Sulfide Removal Rates Research Articles

Electrochemical processes for simultaneous sulfur and energy recoveries from sulfide-containing wastewater

Hydrogen sulfide and dissolved sulfide are notorious and lethal contaminants. The electrochemical process adopting the two-electron sulfide anodic oxidation reaction is an attractive strategy, which can simultaneously recycle and convert the chemical energy and sulfur resources into valued products. Sulfide pollutants are promising electron donors to reduce the electrochemical production cost, which is demonstrated in a sulfide/air fuel cell and a sulfide depolarized electrolyser. Sulfide oxidation behaviors are investigated on the developed IrxRu1-xO2 catalyst. A sulfide/air fuel cell is applied to evaluate the self-driven abilities of sulfur recovery and electricity generation. The sulfide/air fuel cell exhibits a notable discharge current density of > 120 mA cm−2 for 1.0 mol/L Na2S solution and 42.43 ± 1.94 mA cm−2 for the sulfide spent caustic stream. The potentials of sulfide anodic depolarization for electrochemical cost reduction are evaluated in a sulfide depolarized electrolyser for hydrogen production. Its open cell voltage is −0.33 V. For sulfur recovery, the cell can achieve about 20 mA cm−2 at 1.0 V, where the average energy cost of hydrogen production is about 2.39 kWh Nm−3. The sulfide removal rate is 0.26 ± 0.04 kgS m-2h−1, with an average current efficiency of 152.47 ± 28.59 %. This work may shed light on the potential of the incorporation of sulfide contaminants abatement and electrochemical productions.

Insight into the effective electrocatalytic sulfide removal from aqueous solutions using surface oxidized stainless-steel anode and its desulfurization mechanism

The electrochemical oxidation of hydrogen sulfide (H2S) has shown its potential for the real application of H2S emission control in wastewater treatment. In this study, a surface corrosion treatment of stainless steel (SS) was optimized by regulate Ni content in the oxide film on the SS AISI 304 surface for sulfide removal. The X-ray photoelectron spectroscopy and linear sweeping voltammetry results indicated a higher Ni content in the oxide film of surface-oxidized stainless steel (SOSS) attributed to a higher sulfide removal potential. Sulfide removal experiment results showed that SS-150 (with 150 s anodic pretreatment) anodes achieved the highest Ni content of 69% with the best sulfide removal efficiency, i.e., 97% within 48 h, which increased by 20% compared to the untreated SS. This study also demonstrated a strategy for in situ removal of deposited sulfur on the anodes by cathodic treatment at −0.38 V vs. RHE to alleviate the common issue of sulfur passivation. Density functional theory (DFT) calculation revealed that NiOOH was the major active species in SS-150 oxide film for a faster sulfide removal rate. The study developed a SS surface modification process for Ni content regulation that contributed to better sulfide removal efficiency.

Enhancement of sulfide removal and sulfur recovery in piggery wastewater via lighting-anaerobic digestion with bioaugmentation of phototrophic green sulfur bacteria.

Anaerobic pig wastewater treatment commonly generates high sulfide concentrations in the treated wastewater. This study aims to apply phototrophic green sulfur bacteria (PGB) to promote sulfide removal in lighting-anaerobic digestion (lighting-AD) treating pig wastewater. Initially, batch AD tests of pig wastewater with/without PGB addition were carried out under dark (D) and light (L) conditions. The results showed that the lighting-AD with PGB gave a higher growth rate of PGB (0.056h-1) and the highest COD/sulfide removals as compared to the dark-AD with PGB and lighting-AD solely. More experiments under various light intensities were performed in order to find an optimal intensity for PGB growth concurrently with metagenomic changes concerning treatment performance. It appeared that sulfide removal rates had increased as increasing light intensity up to 473lx by giving the highest rate of 12.5mg L-1 d-1 with the highest sulfur element content in the biomass. Contrastingly, many PGB species disappeared at 1350lx exposure subsequently sharply decreasing the rate of sulfide removal. In sum, the application of low light intensities of 400-500lx with bioaugmented PGB could promote PGB growth and activity in sulfide removal in pig wastewater in the lighting of the AD process.

