The trend of the development for Anammox
Society of Environmental Conservation Engineering
Nitrogen removal in wastewater treatment is a biological treatment based primarily on the fundamental principle of nitrification-denitrification.
The nitrification-denitrification process is the biological oxidation of nitrogen compounds including ammonium into nitrites and nitrates and the BOD (biochemical oxygen demand) compounds are reduced to nitrogen gasification. However, when the nitrification-denitrification process is performed, the addition of BOD to denitrify may be required depending on the balance between BOD concentration and nitrogen concentration. Methanol is often used for the extra BOD. However, this electron donor can raise operating costs for nitrogen elimination.
In contrast to this, the development of the anaerobic ammonium oxidation (anammox) process has recently been advanced. The Anammox process, which was newly discovered in Holland in the 1990s, is the conversion reaction of nitrogen. The Anammox process is very close to practical application due to recent progress. Not only has the introduction of the Anammox process progressed overseas, but its introduction is being considered in Japan as well. Anammox is a new biological process for nitrogen gasification of nitrous acid and ammonium with no requirement for an extra electron donor like methanol. In addition, Anammox has various characteristics: 1) feasible reduction in aeration power because of no nitric acid oxidation (energy saving); 2) a shorter residence time and space-saving properties; 3) late proliferation rate owing to less excess sludge volume.
The Anammox process is particularly suitable to sewage with low BOD/N ratio. Thus, various effluents can be applied to the process. Among the various effluents, in particular, the development of the dehydration filtrate of methane fermentation (sludge digestion) for sewage plants is energetically being advanced. In methane fermentation, digestion gas is recovered from organic matter. The filtrate, however, has a negative effect on water quality, such as lower organic components and higher nitrogen concentration. The filtrate of methane fermentation is sent to the wastewater treatment plants. The increase in nitrogen load through this process is likely to affect the treatment. The application of Anammox to the filtrate allows the establishment of a compact treatment system, which also saves energy, with no load to the conventional sewage treatment. Japan Sewage Works Agency not only collaborates with private corporations, but also evaluates and summarizes the results of “Nitrogen Removal Technology Using Anammox Reaction”. In addition to sewage treatment, the application to other types of sewage, which require an inexpensive treatment, is examined and good results are expected in various fields.
Anammox has various processes that depend on biological immobilization methods. Each process has its own property. Thus, the technological developments of Anammox are as follows: organism immobilization method to lower aeration power and chemical additive amount; a method to take advantage of granular sludge as pretreatment required to stabilize the Anammox process; the 2-reactor Anammox process using attachment media, which can keep running costs low.