Abstract

Large amounts of shavings and sludge are generated from wastewater treatment plants of tanneries and are of great concern since their most common destination is their disposal in landfills. In tanning processes chromium salts are the main tanning agents used. The tannery solid residues characteristics suggest that anaerobic digestion is a potential treatment alternative. Therefore this study aimed to analyze the influence of the presence of chromium in the co-digestion of these two leather industry solid residues of major concern both before and after the tanning stage. The presence of chromium in sludge proved to be more suitable than its absence, producing more biogas – 30.34ml/g of VSS (volatile suspended solids) on average – and a greater reduction of organic load – 67.7% on average. This may be due to the low concentration of chromium in essays (up to 15mg/L) being appropriate for many enzymes and co-enzymes in addition to the possible toxicity of the reagents used in the beamhouse process, such as acids and bases, which inhibited the final steps of the anaerobic digestion. The presence of chromium in shavings did not show significant influence probably due to their small proportion in essays.