Mechanism of Dye Degradation during Electrochemical Treatment

Studies were conducted for understanding the electrochemical (EC) degradation mechanism of a triphenylmethane dye, namely, basic green 4 (BG), commonly known as malachite green with aluminum electrode. At the optimum conditions (current density = 117.64 A m^–2, initial dye concentration = 125 mg L^–1, pH = 6.5, electrode gap = 1 cm, and NaCl concentration = 1.5 g L^–1), more than 85% BG degradation was observed within 50 min of treatment. UV–visible and Fourier transform infrared (FTIR) spectroscopy, high performance liquid chromatography (HPLC), gas chromatography–mass spectroscopy (GCMS), and high-resolution mass spectroscopy (HRMS) analysis showed that the degradation occurred via the cleavage of conjugated structure and N-demethylation. The intermediate products identified included hydroxymethylated intermediates during the N-demethylation of the dye; and <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethyl-4,4′-diaminobenzophenone, 4,4′-bisaminobenzophenone and <i>N</i>-methyl-para-aminophenol after cleavage of the conjugated triphenylmethane ring. Zeta potential study indicated a hard acid–base interaction between aluminum ions and hydroxides generated in situ during the EC treatment process and the −N­(CH₃)₂ group of dye molecules. Generation of active species such as hydrogen peroxide, ozone, and chlorinated oxidizing compounds was observed during the EC treatment process and that the BG degradation occurred via a ^•OH radical attack

Electrochemical Treatment of Dye Bearing Effluent with Different Anode–Cathode Combinations: Mechanistic Study and Sludge Analysis

The present study investigates the electrochemical (EC) treatment of actual dye bearing effluent (DBE) with different combinations of aluminum (Al) and stainless steel (SS) electrodes as anode and cathode. Effects of the current density (<i>j</i>) and pH with different anode–cathode combinations (Al–Al, Al–SS, SS–SS, and SS–Al) were studied. The change in zeta (ζ) potential with current density at different times, and the change in colloid particle diameters at different pH, gave information regarding the potential stability of the colloidal suspension. In addition, specific energy consumption and current efficiency have also been calculated. Maximum color, COD, TOC, and turbidity removal efficiencies were found to be 99.90%, 82.50%, 68.8%, and 98.8%, respectively, at <i>j</i> = 117.64 A/m² and pH 8.5 with the SS–SS electrode combination. Solid residue obtained during EC treatment of DBE was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, and pore distribution analysis to propose reutilization of the sludge

Synthesis of bio-based materials from agricultural residues for treatment of petrochemical wastewater

4-Carboxybenzaldehyde (4-CBA), a major component of purified terephthalic acid wastewater, is toxic to living organisms and required to be removed before the discharge of treated wastewater in a natural water body. In this work, the adsorptive removal of 4-CBA was studied using bagasse fly ash (BFA), a waste product from the sugar industry. The adsorption capacity of BFA was compared with the commercially available adsorbent, granular activated carbon (GAC). A 4-factorial, 5-stage central composite design (CCD) was used to optimize 4-CBA removal and adsorption uptake by BFA using response surface methodology (RSM). The variables considered for the study were pH, adsorbent dose (m), initial concentration (Co) and time (t). At the optimum treatment conditions of pH = 4, m = 9 g/L, Co = 100 mg/L and t = 7.5 h, the removal efficiency and adsorption uptake of 4-CBA on BFA were found to be 79% and 9.9 mg/g, respectively. BET surface area of BFA was determined to be 284 m2/g. A kinetic study was performed using a first- and second pseudo-order model. The adsorption equilibrium data were fitted for various adsorption models. A positive value ΔH0 indicates that the adsorption process is endothermic. This study indicated that BFA is a cost-effective adsorbent for the removal of 4-CBA with high adsorption capacity and fast kinetics

Successful introgression of wMel Wolbachia into Aedes aegypti populations in Fiji, Vanuatu and Kiribati.

Pacific Island countries have experienced periodic dengue, chikungunya and Zika outbreaks for decades. The prevention and control of these mosquito-borne diseases rely heavily on control of Aedes aegypti mosquitoes, which in most settings are the primary vector. Introgression of the intracellular bacterium Wolbachia pipientis (wMel strain) into Ae. aegypti populations reduces their vector competence and consequently lowers dengue incidence in the human population. Here we describe successful area-wide deployments of wMel-infected Ae. aegypti in Suva, Lautoka, Nadi (Fiji), Port Vila (Vanuatu) and South Tarawa (Kiribati). With community support, weekly releases of wMel-infected Ae. aegypti mosquitoes for between 2 to 5 months resulted in wMel introgression in nearly all locations. Long term monitoring confirmed a high, self-sustaining prevalence of wMel infecting mosquitoes in almost all deployment areas. Measurement of public health outcomes were disrupted by the Covid19 pandemic but are expected to emerge in the coming years