Methods of biological treatment intensification aimed at removal of heavy metals

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Introduction. The application of microorganisms, capable of using chemical elements with variable valency as terminal electron acceptors, in the wastewater treatment technology can improve the ecological and energy efficiency of biological treatment plants.
 Materials and methods. The co-authors employed the analytical generalization of findings, including the overview of literary sources, laboratory researches involving standard and advanced methodologies and analytical equipment.
 Results. Cr(6+) Мn(4+), highly concentrated in wastewaters of versatile production facilities, deserve attention as terminal electron acceptors. The ability of Асіnеtobacter, a non-adapted aerobic bacteria, to reduce Мn(4+), Сr(6+) in the culture medium under a layer of vasseline oil, was studied in the laboratory environment. In the course of the laboratory research, different aspects of Сr(6+)- и Мn(4+) reduction were studied, namely, the bacteria’s chromate reduction ability, as Сr(6+) concentration change curves were obtained for the process of reduction; the influence of Сr(6+) and Мn(2+) reductions on processes of chromate and manganese reduction was identified; water treatment efficiency boosted by Сr(6+) was identified; changes in the reduction sequence in case of their co-presence in the culture medium were checked; the sequence of Сr(6+) and Мn(4+) reduction in case of their co-cultivation together with the bacteria was identified, as well. A succession of experiments with Pseudomonas bacteria was held to validate the results.
 Conclusions. The experiments have proven that aerobic bacteria, including Асіnеtobacter, P. aeruginosa P-1, P. flurescens var. Pseudo-iodinum P-11, P. Mendocina P-13, P. stutzeri P-19, can develop anaerobic respiration ability under certain conditions. The co-authors have identified that Сr(6+)- and Мn(4+) reduction is applicable by microorganisms, belonging to varied taxonomic groups, in anaerobic cultivation environments, if Сr(6+)- and Мn(4+) act as terminal acceptors of electrons; the co-authors have also reconstructed the reduction sequence: denitrifying bacteria use МnО2 much more efficiently than Сr(6+). Microbial chromate reduction precedes Мn(4+) reduction, while products of their metabolism are less toxic.
 Acknowledgements. The co-authors would like to express gratitude to the executives of the St. Petersburg University of Architecture and Civil Engineering for the research grant and to all reviewers and the editorial team for the publication of this material.