Inhibition and recovery of Anammox biomass subjected to short-term exposure of Cd, Ag, Hg and Pb

• The order of the inhibitory effect of 4 heavy metals was determined as Cd > Ag > Hg > Pb.
• The accumulation of heavy metals could cause deterioration in crude HDH enzyme activity.
• Cd and Hg could exert sustained toxicity on Anammox biomass.
• Mal-effects of Ag and Pb could resume to a large extent after removing these two metals within 96 h.

This study investigated the inhibitory effects of Cd, Ag, Hg and Pb on Anammox biomass by batch experiments. Inhibition effects and recovery performance were monitored in sequence over 24 h and 72 h experimental runs. The IC50 (the 50% inhibitory concentration of nitrogen removal rate) values were calculated as follows: 11.16 ± 0.42 mg/L for Cd; 11.52 ± 0.49 mg/L for Ag; 60.35 ± 2.47 mg/L for Hg. Pb caused only 7.19% decrease on nitrogen removal rate (NRR) even at a dose of 40 mg/L. Hence, the order of the inhibitory effect was determined as Cd > Ag > Hg > Pb. Furthermore, the crude enzyme (hydrazine dehydrogenase) activity and heme c concentration were also depressed under heavy metals exposure. Among four metals, Cd and Hg could exert sustained toxicity on Anammox biomass, but mal-effects of Ag and Pb could resume to a large extent after removing these two metals within 96 h.