Determination of the Acute and Chronic Toxicity of Sulfate from the Sulfur Autotrophic Denitrification Process to Juvenile Zebrafish (Danio rerio).

Sulfur-based materials are widely used as electron donors for denitrification to enhance nitrogen removal from water. This leads to an increased sulfate concentration in the effluent or sulfate accumulation in recirculating aquaculture systems. This study explored acute and chronic toxicity of sulfate to juvenile zebrafish (Danio rerio) and investigated the histopathological changes in the gills of juvenile zebrafish exposed to sulfate. Results show that zebrafish had a high tolerance to sulfate, with no acute toxicity at sulfate concentrations from 250 to 3200 mg/L. For the chronic toxicity study, it was found that zebrafish mortality decreased with the increase in sulfate concentrations ranging from 250 to 1500 mg/L. In contrast, when the sulfate concentration was 1500-3000 mg/L, zebrafish mortality increased with the increasing sulfate concentration. In addition, in the ion balance test, KCl was added to balance the effects of Na+ from the Na2SO4 used to obtain the desired sulfate concentrations, showing that fish mortality correspondingly increased with increasing KCl addition. Furthermore, when living in an environment with elevated sulfate concentrations for a long period, changes were observed in the morphology, behavior, and gill tissue of the zebrafish, including slow and lateral swimming; bottom settling; and large opening and closing, lamellar fusion, and necrosis of gills. This research reveals the toxicity of sulfate to aquatic organisms, providing a scientific basis for the promotion and application of sulfur or sulfur-based materials in autotrophic reduction processes for wastewater treatment.

Effect of nitrate and sulfate coexistence on hydrogen autotrophic reduction of antimonate (Sb(V)) and microbial community structures.

Hydrogen autotrophic bioreduction of antimonate (Sb(V)) to antimonite (Sb(III)) is an alternative approach for removing antimony (Sb) from water. This study investigated Sb(V) reduction kinetics and the effects of various parameters on the Sb(V) removal performance in a hydrogen autotrophic reaction system (HARS). Sb(V) reduction in the HARS was well fitted to the Michaelis-Menten model, showing a positive correlation between the reaction rate and biomass. The maximum specific substrate removal rates were 0.29-4.86 and 6.82-15.87 mg Sb(V)/(g·VSS·h) at initial Sb(V) concentrations of 500 µg/L and 10 mg/L, respectively. Coexisting nitrate significantly inhibited Sb(V) reduction, and the inhibition intensified with increasing nitrate concentration. However, coexisting sulfate had a positive effect on Sb(V) reduction, and the sulfate effectively enhanced total antimony (TSb) removal performance by generating sulfide from sulfate reduction. Illumina high-throughput sequencing technology was used to determine the changes in microbial community structure during different periods in the HARS, revealing the effects of co-existing ions on the dominant Sb(V) reducing bacteria. In the HARS, Longilinea and Terrimonas were the dominant genera in the presence of nitrate, and Longilinea was the dominant genus in the presence of sulfate, at initial Sb(V) concentration of 500 µg/L. When the concentration of Sb(V) was 10 mg/L, Longilinea and Thauera were the dominant genus in the HARS for treating water co-polluted with nitrate and sulfate, respectively. These results provide a theoretical basis of the application of HARS for the bio-remediation of Sb(V) contaminated water.

Electrodialysis ion-exchange membrane bioreactor (EDIMB) to remove nitrate from water: Optimization of operating conditions and kinetics analysis.

Nitrate pollution has become a worldwide problem. In this study, we remove nitrate from water by electrodialysis ion-exchange membrane bioreactor (EDIMB) and enabling simultaneous nitrate enrichment and denitrification. In this reactor, nitrate migrated from the water chamber to the biological chamber via electrodialysis and was degraded by microorganisms. The effects of voltage and biomass concentration on the reactor performance were examined, and the kinetics data of the water chamber and biological chamber were fitted. The experimental results showed that the migration of nitrate in the water chamber conformed to the first-order model, and the constructed zero-Michaelis-Menten model described changes in nitrate concentration in the biological chamber. Furthermore, when the inflow nitrate concentration was 40 mg N/L, 5 V was the best voltage, and 3.00 g VSS/L was the best biomass concentration. The nitrate removal rate in the water chamber was 98.94%, and there was no accumulation of nitrate or nitrite in the biological chamber. Compared with traditional ED processes, the nitrate removal efficiency was 8.86% higher, and the current efficiency was 22.14% higher. The total organic carbon (TOC) of the water chamber was only 1.43 mg C/L, which proves that the structure of the EDIMB confined the denitrifying bacteria and organic carbon donors in the biological chamber and avoided secondary pollution in the water chamber. Microbial community analysis showed that Thauera (66.06%) was the dominant bacterium in the EDIMB system, and Azoarcus (9.81%) was a minor denitrifying genus.

