Treatment of unhairing effluents by activated sludge system

Authors

  • Najwa Mlaik,

    Corresponding author
    1. Ecole Nationale d'Ingénieurs de Sfax ENIS, Laboratoire Eau, Energie et Environnement, Route de Soukra BP W 3038, Sfax, Tunisia
    • Ecole Nationale d'Ingénieurs de Sfax ENIS, Laboratoire Eau, Energie et Environnement, Route de Soukra BP W 3038, Sfax, Tunisia
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  • Mbarka Gouider,

    1. Ecole Nationale d'Ingénieurs de Sfax ENIS, Laboratoire Eau, Energie et Environnement, Route de Soukra BP W 3038, Sfax, Tunisia
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  • Jalel Bouzid,

    1. Ecole Nationale d'Ingénieurs de Sfax ENIS, Laboratoire Eau, Energie et Environnement, Route de Soukra BP W 3038, Sfax, Tunisia
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  • Lassaad Belbahri,

    1. Laboratory of Applied Genetics, School of Engineering of Lullier, Jussy, Switzerland
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  • Steve Woodward,

    1. Department of Plant and Soil Science, University of Aberdeen, Institute of Biological and Environmental Sciences, Aberdeen AB24 3UU, Scotland, United Kingdom
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  • Tahar Mechichi

    1. Ecole Nationale d'Ingénieurs de Sfax ENIS, Laboratoire Eau, Energie et Environnement, Route de Soukra BP W 3038, Sfax, Tunisia
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Abstract

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

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