Influence of anode material on electrochemical oxidation for the treatment of tannery wastewater.

The treatment of tannery wastewater by electrochemical oxidation, mediated by an electro-generated species was carried out under galvanostatic conditions in an electrochemical reactor equipped with anodes based on noble metals and metal oxides (Ti/Pt-Ir, Ti/PbO2, Ti/PdO-Co3O4 and Ti/RhO(x)-TiO2). The decrease in time of chemical oxygen demand, nitrogen (TKN and ammonia), Cr and sulphides was monitored. The study showed that the rate of pollutant removal was significantly influenced by the type of anode material and electrochemical parameters. Different mechanisms contributed to the removal of pollutants when the reactor operated under conditions close to the limiting current for chlorine evolution and under much higher current density, with the reactor performing better at a high current/voltage. The kinetic pseudo-first order model applied for the interpretation of the results showed that the Ti/Pt-Ir and Ti/PdO-Co3O4 anodes performed better than the other two electrodes under the majority of tested conditions, with the highest rate of removal obtained for ammonia (kinetic rate constant k=0.75 min(-1)). Electrochemical oxidation can be applied as a post-treatment after the conventional biological process in order to remove the residual ammonia with low energy consumption (0.4 kWh m(-3)).

Characterization of the catalytic films formed on stainless steel anodes employed for the electrochemical treatment of cuprocyanide wastewaters.

Surface composition changes at stainless steel anodes in an electrochemical reactor applied for the electrochemical treatment of cuprocyanide-containing wastewaters operating under different hydrodynamic conditions were investigated. Under highly alkaline conditions in situ generation of a surface film on the anode with catalytic properties towards cyanide electrolysis was observed. X-ray photoelectron spectroscopy (XPS) results demonstrated that only copper oxi-hydroxide compounds constitute the surface film developed on the stainless steel anodes, as no traces of N- and C-containing compounds were observed. The collected XPS spectra revealed relevant details concerning the oxidation states of copper in the film, and the products Cu2O, CuO and Cu(OH)2 were identified on the surface of the anodes. However, the quantitative proportions of the individual products differ and depend on the type of mixing employed during reactor operation.

Application of electrochemical reactors for industrial waste-water treatment.

The effectiveness of electrochemical reactors for industrial wastewater treatment has been improved since three-dimensional electrodes have been introduced; in fact, limitations of mass transfer can arise, due to the low concentrations of pollutants which may be involved in the process. Three-dimensional electrodes offer a very high electrode area per unit electrode volume and they can act as turbulence promoters or give rise to high linear electrolyte velocity, resulting in high values of mass transport coefficient. However, careful selection of operative parameters is needed in order to obtain high performance. This paper examines the results obtained in our laboratory on the cathodic reduction of copper at RVC electrodes; in particular the interference of dissolved oxygen is studied during the removal of copper from extremely diluted solutions (C < 10 ppm). Some results are also discussed on the removal of organic pollutants by electrochemical oxidation at three-dimensional anode consisting of a fixed bed of carbon pellets.

Biohydrolysis of urea from urea-bearing wastewater.

Biological stabilization of urea is a two staged process; (i) urea hydrolysis and (ii) ammonia stripping/nitrification-denitrification. Ammonia thus produced is either stripped off by usual methods or after converting into nitrate using chemoautotrophic bacteria. On denitrification, nitrate is finally converted into nitrogen gas by means of heterotrophic bacteria. Details of stabilization of urea from urea bearing wastewater using urea biohydrolyser are presented in this paper.

Removal of cyanides by electrooxidation.

The paper describes a study on electro-oxidation of cyanides complexed with copper, present in metal plating wastewater. A detailed voltammetric study has indicated that formation in situ of the electrocatalytic film of copper oxide and electro-oxidation of cyanides probably occurs at the same anode potential. By contrary to other materials at which electro-oxidation of cyanide also occurs, at copper oxide elimination of cyanide occurs at a potential lower then the potential of hydroxide ion discharge.

Electrocoagulation of textile wastewater bearing disperse dyes.

The paper describes a study on the removal of colour from textile wastewater bearing a mixture of three disperse dyes. The experiments were carried out in a reactor equipped with an Al sacrificial anode (100 cm2) and a stainless steel cathode of the same dimensions. Decolorisation occurred as a result of destabilisation of colloids due to an effect of an electric field generated between the electrodes (polarisation coagulation) and the reactions with coagulating compounds, formed in situ during anode oxidation (volumetric coagulation), followed by a subsequent flotation of agglomerates of the particles. During the study the following parameters were varied: initial pH of the solution, current density (between 100 and 300 A m-2) and an initial concentration of the dyes. The best results of elimination of colour, equal to 99%, were obtained during 5 minutes of treatment under the conditions of pH of 9 and the G factor equal to 41.