Rice washing drainage (RWD) embedded in poly(vinyl alcohol)/sodium alginate as denitrification inoculum for high nitrate removal rate with low biodiversity.

Immobilization technology with low maintenance is a promising alternative to enhance nitrate removal from water. In this study, washing rice drainage (RWD) was immobilized by poly(vinyl alcohol)/sodium alginate (PVA/SA) to obtain RWD-PVA/SA gel beads as inoculum for denitrification. When initial nitrate concentration was 50 mg N/L, nitrate was effectively removed at rates of 50-600 mg/(L∙d) using acetate as carbon source (C/N = 1.25). Arrhenius activation energy (Ea) of nitrate oxidoreductase was 28.64 kJ/mol for the RWD-PVA/SA gel beads. Temporal and spatial variation in microbial community structures were revealed along with RWD storage and in the reactors by Illumina high-throughput sequencing technology. RWD-PVA/SA gel beads has a simple (operational taxonomic units (OTUs) ã€ˆ100). Dechloromonas, Pseudomonas, Flavobacterium and Acidovorax were the most four dominant genera in the denitrification reactors inoculated with RWD-PVA/SA gel beads. This study provides an inoculum for denitrification with high nitrate removal performance and simple microbial community structures.

Enhanced biological antimony removal from water by combining elemental sulfur autotrophic reduction and disproportionation.

Antimony (Sb), a toxic metalloid, has serious negative effects on human health and its pollution has become a global environmental problem. Bio-reduction of Sb(V) is an effective Sb-removal approach. This work, for the first time, demonstrates the feasibility of autotrophic Sb(V) bio-reduction and removal coupled to anaerobic oxidation of elemental sulfur (S0). In the S0-based biological system, Sb(V) was reduced to Sb(III) via autotrophic bacteria by using S0 as electron donor. Meanwhile, S0 disproportionation reaction occurred under anaerobic condition, generating sulfide and SO42- in the bio-systems. Subsequently, Sb(III) reacted with sulfide and formed Sb(III)-S precipitate, achieving an effective total Sb removal. The precipitate was identified as Sb2S3 by SEM-EDS, XPS, XRD and Raman spectrum analyses. In addition, it was found that co-existing nitrate inhibited the Sb removal, as nitrate is the favored electron acceptor over Sb(V). In contrast, the bio-reduction of co-existing SO42- enhanced sulfide generation, followed by promoting Sb(V) reduction and precipitation. Illumina high-throughput sequencing analysis revealed that Metallibacterium, Citrobacter and Thiobacillus might be responsible for Sb(V) reduction and S0 disproportionation. This study provides a promising approach for the remediation of Sb(V)-contaminated water.

Synergistic adsorption and advanced oxidation activated by persulfate for degradation of tetracycline hydrochloride using iron-modified spent bleaching earth carbon.

