Hydrogen Sulfide Splitting into Hydrogen and Sulfur through Off-Field Electrocatalysis.

Hydrogen sulfide (H2S), a toxic gas abundant in natural gas fields and refineries, is currently being removed mainly via the Claus process. However, the emission of sulfur-containing pollutants is hard to be prevented and the hydrogen element is combined to water. Herein, we report an electron-mediated off-field electrocatalysis approach (OFEC) for complete splitting of H2S into H2 and S under ambient conditions. Fe(III)/Fe(II) and V(II)/V(III) redox mediators are used to fulfill the cycles for H2S oxidation and H2 production, respectively. Fe(III) effectively removes H2S with almost 100% conversion during its oxidation process. The H+ ions are reduced by V(II) on a nonprecious metal catalyst, tungsten carbide. The mediators are regenerated in an electrolyzer at a cell voltage of 1.05 V, close to the theoretical potential difference (1.02 V) between Fe(III)/Fe(II) and V(II)/V(III). In a laboratory bench-scale plant, the energy consumption for the production of H2 from H2S is estimated to be 2.8 kWh Nm-3 H2 using Fe(III)/Fe(II) and V(II)/V(III) mediators and further reduced to about 0.5 kWh Nm-3 H2 when employing well-designed heteropolyacid/quinone mediators. OFEC presents a cost-effective approach for the simultaneous production of H2 and elemental sulfur from H2S, along with the complete removal of H2S from industrial processes. It also provides a practical platform for electrochemical reactions involving solid precipitation and organic synthesis.

Performance evaluation and microbial community of a sequencing batch biofilm reactor (SBBR) treating mariculture wastewater at different chlortetracycline concentrations.

The effects of chlortetracycline (CTC) on the performance, microbial activity, extracellular polymeric substances (EPS) and microbial community of a sequencing batch biofilm reactor (SBBR) were investigated in treating mariculture wastewater. Low CTC concentration (less than 6 mg/L) had no obvious effect on the SBBR performance, whereas high CTC concentration could inhibit the chemical oxygen demand (COD) and nitrogen removal of the SBBR. The microbial activity of the biofilm in the SBBR decreased with the increase of CTC concentration from 0 to 35 mg/L. The protein (PN) contents were always higher than the PS contents in both loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) at different CTC concentrations. The chemical compositions of LB-EPS and TB-EPS had obvious variations with the increase of CTC concentration from 0 to 35 mg/L. The high-throughput sequencing revealed the effects of CTC on the microbial communities of the biofilm at phylum, class and genus level. The relative abundances of some genera displayed a decreasing tendency with the increase of CTC concentration from 0 to 35 mg/L, such as Nitrospira, Paracoccus, Hyphomicrobium, Azospirillum. However, the relative abundances of the genera Flavobacterium, Aequorivita, Buchnera, Azonexus and Thioalbus increased with the increase of CTC concentration.

Effects of salinity on performance and microbial community structure of an anoxic-aerobic sequencing batch reactor.

The effects of salinity on the performance and microbial community structure of activated sludge were investigated in an anoxic-aerobic sequencing batch reactor (SBR). The removal efficiencies of chemical oxygen demand (COD) and [Formula: see text]-N decreased as the influent salinity increased from 0.5% to 6%. The specific oxygen utilization rate of activated sludge increased from 22.47 to 43.16 mg O2 g(-1) mixed liquid suspended solids (MLSS) h(-1) with the increase in salinity from 0.5% to 4% and subsequently decreased to 18.3 mg O2 g(-1) MLSS h(-1) at 6% salinity. The specific ammonium oxidation rate (SAOR) and specific nitrite oxidation rate (SNOR) decreased slowly at 0.5-1% salinity and then decreased rapidly with the increase in salinity from 1% to 6%. The SNOR diminished at a faster rate than the SAOR with the increase in salinity from 0.5% to 6%. The specific nitrate reduction rate (SNRR) decreased with the increase in salinity, whereas the SNRR was higher than the sum of SAOR and SNOR at 0.5-6% salinity. The denaturing gradient gel electrophoresis profiles revealed obvious changes in microbial community structure at different salinities. Some microbes were capable of tolerating up to 6% salinity in the SBR, such as Planomonospora sphaerica, Nitrosomonas sp. Is32, and Denitromonas sp. D2-1.

Effect of florfenicol on performance and microbial community of a sequencing batch biofilm reactor treating mariculture wastewater.

The effects of florfenicol (FF) on the performance, microbial activity and microbial community of a sequencing batch biofilm reactor (SBBR) were evaluated in treating mariculture wastewater. The chemical oxygen demand (COD) and nitrogen removal were inhibited at high FF concentrations. The specific oxygen utilization rate (SOUR), specific ammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR) and specific nitrate reduction rate (SNRR) were decreased with an increase in the FF concentration from 0 to 35 mg/L. The chemical compositions of loosely bound extracellular polymeric substances (LB-EPS) and tightly bound EPS (TB-EPS) could be affected with an increase in the FF concentration. The high-throughput sequencing indicated some obvious variations in the microbial community at different FF concentrations. The relative abundance of Nitrosomonas and Nitrospira showed a decreasing tendency with an increase in the FF concentration, suggesting that FF could affect the nitrification process of SBBR. Some genera capable of reducing nitrate to nitrogen gas could be inhibited by the addition of FF in the influent, such as Azospirillum and Hyphomicrobium.

