Microbial community structure and function in response to the shift of sulfide/nitrate loading ratio during the denitrifying sulfide removal process

Enhanced nitrogen removal in modular moving bed constructed wetland at low temperature: Optimization of dissolved oxygen distribution and reconfiguration of core microbial symbiosis

Low temperatures can significantly reduce nitrogen (N) removal efficiency of constructed wetlands (CWs), thus limiting the application of this technology in cold climates and cold areas. We developed modular moving bed constructed wetlands (MMB-CWs) by integrating biofilm method into CWs through specialized design and achieved satisfactory N removal under ambient condition. Evaluating the N removal performance of MMB-CWs at low temperature is crucial for promoting CWs in cold climates. This study investigated the N removal performances of MMB-CWs and the variations of core functional genera at low temperature. Results indicated that the MMB-CW with a 60 % substrate filling rate achieved the highest N removal efficiency of 68.6 %, exceeding horizontal subsurface flow CW by 19.5 % (p < 0.05). The incorporation of vertical baffles and partial substrate filling optimized the distribution and concentration of dissolved oxygen. Although microbial community in the MMB-CW experienced a decline in microbial richness and diversity, N-transforming genera became more concentrated. Proteobacteria increased significantly from 46.6 % to 69.0 % (p < 0.05) as temperature decreased, in which the denitrifying genera including unclassified_f__Comamonadaceae, Hydrogenophaga and Acinetobacter increased significantly (p < 0.05) and dominated the N removal process. The distribution of N-transforming functional genes suggested that denitrification was the primary pathway for N removal at low temperature, while anaerobic ammonium oxidation played a pivotal role as well. The findings reveal the mechanism by which the MMB-CW enhance N removal in low C/N wastewater at low temperature, providing strategy and theoretical support for improving the N removal performance of CWs in response to low temperature stress.

Pre-treatment of excess sludge with sulfide-containing wastewater for composite electron donor formation to enhance denitrification

Utilizing the fermentation liquor of excess sludge (ES) for the denitrification process represents an effective strategy for the valorization of ES and achieving environmentally friendly denitrification. However, ES fermentation technologies require significant energy or chemical product inputs. The present study proposes a novel method utilizing sulfide-containing wastewater to pretreat ES for generating dissolved organic matter (DOM), with sulfides and DOM collectively forming a composite electron donor (S-ES-DOM). The introduction of S-ES-DOM enables the establishment of integrated autotrophic and heterotrophic denitrification (IAHD) process, achieving 100 % denitrification efficiency. Molecular analysis identified an increase in biodegradable components within S-ES-DOM, which were effectively utilized during the IAHD process. The functional genes associated with nitrate-sulfide-organic carbon metabolism and electron transfer exhibited upregulation. The mixotrophic microbial community enables flexible adoption of multiple metabolic pathways. This strategy simultaneously achieves low-cost ES valorization and low-carbon nitrate/sulfide removal through integrated nitrogen-sulfur-carbon metabolism.

Sulfur-based mixotrophic denitrification: A promising approach for nitrogen removal from low C/N ratio wastewater

Sulfur-based mixotrophic denitrification has significant potential as a promising denitrification technology for treating low ratio of carbon-to‑nitrogen (C/N) wastewater. This paper provided an in-depth and comprehensive overview of the sulfur-based mixotrophic denitrification process and discussed the underlying mechanisms and functional microorganisms. Possible electron transfer pathways involved in the sulfur-based mixotrophic denitrification process are also analyzed in detail. This review focused on the various sulfur-based electron donors used in the sulfur-based mixotrophic denitrification process, including S0, S2-, S2O32-, and pyrite (FeS2), and their performances when combined with various carbon sources (such as methanol, ethanol, glucose, and woodchips) were also explored. The analysis of the contribution proportion between autotrophic and heterotrophic denitrification suggested an appropriate C/N ratio can emphasize the dominance of autotrophs, thus exerting synergistic effects and reducing the consumption of carbon sources. Additionally, three strategies, including developing new composites, new bioreactors, and new sulfur sources, were proposed to improve the performance and stability of the sulfur-based mixotrophic denitrification process. Finally, the applications (such as secondary effluent, groundwater, and agricultural/urban storm water runoff), challenges, and perspectives of the sulfur-based mixotrophic denitrification were highlighted. This review provided an in-depth insight into the coupling mechanism of sulfur-based autotrophic and heterotrophic denitrification and guidance for the future implementation of the sulfur-based mixotrophic denitrification process.

Enterobacter sp. HIT-SHJ4 isolated from wetland with carbon, nitrogen and sulfur co-metabolism and its implication for bioremediation

Both autotrophic and heterotrophic denitrification are known as important bioprocesses of microbe-mediated nitrogen cycle in natural ecosystems. Actually, mixotrophic denitrification co-driven by organic matter and reduced sulfur substances are also common, especially in hypoxic environments such as estuarine sediments. However, carbon, nitrogen and sulfur co-metabolism during mixotrophic denitrification in natural water ecosystems has rarely been reported in detail. Therefore, this study investigated the co-metabolism of carbon, nitrogen and sulfur using samples collected from four distinct natural water ecosystems. Results demonstrated that samples from various sources all exhibited the ability for co-metabolism of carbon, nitrogen and sulfur. Microbial community analysis showed that Pseudomonas and Paracoccus were dominant bacteria ranging from 65.6% to 75.5% in mixotrophic environment. Enterobacter sp. HIT-SHJ4, a mixotrophic denitrifying strain which owned the capacity for co-metabolism of carbon, nitrogen and sulfur, was isolated and reported here for the first time. The strain preferred methanol as its carbon source and demonstrated remarkable efficiency for removing sulfide and nitrate with below 100 mg/L sulfide. Under weak acid conditions (pH 6.5-7.0), it exhibited enhanced capability in converting sulfide to elemental sulfur. Its bioactivity was evident within a temperature from 25 °C to 40 °C and C/N ratios from 0.75 to 3. This study confirmed the widespread presence of microbial-mediated synergistic carbon, nitrogen and sulfur metabolism in natural aquatic ecosystems. HIT-SHJ4 emerges as a novel strain, shedding light on carbon, nitrogen and sulfur co-metabolism in natural water bodies. Furthermore, it also serves as a promising candidate microorganism for in-situ ecological remediation, particularly in dealing with contamination posed by nitrate, sulfide, and organic matter.

Dietary crude protein and protein solubility manipulation enhances intestinal nitrogen absorption and mitigates reactive nitrogen emissions through gut microbiota and metabolome reprogramming in sheep

Dietary nutrient manipulation (e.g. protein fractions) could lower the environmental footprints of ruminants, especially reactive nitrogen (N). This study investigated the impacts of dietary soluble protein (SP) levels with decreased crude protein (CP) on intestinal N absorption, hindgut N metabolism, fecal microbiota and metabolites, and their linkage with N metabolism phenotype. Thirty-two male Hu sheep, with an age of six months and an initial BW of 40.37 ± 1.18 kg, were randomly assigned to four dietary groups. The control diet (CON), aligning with NRC standards, maintained a CP content of 16.7% on a dry matter basis. Conversely, the experimental diets (LPA, LPB, and LPC) featured a 10% reduction in CP compared with CON, accompanied by SP adjustments to 21.2%, 25.9%, and 29.4% of CP, respectively. Our results showed that low-protein diets led to significant reductions in the concentrations of plasma creatinine, ammonia, urea N, and fecal total short-chain fatty acids (SCFA) (P < 0.05). Notably, LPB and LPC exhibited increased total SCFA and propionate concentrations compared with LPA (P < 0.05). The enrichment of the Prevotella genus in fecal microbiota associated with energy metabolism and amino acid (AA) biosynthesis pathways was evident with SP levels in low-protein diets of approximately 25% to 30%. Moreover, LPB and LPC diets demonstrated a decrease in fecalNH 4 + -N andNO 2 - -N contents as well as urease activity, compared with CON (P < 0.05). Concomitantly, reductions in fecal glutamic acid dehydrogenase gene (gdh), nitrite reductase gene (nirS), and nitric oxide reductase gene (norB) abundances were observed (P < 0.05), pointing towards a potential reduction in reactive N production at the source. Of significance, the up-regulation of mRNA abundance of AA and peptide transporters in the small intestine (duodenum, jejunum, and ileum) and the elevated concentration of plasma AA (e.g. arginine, methionine, aspartate, glutamate, etc.) underscored the enhancement of N absorption and N efficiency. In summary, a 10% reduction in CP, coupled with an SP level of approximately 25% to 30%, demonstrated the potential to curtail reactive N emissions through fecal Prevotella enrichment and improve intestinal energy and N utilization efficiency.

