Removal of reactive blue 21 and reactive red 195 dyes using horseradish peroxidase as catalyst

ABTS as an electron shuttle to accelerate the degradation of diclofenac with horseradish peroxidase-catalyzed hydrogen peroxide oxidation

Horseradish peroxidase (HRP)-catalyzed hydrogen peroxide (H₂O₂) oxidation could degrade a variety of organic pollutants, but the intrinsic drawback of slow degradation rate limited its widespread application. In this study, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) was introduced into HRP/H₂O₂ system as an electron shuttle to enhance diclofenac degradation under neutral pH conditions. The green-colored ABTS radical (ABTS^•+), generated by the oxidation of ABTS with HRP-catalyzed H₂O₂ oxidation, was proved to be the main reactive species for the rapid degradation of diclofenac in HRP/H₂O₂/ABTS system. There was no destruction of ABTS/ABTS^•+ in HRP/H₂O₂/ABTS system, and ABTS was verified as an ideal electron shuttle. The reaction conditions including solution pH (4.5-10.5), HRP concentration (0-8 units mL^-1) and H₂O₂ concentration (0-500 μM) would impact the formation of ABTS^•+, and affect the degradation of diclofenac in HRP/H₂O₂/ABTS system. Moreover, compared with Fenton and hydroxylamine/Fenton systems, HRP/H₂O₂/ABTS system had better diclofenac degradation efficiency, higher H₂O₂ utilization efficiency and stronger anti-interference capacity in actual waters. Overall, the present study provided a meaningful and promising way to enhance the degradation of organic pollutants in water with HRP-catalyzed H₂O₂ oxidation.

Using textile industrial sludge, sewage wastewater, and sewage sludge as inoculum to degrade recalcitrant textile dyes in a co-composting process: an assessment of biodegradation efficiency and compost phytotoxicity

Recalcitrant dyes found in textile wastewater represent a threat for sustainable textile production due to their resistance to conventional treatments. This study assessed an alternative co-composting system for the treatment of recalcitrant textile dyes where textile industrial sludge, sewage wastewater, or sewage sludge were used as microbial compost inocula. The biodegradation efficiency of bioreactor trials and compost quality of the co-composting system were assessed by visible spectrophotometry and by a phytotoxicity test. The co-composting system (dry weight (dw) basis) consisted of 200 g of restaurant organic residues + 200 g sewage sludge (or 100 mL sewage wastewater, or 200 g textile sludge) + 100 mL of a 10% dye solution (Reactive Red 195, or Synolon Brown, or Orange Remazol, or Yellow Synozol, or Reactive Orange 122, or Reactive Black 5). After 60 days of composting, all dyes were biodegraded according to spectrophotometric data, with efficiency varying from 97.2 to 99.9%. Inoculum efficiency ranking was textile sludge > sewage sludge > sewage wastewater. Regarding compost quality, a phytotoxicity study with lettuce showed no toxicity effect. Thus, co-composting can be a low-cost and efficient method for recalcitrant textile dye biodegradation and for managing textile sludge in terms of waste recycling, contributing to environmental sustainability.

Biodegradation of azo dye-containing wastewater by activated sludge: a critical review

The effluent from the textile industry is a complex mixture of recalcitrant molecules that can harm the environment and human health. Biological treatments are usually applied for this wastewater, particularly activated sludge, due to its high efficiency, and low implementation and operation costs. However, the activated sludge microbiome is rarely well-known. In general, activated sludges are composed of Acidobacteria, Bacillus, Clostridium, Pseudomonas, Proteobacteria, and Streptococcus, in which Bacillus and Pseudomonas are highlighted for bacterial dye degradation. Consequently, the process is not carried out under optimum conditions (treatment yield). Therefore, this review aims to contextualize the potential environmental impacts of azo dye-containing wastewater from the textile industry, including toxicity, activated sludge microbiome identification, in particular using the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) as a novel, rapid and accurate strategy for the identification of activated sludge microbiome (potential to enhance treatment yield).

A novel approach to efficient degradation of indole using co-immobilized horseradish peroxidase-syringaldehyde as biocatalyst

Biocatalytic degradation technology has received a great deal of attention in water treatment because of its advantages of high efficiency, environmental friendliness, and no secondary pollution. Herein, for the first time, horseradish peroxidase and mediator syringaldehyde were co-immobilized into functionalized calcium alginate composite beads grafted with glycidyl methacrylate and dopamine. The resultant biocatalyst of the co-immobilized horseradish peroxidase-syringaldehyde system has displayed excellent catalytic performance to degrade indole in water. The degradation rate of 100% was achieved in the presence of hydrogen peroxide even if the indole concentration was changing from 25 mg/L to 500 mg/L. If only the free enzyme was used under the identical water treatment conditions, the degradation of indole could hardly be observed even when the concentration of indole is low at 25 mg/L. This was attributed to the effective co-immobilization of the enzyme and the mediator so that the catalytic activity of horseradish peroxidase and the synergistic catalytic action of syringaldehyde could be fully developed. Furthermore, while the spherical catalyst was operated in succession and reused for four cycles in 50 mg/L indole solution, the degradation rate remained 91.8% due to its considerable reusability. This research demonstrated and provided a novel biocatalytic approach to degrade indole in water by the co-immobilized horseradish peroxidase-syringaldehyde system as biocatalyst.

Designing an immunosensor for detection of Brucella abortus based on coloured silica nanoparticles

Brucellosis has always been a threat to the health and economics of societies. We report a new colorimetric immunoassay based on colored silica nanoparticles for detection of Brucella abortus. An immunosensor was designed based on blue-SiNPs and paramagnetic nanoparticles (PMNPs). The synthesized immunosensor was conjugated with a polyclonal antibody against B. abortus, which was activated by 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and N-hydroxysuccinimide (NHS) to form detection and capture probes, respectively. After adding the conjugates to the bacterial suspension, sandwich structure of PMNPs B. abortus-blue-SiNPs was formed and then separated by a magnet. The blue dye was released from the silica structure and its absorbance was measured at 670 nm with a spectrophotometer. Under optimal conditions, results showed a wide dynamic range from 1.5 × 10³ to 1.5 × 10⁸ cfu mL^-1 with a detection limit of 450 cfu mL^-1. The specificity of the sensor was confirmed in comparison with 5 other bacteria. Also, during the 120-days period, the complex was stable. The results suggested that it can be used in real samples (R² = .9865). This designed colorimetric immunoassay strategy can be used as an alternative, user-friendly and on-site tool for the rapid detection of Brucella spp. compared to other common methods with high sensitivity and specificity in a short time.

Electrochemical detection and quantification of Reactive Red 195 dyes on graphene modified glassy carbon electrode

Reactive Red 195 was detected from industrial waste samples electrochemically on graphene modified glassy carbon electrode (GCE), using both bare and surface changed GCE at different pH media from 1.0 to 13.0. The optimum pH was determined to be 4.0. RR 195 exhibited good linear responds at pH 4.0 on both electrode surfaces. Other parameters, such as accumulation potential, accumulation time, initial scan potential, pulse height, pulse width, and potential scan increment and scan rate are optimized and calibration plot was also derived on different concentrations of the dye. The stripping voltammetric behavior of dye exhibits very low limit of detection on graphene coated electrode (30 ppb). The adsorption of compound on GCE and graphene coated GCE are confirmed using atomic force microscopy studies.