Comparison of the capacity of biological desulfurization of Thiobacillus ferrooxidans from different sulfur-containing substrates with or without additional ferrous iron

Thiobacillus ferrooxidans,abbreviated as T.ferrooxidans is one of the important microorganisms in the field of biological desulfurization.Effects of ferrous iron and sulfur-containing substrates on biological desulfurization of T.ferrooxidans were studied.Results show that in the absence of Fe^(2+),T.ferrooxidans can utilize three kinds of sulfur-containing substrates of Na_(2)S_(2)O_(3),elemental S and Na_(2)SO_(3) for growth and metabolism.For utilization complexity,Na_(2)S_(2)O_(3) was easiest to use,next was elemental S,and Na_(2)SO_(3) was the worst for use.During the utilization of ferrous iron and sulfur-containing substrates by T.ferrooxidans,the iron oxidation system was first started.With the decrease of the Fe^(2+)concentration,the sulfur oxidation system was started,and then the two systems synergistically acted.The presence of three sulfur-containing substrates had different effects on Fe^(2+)oxidation,and elemental S did not inhibit the oxidation of Fe^(2+),while Na_(2)S_(2)O_(3) and Na_(2)SO_(3) had some inhibition on the oxidation of Fe^(2+),especially the inhibition of Na_(2)SO_(3) was significant,and complete oxidation of ferrous iron needed more time.The isolated T.ferrooxidans is applied to the removal of H2S gas,aiming to provide a new technological approach for biological removal of H2S.

Synergistic improvement of nitrogen and phosphorus removal in constructed wetlands by the addition of solid iron substrates and ferrous irons

Sanjiang Plain is intensively used for rice production,and ditch drainage diffuse pollution prevention is crucial.Groundwater,rich in Fe ions,is the main source of irrigation water in this region.In this study,pyrite and zero-valent iron(ZVI)(sponge iron and iron scraps)were used as substrates to identify the synergistic influence of exogenous Fe^(2+)addition and solid iron substrates on pollutant removal in constructed wetlands.Based on the results,iron substrates hardly improved the ammonia removal,mainly because of the physical structure and oxidation activity.At a hydraulic retention time longer than 8 h,the pollution removal efficiency in the zero-valent iron(ZVI)substrate treatment increased significantly,and the removal of nitrate(NO_(3)^(−)-N)and total phosphorus(TP)in the iron scrap substrate treatment reached about 60%and 70%,respectively.The high-throughput sequencing results showed a significant increase in the abundance of microorganisms involved in denitrification and phosphate accumulation in biofilms on ZVI substrates.The highest diversities of such microorganisms in biofilms on iron scraps were found for denitrifying bacteria(Pseudomonas),nitrate-reducing Fe(II)-oxidizing bacteria(Acidovorax),and Dechloromonas with autotrophic denitrification and phosphate accumulation,with a 43%cumulative abundance.Dechloromonas dominated in the iron sponge substrate treatment.The highest relative abundance of Acidovorax was found in the mixed iron substrate(pyrite,sponge iron,and iron scraps)treatment.The addition of ZVI substrate significantly improved the removal of NO^(3)_(−)-N and TP and reduced the hydraulic retention time through the continuous release of Fe^(2+)and the promotion of microbial growth.When designing constructed wetlands for treating paddy field drainage,the appropriate addition of iron scrap substrates is recommended to enhance the pollutant removal efficiency and shock load resistance of CWs.