Impact of sulfadiazine on performance and microbial community of a sequencing batch biofilm reactor treating synthetic mariculture wastewater.

The impact of sulfadiazine on the performance, microbial activity and microbial community of a sequencing batch biofilm reactor (SBBR) were evaluated in treating mariculture wastewater due to the application of sulfadiazine as an antibiotic in mariculture. The COD and nitrogen removals kept stable at 0-6mg/L sulfadiazine and were inhibited at 10-35mg/L sulfadiazine. The microbial activities related to organic matter and nitrogen removals reduced with an increase in sulfadiazine concentration. The presence of sulfadiazine could affect the production and chemical composition of loosely bound extracellular polymeric substances (LB-EPS) and tightly bound EPS (TB-EPS) in the biofilm. High-throughput sequencing demonstrated that sulfadiazine could impact on the microbial richness and diversity of SBBR treating mariculture wastewater. The relative abundances of Nitrosomonas, Nitrospira, Paracoccus, Hyphomicrobium, Rhodanobacter, Thauera and Steroidobacter decreased with an increase in sulfadiazine concentration, indicating that the presence of sulfadiazine decreased the relative abundance of some nitrifying and denitrifying bacteria.

Performance comparison of biofilm and suspended sludge from a sequencing batch biofilm reactor treating mariculture wastewater under oxytetracycline stress.

The performance, extracellular polymeric substances (EPS) and microbial community of a sequencing batch biofilm reactor (SBBR) were investigated in treating mariculture wastewater under oxytetracycline stress. The chemical oxygen demand and [Formula: see text]-N removal efficiencies of the SBBR decreased with the increase of oxytetracycline concentration, and no obvious [Formula: see text]-N and [Formula: see text]-N accumulation in the effluent appeared at less than 10 mg L(-1) oxytetracycline. The specific oxygen utilization rate of the suspended sludge was more than that of the biofilm at different oxytetracycline concentrations. The specific ammonium oxidation rate (SAOR) of the biofilm was more easily affected by oxytetracycline than that of the suspended sludge, whereas the effect of oxytetracycline on the specific nitrite oxidation rate (SNOR) of the biofilm was less than that of the suspended sludge. The specific nitrate reduction rate of both the biofilm and suspended sludge was higher than the sum of the SAOR and SNOR at different oxytetracycline concentrations. The protein and polysaccharide contents in the EPS of the biofilm and suspended sludge increased with the increase of oxytetracycline concentration. The appearance of oxytetracycline in the influent could affect the chemical composition of the loosely bound EPS and tightly bound EPS. The amino, carboxyl and hydroxyl groups might be involved with interaction between EPS and oxytetracycline. The denaturing gradient gel electrophoresis profiles indicated that the variation of oxytetracycline concentration in the influent could affect the microbial communities of both the biofilm and suspended sludge.

Performance and microbial community of a sequencing batch biofilm reactor treating synthetic mariculture wastewater under long-term exposure to norfloxacin.

The performance and microbial community of a sequencing batch biofilm reactor (SBBR) treating synthetic mariculture wastewater were evaluated under long-term exposure to norfloxacin (NFX) due to the overuse of antibiotics during the mariculture. The COD and NH4+-N removals had no distinct change at 0-6mgL-1 NFX and were inhibited at 6-35mgL-1 NFX. The specific oxygen uptake rate (SOUR), specific ammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR) and specific nitrate reduction rate (SNRR) of the biofilm kept a decreasing tendency with the increase of NFX concentration from 0 to 35mgL-1. The presence of NFX promoted the microorganisms to secrete more extracellular polymeric substances (EPS) and affected the chemical compositions of EPS. The microbial richness and diversity showed some obvious variations at different NFX concentrations. The present results demonstrated that NFX inhibited the SBBR performance and should decrease the NFX dosage in the mariculture.

Effect of salinity on extracellular polymeric substances of activated sludge from an anoxic-aerobic sequencing batch reactor.

The effect of salinity on extracellular polymeric substances (EPS) of activated sludge was investigated in an anoxic-aerobic sequencing batch reactor (SBR). The contents of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) were positively correlated with the salinity. The polysaccharide (PS) and protein (PN) contents in both LB-EPS and TB-EPS increased with the increase of salinity. With the increase of salinity from 0.5% to 6%, the PN/PS ratios in LB-EPS and TB-EPS decreased from 4.8 to 0.9 and from 2.9 to 1.4, respectively. The four fluorescence peaks in both LB-EPS and TB-EPS identified by three-dimensional excitation-emission matrix fluorescence spectroscopy are attributed to PN-like substances and humic acid-like substances. The Fourier transform infrared spectra of the LB-EPS and TB-EPS appeared to be very similar, but the differences across the spectra were apparent in terms of the relative intensity of some bands with the increase of salinity. The sludge volume index showed a linear correlation with LB-EPS (R(2)=0.9479) and TB-EPS (R(2)=0.9355) at different salinities, respectively.