Combination of hydrodynamic cavitation with oxidants for efficient treatment of synthetic and real textile wastewater

Combined hydrodynamic cavitation and advanced oxidation process for the degradation of hexamethyl pararosaniline chloride

Wastewater produced by the Textile industry contains dyes, aromatic, phenolic and various complex compounds which seriously harm the environment due to their high toxicity and carcinogenicity. The dyes found in wastewater are the ones frequently used to add colour to various industrial processes. The present study investigates the degradation of hexamethyl pararosaniline chloride (HPC) dye using hydrodynamic cavitation (HC) along with other oxidants. In an HC reactor, the effect of two different cavitating devices venturi and orifice and its combined effect with ZnO, H2O2, KPS, ZnO + H2O2 for the degradation of HPC have been investigated in detail. The effect of several operating parameters such as inlet pressure (3-7 bar), temperature (25-55 °C), initial concentration (50-300 mg/L) and initial pH (2-7) with respect to cavitation time has been analysed based on the removal of colour, TOC and TN. At the optimum initial dye concentration of 100 ppm, a pH of 5, a temperature of 35 °C and a pressure of 4 bar the maximum removal of TOC was found to be 46.4% and 28.4% for the venturi and orifice plate, respectively, for 120 min of treatment time. The study also focused on the combined oxidation approaches and compared that with the individual process. The extent of HPC mineralization rose from 46.4% for only HC to 67.3% and 43.6% for the combined HC + H2O2+ ZnO and H2O2 + ZnO, respectively. Overall, it can be concluded that hydrodynamic cavitation-based combined treatment methods are very effective for the degradation of hexamethyl pararosaniline chloride dye.

Degradation of azo dye (direct red 89) using H2O2/periodate process-parameter optimization and mixture composition evaluation

As a fast and efficient process, a periodate (PI)-based advanced oxidation process was used to degrade direct red 89 (DR89), wherein hydrogen peroxide (H2O2) was employed to activate PI (H2O2/PI process) to investigate the effect of operating parameters and mixture composition. The PI was efficiently activated by H2O2 to degrade 67% of DR89 within 1 min. Acidic pH was more favorable to high-efficiency degradation than the basic pH; at pH 3 degradation rate was 94.31%, while it was only 20.92% at pH 11. The degradation rates were further enhanced with increasing H2O2 and PI dose up to certain optimum values, later it decreased which was dependent upon the amount of hydroxyl (●OH) and iodyl (IO3●) radicals produced. The quenching experiments suggested that IO3●, ●OH, 1O2, and O2●- are the predominant reactive species during H2O2/PI process, while O2●- radicals are the primary precursor of other reactive oxygen species. The results of this study suggested that H2O2/PI is the efficient and rapid treatment method to degrade persistent organic pollutants (POPs) from polluted wastewater sources.

Investigation of singlet oxygen and superoxide radical produced from vortex-based hydrodynamic cavitation: Mechanism and its relation to cavitation intensity

Presently, the hydroxyl radical oxidation mechanism is widely acknowledged for the degradation of organic pollutants based on hydrodynamic cavitation technology. The presence and production mechanism of other potential reactive oxygen species (ROS) in the cavitation systems are still unclear. In this paper, singlet oxygen (1O2) and superoxide radical (·O2-) were selected as the target ROS, and their generation rules and mechanism in vortex-based hydrodynamic cavitation (VBHC) were analyzed. Computational fluid dynamics (CFD) were used to simulate and analyze the intensity characteristics of VBHC, and the relationship between the generation of ROS and cavitation intensity was thoroughly revealed. The results show that the operating conditions of the device have a significant and complicated influence on the generation of 1O2 and ·O2-. When the inlet pressure reaches to 4.5 bar, it is more favorable for the generation of 1O2 and ·O2- comparing with those lower pressure. However, higher temperature (45 °C) and aeration rate (15 (L/min)/L) do not always have positive effect on the 1O2 and ·O2- productions, and their optimal parameters need to be analyzed in combination with the inlet pressure. Through quenching experiments, it is found that 1O2 is completely transformed from ·O2-, and ·O2- comes from the transformation of hydroxyl radicals and dissolved oxygen. Higher cavitation intensity is captured and shown more disperse in the vortex cavitation region, which is consistent with the larger production and stronger diffusion of 1O2 and ·O2-. This paper shed light to the generation mechanism of 1O2 and ·O2- in VBHC reactors and the relationship with cavitation intensity. The conclusion provides new ideas for the research of effective ROS in hydrodynamic cavitation process.

