Mechanical insights into desulfurization by peroxymonosulfate oxidation via a non-reactive oxygen species pathway.

Air pollution by sulfur dioxide (SO2) remains a pressing concern for both the environment and human health. Desulfurization enhanced by persulfate based advanced oxidation processes (PS-AOPs) has been proven to be a feasible method. However, the inherent contradiction between the rapid diffusion mass transfer of SO2 in the "gas-liquid-gas" phase and the limited lifespan of reactive oxygen species (ROS) can not be ignored. Excessive investment in PS is required to sustainably generate ROS to achieve continuous desulfurization performance, which may lead to excessive PS consumption. To address this issue, whether PS can achieve the oxidation absorption of SO2 via a non-reactive oxygen species pathway was investigated. Experimental and computational results demonstrated that peroxymonosulfate (PMS) instead of peroxydisulfate (PDS) had a great SO2 removal performance, the utilization of PS could be effectively achieved by maintaining a 1:1 molar ratio of PMS and removed SO2. The presence of HOO bonds in the PMS introduced a partial positive charge to the oxygen atom, making the PMS polar and more susceptible to be attacked by the nucleophile HSO3-. So SO2 underwent a series of processes including dissolution, dissociation, one-oxygen atom transfer, and ionization before ultimately being converted into SO42- ions, effectively achieving its removal from flue gas. This study may presents a novel approach for achieving high-efficiency flue gas desulfurization.

Low oxygen levels with high redox heterogeneity in the late Ediacaran shallow ocean: Constraints from I/(Ca + Mg) and Ce/Ce* of the Dengying Formation, South China.

Most previous studies focused on the redox state of the deep water, leading to an incomplete understanding of the spatiotemporal evolution of the redox-stratified ocean during the Ediacaran-Cambrian transition. In order to decode the redox condition of shallow marine environments during the late Ediacaran, this study presents I/(Ca + Mg), carbon and oxygen isotope, major, trace, and rare earth element data of subtidal to peritidal dolomite from the Dengying Formation at Yangba, South China. In combination with the reported radiometric and biostratigraphic data, the Dengying Formation and coeval successions worldwide are subdivided into a positive δ13 C excursion (up to ~6‰) in the lower part (~551-547 Ma) and a stable δ13 C plateau (generally between 0‰ and 3‰) in the middle-upper part (~547-541 Ma). The overall low I/(Ca + Mg) ratios (<0.5 µmol/mol) and slightly negative to no Ce anomalies (0.80 < [Ce/Ce*]SN < 1.25), point to low-oxygen levels in shallow marine environments at Yangba. Moreover, four pulsed negative excursions in (Ce/Ce*)SN (between 0.62 and 0.8) and the associated two positive excursions in I/(Ca + Mg) ratios (up to 2.02 µmol/mol) are observed, indicative of weak oxygenations in the shallow marine environments. The comparison with other upper Ediacaran shallow water successions worldwide reveals that the (Ce/Ce*)SN and I/(Ca + Mg) values generally fall in the Precambrian range but their temporal trends differ among these successions (e.g., Ce anomaly profiles significantly different between Yangba and the Yangtze Gorge sections), which point to low oxygen levels with high redox heterogeneity in the surface ocean. This is consistent with the widespread anoxia as revealed by low δ238 U values reported by previous studies. Thus, the atmospheric oxygen concentrations during the late Ediacaran are estimated to be very low, similar to the case during the most Mesoproterozoic to early Neoproterozoic period.

Rapid Vanadium Extraction from Roasted Vanadium Steel Slag via a H2SO4-H2O2 System: Process and Mechanism.

A H2SO4-H2O2 system was developed to enhance the efficacy of vanadium extraction from roasted vanadium steel slag. The optimum parameters and the behavior of vanadium extraction were investigated systematically. When 1 mL of H2O2 per gram of vanadium slag was added to a leaching mixture at 50 °C, along with 30% H2SO4, 80.5% of vanadium extraction was achieved within 15 min. However, without H2O2, only 58.5% of vanadium extraction was achieved at the same leaching time. The H2SO4-H2O2 system facilitated the dissolution of metallic ions in a short time and then triggered the production of strong oxidizing substances, such as HO• and O2 -•, via the Fenton reaction and Fenton-like reaction. Subsequently, the low-valence vanadium, existing in the leaching solution or located on the surface of the particle, was converted to pentavalent vanadium by strongly oxidizing substances, such as H2O2 and its derivatives HO• and O2. The complex oxides on the surface of the particle were destroyed, after which the vanadium inside the particle was gradually exposed to the acid leaching solution. The vanadium was oxidized to pentavalent vanadium, which then entered the leaching solution. Finally, a pathway of vanadium extraction via the H2SO4-H2O2 system was proposed to gain insight into rapid vanadium leaching.

Enhanced biological phosphorus removal from wastewater by current stimulation coupled with anaerobic digestion.