At present, tetracycline hydrochloride (TCH) is a widely used antibiotic, and is often detected in water, posing a serious harm to human and ecological health. In this study, spent bleaching earth (SBE) was pyrolyzed to obtain spent bleaching earth carbon (SBE@C) and the nano Fe0/SBE@C prepared after zero-valent iron loading was adopted to remove TCH in water for the first time. The combination of nano Fe0/SBE@C and PS, the strong adsorption of SBE@C coupled with the oxidation of free radicals could achieve TCH efficient removal. The effects of nano Fe0 load, nano Fe0/SBE@C dosage, solution initial pH, and PS/TCH molar ratio on TCH removal efficiency in nano Fe0/SBE@C + PS system were studied. The results indicate that the optimal reaction conditions are 5% nano Fe0 load, 0.2 g/L nano Fe0/SBE@C dosage, initial pH of 3, PS/TCH molar ratio of 100:1. Under these conditions, TCH removal efficiency could reach 91%. Meanwhile, response surface methodology (RSM) was applied to predict optimal value of reaction conditions. The removal efficiency corresponding to the predicted optimal conditions was consistent with the actual removal efficiency obtained from the experiment. Moreover, six reaction systems were tested, and TCH removal efficiency in the SBE@C + PS system was 22.6%. When nano Fe0 was loaded on SBE@C, TCH removal efficiency in Fe0/SBE@C + PS system increased to 78.2%, in which TCH was first adsorbed on the surface of nano Fe0/SBE@C, and then was degraded by the oxidation of SO4•- and •OH. Totally, the nano Fe0/SBE@C + PS system displayed excellent TCH removal efficiency, good stability and reusability, exhibiting a promise toward TCH removal.

Using a sulfur autotrophic fluidized bed reactor for simultaneous perchlorate and nitrate removal from water: S disproportionation prediction and system optimization.

The sulfur autotrophic reduction (SAR) process is promising in co-reduction of perchlorate and nitrate from aqueous solution. To further understand the reaction process, we developed a sulfur autotrophic fluidized bed reactor where the proceeding extent of sulfur (S) disproportionation was predicted by Response surface methodology (RSM) for the first time. Three fundamental reaction parameters including the hydraulic retention time (HRT), co-existing nitrate concentration ([Formula: see text]) and recirculation ratio (R) were considered for reactor optimization. The results demonstrated that S disproportionation was promoted by long HRT and high R, whereas was inhibited by high [Formula: see text]. Also, the optimal HRT, [Formula: see text] and R were 0.50 h, 10.00 mg/L and 14, respectively, the bioreactor can achieve high reduction efficiency of perchlorate and nitrate (> 98.45%), and generate less sulfate (236.07 mg/L). High-throughput sequencing showed that Chlorobaculum was related to S disproportionation, and Sulfurovum was associated with nitrate/perchlorate reducing. All results indicate that the sulfur autotrophic fluidized bed reactor is a promising candidate for the treatment of perchlorate and nitrate wastewater in future practical applications.

High redox potential promotes oxidation of pyrite under neutral conditions: Implications for optimizing pyrite autotrophic denitrification.

Pyrite autotrophic denitrification (PAD) represents an important natural attenuation process of nitrate pollution and plays a pivotal role in linking nitrogen, sulfur, and iron cycles in a variety of anoxic environments. However, there are knowledge gaps about the oxidation mechanism of pyrite under anaerobic neutral conditions. This study explored the performance of PAD in the presence of EDTA and revealed the mechanism of anaerobic pyrite oxidation and microbial mineral transformation. It was demonstrated that ~200 mV was the electrochemical threshold for converting pyrite into bioavailable forms in PAD conditions, and accelerated pyrite oxidation by Fe3+-EDTA complexes can improve the performance of PAD effectively. Furthermore, genus related to sulfur and nitrogen cycle (Sulfurimonas, Denitrobacter) were found at higher abundances in cultures containing EDTA. The analysis of metagenomic binning showed that the microbial community in PAD culture with EDTA addition exhibited higher levels of functional diversity and redundancy. These results will further the understanding of the oxidation mechanism of pyrite under anaerobic neutral conditions and the corresponding microbial activities, and provide insights into the practical application of PAD.

Wood and sulfur-based cyclic denitrification filters for treatment of saline wastewaters.

This study investigated the performance and microbiome of cyclic denitrification filters (CDFs) for wood and sulfur heterotrophic-autotrophic denitrification (WSHAD) of saline wastewater. Wood-sulfur CDFs integrated into two pilot-scale marine recirculating aquaculture systems achieved high denitrification rates (103 ± 8.5 g N/(m3·d)). The combined use of pine wood and sulfur resulted in lower SO42- accumulation compared with prior saline wastewater denitrification studies with sulfur alone. Although fish tank water quality parameters, including ammonia, nitrite, nitrate and sulfide, were below the inhibitory levels for marine fish production, lower survival rates of Poecilia sphenops were observed compared with prior studies. Heterotrophic denitrification was the dominant removal mechanism during the early operational stages, while sulfur autotrophic denitrification increased as readily biodegradable organic carbon released from wood chips decreased over time. 16S rRNA-based analysis of the CDF microbiome revealed that Sulfurimonas, Thioalbus, Defluviimonas, and Ornatilinea as notable genera that contributed to denitrification performance.

