Treatment of fluoroacetate by a Pseudomonas fluorescens biofilm grown in membrane aerated biofilm reactor

Abstract

Fluorinated organic compounds have widespread applications, and their accumulation in the environment is a concern. Biofilm reactors are an effective technology for the treatment of contaminated wastewater, yet almost no research has been conducted on the effectiveness of biofilms for the biodegradation of fluorinated aliphatic compounds. In this paper we describe experiments undertaken to investigate the degradation of fluoroacetate using a membrane aerated biofilm reactor (MABR) by Pseudomonas fluorescens DSM8341. The concentration of fluoroacetate in the medium influenced biofilm structure, with less dense biofilm observed at lower fluoroacetate loading rates. As biofilm thickness increased, oxygen utilization decreased, probably as a consequence of increased resistance to oxygen transfer. Furthermore, most of the biofilm was anaerobic, since oxygen penetration depth was less than 1000 μm. Biofilm performance, in terms of fluoroacetate removal efficiency, was improved by decreasing the fluoroacetate loading rate, however increasing the intramembrane oxygen pressure had little effect on biofilm performance. A mathematical model showed that while fluoroacetate does not penetrate the entire biofilm, the defluorination intermediate metabolite glycolate does, and consequently the biofilm was not carbon limited at the biofilm−membrane interface where oxygen concentrations were highest. The model also showed the accumulation of the free fluoride ion within the biofilm. Overflow metabolism of glycolate was identified to be most likely a result of a combination of oxygen limitation and free fluoride ion inhibition. The study demonstrated the potential of MABR for treating wastewater streams contaminated with organofluorine compounds.