Electrochemistry

Advanced electrochemical oxidation processes have emerged as a promising method for the destruction of persistent organic material in variable waste streams. Although the process has been successfully employed for wastewater treatment applications, high energy requirements, and the risk of formation of undesirable by-products may limit its application in the field of leachate treatment. This study focuses on the investigation of the feasibility of removing organics and ammonia by electrochemical oxidation coupled with ozone, Fenton or lime. Landfill leachate was treated by two different bench scale electrochemical oxidation reactors coupled with ozone oxidation, Fenton coagulation or lime precipitation. The electrochemical oxidation was conducted using a titanium anode coated with multi-metal oxides (MMO) at three-different current densities for different durations. Treatment performance was determined based on the removal of COD, ammonium-N, and turbidity. A three-level factorial design was established, and response surface methodology (RSM) was introduced to determine the optimum process parameters. The results suggest that the process can remove appreciable amounts of ammonium-N and COD in a very short time, demonstrating that the process is effective in rapidly degrading recalcitrant organics in leachate.

The electrochemical reduction of the cis-dioxo Mo(VI)-catechol complex, MoO2(cat2^2-, is investigated at a mercury electrode in pH 3.5-10 aqueous buffers utilizing the techniques of cyclic voltammetry and controlled potential coulometry. The reduction of MoO2(cat2^2- proceeds
by successive two-proton, one-electron and two- proton, two-electron
transfer steps which produce monomeric Mo(V) and Mo(III) species. At
pH 3.5-7 the Mo(V) monomer is unstable and undergoes dimerization. The
mechanism of the dimerization reaction and the structure of the Mo(V)
dimer produced are determined. At pH 7-10 the monomeric Mo (V) and
2- Mo(III) complexes produced by reduction of MoO2(cat2^2- are stable. A
stable Mo(IV) species is obtained upon reoxidation of the Mo( III )
monomer. The epr spectrum of the monomeric Mo(V) complex and visible
spectra of all oxidation states in alkaline solution arc reported.

The elect;rochemical reduction of Fe2(salen)2O at a platinum electrode
in dimethylsulfoxide is investigated using the techniques of cyclic voltammetry,
controlled potential coulometry and chronoamperometry.
The effects of concentration and addition of a proton source on the
reduction mechanisrn are investigated. The reduction proceeds by two
related mechanisms. At short-times, Fe2(salen)2O is reduced by two
sequential one-electron steps producing an Fe(III)Fe(II) dimer and an
unstable Fe(II) dimer. At long-times the mixed-valence dimer reacts
leading to transfer of 1.5 electrons per Fe2 unit. Mechanisms consistent
with the experimental data are proposed involving the formation of
a tetrameric structure.