Insight into the influence of magnesium on the properties of heterotrophic denitrifying granules

• The effects of Mg2+ on the properties of denitrifying sludge were investigated.
• The results were analyzed using statistical methods.
• Sludge morphology during granulation was observed.

This paper examined the influence of magnesium on denitrifying sludge. Two up-flow anaerobic sludge bed (UASB) reactors were used in the study. R1 was continuously supplied with 50 mg L−1 of divalent magnesium in the wastewater and R0 was used as a control without magnesium. On the 258th day, the sludge properties in R0 and R1 were analyzed when the nitrogen loading rates were both 36.0 kgN m−3 d−1 and the nitrogen removal rates of R0 and R1 were 33.8 and 34.6 kgN m−3 d−1, respectively. The diameters of R0 and R1 were 0.95and1.35 mm, settling velocity (74.5 ± 20.8 and102.0 ± 22.6 m h−1), extracellular polymeric substance (60.8 ± 2.1 and76.0 ± 2.7 mg g−1VSS)and specific denitrifying activity (794.4 ± 9.6 and825.6 ± 4.9 mgN d−1) were also compared. These results addressed that the addition of magnesium to denitrifying reactor is an effective alternative to enhance sludge properties.