Process stability in an anammox UASB reactor with individual and combined thiocyanate and hydraulic shocks

Abstract

Abstract The robustness of an anaerobic ammonium oxidation (anammox) process under individual and combined thiocyanate (SCN−) and hydraulic shocks was investigated. The nitrogen removal performance and stability of a process subjected to transient SCN− (300, 600 and 900 mg L−1), hydraulic shock (2-fold increase in flow rate) and the combined effects of SCN− and hydraulic shock were evaluated. The sensitivity index (SI) was used to characterize the impact of the SCN−, and the SI exhibited a rising trend with increases in shock strength. The higher SI of effluent was reached after exposure to SCN− shocks (900 mg L−1) for 3 h, and the reactor performance was stable at a relatively lower SCN− concentration (300 mg L−1) after exposure to SCN− shocks for 1.5 and 3 h. The shock effect was mainly related to the SCN− concentration rather than the shock time. The similar phenomenon also was found in the test of combined SCN− and hydraulic shocks. The reactor performance in hydraulic shock tests was robust, and the relative low SAA loss ratios (9.2% and 4.0%) were observed. The specific anammox activity and heme c in the shock period were adversely affected, with maximum loss rates of 42.6% and 22.7%, respectively. However, the extracellular polymeric substance content during the shock period increased in varying degrees and antagonized exogenous disturbances. The results for these different shocks suggested that instabilities in the anammox process were dependent on both time and the concentration intensity.