Subcritical water oxidation of 6-aminopenicillanic acid and cloxacillin using H2O2, K2S2O8, and O2

Environmental remediation of emerging contaminants using subcritical water: A review

The continuous rise of emerging contaminants (ECs) in the environment has been a growing concern due to their potentially harmful effects on humans, animals, plants, and aquatic life, even at low concentrations. ECs include human and veterinary pharmaceuticals, hormones, personal care products, pesticides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organic dyes, heavy metals (HMs), and others. The world's growing population contributes to the release of many kinds of chemicals into the environment, which is estimated to be more than 200 billion metric tons annually and results in over 9 million deaths. The removal of these contaminants using conventional physical, chemical, and biological treatments has proven to be ineffective, highlighting the need for simple, effective, inexpesive, practical, and eco-friendly alternatives. Thus, this article discusses the utilization of subcritical water oxidation (SBWO) and subcritical water extraction (SBWE) techniques to remove ECS from the environment. Subcritical water (water below the critical temperature of 374.15 °C and critical pressure of 22.1 Mpa) has emerged as one of the most promising methods for remediation of ECs from the environment due to its non-toxic properties, simplicity and efficiency of application. Furthermore, the impact of temperature, pressure, treatment time, and utilization of chelating agents, organic modifiers, and oxidizing agents in the static and dynamic modes was investigated to establish the best conditions for high ECs removal efficiencies.

Decolouration of azo dyes by radicals generated from K2S2O8 automatically in homogeneous aqueous solutions

In this work, at 15 °C and 25 °C, authors study the decolouration reactions (or degradation reactions or oxidation reactions) of 0.10 mM azo dyes (methyl orange and congo red) by (1) K2S2O8 and (2) Co2+/K2S2O8, expounding the roles of K2S2O8 and Co2+: K2S2O8 can oxidize azo dyes automatically in water by radicals; Co2+ has catalysis for oxidation of K2S2O8, whether Co2+ is from CoSO4 or Co(NO3)2, CoCl2, CoAc2. The decolouration degree of azo dyes in all systems quickens with the increase of the initial concentration of K2S2O8 and the reaction temperature. In the presence and absence of Co2+, comparative experiments are done between the oxidation of K2S2O8 and oxone, K2S2O8 shows weaker oxidation than oxone. The decolouration reaction of methyl orange (MO) in the system of (0.10 mM MO + 2.00 mM K2S2O8) accords with the second order reaction, the reaction rate constants are 4.789 M-1 min-1 at 15 °C and 5.894 M-1 min-1 at 25 °C respectively, the activation energy Ea is 14813 J/mol, and Arrhenius equation is k = 2.328 exp[-14813/(RT)].

A Review: Subcritical Water Extraction of Organic Pollutants from Environmental Matrices

Most organic pollutants are serious environmental concerns globally due to their resistance to biological, chemical, and photolytic degradation. The vast array of uses of organic compounds in daily life causes a massive annual release of these substances into the air, water, and soil. Typical examples of these substances include pesticides, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). Since they are persistent and hazardous in the environment, as well as bio-accumulative, sensitive and efficient extraction and detection techniques are required to estimate the level of pollution and assess the ecological consequences. A wide variety of extraction methods, including pressurized liquid extraction, microwave-assisted extraction, supercritical fluid extraction, and subcritical water extraction, have been recently used for the extraction of organic pollutants from the environment. However, subcritical water has proven to be the most effective approach for the extraction of a wide range of organic pollutants from the environment. In this review article, we provide a brief overview of the subcritical water extraction technique and its application to the extraction of PAHs, PCBs, pesticides, pharmaceuticals, and others form environmental matrices. Furthermore, we briefly discuss the influence of key extraction parameters, such as extraction time, pressure, and temperature, on extraction efficiency and recovery.

Aqueous degradation of 6-APA by hydroxyl radical: a theoretical study

CONTEXT

Degradation reactions of micropollutants such as antibiotics with OH radicals are very important in terms of environmental pollution. Therefore, in this study, the degradation kinetic mechanism of 6-aminopenicillanic acid (6-APA) with OH radical was investigated by density functional theory (DFT) methods.

METHODS

For the calculations, different functionals such as B3LYP, MPW1PW91, and M06-2X were used with a 6-31 g(d,p) basis set. The aquatic effect on the reaction mechanism was investigated by conductor-like polarizable continuum model (CPCM). For the degradation kinetics in aqueous media, the addition of explicit water molecules was also calculated. Subsequent reaction mechanism for the most probable reaction product was briefly discussed.

RESULTS

Among the functionals used, B3LYP results were consistent with the experimental results. Calculated kinetic parameters indicated that the OH-addition path was more dominant than the H-abstraction paths. With the increase of explicit water molecules in the models, the energy required for the formation of transition state complexes decreased. The overall rate constant is calculated as 2.28 × 10¹¹ M^-1 s^-1 at 298 K for the titled reaction.

