Enhancing laccase stability and activity for dyes decolorization using ZIF-8@MWCNT nanocomposite

The continuous use of chemical dyes in various industries,and their discharge into industrial effluents,results in severe problems to human life and water pollution.Laccases have the ability to decolorize dyes and toxic chemicals in industrial effluents as green biocatalysts.Their possible industrial applications have been limited by poor reusability,low stability,and loss of free laccase action.In this research,lac-case was immobilized on zeolitic imidazolate framework coated multi-walled carbon nanotubes(Laccase@ZIF-8@MWCNTs)via metal affinity adsorption to develop an easy separable and stable enzyme.The optimum reaction conditions for immobilized laccase are at a pH of 3.0 and a temperature of 60℃.The immobilized laccase was enhanced in storage and thermal stability.The results indicated that Laccase@ZIF-8@MWCNTs still maintained 68%of its original activity after 10 times of repeated use.Most importantly,the biocatalytic system was applied for decolorization of different dyes(20 mg·L^(-1))without a mediator,and up to 97.4%for Eriochrome black T and 95.6%Acid red 88 was achieved in 25 min.Biocatalysts with these properties may be used in a variety of environmental and industrial applications.

Experimental Study on Decolorization and Degradation of Reactive Brilliant Red X-3B in a White Rot Fungal Biofilm Reactor

Experimental results of an azo dye(reactive brilliant red X 3B, RBR X 3B) decolorization and degradation in a white rot fungal biofilm reactor were introduced and discussed. The fungal biofilm reactor is highly potential for dye decolorization and degradation with the highest decoloring rate of 95% within 96 hours reaction time at initial pH 4.5 under high nitrogen level (HN) (24 mmol/L ammonium tartrate) condition. Experimental conditions, such as nutrient nitrogen levels in reaction mixture and initial pH, significantly affected dye decolorization and degradation. Effluents from this biofilm reactor can be well treated to meet the discharging requirements by use of chemical flocculation.RBR X 3B was first absorbed onto fungal biomass and then degraded gradually. The SH 13 fungus monopolized the biofilm throughout the experiments, though the reactor was exposed to open air for 4 months.

Factors Affecting the Reductive Properties of the Core-Shell SiO2-Coated Iron Nanoparticles

In this study, novel core-shell SiO2-coated iron nanoparticles (SiO2-nZVI) were synthesized using a one-step Stoeber method. The Malachite green degradation abilities of the nanoparticles were investigated. The effects of ethanol/distilled water volume ratio, presence and absence of PEG, tetraethyl orthosilicate (TEOS) dosage, and hydrolysis time used in the nanoparticles preparation process were investigated. The results indicated that the SiO2-coated iron nanoparticles had the highest reduction activity when the particles synthesized with ethanol/H2O ratio of 2:1, PEG of 0.15 ml, TEOS of 0.5 ml and the reaction time was 4 h. The SiO2-nZVI nanoparticles were characterized using Transmission Electron Microscopy (TEM), Energy Dispersive Spectrometry (EDS) and powder X-Ray Diffraction (XRD). The results showed that the average particles diameter of the SiO2-nZVI was 20 - 30 nm. The thickness of the outside SiO2 film is consistent and approximately 10 nm. The results indicated that the nanoparticles coated completely with a transparent SiO2-film. Such nanoparticles could have wide applications in dye decolorization.

Screening of Methyl Red Degrading Bacteria Isolated from Textile Effluents of Savar Area, Dhaka, Bangladesh

Physicochemical properties and metal contents of five dye-based textile effluents collected in summer and winter season, 2016 from Savar, Dhaka, Bangladesh were within the recommended acceptable limit. The average value of all physicochemical parameters was found high in summer season except turbidity. A total of 94 heavy metal resistant bacteria (46 gram positive & 48 gram negative) were isolated from textile effluent samples and among them 17 isolates were multi metal resistant. Highest tolerance level of the isolates was shown at 10 mM concentration against Pb. All the heavy metal resistant bacterial isolates were presumably grouped into 14 genera according to morphological and biochemical assay. Three isolates designated WFB3c (65.41%), WFB4g (62%) and SFB5c (60.07%) were found to potentially degrade dye as well as tolerate heavy metals. Three potential dye decolorizer isolates were screened out and most potential one (WFB3c) was identified as Proteus mirabilis according to the 16S rRNA identification. The isolated bacterial strain Proteus mirabilis would be a potential candidate for microbes based treatment to decolorize dye from textile effluents.