Electro-Fenton_based treatments of real effluents from tanning processes and landfills

Leather industry uses high quantities of water, from 50 to 200 m3 per day, the whole amount of which is usually sent to depuration. At the same time it is noteworthy that tanning processes use large quantities of tannin-based organic compounds, which with all the protein, lipids, greases and hairs, constitute an overcharge of COD (Chemical Oxygen Demand) and BOD (Biological Oxygen Demand) in the tanning effluents. These effluents contain many biorefractory compounds, so low biodegradability index, with COD charge varying from 5000 to 120,000 ppm. This, undoubtedly, causes troubles in the depuration processes. Effective treatment with recycling option of such large quantities of technological waters would: (i) ensure a high diminution in the costs of the entire tanning process (as for that of water consumption and that of salt expenses), (ii) allow to easily depurate the issuing waters with lower costs and (iii) eliminate progressively the negative environmental impact of the final rejects in rivers by reducing considerably (or eliminating) the remaining COD and the quantities of sludge at the end of the depuration process. Depuration sludges are usually stocked in specially conceived landfills. Percolating waters from such landfills contain also high quantities of contaminants, COD from 5000-15000 ppm, and are currently sent to the top of the depuration. Periodical recirculation of the same is done, which, in fact, does not always suffer subsequent treatment. The main process which is presented in this work, Assisted Electroprecipitation, combines physico-chemical aspects of the treatment of water effluents with (electro-)Fenton-based electrochemical oxidation and partial coagulation/precipitation of the ending carbonic compounds. This treatment allows complete COD removal from the effluents. The issued technology is suitable to industrial application specially for the recycling tanning effluents and landfills percolates.