Zero-valent Iron Concentration Research Articles

Bioconversion of pure CO2 to caproic acid with zero valent iron: Optimizing carbon flux distribution in co-cultures of Acetobacterium woodii and Megasphaera hexanoica

Acetobacterium woodii and Megasphaera hexanoica were co-cultured for caproic acid (CA) production from lactic acid (LA) and CO2. Also, various concentrations (1 g/L, 3 g/L, 5 g/L, and 10 g/L) of Zero Valent Iron (ZVI) were supplied to study its impact on the co-culture system. In flask experiments, 10 g/L LA and 1.0 bar CO2 produced 0.6 g/L CA with some biomass growth. ZVI increased LA consumption and CA production. Indeed, 3 g/L ZVI boosted CA production by 186 % and biomass accumulation by 103 %, suggesting that ZVI controls the carbon flux. Subsequent automated bioreactor studies showed that 3 g/L ZVI produced 1.842 g/L CA at stable pH, compared to 0.969 g/L without ZVI (control). Further, metabolic activity showed that both bacteria could directly use H2, generated by ZVI (3 g/L), as electron donor. Higher ZVI concentrations (10 g/L) resulted in Fe2+ causing excessive oxidation pressure on M. hexanoica, with its carbon flux flowing preferentially towards biomass. Enzyme assays confirmed that A. woodii preferred 10 g/L ZVI while M. hexanoica preferred 3 g/L for optimal bioconversion.

Chemical and biological effects of zero-valent iron (ZVI) concentration on in-situ production of H2 from ZVI and bioconversion of CO2 into CH4 under anaerobic conditions

The conversion of carbon dioxide (CO2) to methane (CH4) is a strategy for sequestering CO2. Zero-valent iron (ZVI) has been proposed as an alternative electron donor for the CO2 reduction to CH4. In this study, the effects of ZVI concentrations on the abiotic production of H2 (without the action of microorganisms) in the first part and on the biological conversion of CO2 to CH4 using ZVI as a direct electron donor in the second part were examined. In the abiotic H2 production, the increase in the ZVI concentration from 16 to 32, 64, and 96 g/L was found to have positive effects on both the amounts of H2 generated and the rates of H2 production because the extent of ZVI oxidation positively correlates with increasing surface area. Nevertheless, the increase in ZVI concentration from 96 to 224 g/L did not benefit the H2 production because the ZVI dissolution was suppressed by the increasing aqueous pH above 10. In the bioconversion of CO2 to CH4 using ZVI as an electron donor, the main methanogenesis pathway occurred via hydrogenotrophic methanogenesis at pH 8.7–9.5 driven by the genus Methanobacterium of the class Methanobacteria. At ZVI concentrations of 64 g/L and above, the production of volatile fatty acid (VFA) became clear. Acetate was the main VFA, indicating the induction of homoacetogenesis at ZVI concentrations of 64 g/L and above. In addition, the presence of propionate as the second major VFA suggests the production of propionate from CO2 and acetate under conditions with high H2 partial pressure. The results indicated that the pathway for ZVI/CO2 conversion to CH4 was competitive between hydrogenotrophic methanogenesis and homoacetogenesis.

Weak magnetic field and coexisting ions accelerate phenol removal by ZVI/H2O2 system: Their efficiency and mechanism

