Response Surface Methodology (RSM)-Based Prediction and Optimization of the Fenton Process in Landfill Leachate Decolorization

Treatment of textile wastewater using the Co(II)/NaHCO3/H2O2 oxidation system

Textile wastewater (TWW) is one of the most hazardous wastewaters for ecosystems when it is discharged directly into water streams without adequate treatment. Some organic pollutants, such as dyes in TWW, are considered refractory compounds that are difficult to degrade using conventional chemical and biological methods. The bicarbonate-activated peroxide (BAP) system is an advanced oxidation process (AOP) based on applying H2O2, which has been demonstrated to be a clean and efficient technology for dye degradation, with the advantage of operating under slightly alkaline pH conditions. In this study, response surface methodology (RSM) based on a central composite design (CCD) was used to optimize the degradation of TWW contaminated with the azo dye Acid Black 194 using the BAP system catalyzed with cobalt ions in solution (Co2+). The analysis of variance (ANOVA) technique was applied to identify significant variables and their individual and interactive effects on the degradation of TWW. The optimum reagent concentrations for degrading TWW at 25 °C and with 45 μM Co2+ were 787.61 and 183.34 mM for H2O2 and NaHCO3, respectively. Under these conditions, complete decolorization (≥99.40), 32.20 % mineralization, and 52.02 % chemical oxygen demand removal were achieved. Additionally, the acute toxicity of textile wastewater before and after oxidation was evaluated with guppy fish (Poecilia reticulata), showing a total reduction in mortality after treatment with the Co2+-BAP system. The Co2+-BAP oxidation system is a potential method for textile wastewater treatment, which, in addition to achieving complete decolorization and partial mineralization, improves biodegradability and reduces the toxicity of the treated water.

Improving organic matter and nutrients removal and minimizing sludge production in landfill leachate pre-treatment by Fenton process through a comprehensive response surface methodology approach

Landfill leachate (LL) represents a very complex effluent difficult to treat and to manage which usually requires a chemical pre-treatment. In this study, response surface methodology (RSM) was used to identify the optimum operating conditions of the Fenton process as a pre-treatment of LL in order to reduce the high organic content and simultaneously optimize the BOD₅:TN:TP ratio. The dosages of Fenton process reagents, namely Fe²⁺ and H₂O₂, were used as variables for the implementation of RSM. Chemical oxygen demand (COD), five-days biochemical oxygen demand (BOD₅), total nitrogen (TN), total phosphorus (TP) removals (and simultaneously BOD₅:TN:TP ratio), sludge-to-iron ratio (SIR) and organic removal-to-sludge ratio (ORSR) were selected as target responses. This approach considered the SIR and ORSR parameters which are a useful tool for assessing sludge formation during the process along with organic matter removal. The variables (H₂O₂ and Fe²⁺ concentrations) significantly affected the responses, as the role of oxidation mechanism is dominant with respect to coagulation one. The pH for the process was fixed to 2.8 while the treatment time was set to 2 h. The optimum operational conditions obtained by perturbation and 3D surface plot, were found to be 4262 mg/L and 5104 mg/L for Fe²⁺ and H₂O₂, respectively (H₂O₂/Fe²⁺ molar ratio = 2) with COD, BOD₅, TN and TP removals of 70%, 67%, 84% and 96% respectively, while SIR and ORSR final values were 1.15 L/mol and 33.79 g/L respectively, in accordance with models-predicted values. Moreover, the initial unbalanced BOD₅:TN:TP ratio (9:1:1) was significantly improved (100:6:1), making the effluent suitable for a subsequent biological treatment. The investigated approach allowed to optimize the removal of organic load and nutrients as well as to minimize the sludge formation in Fenton process, providing a useful tool for the operation and management of LL pre-treatment.

