Nitrification/De-Nitrification

• Nitrification/De-Nitrification

Nitrification is traditionally defined as a process in which bacteria (Nitrosomonas and Nitrobacter) convert ammonia in wastewater into Nitrate. This is a multi step process.

First the microorganisms known as Nitrosomonas convert the ammonium into nitrite, then the microorganisms know as Nitrobacter convert the Nitrite into Nitrate.

This process consumes a large amount of oxygen while reducing alkalinity as well

1. NH3 + Nitrosomonas Bacteria + O2 + Alkalinity = NO2 (Nitrite)

2. NO2 + Nitrobacter Bacteria + O2 + Alkalinity = NO3 (Nitrate)

Nitrification is a important process in wastewater treatment. Many Ammonia can be quite harmful if discharged. Examples of the?impacts of ammonia?in a receiving stream include,

• Creates dissolved oxygen sag in receiving stream
• Toxic to fish and other aquatic life
• Nutrient input (when oxidized).

The nitrification process is an autotrophic purely aerobic process that consumes a large amount of oxygen. For every pound of ammonia oxidized, 4.6 pounds of oxygen is consumed. To put this in perspective, for every pound of BOD removed, there is approximately 1 pound of oxygen consumed. It is highly recommended for facilities that nitrify to maintain a DO reading of at least 2.0 mg/l in the nitrification zone. if you are required to nitrify and you have course bubble diffusion, you should seriously consider the use of fine bubble diffusion for this process. There could be significant energy savings as a result.

Nitrifying bactera are slow growing and sensitive to temperature as well. MCRT's will need to increase when the temperature decreases to maintain nitrification. Very little nitrification takes place below about 5 degrees C. Additionally, you need to significantly reduce soluble BOD (typically down to 20-30 mg/l) before nitrification can take place. Many facilities today are facing total nitrogen limits in their permits

• Factors Impacting Nitrification
• pH of 7.0 to 8.0 optimum range for nitrification.
• Approximately 7.2 pounds of alkalinity is consumed for every pound of ammonia oxidized?(Alkalinity as CaCO3)
• Do Not allow alkalinity to drop below 50 mg/l at any point in the process.

• About Nitrogen

Nitrate in Drinking water has been linked to “methemoglobinemia”, that can be a fatal blood disorder affecting infants also known as “blue baby syndrome”.

BASICS OF MICROBIAL GROWTH

The majority of bacteria found in the activated sludge processes are facultative, heterotrophic soil microorganisms that can live either with or without elemental oxygen (DO). They are the main force in removing cBOD via the oxidation process, and can respire aerobically using dissolved oxygen or anaerobically using nitrate (anoxic), however, if elemental oxygen is available it is more efficient and the organisms will consume the dissolved oxygen. Therefore, most heterotrophs use aerobic pathways if dissolved oxygen is available. For the most part, nitrate is used for respiration only after oxygen is depleted. Since microorganisms contained in the activated sludge mixed liquor are primarily of soil origin, it also contains smaller numbers of autotrophic bacteria which are given energy by oxidizing inorganic compounds such as ammonia. Some of these microorganisms , such as Nitrosomonas and Nitrobacter, are slow growing bacteria which will convert ammonia to nitrate.

The following are the basic aerobic and anaerobic respiration pathways:

In summary, the activated sludge process contains?heterotrophic organisms that respire through aerobic (Dissolved Oxygen)or anaerobic pathways (Nitrate). Under Ideal conditions, these organisms can double their population every hour.

The activated sludge process also contains a smaller number of?autotrophic?organisms. These organisms oxidize ammonia (convert it to nitrate). These are slow growing organisms that under ideal conditions may double their population every 24 hours. These?autotrophic?organisms are purely aerobic and require dissolved oxygen.