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

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

Impact of organic carbon on sulfide-driven autotrophic denitrification: Insights from isotope fractionation and functional genes

Additional organics are generally supplemented in the sulfide-driven autotrophic denitrification system to accelerate the denitrification rate and reduce sulfate production. In this study, different concentrations of sodium acetate (NaAc) were added to the sulfide-driven autotrophic denitrification reactor, and the S0 accumulation increased from 7.8% to 100% over a 120-day operation period. Batch experiments revealed a threefold increase in total nitrogen (TN) removal rate at an Ac--C/N ratio of 2.8 compared to a ratio of 0.5. Addition of organic carbon accelerated denitrification rate and nitrite consumption, which shortened the emission time of N2O, but increased the N2O production rate. The lowest N2O emissions were achieved at the Ac--C/N ratio of 1.3. Stable isotope fractionation is a powerful tool for evaluating different reaction pathways, with the 18ε/15ε values in nitrate reduction ranging from 0.5 to 1.0. This study further confirmed that isotope fractionation can reveal denitrifying nutrient types, with the 18ε (isotopic enrichment factor of oxygen)/15ε (isotopic enrichment factor of nitrogen) value approaching 1.0 for autotrophic denitrification and 0.5 for heterotrophic denitrification. Additionally, the 18ε/15ε values can indicate changes in nitrate reductase. There is a positive correlation between the 18ε/15ε values and the abundance of the functional gene napA, and a negative correlation with the abundance of the gene narG. Moreover, 18ε and 15ε were associated with changes in kinetic parameters during nitrate reduction. In summary, the combination of functional gene analysis and isotope fractionation effectively revealed the complexities of mixotrophic denitrification systems, providing insights for optimizing denitrification processes.

Species' functional traits and interactions drive nitrate-mediated sulfur-oxidizing community structure and functioning

IMPORTANCE

Understanding the processes and mechanisms governing microbial community assembly and their linkages to ecosystem functioning has long been a core issue in microbial ecology. An in-depth insight still requires combining with analyses of species' functional traits and microbial interactions. Our study showed how species' functional traits and interactions determined microbial community structure and functions by a well-controlled laboratory experiment with nitrate-mediated sulfur oxidation systems using high-throughput sequencing and culture-dependent technologies. The results provided solid evidences that species' functional traits and interactions were the intrinsic factors determining community structure and function. More importantly, our study established quantitative links between community structure and function based on species' functional traits and interactions, which would have important implications for the design and synthesis of microbiomes with expected functions.

Response of sulfur-metabolizing biofilm to external sulfide in element sulfur-based denitrification packed-bed reactor

Dosing sulfide into the sulfur-packed-bed (S0PB) has great potential to enhance the denitrification efficiency by providing compensatory electron donors, however, the response of sulfur-metabolizing biofilm to various sulfide dosages has never been investigated. In this study, the S0PB reactor was carried out with increasing sulfide dosages by 3.6 kg/m3/d, presenting a decreasing effluent nitrate from 14.2 to 2.7 mg N/L with accelerated denitrification efficiency (k: 0.04 to 0.27). However, 6.5 mg N/L of nitrite accumulated when the sulfide dosage exceeded 0.9 kg/m3/d (optimum value). The increasing electron export contribution of sulfide a maximum of 85.5% illustrated its competition with the in-situ sulfur. Meanwhile, over-dosing sulfide caused serious biofilm expulsion with significant decreases in the total biomass, live cell population, and ATP by 90.2%, 86.7%, and 54.8%, respectively. This study verified the capacity of dosing sulfide to improve the denitrification efficiency in S0PB but alerted the negative effect of exceeded dosing.

Response of the soil microbial community to petroleum hydrocarbon stress shows a threshold effect: research on aged realistic contaminated fields

Introduction

Microbes play key roles in maintaining soil ecological functions. Petroleum hydrocarbon contamination is expected to affect microbial ecological characteristics and the ecological services they provide. In this study, the multifunctionalities of contaminated and uncontaminated soils in an aged petroleum hydrocarbon-contaminated field and their correlation with soil microbial characteristics were analyzed to explore the effect of petroleum hydrocarbons on soil microbes.

Methods

Soil physicochemical parameters were determined to calculate soil multifunctionalities. In addition, 16S high-throughput sequencing technology and bioinformation analysis were used to explore microbial characteristics.

Results

The results indicated that high concentrations of petroleum hydrocarbons (565-3,613 mg•kg^-1, high contamination) reduced soil multifunctionality, while low concentrations of petroleum hydrocarbons (13-408 mg•kg^-1, light contamination) might increase soil multifunctionality. In addition, light petroleum hydrocarbon contamination increased the richness and evenness of microbial community (p < 0.01), enhanced the microbial interactions and widened the niche breadth of keystone genus, while high petroleum hydrocarbon contamination reduced the richness of the microbial community (p < 0.05), simplified the microbial co-occurrence network, and increased the niche overlap of keystone genus.

Conclusion

Our study demonstrates that light petroleum hydrocarbon contamination has a certain improvement effect on soil multifunctionalities and microbial characteristics. While high contamination shows an inhibitory effect on soil multifunctionalities and microbial characteristics, which has significance for the protection and management of petroleum hydrocarbon-contaminated soil.

Aerobic electrotrophic denitrification coupled with biologically induced phosphate precipitation for nitrogen and phosphorus removal from high-salinity wastewater: Performance, mechanism, and microbial community

Electrotrophic denitrification (ED) is a promising nitrogen removal technique; however, the potential of ED coupled with biologically induced phosphate precipitation (BIPP) has not been fully explored. In this study, the performances, mechanisms, and microbial communities of the coupled system were investigated. The results showed that excellent nitrogen and phosphorus removal (both exceeding 92 %) was achieved in the salinity range of 20-60 g/L. ED contributed to approximately 83.4 % of nitrogen removal. BIPP removed approximately 63.5 % of the phosphorus. Batch activity tests confirmed that aerobic/anoxic bio-electrochemical and autotrophic/heterotrophic denitrification worked together for nitrate removal. Sulfate reduction had a negative impact on denitrification. Moreover, phosphorus removal was controlled by ED and calcium ions. The alkaline solution environment created by denitrification may greatly promote the formation of hydroxyapatite. Microbial community analyses indicated that the key bacteria involved in aerobic ED was Arcobacter. These findings will aid in the advanced treatment of high-salinity wastewater.

Complexing agents-free bioelectrochemical trickling systems for highly-efficient mesothermal NO removal: The role of extracellular polymer substances

The biological treatments are promising for nitric oxide (NO) reduction, however, the biotechnology has long suffered from high demands of NO-complexing agents (i.e., Fe(II)EDTA), leading to extra operation costs. In this study, novel complexing agents-free bioelectrochemical systems have been developed for direct NO reduction. The electricity-driven bioelectrochemical trickling system (ED-BTS, a denitrifying biocathode driven by the external electricity and an acetate-consuming bioanode) achieved approximately 68% NO removal without any NO-complexing agents, superior to the bioanode-driven BTS and open-circuit BTS. The extracellular polymeric substances from the biofilms of ED-BTS contained more polysaccharides, humic substrates, and hydrophobic tryptophan that were beneficial for NO reduction. Additionally, the external electricity altered the microbial community toward more denitrifying bacteria and a higher abundance of NO reduction genes (nosZ and cnorB). This study provides a comprehensive understanding of microbial behaviors on the adsorption and reduction of NO and proposes a promising strategy for mesothermal NO biotreatment.

