Degradation of anionic surfactants by Citrobacter braakii

Abstract

Anionic surfactants, as core components of detergent and cosmetic products formulations, contribute significantly to the pollution profile of sewage and wastewaters of all kinds. In Tunisia more than 100 000 m 3 per year of surfactant containing wastewater are released. Treatment by conventional processes such as activated sludge is problematic due to the low kinetics of degradation by unsuitable consortia and to foam production. Bioremediation involves the isolation of suitable microorganisms, adequate process development and in situ biodegradation. The objective of this work was to develop a high performance process for the treatment of anionic surfactant containing wastewater. Screening of bacteria degrading the anionic surfactant sodium lauryl ether sulfate (SLES) was carried out by a conventional enrichment-culture technique. A Citrobacter braakii strain degrading many anionic surfactants was isolated and tested in bioaugmentation for industrial wastewater treatment. It was used for the continuous degradation of highly concentrated SLES synthetic medium and cosmetic industry wastewater. By testing several dilution rates, it was concluded that C. braakii is able to degrade up to 0.065 g l −1 h −1. The hydraulic retention time (HRT) was nearly 20 h. This process was improved by coupling the bioreactor to a mineral microfiltration membrane. This allowed an increase in the SLES elimination rate from 0.065 to 0.15 g l −1 h −1 and to reduce the HRT from 20 to 5 h. Moreover, this integrated system generates microorganism and surfactant free wastewaters able to be rejected without public menace or reused in situ in the industrial process.