Mechanisms of ammonia, calcium and heavy metal removal from nutrient-poor water by Acinetobacter calcoaceticus strain HM12

An Acinetobacter calcoaceticus strain HM12 capable of heterotrophic nitrification-aerobic denitrification (HN-AD) under nutrient-poor conditions was isolated, with an ammonia nitrogen (NH4+-N) removal efficiency of 98.53%. It can also remove heavy metals by microbial induced calcium precipitation (MICP) with a Ca2+ removal efficiency of 75.91%. Optimal conditions for HN-AD and mineralization of the strain were determined by kinetic analysis (pH = 7, C/N = 2.0, Ca2+ = 70.0 mg L-1, NH4+-N = 5.0 mg L-1). Growth curves and nitrogen balance elucidated nitrogen degradation pathways capable of converting NH4+-N to gaseous nitrogen. The analysis of the bioprecipitation showed that Zn2+ and Cd2+ were removed by the MICP process through co-precipitation and adsorption (maximum removal efficiencies of 93.39% and 80.70%, respectively), mainly ZnCO3, CdCO3, ZnHPO4, Zn-3(PO4)(2) and Cd-3(PO4)(2). Strain HM12 produces humic and fulvic acids to counteract the toxicity of pollutants, as well as aromatic proteins to increase extracellular polymers (EPS) and promote the biomineralization process. This study provides a experimental evidence for the simultaneous removal of multiple pollutants from nutrient-poor waters.