Organic matter removal from mother liquor of gas field wastewater by electro-Fenton process with the addition of H2O2: effect of initial pH

Graphene/MoS2-assisted alum sludge electrode induces selective oxidation for organophosphorus pesticides degradation: Co-oxidation and detoxification mechanism

Designing an electrode that can generate abundant free radicals and 1O2, which can effectively degrade and detoxify organophosphorus pesticides (OPPs) through a co-oxidation pathway, is important. In this study, we prepared a electrode GO/MoS2@AS by supporting MoS2 on alum sludge (AS) under graphene oxide (GO) nanoconfinement. The results show that the dominant role of 1O2 at the cathode and •OHads at the anode for degradation, in addition to the involvement of 1O2 in the cathodic degradation mechanism, can be attributed to the abundant precursor •O2- and H2O2. Furthermore, calculations using density functional theory and toxicity prediction of products show that the energy (∆E) requirements of •OHfree to break the C-O bond of the pyridine ring and phosphate group are higher than that required for 1O2, and this non-radical oxidation plays a key role in detoxification. In contrast, accelerating ring opening and oxidation processes are attributed to radical oxidation. Above all, the cathodic detoxification is more effective than anodic detoxification. Three prevalent OPPs, chlorpyrifos, glyphosate, and trichlorfon, were degraded in the GO/MoS2@AS system by over 90 %, with mineralization rates of 76.66 %, 85.46 %, and 82.18 %, respectively. This study provides insights into the co-oxidation degradation and detoxification mechanism mediated by 1O2 and •OHfree.

The treatment of high concentration wastewater in the natural gas processing industry

The operation of the Cansolv tail gas treatment device in natural gas plants generates acidic and alkaline wastewater from the venturi unit and amine purification unit (APU), respectively. The APU wastewater is complex in composition and contains hard-to-degrade organic matter, which can adversely impact the normal functioning of the water treatment system. This study assesses the efficacy of three ozone-based advanced oxidation processes (ozone (O3), ozone/hydrogen peroxide (O3/H2O2), and ozone/Fenton (O3/Fenton)) for treating Cansolv wastewater, with chemical oxygen demand (COD) and total organic carbon (TOC) serving as indicators of organic degradation. The findings demonstrate that all three processes effectively eliminate coloration and reducible sulfur, with O3/Fenton exhibiting superior performance in removing organic substances. The treated wastewater has a clarified light-yellow appearance with residual COD levels at 43 mg L-1. Under the optimum Fenton oxidation conditions (initial pH 5, H2O2 dosage 97.8 mmol L-1, FeSO4·7H2O dosage 550 mg L-1), average TOC and COD removal rates reached 50% and 97%, respectively. After a treatment duration of 60 minutes, the wastewater demonstrated an enhanced membrane-specific flux, confirming the effectiveness of the O3/Fenton oxidation process in mitigating membrane fouling while ensuring the stable operation of the wastewater treatment system.

Insights into the efficient ozonation process focusing on 2,4-di-tert-butylphenol - A notable micropollutant of typical bamboo papermaking wastewater: Performance and mechanism

The present study applied the ozonation process to degrade 2,4-di-tert-butylphenol (2,4-DTBP), an emerging micropollutant detected in typical bamboo pulp and papermaking wastewater (BPPW). The effects of various influencing factors on the degradation performance and corresponding degradation mechanism were investigated. The results showed that ozone could degrade 2,4-DTBP rapidly with a reaction rate constant of (1.80 ± 0.05) × 10⁵ M^-1·s^-1. The removal efficiency of 2,4-DTBP (5 mg/L) could reach 100% when the ozone dosage exceed 6 mg/L in a neutral medium. The presence of coexisting chemicals in BPPW such as Cl^- and HCO₃^- promoted the removal performance of 2,4-DTBP. In contrast, NH₄⁺ and humic acid presented inhibition on 2,4-DTBP removal. The ozonation of 2,4-DTBP was dominated by the ozone molecule, and this was primarily attributed to electrophilic substitution and 1,3-dipolar cycloaddition reactions. Twenty-seven kinds of intermediate products were identified by UPLC-Q-TOF/MS. The variations in their productions were based on the changes in ozone dosage. The degradation pathways were proposed. The toxicity of 2,4-DTBP was weakened after ozonation. As for the ozonation of actual biochemical effluent of BPPW, the desirable treatment performance was obtained. This study proved the feasibility of ozonation and provided data basis for subsequent pilot study.

