Comparison of the characteristics of anammox granules of different sizes

The physical properties and performance of anaerobic ammonium oxidation (anammox) granules of different sizes (0.5 similar to 1.0 mm, 1.0 similar to 1.5 mm, and above 1.5 mm) have been investigated. The values of the settling velocity increased with increasing size of the granules. There was no significant difference in metal contents among granules of different sizes, in which calcium, magnesium and iron were the predominant ions. Different start-up periods showed that larger granules were better able to resist adverse impacts and their activities could quickly be recovered. The specific activities of granules of different sizes were 0.55, 0.62, and 0.52 g N/ (g/VSS/day), respectively, which implied the activity of 1.0 similar to 1.5 mm granules was the highest. Larger anammox granules were better able to resist temperature shock and nitrogenous shock loading. However, larger granules were also shown to contain bigger gas tunnels and interior hollows, which decrease the stability of anammox granules. With the comprehensive consideration of bacteria activity, granule stability and shock resistance capacity, the properties of granules within the size range of 1.0 similar to 1.5 mm were found superior to others in this study.