Lecheng Lei

Copper/activated carbon as catalyst for organic wastewater treatment

Abstract A new heterogeneous copper catalyst was developed using highly porous activated carbon as the catalyst support. The catalyst was designed to promote the oxidation of organic pollutants in dyeing and printing wastewater from the textile industry, which was carried out in a 2 l high-pressure reactor. The new catalyst enhanced the conversion of organic compounds in dyeing and printing wastewater, shortened the reaction time, and lowered the reaction temperature and the system total pressure. The conditions for preparing the catalyst were experimentally optimized according to their catalytic oxidation efficiency in wastewater treatment.

Oxidative degradation of poly vinyl alcohol by the photochemically enhanced Fenton reaction

Abstract The effective degradation of polyvinyl alcohol (PVA) was achieved by the application of the photochemically enhanced Fenton reaction. This ‘Advanced Oxidation Process’ was studied in a batch reactor (V = 0.75 1) using a mercury medium pressure light source. The accuracy of the DOC measurements in function of irradiation and reaction time was remarkably enhanced by the addition of a reduction and precipitation agent, consisting of an aqueous solution of Na3PO4, Na2SO3 and Kl. Effective oxidation was observed when employing low iron(II) concentrations of approximately 1 equivalent of iron(II) per 20 PVA-units (C2H4O) and a stoichiometric amount of H2O2 with respect to the PVA-units to be oxidized.

On the degradability of printing and dyeing wastewater by wet air oxidation

A modified first-order kinetics model was used to study the wet air oxidation of printing and dyeing wastewater. The model simulations are in good agreement with experimental data. The results indicate that a certain fraction of organic pollutants in the printing and dyeing wastewater could not be removed even at elevated temperature and prolonged reaction time. The ratio of degradable organic matter is found independent of temperature and can be improved by using a catalyst.

Catalytic wet air oxidation of dyeing and printing wastewater

The treatment of dyeing and printing wastewater from the textile industry by oxidation was studied. The reaction was carried out in a two-litre high pressure reactor. In order to promote the oxidation of organic pollutants present in the wastewater, experiments were conducted using various catalysts including metal salts, metal oxides, and porous alumina supported metals. All catalysts tested were able to enhance the conversion of organic compounds in wastewater, shorten the reaction time, and lower the reaction temperature. The alumina supported catalyst has an advantage over other catalysts in that it can be easily separated from the treated wastewater by filtration and recycled. The conditions in preparing the catalyst supported by porous alumina were experimentally optimised.

Kinetic study into the wet air oxidation of printing and dyeing wastewater

Abstract This paper presents the results of a study on the treatment of printing and dyeing wastewater from the textile industry by wet air oxidation (WAO). Experiments were conducted in a 2 l autoclave batch reactor. The range of operating temperatures examined was between 423 and 573 K at an oxygen partial pressure of 1.69 MPa standardized at 298 K. Chemical oxygen demand (COD) were measured at regular intervals during each experiment. Experimental data indicate that a certain amount of COD in the printing and dyeing wastewater can be removed by simple WAO. The extent of COD removal by the oxidation process increases with temperature until 523 K. Thermal decomposition during preheating was found to play a significant role in the COD removal with up to 18% COD removed at an operating temperature of 573 K. A first order kinetic model is proposed and tested for the removal of COD by WAO. The fit between the experimental data and the kinetic equation is good. The activation energy obtained is 37.5 kJ/mol K. The model prediction of overall COD removal agrees well with the experimental measurements. The results obtained here are useful for the design of WAO reactor and for the prediction of WAO performance in treating printing and dyeing wastewater.

Homogeneous catalytic wet-air oxidation for the treatment of textile wastewater

An extensive series of experiments was performed to identify suitable catalysts to increase the reaction rate of wet-air oxidation of textile wastewater t relatively mild temperatures an pressures. Wastewater types treated included natural-fiber desizing wastewater, synthetic-fiber desizing wastewater, and printing and dyeing wastewater. Experimental results indicated that all catalysts tested in this investigation significantly increased the chemical oxygen demand (COD) and total organic carbon (TOC) removal rates and total COD and TOC removals. Of all catalysts tested, copper salts were the most effective. Anions in the slat solutions played a role in the catalytic process. Nitrate ions were more effective than sulfate ions. Similarly, copper nitrates were more effective than copper sulfates. A mixture of salts containing different metals performed better than any single salt.

Oxidative degradation of polyvinyl alcohol by the photochemically enhanced Fenton reaction. Evidence for the formation of super-macromolecules

The reaction mechanism of the oxidative degradation of polyvinyl alcohol (PVA) by the photochemically enhanced Fenton reaction has been studied. Fast and efficient degradation was observed in a batch reactor, using a medium pressure mercury arc in a Pyrex envelope and employing 80% of the stoichiometric amount of H2O2 required for the total oxidation of PVA and a concentration ratio as low as 1 mole of iron(II) sulfate per 20 moles of PVA sub-units (C2H4O) Model PVA polymers of three different molecular weights (15,000, 49,000 and 100,000 g mol−1) were found to follow identical degradation patterns. Strong experimental evidence supports the formation of super-macromolecules (MW: 1–5 × 106 g mol−1) consisting of oxidized PVA and trapped iron(III) at an early reaction stage. Low molecular weight intermediates, such as oxalic acid, formic acid or formaldehyde were not found during the PVA degradation, and we may deduce that the manifold of degradation reactions is mainly taking place within the super-macromolecules from which CO2 is directly released.