Synergistic and antagonistic influences of trace elements on volatile fatty acids degradation and methane production during the methanization of a mixture of volatile fatty acids

Anaerobic digestion (AD3) for methane production is also known as methanization. Trace elements (TEs4 ) as supplements are essential for enzyme activities and may improve methanization, but could also be toxic. Volatile fatty acids (VFA5) are formed during the AD of substrates and become inhibitory if accumulated. The level of ambiguity regarding optimum combination and concentration (configuration) of TEs for the improvement of VFA degradation and methane production during methanization is high. Therefore, mesophilic batch AD experiments with TEs supplementation were carried out in 1L reactors. A mixture of VFA (butyric, propionic and acetic acids) that was prepared in different concentrations (28-, 116-, and 213 mmol/L VFA) was used as substrate. The VFA degradation rate and methane production were the main responses that were investigated and analysed using multivariate analyses. The major aim of the work was to model interaction effects of the most important TEs in AD − Ni, Co, Se and Mo, and of VFA. Also, the adaptation time of the methanization process to the TEs was investigated. In the result, TEs supplementation caused variable effects on VFA degradation rate (from −10% to +139%); and methane production (from −33% to +55%). Regarding TEs interactions, for VFA degradation rate, the significant synergistic interactions included VFA*Se, Ni*Mo, VFA*Mo and Ni*Se; and the antagonistic interaction was Co*Mo. Similarly, for methane production, the significant synergistic interaction included Ni*Co and the antagonistic interaction was VFA*Ni.

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Synergistic and antagonistic influences of trace elements on volatile fatty acids degradation and methane production during the methanization of a mixture of volatile fatty acids