Treatment of unhairing effluents by activated sludge system

Najwa Mlaik, Mbarka Goudier, Jalel Bouzid, Lassaad Belbahri, Stephen Woodward, Tahar Mechichi

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


The unhairing step in leather manufacture generates a highly hazardous and alkaline wastewater. This article reports the evaluation of an activated sludge system for the treatment of unhairing wastewater and effluent detoxification, assessed by seed germination tests.

The activated sludge system reactor was fed for 112 days with diluted unhairing effluent; the operation strategy included increasing the organic loading rate (OLR) from 0.7 to 1.6 g chemical oxygen demand (COD) L-1 d-1. COD and suspended solids (SS) removal efficiencies were up to 85 and 80%, respectively, for an OLR lower than 1.4 g COD L-1 d-1.

Sulphide removal efficiency was ~90%, as sulphide was oxidized to other species such as sulphate. The biological oxidation of thiosulphates into tetrathionates was also investigated.

The effect of untreated and treated unhairing wastewater on seed germination of maize, sorghum, and wheat was examined. Treatment decreased the phytotoxicity of the wastewater. Indeed, germination was inhibited when effluent dilution was lower than 90% of untreated wastewater, whereas a positive effect of treated wastewater was noticed.

Phytotoxicity assays showed that biological treatment of unhairing wastewater contributed to a decrease in toxicity of the effluent. © 2010 American Institute of Chemical Engineers Environ Prog, 2011

Original languageEnglish
Pages (from-to)337-346
Number of pages10
JournalEnvironmental Progress and Sustainable Energy
Issue number3
Early online date10 Sept 2010
Publication statusPublished - Oct 2011


  • unhairing effluent
  • activated sludge system
  • sulphide oxidation
  • phytotoxicity
  • germination index


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