Anammox is a method used to clean wastewater by removing nitrogen. This process uses bacteria called anammox bacteria. These bacteria do not need organic carbon to survive. Instead, they use ammonium and nitrite to create dinitrogen gas. Wastewater treatment plants are starting to use anammox technology to improve the removal of ammonia and nitrogen from water.
Morphology and physiology
Anammox bacteria are found in wastewater treatment plants, lakes, areas with very low oxygen, and coastal sediments. These bacteria depend on temperature for growth, needing temperatures between 30°C and 40°C. Their growth is also affected by pH, with the best growth occurring when pH is between 6.5 and 8.3. Anammox bacteria have a special membrane called an anammoxosome that makes up 50% to 70% of the cell. Their outer membrane is covered with ladderane lipids.
Chemical process
Anammox bacteria need ammonia and nitrite to carry out their metabolism. Nitrate and nitrite are created by microorganisms in wastewater treatment plants during sewage processing. Ammonia monooxygenase changes ammonia in wastewater into nitrite during nitrification.
Anammox bacteria, which belong to the Planctomycetota phylum, carry out anaerobic ammonium oxidation reactions. The anammoxosome is a part inside anammox bacteria where these reactions happen. A proton gradient forms across the anammoxosome membrane, beginning a catabolic reaction. Nitrate is changed into nitric oxide with the help of nitrate reductase, the first step in the process. Anammox converts ammonium into nitrite, which is then reduced to hydroxylamine. Hydroxylamine and ammonia combine to create hydrazine, which is then turned into nitrogen gas.
Impacts on wastewater treatment
Wastewater is usually a mixture of solid and liquid materials. The makeup of wastewater depends on how it was created. "Wastewater" can include water from homes, water from industries, or water that flows over land surfaces. Treating wastewater to improve sanitation is a major challenge in developing countries because untreated wastewater can pollute drinking water.
Anammox bacteria are used in treatment facilities to help change sewage wastewater into sludge ash, which is later used as fertilizer for farming. Sludge ash can be used as fertilizer because it contains high amounts of phosphorus and other nutrients needed for plants to grow. During wastewater treatment, struvite can form as a crystal. Struvite is made of magnesium, ammonium, and phosphate. Adding magnesium to wastewater that already has ammonium and phosphate creates a 1:1:1 mole ratio, allowing these three elements to combine and form struvite. Struvite crystals contain nutrients important for plant growth that are easy to use and transport. This process also helps recover nitrogen and phosphorus from wastewater, which improves the quality of surface water because these elements are major causes of eutrophication. If eutrophication occurs, an anammox cycle can happen in areas without oxygen and with high levels of nitrite and ammonia. These two compounds are needed to start the anammox cycle and are found in wastewater in large amounts. Anammox bacteria can help remove excess nitrite and ammonia from wastewater.