Electrochemical sulfate production from sulfide-containing wastewaters and integration with electrochemical nitrogen recovery

Electrochemical methods can help manage sulfide in wastewater, which poses environmental and health concerns due to its toxicity, malodor, and corrosiveness. In addition, sulfur could be recovered as fertilizer and commodity chemicals from sulfide-containing wastewaters. Wastewater characteristics vary widely among wastewaters; however, it remains unclear how these characteristics affect electrochemical sulfate production. In this study, we evaluated how four characteristics of influent wastewaters (electrolyte pH, composition, sulfide concentration, and buffer strength) affect sulfide removal (sulfide removal rate, sulfide removal efficiency) and sulfate production metrics (sulfate production rate, sulfate production selectivity). We identified that electrolyte pH (3 × difference, i.e., 25.1 to 84.9 μM h−1 in average removal rate within the studied pH range) and sulfide concentration (16 × difference, i.e., 82.1 to 1347.2 μM h−1 in average removal rate) were the most influential factors for electrochemical sulfide removal. Sulfate production was most sensitive to buffer strength (6 × difference, i.e., 4.4 to 27.4 μM h−1 in average production rate) and insensitive to electrolyte composition. Together, these results provide recommendations for the design of wastewater treatment trains and the feasibility of applying electrochemical methods to varying sulfide-containing wastewaters. In addition, we investigated a simultaneous multi-nutrient (sulfur and nitrogen) process that leverages electrochemical stripping to further enhance the versatility and compatibility of electrochemical nutrient recovery.

Response of sulfide autotrophic denitrification process and microbial community to oxytetracycline stress

The coexistence of antibiotics with sulfide and nitrate is common in sewage. Thus, this study explored the removal performance of nitrate and sulfide, and the response of extracellular polymer substances (EPS) and the microbial community to the sulfide autotrophic denitrification (SAD) process under oxytetracycline (OTC) stress. In Phase Ⅰ, the SAD system showed favouranle performance (nitrate removal rate ＞ 92.57%, sulfide removal rate ＞ 97.75%). However, in Phase Ⅳ, at OTC concentrations of 10, 15, and 20 mg/L, the NRE decreased to 76.13%, 40.71%, 11.37%, respectively, and the SRE decreased to 97.58%, 97.09%, 92.84%, respectively. At OTC concentrations of 0, 10, 15, and 20 mg/L, the EPS content were 1.62, 1.75, 2.03, and 1.42 mg/gVSS, respectively. The results showed that SAD performance gradually deteriorated under OTC stress. In particular, when the OTC concentration was 20 mg/L, the EPS content was lower than that of the control test, which could be attributed to the occurrence of microbial death. Finally, high-throughput sequencing results showed that OTC exposure led to gradual domination by heterotrophic denitrifying bacteria.

Process optimization and mechanism for removal of high-concentration chlorine from municipal solid waste incineration fly ash washing wastewater by Friedel's salt

Waterwashing is an important pretreatment method for the reuse of municipal solid waste incineration (MSWI) fly ash. However, the presence of high levels of chlorides and small amounts of sulfides in the waterwashing solution makes it difficult to treat and reuse. Therefore, in this study, a calcium sulfate- Friedel's salt precipitation method was used to dechlorinate and desulfurize in the MSWI fly ash washing solution. This paper mainly focused on the chloride removal, and the effects of factors such as reagent ratios, temperature, and reaction time on chloride removal rate and the two-stage dechlorination and desulfurization process were optimized. The experimental results indicated that when the ratio in the first stage was n(Ca):n(Al):n(Cl) = 3:1.5:1, and in the second stage, n(Ca):n(Al):n(Cl) = 8:4:1, a chloride removal rate of up to 90.5% and a sulfide removal rate of over 99.88% could be obtained. The deposited particles were analyzed by using FE-SEM, XRD, and FTIR to investigate their size, morphology, phase composition, and functional groups. The study revealed that excessively high or low reagent ratios could reduce the interlayer spacing of Friedel's salt. Additionally, high temperatures led to the decomposition of Friedel's salt, and the dechlorination efficiency was affected.

Screening and combination selection of multifunctional actinomycetes for aerobic composting.

