Mineralization of LCFA associated with anaerobic sludge: Kinetics, enhancement of methanogenic activity, and effect of VFA

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Abstract
Long‐chain fatty acids (LCFA) associated with anaerobic sludge by mechanisms of precipitation, adsorption, or entrapment can be biodegraded to methane. The mineralization kinetics of biomass‐associated LCFA were established according to an inhibition model based on Haldane's enzymatic inhibition kinetics. A value around 1,000 mg COD‐LCFA·.g VSS−1 was obtained for the optimal specific LCFA content that allowed the maximal mineralization rate. For sludge with specific LCFA contents of 2,838 ± 63 and 4,571 ± 257 mg COD‐LCFA·.g VSS−1, the specific methanogenic activities in the presence of acetate, butyrate, and H2/CO2 were significantly enhanced after the mineralization of the biomass‐associated LCFA. For sludge with a specific LCFA content near the optimal value defined by the kinetic model, the effect of adding VFA to the medium was studied during the mineralization of the biomass‐associated LCFA. Different patterns were obtained for each individual substrate. Acetate and butyrate were preferentially consumed by the consortium, but in the case of propionate no evidence of a sequential consumption pattern could be withdrawn. It was concluded that LCFA do not exert a bactericidal neither a permanent toxic effect toward the anaerobic consortia. A discussion is addressed to the relative roles of a reversible inhibitory effect and a transport limitation effect imposed by the LCFA surrounding the cells.