Synergetic adsorption and Fenton-like degradation of tetracycline hydrochloride by magnetic spent bleaching earth carbon: Insights into performance and reaction mechanism.

In this study, the synergetic adsorption and Fenton-like degradation of tetracycline hydrochloride (TCH) by magnetic spent bleaching earth carbon (Mag-SBE@C) with H2O2 were developed and performed, with 91.5% of TCH degradation efficiency and 42.1% of TOC removal efficiency. The effects of the reaction parameters (temperature, initial pH, catalyst dosage, molar ratio of TCH to H2O2) on TCH degradation in Mag-SBE@C/H2O2 system were studied. Under the optimal conditions (temperature 41.1 °C, initial pH 4.89 and molar ratio of H2O2 to TCH 114.435) forecasted by response surface methodology (RSM), high TCH degradation efficiency (99%) was achieved. Also, four cycling tests were performed to confirm the excellent stability and regeneration ability of Mag-SBE@C in presence of H2O2. In addition, the characteristics of Mag-SBE@C after reaction are analyzed in details via scanning electron microscope (SEM), energy dispersive spectrometer (EDS), Brunner-Emmet-Teller (BET), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrum (FTIR) and X-ray diffraction (XRD), and it was found that Fe3O4 nanoparticles on Mag-SBE@C surface acted as co-catalyst and participated in degradation and improved reaction efficiency, while its properties were not greatly changed. The quenching experiments showed that hydroxyl radicals on Mag-SBE@C surface (OHadsorption) were dominant in Mag-SBE@C/H2O2 system. Meanwhile, three possible TCH degradation pathways were given based on the possible intermediates determined by liquid chromatography quadrupole-time-of-flight mass spectrometry (LC-Q-TOF-MS/MS). Mag-SBE@C is an excellent heterogeneous Fenton-like catalyst, exhibiting greatly potential to antibiotics elimination.

Sorption of perfluoroalkylated substances (PFASs) onto granular activated carbon and biochar.

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) have attracted increasing concerns owing to their potential ecotoxicological effects. The sorption of PFASs, i.e. perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorobutanoic acid (PFBA) and perfluorobutansulfonic acid (PFBS), by granular activated carbon (GAC) and softwood-derived biochar was studied. The sorption equilibrium of PFASs on GAC was obtained within 3-24 h, while the time required to reach equilibrium for biochar was 12-48 h. PFASs sorption on both GAC and biochar were well represented by the pseudo-second-order model. In the case of sorption isotherms, the PFAS sorption capacity was chain-length dependent with following order: PFOS > PFOA > PFBS > PFBA. GAC exhibited high maximum Langmuir sorption capacity for both PFOS (123.5 µmol g-1) and PFOA (86.2 µmol g-1), which were 43% and 39.6% greater than biochar. The maximum sorption capacity for PFBS on GAC (48.3 µmol g-1) was higher than that for PFBA (31.4 µmol g-1), while the opposite sorption trend was observed for biochar. The sorption mechanisms involved both electrostatic attraction and hydrophobic interaction. The sorption of PFASs increased with the decrease in pH. The competitive sorption of PFASs occurred during the sorption process, resulting in decreased PFASs removal efficiencies. The Fourier transform infrared (FTIR) analyses indicated the presence of a variety of functional groups on the surfaces of adsorbents. Some FTIR responses shifted after sorption, indicating electronic interactions during sorption. All the results indicate that adsorption technology is a feasible method to control the contamination of PFASs, and both GAC and biochar are effective adsorbents for PFASs removal from wastewater.

A sulfur-based cyclic denitrification filter for marine recirculating aquaculture systems.

