ELECTRO-FENTON-BASED TREATMENTS OF REAL EFFLUENTS FROM TANNING PROCESSES AND LANDFILLS

摘要

Leather industry uses high quantities of water, from 50 to 200 m~3 d~(-1) and tanning processes use large quantities of tannin-based organic compounds, which with all the protein, lipids, greases and hairs, constitute high amounts of COD (chemical oxygen demand) and BOD (biological oxygen demand) with many biorefractory compounds in the tanning effluents. Effective treatment with recycling option of such large quantities of technological waters would: 1) reduce the costs of the entire tanning process (as for that of water consumption and that of salt expenses), 2) allow to easily depurate the issuing waters with lower costs, and 3) eliminate progressively the negative environmental impact of the final effluent discharge into rivers by reducing considerably (or eliminating) the remaining COD and the quantities of sludge at the end of the treatment process.rnDepuration sludges are usually stocked in specially conceived landfills. Leachate from such landfills contains also high quantities of contaminants, COD from 5000-15000 ppm, and requires further treatment. Periodical recirculation of the leachate is done, which, in fact, does not always suffer subsequent treatment.rnThe main process presented in this work, H_2O_2-assisted electroprecipitation (AEP) with sacrificial Fe anode coupled with Ti(Pt) cathode, combines physico-chemical aspects of the treatment of water effluents with electro-Fenton(EF)-based electrochemical oxidation and partial coagulation/precipitation of the remaining compounds. The COD removal is 90% in 8 h for the desalting wastewater and in the range 60-80% in 6 h for the leachate during AEP treatment. EF and photoelectron-Fenton on boron doped diamond (BDD) anode coupled with O_2-diffusion cathode also allow high degradation efficiency (75-80%), limited by oxalate-complexes formation and the presence of suspended solids. BDD anodic oxidation achieves 99% destruction of COD in a longer time, more than 20 h. AEP treatment, alone or in combination with complementary treatment, allows complete COD removal from the effluents. The AEP-technology is suitable to industrial application specially for the recycling of tanning effluents and landfill leachate.