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

It was shown that the concentration of heavy metal ions Fe3+, Cu2+, Cr3+ and Zn2+, which are contained in the fermentation medium, affects the process of biogas production. The aim of this paper was to establish the concentration of ions, which makes it possible to increase the yield of biogas and the methane content in it. The total yield of biogas per unit of dry organic matter, methane and the kinetics of changes in the yield of biogas during fermentation of cattle manure in the presence of different concentrations of metal ions in the anaerobic environment. It was established that the content of Fe3+, Cu2+ is up to 80 mg/dm3, Cr3+ and Zn2+ is up to 50 mg/dm3 in the medium lead to increased methane production by anaerobic association of microorganisms due to the effect on the activity of enzyme systems in comparison with the sample without the addition of metal ions. It was found that the rational concentrations to increase the methane yield in the biogas obtained by fermentation of cattle manure are: Fe3+-20 - 40 mg/dm3, Cu2+-40 - 60 mg/dm3, Cr3+-10 mg/dm3. The increase in the concentration of metal ions above rational values leads to a decrease in the methane content in biogas. It was shown that zinc ions have a positive effect on methane production, but reduce the total biogas yield and, accordingly, the degree of conversion of organic raw materials. Therefore, the rational concentration of Zn2+ in the fermentation medium is 10 mg/dm3.