Effect of Loading in Soil Slurry-Sequencing Batch Reactors on Biosurfactant Production and Foaming

Abstract

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 bisurfactant were measured, with emulsification capacity (EC), foam thickness, and O\d2 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 \ICandida tropicalis, Brevibacterium casei, Flavobacterium aquatile, Pseudomonas aeruginosa,\N and \IPseudomonas fluorescens\N 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 (\IC. tropicalis, P. aeruginosa, P. fluorescens\N) relative to total counts increased from 21 to 86% as loading increased from 5 to 50%.