Abstract
Anaerobic treatment of saline and protein‐rich effluents reduces the organic concentration but forms ammonium that hinders nitrogen removal in a later aerobic treatment. The goal of this work was to optimize the design of a denitrifying–nitrifying system for the simultaneous removal of organic matter and nitrogenous compounds from fishery effluents to meet the Chilean legal standards and to compare pre‐ and postdenitrification processes in the biological treatment of high‐strength effluents to minimize the total volume of biological reactors required. A predenitrifying system, that included three reactors—acidifying anaerobic filter, denitrifying (anoxic) filter, and aerobic‐active sludge (nitrifying reactor) with recycle to the denitrifying reactor—reduced nitrogen to 0.33 g of total ammonia nitrogen (TAN) L^−1^, well above the allowed 0.05 g total nitrogen L^−1^. The predenitrifying system with a second denitrifying reactor, to which organic matter was added, met the legal organic matter and nitrogen emission concentrations (0.042 g TAN L^−1^). Conversions were 99.0, 92.5, 90.9, and 99.0% for the anaerobic digestion, first denitrification, nitrification, and second denitrification, respectively. © 2005 American Institute of Chemical Engineers Environ Prog, 2005