To screen the most effective combination of multipurpose actinomycete strains for aerobic composting, lignocellulose-degrading strains were obtained through enrichment culture, separation and purification, and multiselection culture. The isolated strains were identified on the basis of morphology and 16S rRNA gene sequencing and comparison. The obtained actinomycetes were screened for the lignocellulose degradation rate, ammonia and hydrogen sulfide removal rate, and cellulase activity. Subsequently, a combination of strains with ecological coordination and complementary functions was determined through antagonistic tests. The combined strains were subjected to a straw fermentation test to evaluate their degradation effect. As a result, 20 strains of actinomycetes were isolated and identified from more than 56 samples from different sources, including 18 strains of Streptomyces sp. and 2 strains of Nocardiopsis sp. After a number of screenings, eight strains of actinomycetes with strong function were obtained. From the results of function and antagonistic tests, strains A3, A7, A8, A11, and A16 were selected to form consortia. The straw fermentation test showed that the lignocellulose degradation rate of the strain combination was as high as 39.8%, which was significantly higher than that of eachevery single strain (P < 0.05). The screened multifunctional actinomycete strains and their combination enriched the actinomycete germplasm resources used for microbial enhanced aerobic composting.IMPORTANCEWith the development of animal husbandry in China, the production of a large amount of livestock and poultry manure has become one of the main agricultural pollution sources. High-temperature aerobic composting stands out as one of the most crucial methods for the safe and resourceful utilization of livestock and poultry manure, serving as an essential link between crop cultivation, animal breeding, and sustainable agricultural development. Numerous studies have demonstrated that the addition of exogenous multifunctional bacterial agents to compost reduces not only harmful emissions but also sequesters or increases essential nutrients. However, these efficacies depend on the specific functions of the bacteriophage itself, the harmonization and complementarity within the colony, and its ability to adapt to the environment. In recent years, relatively few studies have been conducted on actinomycetes. This experiment provides excellent actinomycete resources for the production of high-efficiency and high-quality compost compound microbial agents of manure and straw.

Effect of chemical composition of coal ash used to prepare granulated coal ash on the removal of hydrogen sulfide from water.

Granulated coal ash was prepared by mixing coal ash derived from a coal electric power plant and blast furnace cement, to remove hydrogen sulfide from aquatic environment. In this study, we investigate the effects of the composition of the coal ash used to prepare the granulated coal ash on its hydrogen sulfide removal performance. Manganese, magnesium, and calcium contents in the granulated coal ash were found to be the major factors in controlling the rate of hydrogen sulfide removal. The kinetics of hydrogen sulfide removal by the granulated coal ash were expressed as a first-order equation with a rate constant of 0.0081- 0.080 h-1 . The rate constant for hydrogen sulfide removal obtained in this study corelated well with the manganese content in the granulated coal ash. The increasing surface pH attributed to the hydrolysis of calcium and magnesium on the surface of the granulated coal ash slightly increased the hydrogen sulfide removal rate.

Continuous H2S removal from biogas using purple phototrophic bacteria

Biogas from anaerobic digestion requires desulfurisation before its intended use due to the corrosive nature of H2S. Anaerobic digesters produce biogas continuously and require a continuous process for desulfurisation. Commonly, H2S is removed using adsorption to solid media (iron sponge) or absorption and removal through chemical processes (scrubbing), requiring regeneration or replacement of sorbents. As an alternative, a continuous, anaerobic H2S removal process, utilising purple phototrophic bacteria was developed. The removal is driven by light as an energy source and potentially reduces the requirement for caustic. A desulfurisation bubble column was fed continuously with a synthetic biogas mixture (2000/5000 ppmV H2S, 30% CO2, CH4 balance) at sulfide loading rates ranging from 3.06 to 11.88 mg-S d−1. The liquid was inoculated with purple phototrophic bacteria, nutrients supplied via centrate, an anaerobic digestion residue, and externally irradiated with IR-light. The maximum sulfide removal rate was 10.13 ± 0.06 mg-S (Lh)−1 at a loading rate of 11.83 mg-S (Lh)−1, and the biomass oxidised the sulfide to sulfate utilising electrons for growth. Initially, caustic was dosed to control pH, which was replaced by hydraulic flushing (HRT 4 days), resulting in a mean pH of 6.8 at applied sulfide loading rate of 9.44 mg-S (Lh)−1. A reduction in HRT to 2 days resulted in performance loss. Thus, controlling the biomass inventory was found to be the major challenge of the process. Overall, the process can run caustic-free, and integrate with anaerobic digestion using the centrate as a nutrient source, with light supply limiting feasibility for night-time operation in a scaled process.

