The aim of this section and the following sections is to consider the number of environmental factors affecting the rate of growth and nitrification of a nitrifying biomass. A combined kinetic expression is proposed which accounts for the effect of ammonia concentration, temperature, pH, organic content, and dissolved oxygen concentration.
At several points, references are made to data obtained from various types of nitrification processes. One distinction that needs to be clearly understood in this Chapter is the difference between combined carbon oxidation-nitrification processes and the separate stage nitrification process (also called a tertiary nitrifying treatment process). The combined carbon oxidation-nitrification processes oxidize a high proportion of influent organics relative to the ammonia nitrogen content. This causes relatively low populations of nitrifiers to be present in the treatment plant relative to oxidizers of the total bacterial biomass.
Separate stage nitrification systems, on the other hand, have a relatively low organic load, relative to the ammonia load. As a result, higher proportions of nitrifiers are obtained.
A nitrifying activity test was proposed by Tomlinson et al. (1966) and later by Painter and Loveless (1981). The test is able to determine the activity of sludge to oxidize ammonia and ii is therefore suitable to determine the kinetics of the nitrification in activated sludge.
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