New insights on the decolorization of waste flows by Saccharomyces cerevisiae strain - A systematic review

One of the common causes of water pollution is the presence of toxic dye-based effluents, which can pose a serious threat to the ecosystem and human health. The application of Saccharomyces cerevisiae (S. cerevisiae) for wastewater decolorization has been widely investigated due to their efficient removal and eco-friendly treatments. This review attempts to create an awareness of different forms and methods of using Saccharomyces cerevisiae (S. cerevisiae) for wastewater decolorization through a systematic approach. Overall, some suggestions on classification of dyes and related environmental/health problems, and treatment methods are discussed. Besides, the mechanisms of dye removal by S. cerevisiae including biosorption, bioaccumulation, and biodegradation and cell immobilization methods such as adsorption, covalent binding, encapsulation, entrapment, and self-aggregation are discussed. This review would help to inspire the exploration of more creative methods for applications and modification of S. cerevisiae and its further practical applications.

Synergistic degradation of Congo Red by hybrid advanced oxidation via ultraviolet light, persulfate, and hydrodynamic cavitation

In the present study, hybrid activation of sodium peroxydisulfate (PS) by hydrodynamic cavitation and ultraviolet radiation was investigated for Congo Red (CR) degradation. Experiments were conducted using the Box-Benken design on inlet pressure (2-6 bar), PS concentration (0-50 mg. L-1) and UV radiation power (0-32 W). According to the results, at the optimum point where the pressure, PS concentration and UV radiation power were equal to 4.5 bar, 30 mg. L-1 and 16 W respectively, 92.01% of decolorization was achieved. Among the investigated processes, HC/UV/PS was the best process with the rate constant and synergetic coefficient of 38.6 × 10-3 min-1 and 2.76, respectively. At the optimum conditions, increasing the pollutant concentration from 20 mg. L-1 to 80 mg. L-1 decrease degradation rate from 92.01 to 45.21. Presence of natural organic mater (NOM) in all concentrations inhibited the CR degradation. Quenching experiments revealed that in the HC/UV/PS hybrid AOP free radicals accounted for 63.4% of the CR degradation, while the contribution of sulfate (SRs) and hydroxyl radicals (HRs) was 53.1% and 46.9%, respectively.

Mesoporous bimetallic S-doped nanoparticles prepared via hydrothermal method for enhanced photodegradation of 4-chlorophenol

Magnesium oxides (MgO) have gained shown significant promise for a variety of applications, which can be modified by ions doping. In this study, bimetallic Ag-doped S-MgO nanoparticles were prepared by hydrothermal method and used for photocatalytic degradation of 4-chlorophenl (4-CP). EDX suggested the presence of no impurities, which mainly contained Mg, Ag, and S elements, suggesting that S and Ag were incorporated into the lattice of MgO as a result of successful doping. Estimated bandgap of Ag-doped S-MgO nanoparticles was 3.7 eV, lower than MgO (7.8 eV), but useful to improve optical characteristics and photocatalytic efficiency to degrade 4-CP up to a maximum of 99.60 ± 0.50%. The synergetic parameter during photocatalysis of 4-CP was 6.91, confirming the degradation of 4-CP. Quenching experiments proved the presence of hydroxyl radicals (•OH) and singlet dioxygen (1O2) that were critical in 4-CP degradation. The kinetics rate constant was increased by 24.8% from 0.086 ± 0.004 to 0.108 ± 0.005 min-1 by the addition of sulfate in the reaction medium. The work proposes a new synthetic method for preparing catalysts that are capable of producing in-situ •OH radicals and 1O2 to decompose the organic contaminants.