Nitrogen removal from saline wastewater is challenging due to adverse effects of salinity on biological processes. A novel sulfur-autotrophic cyclic denitrification filter (CDF) was tested for marine recirculating aquaculture systems (RAS) under varying conditions. Low ammonia, nitrite and sulfide concentrations were maintained at residence times between 4 and 12 h. After introduction of Poecilia sphenops, concentrations of NH4+-N, NO2--N, NO3--N were maintained below 1, 1, and 60 mg/L, respectively. Fish waste inputs to the CDF contributed to mixotrophic denitrification and low sulfate production. A mass balance showed that 7% of the feed nitrogen was assimilated by fish, 6% was removed by passive denitrification (e.g., in anoxic zones in filters), 60% in the CDF and 27% was discharged during sampling and solids removal. Daily fresh water addition was <2% of fish tank volumes. The results are promising as a low cost alternative for saline wastewater denitrification.

Using the modified pine wood as a novel recyclable bulking agent for sewage sludge composting: Effect on nitrogen conversion and microbial community structures.

This study investigated the effect of a recoverable sulphuric acid and sodium hydroxide-modified pinewood (MOP) as a bulking agent during sewage sludge and sawdust composting (MOPC), with a control experiment using unpretreated pinewood (UNP; UNPC) as the bulking agent. Results show that addition of MOP effectively promoted the degradation of organic matter during composting. The maximum temperature increased by 1.50 °C and the high temperature period (T > 50 °C) of composting was extended 4 days longer than the control experiment. Furthermore, MOP addition reduced the loss of nitrogen by 9.40%. High-throughput sequencing analysis showed that the bacterial communities in the UNPC and MOPC treatments were significantly different. Pseudoxanthomonas was the dominant bacteria during the thermophilic and cooling phases of the MOPC treatment. In addition, the recycling efficiency of the UNP and MOP was 99.18% and 99.37%, respectively.

Magnetic spent bleaching earth carbon (Mag-SBE@C) for efficient adsorption of tetracycline hydrochloride: Response surface methodology for optimization and mechanism of action.

The utilization of spent bleaching earth (SBE)-based materials for adsorption of pollutants from water and wastewater has received growing attention. In this work, a comparative study of magnetic spent bleaching earth carbon (Mag-SBE@C) and spent bleaching earth carbon (SBE@C) was performed to remove tetracycline hydrochloride (TCH) from aqueous solutions. Mag-SBE@C exhibits the larger adsorption capacity (0.238 mmol/g) obtained by the Langmuir model than the original SBE@C (0.150 mmol/g). The adsorption process fits well with the pseudo second-order model and is found to be exothermic (ΔH0 < 0) and spontaneous (ΔG0 < 0). The optimal adsorption conditions (Mag-SBE@C dose 2.217 g/L, initial TCH concentration 0.113 mmol/L, initial solution pH 6.533) predicted by the response surface methodology (RSM) are consistent with the actual verification results. The inhibition extents of coexisting cations are ranked in a decline: Al3+ > Cu2+ > Fe3+ > Mg2+ > K+ > Na+. Various characterization results indicate that the adsorption mechanism of TCH by Mag-SBE@C likely includes the π-π interactions, hydrogen bonding, electrostatic interactions, π-cations interactions, FeN covalent bonding, and changes in physical and chemical properties. Mag-SBE@C is easily solid-liquid separated using magnetic field, and can be potentially reused for 13 times before completely losing its activity, exhibiting great potential to antibiotics elimination.

Distribution of perfluoroalkyl substances (PFASs) in aquatic plant-based systems: From soil adsorption and plant uptake to effects on microbial community.

