Roles of EDTA washing and Ca2+ regulation on the restoration of anammox granules inhibited by copper(II)

We investigated the feasibility of using ethylene diamine tetraacetic acid (EDTA) washing followed by Ca2+ enhancement for the recovery of anammox reactors inhibited by Cu(II). Kinetic experiments and batch activity assays were employed to determine the optimal concentration of EDTA and washing time; and the performance and physiological dynamics were tracked by continuous-flow monitoring to evaluate the long-term effects. The two-step desorption process revealed that the Cu in anammox granules was primarily introduced via adsorption (approximately, 80.5%), and the portion of Cu in the dispersible layer was predominant (accounting for 71.1%). Afterwards, the Cu internalized in the cells (approximately, 14.7%) could diffuse out of the cells and be gradually washed out of the reactor over the next 20 days. The Ca2+ addition that followed led to an accelerated nitrogen removal rate recovery slope (0.1491 kgN m(-3) d(-2)) and a normal biomass growth rate (0.054 d(-1)). The nitrogen removal rate returned to normal levels within 90 days and gradual improvements in granular characteristics were also achieved. Therefore, this study provides a new insight that externally removing the adsorbed heavy metals followed by internally repairing the metabolic system may represent an optimal restoration strategy for anammox consortium damaged by heavy metals. (C) 2015 Elsevier B.V. All rights reserved.