A promising approach for simultaneous removal of ammonia and multiple heavy metals from landfill leachate by carbonate precipitating bacterium.

The effective and cheap remediation of ammonia (NH) and multiple heavy metals from landfill leachate is currently a grand challenge. In this study, Paracoccus denitrificans AC-3, a bacterial strain capable of heterotrophic nitrification aerobic denitrification (HNAD) and carbonate precipitation, exhibited good tolerance to a variety of heavy metals and could remove 99.70% of NH, 99.89% of zinc (Zn), 97.42% of cadmium (Cd) and 46.19% of nickel (Ni) simultaneously after 24 h of incubation. The conversion pathway of NH by strain AC-3 was dominated by assimilation (84.68%), followed by HNAD (14.93%), and the increase in environmental pH was mainly dependent on assimilation rather than HNAD. Calcium (Ca) primarily played four roles in heavy metal mineralization: (ⅰ) improving bacterial tolerance to heavy metals; (ⅱ) ensuring the HNAD capacity of strain AC-3; (ⅲ) co-precipitating with heavy metals; and (ⅳ) precipitating into calcite to adsorb heavy metals. The heavy metals removal mechanisms were mainly calcite adsorption and formation of carbonate and hydroxide precipitation for Zn, co-precipitation for Cd, and adsorption for Ni. The Zn, Cd, and Ni precipitates displayed unique morphologies. This research provided a promising biological resource for the simultaneous remediation of NH and heavy metals from landfill leachate.