Denitrifying (SAD) process. Firstly, ammonia (1760 ± 126 mg N/L) in wastewater was oxidized to nitrite in a partial nitrification sequencing batch reactor (PN-SBR). Next, 93% PN-SBR effluent and concentrated external waste activated sludge (WAS; MLSS = 23057 ± 6014 mg/L) were introduced to an anoxic reactor for integrated fermentation and denitrification (IFD-SBR). Finally, ammonia (101.4 ± 13.8 mg N/L) released by fermentation in the IFD-SBR and residual 7% nitrite in the PN-SBR were removed through the anaerobic ammonium oxidation (anammox) process in the SAD up-flow anaerobic sludge bed (SAD-UASB). In addition, NO₃^--N generation during the anammox process could be reduced to nitrite by partial denitrification (PD) and reused as substrate for anammox. A satisfactory total nitrogen (TN) removal efficiency (98.3%), external sludge reduction rate (2.5 kg/m³ d) and effluent TN concentration (16.7 mg/L) were achieved after long-term operation (280 days). The IFD-SBR and SAD-UASB contributed to 81.9% and 12.3% nitrogen removal, respectively. Microbial analysis showed that anammox bacteria (1.5% Candidatus Brocadia) cooperated well with partial denitrifying bacteria (4.3% Thauera) in SAD-UASB, and average nitrogen removal contribution were 83.1% during significant stability of anammox and 9.2% during the denitrification process, respectively. The three-stage SAD process provides an environmental and economic approach for landfill leachate treatment since it has the advantage of 25.4% less oxygen, 100% organic matter savings and 47.9% less external sludge than traditional biological processes.

Recent advances in partial denitrification in biological nitrogen removal: From enrichment to application

To maximize energy recovery, carbon capture followed by shortcut nitrogen removal is becoming the most promising route in biological wastewater treatment. As the intermediate of microbial denitrification, nitrite could serve as a substrate for anammox bacteria, while N₂O is a combustion promoter that can increase 37% energy release from CH₄ than O₂. Therefore, the important advances in partial denitrification (PD) that produces nitrite or N₂O as the main product using inorganic or organic electron donors were critically reviewed. Specifically, the enrichment strategies of PD microorganisms were obtained by analyzing the selection pressures, metabolism, physiology, and microbiology of these microorganisms. Furthermore, some prospective and promising processes integrating PD microorganisms and the bottlenecks of current applications were discussed. The obtained knowledge would provide new insights into the upgrading of current WWTPs involving commitment to achieve nitrogen removal from wastewaters more economically and environmentally friendly.

Mixed carbon source improves deep denitrification performance in up-flow anaerobic sludge bed reactor

To investigate the advantages of mixed carbon source over a single one in deep denitrification, sodium acetate, glucose and their mixture were used as carbon sources in present study. Denitrification performance, effluent pH, microbial community and carbon source cost were taken into account. With the same influent NO₃ ^--N concentration of 50 mg/L and the same C/N ratio of 1.5, the NO₃ ^--N removal rate with the mixed carbon source (96.53%) was slightly lower than that with sodium acetate (98.15%), but significantly higher than that with glucose (74.69%). The specific denitrification rates of the sodium acetate, glucose and sodium acetate/glucose reactor were 47.7, 29.7 and 45.4 mg N/g VSS d, respectively. The effluent pH with sodium acetate varied in the range of 9.13-9.60, exceeding the discharge standard limit of 9.0, whereas the sodium acetate/glucose reactor could keep pH in the range of 7.80-8.23. The 16S rRNA gene-based high-throughput sequencing revealed that carbon sources determined the microbial community structure and the sludge Shannon index with the mixed carbon source was the highest. Furthermore, cost estimation indicated that the mixed carbon source was the cheapest. This study is significant as it tests reasonable selection of carbon sources for deep denitrification in practice.

