IN addition to the free ammonia concentration and changes in environmental parameters (temperature and Ph)), adaptation of the microorganisms to ammonia is also related to ammonia inhibition ( Table 2). In an unadapted process, ammonia inhibition occurred at 0.08-0.15 gN/l free ammonia concentration ( Braun et al. 1981; de Baere et al. 1984; IKbal et al. 2003), while an adapted inhibition during