Wastewater Management Fact Sheet
INTRODUCTION
Discharge permits for treated wastewater from
publicly owned treatmentworks (POTWs) often
include effluent limitations for nutrients. Total
maximum daily loads (TMDLs) for nutrients are
being developed for many waterbodies
throughout the United States. TMDLs and other
water quality-drivers have resulted in POTWs
having to comply with more stringent effluent
limitations for parameters such as total nitrogen
Untreated domestic wastewater contains
ammonia. Nitrification is a biological process
that converts ammonia to nitrite and nitrite to
nitrate. If standards require that the resulting
nitrate be removed, one treatment alternative is
the process of denitrification, in which nitrate is
reduced to nitrogen gas. One treatment system
used for denitrifying wastewater effluent is the
denitrifying filter. In addition to the reduction of
total nitrogen, this treatment process removes
suspended solids from the effluent.
NITRIFICATION/DENITRIFICATION
Nitrificationis a microbial process by which
ammonia is sequentially oxidized to nitrite and
then to nitrate. The nitrification process is
accomplished primarily by two groups of
autotrophic nitrifying bacteria that can build
organic molecules by using energy obtained
from inorganic sources––in this case, ammonia
or nitrite.
In the first step of nitrification, ammonia-oxidizing bacteria oxidize ammonia to nitrite
according to equation (1):
NH3+ O2 ÆNO2
–
+ 3H
+
+ 2e
–
(1)
Nitrosomonas is the most frequently identified
genus associated with this step, although other
genera, including Nitrosococcus and
Nitrosospira, may be involved. The subgenera
Nitrosolobus and Nitrosovibrio can also
autotrophically oxidize ammonia.