The mixed/mixotrophic nitrogen removal for the effective and sustainable treatment of wastewater: From treatment process to microbial mechanism

Biological nitrogen removal (BNR) is one of the most important environmental concerns in the field of wastewater treatment. The conventional BNR process based on heterotrophic nitrogen removal (HeNR) is suffering from several limitations, including external carbon source dependence, excessive sludge production, and greenhouse gas emissions. Through the mediation of autotrophic nitrogen removal (AuNR), mixed/mixotrophic nitrogen removal (MixNR) offers a viable solution to the optimization of the BNR process. Here, the recent advance and characteristics of MixNR process guided by sulfur-driven autotrophic denitrification (SDAD) and anammox are summarized in this review. Additionally, we discuss the functional microorganisms in different MixNR systems, shedding light on metabolic mechanisms and microbial interactions. The significance of MixNR for carbon reduction in the BNR process has also been noted. The knowledge gaps and the future research directions that may facilitate the practical application of the MixNR process are highlighted. Overall, the prospect of the MixNR process is attractive, and this review will provide guidance for the future implementation of MixNR process as well as deciphering the microbially metabolic mechanisms.

Pyrite-Based Autotrophic Denitrifying Microorganisms Derived from Paddy Soils: Effects of Organic Co-Substrate Addition

The presence of organic co-substrate in groundwater and soils is inevitable, and much remains to be learned about the roles of organic co-substrates during pyrite-based denitrification. Herein, an organic co-substrate (acetate) was added to a pyrite-based denitrification system, and the impact of the organic co-substrate on the performance and bacterial community of pyrite-based denitrification processes was evaluated. The addition of organic co-substrate at concentrations higher than 48 mg L^-1 inhibited pyrite-based autotrophic denitrification, as no sulfate was produced in treatments with high organic co-substrate addition. In contrast, both competition and promotion effects on pyrite-based autotrophic denitrification occurred with organic co-substrate addition at concentrations of 24 and 48 mg L^-1. The subsequent validation experiments suggested that competition had a greater influence than promotion when organic co-substrate was added, even at a low concentration. Thiobacillus, a common chemolithoautotrophic sulfur-oxidizing denitrifier, dominated the system with a relative abundance of 13.04% when pyrite served as the sole electron donor. With the addition of organic co-substrate, Pseudomonas became the dominant genus, with 60.82%, 61.34%, 70.37%, 73.44%, and 35.46% abundance at organic matter concentrations of 24, 48, 120, 240, and 480 mg L^-1, respectively. These findings provide an important theoretical basis for the cultivation of pyrite-based autotrophic denitrifying microorganisms for nitrate removal in soils and groundwater.

Biologically induced phosphate precipitation in heterotrophic nitrification processes of different microbial aggregates: Influences of nitrogen removal metabolisms and extracellular polymeric substances

Phosphorus (P) removal occurred in heterotrophic nitrification process, but its mechanism has not been fully explored. In this study, the P removal performances, pathways, and mechanisms in heterotrophic nitrification processes of different microbial aggregates (activated sludge and biofilm) were investigated. The results showed that the biofilm reactor had more efficient total nitrogen removal (98.65%) and phosphate removal (94.17%). Heterotrophic nitrification and denitrification processes generated alkalinity for biologically induced phosphate precipitation (BIPP), which contributed to 64.12%-78.81% of the overall P removal. The solid phase P content reached 48.03 mg/gSS with hydroxyapatite and calcium phosphate formation. The study clarified that biofilm was beneficial to BIPP because of the nitrogen removal metabolism and extracellular polymeric substance (EPS). Heterotrophic nitrogen removal metabolism was the driving force of BIPP, while EPS with abundant carboxyl and amide groups promoted the precipitation. The study would provide new insights into simultaneous nutrients removal and P recovery from wastewater.

Recent Advances in Autotrophic Biological Nitrogen Removal for Low Carbon Wastewater: A Review

Due to carbon source dependence, conventional biological nitrogen removal (BNR) processes based on heterotrophic denitrification are suffering from great bottlenecks. The autotrophic BNR process represented by sulfur-driven autotrophic denitrification (SDAD) and anaerobic ammonium oxidation (anammox) provides a viable alternative for addressing low carbon wastewater. Whether for low carbon municipal wastewater or industrial wastewater with high nitrogen, the SDAD and anammox process can be suitably positioned accordingly. Herein, the recent advances and challenges to autotrophic BNR process guided by SDAD and anammox are systematically reviewed. Specifically, the present applications and crucial operation factors were discussed in detail. Besides, the microscopic interpretation of the process was deepened in the viewpoint of functional microbial species and their physiological characteristics. Furthermore, the current limitations and some future research priorities over the applications were identified and discussed from multiple perspectives. The obtained knowledge would provide insights into the application and optimization of the autotrophic BNR process, which will contribute to the establishment of a new generation of efficient and energy-saving wastewater nitrogen removal systems.

Hydrogen Sulfide Production with a Microbial Consortium Isolated from Marine Sediments Offshore

Hydrogen, electric energy production, and metal toxic bioremediation are some of the biotechnological applications of sulfate-reducing organisms, which potentially depend on the sulfide produced. In this study, offshore of Yucatan, the capacity to produce hydrogen sulfide using microbial consortia from marine sediment (SC469, PD102, SD636) in batch reactors was evaluated. Kinetic tests were characterized by lactate oxidation to acetate, propionate, CO2 and methane. The inoculum SC469, located in open-ocean, differed strongly in microbial diversity and showed better performance in substrate utilization with the highest hydrogen sulfide production (246 mmolg−1 VSS) at a specific hydrogen sulfide rate of 113 mmol g−1 VSS d−1 with a 0.79 molar ratio of sulfate/lactate. Sulfate-reducing microbial consortia enriched in the laboratory from marine sediments collected offshore in Yucatan and with a moderate eutrophication index, differed strongly in microbial diversity with loss of microorganisms with greater capacity for degradation of organic macromolecules. The sulfate-reducing microorganisms were characterized using Illumina MiSeq technology and were mainly Desulfomicrobium, Clostridium and Desulfobacter.

Can radicals-orientated chemical oxidation improve the reduction of antibiotic resistance genes (ARGs) by mesophilic anaerobic digestion of sludge?

The dissemination of antibiotic resistance genes (ARGs) increases risks towards human health and environmental safety. This work investigates the control of ARGs abundance and bacterial community evolution involved in waste activated sludge (WAS) treatment by chemical conditioning and subsequent mesophilic anaerobic digestion (MAD). The different chemical oxidation processes of ferrous iron-activated oxone and hydrogen peroxide (PMS-Fe²⁺ and H₂O₂-Fe²⁺) and thermal-activated oxone (PMS@80 ℃) were investigated, and the ferric chloride (FeCl₃) and inactivated oxone (PMS) were compared. PMS@80 ℃ decreased the absolute abundance of most ARGs by 10.6-99.3% and that of total ARGs by 66.3%. Interestingly, oxidation pretreatment increased rather than decreased the relative abundance of most ARGs. MAD with PMS@80 ℃ pretreatment increased the absolute abundance of total ARGs by 51.6%, and other MAD processes decreased it by 8.6-47.4%. PMS-Fe²⁺ and PMS@80 ℃ negatively inhibited methane production from 98.3 to 81.7 and 94.4 mL/g VSS in MAD. MAD effluent showed high abundance of Arcobacter genus in the range of 8.1-17.4% upon PMS-based pretreatment, possibly related to sulfur oxidation, nitrate reduction, and blaVEB enrichment. The radicals-orientated chemical oxidation can hardly improve the ARGs elimination by MAD due to the extremely high competitive organics in sludge.

Effects of different carbon sources on the efficiency of sulfur-oxidizing denitrifying microorganisms

This study aims to compare the effects of different carbon sources on sulfur-oxidizing denitrifying microorganisms by using glucose, ethanol, and acetate as carbon sources. Under the same chemical oxygen demand Cr (COD_Cr), nitrate, and sulfide concentrations, the removal rate of nitrate and total organic carbon, and the yield of elemental sulfur in a static experiment and a continuous flow reactor with glucose as the carbon source were lower than those with ethanol and acetic acid as the carbon source. The core sulfur-oxidizing denitrifying bacteria that use glucose as the carbon source were Azoarcus, Geoalkalibacter, and Mangroviflexus; those that use ethanol as the carbon source were Arcobacter, Pseudomonas, and Thauera; those that use acetate as the carbon source were Pseudomonas and Azoarcus. The metabolic activity of microorganisms that use different carbon sources was explained by functional gene detection. The fluctuation of gltA, a functional gene indicating heterotrophic metabolism of microorganisms, was small in three reactors, but that of the sulfur oxidation gene, Sqr, in the reactor with acetic acid as the carbon source was larger. Our results suggest that acetate is a more suitable carbon source for denitrification-desulfurization systems.

