Browsing by Author "Xu X.-J."

Limited-oxygen mediated synergistic relationships between sulfate-reducing bacteria (SRB), nitrate-reducing bacteria (NRB) and sulfide-oxidizing bacteria (SOB, including nitrate-reducing, sulfide-oxidizing bacteria NR-SOB) were predicted to simultaneously remove contaminants of nitrate, sulfate and high COD, and eliminate sulfide generation. A lab-scale experiment was conducted to examine the impact of limited oxygen on these oxy-anions degradation, sulfide oxidation and associated microbial functional responses. In all scenarios tested, the reduction of both nitrate and sulfate was almost complete. When limited-oxygen was fed into bioreactors, S0 formation was significantly improved up to ~70%. GeoChip 4.0, a functional gene microarray, was used to determine the microbial gene diversity and functional potential for nitrate and sulfate reduction, and sulfide oxidation. The diversity of the microbial community in bioreactors was increased with the feeding of limited oxygen. Whereas the intensities of the functional genes involved in sulfate reduction did not show a significant difference, the abundance of the detected denitrification genes decreased in limited oxygen samples. More importantly, sulfide-oxidizing bacteria may alter their populations/genes in response to limited oxygen potentially to function more effectively in sulfide oxidation, especially to elemental sulfur. The genes fccA/fccB from nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB), such as Paracoccus denitrificans, Thiobacillus denitrificans, Beggiatoa sp., Thiomicrospira sp., and Thioalkalivibrio sp., were more abundant under limited-oxygen condition. ? 2014 Elsevier B.V.

Autotrophic denitrification process is an effective strategy for treating sulfide and nitrate-enriched wastewater with low organic carbon. This study determined the sulfide oxidation and nitrate reduction rates and characterized the dominant bacteria and microbial community structure stimulated by micro-aerobic conditions in autotrophic denitrification system. With gradually increased sulfide concentration, the sulfide removal rate decreased to 37.8% at S 2? = 600 mg/L, while the peak sulfide and nitrate removal rates (100% and 53.8%) were achieved at S 2? = 800 mg/L with the air aeration rate of 20 mL/min. The Illumina sequencing results indicated that Thiobacillus accounted for 63% of total operational taxonomic units at generic level with sulfide concentration of 200 mg/L under anaerobic condition. However, Azoarcus, Thauera and Aliidiomorina became the dominant genera under micro-aerobic condition and their abundance significantly and positively related to the sulfide concentration and aeration rate (p < 0.05). According to the 16S metaproteomics functional composition prediction, one potential mechanism for autotrophic denitrifying under micro-aerobic condition was deduced that the oxidation of sulfide to thiosulfate further to sulfite was reinforced by trace oxygen, while the sulfite reductase activity was restrained. The decreased sulfide concentration weakened the toxicity inhibition on denitrifiers and accordingly the performance of autotrophic denitrification process was enhanced by micro-aerobic condition. ? 2018 Elsevier B.V.

Sulfide biooxidation by the novel sulfide-oxidizing bacteria Pseudomonas sp. C27, which could perform autotrophic and heterotrophic denitrification in mixotrophic medium, was studied in batch and continuous systems. Pseudomonas sp. C27 was able to oxidize sulfide at concentrations as high as 17.66 mM. Sulfide biooxidation occurred in two distinct stages, one resulting in the formation of sulfur with nitrate reduction to nitrite, followed by thiosulfate formation with nitrite reduction to N2. The composition of end-products was greatly impacted by the ratio of sulfide to nitrate initial concentrations. At a ratio of 0.23, thiosulfate represented 100% of the reaction products, while only 30% with a ratio of 1.17. In the continuous bioreactor, complete removal of sulfide was observed at sulfide concentration as high as 9.38 mM. Overall sulfide removal efficiency decreased continuously upon further increases in influent sulfide concentrations. Based on the experimental data kinetic parameter values were determined. The value of maximum specific growth rate, half saturation constant, decay coefficient, maintenance coefficient and yield were to be 0.11h-1, 0.68 mM sulfide, 0.11h-1, 0.21 mg sulfide/mg biomass h and 0.43 mg biomass/mg sulfide, respectively, which were close to or comparable with those reported in literature by other researches.

Biological treatment of sulfate-laden wastewater consists of two separate reactors to reduce sulfate to sulfide by sulfate-reducing bacteria (SRB) and to oxidize sulfide to sulfur (S 0) by sulfide oxidation bacteria (SOB). To have SRB+SOB in a single reactor faced difficulty of low S 0 conversion. This study for the first time revealed that dissolved oxygen (DO) level can be used to manipulate SRB+SOB reactions in a single reactor. This work demonstrated successful operation of an integrated SRB+SOB reactor under micro-aerobic condition. At DO=0.10-0.12mgl -1, since the activities of SOB were enhanced by limited oxygen, the removal efficiency for sulfate reached 81.5% and the recovery of S 0 peaked at 71.8%, higher than those reported in literature. At increased DO, chemical oxidation of sulfide with molecular oxygen competed with SOB so conversion of S 0 started to decline. At DO>0.30mgl -1 activities of SRB were inhibited, leading to failure of the SRB+SOB reactor. ? 2012 Elsevier Ltd.

