Microbial Degradation of Anionic Surfactants from Laundry Detergents Commonly Discharged into a Riverine Ecosystem

Abstract

The biodegradability of anionic surfactants and the presence of surfactant degrading bacteria in the New Calabar River situated in Choba, Nigeria was investigated. Eleven (11) locally manufactured and six (6) imported brands were studied alongside sodium dodecyl sulphate (SDS) used as a standard. Total heterotrophic counts were determined using the spread plate technique on nutrient agar while mineral salt agar was used for the isolation and enumeration of the detergent utilisers. The river die-away Methylene Blue Active Substance (MBAS) technique was used to determine the extent of primary degradation of the surfactants in the detergents. Investigations revealed that the growth of surfactant-utilising bacteria was supported by all the detergents, at a concentration of 3 mg/L. The locally formulated brands were found to support less growth and were thus concluded to be less prone to bacterial utilisation when compared to imported brands and SDS indicating that the latter was a more ready source of carbon at the concentration used. The detergent-utilising bacteria isolated were Bacillus, Pseudomonas, Klebsiella, Enterobacter, Escherichia coli and Staphylococcus aureus. The anionic surfactants in imported detergents were more biodegradable than in locally manufactured ones. At the end of the 28 day test period, the locally manufactured detergents had 15 – 44% surfactant un-degraded based on the presence of the Methylene Blue Active Substance (MBAS) while the imported brands had 5 – 8% surfactant remaining. SDS had the lowest value of 3% surfactant un-degraded.