: The addition of exogenous to poultry manure and synthetic NH 4Cl medium was used to study the e †ect of ammonia-nitrogen on the activity and composition of a methanogenic consortium. Results indicated that the production of biogas and methane was not a †ected by the variation in con-NH 4 Cl centration within the range 2È10 g dm~3 (0É5È2É6 g dm~3). At higher N-NH 4 values of ammonium (10È30 g dm~3 or 2È8 g dm~3) a signiÐcant N-NH 4 decline in both parameters (by 50È60% for biogas and 80È90% for methane) was observed. A signiÐcant decrease in the numbers of bacteria of all physiological groups (especially proteolytic and methanogenic) was observed when more than 30 g dm~3 (7É8 g dm~3) was added to the fermentation medium. NH 4 Cl N-NH 4 The addition of 10% (w/v) of powdered phosphorite ore enhanced the production of biogas and methane at concentrations up to 30 g dm~3, and NH 4 Cl also changed the composition of the methanogenic consortium. A partial recovery in the numbers of proteolytic and methanogenic bacteria coupled with the decrease in the density of sulphate-reducers was observed. High concentrations (more than 50 g dm~3) of seemed to cause irreversible inhibition of NH 4 Cl methanogenesis which could not be eliminated by the addition of phosphorites.

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