A novel polysaccharides-based bioflocculant produced by Bacillus subtilis ZHX3 and its application in the treatment of multiple pollutants.

A high bioflocculant-producing bacterial strain was identified and named Bacillus subtilis ZHX3. Single-factor experiments suggested that 10 g/L starch and 5 g/L yeast extract were optimal for strain ZHX3 to produce bioflocculant MBF-ZHX3. The maximum flocculating rate reached 95.5%, and 3.14 g/L product was extracted after 3 days of cultivation. MBF-ZHX3 was mainly composed of polysaccharides (77.2%) and protein (14.8%). The polysaccharides contained 28.9% uronic acid and 3.7% amino sugar. Rhamnose, arabinose, galactose, glucose, mannose, and galacturonic acid in a molar ratio of 0.35:1.83:3.09:12.66:0.46:3.81 were detected. MBF-ZHX3 had a molecular weight of 10,028 Da and contained abundant groups (-OH, CO, >PO, C-O-C) contributing to flocculation. Adsorption and bridging was considered as the main flocculation mechanism. MBF-ZHX3 was more effective in decolorizing dyes, removing heavy metals and flotation reagents compared to polyacrylamide. The results implied that MBF-ZHX3 has the potential to substitute polyacrylamide in wastewater treatment because of its excellent biological and environmental benefits.

Biodegradation of phenol and dyes with horseradish peroxidase covalently immobilized on functionalized RGO-SiO2 nanocomposite.

Horseradish peroxidase (HRP) was immobilized onto a functionalized reduced graphene oxide-SiO2 through the covalent bonding process. By using scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR), the formed nanocomposites were characterized. The kinetic parameters including the catalytic constant, kcat, and the catalytic efficiency, kcat/Km, increased 5.5 and 6 times, respectively, after immobilization. The circular dichroism analysis demonstrated that the α-helical content increased from 39% to 46% after immobilization. The immobilization improved the reusability of HRP as 70% of initial activity retained after 10 cycles. Due to the buffering effect, the immobilized HRP was less sensitive to pH changes as compared to the free HRP. At temperature 40 °C and during 90 min, the immobilized HRP retained 90% of the initial activity while 70% of initial activity remained for the free HRP. After 35-day storage, no reduction in the activity was observed for the immobilized HRP. The removal efficiency for phenol concentration (2500 mg/L) obtained 100% and 50% for the immobilized and free HRP, respectively. The results showed that the immobilized HRP promoted the dyes decolorization from 2-fold until 26-fold as compared to the free HRP. The decolorization efficiencies reached 100% for most dyes in the case of immobilized HRP.

Decolorization and detoxification of textile dyes using a versatile Streptomyces laccase-natural mediator system.

Currently, there is increasing interest in assessing the potential of bacterial laccases for industrial and environmental applications especially in harsh conditions. The environmental impact of the textile industry requires novel and effective technologies to mitigate the presence of dyes in wastewaters before discharging into the environment. Dyes usually remain stable in the presence of a variety of chemicals, light and are recalcitrant to microbial degradation. Among available technologies the biological treatments offer environmentally friendly strategies for decolorizing and detoxifying these compounds. The recent discovery of versatile laccases in streptomycetes opens up new opportunities for their commercial application. The aim of this study is to assess the potential of a novel bacterial laccase SilA produced by Streptomyces ipomoeae CECT 3341 active over wide temperature and pH ranges for use as an eco-friendly, biological treatment for the degradation of textile dyes. Insights into the enhancement of the oxidative action of this enzyme through the use of natural redox mediators are presented together with an assessment of the potential toxicity of the degradation products. Our results confirm that the combination of the laccase and natural mediators such as acetosyringone and methyl syringate enhanced the decolorization and detoxification of a variety of textile dyes up to sixfold and 20-fold, respectively. Mediator concentration was found to have a significant effect (p < 0.05) on dye decolorization at 60 °C; thus, the decolorization of Acid Orange 63 increased from 6 to 70-fold when the mediator concentration was increased from 0.1 to 0.5 mM. Further, the toxicity of tartrazine decreased 36-fold when the SilA-MeS system was used to decolorize the dye. The thermal properties of the SilA coupled with the stability of SilA at high pH suggest a potential commercial application for use in the decolorization of textile wastewaters which generally are performed at high temperature (>55 °C) and salinity and neutral pH, conditions which are unfavourable for conventional fungal laccases.

Enhanced catalytic efficiency of CotA-laccase by DNA shuffling.

