Anaerobic degradation and inhibitory effects of linoleic acid

The anaerobic degradability and inhibitory effects of linoleic acid, an 18 carbon acid with two double bonds (C18:2) commonly found in vegetable oils, were examined at 21°C. Linoleic acid was anaerobically degraded to unsaturated and saturated products. Unsaturated oleic (C18:1) and palmitoleic (C16:1) acids were transiently formed while saturated palmitic (C16:0) and myristic (C14:0) acids were stoichiometrically produced and may have inhibited their own subsequent degradation. Ultimately, all detected byproducts, including lauric (C12:0) and hexanoic (C6:0) acids, were degraded with the exception of acetic acid which accumulated. Linoleic acid at concentrations of 30 mg l−1 or more completely inhibited aceticlastic methanogenesis. Although hydrogenotrophic methanogenesis was slightly inhibited by 30 mg l−1 of linoleic acid or more, hydrogen consumption remained robust. Anaerobic systems to treat wastewaters with linoleic acid-containing vegetable oils may require two separate stages to minimize the inhibition of aceticlastic methanogens by linoleic acid.