Efficient removal of naphthenic acids from real petroleum wastewater by natural pyrite activated persulfate system

The petroleum wastewater (PWW) contains a diverse range of recalcitrant organic contaminants. Of particular concern is the removal of naphthenic acids (NAs) due to the high toxicity and persistence. Persulfate (PS) based oxidation processes have shown promising in treating refractory wastewater, while the high costs of prepared catalysts limited their widespread implementation. This study aims to develop a cost-effective natural pyrite activated PS system for PWW treatment. The removal of NAs by pyrite/PS system was initially investigated. More than 90% of cyclohexanoic acid (CHA), a model NA, was removed in pyrite/PS system (2.0 g/L pyrite, 4.0 mM PS) at initial pH of 3-11. Scavenging experiments revealed that Fe(II) on pyrite surface was the reactive site for PS activation to generate reactive species, including sulfate radical (SO4·-), Fe(IV) and hydroxyl radical (·OH) for CHA degradation. Reactions of Fe(III) with S helped restore Fe(II) and enhance PS activation, resulting in the sustained catalytic activity of pyrites over five cycles. Cl-, SO42- and NO3- below 10 mM had minimal impact on CHA degradation in pyrite/PS system. However, over 1 mM of HCO3- inhibited 80% of CHA removal due to the buffer effect to maintain the high solution pH. Removing HCO3- from real PWW restored the removal of CHA and of total organic carbon (TOC) to over 90% and 71.3% in pyrite/PS system, respectively. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) results indicated that O2‒6 species including NAs were primarily eliminated through mineralization and oxygen addition. Besides, O3-5S, NO3-5S and N3O2‒4 species were the most susceptible to oxidation in PWW, resulting in the increase of the oxidation level (i.e., O/Cwa) from 0.41 to 0.56 after treatment. This study provides valuable insights into the treatment of NAs in real PWW, and potential application of natural minerals in the treatment of industrial wastewater.

Hydrodynamic cavitation coupled with zero-valent iron produces radical sulfate radicals by sulfite activation to degrade direct red 83

In the present research, hydrodynamic cavitation (HC) and zero-valent iron (ZVI) were used to generate sulfate radicals through sulfite activation as a new source of sulfate for the efficient degradation of Direct Red 83 (DR83). A systematic analysis was carried out to examine the effects of operational parameters, including the pH of the solution, the doses of ZVI and sulfite salts, and the composition of the mixed media. Based on the results, the degradation efficiency of HC/ZVI/sulfite is highly dependent upon the pH of the solution and the dosage of both ZVI and sulfite. Degradation efficiency decreased significantly with increasing solution pH due to a lower corrosion rate for ZVI at high pH. The corrosion rate of ZVI can be accelerated by releasing Fe2+ ions in an acid medium, reducing the concentration of radicals generated even though ZVI is solid/originally non-soluble in water. The degradation efficiency of the HC/ZVI/sulfite process (95.54 % + 2.87%) was found to be significantly higher under optimal conditions than either of the individual processes (<6% for ZVI and sulfite and 68.21±3.41% for HC). Based on the first-order kinetic model, the HC/ZVI/sulfite process has the highest degradation constant of 0.035±0.002 min-1. The contribution of radicals to the degradation of DR83 by the HC/ZVI/sulfite process was 78.92%, while the contribution of SO4•- and •OH radicals was 51.57% and 48.43%, respectively. In the presence of HCO3- and CO32- ions, DR83 degradation is retarded, whereas SO42- and Cl- ions promote degradation. To summarise, the HC/ZVI/sulfite treatment can be viewed as an innovative and promising method of treating recalcitrant textile wastewater.