The Effects of long chain Fatty Acids (LCFA) on Sulfate Removal in an Acclimated Mixed Anaerobic Culture.

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Courtesy of Water Environment Federation (WEF)

Introduction

Oleic acid (OA) and stearic acid (SA), two long chaing fatty acids (LCFAs) possessing 18 carbons, were used to inhibit methanogensis in an anaerobic mixed culture converting sulfate to sulfide. Under anaerobic conditions, SRB oxidize simple organic compounds by utilizing sulfate as an electron acceptor and generate sulfide (S-2) and alkalinity. In mixed anaerobic communities, evidence has shown that sulfate reducing bacteria (SRB) outcompete aceticlastic methanogens, for acetate. However, SRB and methane producing bacteria (MPB) are terminal degraders and their roles are analogous in anaerobic microbial systems (McCartney and Oleszkiewicz, 1993; and Lens et al, 1998)
hence there is always a competition between SRBs and MPBs. Competition between the latter microorganisms for electron equivalencies from hydrogen and acetate causes the process to become less efficient because a fraction of the reducing equivalence is consumed for methane production instead of sulfate reduction (Weijma, 2002). LCFAs
are easily available from agriculture sources, relatively inexpensive and slowly degrading (Lalman and Bagley, 2001 and 2002). The role of LCFAs is as follows: 1. they inhibit aceticlastic and hydrogenotrophic methanogens and 2. their degradation to acetate plus hydrogen is a useful source of electrons for sulfate reduction. The objective of the work
was to assess the effects of OA and SA on sulfate reduction in mixed anaerobic batch cultures maintained at 37 ± 2oC.

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