Performance and microbial diversity of denitrifying biofilms on polyurethane foam coupled with various solid carbon sources for nitrate-rich water purification

This study investigated the performance and microbial communities of denitrifying biofilms on polyurethane foam coupled with various solid carbon sources of acid- and alkali-pretreated rice straw and rice husk. Results showed that acid and alkali-pretreated rice straw both had higher TOC release rates (0.041-0.685 mg g^-1 day^-1) than those of rice husk (0.019-0.160 mg g^-1 day^-1) over a month, while acid pretreatment of rice husk and rice straw had a much higher organics release rate than that of alkali pretreatment and non-pretreatment, respectively. Acid-pretreated rice straw achieved the most efficient TN removal performance (82.06 ± 3.65%) with the lower occurrences of NH₄⁺-N during denitrification than that of alkali-pretreated rice straw (80.05 ± 4.12%) over more than a month operation. However, alkali pretreatment of rice husk demonstrated much more significantly efficient TN removal efficiency (80.39 ± 2.1%) than did acid pretreatment (69.59 ± 13.43%). MiSeq sequencing analysis showed that the four biofilm samples attached on polyurethane foam with the addition of pretreated rice straw or rice husk had a range of 13-15 differentially abundant phylum and 81-123 differentially abundant genera in comparison with biofilm without extra solid carbon sources, and a higher TN removal efficiency demonstrated more types of differentially abundant genera.

Optimization of Wastewater Phosphorus Removal in Winter Temperatures Using an Anaerobic–Critical Aerobic Strategy in a Pilot-Scale Sequencing Batch Reactor

Biological phosphorus removal using an anaerobic–aerobic sequencing batch reactor (SBR) in a low temperature can be difficult to remove, and aeration always accounts for nearly half of the total electricity costs at many wastewater treatment plants. In this study, a pilot-scale anaerobic–critical aerobic SBR (A–CA SBR) was developed for synthetic domestic wastewater. More importantly, the phase, whose concentration of diffused oxygen was controlled at 1.0–1.5 mg/L, was defined as a critical aerobic phase, which reduced expenses during the operation. To be specific, half of the ammonia was removed within 10 days and no NO3−–N was accumulated during the process. From the SEM and metagenome analysis, Rhodocyclus, Zooglea, Dechloromonas, and Simplicispira had the ability to remove phosphorus and NO3−–N simultaneously, which proved the existence of a potential double-layer sludge structure under an A–CA operational condition. All of the results disclose that the pilot-scale A–CA SBR is a reliable manipulation strategy for phosphorus removal under low temperatures, which can hopefully apply to practical wastewater remediation.

Enhanced removal of nitrate and refractory organic pollutants from bio-treated coking wastewater using corncobs as carbon sources and biofilm carriers

The quality of the bio-treated coking wastewater (BTCW) is difficult to meet increasingly stringent coking wastewater discharge standards and future wastewater recycling needs. In this study, the pre-treatment process of BTCW was installed including the two up-flow fixed-bed bioreactors (UFBRs) which were separately filled with alkali-pretreated or no alkali-pretreated corncobs used as solid carbon sources as well as biofilm carriers. Results showed that this pre-treatment process could significantly improve the biodegradability of BTCW and increase the C/N ratio. Thus, over 90% of residual nitrate in BTCW were removed stably. Furthermore, GC-MS analysis confirmed that the typical refractory organic matters decreased significantly after UFBRs pre-treatment. High-throughput sequencing analysis using 16S rRNA demonstrated that dominant denitrifiers, fermentative bacteria and refractory-organic-pollutants-degrading bacteria co-existed inside the UFBRs system. Compared with no alkali-pretreated corncobs, alkali-pretreated corncobs provided more porous structure and much stable release of carbon to guarantee the growth and the quantity of the functional bacteria such as denitrifiers. This study indicated that the UFBRs filled with alkali-pretreated corncobs could be utilized as an effective alternative for the enhanced treatment of the BTCW.

