POPULATION-DYNAMICS AND NITRITE - BUILDUP IN ACTIVATED-SLUDGE AND BIOFILM PROCESSES FOR NITROGEN REMOVAL

This article has the objective of showing the cause effect relationshi p between the dynamics of growth of autotrophic populations involved i n nitrification and the uncontrolled accumulation of nitrite ions. Thi s accumulation results in a disequilibrium in number or viability betw een the genera Nitrosomonas and Nicrobacter. This disequilibrium can b e imposed, for example, by an inhibition of the activity of the genus Nitrobacter linked to the presence of free ammonia in the environment. The threshold of inhibition and the resultant degree of accumulation of nitrite depend both on the history of the sludge utilised as inocul um (mixed autotrophic population or enriched in one of two sources) an d on the hydraulic regime of the reactor (completely mixed reactor for the activated sludges and piston reactor for the fixed cultures). The se results enable us to better understand the behaviour of a nitrifica tion reactor and to propose solutions either to avoid the accumulation of nitrites or to intensify this accumulation with the goal of propos ing a new process of nitritation-denitritation via the nitrites route (nitrates shunt).