Biological Methods for Ammonia Nitrogen Removal

Elevated ammonia nitrogen levels in water bodies pose significant risks to aquatic life and human health, making its removal a critical environmental priority. Biological methods have emerged as the most sustainable and cost-effective approaches, leveraging natural microbial and plant processes to convert or assimilate ammonia without the need for harsh chemicals. 

These methods primarily exploit the nitrogen cycle, particularly nitrification, denitrification, and anammox, along with plant-based uptake systems.

The most widely applied biological method is the conventional nitrification-denitrification process. In this two-stage system, ammonia-oxidizing bacteria (such as Nitrosomonas) first convert ammonia to nitrite, followed by nitrite-oxidizing bacteria (such as Nitrobacter) that further oxidize nitrite to nitrate under aerobic conditions. Subsequently, facultative anaerobic bacteria (such as Pseudomonas) reduce nitrate to nitrogen gas, which escapes harmlessly into the atmosphere. 

This approach is commonly implemented in activated sludge systems, sequencing batch reactors, and biofilters, making it the backbone of municipal and industrial wastewater treatment plants. A more energy-efficient alternative is the anaerobic ammonium oxidation (anammox) process, where specialized bacteria directly convert ammonia and nitrite to nitrogen gas under anoxic conditions. Anammox significantly reduces aeration costs and sludge production, making it particularly attractive for treating high-strength ammonia wastewaters such as digester supernatant or landfill leachate.

Beyond engineered systems, phytoremediation offers a passive yet effective biological solution. Constructed wetlands and floating treatment wetlands utilize aquatic plants like water hyacinth, duckweed, and reeds to assimilate ammonia directly for growth. 

These plants also provide attachment surfaces for nitrifying and denitrifying biofilms, creating a synergistic rhizosphere effect that enhances nitrogen removal. Additionally, algae-based systems have gained attention, where microalgae such as Chlorella and Scenedesmus uptake ammonia as a nutrient source, simultaneously producing oxygen that supports bacterial nitrification. These green technologies are particularly suitable for polishing treated effluent, managing agricultural runoff, or restoring natural water bodies with moderate ammonia levels.