The integrated wastewater discharge standard for phosphorus has become increasingly strict. In this study, a synergetic current stimulation system coupled with anaerobic digestion was used to enhance phosphorus removal from wastewater. The effects of current intensity, pH, and methane (CH4) synthesis on phosphorus removal were investigated. As direct current was supplied to an anaerobic bioreactor, the removal of sewage total phosphorus was significantly enhanced. The conditions of weak acid and low negative oxidation-reduction potential facilitated the phosphorus removal from wastewater. The optimal parameters for the dephosphorisation process were a current intensity of 100 mA and a pH of 6.0. When the anaerobic digestion process was inhibited by the reagent 2-bromoethanesulphonic acid sodium (BES), abundant metabolic intermediates accumulated and methanogenesis clearly decreased. Affected by the current stimulation and the inhibition of CH4 synthesis, the formation of gaseous phosphine (PH3) was greatly improved, and then PH3 escaped from the digestion mixture after it was absorbed by microbial cells. The maximum PH3 content of the digestion gas was 41.8 mg m-3 in the reactor supplied with a current of 100 mA and BES addition of 10 mmol L-1, and the phosphorus removal in this digestion system reached 55.2% at 6 d; however, the removal in the conventional anaerobic digestion system was only 17.7% after the same amount of time. Finally, a pathway of enhanced anaerobic biological phosphorus removal was proposed to better understand the inherent synergistic mechanism.

Effects of reactive oxygen species scavengers on thermophilic micro-aerobic digestion for sludge stabilization.

In thermophilic digestion systems, sludge stabilization may be adversely impacted by high concentrations of ammonia nitrogen or the rapid accumulation of fatty acids; however, few studies have focused on the mitigation of the inhibition of reactive oxygen species (ROS). In this study, fulvic acids or tea polyphenols were introduced to a thermophilic digestion system and the effects of ROS scavengers on sludge stabilization were investigated. As fulvic acids or tea polyphenols were added to sludge, they reacted with metal cations, such as Cu2+ and Zn2+, to form stable complexes that enabled active metal ions to be transported into cells to enhance the oxidase activities. Therefore, the digestion systems presented a lower O2•- content compared with that of a control group with no additive. Both fulvic acids and tea polyphenols mitigated the adverse effects of the ROS and enhanced the reduction of volatile solids (VS), however, fulvic acids better facilitated the sludge stabilization. The optimal dosage was 0.3% of the total solids as fulvic acids were added to the sludge every 48 h. The VS reduction in the digester reached 38.2% at 14 d, which was clearly higher than that in the control group. The pathway of ROS scavengers affecting sludge stabilization was proposed, and it may be helpful to gain deeper insight into the characteristics of thermophilic digestion processes as well as the mechanism of sludge stabilization.

Effects of pH on the biodegradation characteristics of thermophilic micro-aerobic digestion for sludge stabilization.

For a thermophilic micro-aerobic digestion (TMAD) system, the pH is closely related to the production of short-chain fatty acids and ammonia release. Batch experiments at different pH values were carried out to elucidate the effects of pH on the biodegradation characteristics of TMAD processes. A digester at pH 9.0 maintained better performance of sludge stabilization than acidic and neutral digestion systems, and the reduction of volatile solids reached ≤41.3% on day-10. We proposed a pathway of proton transfer in the TMAD system. An acidic digestion environment, in general, resulted in K+ deficiency, low enzyme activity, and oxidative stress. An alkaline digestion environment facilitated substrate oxidation, accelerated humification, and prevented the inhibition caused by the accumulated acids or ammonia nitrogen. The pH and digestion time affected the microbial population and species richness significantly. An alkaline digestion system presented lower bacterial diversity and maintained a higher richness of functional microbes such as Paenalcaligenes and Pseudogracilibacillus. Hence, an alkaline digestion system maintained a relatively high oxidase activity, and mitigated the potential oxidative stress for thermophiles.

Impacts of ammonia nitrogen on autothermal thermophilic micro-aerobic digestion for sewage sludge treatment.

The concentration of ammonia nitrogen is relatively high during autothermal thermophilic micro-aerobic digestion (ATMAD), which could significantly affect the sludge stabilization. This paper aims to investigate the impacts of ammonia nitrogen on ATMAD process, batch experiments were carried out with dosage of certain amount of NH4HCO3 into digestion system. The total ammonia nitrogen (TAN) was considered as a suitable indicator to characterize the ammonia inhibition. As the TAN reached to approximately 1000 mg L-1, the sludge digester presented a relatively low removal of volatile solids, due to adverse effects of ammonia nitrogen on sludge digestion. Three pathways that closely related to ammonia inhibition were investigated in this research. Digestion system could be inhibited by high TAN due to K+ deficiency of the cells and the decline of Mg2+ in the cytoplasm, and the accumulations of reactive oxygen species lead to oxidative stress for the microbes. Ammonia inhibition can be mitigated by the increase of oxidative enzyme.

Progressive Indosinian N-S deformation of the Jiaochang structure in the Songpan-Ganzi fold-belt, Western China.