Human activity and industrial production have led to phenol becoming a significant risk factor. The proper treatment of phenol in wastewater is essential. In this study, the utilization of weak magnetic field (WMF) and zero-valent iron (ZVI) was proposed to activate H2O2 to degrade phenol contaminant. The results show that the weak magnetic field has greatly enhanced the reaction rate of ZVI/H2O2 removal of phenol. The removal rates of phenol by ZVI/H2O2/WMF generally decreased with increasing initial pH and phenol concentrations, and firstly increase and then decrease with increasing Fe0 or H2O2 dosage. When the initial pH is 5.0, ZVI concentration of 0.2 g L−1, H2O2 concentration of 6 mM, and phenol concentration of 100 mg L−1 were used, complete removal of phenol can be achieved within 180 min at 25 °C. The degradation process was consistent with the pseudo-first-order kinetic model when the experimental data was fitted. The ZVI/H2O2/WMF process exhibited a 1.05–2.66-fold enhancement in the removal rate of phenol under various conditions, surpassing its counterpart lacking WMF. It was noticed that the presence of 1–5 mM of Ca2+, Mg2+, Cl−, SO42− ions can significantly enhance the kinetics of phenol removal by ZVI/H2O2 system with or without WMF to 2.22–10.40-fold, but NO3−, CO32−, PO43− inhibited the reaction significantly in the following order: PO43− > CO32− > NO3−. Moreover, pre-magnetization for 3 min could enhance the ZVI/H2O2 process which was valuable in treatment of real wastewater. The hydroxyl radical has been identified as the primary radical species responsible for phenol degradation. The presence of WMF accelerates the corrosion rate of ZVI, thereby promoting the release of Fe2+ ions, which in turn induces an increased production of hydroxyl radicals and facilitates phenol degradation. The compounds hydroquinone, benzoquinone, catechol, maleic acid, and CO2 were identified using GC-MS, and degradation pathways were proposed. Employing WMF in combination with various ions like Ca2+, Mg2+, Cl−, SO42− is a novel method, which can enhance oxidation capacity of ZVI/H2O2 and may lead to economic benefit.

PH and Heat Pretreatments with Zero-Valent Iron Addition to Enhance Biogas Production from Cassava Pulp Wastewater: Optimization and Comparison of Mathematical Models

Pretreatments of pH and heat with zero-valent iron (ZVI) additions enhance anaerobic digestion and increase reducing sugar availability for optimum biogas production. This study aimed to optimize the conditions of different pH and heat pretreatment with additional ZVI to yield higher biogas amounts from the anaerobic digestion (AD) of cassava wastewater. Thirteen pH conditions, ten ZVI concentrations, and eleven heating periods were varied and measured to optimize the standard conditions. Four mathematical models that are widely used to evaluate the cumulative biogas production were employed, namely, the Modified Gompertz, Logistic, Transference, and Exponential models. The pretreatment of pH 10 and 35 min of boiling time with a ZVI concentration of 60 g·kg·TVS−1 produced the highest cumulative biogas at the end of the AD process. The Logistic and Modified Gompertz models were better fitted with the experimental data than the other models. Interestingly, the optimized conditions altered the biogas production rate but prolonged the lag phase. A reasonably positive correlation was also found between the FeOOH amount and biogas production rate in the LF and MG models. These optimal fitted models, kinetics parameters, and possible correlations are novel findings that can help develop extensive scale developments for biogas generation from cassava wastewater.

The disinhibition effect of iron-based particles on anaerobic digestion of florfenicol-containing cow manure: Performance and mechanism

The overuse of antibiotics has caused problems such as environmental pollution, increased antibiotic resistance of pathogenic bacteria, and inhibition of engineered microbial processes such as anaerobic digestion (AD). At present, mitigating the inhibition of antibiotics on the process of microbial recycling of organic matter by using additives has always been a research hotspot. In this study, the effects of the addition of three iron-based particles including zero-valent iron (ZVI), Fe2O3 and Fe3O4 on the biogas yield during the AD of cow manure containing florfenicol (FLO) were studied. It was found that by alleviating the acid accumulation, the addition of low-concentration ZVI, Fe2O3 and high-concentration Fe3O4 enhanced the maximum methane production rate of FLO-containing cow manure during AD to 3.5, 1.7 and 3.6 times, respectively, while high concentration of ZVI will lead to the crash of the AD system due to the rise of pH. Within the concentration range of iron-based particles dosed in this study, the Fe3O4 dosage showed a significant positive correlation with the cumulative methane production enhancement rate (p < 0.01). The sum of the relative abundances of Limnobacter and Pseudomonas was correlated with the absolute abundance of floR gene with the Pearson correlation coefficient of 0.9457 (p < 0.01), indicating the possibility of these two genera being the potential host bacteria for floR gene.