Combination of nitrate and sodium nitroprusside dosing for sulfide control with low carbon source loss in sewer biofilm reactors

Nitrate has been widely used in sewer systems for sulfide control. However, significant chemical consumption and the loss of carbon source were observed in previous studies. To find a feasible and cost-effective control strategy of the sulfide control, the effect of nitrate combined with sodium nitroprusside (SNP) dosage strategy was tested in lab-scale sewer biofilm reactors. Results showed that nitrate and SNP were strongly synergistic, with 30 mg N/L nitrate and 20 mg/L SNP being sufficient for sulfide control in this study. While large amount of nitrate alone (100 mg N/L) is required to achieve the same sulfide control effectiveness. Meanwhile, the nitrate combined with SNP could reduce the organic carbon source loss by 80%. Additionally, the high-throughput sequencing results showed that the relative abundance of autotrophic, nitrate reducing-sulfide oxidizing bacteria genera (a-NR-SOB) such as Arcobacter and Sulfurimonas was increased by around 18%, while the heterotrophic, nitrate-reducing bacteria (hNRB) such as Thauera was substantially reduced. It demonstrated that the sulfide control was mainly due to the a-NR-SOB activity under the nitrate and SNP dosing strategy. The microbial functional prediction further revealed that nitrate and SNP promoted the dissimilatory nitrate reduction process which utilizes sulfide as an effective electron donor. Moreover, economic assessment indicated that using the combination of nitrate and SNP for sulfide control in sewers would lower the chemical costs by approximately 35% compared with only nitrate addition.

Comparative analysis of microbial communities from different full-scale haloalkaline biodesulfurization systems

Abstract

In biodesulfurization (BD) at haloalkaline and dO₂-limited conditions, sulfide-oxidizing bacteria (SOB) effectively convert sulfide into elemental sulfur that can be used in agriculture as a fertilizer and fungicide. Here we show which bacteria are present in this biotechnological process. 16S rRNA gene amplicon sequencing of biomass from ten reactors sampled in 2018 indicated the presence of 444 bacterial Amplicon Sequence Variants (ASVs). A core microbiome represented by 30 ASVs was found in all ten reactors, with Thioalkalivibrio sulfidiphilus as the most dominant species. The majority of these ASVs are phylogenetically related to bacteria previously identified in haloalkaline BD processes and in natural haloalkaline ecosystems. The source and composition of the feed gas had a great impact on the microbial community composition followed by alkalinity, sulfate, and thiosulfate concentrations. The halophilic SOB of the genus Guyparkeria (formerly known as Halothiobacillus) and heterotrophic SOB of the genus Halomonas were identified as potential indicator organisms of sulfate and thiosulfate accumulation in the BD process.

Key points

• Biodesulfurization (BD) reactors share a core microbiome

• The source and composition of the feed gas affects the microbial composition in the BD reactors

• Guyparkeria and Halomonas indicate high concentrations of sulfate and thiosulfate in the BD process

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11771-y.

The potential of electrotrophic denitrification coupled with sulfur recycle in MFC and its responses to COD/SO42- ratios

Electrotrophic denitrification is a promising novel nitrogen removal technique. In this study, the performance and the mechanism of electrotrophic denitrification coupled with sulfate-sulfide cycle were investigated under different anodic influent COD/SO₄^2- ratios. The results showed that electrotrophic denitrification contributed to more than 22% total nitrogen removal in cathode chamber. Higher COD/SO₄^2- ratios would deteriorate the sulfate reduction but enhance methane production. Further mass balance indicated that the electron flow utilized by methanogenic archaea (MA) increased while that utilized by sulfate-reducing bacteria (SRB) decreased as the COD/SO₄^2- ratio increased from 0.44 to 1.11. However, higher COD/SO₄^2- ratios would produce more electrons to strengthen electrotrophic denitrification. Microbial community analysis showed that the biocathode was predominantly covered by Thiobacillus that encoded with narG gene. These findings collectively suggest that electrotrophic denitrification could be a sustainable approach to simultaneously remove COD and nitrogen under suitable COD/SO₄^2- ratio based on sulfur cycle in wastewater.

Sulfur transformation and bacterial community dynamics in both desulfurization-denitrification biofilm and suspended activated sludge

Types of microbial aggregates have essential effects on bacterial communities' characteristics, thus affecting the pollutants removal. An up-flow biofilm reactor was used to study the different performances of S^2-/NO₂^- removal and functional genes in suspended sludge and biofilms. The metabolic pathways of sulfurous and nitrogenous pollutants in the desulfurization-denitrification process were proposed. The results showed that S⁰ formation dominated the reactor with a high S^2- concentration. Autotrophic Sulfurovum responsible for S^2-/S⁰ oxidation was the only dominant bacteria in suspended sludge. Heterotrophic Desulfocapsa responsible for SO₄^2- reduction coexisted with Sulfurovum and dominated in biofilms. S^2- oxidation to S⁰ was catalyzed via fccA/B and sqr genes in suspended sludge. S₃^2-/S⁰ oxidation to SO₄^2- was catalyzed via dsrA/B gene in biofilms. SO₄^2- and NO₂^- were removed via the dissimilatory sulfate reduction and denitrification pathway, respectively. This work provides a fundamental and practical basis for optimizing suspended sludge/biofilm systems for S^2-/NO₂^- removal.

Performance evaluation and mechanism of nitrogen removal in a packed bed reactor using micromagnetic carriers at different carbon to nitrogen ratios

Advanced nitrogen removal of effluent discharged from secondary treatment systems can avoid eutrophication. However, the lack of biodegradable organics limits biodenitrification. Packed bed reactors filled with carriers with different micromagnetic field (MMF) strengths were used to perform tertiary denitrification. The results showed that MMF significantly improved the denitrification performance, especially at low C/N ratios. Total nitrogen (TN) removal was increased by 4.12% with 0.6 mT MMF when C/N = 4 and increased by 7.06% and 8.06% with 0.3 mT and 0.9 mT MMFs when C/N = 3, respectively. Zooglea, Flavobacterium, and Denitratisoma contributed to the advanced denitrification performance under MMF. In addition, 0.6 mT MMF enhanced nitrogen metabolism and ABC transporter protein and two-component system activities of microorganisms under C/N = 4; 0.3 mT and 0.9 mT MMFs increased nitrogen, carbohydrate, and amino acid metabolism and ABC transporter protein activities under C/N = 3. These findings indicate that MMF has great potential for advanced denitrification from secondary effluent.

Importance of thermodynamics dependent kinetic parameters in nitrate-based souring mitigation studies

Souring is the unwanted formation of hydrogen sulfide (H₂S) by sulfate-reducing microorganisms (SRM) in sewer systems and seawater flooded oil reservoirs. Nitrate treatment (NT) is one of the major methods to alleviate souring: The mechanism of souring remediation by NT is stimulation of nitrate reducing microorganisms (NRM) that depending on the nitrate reduction pathway can outcompete SRM for common electron donors, or oxidize sulfide to sulfate. However, some nitrate reduction pathways may challenge the efficacy of NT. Therefore, a precise understanding of souring rate, nitrate reduction rate and pathways is crucial for efficient souring management. Here, we investigate the necessity of incorporating two thermodynamic dependent kinetic parameters, namely, the growth yield (Y), and F_T, a parameter related to the minimum catabolic energy production required by cells to utilize a given catabolic reaction. We first show that depending on physiochemical conditions, Y and F_T for SRM change significantly in the range of [0-0.4] mole biomass per mole electron donor and [0.0006-0.5], respectively, suggesting that these parameters should not be considered constant and that it is important to couple souring models with thermodynamic models. Then, we highlight this further by showing an experimental dataset that can be modeled very well by considering variable F_T. Next, we show that nitrate based lithotrophic sulfide oxidation to sulfate (lNRM₃) is the dominant nitrate reduction pathway. Then, arguing that thermodynamics would suggest that S° consumption should proceed faster than S⁰ production, we infer that the reason for frequently observed S⁰ accumulation is its low solubility. Last, we suggest that nitrate based souring treatment will suffer less from S⁰ accumulation if we (i) act early, (ii) increase temperature and (iii) supplement stoichiometrically sufficient nitrate.