This study systematically explored the distribution of perfluoroalkyl substances (PFASs) through soil adsorption and plant bioaccumulation in aquatic plant-based systems, derived from a surface flow constructed wetland (CW) planted with Typha angustifolia. The water-soil-plant systems were fortified with eight perfluoroalkyl subsntances (PFASs) at different concentrations. The potential for individual PFAS adsorption onto soil substrate and bioaccumulation in the plants increased with the increasing PFAS initial concentrations. Longer-chain PFASs exhibited higher affinity to soil substrate compared to shorter-chain PFASs. The highest concentration in the soil was observed for PFOS (51.3 ng g-1), followed by PFHxS (9.39 ng g-1), and PFOA (5.53 ng g-1) at low PFAS level. The perfluoroalkyl chain length dependent trend was also seen in the roots with the highest individual PFAS concentration for PFOS (68.9 ng g-1), followed by PFOA (18.5 ng g-1) and PFHxS (13.4 ng g-1). By contrast, shorter-chain PFASs were preferentially translocated from roots to shoots in Typha angustifolia. A significant (p < 0.05) positive correlation between bioaccumulation factor (BAFplant/water) (whole plant) and perfluoroalkyl chain length was observed. PFASs content in the plant compartments increased with increasing PFAS concentrations in the soil. Mass balance analysis indicates that approximately 40.7-99.6% of PFAS mass added to the system was adsorbed onto the soil and bioaccumulated in the plant tissues of T. angustifolia. Soil adsorption played a vital role in PFAS mass distribution. The results of Illumina high-throughput sequencing show that the bacterial diversity decreased upon PFAS exposure. The most predominant phyla retrieved were Proteobacteria (24.7-39.3%), followed by Actinobacteria (4.2-41.1%), Verrucomicrobia (7.9-25.1%), Bacteroidetes (10.2-20.4%), Cyanobacteria (0.4-16.5%), and Firmicutes (1.1-6.4%). The PFAS enrichment caused the changes (p > 0.05) in the structure and composition of bacterial community. This study helps to gain insight into a better understanding of the potential for PFASs distribution in an aquatic plant-based system and the impact on dynamic of microbial community exposed to PFASs.

Characterizations of dissolved organic matter and bacterial community structures in rice washing drainage (RWD)-based synthetic groundwater denitrification.

In this study, characteristics of dissolved organic matter (DOM) and bacterial community structure in rice washing drainage (RWD)-based groundwater denitrification systems inoculated with and without seeding sludge were investigated. Complete nitrate removal was achieved with a maximum denitrification rate of 64.1 mg NO3--N·(gVSS·h)-1. Analysis of three-dimension fluorescence excitation-emission matrix (FEEM) identified three main compositions of DOM associated with tryptophan protein-like, aromatic protein-like, and polycarboxylate humic acid-like substances in the inoculated system, while one composition associated with tryptophan protein-like substance in the un-inoculated system. Illumina sequencing analysis revealed a distinguished bacterial community structure in two systems over time. Notably, the microbial diversity was significant lower in the un-inoculated system than that in the system inoculated with seeding sludge. The predominant phyla shifted from Proteobacteria (49.2%), Bacteroidetes (20.5%) and Chloroflexi (14.8%) in the seeding sludge to Bacteroidetes (56.3%) and Proteobacteria (37.7%) after the RWD addition in the inoculated system. With RWD as sole microbe source, temporal changes in the bacterial structure from Proteobacteria (99.4%) and Bacteroidetes (5.3%) to Proteobacteria (88.8%) and Bacteroidetes (10.3%) were observed in the un-inoculated system. Specific comparison down to the genus level showed the dominant denitrifying bacteria of Thiobacillus, Anaerolineaceae and Methylophilaceae in the seeding sludge. Ideonella, Cloacibacterium and Enterobacter were dominant after the RWD addition in the inoculated system, while Stenotrophomonas and Enterobacter were dominant genera when RWD as sole bacteria source in the un-inoculated system. This finding indicates that both RWD addition and inoculation had strong impacts on bacterial community structure.

Biological denitrification in marine aquaculture systems: A multiple electron donor microcosm study.

There is a lack of information on denitrification of saline wastewaters, such as those from marine recirculating aquaculture systems (RAS), ion exchange brines and wastewater in areas where sea water is used for toilet flushing. In this study, side-by-side microcosms were used to compare methanol, fish waste (FW), wood chips, elemental sulfur (S0) and a combination of wood chips and sulfur for saline wastewater denitrification. The highest denitrification rate was obtained with methanol (23.4 g N/(m3·d)), followed by FW (4.5 g N/(m3·d)), S0 (3.5 g N/(m3·d)), eucalyptus mulch (2.6 g N/(m3·d)), and eucalyptus mulch with sulfur (2.2 g N/(m3·d)). Significant differences were observed in denitrification rate for different wood species (pine > oak ≫ eucalyptus) due to differences in readily biodegradable organic carbon released. A pine wood-sulfur heterotrophic-autotrophic denitrification (P-WSHAD) process provided a high denitrification rate (7.2-11.9 g N/(m3·d)), with lower alkalinity consumption and sulfate generation than sulfur alone.