Degradation of amaranth by persulfate activated with zero-valent iron: influencing factors, response surface modeling

In this study, zero-valent iron (ZVI) is applied to activate persulfate (PDS) for the degradation of amaranth (AMR). The effects of PDS concentration, ZVI concentration, solution pH , temperature, and reaction time on the degradation of AMR by the ZVI/PDS advance oxidation process are investigated. Sulfate and hydroxyl radicals are involved in the main reaction pathway of AMR and sulfate radical acts as a dominant oxidant. The CCD (central composite design) plan is chosen to build the RSM model for the prediction of AMR degradation. ANOVA analysis shows that the secondary fitting model had great fitness with R2 = 0.997, R_{{{text{adj}}}}^{2} = 0.936, p-value of lack of fit = 0.107. Optimum conditions for 98% AMR removal given by RSM are PDS concentration = 7.33 mM, ZVI dosage = 17.79 mM, initial pH 4.62, temperature = 59.49 °C, reaction time = 9.88 min which is proved to be very closed to the real removal rate of 96.78%. Sensitivity analysis indicates that the relative importance of the influencing parameters is of the following order: temperature, PDS concentration, pH , ZVI dosage, and reaction time. The PDS/ZVI system shows an acceptable RSE of about 75% and TOC removal of 85% on AMR oxidation. Finally, the possible pathway of AMR degradation is proposed.

Bioproduction of acetic acid from carbon dioxide as single substrate and zero valent iron (ZVI) by clostridia

Developing innovative bioprocess strategies for carbon capture and utilization has been a major focus of research over the past decade as a way of creating a more resilient world. In this study, zero-valent iron (ZVI) was utilized to generate hydrogen, which was then utilized as an electron donor for CO2 reduction by either Clostridium aceticum or Clostridium carboxidivorans. For this bioprocess, an early acidic condition in the reactors facilitated more hydrogen production and thereby more acetic acid accumulation, in contrast to later acidification, elucidating the role of pH in ZVI-CO2 bioconversion. Acetic acid was produced as single end product of the process in both batch bottle studies with no pH control as well as in reactor studies with pH regulation. This is, to the best of our knowledge, the first report on selective pure CO2 bioconversion to acetic acid by clostridia, with ZVI. In order to minimize costs, scrap iron rather than pure ZVI can be used for scaling-up. By lowering the pH to 6.6 for C. aceticum, in reactor studies with 75 g/L ZVI, some ethanol production (125 mg/L) was also observed, besides acetic acid. In reactor studies, a maximum acetic acid concentration of about 2 g/L was obtained at ZVI concentrations of 50 and 75 g/L. Thus, ZVI dosage and medium pH have a major effect on the metabolites generated during CO2 utilization.

Isotope fractionation of diethyl phthalate during oxidation degradation by persulfate activated with zero-valent iron

This study reports the 13C and 2H isotope fractionation associated with the oxidation of diethyl phthalate (DEP) by persulfate (PS) activated with zero-valent iron (ZVI) using three concentration levels (0.2, 0.5 and 1.0 g L−1) at different pH values, 3, 7 and 11, respectively. The results showed that the degradation of DEP followed a pseudo first-order kinetics. The fastest degradation was found at neutral conditions (pH 7). Similar carbon and hydrogen isotope fractionation (εC and εH) was observed during the oxidation of DEP by ZVI activated PS at pH 3, 7 and 11. At ZVI concentration of 0.5 g L−1, the correlation of 13C and 2H fractionation (Λ) were obtained to be 12.7 ± 3.5, 11.1 ± 4.2 and 12.0 ± 2.9 at pH 3, 7 and 11, respectively. The concentration of ZVI has no effect on the correlation of 13C and 2H fractionation (Λ). In addition, radical quenching approach and electron paramagnetic resonance (EPR) were combined to explore the dominant radical species in the ZVI activated PS reaction, and hydroxyl radical (•OH) was found to be the predominant radical at all pH studied. The results of CSIA show the addition of •OH to the aromatic ring of DEP is the main reaction mechanism, which is consistent with the results of radical quenching experiment and EPR study. Carbon and hydrogen apparent kinetic isotope effects (AKIEs) obtained from •OH reactions with DEP supported the hypothesis of CH bond cleavage. Thus, carbon and hydrogen isotope enrichment factors clearly distinguish the different reaction mechanisms and hence, are a promising approach to improve understanding of radical species reaction pathways for chemical oxidation of DEP.

