Anammox in the mainstream – what is the problem?

Magazine article, 2012

When Swedish wastewater treatment plants were rebuilt to include enhanced nitrogen removal, anaerobic ammonium oxidation (anammox) was far from being a mature technology. During the 2000s, the process has been introduced into sludge liquor treatment worldwide. The step to introduce anammox in the mainstream is decreasing, but lab- and pilot-scale studies on real municipal wastewater are yet lacking. However, several pilot studies are ongoing or will be started shortly. Difficulties to introduce anammox in the mainstream are still many. Anammox is favored by a separate treatment step for COD removal, by outcompeting nitrite oxidisers with the help of low oxygen concentrations, intermittent aeration and competition with anammox bacteria for nitrite, and by having a long solid retention time. Moving Bed Biofilm Reactor (MBBR), granular reactors, and activated sludge with hydrocyclones to recirculate anammox granules in the excess sludge, are the most promising systems. Sjölunda wastewater treatment plant in Malmö, Sweden, has a separate step for COD removal and denitrification is based on an MBBR for post-denitrification with methanol. VA SYD is now starting a pilot project to study the nitritation-anammox process in the mainstream in an MBBR with the aim of achieving a robust process, and to be able to use the already existing MBBRs for anammox in the mainstream.