Combined Еffects of Heavy Metal Ions (Fe3+-Cu2+, Fe3+-Zn2+, Fe3+-Cr3+, Cu2+-Zn2+, Cu2+-Cr3+ and Zn2+-Cr3+) on the Productivity of Biogas and Biomethane Production

Abstract. Background. Determining the effect of combined metal action on the anaerobic microbial association during the fermentation process and methane production. Objective. To investigate the effect of the simultaneous interaction of heavy metal ions (Zn–Fe, Zn–Cu, Zn–Cr, Fe–Cu, Fe–Cr, Cu–Cr) on the process of biogas production and methane formation in it. Methods. A laboratory study performed under conditions approximating industrial biogas production, involving the application of heavy-metal-ion salts and the measurement of the quantitative and qualitative composition of the final product. Results. The combined effect of two heavy-metal ions on biogas production by an anaerobic microbial association is specific: the synergy of certain metal ions may stimulate the biosynthesis of biomethane while simultaneously inhibit-ing biogas production. In particular, Fe (20 mg/dm³) – Cu (40 mg/dm³) and Fe (20 mg/dm³) – Cr (10 mg/dm³) exhibit a slight positive effect on biogas yield compared to the control, whereas the interaction of these metal ions with Zn (5 mg/dm³) reduces the biogas yield but improves its qualitative composition — the methane content increases. Conclusions. The combined effect of two heavy-metal ions generally reduces biogas production compared to the con-trol; however, it stimulates the production of a higher methane content in the biogas. Compared with the effect of a sin-gle heavy metal, the combined exposure does not have a positive impact on biogas production, which is attributed to the elevated concentrations of metal ions used in the experiment.