Comparison between UVA- and zero-valent iron-activated persulfate processes for degrading propylparaben.

Conventional wastewater treatments are not efficient in removing parabens, which may thus end up in surface waters, posing a threat to aquatic biota and human health. As an alternative treatment, persulfate (PS)-driven advanced oxidation technologies have gained growing attention for removing these pollutants. In this study, the degradation of propylparaben (PrP) by UVA- and zero-valent iron (ZVI)-activated persulfate was investigated. The effects of initial PS concentration ([PS]0) and irradiance or ZVI concentration were explored using the Doehlert experimental design. For the UVA-activated system, the specific PrP degradation rate (k) and percent removal were consistently higher for increasing [PS]0 and irradiance, varying in the ranges 0.0053-0.0192min-1 and 37.9-77.3%, respectively. In contrast, extremely fast PrP degradation was achieved through the ZVI/PS process (0.3304 < k < 0.9212min-1), with removal percentages above 97.5%; in this case, paraben degradation was hindered for a ZVI dosage beyond 40mgL-1. Regarding toxicity, ECOSAR predictions suggest that the degradation products elucidated by LC-MS/MS are less toxic than PrP toward fish, daphnid, and green algae. In addition, both processes showed to be strongly dependent on the water matrix, being ZVI/PS more impacted for a MBR effluent, although its performance was much better than that exhibited by the UVA-driven process (t1/2 of 65.4 and 276.1min, respectively).

Efficient removal of ciprofloxacin in aqueous solutions by zero-valent metal-activated persulfate oxidation: A comparative study

The removal mechanisms of ciprofloxacin (CIP) in an aqueous solution using the persulfate (PS) oxidation system activated by zero-valent metals (ZVMs), such as zero-valent iron (ZVI), zero-valent aluminum (ZVA), and zero-valent copper (ZVC), were compared. The CIP removal followed the pseudo-first-order kinetics in all the PS oxidation processes mediated by the ZVMs. The influence of factors of the PS oxidation system, such as pH, and concentrations of both ZVMs and PS, was analyzed. Our results indicate that ZVI/PS process resulted in the highest removal of CIP at 84.5 ± 1.3 % (kobs = 29.8 × 10−3 min-1) within 60 min with pHo of 3.0, a molar dosage of PS at 2.25 mM and concentration of ZVI at 126 mg L-1. However, CIP was only removed to the extent of 73.3 ± 2.5 % with kobs = 21.9 × 10−3 min-1 by ZVA/PS with pHo of 3.0, [PS]o = 2.25 mM and concentration of ZVA at 81 mg L-1. Finally, for ZVC/PS system, the removal efficiency of CIP was lowest at 59.9 ± 3.2 % with constant rate kobs = 15 × 10−3 min-1 when optimum conditions were initial pH of 4.0, [PS]o = 2.25 mM and dosage of ZVC at 192 mg L-1. Based on X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) spectra, Fe2+, and Fe3+ ions from ZVI, Al3+ ions from ZVA, and Cu+ and Cu2+ ions from ZVC were released by PS oxidation. Moreover, active radicals (HO*, SO4*–) determined as primary agents to total oxidation performance, were generated through the activation of PS by intermediate ion metals.

Effect of hydraulic retention time, ZVI concentration, and Fe2+ concentration on autotrophic denitrification efficiency with iron cycle bacterium strain CC76

ABSTRACT The immobilized reactor of iron-reducing bacteria and zero-valent iron (ZVI) integrated system was established. This study has shown that the effects of hydraulic retention times (9, 11, 13 h), ZVI concentrations (2, 4, 6, 8 mg/L), and Fe2+ concentrations (5, 10, 15 mg/L) on the denitrification characteristics of iron cycle bacterium strain CC76. The results show that the longer the HRT is, the stronger ability of bacteria to remove nitrate. When ZVI concentration was 4 mg/L and the Fe2+ concentration is 15 mg/L, the removal efficiency of nitrate was the highest, reaching the maximum value of 93.02% (1.07 mg/L/h). Since increasing ZVI concentration in a certain range can not only promote chemical reduction but also make use of strain CC76 as an electron donor. Also, the abundance of strain CC76 decreased with the increase of ZVI concentration, which indicated that adding a low concentration of ZVI could reduce the inhibitory effect on bacteria. Hypothesis analysis of principal components showed that a low concentration of ZVI is beneficial to increase nitrate removal rate. Community structure analysis indicated that strain CC76 and related bacteria were the most abundant bacteria in the reactor.