Investigating role of abiotic side and finding optimum abiotic condition for improving gas biodesulfurization using Thioalkalivibrio versutus

Hydrogen sulfide (H2S) is a super toxic substance that produces SOx gases when combusted. Therefore, it should be removed from gas streams. Biodesulfurization is one of the developing methods for removing sulfide. Gas biodesulfurization must be accelerated to be competitive with chemical processes. This process has two sides: biotic and abiotic sides. To increase the rate of sulfide removal, this substance should be given to the bacteria in the maximum amount (Max. − RHS B). Therefore, it is necessary to minimize the rate of adverse abiotic reactions of sulfide (Min. − RHS A). Minimizing the sulfide reaction with biosulfur and oxygen and thiosulfate generation (Min. − RHS thio2) was assessed in de-microbized medium. It was concluded that the pH should be kept as low as possible. The kinetics of thiosulfate formation from sulfide oxidation (− RHS thio1) are strongly dependent on the sulfide concentration, and to minimize this reaction rate, sulfide should be gently injected into the culture. To minimize sulfide reduction to hydrogen sulfide (Min. − RHS rev), the pH should be kept as high as possible. Using the Design Expert v.13, a model was driven for the abiotic side to obtain optimum condition. The pH value was found to be 8.2 and the sulfide concentration to 2.5E−05 M. Thioalkalivibrio versutus cultivation under identified abiotic conditions resulted in biological removal of sulfide up to 1.5 g/h. The culture was not able to remove 2 g/h input sulfide, and to increase this, the biotic side should be studied.

Characterization of sulfide oxidation and optimization of sulfate production by a thermophilic Paenibacillus naphthalenovorans LYH-3 isolated from sewage sludge composting

The sulfur-containing odor emitted from sludge composting could be controlled by sulfide oxidizing bacteria, yet mesophilic strains show inactivation during the thermophilic stage of composting. Aimed to investigate and characterize the thermotolerant bacterium that could oxidize sulfide into sulfate, a heterotrophic strain was isolated from sewage sludge composting and identified as Paenibacillus naphthalenovorans LYH-3. The effects of various environmental factors on sulfide oxidation capacities were studied to optimize the sulfate production, and the highest production rate (27.35% ± 0.86%) was obtained at pH 7.34, the rotation speed of 161.14 r/min, and the inoculation amount of 5.83% by employing Box-Behnken design. The results of serial sulfide substrates experiments indicated that strain LYH-3 could survive up to 400 mg/L of sulfide with the highest sulfide removal rate (88.79% ± 0.35%) obtained at 50 mg/L of sulfide. Growth kinetic analysis presented the maximum specific growth rate µm (0.5274 hr−1) after 22 hr cultivation at 50°C. The highest enzyme activities of sulfide quinone oxidoreductase (0.369 ± 0.052 U/mg) and sulfur dioxygenase (0.255 ± 0.014 U/mg) were both obtained at 40°C, and the highest enzyme activity of sulfite acceptor oxidoreductase (1.302 ± 0.035 U/mg) was assessed at 50°C. The results indicated that P. naphthalenovorans possessed a rapid growth rate and efficient sulfide oxidation capacities under thermophilic conditions, promising a potential application in controlling sulfur-containing odors during the thermophilic stage of sludge composting.

The interaction between Pseudomonas C27 and Thiobacillus denitrificans in the integrated autotrophic and heterotrophic denitrification process

Compared to autotrophic and heterotrophic denitrification process, the integrated autotrophic and heterotrophic denitrification (IAHD) shows wider foreground of applications in the actual wastewaters with organic carbon, nitrogen and sulfur co-existing. The efficient co-removal of sulfur, nitrogen, and carbon in the IAHD system is guaranteed by the interaction between heterotrophic and autotrophic denitrificans. In order to further explore the interaction between functional bacteria, Pseudomonas C27 and Thiobacillus denitrifcans were selected as typical heterotrophic and autotrophic bacteria, and their characteristics metabolic responses to different sulfide concentrations were studied. Pseudomonas C27 had higher metabolic activity than T. denitrificans in the IAHD medium with sulfide concentration of 3.12–15.62 mmol/L. Moreover, the fastest sulfide removal rate (0.35 mmol/L·h) was achieved with a single inoculation of Pseudomonas C27. Meanwhile, in mixed inoculant conditions, the interaction between Pseudomonas C27 and T. denitrificans (P:T = 3:1, P:T = 1:1 and P:T = 1:3) yielded the highest sulfide removal efficiency (more than 85%) when sulfide concentration was 6.25–12.5 mmol/L. Additionally, the sulfide removal rate increased with the inoculation proportion of Pseudomonas C27. Thus, this apparent interaction provided a theoretical basis for further understanding and guidance on the efficient operation of IAHD system.

