Oxidative unhairing versus sulphide use. A critical comparison

The conventional unhairing process is one of the most pollutant steps in the leather tanning process, which usually involves great amounts of sulfides lime and soda ash, generating higher BOD and COD values in the wastewater. In this work, we have investigated different oxidative agents, combined or not with enzymes, as a possible replacing agent of sulfides as an unhairing agent. Peroxymonocarbonate anion, Persulfate anions (peroxymonosulfate and peroxydisulfate anion) and Peroxynitrite anion have been chosen and the dehairing of a bovine leather has been performed. The performance has been compared in terms of dehairing ability, time, suspended solids, pH, conductivity, COD and Nitrogen (Kjeldahl). All the tests were compared with a pilot test (hair-saving sulfide unhairing) and with a hydrogen peroxide dehairing. The results show the great ability of percarbonate, combined with enzymes, to give complete unhairing in 16 h, no grain damage in absence of sulfides, and great homogeneity after dyeing tests. The results, also, showed a greater reduction of the pollutant in the waste water.Peer Reviewe