Abstract
Competitive interaction between sulfate-reducing bacteria (SRB) and methane producing bacteria (MPB) for hydrogen and for acetate in anaerobic degradation of long chain fatty acids (LFAs) was investigated using two different sludge consortia: the one (referred to as R1) grown in a sulfate-free medium and the other (R2) in a sulfate-rich medium. Both sludges were cultivated in parallel for six months in a fill-and-draw mode on palmitate (C 16, saturated LFA).
R1 sludge finally reached a very low sulfate-reducing activity (SRA, 0.019 gCOD·gVSS-1·d-1) and a very high methaneproducing activity (MPA, 10.1 gCOD·gVSS-1·d-1) for hydrogen-fed vial test: the ratio of SRA/MPA (both on the basis of COD equivalent) was only 0.0019. On the contrary, R2 sludge was characterized by a high hydrogen-fed SRA (1.15 gCOD·gVSS-1·d-1) and by a low hydrogen-fed MPA (0.0093 gCOD·gVSS-1·d-1): the SRA/MPA ratio was 123. The results of hydrogen-trophic MPN enumeration showed a similar tendency: the SRB/MPB ratios were 1/103.6 and 102.0 for R1 and R2 sludge, respectively. Therefore, degradation of palmitate into acetate was performed by a symbiosis between proton-reducing acetogenic bacteria (PRB) and MPB in R1 sludge, whereas by a syntrophic association between PRB and SRB in R2 sludge.
