Enhanced anaerobic treatment of CSTR-digested effluent from chicken manure: The effect of ammonia inhibition

The effect of ammonia inhibition was evaluated during the enhanced anaerobic treatment of digested effluent from a 700 m(3) chicken-manure continuous stirred tank reactor (CSTR). A 12.3 L internal circulation (IC) reactor inoculated with an anaerobic granular sludge and operated at 35 +/- 1 degrees C was employed for the investigation. With a corresponding organic loading rate of 1.5-3.5 kg-COD/m(3) d over a hydraulic retention time of 1.5 d, a maximum volumetric biogas production rate of 1.2 m(3)/m(3) d and TCOD (total COD) removal efficiency ranging from 70% to 80% was achieved. However, the continual increase in the influent TAN content led to ammonia inhibition in the methanogenesis system. The SCOD/TAN (soluble COD/total ammonia nitrogen) ratio was presented to be the key controlling factor for the anaerobic treatment of semi-digested chicken manure, and further validation through shock loading and ammonia inhibition experiments was conducted. The threshold value of the SCOD/TAN ratio was determined to be 2.4 (corresponding to a TAN of 1250 mg/L) at an influent pH of 8.5-9. (C) 2011 Elsevier Ltd. All rights reserved.