Occurrence of anammox bacteria in a traditional full-scale wastewater treatment plant and successful inoculation for new establishment

A new biochemical pathway for reactive nitrogen removal from wastewater has been recognized as anaerobic ammonium oxidation (anammox) since its first discovery in the 1990's. Over the past decades, many studies have been focused on laboratory–scale reactors for enrichment of the anammox bacteria for potential applications on an industrial scale. The research reported here investigated the occurrence, community diversity and abundance of anammox bacteria observed for the first time in a full-scale wastewater treatment plant (Plant N) in Taiwan and then successful inoculation of the initially enriched anammox bacteria granules into another full-scale wastewater treatment plant (Plant S). The community composition was similar in both plants, showing similarity in the existence of Ca. Brocadia as the dominating genus of anammox bacteria. Inoculation of the existing sludge containing active anammox bacteria into other plant resulted in an effective establishment of anammox bacteria in as little as 6 months in a full-scale wastewater treatment plant. The abundance of anammox bacteria was significantly different between these two plants with the newly inoculated one containing 2 to 100 times higher gene copies of the anammox bacteria than Plant N serving as an inoculum. In addition, differences were also observed between the sludge and immobilizing carrier materials, which supported the colonization of anammox bacteria and retained them to reach to a much high density in the wastewater treatment system. Based on qPCR results and TEM observation, anammox bacteria in those treatment plants were active and contributed to inorganic N removal. The inoculation study showed that anammox process can be activated without re-design of the system and inoculation was successful to activate anammox process effectively to achieve the inorganic N removal in conventional wastewater treatment plants.