Nitrifying bacteria in wastewater reservoirs

Area of Science:

• Environmental Microbiology
• Wastewater Treatment
• Ammonia Oxidation

Background:

• Deep wastewater reservoirs store effluents for irrigation, presenting challenges with high ammonia concentrations and anoxia.
• Ammonia toxicity impacts photosynthetic microorganisms and promotes anoxic conditions in stored wastewater.

Purpose of the Study:

• To investigate the population dynamics and nitrification rates of bacteria in wastewater reservoirs.
• To compare nitrification in situ within reservoirs versus controlled laboratory conditions.

Main Methods:

• Studied two wastewater reservoirs with varying organic loads and oxygenation levels.
• Employed serial dilutions and microscopy with specific antibodies for bacterial enumeration.
• Conducted laboratory experiments under controlled oxygen concentrations.

Main Results:

• Bacterial counts by dilution and microscopy differed by less than one order of magnitude.
• Optimal oxygen for ammonia-oxidizer growth was ~0.2 mg/L; significant nitrification occurred at 0.05 mg/L.
• Viable populations of Nitrosomonas and Nitrobacter survived in anaerobic reservoir environments, unlike in laboratory media.

Conclusions:

• Wastewater reservoirs sustain viable, though not actively nitrifying, populations of key nitrifying bacteria in anaerobic zones.
• In situ nitrification rates in reservoirs are 10-100 times slower than in laboratory conditions.
• Factors causing in situ nitrification inhibition remain unidentified.