Nitrogen removal mechanism and microbial community changes of bioaugmentation subsurface wastewater infiltration system

Limited nitrogen removal capacity (mainly nitrate, NO₃^--N) remains a major challenge for subsurface wastewater infiltration system (SWIS). Two nitrogen-removing strains have been isolated from SWIS and inoculated to SWIS to investigate the effect of bioaugmentation on nitrogen removal performance and mechanism. The results showed bioaugmentation improved the removal efficiencies of NH₄⁺-N from 86.81% to 92.86% and TN from 74.90% to 86.55% and running stability compared to unbioaugmentation SWIS. 16 s rRNA amplicon sequencing results of the bacterial indicated that bioaugmentation altered the microbial community structure especially at 150 cm depth and increased the relative abundance of bacteria associated with nitrogen removal, significantly increasing the abundance of Rhizobiales_Incertae_Sedis and Lachnospiraceae. Furthermore, the relation between internal microbial characteristics and operational factors indicated that Hyphomicrobiaceae and Gemmatimonadaceae were also closely related to nitrogen removal. Predicted function profiles revealed that bioaugmentation enhanced the activity of nitrogen removal enzymes (Hao, NorBC, NasAB, NarGHI, NirBD and NosZ).

Carbon selection for nitrogen degradation pathway by Stenotrophomonas maltophilia: Based on the balances of nitrogen, carbon and electron

A novel strain DQ01 capable of simultaneous removal of nitrate and ammonium under the aerobic condition was isolated from the landfill leachate and identified as Stenotrophomonas maltophilia. The result showed that S. maltophilia had carbon selection for the nitrogen removal pathway, and preferred to utilize carboxylate rather than carbohydrate, as carboxylate could directly participate in TCA cycle without Embden Meyerhof Parmas (EMP). Nitrogen and carbon balances confirmed that the ammonium assimilation was the main or even sole removal pathway for S. maltophilia, and carboxylate was more conducive to heterotrophic nitrification-aerobic denitrification (HN-AD) process due to the serious self-alkalization and higher reduction potential of carboxylate, which followed: NH₄⁺ → NO₂^- → NO₃^- → NO₂^- → NO due to the lack of nor and nos. Meanwhile, the higher C/N and nitrate could generate a more powerful ion transport driving force to accelerate the electron transfer in the denitrifying respiratory chain.

Pretreatment-promoted sludge fermentation liquor improves biological nitrogen removal: Molecular insight into the role of dissolved organic matter

Waste activated sludge (WAS) can be used as carbon sources to support biological nutrient removal (BNR). In this study, thermal-alkaline (THALK), ozonation (OZN), electrolysis (EC) and NaClO-promoted electrolysis (EC-AOP) were investigated to facilitate WAS solubilization and production of volatile fatty acids (VFAs). EEMF-PARAFAC and FT-ICR-MS were employed to characterize the transformation of dissolved organic matter (DOM) in WAS fermentation liquors at molecular level. THALK achieved the highest fluorescence intensity of C1 protein after pretreatment. Proteins and lipids were the dominant DOM in the pretreated WAS, while the DOM shifted towards substances with higher H/C and lower O/C after fermentation. The BNR results showed that THALK (100%) and EC-AOP (96.9%) outperformed other groups (78.9-90.3%) in terms of NO₃-N removal, indicating the significant impact of DOM compositions. Overall, these results demonstrated that THALK and EC-AOP effectively enhanced release of VFAs and DOM, which subsequently improved NO₃-N removal efficiency.

Nitrate removal performance and diversity of active denitrifying bacteria in denitrification reactors using poly(L-lactic acid) with enhanced chemical hydrolyzability

Poly(L-lactic acid) (PLLA) can be used as an external electron donor in denitrification reactors to treat drinking water, aquaculture water, and industrial wastewater with an imbalanced carbon/nitrogen ratio. However, for PLLA to function in these applications, its chemical hydrolyzability requires improvement. Although the adjustment of the crystallinity (X_c) is effective in improving the hydrolyzability of PLLA, the condition for the X_c of PLLA, in which a sufficient amount of lactic acid is released for denitrification, must be clarified. Therefore, this study investigated the effective X_c range and optimal PLLA content as an electron donor for continuous nitrate removal in denitrification reactors. This study also explored the abundance, succession, and diversity of active denitrifying bacteria in denitrification reactors. The nitrate removal activity of activated sludge using the highly crystalline PLLA (X_c = 39.4%) was 1.8 mg NO₃^- -N g MLSS^-1 h^-1, which is 2.4 times higher than that using the nearly amorphous PLLA (X_c = 0.9%). During the 57 days of operation, the denitrification reactor with 3% (w/v) highly crystalline PLLA continued to completely remove nitrate, with a maximum nitrate removal activity of 22.8 mg NO₃^- -N g MLSS^-1 h^-1. The 16S rRNA amplicon sequencing and clone library analyses are using transcripts of two nitrite reductase genes, encoding cytochrome cd₁ nitrite reductase, and copper-containing nitrite reductase revealed that bacteria belonging to the families Comamonadaceae, Rhodocyclaceae, and Alcaligenaceae were active denitrifying bacteria in the denitrification reactor using PLLA.

