This paper presents an integrated approach of the main reasons for the accumulation of volatile fatty acids (VFAs) in anaerobic reactors. The build up of acetate during shock loads and/or stress conditions is likely to occur due to kinetic limitations of methanogenic microrganisms, which is enhanced by pH reduction. Acumulation of acetate and hydrogen in the liquid phase will set the stage for the accumulation of other VFAs, such as propionate and butyrate, due to thermodynamic inhibition. By mantaining the ideal growth conditions for the methanogens it may be possible to reduce the acetate build up, although it may not be effective in reducing the concentration of dissolved hydrogen so that thermodynamic inhibition is avoided. The strategies to mitigate themodynamic inhibition could involve regulation of acetate by means of membrane or resins, and spacial separation of microrganisms by granulation or staging.
Anaerobic treatment; process stability; kinetics; thermodynamics; mass transfer; population dynamics; nutrients deficiency
