Kinetic response of perturbed marine nitrification systems.

These two nitrification steps are ac complished by microorganisms of the genera Nitrosomonas and Nitrobacter, re spectively, although at least one other ammonium-oxidizing bacterium, Nitrocys tis oceanus, has been identified in marine systems.1 Ammonium and nitrite ion are both intermediates in the normal ecological cycling of nitrogen, however.2 Nitrogenous discharges from population and industrial centers into streams and estuaries may lead to high local concentrations of am monium and nitrite ions. Because both of these ions are toxic to many species,3 the rate at which these chemicals in detrimental concentrations may be diluted or converted to a less toxic form is an im portant factor in the prevention of environ mental degradation and in the recovery process of polluted waters. In waste treatment facilities, these bene ficial chemical conversions are accom plished before the discharge of waste into the environment. In these facilities, cul tivation of bacteria on a solid carrier allows dense populations to develop. This method of bacterial cultivation may also serve as an important means of studying the metabolic activities of microbial popula tions because different environmental fac tors, which closely approximate natural conditions, may be imposed on the bac terial populations.4 The engineering designs for the mass cultivation of nitrifying bacteria for water treatment take many forms. These range from nearly continuous systems, such as activated sludge, in which microorganisms grow on solid suspended particles that are constantly being removed, to bed filters, such as the subgravel filter, in which the bacteria grow on an immobile gravel bed. The work reported in this paper uses the subgravel biological filter56 to study the batch conversion of ammonium chloride to nitrate ion by a mixed population of nitrifying bacteria. The batch bacterial cultivation process was selected over the continuous culture method because