Dosing low-level ferrous iron in coagulation enhances the removal of micropollutants, chlorite and chlorate during advanced water treatment

Drinking water utilities are interested in upgrading their treatment facilities to enhance micropollutant removal and byproduct control.Pre-oxidation by chlorine dioxide(ClO_(2))followed by coagulation-flocculation-sedimentation and advanced oxidation processes(AOPs)is one of the promising solutions.However,the chlorite(ClO_(2)^(-))formed from the ClO_(2) preoxidation stage cannot be removed by the conventional coagulation process using aluminum sulfate.ClO_(2)^(–)negatively affects the post-UV/chlorine process due to its strong radical scavenging effect,and it also enhances the formation of chlorate(ClO_(3)^(–)).In this study,dosing micromolar-level ferrous iron(Fe(II))into aluminum-based coagulants was proposed to eliminate the ClO_(2)^(–)generated from ClO_(2) pre-oxidation and benefit the post-UV/chlorine process in radical production and ClO_(3)^(–)reduction.Results showed that the addition of 52.1-μmol/L FeSO_(4) effectively eliminated the ClO_(2)^(-)generated from the pre-oxidation using 1.0 mg/L(14.8μmol/L)of ClO 2.Reduction of ClO_(2)^(-)increased the degradation rate constant of a model micropollutant(carbamazepine)by 55.0%in the post-UV/chlorine process.The enhanced degradation was verified to be attributed to the increased steady-state concentrations of HO^(-)·and ClO_(2)·by Fe(II)addition.Moreover,Fe(II)addition also decreased the ClO_(3)^(–)formation by 53.8%in the UV/chlorine process and its impact on the formation of chloroorganic byproducts was rather minor.The findings demonstrated a promising strategy to improve the drinking water quality and safety by adding low-level Fe(II)in coagulation in an advanced drinking water treatment train.

Iron Reduction and Adsorption on Shewanella Putrefaciens nearby Landfills in Northwest Florida

In Northwest Florida, the soil is mainly covered by poorly drained sandy soil of Myakka, which is characterized by a subsurface accumulation of humus and AI and Fe oxides. When organic rich landfill leachate is leaked to the iron rich soils, ferrous iron is released with the oxidation of organic compounds in the leachate. In this research, we investigated the activities of S. putrefaciens in reducing iron oxide in the iron rich soil of Northwest Florida with landfill leachate serving as the carbon source. S. putrefaciens had similar maximum specific growth rate and half saturation coefficients for all the leachate and soil samples. The average maximum specific growth rate was 0.008 hr^-1 and the average half saturation coefficient was 243.8 mg/L. Averagely, 2.2 mg ferrous iron was generated per mg COD consumed. In addition, adsorption of reduced ferrous iron on S. putrefaciens was further characterized. Ferrous iron adsorption on S. putrefaciens was a kinetic process, which increased with the increase of the reaction time. Equilibrium ferrous iron adsorption on S. putrefaciens can be reached after three hours. Ferrous iron had linear adsorption isotherms on S. putrefaciens for the pH range of 5 to 9.

Characterization of Gleyization of Paddy Soils in the Middle Reaches of the Yangtze River

The gleyisation of representative paddy soils in the middle reaches of the Yangtze caver was characterized,taking oxidation-reduction potential(Eh),the amount of active reducing substances and the forms of iron and manganese as the parameters.The Eh value was linearly related with the logarithm of the amount of active reducing substances, which was contributed by ferrous iron by 83% on an avers.The degree of gleyization of dament horizons was graded as ungleyed,slightly gleyed,mildly gleyed and gleyed.The Eh of the four grades was>500,300-500,100-300 and<100 mV,respectively, and the corresponding amoks of active reducing substances was<1,1-7,7-30 and>30 mmol.kg(-1),respectively.The amount of ferrous iron of the four grades was<0.5,0.5-5,5-25 and > 25 mmol kg-1,respectively.The extent of gleyisation of a soil was classified as upper-gleyed, middle-gleyed and lower-gleyed, depending on whether the depth of the gley horbon was less than 30 cm,30-60 cm or more than 60 cm.

