Sodium lauryl ether sulfate (SLES) degradation by nitrate-reducing bacteria

Harm Vreeling,Rozelin Aydin,Mauricio R Dimitrov,Ana J Cavaleiro,Pedro A García-Encina,Alfons J M Stams,Ana M S Paulo,Caroline M Plugge

doi:10.1007/s00253-017-8212-x

Abstract

The surfactant sodium lauryl ether sulfate (SLES) is widely used in the composition of detergents and frequently ends up in wastewater treatment plants (WWTPs). While aerobic SLES degradation is well studied, little is known about the fate of this compound in anoxic environments, such as denitrification tanks of WWTPs, nor about the bacteria involved in the anoxic biodegradation. Here, we used SLES as sole carbon and energy source, at concentrations ranging from 50 to 1000 mg L−1, to enrich and isolate nitrate-reducing bacteria from activated sludge of a WWTP with the anaerobic-anoxic-oxic (A2/O) concept. In the 50 mg L−1 enrichment, Comamonas (50%), Pseudomonas (24%), and Alicycliphilus (12%) were present at higher relative abundance, while Pseudomonas (53%) became dominant in the 1000 mg L−1 enrichment. Aeromonas hydrophila strain S7, Pseudomonas stutzeri strain S8, and Pseudomonas nitroreducens strain S11 were isolated from the enriched cultures. Under denitrifying conditions, strains S8 and S11 degraded 500 mg L−1 SLES in less than 1 day, while strain S7 required more than 6 days. Strains S8 and S11 also showed a remarkable resistance to SLES, being able to grow and reduce nitrate with SLES concentrations up to 40 g L−1. Strain S11 turned out to be the best anoxic SLES degrader, degrading up to 41% of 500 mg L−1. The comparison between SLES anoxic and oxic degradation by strain S11 revealed differences in SLES cleavage, degradation, and sulfate accumulation; both ester and ether cleavage were probably employed in SLES anoxic degradation by strain S11.

Highlights

Anionic surfactants account for 60% of worldwide surfactants production (Holmberg et al 2002) and sodium lauryl ether sulfate (SLES) is one of the most commonly used
The average concentration of anionic surfactants in domestic wastewater can vary between 0.4 and 12 mg L−1 (HERA 2002; HERA 2004; HERA 2013), higher concentrations are frequently present in industrial wastewater, e.g., from the cosmetic industry, or in wastewater from surfactant-based technologies used for the cleanup of contaminated soils and aquifers (Huang et al 2015; Shah et al 2016; Zhang et al 1999)
Bacterial strains from the genera Pseudomonas and Aeromonas were obtained

Summary

Introduction

Anionic surfactants account for 60% of worldwide surfactants production (Holmberg et al 2002) and sodium lauryl ether sulfate (SLES) is one of the most commonly used. SLES is a mixture of linear primary alkyl ether sulfates (AES) present in the formulation of several commercial detergents and personal care products (Khleifat 2006). SLES forms micelles at a concentration higher than 300 mg L−1 (Aoudia et al 2009), and 3000 mg L−1 was the concentration of anionic surfactants (mainly SLES) in the wastewater from a cosmetic production plant (Aloui et al 2009)

Methods

Results

Conclusion