Ultrasonic desulfurization of amphiphilic magnetic-Janus nanosheets in oil-water mixture system

Fe3O4 was obtained by reacting FeCl2 and FeCl3 with polyethylene glycol, and labeled onto a amphiphilic Janus nanosheet. It was confirmed by infrared spectroscopy, SEM, AFM and EDS that the Fe3O4 nanoparticles changed from hydrophilic to amphiphilic. The oxidative desulfurization performance of amphiphilic iron oxide was studied. Results showed that the Janus nanosheets labeled with Fe3O4 could significantly improve the removal rate of thiophene sulfide in simulated oil synergistically with ultrasonic waves, and the desulfurization rate could reach 100%. Further, the effect of ultrasound on the sensing ability of the oil–water interface was studied and the ultrasonic attenuation coefficient was calculated. In addition to the desulfurization mechanism of Fe3O4, it was found that although the ultrasonic attenuation coefficient of the amphiphilic nanosheets was high, the number of hydroxyl radicals determined the desulfurization efficiency. The amphiphilic Fe ions were more favorable for the formation of hydroxyl radicals than the single hydrophilic ones.

Pollutant-Removing Biofilter Strains Associated with High Ammonia and Hydrogen Sulfide Removal Rate in a Livestock Wastewater Treatment Facility

This study analyzed the microbial community metagenomically to determine the cause of the functionality of a livestock wastewater treatment facility that can effectively remove pollutants, such as ammonia and hydrogen sulfide. Illumina MiSeq sequencing was used in analyzing the composition and structure of the microbial community, and the 16S rRNA gene was used. Through Illumina MiSeq sequencing, information such as diversity indicators as well as the composition and structure of microbial communities present in the livestock wastewater treatment facility were obtained, and differences between microbial communities present in the investigated samples were compared. The number of reads, operational taxonomic units, and species richness were lower in influent sample (NLF), where the wastewater enters, than in effluent sample (NL), in which treated wastewater is found. This difference was greater in June 2019 than in January 2020, and the removal rates of ammonia (86.93%) and hydrogen sulfide (99.72%) were also higher in June 2019. In both areas, the community composition was similar in January 2020, whereas the influent sample (NLF) and effluent sample (NL) areas in June 2019 were dominated by Proteobacteria (76.23%) and Firmicutes (67.13%), respectively. Oleiphilaceae (40.89%) and Thioalkalibacteraceae (12.91%), which are related to ammonia and hydrogen sulfide removal, respectively, were identified in influent sample (NLF) in June 2019. They were more abundant in June 2019 than in January 2020. Therefore, the functionality of the livestock wastewater treatment facility was affected by characteristics, including the composition of the microbial community. Compared to Illumina MiSeq sequencing, fewer species were isolated and identified in both areas using culture-based methods, suggesting Illumina MiSeq sequencing as a powerful tool to determine the relevance of microbial communities for pollutant removal.

Eight-membered ring petal-shaped V8 cluster: An efficient heterogeneous catalyst for selective sulfur oxidation

An eight-membered ring petal-shaped cluster [V8ⅣO8(CH3O)16(C2O4)](C6NH16)2(CH3OH)2 (V8) has been successfully designed and synthesized via hydrothermal method. Structure analysis revealed that each vanadium atom was in an octahedral geometrical configuration six-coordinated, two adjacent vanadium atoms were linked by oxygen atoms on oxalic acid to form a ring. The selective sulfur oxidation experiments reveal that V8 had good catalytic activity under mild conditions, and the removal rate of phenyl sulfide was >99% within 4 h at 40 °C. In addition, the open aperture Z-scan test of V8 was carried out and found that V8 also has latent application value as nonlinear optical (NLO) material.