Performance and microbial community of simultaneous removal of NO3--N, Cd2+ and Ca2+ in MBBR

A moving-bed biofilm reactor (MBBR) containing immobilized Acinetobacter sp.CN86 was operated to investigate the simultaneous denitrification, bio-mineralization and cadmium removal performance. Effects of hydraulic residence time (HRT) (4 h, 6 h and 8 h), pH (6.0, 7.0 and 8.0) and influent Cd²⁺ concentrations (10 mg/L, 30 mg/L and 50 mg/L) were assessed on the simultaneous removal of nitrate, Cd²⁺ and Ca²⁺. Results indicate that the highest pollutant removal efficiency (98.33% (1.866 mg/L·h) for NO₃^--N; 99.36% (1.242 mg/L·h) for Cd²⁺; 68.80% (15.480 mg/L·h) for Ca²⁺) was achieved under the conditions of a hydraulic residence time of 8 h, pH of 7.0 and initial Cd²⁺ concentration of 10 mg/L. Analyses of microbial distribution and community structures showed that Acinetobacter sp.CN86 was the main contributor (occupy 15.3% at the species level) to the effective removal of multiple pollutants in the MBBR. In addition, the main gas and precipitation components in the biofilm reactor were identified by gas chromatography, scanning electron microscope, and X-ray diffraction analyses.

A novel pilot-scale tubular bioreactor-enhanced floating treatment wetland for efficient in situ nitrogen removal from urban landscape water: Long-term performance and microbial mechanisms

In order to strengthen in situ nitrogen removal of urban landscape water, a novel pilot-scale tubular bioreactor-enhanced floating treatment wetland (TB-EFTW) was constructed, and the long-term performance and responsible microbial mechanisms were investigated in this study. The results showed that the system could remove 81.5% nitrogen from the landscape water after 240 days' operation. Moreover, the contribution rate of plant absorption to nitrogen was low (8.3%), which indicated that microbial biotransformation rather than plant absorption played a more key role in nitrogen removal in TB-EFTW system. The declining dissolved oxygen (DO) concentration along the axial direction of tubular bioreactor (TB) resulted in the sequential bacterial community of nitrifying, aerobic denitrifying, and anoxic denitrifying bacteria in the front, middle, and final part of TB. High-throughput sequencing results demonstrated that the internal environment of the system realized the coexistence of nitrifying, aerobic denitrifying and anoxic denitrifying process. The reason was mainly because that oxic-anoxic (O-A) areas were formed in sequence along the axial direction of tubular bioreactor. Overall, a unique advantage in nitrogen removal was achieved in TB-EFTW, which could provide important references for in situ treatment of urban landscape water. PRACTITIONER POINTS: TB-EFTW strengthened nitrogen removal for in situ urban landscape water treatment. Microbial conversion played a key role in nitrogen removal of the TB-EFTW system. The unique distribution of oxic-anoxic (O-A) areas was formed in sequence along the TB. Nitrification, aerobic, and anoxic denitrification were synergistically involved in the TB.

Biological removal of nitrogen oxides by microalgae, a promising strategy from nitrogen oxides to protein production

Nitrogen oxides (NO_x) are the components of fossil flue gases that give rise to serious environmental and health hazards. Among the available techniques for NO_x removal, microalgae-based biological removal of NO_x (BioDeNO_x) is a promising and competent technology with eco-friendly path of low energy and low-cost solution for the pollution. In this review article, current biological technologies including bacteria-based and microalgae-related BioDeNO_x are discussed. Comparing to direct BioDeNO_x approach, indirect BioDeNO_x by microalgae is more promising since it is more stable, reliable and efficient. By transforming inorganic nitrogen nutrients to organic nitrogen, microalgae can potentially play an important role in converting NO_x into high-value added products. The microalgae-based BioDeNO_x process displays an attractive prospect for flue gas treatment to reduce environmental NO_x pollution and potentially supply protein products, establishing an efficient circular-economy strategy.