Simultaneous removal of chromium and arsenate from contaminated groundwater by ferrous sulfate:Batch uptake behavior

Chromium and/or arsenate removal by Fe（Ⅱ） as a function of pH, Fe（Ⅱ） dosage and initial Cr（Ⅵ）/As（Ⅴ） ratio were examined in batch tests. The presence of arsenate reduced the removal efficiency of chromium by Fe（Ⅱ）, while the presence of chromate significantly increased the removal efficiency of arsenate by Fe（Ⅱ） at pH 6-8, In the absence of arsenate, chromium removal by Fe（Ⅱ） increased to a maximum with increasing pH from 4 to 7 and then decreased with a further increase in pH. The increment in Fe（Ⅱ） dosage resulted in an improvement in chromium removal and the improvement was more remarkable under alkaline conditions than that under acidic conditions. Chromium removal by Fe（Ⅱ） was reduced to a larger extent under neutral and alkaline conditions than that under acidic conditions due to the presence of 10 μtmol/L arsenate. The presence of 20 μmol/L arsenate slightly improved chromium removal by Fe（Ⅱ） at pH 3.9-5,8, but had detrimental effects at pH 6.7-9.8. Arsenate removal was improved significantly at pH 4-9 due to the presence of 10μmol/L chromate at Fe（Ⅱ） dosages of 20-60 μmol/L. Elevating the chromate concentration from 10 to 20μmol/L resulted in a further improvement in arsenate removal at pH 4.0-4.6 when Fe（Ⅱ） was dosed at 30-60 μmol/L.

Impact of different benthic animals on phosphorus dynamics across the sediment-water interface

As a diagenetic progress, bioturbation influences solute exchange across the sediment-water interface （SWI）. Different benthic animals have various mechanical activities in sediment, thereby they may have different effects on solute exchange across the SWI. This laboratory study examined the impacts of different benthic animals on phosphorus dynamics across the SWI. Tubificid worms and Chironomidae larvae were introduced as model organisms which, based on their mechanical activities, belong to upward-conveyors and gallery-diffusers, respectively. The microcosm simulation study was carried out with a continuous flow culture system, and all sediment, water, and worms and larvae specimens were sampled from Taihu Lake, China. To compare their bioturbation effects, the same biomass （17.1 g wet weight （ww）/m ^2 ） was adopted for worms and larvae. Worms altered no oxygen penetration depth in sediment, while larvae increased the O 2 penetration depth, compared to the control treatment. Their emergence also enhanced sediment O 2 uptake. The oxidation of ferrous iron in pore water produced ferric iron oxyhydroxides that adsorbed soluble reactive phosphorus （SRP） from the overlying water and pore water. Larvae built obviously oxidized tubes with about 2 mm diameter and the maximum length of 6 cm in sediment, and significantly decreased ferrous iron and SRP in the pore water compared to the control and worms treatments. Worms constructed no visually-oxidized galleries in the sediment in contrast to larvae, and they did not significantly alter SRP in the pore water relative to the control treatment. The adsorption of ferric iron oxyhydroxides to SRP caused by worms and larvae inhibited SRP release from sediment. Comparatively, worms inhibited more SRP release than larvae based on the same biomass, as they successively renewed the ferric iron oxyhydroxides rich oxidation layer through their deposition.

Identification of ferroptosis as a novel mechanism for antitumor activity of natural product derivative a2 in gastric cancer

Ferroptosis is a type of cell death accompanied by iron-dependent lipid peroxidation,thus stimulating ferroptosis may be a potential strategy for treating gastric cancer,therapeutic agents against which are urgently required.Jiyuan oridonin A(JDA) is a natural compound isolated from Jiyuan Rabdosia rubescens with anti-tumor activity,unclear anti-tumor mechanisms and limited water solubility hamper its clinical application.Here,we showed a2,a new JDA derivative,inhibited the growth of gastric cancer cells.Subsequently,we discovered for the first time that a2 induced ferroptosis.Importantly,compound a2 decreased GPX4 expression and overexpressing GPX4 antagonized the anti-proliferative activity of a2.Furthermore,we demonstrated that a2 caused ferrous iron accumulation through the autophagy pathway,prevention of which rescued a2 induced ferrous iron elevation and cell growth inhibition.Moreover,a2 exhibited more potent anti-cancer activity than 5-fluorouracil in gastric canc er cell line-derived xenograft mice models.Patient-derived tumor xenograft models from different patients displayed varied sensitivity to a2,and GPX4 downregulation indicated the sensitivity of tumors to a2.Finally,a2 exhibited well pharmacokinetic characteristic s.Overall,our data suggest that inducing ferroptosis is the major mechanism mediating anti-tumor activity of a2,and a2 will hopefully serve as a promising compound for gastric cancer treatment.

