Anaerobic ammonium oxidation: from laboratory to full-scale application

Abstract

From discovery in the early 1990s to completion of full-scale anammox reactor, it took almost two decades to uncover the secret veil of anammox bacteria. There were three milestones during the commercialization of anammox: the development of the first enrichment culture medium, the completion of the first commercial anammox reactor, and the fast start-up of full-scale anammox plant. Till now, the culture of anammox bacteria experienced a big progress through two general strategies: (a) to start up a reactor from scratch and (b) to seed the reactor with enriched anammox sludge. The first full-scale anammox reactor took 3.5 years to realize full operation using the first approach due to several reasons besides the lack of anammox sludge. On the other hand, the first Asian anammox reactor started up in two months, thanks to the availability of anammox seed. Along with the implementation of anammox plants, anammox eventually becomes the priority choice for ammonium wastewater treatment.

Figure 1

The biological N cycle (based in part on Arrigo [13]). DNRA, dissimilatory nitrate reduction to ammonium.

Figure 2

The specific red color of anammox bacteria (a), the typical irregular shapes of anammox bacteria displayed by scanning electron microscopy (b), and transmission electron microscopy images (c).

Figure 3

Possible biochemical pathway and cellular localization of the enzyme systems involved in anammox reaction. Figure modified, with permission, from FEMS Microbiology Reviews [26] and Process Biochemistry [2].

Figure 4

Hypothetical metabolic pathways and reversed electron transport in the anammoxosome. (a) Anammox catabolism that uses nitrite as the electron acceptor for the creation of a proton motive force over the anammoxosomal membrane. (b) Proton motive force-driven reversed electron transport combines central catabolism with nitrate reductase (NAR) to generate ferredoxin for carbon dioxide reduction in the acetyl-CoA pathway. HAO, hydrazine oxidoreductase; HD, hydrazine dehydrogenase; HH, hydrazine hydrolase; NIR, nitrite oxidoreductase; Q, quinine. Light blue diamonds, cytochromes; blue arrows, reductions; pink arrows, oxidations. Figure modified, with permission, from Nature [29].

Figure 5

Schematic diagram of the anammox nonwoven membrane reactor (ANMR) [40, 41].

Figure 6

(a) Transmission electron micrograph showing dormant cells in the seed granule (bar = 2 μm). (b) Transmission electron micrograph showing the anammox bacteria in the interior of granules (bar = 2 μm).