Revealing the role of nitrate on sulfide removal coupled with bioenergy production in Chlamydomonas sp. Tai-03: Metabolic pathways and mechanisms

Recently, simultaneous sulfide removal and bioenergy production by microalgal treatment have attracted growing attention. However, the response of nitrogen metabolism to the sulfide-removal process has yet to be explored. Here, variable levels of sulfide could be completely removed by Chlamydomonas sp. Tai-03 under both high and low nitrate conditions in synthetic wastewaters. The highest sulfide removal rate of 5.56 mg-S L−1 h−1 was achieved with the addition of 100 mg L−1 sulfide in the presence of high nitrate. Meanwhile, sulfide was chemically oxidized to sulfate and then ingested by microalgae. Interestingly, sulfide-removal efficiency critically depended on nitrate concentration. Sulfide can also enhance the ability of microalgae to assimilate nitrogen. Based on the analysis of sulfur- and nitrogen-related metabolic profiling, serine as a precursor decreased by 94 % under low levels of nitrate, which induced the significant inhibition of cysteine and methionine biosynthesis. The results indicated that nitrogen source played a critical role in the sulfur cycle because of the positive relationship between the aforementioned metabolic processes and nitrate concentration. Additionally, sulfide can improve lipid and carbohydrate productivity under high levels of nitrate. This study enhances our understanding of the mechanisms underlying the simultaneous removal of sulfide and alternative bioenergy production.

Autotrophic sulfide removal by mixed culture purple phototrophic bacteria

Current H2S treatment methods for sour gases require considerable amounts of chemicals and energy, or in case of biological treatment, unwanted diluents such as oxygen or nitrogen may be introduced. In order to reduce those requirements, the viability of an anaerobic biological H2S removal process using purple phototrophic bacteria (PPB) was investigated in this study. PPB can use sunlight, and centrate as nutrient source, thus potentially reducing energy and chemical requirements. An added benefit is the production of biomass with potential uses, such as single cell protein. An inoculum of PPB enriched from domestic wastewater was grown photoautotrophically with sulfide as the electron donor and inorganic carbon in a mixed culture. Additionally, synthetic medium and centrate as well as high (56 ± 11 Wm-2) and low (27 ± 3 Wm-2) IR irradiation were trialled. Finally, a process model was developed to study biomass specific removal rates and yield. The results showed that a mixed culture of PPB removed sulfide completely in synthetic media (121 ± 9 mg-S.L−1) at a maximum rate of 1.79 ± 0.16 mg-S(Lh)−1 (low irradiance) and 2.9 mg-S(Lh)−1 (high irradiance). The pH increased in both experiments from about 8.5 to 9. Sulfide removal rates using centrate and low irradiance were similar. However Fe and Mn were found to be limiting growth and sulfide removal. In all experiments, Chromatiaceae (purple sulfur bacteria) were most abundant at the end of the experiment, while at the start purple non-sulfur bacteria were most abundant (from the inoculum). Process modelling and experimental work identified the sulfide oxidation to be a multi-step process with accumulation of intermediates. Specific rates were directly dependent on light input, doubling at high irradiance. Sulfide oxidation was estimated at 0.100 ± 0.014 h−1 (0.085 ± 0.012 g-S(g-VS.h)−1) at low irradiance, and the biomass yield at 0.86 ± 0.05 mg-COD.mg-COD−1. This process model enables the virtual evaluation of autotrophic sulfide removal by PPB in a continuous scaled-up process. Overall, the photoautotrophic removal of sulfide seems to be a viable option, especially because of the possibility of using sunlight as an energy source and centrate as a nutrient source.

Heterotrophic sulfide-oxidizing nitrate-reducing bacteria enables the high performance of integrated autotrophic-heterotrophic denitrification (IAHD) process under high sulfide loading