Soil Biogeochemical Cycle Couplings Inferred from a Function-Taxon Network

Soil biogeochemical cycles and their interconnections play a critical role in regulating functions and services of environmental systems. However, the coupling of soil biogeochemical processes with their mediating microbes remains poorly understood. Here, we identified key microbial taxa regulating soil biogeochemical processes by exploring biomarker genes and taxa of contigs assembled from metagenomes of forest soils collected along a latitudinal transect (18° N to 48° N) in eastern China. Among environmental and soil factors, soil pH was a sensitive indicator for functional gene composition and diversity. A function-taxon bipartite network inferred from metagenomic contigs identified the microbial taxa regulating coupled biogeochemical cycles between carbon and phosphorus, nitrogen and sulfur, and nitrogen and iron. Our results provide novel evidence for the coupling of soil biogeochemical cycles, identify key regulating microbes, and demonstrate the efficacy of a new approach to investigate the processes and microbial taxa regulating soil ecosystem functions.

Effects of phenol on extracellular polymeric substances and microbial communities from aerobic granular sludge treating low strength and salinity wastewater

The effects of phenol on aerobic granular sludge including extracellular polymeric substances (EPS) and microbial community were investigated for low strength and salinity wastewater treatment. Elevated phenol over 20 mg/L stimulated biological phosphorus removal mainly via co-metabolism with nearly complete phenol degradation, whereas resulted in significant accumulation of nitrate around 4 mg/L. Aerobic granules kept structural stability via enhancing production of extracellular polymeric substances (EPS), especially folds of polysaccharides (PS) and varying functional groups identified through EEM, FTIR and XPS spectral characterizations at increasing phenol loads. Illumina MiSeq sequencing results indicated that elevated phenol decreased the bacterial diversity and richness, and caused remarkable variations in structural and compositions of microbial population. Multiple halophilic bacteria including Stappia, Luteococcus, and Formosa laid the biological basis for stability of aerobic granules and efficient biological nutrients and phenol removal. Redundancy analysis (RDA) suggested the key role of phenol in shaping the relative abundances and predominant genera. This study proved that aerobic granular sludge was feasible for low-saline and phenol-laden low-strength wastewater treatment.

Relationship between functional bacteria in a denitrification desulfurization system under autotrophic, heterotrophic, and mixotrophic conditions

The denitrification desulfurization system can be used to remediate wastewater containing carbon, nitrogen, and sulfur. However, the relationship between autotrophic and heterotrophic bacteria remains poorly understood. To better understand the roles and relations of core bacteria, an expanded granular sludge bed (EGSB) reactor was continuously operated under autotrophic (stage I), heterotrophic (stage II) and mixotrophic (stages III-VII) conditions with a 490-day period. Stage IV represented the excellent S⁰ recovery rate (69.5%). The different trophic conditions caused the obvious succession of dominant bacterial genera. Autotrophic environment (stage I) enriched mostly Thiobacillus, and heterotrophic environment (stage II) was dominated with Azoarcus and Pseudomonas. Thauera, Arcobacter and Azoarcus became the predominant genera under mixotrophic conditions (stage III-VII). Strains belonged to these core genera were further isolated, and all seven isolates were confirmed with denitrifying sulfur oxidation capacity. Heterotrophic strain HDD1 (genus of Thauera) possessed both the highest sulfide degradation and S⁰ recovery rates. Expression levels of cbbM and gltA genes were positively related with the autotrophic and heterotrophic conditions, respectively. NirK gene was highly expressed between log 3.7-log 4.3 during the entire run. Expression of both sqr and soxB genes were closely related with sulfur conversion. More than 57.5% of S⁰ recovery rate could be obtained as sqr gene expression was greater than log 3.2, and while, sulfate was the primary form as soxB gene expression higher than log 3.9. The correlation between core microbial genera was very low from network, indicating a complex and non-specific mutualistic network between bacterial functional groups under each nutrient condition, and a stable coexistence state was possibly formed through utilizing each the secondary or waste metabolites in the mixotrophic conditions. This relationship was beneficial to the stability of the microbial community structure in the denitrification desulfurization system.

Enhanced nitrogen removal by simultaneous nitrification-denitrification and further denitrification (SND-DN) in a moving bed and constructed wetland (MBCW) integrated bioreactor

With the main objective of improving the removal of nitrogen from domestic wastewater and more sustainably, a moving bed and constructed wetland (MBCW) integrated bioreactor was fabricated and evaluated with continuous and intermittent aeration operations. The hybrid system achieves average removal efficiencies up to 90.4 ± 0.8% of chemical oxygen demand (COD), 91.8 ± 1.2% of ammonia nitrogen (NH₄⁺-N), and 77.0 ± 2.6% of total nitrogen (TN), respectively, through a simultaneous nitrification-denitrification and further denitrification (SND-DN) process. This occurs through an intermittent aeration operation followed by continuous aeration with a dissolved oxygen (DO) of 4.0 mg L^-1 due to the complementary and coordinated action of mixed biocarriers. It has resulted in the improvement of the efficiency of SND from 5.9 to 35.3% and in the removal via wetland for DN, between 2.42 and 2.45 g m^-2·d^-1, respectively. The analysis of extracellular polymeric substances (EPS) and high-throughput sequencing demonstrated the enhanced SND mechanism and the evolution of microbial species within the biofilm structure. The total relative abundance of nitrifying bacteria, more aggregated outside the biofilm, decreased by 7.66% compared to denitrifying bacteria, mostly accumulated inside, which increased by 5.49%, respectively.

Bioaugmentation with Thiobacillus sp. H1 in an autotrophic denitrification desulfurization microbial reactor: Microbial community changes and relationship

Thiobacillus sp. H1 was isolated and made into solid bacterial agent. The Thiobacillus sp. H1 agent was dosed into two reactor (all the agent dosed one-time, and multi-dosing bacteria evenly) and run for 40 days, a start-up with no microbial agent bioreactor as control. We found that the operational performance of multi-dosing inoculum reactor was stable, and the amount of elemental sulfur produced remained stable at 143.2-152.3 mg/L. The amount of elemental sulfur generated in the reactor without the addition of the inoculum was gradually increased, and the amount of elemental sulfur generated in the reactor with the inoculum added at one-time was decreased. Two kinds of Thiobacillus gen. and unclassified betaproteobacteria that coordinated the overall community function in the autotrophic denitrification desulfurization system with high-throughput sequencing. The trend of FccAB gene in each bioreactor was similar with the trend of elemental sulfur in the effluent. On the 5th day, the copy number of FccAB in bioreactor II was the highest among the three bioreactors, reaching 11.8 log copies L/g. This study explores the possibility of artificially synthesized denitrifying desulfurization flora in the future.

Succession of functional bacteria in a denitrification desulphurisation system under mixotrophic conditions

Large-scale use of ammonia, sulphate, and nitrate in industrial manufacturing has resulted in the generation of industrial wastewater pollutants. However, approaches to eliminate such contamination have not been extensively studied. Accordingly, in this study, we investigated the succession of bacteria under different influent loadings in a mixotrophic denitrification desulphurisation system. Four expanded granular sludge bed reactors were operated simultaneously. The sulphide loading of reactor I was 1.2 kg/m³‧day, the sulphide load of reactor II was 2.4 kg/m³‧day, and the sulphide load of reactor III was 3.6 kg/m³‧day. The molar ratio of carbon versus nitrogen in the influent under each condition was fixed at 1.26:1, and the molar ratio of sulphur versus nitrogen was fixed at 5:6; each reactor was operated for 90 days. Reactor IV was a verification reactor. The three conditions were repeated, and each condition was operated for 90 days. Middle- and late-stage samples under each condition were sequenced using a high-throughput sequencer. Azoarcus, Thauera, Arcobacter, and Pseudomonas were the core genera of the denitrification desulphurisation system under mixotrophic conditions. The genus Azoarcus was a cornerstone genus of mixotrophic conditions, as demonstrated using the random forest model and correlation network analysis.

