Factors influencing 4 - fluorobenzoate degradation in biofilm cultures of 1 Pseudomonas knackmussii B - 13

19 Membrane aerated biofilm reactors (MABRs) have potential in wastewater treatment as they 20 permit simultaneous COD minimisation, nitrification and denitrification. Here we report on 21 the application of the MABR to the removal of fluorinated xenobiotics from wastewater, 22 employing a Pseudomonas knackmussii monoculture to degrade the model compound 423 fluorobenzoate. Growth of biofilm in the MABR using the fluorinated compound as the sole 24 carbon source occurred in two distinct phases, with early rapid growth (up to 0.007 h) 25 followed by ten-fold slower growth after 200 h operation. Furthermore, the specific 426 fluorobenzoate degradation rate decreased from 1.2 g gh to 0.2 g gh, indicating a 27 diminishing effectiveness of the biofilm as thickness increased. In planktonic cultures 28 stoichiometric conversion of substrate to the fluoride ion was observed, however in the 29 MABR, approximately 85 % of the fluorine added was recovered as fluoride, suggesting 30 accumulation of ‘fluorine’ in the biofilm might account for the decreasing efficiency. This 31 was investigated by culturing the bacterium in a tubular biofilm reactor (TBR), revealing that 32 there was significant fluoride accumulation within the biofilm (0.25 M), which might be 33 responsible for inhibition of 4-fluorobenzoate degradation. This contention was supported by 34 the observation of the inhibition of biofilm accumulation on glass coverslips in the presence 35 of 40 mM fluoride. These experiments highlight the importance of fluoride ion accumulation 36 on biofilm performance when applied to organofluorine remediation. 37 38