Al/TiO2 composite as a photocatalyst for the degradation of organic pollutants

TiO₂ is a catalyst that can effectively degrade organic pollutants with the following advantages, low cost, simplicity, and pollution-free nature. In recent years, the non-noble plasmonic metal Al has effectively improved the photocatalytic performance of TiO₂. However, the current reports are limited to the photocatalytic performance of Al/TiO₂ on the substrate, which requires expensive large-scale vacuum equipment. In this study, monodispersed Al particles were proposed to enhance the photocatalysis of TiO₂. The localized surface plasmon resonance (LSPR) effect of Al is proven by finite difference time domain method (FDTF) simulation. Then, Al/TiO₂ composites were prepared by combining monodispersed Al and TiO₂. The influence of ligand (glutathione (GSH), glutamic acid (GAG), or 3-mercaptopropane acid (MPA)), Al size (40 to 300 nm), and the ratio of Al to TiO₂ (0.5:1 to 10:1) on the photocatalytic degradation of methylene blue (MB) by Al/TiO₂ were discussed. The obtained results showed that the Al/TiO₂ composite which were prepared with 200 nm Al particles, GSH as the ligand bridge, and an Al:TiO₂ ratio of 1:1 had the best MB degradation effect. It can degrade 97.7% of 10 mg/L MB in 100 min. The reaction rate of the Al/TiO₂ composite with the optimal photocatalytic performance is k=3.36×10^-2 min^-1, which is 10 times that of P25 TiO₂. In addition, Al/TiO₂ has a good photocatalytic effect on rhodamine B (RhB) and crystal violet (CV). Therefore, Al/TiO₂ composites with the advantage of high efficiency are a type of potential photocatalytic material that can be used for the photocatalytic treatment of organic pollutants in water.

Feasibility of resource utilization of the refractory evaporation concentrate of gas field wastewater exhibiting high salinity: Application of UV/Fenton, desulfurization, distillation and crystallization process after pre-treatment

The evaporation concentrate of gas field wastewater (EC-GFW) is a new type of refractory actual wastewater produced by the three-effect evaporation of gas field wastewater, exhibiting extremely high salinity and complex organic components. This study proposed a set of processes consisting of AOPs, precipitation, distillation, and crystallization for the systematic treatment of EC-GFW. In this paper, the optimal conditions for the processes after pre-treatment were investigated. The optimal operating parameters of UV/Fenton process were determined to be 180 min of reaction time, 4 of initial pH, 0.6 mol/L of H₂O₂ dosage, 10:1 of n(H₂O₂): n(Fe²⁺) value, and 30 W of UV power. Fenton's reagent was added in two steps (0 min and 90 min) for effective utilization. The results showed that the TOC (Total organic carbon) removal efficiency during the two-stage oxidation reached 93% with TOC in the effluent of 132 mg/L. Then, 82.3% of sulfate ions were removed by the desulfurization process using 50 g/L of CaCl₂ within 10 min at a pH of 5 before distillation. It was found that the TOC in the influent of distillation played a decisive role in the quality of the effluent and purity of the crystalline salt, which was expected to be controlled lower than 132 mg/L. The final condensate could utilize to reuse, 99% of main pollutants of which have been removed, reducing the pressure of water supply on site. Simultaneously, the industrial-grade NaCl with extensive application prospect can be recovered. The harmless disposal and resource utilization of EC-GFW was achieved on a laboratory scale, providing the data support and theoretical guidance for treating EC-GFW at gas field project site.