Bacterial CotA-laccases exhibit higher activity in alkaline pH and salt concentration conditions compared to laccases from white-rot fungi. They are considered as green catalysts in decolorizing of industrial dyes. However, CotA-laccases are limited due to the low yield and catalytic efficiency as the spore-bound nature of CotA. A DNA shuffling strategy was applied to generate a random mutation library. To improve laccase activities, a mutant (T232P/Q367R 5E29) with two amino acid substitutions was identified. The catalytic efficiency of mutant 5E29 was 1.21 fold higher compared with that of the wild-type. The Km and kcat values of 5E29 for SGZ were of 20.3 ± 1.3 µM and 7.6 ± 2.7 s-1. The thermal stability was a slight enhancement. Indigo Carmine and Congo red were efficiently decolorized by using this mutant at pH 9.0. These results provide that 5E29 CotA-laccase is a good candidate for biotechnology applications under alkaline condition, with an effective decolorization capability.

Laccase Immobilized onto Zirconia⁻Silica Hybrid Doped with Cu2+ as an Effective Biocatalytic System for Decolorization of Dyes.

Nowadays, novel and advanced methods are being sought to efficiently remove dyes from wastewaters. These compounds, which mainly originate from the textile industry, may adversely affect the aquatic environment as well as living organisms. Thus, in presented study, the synthesized ZrO2-SiO2 and Cu2+-doped ZrO2-SiO2 oxide materials were used for the first time as supports for laccase immobilization, which was carried out for 1 h, at pH 5 and 25 °C. The materials were thoroughly characterized before and after laccase immobilization with respect to electrokinetic stability, parameters of the porous structure, morphology and type of surface functional groups. Additionally, the immobilization yields were defined, which reached 86% and 94% for ZrO2-SiO2-laccase and ZrO2-SiO2/Cu2+-laccase, respectively. Furthermore, the obtained biocatalytic systems were used for enzymatic decolorization of the Remazol Brilliant Blue R (RBBR) dye from model aqueous solutions, under various reaction conditions (time, temperature, pH). The best conditions of the decolorization process (24 h, 30 °C and pH = 4) allowed to achieve the highest decolorization efficiencies of 98% and 90% for ZrO2-SiO2-laccase and ZrO2-SiO2/Cu2+-laccase, respectively. Finally, it was established that the mortality of Artemia salina in solutions after enzymatic decolorization was lower by approx. 20% and 30% for ZrO2-SiO2-laccase and ZrO2-SiO2/Cu2+-laccase, respectively, as compared to the solution before enzymatic treatment, which indicated lower toxicity of the solution. Thus, it should be clearly stated that doping of the oxide support with copper ions positively affects enzyme stability, activity and, in consequence, the removal efficiency of the RBBR dye.

Microbial fuel cells coupling with the three-dimensional electro-Fenton technique enhances the degradation of methyl orange in the wastewater.

The emission of the source effluent of azo dyes has resulted in a serial of environmental problems including of the direct damage of the natural esthetics, the inhibition of the oxygen exchange, the shortage of the photosynthesis, and the reduction of the aquatic flora and fauna. A bioelectrochemical platform (3D-EF-MFCs) combining two-chamber microbial fuel cells and three dimensional electro-Fenton technique were delicately designed and assembled to explore the decolorization, bio-genericity performance of the methyl orange, and the possible biotic-abiotic degradation mechanisms. The 3D-EF-MFCs processes showed higher decolorization efficiencies, COD removals, and better bioelectricity performance than the pure electro-Fenton-microbial fuel cell (EF-MFC) systems. The two-chamber experiments filling with the granular activated carbons were better than the single-chamber packing system on the whole. The moderate increase of Fe2+ ions dosing in the cathode chamber accelerated the formation of •OH, which further enhanced the degradation of the methyl orange (MO). The cathode-decolorization and COD removals were decreased with the increase of MO concentration. However, the degradation performance of MO was indirectly improved in the anode compartment at the same conditions. The bed electrodes played a mediator role in the anode and cathode chambers, certainly elevated the voltage output and the power density, and lowered the internal impedance of EF-MFC process.

Effectiveness of Dyes Removal by Mixed Fungal Cultures and Toxicity of Their Metabolites.

Decolorization of brilliant green (0.06 g/L), Evans blue (0.15 g/L), and their mixture (total concentration 0.08 g/L, proportion 1:1 w/w) by fungi was studied. Fungal strains [Pleurotus ostreatus (BWPH), Gloeophyllum odoratum (DCa), and Fusarium oxysporum (G1)] were used separately and as a mixture of them. Zootoxicity (Daphnia magna) and phytotoxicity (Lemna minor) changes were estimated after the end of experiment. Mixtures of fungal strains were less effective in decolorization process than the same strains used separately (as a single strains). After 96 h of experiment, living biomass of strain BWPH removed up to 95.5 %; DCa, up to 84.6 %; G1, up to 79.2 % where mixtures BWPH + DCa removed up to 74.3 %; and BWPH + G1, only up to 32.2 % of used dyes. High effectiveness of dyes removal not always corresponded with decrease of toxicity. The highest decrease of zootoxicity and phytotoxicity (from V to III toxicity class or to even nontoxic) was noticed for single strains, while no changes or slight toxicity decrease was noticed in samples with strains mixtures.