Ammonia Inhibition in the Anaerobic Treatment of Fishery Effluents

Inhibition of the organic matter consumption rate of a saline and rich proteic effluent by free ammonia was assessed in anaerobic filters at 37 degrees C. Inhibition of substrate (total organic carbon, TOC) consumption rate by ammonia was fitted by the Luong and noncompetitive models. Calculated kinetic parameters using the Luong model were maximum specific growth rate, micromax = 0.28 day(-1); average saturation constant, Ks = 568 mg TOC/L; Luong inhibition parameter, KNH3 = 1707mg ammonia-nitrogen (NH3-N)/L; and Luong exponent, gamma = 0.283 and the noncompetitive calculated parameters were umax= 0.26 day(-1), Ks = 703 mg TOC/L, and inhibition parameter, INH3 = 325 mg NH3-N/L. The Luong and noncompetitive models predicted 50% inhibition of the substrate consumption rate at ammonia concentrations of 147 and 325 mg NH3-N/L, respectively, suggesting biomass adaptation to the ammonia concentration (80 mg NH3-N/L as average) at which the anaerobic filters were previously operating. Ammonia formation by anaerobic digestion of fishing effluent would produce a maximum of 65.1 and 58.6% inhibition of the efficiency, predicted by the Luong and noncompetitive models, respectively. Ammonia influence on the digestion steps was determined by comparing fishing effluent with volatile fatty acids as substrates. The noncompetitive model predicted a 50% inhibition of methane production rate at ammonia concentrations of 196.6 and 188.6 mg NH3-N/L for fishing effluent and volatile fatty acids, respectively, suggesting that the methanogenic step is the one most affected by ammonia.