Impact of Nano Zero-Valent Iron (NZVI) on Methanogenic Activity, Physiological Traits, and Microbial Community Structure in Anaerobic Digestion

Effects of short-term nano zero-valent iron (NZVI) and zero-valent iron (ZVI) exposure on methanogenic activity of anaerobic sludge, physiological traits, composition of phospholipid fatty acids (PLFA), and microbial community structure were investigated. Results show that accumulated methane production decreased with an increase of NZVI concentration; yet, methane production only changed slightly with the same concentration of ZVI. In the NZVI (100-5000 mg·L-1) sets, dissolved iron (DFe) concentrations were 1.6-7.4 times that of the control value at 5 d, whereas DFe was only slightly above the control in the ZVI set (5000 mg·L-1). The concentration of extracellular polymeric substances and cell viability decreased to 21.1% and 79.7%, respectively, of the control in the 5000 mg·L-1 NZVI treatments. Coenzyme F420 and coenzyme M decreased to 40.2% and 61.1%, respectively, of the control in the 5000 mg·L-1 NZVI treatments, which were significantly increased to 1.3 times that of the control value in the 100 mg·L-1 NZVI and 5000 mg·L-1 ZVI treatments. The order of unsaturation and branch PLFA content was ZVI-5000 (21.18%) > control (19.37%) > NZVI-1000 (16.69%) > NZVI-5000 (15.94%) > NZVI-100 (12.08%). High NZVI concentration (5000 mg·L-1) resulted in an increase of DFe and a decrease of cell membrane fluidity and key coenzyme activity of methanogenesis, which led to the inhibition of methane production. Principle component analysis and redundancy analysis indicated that differences in the microbial community existed among these treatments and that Nakamurella, Bacillus, Trichococcus, and Petrimonas showed tolerance to NZVI.

Enhanced hydrogen fermentation by zero valent iron addition

In this study, zero valent iron (ZVI) was applied to enhance hydrogen fermentation (H2). Glucose was used as a substrate at various concentrations of 5–40 g COD/L, and ZVI concentration was adjusted at 0–10 g/L. Without ZVI addition, H2 yield decreased as substrate concentration increased, due to organic acids accumulation as substrate concentration increased. At low substrate concentration of 5 g COD/L, there was a slight increase of H2 yield from 1.4 to 1.5 mol H2/mol glucose added by ZVI addition. However, the increment was substantial at higher substrate range. For example, H2 yield increased from 0.9 to 1.2–1.5 mol H2/mol hexoseadded by ZVI addition at 20 g COD/L. The results indicated that ZVI may create a more favorable environment for anaerobic microbial acidogenesis with providing buffering effect to prevent pH drop due to produced hydroxyl ions as it dissolved. These changes of environmental conditions also brought differences on organic acids profile and microbial community, and those may affect to overall H2 fermentation performances.

Effect of zero-valent iron on biological denitrification in the autotrophic denitrification system

This study investigated nitrate removal using biological denitrification by the iron-reducing bacteria strain CC76 combined with zero-valent iron (ZVI) in simulated groundwater under anaerobic conditions. The mechanism of nitrate reduction as well as the process of iron cycling by strain CC76 and ZVI were studied. During growth experiments, the strain CC76 showed the ability to utilize Fe2+ (electron donor) produced from the stimulated corrosion of ZVI for the nitrate removal. ZVI exerted inhibitive effects on the growth of strain CC76 in the early stage. However, the strain CC76 was able to tolerate the presence of ZVI in the long term. Moreover, three factors (temperature, initial pH, and ZVI concentration) were selected as effective factors and were optimized using a central composite design of response surface methodology. Based on the statistical analysis, a temperature of 30.44 °C, initial pH of 6.11, and ZVI concentration of 5.89 g/L were determined to be the optimum values. The effect of Fe2+/ZVI ratio was also explored and compared with ZVI alone, a certain amount of a mixture of Fe2+ and ZVI showed a higher nitrate removal ability. Moreover, scanning electron microscopy and X-ray diffraction analyses showed the corrosion of ZVI occurred after reaction in the autotrophic denitrification system.

