Denitrification retention time

Both these reactions occur in the aeration tank of the activated sludge plant and are favored in general by long retention time, low organic loading, large amounts of suspended solids, and high temperatures. The subsequent process, denitrification, removes nitrate from wastewater and occurs in the anaerobic condition (reaction (3))... 

Denitrification is typically the dominant pathway of nitrate ranoval in wetlands. Thus, the nitrate reduction rates presented in Tables 8.10 and 8.11 represent denitrification rates. Rates are presented on areal basis (Table 8.10) and as first-order rate constants (Table 8.11). Nitrate reduction rates reported for constructed wetlands are in the range of 3-1,020 mg N m day In most wetlands, denitrification rates are limited not only by nitrate concentration but also by hydraulic retention time (or contact time of nitrate with anaerobic zones) and diffusion/mass flow of nitrate from aerobic zones to anaerobic sites (Martin and Reddy, 1997). Denitrification rates are usually higher in soils receiving steady loading of nitrate than in soils receiving low or negligible nitrate levels (Cooper, 1990 Gale et al., 1993). 

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