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

Abstract

The effective and cheap remediation of ammonia (NH+4) 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+4, 99.89% of zinc (Zn2+), 97.42% of cadmium (Cd2+) and 46.19% of nickel (Ni2+) simultaneously after 24 h of incubation. The conversion pathway of NH+4 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 (Ca2+) 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 Zn2+, co-precipitation for Cd2+, and adsorption for Ni2+. The Zn2+, Cd2+, and Ni2+ precipitates displayed unique morphologies. This research provided a promising biological resource for the simultaneous remediation of NH+4 and heavy metals from landfill leachate.