Zero-Valent Iron Enhances Biocathodic Carbon Dioxide Reduction to Methane.

Methanogenic bioelectrochemical systems (BESs), which convert carbon dioxide (CO2) directly to methane (CH4), promise to be an innovative technology for anaerobic digester biogas upgrading. Zero-valent iron (ZVI), which has previously been used to improve CH4 production in anaerobic digesters, has not been explored in methanogenic biocathodes. Thus, the objective of this study was to assess the effect of biocathode ZVI on BES performance at 1 and 2 g/L initial ZVI concentrations and at various cathode potentials (-0.65 to -0.80 V versus SHE). The total CH4 produced during a 7-day feeding cycle with 1 and 2 g/L initial ZVI was 2.8- and 2.9-fold higher, respectively, than the mean CH4 production in the four prior cycles without ZVI addition. Furthermore, CH4 production by the ZVI-amended biocathodes remained elevated throughout three subsequent feeding cycles, despite catholyte replacement and no new ZVI addition. The fourth cycle following a single ZVI addition of 1 g/L and 2 g/L yielded 123% and 231% more total CH4 than in the non-ZVI cycles, respectively. The higher CH4 production could not be fully explained by complete anaerobic oxidation of the ZVI and utilization of produced H2 by hydrogenotrophic methanogens. Microbial community analysis showed that the same phylotype, most closely related to Methanobrevibacter arboriphilus, dominated the archaeal community in the ZVI-free and ZVI-amended biocathodes. However, the bacterial community experienced substantial changes following ZVI exposure, with more Proteobacteria and fewer Bacteroidetes in the ZVI-amended biocathode. Furthermore, it is likely that a redox-active precipitate formed in the ZVI-amended biocathode, which sorbed to the electrode and/or biofilm, acted as a redox mediator, and enhanced electron transfer and CH4 production. Thus, ZVI may be used to increase biocathode CH4 production, assist in the start-up of an electromethanogenic biocathode, and/or maintain microbial activity during voltage interruptions.

Removal of Manganese and Copper from Contaminated Groundwater Generated from Mines Landfills Waste Using ZV-I, AC and NZ in PRB Technology

In this study, Zero Valent Iron (ZV-I), Activated Carbon (AC) and Natural Zeolite (NZ) were utilized as reactive material for testing its effectiveness for removal manganese and copper in the waste of Mine Landfills. Hereby, four parameters were taken in this study which is initial concentration of metal, initial groundwater alkalinity PH and dosage of reactive ZV-I, AC, or NZ. Batch results show that ZV-I is the most effective materials for removal manganese and copper up to 48 ppm at low concentration of ZV-I 1990-4990 ppm while initial pH range varies between three through seven. The study discovered that ZV-I reactive compound can be used effectively for manganese removal through settling and adsorption on ZV-I, while copper is basically removed by ZV-I through direct reductive settling. Also, ACcompared to ZV-I reactive material has not significant effect on manganese removal whereas AC basically removed manganese by adsorption while Copper is removed basically by settling. The removal of Copper and manganese can be increased by increasing detention time and dosage of carbon. The study showed that manganese and copper are removed slowly and ineffective by NZ compound.

Zero-valent iron-activated persulfate oxidation of a commercial alkyl phenol polyethoxylate

ABSTRACTAqueous Triton X-45 (TX-45; 20 mg/L; original total organic carbon (TOC) = 14 mg/L), a representative, commercially important alkylphenol polyethoxylate, was subjected to persulfate (PS) oxidation activated with zero-valent iron (ZVI) nanoparticles. After optimization of the ZVI/PS treatment combination (1 g/L ZVI; 2.5 mM PS at pH5) in terms of pH (3–9), ZVI (0.5–5 g/L) and PS (0.5–5.0 mM) concentrations, TX-45 could be efficiently (>90%) degraded within short treatment periods (<60 min) accompanied with significant (>40%) TOC removals. The degree of PS consumption and Fe release was also followed during the experiments and a positive correlation existed between enhanced TX-45 removals and ZVI-activated PS consumption rates accompanied with a parallel Fe release. Acute toxicity tests were conducted using two different bioassays to examine the toxicological safety of the ZVI/PS oxidation system. Acute toxicity profiles significantly decreased from an original value of 66% relative inhibition to 21% and from 16% relative inhibition to non-toxic values according to Vibrio fischeri and Pseudokirchneriella subcapitata bioassays, respectively. The photobacterium V. fischeri appeared to be more sensitive to TX-45 and its degradation products than the microalgae P. subcapitata.

