Water recovery from yarn fabric dyeing wastewater using electrochemical oxidation and membrane processes

High adsorptive performance of chitosan-microalgae-carbon-doped TiO2 (kronos)/ salicylaldehyde for brilliant green dye adsorption: Optimization and mechanistic approach

A composite of chitosan biopolymer with microalgae and commercial carbon-doped titanium dioxide (kronos) was modified by grafting an aromatic aldehyde (salicylaldehyde) in a hydrothermal process for the removal of brilliant green (BG) dye. The resulting Schiff's base Chitosan-Microalgae-TiO2 kronos/Salicylaldehyde (CsMaTk/S) material was characterised using various analytical methods (conclusive of physical properties using BET surface analysis method, elemental analysis, FTIR, SEM-EDX, XRD, XPS and point of zero charge). Box Behnken Design was utilised for the optimisation of the three input variables, i.e., adsorbent dose, pH of the media and contact time. The optimum conditions appointed by the optimisation process were further affirmed by the desirability test and employed in the equilibrium studies in batch mode and the results exhibited a better fit towards the pseudo-second-order kinetic model as well as Freundlich and Langmuir isotherm models, with a maximum adsorption capacity of 957.0 mg/g. Furthermore, the reusability study displayed the adsorptive performance of CsMaTk/S remains effective throughout five adsorption cycles. The possible interactions between the dye molecules and the surface of the adsorbent were derived based on the analyses performed and the electrostatic attractions, H-bonding, Yoshida-H bonding, π-π and n-π interactions are concluded to be the responsible forces in this adsorption process.

Fabric dyeing wastewater treatment and salt recovery using a pilot scale system consisted of graphite electrodes based on electrooxidation and nanofiltration

In this study, color removal, suspended solids removal, and salt recovery were investigated from different fabric dyeing wastewaters using a pilot scale treatment system. A pilot scale system was installed in the wastewater outlet area of five different textile companies. Experiments were planned for pollutant removal and salt recovery from wastewater. First, the wastewater was treated by electrooxidation (EO) using graphite electrodes. After a reaction time of 1 h, the wastewater was passed throughout the granular activated carbon (AC) coloumn. The pre-treated wastewater was passed through the membrane (NF) system to recover the salt in the wastewater. Finally, the recovered salt water was used for fabric dyeing. In the pilot scale treatment system (EO + AC + NF), 100% of suspended solids (SS) and an average of 99.37% of color were removed from fabric dyeing wastewaters. At the same time, a high amount of salt water was recovered and reused. Optimum conditions were determined as 4 V current, 1000 A power, wastewater's own pH values and 60 min of reaction time. The energy and operating cost for treatment of 1 m3 of wastewater were determined as 40.0 kWh/m3 and 2.2 US$/m3, respectively. In addition to the prevention of environmental pollution by the treatment of wastewater using the pilot-scale treatment system, the reuse of the recovered water will contribute to the protection of our valuable water resources. In addition, using the NF membrane process after the EO system, it will be possible to recover salt from wastewater with high salt content such as textile wastewater.

Eco-Friendly Detoxification of Congo Red Dye from Water by Citric Acid Activated Bioadsorbents Consisting of Watermelon and Water Chestnuts Peels Collected from Indigenous Resources

The native peels of two cheap, locally available adsorbents, watermelon (PWM) and water chestnuts (PWC), were chemically processed with different chemicals as modifying agents for the determination and assessment of their adsorption ability for the removal and clearance of harmful, venomous, and pernicious Congo red (CGR), as an acidic nature anionic dye, from the aqueous system. In successive batch experiments, the citric acid-treated peels CPWM and CPWC have shown more promising adsorption performance than their raw and untreated peel counterparts due to the availability of additional adsorption active binding sites evidenced through FT-IR and SEM characterizations. In the Langmuir and Temkin models, the correlation coefficients ( $R^2$ ) for the adsorptive removal of CGR on CPWM, PWM, CPWC, and PWC are very close to unity, 0.99 for each case of adsorption performance. Furthermore, the $q_{\max }$ nonlinear statistical results for the elimination of CGR on citric acid-treated adsorbents (CPWM and CPWC) are 8.3 and 7.95 mg/g whereas for their unmodified forms (PWM and PWC) are 2.23 and 4.32 mg/g, respectively, reflecting homogenous and monolayer adsorption mechanism. The greater values of $B_T$ 1.4 and 1.3 J/mole, for adsorptive removal of dye on CPWM and CPWC, respectively, as compared to their unmodified forms PWM and PWC which are 0.53 and 0.55 J/mole, respectively, indicate the stronger adsorbate-adsorbent associations. The mechanism follows the pseudo second order in the better mode, while thermodynamic statics for ΔH0,ΔG0, ΔS0, and ΔE0, indicate spontaneous and exothermic behavior of adsorption. This study tends to suggest that citric acid-modified adsorbents CPWM and CPWC may indeed be exploited efficiently to eliminate Congo red dye from wastewater.

A hybrid process for leachate wastewater treatment: Evaporation and reverse osmosis/sequencing batch reactor

In this study, a hybrid process for leachate wastewater treatment including evaporation and reverse osmosis (RO) membrane or biological treatment systems was suggested. Experiments were performed on a real landfill leachate wastewater. The leachate was subjected to evaporation; as a result, a distillate was obtained containing less organic matter and less substantial amounts of other pollutants, as ammonium salts and total phenols were removed. Tests were carried out at different evaporation temperatures and times. The initial leachate pH was adjusted and optimized. For optimum conditions, each of chemical oxygen demand (COD), total phenol, and ammonium salt concentrations were reduced to 99.99%, 95.00%, and 83.00%, respectively. The distillate of the first stage of the proposed process was then exposed to RO membrane system, as a first study, under different transmembrane pressure of 20, 30, and 40 bar and at different pH values of 7, 8, and 9. As a second suggested treatment system, the distillate was subjected to a biological treatment process for 30 days as a retention time, pH = 6, and room temperature 25°C ± 1°C. At the end of the research study, a comparison was conducted between results obtained with RO membrane separation and biological treatment system as two distinct treatment systems proposed for leachate landfill wastewater treatment. Although both systems were effective for landfill leachate wastewater treatment, however, with the RO membrane separation system, COD removal efficiency reached 99.99%. In the other hand, with biological treatment process, COD elimination was as much as 90.00%. Certainly, evaporation and RO are not novel ways of landfill leachate treatment; however, few studies have attempted to use similar combined system for landfill leachate wastewater treatment and attained effective results of treated water. PRACTITIONER POINTS: A hybrid process of evaporation and RO membrane or biological treatment systems was suggested for leachate wastewater treatment. For optimum conditions, COD, total phenols, and ammonium salt reductions were achieved to 99.99%, 95%, and 83%, respectively, after the first evaporation stage. The distillate of the first stage of the proposed process was then exposed to RO membrane system and biological treatment system. Different transmembrane pressure and different pH values were optimized for RO.