Nitrification substrate concentration

Both steps are influenced by dissolved oxygen and the corresponding substrate concentration. The nitrification as a wastewater treatment process benefits greatly from biomass retention, owing to the relatively slow growth rates of the nitrifiers. 

Based partly on anecdotal evidence from culture work, observations in waste water treatment systems with very high particulate loads, the tendency of nitrifiers to grow in aggregates in bioreactor biofilms, and the prevalence of small particles in natural waters, it has been suggested that nitrification occurs mainly on particles and is mediated by particle-attached bacteria (Hagopian and Riley, 1998). Nitrifier sequences were found both associated with particles and in the bulk seawater phase in the northwestern Mediterranean Sea. In the clone library of 16S rRNA sequences, Nitrosomonas-like sequences were preferentially associated with particles and Nitrosospira-]ike sequences dominated in clones from the planktonic phase (PhiUips et al, 1999). This may indicate niche preference by the different groups on the basis of attachment to particles, substrate concentration or other physical/... 

In cultures of nitrifying bacteria, the dependence of nitrification rate on substrate concentration is first order at low concentrations (10—100 pM these... 

Nitrification is affected by environmental factors such as temperature, pH, substrates concentrations (O2, NH3, and N02"), and organic matter (Bernet Sperandio, 2009). Such parameters can cause an effect on both the anabolic (biosynthetic process) and catabolic (respiratory process) processes. 

Several comprehensive studies of N assimilation in the North Pacific trades biome have been conducted over the past several decades. Gundersen and his colleagues (1974, 1976) were the first to estabhsh N2 fixation as a source of new N to the open ocean ecosystem, and concluded that it was a more important source of fixed N than wet deposition from the atmosphere (see Case Studies section). They also made measurements of the rates of nitrification, denitrification and assimilatory nitrate-reduction. These latter experiments involved the addition of fairly high concentrations of exogenous N substrates (NH4 , N02, NOa ) and extended incubations (days to months), so the rates reported must be viewed as potential rates at best. 

Activated sludge is a mixed culture of many organisms. Chromium(VI) concentrations of 0.5 mg caused significant inhibition of the nitrification process but did not materially affect the organic substrate removal illustrating the differences in sensitivity of types of microorganisms to heavy metal loads (Vankova et al. 1999 Stasinakis et al. 2003). 

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