Adsorption technology and mechanism of As(III) and As(V) in wastewater by iron modified rice husk biochar

Arsenic pollution has become a common phenomenon, which seriously endangers the environment and poses a greatthreat to human health. In this paper, a novel method has been developed for simultaneous removal of composite arsenicpollution based on the modified rice husk biochar as an efficient adsorbent. Iron modified rice husk biochar (MRHB)adsorbent has been prepared using rice husk as raw material, NaHCO3 as pore expander, FeCl3ꞏ6H2O as modifier and NaOHas precipitant. The adsorption characteristics of MRHB for As(Ⅲ) and As(V) has been investigated on the basis of batchexperiments. X-ray diffraction, scanning electron microscopy, and Fourier Transform Infrared were carried out tocharacterize the composition and structure of MRHB. The results show that the arsenic concentration of 1.0 mg/L, adsorbentdosage of 1.0 g/L, the maximum removal rates of As(Ⅲ) and As(V) are 99.88% and 99.93% at pH of 5. The adsorptionperformance of MRHB for As(V) and As(V) fits well to the pseudo-second-order kinetic model, indicating that thechemisorption control plays a dominant role in adsorption process. Results from this study demonstrated the promise ofMRHB in application as an efficient and environmentally friendly adsorbent for composite arsenic pollution

Influence of chemical oxidant on degradation of benzo[a]pyrene metabolites by the bacterium-Zoogloea sp.

It is neither comprehensive nor appropriate that the bioremediation of a benzo[a]pyrene (BaP)-contaminated environment be assessed only by its high degradation extent because its metabolites\u27 chemical structures are similar to the parent compound and maybe equally toxic. Therefore, further degradation of BaP metabolites is significant. Three methods, combining the Zoogloea sp. with potassium permanganate, combining the Zoogloea sp. with H2O2, Zoogloea sp. alone, were investigated to degrade cis-BP4,5-dihydrodiol and cis-BP7,8-dihydrodiol, which are the metabolites of BaP formed by bacterium-Zoogloea sp. Optimum parameters of degradation in the best method are that: of the three methods, coupling the Zoogloea sp. and KMnO4 is the best; compared with cis-BP7,8-dihydrodiol, cis-BP4,5-dihydrodiol is the more liable to be accumulated in pure cultures; the degradation effect of the two metabolites is optimal when the initial concentration of KMnO4 in the cultures is 0.05%; initial concentration of cis-BP4,5-dihydrodiol and cis-BP7,8-dihydrodiol is 4 mg L&minus;1, 8 mg L&minus;1, respectively; cometabolic substance is salicylic acid or sodium succinate. The degradation extent of cis-BP4,5-dihydrodiol and cis-BP7,8-dihydrodiol using combining the Zoogloea sp. and KMnO4 reach 76.1% and 85.9% after 12 days of cultivation, respectively, which were more than twice compared with conventional method.<br /

Effective Technique and Mechanism for Simultaneous Adsorption of As(III/V) from Wastewater by Fe-ZIF-8@MXene

YesArsenic (As) contamination of surface water has become a global concern, especially for the third world countries, and it is imperative to develop advanced materials and an effective treatment method to address the issue. In this paper, iron doped ZIF-8@MXene (Fe-ZIF-8@MXene) was prepared as a potential adsorbent to effectively and simultaneously remove As(III/V) from wastewater. To investigate this, Fe-ZIF-8@MXene was characterized before and after the removal of mixed As(III/V). The results of Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), specific surface area (BET) and point of zero charge (pHpzc) showed that Fe-ZIF-8@MXene was prepared successfully and kept a stable structure after As(III) and As(V) adsorption. The particle size of Fe-ZIF-8@MXene was in the range of 0.5 μm to 2.5 μm, where its BET was 531.7 m2/g. For both contaminants, adsorption was found to follow pseudo-second-order kinetics and was best-fitted by the Langmuir adsorption model with correlation coefficients (R2) of 0.998 and 0.997, for As(III) and As(V), respectively. The adsorbent was then applied to remove As from two actual water samples, giving maximum removal rates of 91.07% and 98.96% for As(III) and As(V), respectively. Finally, removal mechanisms for As(III/V) by Fe-ZIF-8@MXene were also explored. During the adsorption, multiple complexes were formed under the effect of its abundant surface functional groups involving multiple mechanisms, which included Van der Waals force, surface adsorption, chemical complexation and electrostatic interactions. In conclusion, this study demonstrated that Fe-ZIF-8@MXene was an advanced and reusable material for simultaneous removal of As(III/V) in wastewater

Adsorption technology and mechanism of As(III) and As(V) in wastewater by iron modified rice husk biochar

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Degradation mechanisms of benzo[a]pyrene and its accumulated metabolites by biodegradation combined with chemical oxidation

A high degradation extent of benzo[a]pyrene (BaP) should not be considered as the sole desirable criterion for the bioremediation of BaP-contaminated soils because some of its accumulated metabolites still have severe health risks to human. Two main metabolites of BaP, benzo[a]pyrene-1,6-quinone (BP1,6-quinone) and 3-hydroxybenzo[a]pyrene (3-OHBP) were identified by high performance liquid chromatography (HPLC) with standards. This study was the first time that degradation of both BaP and the two metabolites was carried out by chemical oxidation and biodegradation. Three main phases during the whole degradation process were proposed.Hydrogen peroxide&ndash;zinc (H2O2&ndash;Zn), the fungus &ndash; Aspergillus niger and the bacteria &ndash; Zoogloea sp. played an important role in the different phases. The degradation parameters of the system were also optimized, and the results showed that the effect of degradation was the best when fungus&ndash;bacteria combined with H2O2&ndash;Zn, the concentration range of BaP in the cultures was 30&ndash;120 mg/l, the initial pH of the cultures was 6.0. However, as co-metabolites, phenanthrene significant inhibited the degradation of BaP. This combined degradation system compared with the conventional method of degradation by domestic fungus only, enhanced the degradation extent of BaP by more than 20% on the 12 d. The highest accumulation of BP1,6-quinone and 3-OHBP were reduced by nearly 10% in the degradation experiments, which further proved that the combined degradation system was more effective as far as joint toxicity of BaP and its metabolites are concerned.<br /