Application of activated sludge for odor control in wastewater treatment plants: Approaches, advances and outlooks

Odors from wastewater treatment plants (WWTPs) have attracted extensive attention and stringent environmental standards are more widely adopted to reduce odor emissions. Biological odor treatment methods have broader applications than the physical and chemical counterparts as they are environment-friendly, cost-effective and generate low secondary wastes. The aqueous activated sludge (AS) processes are among the most promising approaches for the prevention or end-of-pipe removal of odor emissions and have the potential to simultaneously treat odor and wastewater. However, AS deodorization biotechnologies in WWTPs still need to be further systematically summarized and categorized while in-depth discussions on the characteristics and underlying mechanisms of AS deodorization process are still lacking. Recently, considerable studies have been reported to elucidate the microbial metabolisms in odor control and wastewater treatment. This paper reviews the fundamentals, characteristics, advances and field experiences of three AS biotechnologies for odor treatment in WWTPs, i.e., AS recycling, microaeration in AS digester and AS diffusion. The underlying deodorization mechanisms of typical odors have been revealed through the summary of recent advances on multi-element conversions, metabolic interactions of bacteria, microscopic characterization and identification of functional microorganisms. Future research aspects to advance the emerging deodorization AS process, such as deodorization mechanisms, simultaneous odor and water treatment, synergistic treatment with other air emissions, are discussed.

Potential applications of endogenous sulfide for enhanced denitrification of low C/N domestic wastewater in anodic mixotrophic denitrification microbial fuel cell: The mechanism of electrons transfer and microbial community

Anodic mixotrophic denitrification microbial fuel cell (MFC) was developed for pollutants removal and electricity generation in treatment of low C/N domestic wastewater. The experimental results show that the MFC achieved up to 100% of acetate, 100% of sulfide, and more than 91% of nitrate removal efficiency in all the MFCs. Particularly, thiosulfate was generated as the main intermediate of sulfide oxidation, and the sulfate generation ratio ranged from 66.93% to 73.76%. Those electrons produced during the acetate and sulfide oxidation were mainly used for denitrification and electricity generation. The microbial community analysis revealed that heterotrophic denitrifying bacteria (HDB) and sulfide-based autotrophic denitrifying bacteria (SADB) were the dominant bacteria for pollutants removal, and those facultative autotrophic bacterium (FAB) were key functional genera for high sulfate generation under both low and high sulfide concentrations. Meanwhile, the microbial functional prediction revealed that sulfide oxidation gene of Sqr and Sox were highly expressed. Moreover, a preliminary sulfide-based autotrophic denitrification (SAD) potential estimation indicated that the sulfide generated in the WWTPs had great potential for denitrification.

Coupled substrate removal and electricity generation in microbial fuel cells simultaneously treating sulfide and nitrate at various influent sulfide to nitrate ratios

The current work coupled simultaneous sulfide and nitrate removal in a Microbial Fuel Cell (MFC). The substrate removal and electricity generation were coupled at influent Sulfide to Nitrate molar ratios (S/N ratios) of 5:0, 5:1, 5:2 and 5:3. The sulfide concentrations used included: 60 mg S/L, 300 mg S/L, 540 mg S/L, 780 mg S/L and 1020 mg S/L. The effect of S/N ratio on the performance of substrate removal was greater at higher influent sulfide concentration. The electricity generation also varied at different influent sulfide concentrations and S/N ratios. The number of electrons generated at S/N ratio of 5:2 was the largest at any fixed influent sulfide concentration. The Pearson correlation showed that effluent sulfate concentration and nitrogen gas had significant positive correlations with steady state voltage (or electronic quantity). Moreover, the simulation models were developed to establish the relation between substrate removal and electricity generation at various S/N ratios.

Performance of a novel IAHD-DSR process with methane and sulfide as co-electron donors

A novel integrated autotrophic and heterotrophic denitrification- denitrifying sulfide removal (IAHD-DSR) process was established in this study for biogas desulfurization to simultaneously remove nitrogen in wastewater. The study demonstrated that the system could utilize methane and sulfide as co-electron donors to replace organic carbon source in IAHD process. Three batch tests (B1, B2 and B3) were set up with IAHD sludge to explore how the novel process works. According to mass balance in B2, methane oxidation and sulfide oxidation contributed 18.75 % and 71.25 % to nitrate removal, respectively; however, the contribution of methane oxidation to total nitrogen (TN) removal reached 84.36 %. Sulfide was mainly responsible for the reduction of nitrate to nitrite, while the methane was for nitrite to nitrogen gas in the presence of insufficient sulfide as electron donors. The TN removal in B2 was almost the same as in normal IAHD-DSR process B3-C. The functional genes mcrA and pmoA responsible for methane oxidation were detected in all three batches, with the abundance of 2.23 ×10⁶ copies/(g dry soil) for mcrA in B1 being the highest in three batches. The sulfide addition in B2 increased the abundance of gene pmoA, indicating the enhancement of nitrite reduction coupled with methane oxidation.

Recirculation ratio regulates denitrifying sulfide removal and elemental sulfur recovery by altering sludge characteristics and microbial community composition in an EGSB reactor

Expanded granular sludge blanket (EGSB) is regarded as a promising reactor to carry out denitrifying sulfide removal (DSR) and elemental sulfur (S⁰) recovery. Although the recirculation ratio is an essential parameter for EGSB reactors, how it impacts the DSR process remains poorly understood. Here, three lab-scale DSR-EGSB reactors were established with the different recirculation ratios (3:1, 6:1 and 9:1) to evaluate the corresponding variations in pollutant removal, S⁰ recovery, anaerobic granular sludge (AGS) characteristics and microbial community composition. It was found that an intermediate recirculation ratio (6:1) could facilitate long-term reactor stability. Adequate recirculation ratio could enhance S⁰ recovery, but an excessive recirculation ratio (9:1) was likely to cause AGS fragmentation and biomass loss. The S⁰ desorbed more from sludge at higher recirculation ratios, probably due to the enhanced hydraulic disturbance caused by the increased recirculation ratios. At the low recirculation ratio (3:1), S⁰ accumulation as inorganic suspended solids in AGS led to a decrease in VSS/TSS ratio and mass transfer efficiency. Although typical denitrifying and sulfide-oxidizing bacteria (e.g., Azoarcus, Thauera and Arcobacter) were predominant in all conditions, facultative and heterotrophic functional bacteria (e.g., Azoarcus and Thauera) were more adaptable to higher recirculation ratios than autotrophs (e.g., Arcobacter, Thiobacillus and Vulcanibacillus), which was conducive to the formation of bacterial aggregates to response to the increased recirculation ratio. The study revealed recirculation ratio regulation significantly impacted the DSR-EGSB reactor performance by altering AGS characteristics and microbial community composition, which provides a novel strategy to improve DSR performance and S⁰ recovery.

Long term performance and dynamics of microbial biofilm communities performing sulfur-oxidizing autotrophic denitrification in a moving-bed biofilm reactor

Sulfide-oxidizing autotrophic denitrification (SOAD) implemented in a moving-bed biofilm reactor (MBBR) is a promising alternative to conventional heterotrophic denitrification in mainstream biological nitrogen removal. The sulfide-oxidation intermediate - elemental sulfur - is crucial for the kinetic and microbial properties of the sulfur-oxidizing bacterial communities, but its role is yet to be studied in depth. Hence, to investigate the performance and microbial communities of the aforementioned new biosystem, we operated for a long term a laboratory-scale (700 d) SOAD MBBR to treat synthetic saline domestic sewage, with an increase of the surface loading rate from 8 to 50 mg N/(m²·h) achieved by shortening the hydraulic retention time from 12 h to 2 h. The specific reaction rates of the reactor were eventually increased up to 0.37 kg N/(m³·d) and 0.73 kg S/(m³·d) for nitrate reduction and sulfide oxidation with no significant sulfur elemental accumulation. Two sulfur-oxidizing bacterial (SOB) clades, Sox-independent SOB (SOB_I) and Sox-dependent SOB (SOB_II), were responsible for indirect two-step sulfur oxidation (S^2-→S⁰→SO₄^2-) and direct one-step sulfur oxidation (S^2-→SO₄^2-), respectively. The SOB_II biomass-specific electron transfer capacity could be around 2.5 times greater than that of SOB_I (38 mmol e^-/(gSOB_II·d) versus 15 mmol e^-/(gSOB_I·d)), possibly resulting in the selection of SOB_II over SOB_I under stress conditions (such as a shorter HRT). Further studies on the methods and mechanism of selecting of SOB_II over SOB_I in biofilm reactors are recommended. Overall, the findings shed light on the design and operation of MBBR-based SOAD processes for mainstream biological denitrification.

