Anammox in the mainstream – what is the problem?

When Swedish wastewater treatment plants were rebuilt to include enhanced nitrogen removal, anaerobic ammoniumoxidation (anammox) was far from being a mature technology. During the 2000s, the process has beenintroduced 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 pilotstudies are ongoing or will be started shortly. Difficulties to introduce anammox in the mainstream are stillmany. Anammox is favored by a separate treatment step for COD removal, by outcompeting nitrite oxidiserswith the help of low oxygen concentrations, intermittent aeration and competition with anammox bacteria fornitrite, and by having a long solid retention time. Moving Bed Biofilm Reactor (MBBR), granular reactors, andactivated sludge with hydrocyclones to recirculate anammox granules in the excess sludge, are the most promisingsystems. Sj\uf6lunda wastewater treatment plant in Malm\uf6, Sweden, has a separate step for COD removal anddenitrification is based on an MBBR for post-denitrification with methanol. VA SYD is now starting a pilotproject to study the nitritation-anammox process in the mainstream in an MBBR with the aim of achieving arobust process, and to be able to use the already existing MBBRs for anammox in the mainstream