Primary, secondary and tertiary economic activities produce waste that should be properly
managed and treaty. Skins are byproducts of the meet industry used as raw material in
tanneries. The tanning process generates great quantities of byproducts and waste. Several
quantities of solid waste containing chromium, in powder form, are generated in the tanning
process. One t of raw skin generates in the end of the process 200 kg of leather, 250 kg of
tanned solid waste, 350 kg of non tanned solid waste and 100 kg are lost in liquid waste. In the
last years, laboratory research describe protein and chromium recovery processes. In these
processes, chrome shavings are digested with alkaline protease, producing two liquids
fractions, a gelatin and a collagen hydrolysate. The molecular weight spectrum of the
recovered protein shows that the average molecular weight is too low. Researching for a
protein modification process environmentally friendly generating high molecular weight
protein, combined tanning processes were tested. The combined tanning processes, where
bigger complexes are formed into the polipeptidical chain of hides by crosslinks, are
aluminum/mimosa tanning and glutaraldehyde/mimosa tanning, where greater hydrothermal
stability is achieved. The aim of this work is to verify potential modifications in hidrolysated
protein, generating a product of tanning power by the addition of different tanning agents. The
controlled variables are molecular weight by GPC, chemical treatment, hide powder
interaction, leather characteristics like filling, grain, physical-mechanical resistance and dyeing
and residual bath parameters like total solids content, COD and BOD. The obtained results
appoint for the possibility to use hidrolysated protein with glutaraldehyde like retanning agent
in quality leathers, with good physical-mechanical resistance, good filling and firm grain. The
results of the analysis from the residual bath appoint to good exhaustion of the offered
chemicals, indicating the existence of interaction between the modified material and the
leather collagen.