The success of denitrifying sulfide removal (DSR) processes, which simultaneously degrade sulfide, nitrate and organic carbon in the same reactor, counts on synergetic growths of autotrophic and heterotrophic denitrifiers. Feeding wastewaters at high C/N ratio would stimulate overgrowth of heterotrophic bacteria in the DSR reactor so deteriorating the growth of autotrophic denitrifiers. The DSR tests at C/N = 1.26:1, 2:1 or 3:1 and S/N = 5:6 or 5:8 under anaerobic (control) or micro-aerobic conditions were conducted. Anaerobic DSR process has <50% sulfide removal with no elemental sulfur transformation. Under micro-aerobic condition to remove <5% sulfide by chemical oxidation pathway, 100% sulfide removal is achieved by the DSR consortia. Continuous-flow tests under micro-aerobic condition have 70% sulfide removal and 55% elemental sulfur recovery. Trace oxygen enhances activity of sulfide-oxidizing, nitrate-reducing bacteria to accommodate properly the wastewater with high C/N ratios. ? 2017 Elsevier Ltd

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. ? 2018 Elsevier Ltd

The biological degradation of nitrate and sulfate was investigated using a mixed microbial culture and lactate as the carbon source, with or without limited-oxygen fed. It was found that sulfate reduction was slightly inhibited by nitrate, since after nitrate depletion the sulfate reduction rate increased from 0.37 mg SO 4 2- /mg VSS d to 0.71 mg SO 4 2- /mg VSS d, and the maximum rate of sulfate reduction in the presence of nitrate corresponded to 56 % of the non-inhibited sulfate reduction rate determined after nitrate depleted. However, simultaneous but not sequential reduction of both oxy-anions was observed in this study, unlike some literature reports in which sulfate reduction starts only after depletion of nitrate, and this case might be due to the fact that lactate was always kept above the limiting conditions. At limited oxygen, the inhibited effect on sulfate reduction by nitrate was relieved, and the sulfate reduction rate seemed relatively higher than that obtained without limited-oxygen fed, whereas kept almost constant (0.86-0.89 mg SO 4 2- /mg VSS d) cross the six R OS states. In contrast, nitrate reduction rates decreased substantially with the increase in the initial limited-oxygen fed, showing an inhibited effect on nitrate reduction by oxygen. Kinetic parameters determined for the mixed microbial culture showed that the maximum specific sulfate utilization rate obtained (0.098±0.022 mg SO 4 2- /(mg VSS h)) was similar to the reported typical value (0.1 mg SO 4 2- /(mg VSS h)), also indicating a moderate inhibited effect by nitrate. ? 2014 Springer-Verlag.

A mathematical model of carbon, nitrogen and sulfur removal (C-N-S) from industrial wastewater was constructed considering the interactions of sulfate-reducing bacteria (SRB), sulfide-oxidizing bacteria (SOB), nitrate-reducing bacteria (NRB), facultative bacteria (FB), and methane producing archaea (MPA). For the kinetic network, the bioconversion of C-N by heterotrophic denitrifiers (NO3 − → NO2 − → N2), and that of C-S by SRB (SO4 2− → S2−) and SOB (S2− → S0) was proposed and calibrated based on batch experimental data. The model closely predicted the profiles of nitrate, nitrite, sulfate, sulfide, lactate, acetate, methane and oxygen under both anaerobic and micro-aerobic conditions. The best-fit kinetic parameters had small 95% confidence regions with mean values approximately at the center. The model was further validated using independent data sets generated under different operating conditions. This work was the first successful mathematical modeling of simultaneous C-N-S removal from industrial wastewater and more importantly, the proposed model was proven feasible to simulate other relevant processes, such as sulfate-reducing, sulfide-oxidizing process (SR-SO) and denitrifying sulfide removal (DSR) process. The model developed is expected to enhance our ability to predict the treatment of carbon-nitrogen-sulfur contaminated industrial wastewater. © 2016 Elsevier B.V.