Spatial green growth in China: exploring the positive role of investment in the treatment of industrial pollution

The industrial sector of China is critical to the country's economic growth. On the other side, industrialisation has resulted in a high rate of emissions, pushing China to spend extensively on industrial pollution remediation. As a result, this study looks at the relationship between investment completed in the treatment of industrial pollution and economic development. Initially, the study used the global Moran's I test (Queen's contiguity matrix) to find spatial autocorrelation for the 'investment completed in the treatment of industrial pollution' factor, where the study found a positive association across Chinese provinces, and suggest the existence of spatial autocorrelation. Thereafter, a time-fixed effect spatial error model was used due to the lowest Akaike information criterion and Bayesian information criterion to analyse regional data of China from 1999 to 2018. The data reveal a positive association between investment completed in the treatment of industrial pollution and regional economic growth, both in the short and long term. Furthermore, the negative consequences of urban wages and foreign investment on investment completed in the treatment of industrial pollution are having the reverse effect on regional green development, necessitating ecologically friendly actions to mitigate the negative environmental effects of both. The results highlight the need for policymakers in other countries to review their plans for economic expansion and create environmentally friendly legislation. By implementing the Chinese green economic growth model, policymakers in industrially polluting nations can reduce industrial pollution and foster green growth in their nation.

Degradation of Diazepam with Gamma Radiation, High Frequency Ultrasound and UV Radiation Intensified with H2O2 and Fenton Reagent

A degradation study of diazepam (DZP) in aqueous media by gamma radiation, high frequency ultrasound, and UV radiation (artificial-solar), as well with each process intensified with oxidizing agents (H2O2 and Fenton reagent) was performed. The parameters that influence the degradation of diazepam such as potency and frequency, irradiation dose, pH and concentration of the oxidizing agents used were studied. Gamma radiation was performed in a 60Co source irradiator; an 11 W lamp was used for artificial UV radiation, and sonification was performed at frequency values of 580 and 862 kHz with varying power values. In the radiolysis a 100% degradation was obtained at 2500 Gy. For the sonolysis, 28.3% degradation was achieved after 180 min at 862 kHz frequency and 30 W power. In artificial photolysis, a 38.2% degradation was obtained after 300 min of UV exposure. The intensification of each process with H2O2 increased the degradation of the drug. However, the best results were obtained by combining the processes with the Fenton reagent for optimum H2O2 and Fe2+ concentrations, respectively, of 2.95 mmol L−1 and of 0.06 mmol L−1, achieving a 100% degradation in a shorter treatment time, with a dose value of 750 Gy in the case of gamma radiation thanks to increasing in the amount of free radicals in water. The optimized processes were evaluated in a real wastewater, with a total degradation at 10 min of reaction.

Application of Response Surface Methodology for Optimization of Nanosized Zinc Oxide Synthesis Conditions by Electrospinning Technique

Zinc oxide (ZnO) is a well-known semiconductor material due to its excellent electrical, mechanical, and unique optical properties. ZnO nanoparticles are widely used for the industrial-scale manufacture of microelectronic and optoelectronic devices, including metal oxide semiconductor (MOS) gas sensors, light-emitting diodes, transistors, capacitors, and solar cells. This study proposes optimization of synthesis parameters of nanosized ZnO by the electrospinning technique. A Box–Behnken design (BB) has been applied using response surface methodology (RSM) to optimize the selected electrospinning and sintering conditions. The effects of the applied voltage, tip-to-collector distance, and annealing temperature on the size of ZnO particles were successfully investigated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirm the formation of polyvinylpyrrolidone-zinc acetate (PVP-ZnAc) fibers and nanostructured ZnO after annealing. X-ray diffraction (XRD) patterns indicate a pure phase of the hexagonal structure of ZnO with high crystallinity. Minimal-sized ZnO nanoparticles were synthesized at a constant applied potential of 16 kV, with a distance between collector and nozzle of 12 cm, flow rate of 1 mL/h, and calcination temperature of 600 °C. The results suggest that nanosized ZnO with precise control of size and morphology can be fabricated by varying electrospinning conditions, precursor solution concentration, and sintering temperature.