Anammox deammonification is a biological treatment process that uses a microbial process known as anammox to convert ammonia to nitrogen gas. The process can be an important step in removing nitrogen from wastewater.
The name ‘anammox’ is an abbreviation for anaerobic ammonium oxidation, wherein bacteria, often known as anammox bacteria, convert nitrite and ammonium into nitrogen.
Anammox deammonification is sometimes referred to as simply ‘deammonification.’ The anammox process is involved in only one of the two steps necessary to convert ammonia to nitrogen gas. Deammonification is achieved through two biological processes: partial nitritation and denitritation. Because of this, the entire process can also sometimes be referred to as ‘partial-nitritation/anammox.’
Under partial nitritation, aerobic oxidation turns about half of the ammonia (NH4) to nitrite (NO2). The bacteria performing this oxidation is called autotrophic aerobic ammonia oxidizing bacteria (AerAOB).
Under denitritation, the anammox reaction occurs. In this step, anammox bacteria oxidizes ammonia into nitrogen gas (N2) and nitrate (NO3), using the nitrite as an electron acceptor.
Anammox deammonification is applied as part of onsite biological treatment. The process can introduce anammox bacteria to wastewater through suspended growth or attached growth systems.
Watch the video on anammox deammonification with Veolia:
Watch a video on anammox deammonification here.
Brief history anammox bacteria
The existence of anammox bacteria is a relatively new discovery for science: the first description of anammox bacteria occurred in the mid-1990s. Since then, anammox bacteria has been found in countless environments, particularly in areas of water with low oxygen. Wastewater treatment plants have observed anammox processes occurring naturally worldwide.
The wastewater sector was quick to employ this anaerobic ammonium oxidation to treatment processes. In 2002, the first full-scale anammox reactor began operation at a sludge treatment plant in the Netherlands. In 2019, the Water Research Foundation (WRF) estimated that were about 14 full-scale deammonification processes in the U.S.
Benefits of anammox deammonification
Nitrogen removal is an essential part of wastewater treatment. Effluent with a high nitrogen load can cause eutrophication, algal blooms, and dangers to drinking water safety.
Anammox deammonification can best be compared to a similar, more conventional process for nitrogen removal such as nitrification/denitrification.
The ability of anammox deammonification to directly turn nitrate into nitrogen gas, and to do so anaerobically, offers process advantages over those traditional counterparts:
- It requires fewer dedicated steps than nitrification/denitrification.
- It does not need to use organic carbon.
- It can consume carbon dioxide, rather than release it.
- It consumes less oxygen and produces less biomass.
- It only needs approximately 60% of the aeration energy required for nitrification/denitrification.
Downsides of the treatment method
However, anammox deammonification also comes with drawbacks:
- Anammox bacteria is slow to grow, leading to long start-up periods for the process’s sludge. The doubling time may be 10 to 14 days. The first-generation process had a start-up period of two years — contemporary anammox-seeded sludge can see a start-up period of 50 days.
- Routine operations like maintenance can lead to a loss of sludge. Paired with the slow growth, this can lead to long recovery times.
- Researchers have only described 10 species of anammox bacteria — a small faction of the species that likely exist.
- Researched species of anammox bacteria generally thrive in alkaline wastewater, requiring the addition of an alkaline substance.
- Because full-scale anammox deammonification is only two decades old, with ongoing research behind the processes and bacteria, the market for deammonification solutions is not yet fully matured.
Conclusion
Anammox deammonification, though a very new practice, offers advantages over traditional nitrification/denitrifcation. Deammonification requires less energy and produces fewer emissions, making it an attractive solution for reducing emissions in the wastewater sector.
The most significant problems for anammox deammonification are the immaturity of the practice and the slow growth rate of anammox bacteria.
