Noncarbonaceous matter, such as ammonia, is produced during the hydrolysis of proteins. It is now known that a number of bacteria are capable of oxidizing ammonia to nitrite and subsequently to nitrate. The generalized reactions are as follows:
*Conversion of ammonia to nitrite (as typified by Nitrosomonas):
NH3 + 3/2O2 → HNO2 + H2O
*Conversion of nitrite to nitrate (as typified by Nitrobacter):
HNO2 + 1/2O2 → HNO3
*Overall conversion of ammonia to nitrate:
NH3 + 2O2 → HNO3 + H2O
The oxygen demand associated with the oxidation of ammonia to nitrate is called the nitrogenous biochemical oxygen demand (NBOD).
Because the reproductive rate of the nitrifying bacteria is slow, it normally takes from 6 to 10 days for them to reach significant numbers to exert a measurable oxygen demand. However, if a sufficient number of nitrifying bacteria is present initially, the interference caused by nitrification can be significant.
When nitrification occurs in the BOD test, erroneous interpretations of treatment operating date are possible. For example, assume the effluent BOD from a biological treatment process is 20 mg/L without nitrfication and 40 mg/L with nitrification. If the influent BOD to the treatment process is 200 mg/L, then the corresponding BOD removal efficiency would be reported as 90 adn 80 percent without and with nitrification, respectively. Thus, if nitrification is occurring but is not suspected, it might be concluded that the treatment process is not performing well, when in actuality it is performing quite well
NH3 + 3/2O2 → HNO2 + H2O
*Conversion of nitrite to nitrate (as typified by Nitrobacter):
HNO2 + 1/2O2 → HNO3
*Overall conversion of ammonia to nitrate:
NH3 + 2O2 → HNO3 + H2O
The oxygen demand associated with the oxidation of ammonia to nitrate is called the nitrogenous biochemical oxygen demand (NBOD).
Because the reproductive rate of the nitrifying bacteria is slow, it normally takes from 6 to 10 days for them to reach significant numbers to exert a measurable oxygen demand. However, if a sufficient number of nitrifying bacteria is present initially, the interference caused by nitrification can be significant.
When nitrification occurs in the BOD test, erroneous interpretations of treatment operating date are possible. For example, assume the effluent BOD from a biological treatment process is 20 mg/L without nitrfication and 40 mg/L with nitrification. If the influent BOD to the treatment process is 200 mg/L, then the corresponding BOD removal efficiency would be reported as 90 adn 80 percent without and with nitrification, respectively. Thus, if nitrification is occurring but is not suspected, it might be concluded that the treatment process is not performing well, when in actuality it is performing quite well
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