Resource degradation of pharmacy sludge in sub-supercritical system with high degradation rate of 99% and formic acid yield of 32.44

In response to the social goal of 'carbon peak and carbon neutral' in the 14th Five-Year Plan of China, this article used Enrofloxacin (ENR), a common antibiotic, as a model compound to study the method of efficiently degrading pharmaceutical sludge and simultaneously producing Formic Acid (FA), hydrogen storage energy, in a sub-supercritical system. The Ni/SnO2 bimetallic catalyst, which was prepared by the equal volume impregnation method, was used for the liquid phase catalysis. As shown by the results, when the reaction temperature was 330°C, and the addition amount of H2O2 was 0.38 mL, the degradation rate of antibiotics could reach 99% after the reaction proceeded for 6 h. In terms of the resource utilization, the yield of FA could reach up to 32.44%. The resource utilization efficiency with Ni/SnO2 catalyst in sub-/supercritical reaction was about 2.5 times higher than that without catalyst. The kinetic reaction model was established to explore the reaction rate of the antibiotic degradation process. In addition, the Ea and the frequency factor of the reaction were 6455 J/mol and 5.78, respectively. As shown by characterization, the prepared Ni/SnO2 bimetallic catalyst had good activity and has already passed repeated stability experiments. In short, this method has broad application prospects in antibiotic catalysis and resource degradation.

Water recovery from pistachio processing plant wastewater using subcritical water oxidation method

This study aims to apply an efficient and environmentally friendly subcritical water oxidation (SWO) method for the treatment of pistachio processing plant wastewater (PPPW). The effects of temperature (336.2-399.8 K), the concentration of H₂O₂ (0.08-0.92 M) and treatment time (6.4-73.6 min) on the oxidation of PPPW were investigated using the SWO method and experimental parameters were optimized using the response surface method. While the highest chemical oxygen demand (COD) removal was obtained as 53.8% in 73.6 min at 373 K using 0.5 M of H₂O₂, the highest obtained total phenol (TP) and color removals were 92.80%, and 99.6%, respectively, in 20 min at 373 K using 0.75 M of H₂O₂. R² values of COD, TP and color removal models were 0.9694, 0.9868 and 0.9649, respectively, and F values of the models were 35.24, 82.86 and 30.54, in the same order. In the vast majority of the experimental samples, the concentrations of nitrate, total phosphate, total nitrogen and suspended solids were found to be decreased while the nitrite concentration was increased after the SWO process. The effectiveness of SWO in water recovery from PPPW was demonstrated by the high, COD, TP and color removal values obtained.

Degradation of ticarcillin by subcritical water oxidation method: Application of response surface methodology and artificial neural network modeling

This study was performed to investigate the mineralization of ticarcillin in the artificially prepared aqueous solution presenting ticarcillin contaminated waters, which constitute a serious problem for human health. 81.99% of total organic carbon removal, 79.65% of chemical oxygen demand removal, and 94.35% of ticarcillin removal were achieved by using eco-friendly, time-saving, powerful and easy-applying, subcritical water oxidation method in the presence of a safe-to-use oxidizing agent, hydrogen peroxide. Central composite design, which belongs to the response surface methodology, was applied to design the degradation experiments, to optimize the methods, to evaluate the effects of the system variables, namely, temperature, hydrogen peroxide concentration, and treatment time, on the responses. In addition, theoretical equations were proposed in each removal processes. ANOVA tests were utilized to evaluate the reliability of the performed models. F values of 245.79, 88.74, and 48.22 were found for total organic carbon removal, chemical oxygen demand removal, and ticarcillin removal, respectively. Moreover, artificial neural network modeling was applied to estimate the response in each case and its prediction and optimizing performance was statistically examined and compared to the performance of central composite design.

Subcritical water oxidation of propham by H2O2 using response surface methodology (RSM)

This study was conducted to investigate the degradation of propham, which is a compound that pollutes water and seriously threatens human health, by subcritical water oxidation and using H₂O₂ as an oxidising agent. The maximum total organic carbon removal rate of propham was obtained as 73.65% at 40 min of treatment time and 60 mM of H₂O₂ concentration and 373 K of temperature. In addition, response surface method based on the Box-Behnken design was applied to design the degradation experiments of propham for determination of the combined effects of process variables, namely temperature, concentration of oxidising agent and treatment time. The proposed quadratic model of propham degradation, which was examined with the analysis of variance, was used for navigating the design space. The R² and adjusted R² values of the model were determined as 0.9921 and 0.9819 respectively. It was shown that propham was effectively degraded, thus could be removed from the water by using an environmentally friendly method.