Effect of loading in soil slurry-sequencing batch reactors on biosurfactant production and foaming

Daniel P. Cassidy, Andrew J. Hudak, Ahmed A. Murad

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


A soil contaminated with diesel fuel (DF) was treated in 8-L soil slurry sequencing batch reactors with 10-day retention times and different volumetric loadings: 5, 10, and 50% of the reactor volume per cycle. Concentrations of DF, DF-degrading microorganisms, and biosurfactant were measured, with emulsification capacity (EC), foam thickness, and O2 uptake. Foaming coincided with nonzero values of EC, a measure of free (i.e., non-DF-bound) surfactants. Higher surfactant levels increased DF emulsification and foaming and reduced DF stripping. Concentrations of Candida tropicalis, Brevibacterium casei, Flavobacterium aquatile, Pseudomonas aeruginosa, and Pseudomonas fluorescens were determined. Biosurfactant production and DF degradation increased with increased loading. Biosurfactants exceeded the critical micelle concentration early in the cycle but were completely degraded by the cycle's end. Orders-of-magnitude differences in effluent concentrations of individual species were observed. Culture-based counts of surfactant-producing species (C. tropicalis, P. aeruginosa, P. fluorescens) relative to total counts increased from 21 to 86% as loading increased from 5 to 50%.

Original languageEnglish
Pages (from-to)575-582
Number of pages8
JournalJournal of Environmental Engineering
Issue number7
Publication statusPublished - Jul 2002
Externally publishedYes


  • Emulsions
  • Foam
  • Hydrocarbons
  • Slurries
  • Soils
  • Surface-active agents

ASJC Scopus subject areas

  • Environmental Engineering
  • Civil and Structural Engineering
  • Environmental Chemistry
  • General Environmental Science


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