Denitrification and microbial community in MBBR using A. donax as carbon source and biofilm carriers for reverse osmosis concentrate treatment

In this study, raw Arundo donax (A. donax) pieces were applied as carbon source and biofilm carriers for denitrification in a lab-scale moving bed biofilm reactor (MBBR) for the treatment of reverse osmosis concentrate gathered from local wastewater reuse plant. At stable phase (about 60 days), efficient denitrification performance was obtained with 73.2% ± 19.5% NO₃^--N average removal and 8.10 ± 3.45 g N/(m³·day) NO₃^--N average volumetric removal rate. Mass balance analysis showed that 4.84 g A. donax was required to remove 1 g TN. Quantitative real-time PCR analysis results showed that the copy numbers of 16S r-RNA, narG, nirS, nosZ and anammox gene of carrier biofilm and suspended activated sludge in the declination phase (BF2 and AS2) were lower than those of samples in the stable phase (BF1 and AS1), and relatively higher copy numbers of nirS and nirK genes with lower abundance of narG and nosZ genes were observed. High-throughput sequencing analysis was conducted for BF2 and AS2, and similar dominant phyla and classes with different abundance were obtained. The class Gammaproteobacteria affiliated with the phylum Proteobacteria was the most dominant microbial community in both BF2 (52.6%) and AS2 (41.7%). The PICRUSt prediction results indicated that 33 predictive specific genes were related to denitrification process, and the relative abundance of 18 predictive specific genes in BF2 were higher than those in AS2.

Effects of carbon availability in a woody carbon source on its nitrate removal behavior in solid-phase denitrification

Woody biomass is the most common natural carbon source applied in solid-phase denitrification (SPD). However, its denitrification ability is low in the SPD process due to its poor carbon availability. In this study, sawdust samples were pretreated to various degrees, and then filled into SPD bioreactors to reveal the relationship between carbon availability and denitrification behaviors. The behaviors include the denitrification process, internal effects of major factors (carbon availability, pH and temperature), and the presence of bacterial communities. Results shown that the long-term denitrification rate of pretreated sawdust was increased by 4.5-4.8 times over that of untreated sawdust (29.3 mg N L^-1 sawdust d^-1). However, despite improving the pretreatment degree of the sawdust in the bioreactor, the long-term denitrification rate shown no further increase. The denitrification rate was most influenced by the temperature, followed by the pH, and then the sawdust pretreatment degree. The denitrification rate increased with decreasing pH and rising temperature of the pretreated sawdust. The removed nitrate was rarely converted into nitrite or nitrous oxide, but ammonium was produced at high pH and temperature for the pretreated sawdust. The adverse effects of ammonium and dissolved organic carbon (DOC) reduced when the pH of the pretreated sawdust was lowered to 6.5. Hydrolytic and denitrifying bacteria formed the main SPD bioreactor bacteria, whose abundances increased with increasing sawdust pretreatment degree. The results were beneficial to reduce the hydrolytic retention time and adverse products for the SPD system using woody carbon source.

A Comparison of Clustering and Prediction Methods for Identifying Key Chemical–Biological Features Affecting Bioreactor Performance

Chemical–biological systems, such as bioreactors, contain stochastic and non-linear interactions which are difficult to characterize. The highly complex interactions between microbial species and communities may not be sufficiently captured using first-principles, stationary, or low-dimensional models. This paper compares and contrasts multiple data analysis strategies, which include three predictive models (random forests, support vector machines, and neural networks), three clustering models (hierarchical, Gaussian mixtures, and Dirichlet mixtures), and two feature selection approaches (mean decrease in accuracy and its conditional variant). These methods not only predict the bioreactor outcome with sufficient accuracy, but the important features correlated with said outcome are also identified. The novelty of this work lies in the extensive exploration and critique of a wide arsenal of methods instead of single methods, as observed in many papers of similar nature. The results show that random forest models predict the test set outcomes with the highest accuracy. The identified contributory features include process features which agree with domain knowledge, as well as several different biomarker operational taxonomic units (OTUs). The results reinforce the notion that both chemical and biological features significantly affect bioreactor performance. However, they also indicate that the quality of the biological features can be improved by considering non-clustering methods, which may better represent the true behaviour within the OTU communities.

