Catalytical efficiency, mechanism and characterization of hydrolysed waste eggshell in the subcritical water oxidation of pistachio processing wastewater

Treatment of pistachio processing industry wastewaters by supercritical water oxidation in a continuous-flow reactor

The objective of the present study is the treatment of pistachio processing industry wastewaters (PPIW) using the supercritical water oxidation method. The experiments were conducted within a 400-600°C temperature range and a 30-150 s reaction time range, while maintaining a constant pressure of 25 MPa and using an O2/COD ratio of 1:1. To observe the effects of the initial PPIW and O2 concentrations on the treatment efficiency, experiments were also conducted with O2/COD ratios ranging from 0.5 to 3, while maintaining a constant reaction temperature and time of 500°C and 60 s, respectively. The influence of reaction temperature, reaction time and O2/COD ratio on the total organic carbon (TOC) and total nitrogen (TN) contents of the liquid PPIW effluents were investigated. Treatment efficiencies up to 99.75% regarding TOC conversion and 78.72% regarding TN conversion were obtained in very short reaction times. Additionally, the kinetics of oxidation of PPIW was studied, and reaction rate expressions based on TOC and TN were proposed.

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.

A comparison of the performance of conventional and eco-friendly extraction methods in the evaluation of total phenolics, antioxidant activity, and chemical composition of anise

In this work, the essential oil of Pimpinella anisum seeds was obtained by six different extraction methods. In the chemical composition analysis, 4, 6, 4, 1, 20, and 8 compounds were detected in the extracts obtained by Soxhlet, Ultrasonic-assisted (UAE), hydrodistillation using Clevenger apparatus (HDC), subcritical water extraction (SWE), supercritical carbon dioxide extraction (ScCO2) using three solvents (methanol (ScCO2-Met), ethanol (ScCO2-Et), and hexane (ScCO2-H)) and supercritical 1,1,1,2-tetrafluoroethane (ScR134a) methods, respectively. Also, the performances of the applied methods were compared by analysing the total phenolic content (TPC) and antioxidant activity of the extracts. Anethole was the main component of all extracts obtained by SWE (94.5%) and Soxhlet (94.5%) methods, respectively. Also, TPC values were the highest (508.5 mg GAE/100 g kb) in ScR134a extract and the lowest (27.77 mg GAE/100 g kb) in HDC extracts. The antioxidant capacity was found to be the highest in ScCO2-H (IC50 = 1.58 mg/mL) and the lowest in Soxhlet extracts (IC50 = 0.07 mg/mL). The results showed the great effectiveness of eco-friendly extraction SWE, ScCO2-Et, and ScR134a methods.

The advanced treatment of textile printing and dyeing wastewater by hydrodynamic cavitation and ozone: Degradation, mechanism, and transformation of dissolved organic matter

The emission standards for textile printing and dyeing wastewater are stricter due to serious environmental issues. A novel technology, hydrodynamic cavitation combined with ozone (HC + O₃), has attracted wide attention in wastewater advanced treatment, whereas the contaminants removal mechanism and transformation of dissolved organic matter (DOM) were rarely reported. This study investigated the removal efficiency and mechanism of HC + O₃. The maximum removal rates of UV₂₅₄, chrominance, COD_Cr, and TOC were 64.99%, 91.90%, 32.30%, and 36.67% in 60 min, respectively, at the inlet pressure of 0.15 MPa and O₃ dosage of 6.25 mmol/L. The synergetic coefficient of HC + O₃ was 2.77. The removal of contaminants was the synergy of ¹O₂, ·OH and ·O₂^-, and high molecular weight and strong aromaticity organic matters were degraded effectively. The main components in DOM were tryptophan-like and tyrosine-like, which were effectively removed after HC + O₃. Meanwhile, most DOM had decreased to low apparent relative molecular weight (LARMW) compounds. Additionally, the HC + O₃ effluent can reach the emission standard in 60 min for 8.07 USD/m³. It can be concluded that HC + O₃ is an effective technology for the advanced treatment of industrial wastewater. This study will provide suggestions for the engineering application of HC + O₃.