Integrated field data, microstructural and three-dimensional strain analyses are used to document coaxial N-S shortening and southward increase in deformation intensity and metamorphism at the Jiaochang structure. Two episodes of deformation (D1,D2) with localized post-D2 deformation have been identified in the area. The first deformation (D1) episode is defined by a main axial-plane of parallel folds observable on a micro- to kilometer-scale, while the second episode of deformation (D2) is defined by micro-scale metamorphic folds, associated with E-W oriented stretching lineation. These processes are the result of Indosinian tectonism (Late Triassic to Early Jurassic) characterized by nearly coaxial N-S compression and deformation. This is indicated by E-W trending, sub-parallel to parallel foliation (S1, e.g. axial-plane of folds, and S2, i.e. axial-plane of metamorphic folds, crenulation cleavage) and lineation (L1, e.g. axis of folds, and L2, i.e. stretching lineation, axis of metamorphic folds and B-axis of echelon lens). Most of the porphyroblasts and minerals (e.g. pyrite, biotite) show two growth phases with localized growth in the third phase (muscovite). The progressive D1-D2 structure is widespread in the south of the Jiaochang area, but only D1 structure crops out at the north. The strain intensity (γ), compression ratios (c%) and octahedral strain intensity (εs) are similar across the Jiaochang structure (i.e., γ ≈ 1.8, c ≈ 27%, εs = 0.9), showing a broad range of Flinn values (K = 0.77 to 7.57). The long-axis orientations are roughly symmetric between two limbs of the structure. Therefore, we suggest that the architecture of the Jiaochang structure has been controlled by coaxial N-S shortening and deformation (D1-D2) during the Indosinian tectonic epoch, with insignificant post-D2 deformation.

The one-stage autothermal thermophilic aerobic digestion for sewage sludge treatment: stabilization process and mechanism.

Batch experiment was carried out in a simulated thermophilic aerobic digester to investigate the digestion process of one-stage autothermal thermophilic aerobic digester and to explore the sludge stabilization mechanism. Volatile solids removal was 38.4% at 408 h and 45.0% at 552 h. Chemical oxidation demand, total nitrogen, and ammonia nitrogen in supernatant increased rapidly up to 168 h, and all of them fluctuated moderately after 360 h. Volatile fatty acid (VFA) accumulated rapidly up to 24 to 168 h, then declined sharply, reaching a low concentration after 312 h. Propionic, iso-valeric, and iso-butyric acids, in addition to acetic acids, were also the major components of VFA. As the biochemical metabolic process was inhibited under oxygen-deficiency condition, the digestion system can produce acetic, propionic, butyric acids and other VFA constituents to meet the demand for NAD(+) and maximize ATP generation. The ORP affected the VFA production and depletion as well as sulfate levels.

Isolation, identification and utilization of thermophilic strains in aerobic digestion of sewage sludge.

Two representative thermophilic bacterial strains (T1 and T2) were isolated from a one-stage autothermal thermophilic aerobic digestion pilot-scale reactor. 16S rRNA gene analysis indicated that they were Hydrogenophilaceae and Xanthomonodaceae. These isolated strains were inoculated separately and/or jointly in sewage sludge, to investigate their effects on sludge stabilization under thermophilic aerobic digestion condition. Four digestion conditions were tested for 480 h. Digestion without inoculation and inoculation with strain T2, as well as joint- inoculation with strains T1 and T2, achieved 32.6%, 43.0%, and 38.2% volatile solids (VS) removal, respectively. Removal in a digester inoculated with stain T1 only reached 27.2%. For the first 144 h, the three inoculated digesters all experienced higher VS removal than the digester without inoculations. Both specific thermophilic strains and micro-environment significantly affected the VS removal. DGGE profiles revealed that the isolated strains T1 and T2 can successfully establish in the thermophilic digesters. Other viable bacteria (including anaerobic or facultative microbes) also appeared in the digestion system, enhancing the microbial activity.

Chemical and microbial changes during autothermal thermophilic aerobic digestion (ATAD) of sewage sludge.

Autothermal thermophilic aerobic digestion (ATAD) is a promising process for sewage sludge stabilization. Batch experiments were conducted on sewage sludge collected from a municipal wastewater treatment plant in Shanghai, China, to evaluate the effectiveness of the ATAD system by determining changes in volatile suspended solids (VSSs) and to study its microbial diversity by denaturing gradient gel electrophoresis of 16S rRNA gene sequences amplified by PCR. The digestion system achieved rapid degradation of the organic substrate at 55 degrees C. The VSS was removed by up to 45.3% and 50.4% at 216 h and 264 h, respectively, while NH(4)(+)-N, chemical oxidation demand and total organic carbon of supernatant as well as total nitrogen did not exhibit obvious declines after 168 h. The microbial diversity changed during the thermophilic process as thermophiles belonging to the Hydrogenophilaceae, Thermotogaceae, Clostridiaceae and the genus Ureibacillus replaced less temperature-tolerant microorganisms such as Sphingobacteriaceae and the genus Trichococcus.