Complete removal of nitrogen, sulfur and carbon in wastewaters by denitrifying sulfide removal (DSR) process can be achieved at stoichiometry sulfide to nitrate ratio (S/N) of 1:1 in expanded granular sludge bed reactor. Wastewaters with varying S/N ratios can adversely impact the DSR performances with deterioration of synergetic cooperation between autotrophic and heterotrophic denitrifiers. DO (dissolved oxygen) serves effectively as supplementary electron receiver for sulfide oxidation, leaving more nitrate for heterotrophic denitrifiers to utilize acetate. The optimal oxygen to sulfide molar ratio (DO/S) is 0.5:1 for complete removal of sulfide, nitrate and acetate at different S/N ratios. The heterotrophic denitrification rate was decreased to 0.03 ± 0.002, 0.24 ± 0.011 and 0.35 ± 0.027 NO3 −-N·h−1·gVSS−1 at S/N ratio of 5:2, 5:5 and 5:8, respectively, when DO/S of 3:1 was performed. This optimal condition was proposed as an easy-to-implement control criterion for subsiding the adverse impact by varying S/N ratios in handling real wastewaters. © 2018 Elsevier Ltd

The succession of complex internal sulfur cycles and sulfide-oxidizing bacteria community has been observed during wastewater treatment under microaerophilic conditions or denitrifying conditions. However, research on the microbial community involved in sulfur cycles under microaerophilic denitrifying conditions is scarce. In this study we characterized the dominant bacteria and microbial community structure stimulated by microaerophilic conditions in a sulfate and nitrate co-reduction system. Full denitrification was accomplished and the sulfate removal efficiency ranged from 79.93% to 96.81% for all the tested scenarios, with the degree of sulfate reduction slightly decreased with higher O 2 feeding rate. The proportion of S 0 to influent SO 4 2? was much greater at microaerophilic stages (27.5–69.2%) versus the anaerobic stage (11.1%). The peak S 0 recovery (69.2%) was achieved at O 2 ?=?4.0?mL/min. Illumina sequencing technology was used to characterize the bacterial community and the results indicated that Bacteroidetes, Firmicutes, Proteobacteria, Spirochaetae and Synergistetes members were dominant in microbial communities, however the variation of these dominant members across all the operating conditions did not well respond to reactor performance. Further analysis revealed that the structure of the microbial community, including community richness and evenness, might better respond to reactor performance, which deserves more research in future. ? 2017

Integrated simultaneous desulfurization and denitrification (ISDD) process has proven to be feasible for the coremoval of sulfate, nitrate, and chemical oxygen demand (COD). In this study, we aimed to reveal the microbial community dynamics in the ISDD process with different influent nitrate (NO3 ?) concentrations. For all tested scenarios, full denitrification was accomplished while sulfate removal efficiency decreased along with increased influent NO3 ?concentrations. The proportion of S0to influent SO4 2?maintained a low level (5.6–17.0%) regardless of the increased influent NO3 ?concentrations. Microbial community analysis results showed that higher influent NO3 ?concentrations affected the microbial community structure greatly. Phyla Proteobacteria, Spirochaetae, Firmicutes, Synergistetes, and Chloroflexi dominated in all the community compositions, of which Proteobacteria exhibited a clear difference among eight microbial samples. Members of δ-Proteobacteria, with 16S rRNA gene sequences related to Desulfobulbus, were clearly decreased at influent NO3 ?= 3000 and 3500 mg/L, suggesting an inhibitory effect of NO3 ?on sulfate reduction. In contrast, as influent NO3 ?concentration increased, microbial community was notably enriched in γ-Proteobacteria and ε-Proteobacteria, which revealed the enrichment of 16S rRNA gene sequences related to Pseudomonas (γ-Proteobacteria), and Arcobacteria and Sulfurospirillum (ε-Proteobacteria). ? 2016 Elsevier Ltd

Micro-aerobic condition has proven to be effective in enhancing sulfide oxidation to elemental sulfur (S0) during integrated simultaneous desulfurization and denitrification process (ISDD). In this study we investigated and compared the performance and microbial community of ISDD process operating under initially anoxic, then micro-aerobic and finally switch back to anoxic condition. For all the three tested scenarios, comparable bioreactor performance in terms of sulfate (95.0 ± 4.4%, 90.6 ± 3.8%, 89.8 ± 3.5%) and nitrate (∼100%) removal was achieved. However, a shift of ISDD bioreactor from micro-aerobic to anoxic environment clearly increased the S0 production (30.6%), relative to that at initial anoxic condition (14.2%). Further anoxic bioreactor operation with different influent nitrate concentrations also obtained satisfactory performance particularly in terms of S0 production. Microbial community analysis results showed that functional microorganisms selectively enriched at micro-aerobic condition, particularly sulfide-oxidizing bacteria (SOB), could also function well and enhance S0 production when bioreactor switching from micro-aerobic to anoxic environment. We proposed that micro-aerobic strategy could function as a bio-selector and provide a new idea in functional microorganisms selectively enrichment for wastewater treatment. © 2018 Elsevier Ltd