Continuous sulfur biotransformation in an anaerobic-anoxic sequential batch reactor involving sulfate reduction and denitrifying sulfide oxidization

The pathways and intermediates of continuous sulfur biotransformation in an anaerobic and anoxic sequential batch reactor (AA-SBR) involving sulfate reduction (SR) and denitrifying sulfide oxidization (DSO) were investigated. In the anoxic phase, DSO occurred in two sequential steps, the oxidation of sulfide (S^2-) to elemental sulfur (S⁰) and the oxidation of S⁰ to sulfate (SO₄^2-). The oxidation rate of S^2- to S⁰ was 3.31 times faster than that of S⁰ to SO₄^2-, resulting in the accumulation of S⁰ as a desired intermediate under S^2--S/NO₃^--N ratio (molar ratio) of 0.9:1. Although, approximately 60% of generated S⁰ suspended in the effluent, about 40% of S⁰ retained in the sludge, which could be further oxidized or reduced in anoxic or anaerobic phase. In anoxic, S⁰ was subsequently oxidized to SO₄^2- under S^2--S/NO₃^--N ratio of 0.5:1. In anaerobic, S⁰ coexist with SO₄^2- (in fresh wastewater) were simultaneously reduced to S^2-, and the reduction rate of SO₄^2- to S^2- was 3.17 times faster than that of S⁰ to S^2-, resulting in a higher production of S⁰ in subsequent anoxic phase. Microbial community analysis indicated that SO₄^2-/S⁰-reducing bacteria (e.g. Desulfomicrobium and Desulfuromonas) and S^2-/S⁰-oxidizing bacteria (e.g. Paracoccus and Thermothrix) co-participated in continuous sulfur biotransformation in the AA-SBR. A conceptual model was established to describe these main processes and key intermediates. The research offers a new insight into the reaction processes optimization for S⁰ recovery and simultaneous removal of SO₄^2- and NO₃^- in an AA-SBR.

H2S removal and microbial community composition in an anoxic biotrickling filter under autotrophic and mixotrophic conditions

Removal of H₂S from gas streams using NO₃^--containing synthetic wastewater was investigated in an anoxic biotrickling filter (BTF) at feed N/S ratios of 1.2-1.7 mol mol^-1 with an empty bed residence time of 3.5 min and a hydraulic retention time of 115 min. During 108 days of operation under autotrophic conditions, the BTF showed a maximum elimination capacity (EC) of 19.2 g S m^-3 h^-1 and H₂S removal efficiency (RE) >99%. When the BTF was operated under mixotrophic conditions by adding organic carbon (10.2 g acetate m^-3 h^-1) to the synthetic wastewater, the H₂S EC decreased from 16.4 to 13.1 g S m^-3 h^-1, while the NO₃^- EC increased from 9.9 to 11.1 g NO₃^--N m^-3 h^-1, respectively. Thiobacillus sp. (98-100% similarity) was the only sulfur-oxidizing nitrate-reducing bacterium detected in the BTF biofilm, while the increased abundance of heterotrophic denitrifiers, i.e. Brevundimonas sp. and Rhodocyclales, increased the N/S ratio during BTF operation. Residence time distribution tests showed that biomass accumulation during BTF operation reduced gas and liquid retention times by 17.1% and 83.5%, respectively.

Regulation of influent sulfide concentration on anaerobic denitrifying sulfide removal

The objective of this study is to find a comprehensive regulation for sulfide removal and elemental sulfur transformation based on the denitrifying sulfide removal process. The experiment was performed based on several influent sulfide concentrations (150-600 mg/L) and nitrate-to-sulfur (N/S) molar ratios (0.5-2.0) at reaction times of 24 and 48 h. Sulfide and nitrate removals were mainly dependent on the influent sulfide concentration at sulfide concentrations of 150-200 and 400-600 mg/L, but on the N/S ratio at sulfide concentrations of 250-350 mg/L. Up to 99.7% and 93.8% of sulfide and nitrate were removed, respectively, with 26.5% of elemental sulfur formed at sulfide concentrations of 250-350 mg/L (N/S of 1.0). Only 4-9.4% of elemental sulfur was formed, with sulfide and nitrate removals of 99.9% and 98.7%, respectively, at sulfide concentrations of 150-200 mg/L. Meanwhile, 46.9-94.7% of sulfate was formed with a nitrogen gas conversion rate of 18.2-57.1%. Fewer microorganisms were detected by fluorescence in situ hybridization (FISH) at high sulfide concentrations of 400-600 mg/L, suggesting that the processes of anaerobic denitrification and desulfurization were inhibited.

Zeolite powder based polyurethane sponges as biocarriers in moving bed biofilm reactor for improving nitrogen removal of municipal wastewater

This study aims to enhance nitrogen removal efficiency of a moving bed biofilm reactor (MBBR) by developing a new MBBR with zeolite powder-based polyurethane sponges as biocarriers (Z-MBBR). Results indicated the total nitrogen (TN) removal efficiency and simultaneous nitrification and denitrification (SND) performance in Z-MBBR were nearly 10% higher than those in the conventional MBBR with sponges as biocarriers (S-MBBR). About 84.2 ± 4.8% of TN was removed in Z-MBBR compared to 75.1 ± 6.8% in S-MBBR. Correspondingly, the SND performance in Z-MBBR and S-MBBR was 90.7 ± 4.1% and 81.7 ± 6.5%, respectively. The amount of biofilm attached to new biocarriers (0.470 ± 0.131 g/g carrier) was 1.3 times more than that of sponge carriers (0.355 ± 0.099 g/g carrier). Based on the microelectrode measurements and microbial community analysis, more denitrifying bacteria existed in the Z-MBBR system, and this can improve the SND performance. Consequently, this new Z-MBBR can be a promising option for a hybrid treatment system to better nitrogen removal from wastewater.

Anammox granule as new inoculum for start-up of anaerobic sulfide oxidation (ASO) process and its reverse start-up

The feasibility of implementing anaerobic ammonium oxidation (anammox) granules to start up high-loading anaerobic sulfide oxidation (ASO) in an upflow anaerobic sludge bed (UASB) reactor was investigated. An innovation method of the reverse start-up of anammox was also validated. Firstly, the reactor was operated to treat sulfide-rich wastewaters into which nitrite was introduced as an electron acceptor. An high-rate performance with sulfide and nitrate removal rates of 105.5 ± 0.11 kg S m^-3 d^-1 and 28.45 ± 3.40 kg N m^-3 d^-1, respectively, was accomplished. Sulfurovum were enriched with the increase of the substrate load and then conquered Candidatus Kuenenia to be the predominant bacteria. Excitation-emission matrix (EEM) spectroscopy showed that the intensities of fluorescence decreased and protein-like substrates were the main components associated with the process of start-up. FT-IR analysis found that the main functional groups indicator were O-H groups. Secondly, the reverse start-up of anammox (achieving 90% TN removal) was achieved immediately when the substrate changed. 16S rRNA analysis indicated the successfully enrichment of anammox bacteria (Candidatus Kuenenia). These results suggest that anammox granules can act as inoculum of high-loading ASO process and the reverse start-up provides a new perspective for the fast initiation of anammox process.

Bio-mixotrophic perchlorate reduction to control sulfate production in a step-feed sulfur-based reactor: A study of kinetics, ORP and bacterial community structure

Excess sulfate production and low concentration of perchlorate removal are the main problems for sulfur-based perchlorate reduction reactor. In this study, the problems were firstly solved by step-feeding under mixotrophic conditions. The performances of step-feed sulfur-based reactor (SFSBR) and up-flow sulfur-based reactor (UFSBR) are compared. At perchlorate of 194 mg/L, acetate of 28.8 mg/L and hydraulic retention time of 0.9 h, the Half-order reaction rate constant and the sulfate production of SFSBR were 29.7 mg^1/2/L^1/2·h and 171 mg/L, respectively, which were superior to those of UFSBR. The oxidation-reduction potential values of SFSBR were lower than that of UFSBR. Meanwhile, the biodiversity along the height of the reactor was decreased by step-feeding. Principal component analysis showed significant interrelations existed among the bacterial community composition and the operational/environmental conditions in each treatment zone. Consequently, the SFSBR provides an effectively alteration for the removal of high perchlorate concentration and control sulfate.