Removal of selenite by zero-valent iron combined with ultrasound: Se(IV) concentration changes, Se(VI) generation, and reaction mechanism

In this paper, the performance and application of zero-valent iron (ZVI) assisted by ultrasonic irradiation for the removal of selenite (Se(IV)) in wastewater was evaluated and reaction mechanism of Se(IV) with ZVI in such systems was investigated. A series of batch experiments were conducted to determine the effects of ultrasound power, pH, ZVI concentration, N2 and air on Se(IV) removal. ZVI before and after reaction with Se(IV) was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Results indicated that ultrasound can lead to a significant synergy in the removal of Se(IV) by ZVI because ultrasound can promote the generation of OH and accelerate the advanced Fenton process. The primary reaction products of ZVI and Se(IV) were Se0, ferrihydrite, and Fe2O3.

Zero-valent iron (ZVI) activation of persulfate (PS) for oxidation of bentazon in water

Bentazon (BTZ) in water, a broadly used herbicide in agriculture, is toxic to human beings and has a negative impact on ecosystem. In this study, zero-valent iron (ZVI) activation of persulfate (PS) for the oxidation of BTZ was investigated. More active sulfate radicals produced from the system were principally responsible for the BTZ degradation. The BTZ removal well followed a pseudo-first-order (PFO) kinetics pattern. Key factors affecting the treatment were tested, including ZVI concentration, PS dose, initial BTZ concentration, initial solution pH, temperature and common coexisting ions in water. Under the optimal ZVI (4.477mM) and PS (0.262mM) concentrations, 0.021mM BTZ was totally removed at an initial pH⩽7.Generally, lower BTZ concentration, lower pH and higher temperature favored the treatment. Different coexisting ions exhibited different effects. Al3+, Cl− and NO3− improved the treatment; NH4+, Ca2+, and Mg2+ did not significantly influence the BTZ removal; and, Mn2+, Cu2+, CO32−, HCO3−, PO43−, HPO42− and H2PO4− inhibited the BTZ degradation. Most of BTZ were not mineralized, and instead degraded into three major degradation products including 2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide (P1, C7H6N2O3S), 2-aminobenzoic acid (anthranilic acid) (P3, C7H7NO2), and 2-amino-2-sulfobenzoic acid (P5, C7H7NO5S). This study demonstrates that ZVI/PS is a viable alternative for controlling BTZ-induced water pollution.

Decolorization of azo dyes Orange G using hydrodynamic cavitation coupled with heterogeneous Fenton process

The present work demonstrates the application of the combination of hydrodynamic cavitation (HC) and the heterogeneous Fenton process (HF, Fe0/H2O2) for the decolorization of azo dye Orange G (OG). The effects of main affecting operation conditions such as the inlet fluid pressure, initial concentration of OG, H2O2 and zero valent iron (ZVI), the fixed position of ZVI, and medium pH on decolorization efficiency were discussed with guidelines for selection of optimum parameters. The results revealed that the acidic conditions are preferred for OG decolorizaiton. The decolorization rate increased with increasing H2O2 and ZVI concentration and decreased with increasing OG initial concentration. Besides, the decolorization rate was strongly dependent on the fixed position of ZVI. The analysis results of degradation products using liquid chromatography–ESI–TOF mass spectrometry revealed that the degradation mechanism of OG proceeds mainly via reductive cleavage of the azo linkage due to the attack of hydroxyl radical. The present work has conclusively established that the combination of HC and HF can be more energy efficient and gives higher decolorization rate of OG as compared with HC and HF alone.