Effect of temperature on tertiary nitrogen removal from municipal wastewater in a PHBV/PLA-supported denitrification system

In this study, a poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(lactic acid) (PHBV/PLA)-supported denitrification system was built to remove nitrogen from municipal wastewater treatment plant secondary effluent, and the influence of operating temperature on nitrogen removal was further investigated. Results indicated that a PHBV/PLA-supported denitrification system could effectively fulfill the tertiary nitrogen removal. The nitrogen removal efficiency gradually declined with the operating temperature decreasing, and the denitrification rate at 30 °C was 5 times higher than that at 10 °C. Meanwhile, it was found that a slight TOC accumulation only occurred at 30 °C (with an average of 2.03 mg/L) and was avoided at 10~20 °C. The reason for effluent TOC variation was further explained through the consumption and generation pathways of TOC in this system. Furthermore, the temperature coefficient was about 0.02919, indicating that the PHBV/PLA-supported denitrification system was a little sensitive to temperature. A better knowledge of the effect of operating temperature will be significant for the practical application of the solid-phase denitrification system.

Enhanced biofilm formation and denitrification in biofilters for advanced nitrogen removal by rhamnolipid addition

Denitrification biofilters (DNBFs) are widely used in advanced nitrogen removal of wastewater with low C/N and effective biofilm formation is critical to their long-term operation. Hereby the influence of rhamnolipid addition in DNBFs was investigated for the first time. Gradient concentrations (0, 20, 40, 80, 120 mg/L) of rhamnolipid were applied to investigate nitrogen removal, biofilm properties and microbial community of lab-scale DNBFs. A significant increase of nitrogen removal was observed in rhamnolipid-treated DNBFs (p < 0.05). Total solid (TS), extracellular polymeric substances (EPS) and adhesion force of biofilms in DNBF with 120 mg/L rhamnolipid reached the maximum, which were 2.17, 2.15 and 3.36 times of those in the control, respectively. Moreover, rhamnolipid exhibited an improvement in abundance of Simplicispira and Gemmatimonas which were responsible for enhanced biofilm formation and denitrification. The results suggested that rhamnolipid addition can be a novel strategy to improve the start-up and denitrification performance of DNBFs.

A pilot-scale deep bed denitrification filter for secondary effluent treatment using sodium acetate as external carbon

A pilot-scale quartz sand deep bed denitrification filter (DBDF) using sodium acetate as the additional carbon source was implemented to treat secondary effluent, with a high nitrate nitrogen (NO₃ -N) concentration and low C/N ratio, from an urban municipal water resource recovery facility. By the 18th day, results showed that the removal efficiency of NO₃ -N and the chemical oxygen demand (COD) were stable at above 85% and 70%, respectively. When the filter layer depth was set to 1,600 mm and the concentration of additional sodium acetate was maintained at 51 mg/L, the total nitrogen and COD concentrations of the DBDF effluent were stabilized below 5 and 30 mg/L, respectively. The quartz sand DBDF had a good effect on the removal of dissolved organic matter, especially for aromatic protein-like and tryptophan protein-like substances. Bacteria with denitrification function, such as Cloacibacterium and Zoogloea, became increasingly dominant with increasing filling layer depth. PRACTITIONER POINTS: The denitrification filter had a good effect on the removal of aromatic protein-like and tryptophan protein-like substances. Cloacibacterium and Zoogloea became increasingly dominant with increasing filling layer depth.