Interactions of functional bacteria and their contributions to the performance in integrated autotrophic and heterotrophic denitrification

Compared to autotrophic and heterotrophic denitrification process, the Integrated autotrophic and heterotrophic denitrification (IAHD) has wider foreground of applications in the condition where the organic carbon, nitrate and inorganic sulfur compounds usually co-exist in the actual wastewaters. As the most well-known IAHD process, the denitrifying sulfide removal (DSR) could simultaneously convert sulfide, nitrate and organic carbon into sulfur, dinitrogen gas and carbon dioxide, respectively. Thus, systematical metabolic functions and contributions of autotrophic and heterotrophic denitrifiers to the IAHD-DSR performance became an problem demanding to be promptly studied. In this work, three upflow anaerobic sludge bioreactors (UASBs) were individually started up in autotrophic (a-DSR), heterotrophic (h-DSR) and mixotrophic conditions (m-DSR). Then, the operating conditions of each bioreactor were switched to different trophic conditions with low and high sulfide concentrations in the influent (200 and 400 mg/L). The removal efficiencies of sulfide, nitrate and acetate all reached 100% in all three bioreactors throughout the operational stages. However, the sulfur transformation ratio ranged from 34.5% to 39.9% at the low sulfide concentration and from 76.8% to 86.7% at the high sulfide concentration in the mixotrophic conditions. Microbial community structure analyzed by the Illumina sequencing indicated that Thiobacillus, which are autotrophic sulfide-oxidizing, nitrate-reducing bacteria (a-soNRB), was the dominant genus (81.3%) in the a-DSR bioreactor. With respect to the mixotrophic conditions, at low sulfide concentration in the m-DSR bioreactor, Thiobacillus (a-soNRB) and Thauera, which are heterotrophic nitrate-reducing bacteria (hNRB), were the dominant genera, with percentages of 48.8% and 14.9%, respectively. When the sulfide concentration in the influent was doubled, the percentage of Thiobacillus decreased by approximately 9-fold (from 48.8% to 5.4%), and the total percentage of Azoarcus and Pseudomonas, which are heterotrophic sulfide-oxidizing, nitrate-reducing bacteria (h-soNRB), increased by approximately 6-fold (from 10.1% to 59.4%). Therefore, the following interactions between functional groups and their functional mechanisms in the DSR process were proposed: (1) a-soNRB (Thiobacillus) and hNRB (Thauera) worked together to maintain the performance under the low sulfide concentration; (2) h-soNRB (Azoarcus and Pseudomonas) took the place of a-soNRB and worked together with hNRB (Thauera and Allidiomarina) under the high sulfide concentration; and (3) a-soNRB (such as Thiobacillus) were possibly the key bacteria and may have contributed to the low sulfur transformation, and h-soNRB may be responsible for the high sulfur transformation in the DSR process.

Toxic effects of vanadium (V) on a combined autotrophic denitrification system using sulfur and hydrogen as electron donors

Vanadium (V) is a common heavy metal and often co-occurs with nitrate in effluents from mining and metal finishing industry. In the present study, the toxic effects of V(V) were examined in a sulfur and hydrogen based autotrophic denitrification system. This combined system achieved simultaneously microbial denitrification and V(V) reduction. High concentration of V(V) (60 and 100 mg/L) inhibited the denitrification activities, while 30 mg/L V(V) had a very slight effect. V(V) induced increases of lactate dehydrogenase release and reactive oxygen species production, which may inhibit nitrate and nitrite reductases activities and abundances of denitrifying functional genes. Moreover, the extracellular polymeric substance production was also suppressed under V(V) stress, thereby decreasing the amount of biofilm biomass. Microbial community analyses suggesting the genus Bacillus may have higher tolerance to V(V). These findings can provide scientific basis for the optimized design of treatment system to remove nitrate and V(V) simultaneously.

Biodesulfurization of sulfide wastewater for elemental sulfur recovery by isolated Halothiobacillus neapolitanus in an internal airlift loop reactor

The biodesulfurization of sulfide wastewater for elemental sulfur recovery by isolated Halothiobacillus neapolitanus in an internal airlift loop reactor (IALR) was investigated. The flocculant producer Pseudomonas sp. strain N1-2 was used to deposit the produced elemental sulfur during biodesulfurization. The functional group analysis indicated that biofloculation was closely associated with NH and CO. The biodesulfurization system performed well under moderate water quality fluctuations (1.29-3.88 kg·m^-3·d^-1 COD; 1.54-3.08 kg·m^-3·d^-1·S^2-) as it maintained stable S^2- removal and sulfur flocculation rates. Meanwhile, the qRT-PCR analysis indicated that the transcriptional level of cbbL decreased in the presence of organic carbon, while the expressions of sqr, sat, and cytochrome C3 increased under higher sulfide stress. Moreover, the relative proportions of Halothiobacillus was strengthened via microbial intervention of the LJN1-3 strain. The S^2- removal efficiency and elemental sulfur production was further improved by 32.5% and 28.2%, respectively, in an IALR.

High recycling efficiency and elemental sulfur purity achieved in a biofilm formed membrane filtration reactor

Elemental sulfur (S⁰) is always produced during bio-denitrification and desulfurization process, but the S⁰ yield and purification quality are too low. Till now, no feasible approach has been carried out to efficiently recover S⁰. In this study, we report the S⁰ generation and recovery by a newly designed, compact, biofilm formed membrane filtration reactor (BfMFR), where S⁰ was generated within a Thauera sp. strain HDD-formed biofilm on membrane surface, and then timely separated from the biofilm through membrane filtration. The high S⁰ generation efficiency (98% in average) was stably maintained under the operation conditions with the influent acetate, nitrate and sulfide concentration of 115, 120 and 100 mg/L, respectively, an initial inoculum volume of approximate 2.4 × 10⁸ cells, and a membrane pore size of 0.45 μm. Under this condition, the sulfide loading approached 62.5 kg/m³·d, one of the highest compared with the previous reports, demonstrating an efficient sulfide removal and S⁰ generation capacity. Particular important, a solid analysis of the effluent revealed that the recovered S⁰ was adulterated with barely microorganisms, extracellular polymeric substances (EPSs), or inorganic chemicals, indicating a fairly high S⁰ recovery purity. Membrane biofilm analysis revealed that 80.7% of the generated S⁰ was accomplished within 45-80 μm of biofilm from the membrane surface and while, the complete membrane fouling due to bacteria and EPSs was generally observed after 14-16 days. The in situ generation and timely separation of S⁰ from the bacterial group by BfMFR, effectively avoids the sulfur circulation (S^2- to S⁰, S⁰ to SO₄^2-, SO₄^2- to HS^-) and guarantees the high S⁰ recovery efficiency and purity, is considered as a feasible approach for S⁰ recovery from sulfide- and nitrate-contaminated wastewater.

Redox-active reactions in denitrification provided by biochars pyrolyzed at different temperatures

The aim of this study was to investigate the role of redox-active components of biochar in the denitrification processes and N₂O reduction. Both biochars pyrolyzed at 300 and 800°C were separated into two redox-active components (i.e., dissolved aromatic moieties and condensed aromatic structure), then applied to study the reduction process of denitrifying bacteria from a paddy soil. Results demonstrated three main pathways of the biochar redox-active components for the denitrification processes and N₂O reduction. The biochar at 300°C and its redox-active components accelerated the first step of denitrification (i.e., NO₃^- reduction), attributable to the oxidation of reduced phenolic moities to donate electrons. The biochar at 800°C and both redox-active components decreased total N denitrified because their dominant quinone moieties and electrical conductivity structure served as alternative electron acceptors. All the biochar treatments accelerated the last step of denitrification and decreased N₂O emission by 74.1%-99.9%. As electron donor, the biochar at 300 °Csignificantly increased humic acid-oxidizing and nitrate-reducing bacteria in the nosZ-harbouring bacterial community, which promoted N₂O reduction. The biochar at 800°C as electron sink decreased N₂O production, and as electron shuttle for nosZ-harbouring denitrifying bacteria, its electrical conductivity structure enhanced N₂O reduction.