Micro-aerobic enhancement technology has been developed as an effective tool to enhance simultaneous removal of sulfide, nitrate and organic carbon during the integrated autotrophic-heterotrophic denitrification (IAHD) process under high loading; however, its mechanism of enhancement for functional bacteria remains ambiguous. In this study, we discovered that heterotrophic sulfide-oxidizing nitrate-reducing bacteria (h-soNRB) are responsible for enhancing IAHD performance under micro-aerobic conditions with high sulfide loading. In a continuous IAHD bioreactor, aeration rate of 2.6 mL min−1·L−1 promoted 2 to 4 times higher removal efficiencies of sulfide, nitrate and acetate with an influent sulfide concentration of 18.75 mmol/L. Metagenomic analysis revealed that trace oxygen stimulated the abundance of genes responsible for sulfide oxidation (sqr, glpE, pdo, sox and cysK), which were upregulated by 15.2%–129.9%, and the genes encoding nitrate reductase were up-regulated by 67.4%. The increased acetate removal efficiency was attributed to upregulation of ack, pta and TCA cycle related genes. The h-NRB Pseudomonas, Azoarcus, Thauera and Halomonas were detected and regarded as h-soNRB in our bioreactor. According to Illumina MiSeq sequencing, these genera were absolutely dominant in the micro-aerobic microbial community at relative abundances ranging from 82.72% to 90.84%. The sulfide, nitrate and acetate removal rates of Pseudomonas C27, a typical h-soNRB, were at least 10 times higher under micro-aerobic conditions than under anaerobic conditions. Besides, the sulfur, nitrogen and carbon metabolic network was constructed based on the Pseudomonas C27 genome. The pdo and cysK genes found in this strain may be the most advantageous for autotrophic sulfide oxidizing nitrate reducing bacteria (a-soNRB), which are closely related to the high-efficiency sulfide, nitrate and acetate removal performance under high sulfide concentrations and a limited oxygen supply. In addition, after micro-aerobic cultivation, the anaerobic sulfide loading tolerance of the IAHD bioreactor increased from 18.75 to 37.5 mmol/L with sulfide, nitrate and acetate removal efficiencies increasing 1.5 to 3 times, which suggests that intermittent micro-aeration might be a more economical and efficient regime for high-sulfide IAHD regulation.

A novel strategy for anammox consortia preservation: Transformation into anoxic sulfide oxidation consortia

The preservation of anaerobic ammonia oxidation (anammox) consortia is crucial for the rapid start-up and the process stability of the anammox based bioreactor. This work proposed and evaluated the feasibility of an anammox consortia preservation strategy, in which the anammox sludge was transformed into intermediate anoxic sulfide oxidation (ASO) functional microorganisms. Initially, the ASO process was successfully started up by inoculating anammox sludge and the overall sulfide and nitrate removal rates stabilized at 57.5 ± 0.22 and 10.0 ± 0.18 kg m−3 day−1, respectively. Then, the bioreactor function was reversely transformed into anammox, whose nitrogen removal rate reached 1.68 kg m−3 day−1. Granule characteristics analysis revealed that both biomass and extracellular polymeric substance content returned to their original states after the reverse start-up. Although the population of Candidatus_Kuenenia was greatly declined during ASO process, its richness was successfully recovered after the reverse start-up of the anammox process. The inferred metagenomes analysis demonstrated that the shifts in functional microorganisms were related to variation in the main metabolic pathways. The specific activities of anammox and ASO both are regarded as key indicators for the successful start-up of bioreactor. This work revealed a novel technique for the preservation of anammox consortia and might be a potential strategy for overcoming the drawback of long start-up time.

Mechanisms of sulfur selection and sulfur secretion in a biological sulfide removal (BISURE) system

Biological desulfurization technology is a sustainable process for the sulfide removal from biogas, which has multiple advantages. In this study, a biological sulfide removal (BISURE) system was established to investigate the working performances and process mechanisms. The results showed that the sulfide removal rate was 2.30 kg-S/(m3 d), the sulfide removal efficiency was higher than 98%, the sulfur production rate was 1.76 kg-S/(m3 d), the sulfur selectivity was 75.02 ± 3.63% and the main form of products (sulfur compounds) was Rosickyite-S and S8. The performance of BISURE system was supported by the dominant genus (abundance more than 60%) of sulfur-oxidizing bacteria (SOB) which shifted to Thiovirga at the high SLR. The sqr and dsrA genes could serve as the indicators for the pathway of two-step sulfide oxidation, i.e. “partial sulfide oxidation (PSO, sulfide → sulfur)” and “complete sulfide oxidation (CSO, sulfur → sulfate)”. The sulfur selectivity was improved by enhancing PSO and inhibiting CSO with the indication of two genes. The cellular sulfur secretion was revealed, and the “outer-membrane vesicles (OMVs)-dependent” sulfur-secreting hypothesis was proposed to explain the transportation of elemental sulfur from inside to outside of SOB cells. The findings of this work provide a new perspective to understand the sulfur selection of sulfide bio-oxidation and the sulfur secretion of SOB cells so as to promote the development of biological desulfurization technology.