Bacterial community activity and dynamics in the biofilm of an experimental hybrid wetland system treating greywater

The objectives of this study were to determine the biofilm microbial activity and bacterial community structure and successions in greywater treatment filters and to relate the treatment efficiency to the bacterial community parameters. This 10-month study was performed in a newly established experimental system for domestic greywater treatment that consisted of three parallel vertical flow filters (VFs) followed by a horizontal flow filter (HF). A rapid increase in the bacterial community abundance occurred during the first 85 days of filter operations, followed by a short-term decrease and the stabilization of the 16S rRNA gene copy numbers at average levels of 1.2 × 10⁹ and 3.2 × 10⁸ copies/g dw in VFs and HF, respectively, until the end of the experiment. The dominant bacterial phyla and genera differed between the VFs and HF. The temporal variation in the bacterial community structure was primarily related to the species replacement, and it was significantly affected by the influent organic carbon and nitrogen compounds in the VFs and the ammonia and organic carbon in the HF filters. Despite the differences in the community structure and assembly mechanisms, the temporal dynamics of the bacterial community showed high congruence between the filter types. The treatment efficiency was related to the biofilm bacterial community diversity and abundance and the abundance of certain bacterial genera in the VF filters. The results suggest that the dominant pathway of nitrogen removal by greywater treatment VFs occurs via coupled heterotrophic nitrification and denitrification, while the contribution of aerobic denitrification is temporally variable in these filters.

The cotreatment of landfill leachate and high-nitrate wastewater using SBRs: evaluation of denitrification performance and microbial analysis

Resourceful disposal of landfill leachate has always been an intractable worldwide problem. This study was conducted to investigate the feasibility of biologically treating a combined waste stream of landfill leachate and high-concentration nitrate nitrogen (high-nitrate) wastewater. Raw landfill leachate was pretreated using anaerobic fermentation and ammonia stripping to improve biodegradability. The control sequencing batch reactor (SBR, named R0) was fed only with synthetic high-nitrate wastewater with sodium acetate as the carbon source, whereas the other experimental SBR (named R1) was loaded with mixtures containing leachates. Excessive increase in leachate adversely affected the cotreatment, and it was concluded that the landfill leachate volume ratio should never exceed 7.5% of the total wastewater (14% of the initial COD) based on further batch experiments. The maximum specific denitrification rate of 58.05 mg NO₃⁻-N (gVSS h)⁻¹ was attained in R1, while that of 32.32 mg NO₃⁻-N (gVSS h)⁻¹ was obtained in R0. Illumina MiSeq sequencing revealed that adding landfill leachate did not change the fact that Pseudomonas, Thauera, and Pannonibacter dominant in the sodium acetate supported the denitrification systems, but led to the adjustment of their relative abundance. Moreover, the narG, nirK, nirS, and norB denitrifying genes exhibited increased abundance by 138–980% in the cotreated system, which was confirmed by q-PCR analyses. These findings reveal that the denitrification efficiency of activated sludge in SBR cotreated with landfill leachate and high-nitrate wastewater significantly improved, and this may contribute toward the understanding of the molecular mechanisms of biological denitrification under the blending treatment of leachate and high-nitrate wastewater.

Resourceful disposal of landfill leachate has always been an intractable worldwide problem.

Enhancement of the adaptability of anammox granules to zinc shock by appropriate organic carbon treatment

Heavy metals, which are commonly present in high ammonia-containing wastewater, can cause inhibitory effects to anammox reaction. This study proposes a novel approach to enhance the adaptability of anammox granules to heavy metal [Zn(II)] shock by organic carbon (sodium acetate, NaAc) treatment, paying special attention to optimization of the treatment dosage and duration. For granules treated with 200 mg chemical oxygen demand (COD)/L NaAc for 2 d, the activity recovery (six cycles) efficiency after Zn(II) (40 mg/L) shock reached 127.4%. The extracellular polymeric substance (EPS) production increased by 168% and heterotrophic bacteria mildly proliferated (increased by 14%) in such granules compared with the control. The dramatic recovery capacity was likely due to the entrapment and barrier function of EPS and the outer-layer proliferated heterotrophic bacteria. This finding offers a useful process to enable maximum adaptability of anammox granules from heavy metals shocks, allowing anammox technology to be more widely applied.