Individual and combined effects of substrate, heavy metal and hydraulic shocks on an anammox system

• Anammox performance under different transient stresses was investigated.
• The reactor exhibited different responses to different shocks.
• Specific anammox activity under various shocks was monitored.
• Effects of different shocks were compared.
• System stability and recovery under the transient shock loads were discussed.

Factors such as substrate fluctuations, increased inflow rates and heavy metal presence exert individual and combined effects on anaerobic ammonium oxidation (anammox) systems in real applications; therefore, the performance stability and resilience of such systems were investigated in an upflow anaerobic sludge blanket (UASB) reactor. A 1.5- and 2.0-fold increase in substrate concentration, 2/3- and 1/2-fold decrease in hydraulic retention time (HRT), and 5.95 and 12.9 mg L−1 transient Cu(II) shock were applied either individually or in combination for durations of 2 and 4 h. The nitrogen removal efficiency of the system varied considerably when all of the shocks were applied. The magnitude of the effect of the combined shock loads on the system decreased in the following order: (substrate shock + hydraulic shock) > (substrate shock + heavy metal shock) > (hydraulic shock + heavy metal shock). The specific anammox activity (SAA) was adversely affected by the individual substrate and hydraulic shocks, with maximum SAA loss rates of 51.9% and 63.6%, respectively. The SAA was inhibited by the substrate and hydraulic shock combination, whereas it was not strongly affected by the heavy metal and hydraulic shock combination. Thus, the system could withstand certain shock intensities and exhibited considerable resilience.