Effects of Fe(II) on anammox community activity and physiologic response

Though there are many literatures studying the effects of iron on anammox process,these studies only focus on the reactor performance and/or the microbial community changes,the detailed effects and mechanisms of Fe(II)on anammox bacterial activity and physiology have not been explored.In this study,four Fe(II)concentrations(0.03,0.09,0.12 and 0.75 mmol/L)were employed into the enriched anammox culture.The enhancement and inhibition effects of Fe(II)on anammox process and bacterial physiology were investigated.It was discovered that the anammox process and bacterial growth were enhanced by 0.09 and 0.12 mmol/L Fe(II),in which the 0.12 mmol/L Fe(II)had advantage in stimulating the total anammox activity and bacterial abundance,while 0.09 mmol/L Fe(II)enhanced the relative anammox activity better.The anammox activity could be inhibited by 0.75 mmol/L Fe(II)immediately,while the inhibition was recoverable.Both 0.09 and 0.12 mmol/L Fe(II)induced more genes being expressed,while didn’t show a stimulation on the relative expression level of functional genes.And anammox bacteria showed a stress response to detoxify the Fe inhibition once inhibited by 0.75 mmol/L Fe(II).This study provides more information about physiologic response of anammox bacteria to external influence(enhancement and inhibition),and may also instruct the future application of anammox process in treating various sources of wastewater(containing external disturbances such as heavy metals)and/or different treatment strategies(e.g.from side-stream to main-stream).

Effects of riboflavin and desferrioxamine B on Fe(Ⅱ)oxidation by 0_(2)

Flavins and siderophores secreted by various plants,fungi and bacteria under iron(Fe)deficient conditions play important roles in the biogeochemical cycling of Fe in the environment.Although the mechanisms of flavin and siderophore mediated Fe(Ⅱ)reduction and dissolution under anoxic conditions have been widely studied,the influence of these compounds on Fe(ID)oxidation under oxic conditions is still unclear.In this study,we investi-gated the kinetics of aqueous Fe(Ⅱ)(17.8μM)oxidation by O_(2)at pH 5-7 in the presence of riboflavin(oxidized(RBF)and reduced(RBFH_(2)))and desferrioxamine B(DFOB)as representative flavins and siderophores,respec-tively.Results showed that the addition of RBF/RBFH_(2)or DFOB markedly accelerates the oxidation of aqueous Fe(Ⅱ)by O_(2).For instance,at pH 6,the rate of Fe(Ⅱ)oxidation was enhanced 20-70 times when 10μM RBFH_(2)was added.The mechanisms responsible for the accelerated Fe(Ⅰ)oxidation are related to the redox reactivity and complexation ability of RBFH_(2),RBF and DFOB.While RBFH_(2)does not readily complex Fe(Ⅰ)/Fe(Ⅱ),it can activate O_(2)and generate reactive oxygen species,which then rapidly oxidize Fe(Ⅱ).In contrast,both RBF and DFOB do not reduce O_(2)but react with Fe(Ⅱ)to form RBF/DFOB-complexed Fe(Ⅱ),which in turn accelerates Fe(Ⅰ)oxidation.Furthermore,the lower standard reduction potential of the Fe(Ⅰ)-DFOB complex,compared to the Fe(Ⅰ)-RBF complex,correlates with a higher oxidation rate constant for the Fe(Ⅰ)-DFOB complex.Our study reveals an overlooked catalytic role of flavins and siderophores that may contribute to Fe(Ⅱ)/Fe(Ⅱ)cycling at oxic-anoxic interfaces.